NEUROSCIENCES – ANATOMY

The lateral ventricles are paired structures located within each cerebral hemisphere. They contain choroid plexuses, which are responsible for producing cerebrospinal fluid (CSF). These ventricles have anterior, posterior, and inferior horns that extend into different regions of the brain.

Other options:

1. It is present in the cavity of diencephalon: Incorrect. The lateral ventricles are located in the cerebral hemispheres, not the diencephalon.
2. Communicate with the third ventricle via foramen of Magendie: Incorrect. The lateral ventricles communicate with the third ventricle via the foramen of Monro (interventricular foramen).
3. Present in the midline between two cerebral hemispheres: Incorrect. The lateral ventricles are located in the hemispheres and are not midline structures.
4. Having posterior horn extending into the temporal lobe: Incorrect. The inferior horn extends into the temporal lobe, while the posterior horn extends into the occipital lobe.

The interventricular foramen of Monro is a small opening that connects each lateral ventricle to the third ventricle. The anterior boundary of the foramen of Monro is formed by the anterior column of the fornix, a bundle of white matter fibers that originate from the hippocampus and curve anteriorly to join the mammillary bodies.

The other structures mentioned do not form the anterior boundary:

• Crura of fornix: Posterior part of the fornix, extending from the hippocampus.
• Posterior column of fornix: Incorrect terminology; this is part of the crura.
• Body of fornix: Lies superior to the foramen and is not part of its boundaries.
• Fimbria of fornix: Part of the hippocampus, not near the foramen of Monro.

The phrenic nerve is responsible for innervating the diaphragm, which is the primary muscle involved in breathing. Damage to the phrenic nerve due to complete cord transection at the cervical level (especially above the level of C3-C5, where the phrenic nerve originates) would impair the diaphragm’s ability to contract properly. This results in labored breathing or respiratory distress, as the diaphragm is essential for normal breathing.

Here’s why the other options are incorrect:

1. Hypoglossal nerve: The hypoglossal nerve innervates the muscles of the tongue and does not have a direct role in controlling breathing.
2. Accessory nerve: The accessory nerve controls the trapezius and sternocleidomastoid muscles, which assist with head and neck movements but do not directly impact respiration.
3. Vagus nerve: The vagus nerve is involved in parasympathetic control of various organs, including the heart and lungs, but damage to the vagus nerve alone would not directly cause labored breathing in the context of cervical cord transection.
4. Recurrent laryngeal nerve: This nerve controls the muscles of the larynx (voice box) and is involved in speech and swallowing. While it can affect breathing through its control of the larynx, it is not as critical to overall respiratory function as the phrenic nerve.

The thalamus is the major relay center for sensory information in the brain. It receives sensory inputs from various parts of the body (except olfaction) and relays them to the appropriate areas of the cerebral cortex for further processing. For example:

• Somatosensory information (touch, pain, temperature) is relayed to the primary somatosensory cortex.
• Visual information is relayed to the primary visual cortex.
• Auditory information is relayed to the primary auditory cortex.

Why the Other Options Are Wrong:

1. Red nucleus:
   • The red nucleus is located in the midbrain and is involved in motor coordination, particularly the rubrospinal tract. It is not a sensory relay center.
2. Hypothalamus:
   • The hypothalamus regulates autonomic functions, hormone release, and homeostasis (e.g., temperature, hunger, thirst). It is not a sensory relay center.
3. Cerebellum:
   • The cerebellum is involved in motor coordination, balance, and posture. It does not function as a sensory relay center.
4. Basal nucleus:
   • The basal nuclei (or basal ganglia) are involved in motor control and procedural learning. They are not sensory relay centers.

This nerve controls the only muscle that abducts the eye and is commonly affected by increased intracranial pressure.

The anterior cerebral artery (ACA) supplies the medial portion of the frontal and parietal lobes, which includes the primary motor and sensory cortex for the lower limb.

• The motor homunculus in the precentral gyrus (primary motor cortex) is somatotopically arranged, with the lower limb representation on the medial surface of the hemisphere (supplied by the ACA).
• ACA stroke or occlusion leads to contralateral lower limb weakness (paresis or paralysis) and sensory deficits.
• It may also be associated with urinary incontinence and frontal lobe dysfunction (apathy, personality changes).

Why the Other Options Are Wrong:

1. Middle Cerebral Artery (MCA) (Incorrect)

   • The MCA supplies the lateral surface of the cerebral hemisphere, including areas controlling the face, upper limb, and speech (Broca’s & Wernicke’s areas).
   • MCA infarction causes contralateral upper limb and facial weakness, not lower limb weakness.

2. Middle Meningeal Artery (Incorrect)

   • The middle meningeal artery (MMA) is a branch of the maxillary artery and does not supply the brain itself.
   • It is involved in epidural hematomas due to trauma, particularly at the pterion, but does not contribute to motor deficits.

3. Vertebral Artery (Incorrect)

   • The vertebral arteries supply the brainstem, cerebellum, and posterior brain regions via the basilar artery.
   • Occlusion affects posterior circulation, leading to dizziness, ataxia, and brainstem dysfunction, rather than isolated lower limb weakness.

4. Posterior Cerebral Artery (PCA) (Incorrect)

   • The PCA supplies the occipital lobe, affecting vision rather than motor function.
   • PCA infarcts cause contralateral homonymous hemianopia (loss of the same visual field in both eyes).

Upper Motor Neuron (UMN) lesions occur due to damage to the corticospinal tract or other descending motor pathways in the brain or spinal cord before synapsing with lower motor neurons.

Key Features of UMN Lesions:

✔ Spastic paralysis (increased muscle tone and resistance to movement).
✔ Hyperactive deep tendon reflexes (DTRs) due to loss of inhibitory control.
✔ Positive Babinski sign (toes extend instead of flexing when the sole is stroked).
✔ Disuse atrophy (muscle wasting occurs over time due to lack of use but is slower and less severe compared to LMN atrophy).

Why the Other Options Are Wrong:

1. Fasciculations ❌
   • Seen in Lower Motor Neuron (LMN) lesions, not UMN lesions.
   • Fasciculations are spontaneous twitches due to motor unit degeneration.
2. Hypoactive Muscle Stretch Reflex ❌
   • UMN lesions cause hyperactive reflexes (hyperreflexia) due to the loss of inhibitory control over the reflex arc.
3. Decreased Muscle Tone ❌
   • UMN lesions cause increased muscle tone (spasticity), not decreased tone.
   • LMN lesions lead to flaccid paralysis and hypotonia.
4. Flaccid Paralysis ❌
   • Flaccid paralysis occurs in LMN lesions due to loss of direct innervation to the muscles.
   • UMN lesions cause spastic paralysis due to loss of voluntary control with increased tone.

It is only present in the cerebral region

This statement is incorrect because gray matter is not limited to the cerebral region. Gray matter is present throughout the CNS, including the spinal cord, brainstem, cerebellum, and cerebrum. In the spinal cord, gray matter is located centrally and has an H-shaped or butterfly-like appearance. In the brain, gray matter forms the outer layer (cortex) and is also present in deep nuclei.

Why the Other Options Are Correct:

1. It is present in all segments
   This statement is correct. Gray matter is present in all segments of the CNS, from the spinal cord to the brain.
2. Gray matter is unmyelinated
   This statement is correct. Gray matter consists primarily of neuronal cell bodies, dendrites, and unmyelinated axons. Myelinated axons are found in white matter.
3. It surrounds the central canal
   This statement is correct. In the spinal cord, gray matter is arranged around the central canal, which is filled with cerebrospinal fluid (CSF).
4. It is H-shaped
   This statement is correct. In the spinal cord, gray matter has an H-shaped or butterfly-like appearance when viewed in cross-section.

The sublimbic cortex is associated with the limbic system, which controls emotions, memory, and autonomic functions. While the septal nuclei, basal ganglia, and amygdala are considered part of this system, the epithalamus is not directly involved in these functions.

The epithalamus is part of the diencephalon, and its main components are:

Pineal gland → Regulates circadian rhythms via melatonin secretion.

Habenular nuclei → Modulates neurotransmitters like dopamine and serotonin, affecting emotional responses to pain.

Even though the habenula has some limbic connections, the epithalamus as a whole is not classified as part of the sublimbic cortex.

Why the Other Options Are Part of the Sublimbic Cortex:

Septal nuclei ✅ (Part of sublimbic cortex)

Involved in reward, reinforcement, and emotional processing.

Strongly connected to the hippocampus and hypothalamus.

Basal ganglia ✅ (Part of sublimbic cortex)

Although mainly for motor control, the ventral striatum (nucleus accumbens) plays a key role in motivation and reward.

Amygdala ✅ (Part of sublimbic cortex)

Involved in fear, emotions, and memory processing.

A core limbic structure.

Thalamus ✅ (Has limbic connections but is not the correct answer here)

The anterior nucleus of the thalamus is involved in memory processing and connects to the limbic system.

While the thalamus is primarily a sensory relay station, parts of it do interact with the limbic system.

The frontal lobe is responsible for personality, social behavior, decision-making, and emotional regulation. Damage to the frontal lobe, particularly the prefrontal cortex, can result in:

• Personality changes (e.g., impulsivity, disinhibition)
• Emotional instability (e.g., mood swings, apathy)
• Poor judgment and decision-making
• Socially inappropriate behavior

Damage to the orbitofrontal cortex, a region of the frontal lobe, is particularly associated with impaired emotional regulation and social behavior.

Why the other options are incorrect:

1. Occipital lobe:
   • Primarily responsible for visual processing.
   • Damage leads to visual deficits (e.g., cortical blindness, visual agnosia), not social and emotional changes.
2. Parietal lobe:
   • Involved in sensory processing, spatial awareness, and proprioception.
   • Damage can cause neglect syndromes and difficulty with coordination, but not significant personality or emotional changes.
3. Paracentral lobule:
   • Located on the medial surface of the cerebral hemisphere and controls motor and sensory function of the lower limb.
   • It is not directly involved in social or emotional behavior.
4. Temporal lobe:
   • The temporal lobe is involved in memory, language comprehension, and auditory processing.
   • While the amygdala and limbic system (part of the medial temporal lobe) contribute to emotions, major personality and social changes are more strongly linked to the frontal lobe.

The primary visual cortex (Brodmann area 17) is located in the occipital lobe, specifically in the calcarine sulcus. It receives visual information from the lateral geniculate nucleus (LGN) of the thalamus via the optic radiations.

• A vascular lesion of the primary visual cortex, typically due to an infarct in the posterior cerebral artery (PCA), results in contralateral homonymous hemianopia with macular sparing.
• Macular sparing occurs because the macular representation in the occipital lobe receives dual blood supply from both the posterior cerebral artery (PCA) and the middle cerebral artery (MCA).

Why not the other options?

• Binasal hemianopia → Results from bilateral compression of the optic nerves at the optic chiasm, often due to internal carotid artery aneurysms, not a cortical lesion.
• Blindness → Would occur with bilateral occipital lobe damage or bilateral optic nerve lesions, but a vascular lesion in one hemisphere would not cause total blindness.
• Bitemporal hemianopia → Results from optic chiasm compression, typically due to a pituitary tumor, not a cortical lesion.
• Contralateral homonymous hemianopia → This occurs with lesions of the optic tract, LGN, or optic radiations, but without macular sparing. A cortical lesion in Brodmann area 17 results in homonymous hemianopia with macular sparing.

Thus, contralateral homonymous hemianopia with macular sparing is the correct answer, as it is the hallmark of primary visual cortex lesions due to PCA infarcts.

A hemorrhage in the pons (pontine hemorrhage) is strongly suggested by the combination of:

• Facial and limb paralysis → Indicates corticospinal and corticobulbar tract involvement, which pass through the pons.
• Pinpoint pupils → Caused by damage to the descending sympathetic fibers, which run in the pons and control pupil dilation. Loss of sympathetic input leads to unopposed parasympathetic activity, causing miosis (pinpoint pupils).

Pontine hemorrhages are often due to hypertensive hemorrhages, commonly affecting the paramedian branches of the basilar artery. These hemorrhages can cause coma, quadriplegia, and loss of horizontal eye movements if severe.

Why the Other Options Are Wrong:

1. Cerebrum:

   • A cerebral hemorrhage (e.g., in the basal ganglia or lobar regions) can cause contralateral weakness or sensory loss but does not typically cause pinpoint pupils. Instead, it may present with dilated or asymmetric pupils if there is herniation.

2. Midbrain:

   • A midbrain hemorrhage can cause coma and abnormal posturing due to damage to the reticular activating system.
   • Pupillary findings in midbrain lesions typically include blown (dilated) pupils due to involvement of the Edinger-Westphal nucleus or midposition fixed pupils (if both sympathetic and parasympathetic pathways are disrupted). Pinpoint pupils are not characteristic of midbrain damage.

3. Medulla:

   • A medullary hemorrhage can cause respiratory depression, dysphagia, and loss of gag reflex, but pinpoint pupils are not a hallmark feature.
   • The medulla contains the dorsal vagal nucleus and autonomic centers, but sympathetic pathways controlling pupil dilation do not primarily pass through the medulla.

4. Cerebellum:

   • A cerebellar hemorrhage typically presents with ataxia, vertigo, dysmetria, and nystagmus, but it does not cause pinpoint pupils or limb paralysis unless there is secondary brainstem compression.

The lateral lemniscus is the major ascending auditory pathway in the brainstem. It carries auditory signals from the cochlear nuclei and superior olivary complex to the inferior colliculus, which is the primary relay center for auditory processing in the midbrain.

The pathway follows this sequence:

1. Cochlear nuclei (medulla) →
2. Superior olivary complex (pons) →
3. Lateral lemniscus (pons to midbrain) →
4. Inferior colliculus (midbrain) →
5. Medial geniculate nucleus (thalamus) →
6. Primary auditory cortex (temporal lobe, Brodmann area 41 & 42)

Why not the other options?

• Crus cerebri → Contains motor fibers from the cortex to the brainstem and spinal cord, unrelated to auditory processing.
• Superior colliculus → Involved in visual reflexes, not auditory processing.
• Lateral geniculate nucleus (LGN) → Relay center for visual information in the thalamus, not auditory.
• Medial lemniscus → Part of the dorsal column-medial lemniscus pathway, carrying somatosensory (touch, proprioception) signals, not auditory signals.

Thus, the inferior colliculus is the correct answer as it is the first major auditory processing center in the midbrain.

The paraventricular nucleus (PVN) of the hypothalamus is activated during suckling and plays a crucial role in the release of oxytocin. When a baby suckles at the breast, sensory signals are sent to the hypothalamus, which then stimulates the paraventricular and supraoptic nuclei to release oxytocin from the posterior pituitary. Oxytocin triggers the milk ejection reflex (let-down reflex) by causing contraction of myoepithelial cells in the mammary glands.

Why the other options are incorrect:

1. Anterior nucleus:
   • The anterior hypothalamus is involved in thermoregulation (heat dissipation), not in oxytocin release.
2. Supraoptic nucleus:
   • The supraoptic nucleus (SON) also produces oxytocin, but the paraventricular nucleus is the primary center activated in response to suckling.
3. Suprachiasmatic nucleus:
   • The suprachiasmatic nucleus (SCN) regulates the circadian rhythm and sleep-wake cycles, not lactation.
4. Posterior nucleus:
   • The posterior hypothalamus is involved in sympathetic nervous system activation and thermoregulation, not breastfeeding.

The vestibulospinal tract is a descending motor pathway originating from the vestibular nuclei in the brainstem. It plays a key role in postural control and balance by facilitating extensor muscles (anti-gravity muscles).

There are two divisions of the vestibulospinal tract:

1. Lateral vestibulospinal tract – Excites extensor muscles (especially in the legs and back) to help maintain posture and balance.
2. Medial vestibulospinal tract – Controls head and neck position for maintaining equilibrium.

Why the Other Options Are Wrong:

1. Facilitates flexor muscles – Incorrect. The vestibulospinal tract primarily activates extensor muscles, while flexor facilitation is mainly controlled by the rubrospinal tract.
2. Reflex postural movement – Partially correct but not specific enough. While the vestibulospinal tract is involved in postural adjustments, its primary function is enhancing extensor tone to prevent falling.
3. Sympathetic control – Incorrect. Autonomic (sympathetic) control is mediated by the hypothalamus and spinal intermediolateral cell columns, not the vestibulospinal tract.
4. Rapid, skilled voluntary movement – Incorrect. Fine, voluntary movements are controlled by the corticospinal tract, not the vestibulospinal tract, which is more involved in automatic postural regulation.

In the central nervous system (CNS), the process of myelination is performed by oligodendrocytes, which wrap their membranes around axons to form the myelin sheath. This myelination enhances the speed and efficiency of electrical signal transmission.

Other options:

1. Schwann cells: These carry out myelination in the peripheral nervous system (PNS), not the brain.
2. Myelination of nerve tracts is largely completed by the fourth year of life: Incorrect. While myelination is most active in infancy, it continues well into adolescence and early adulthood for some regions.
3. The sensory fibers are myelinated last: Incorrect. Sensory fibers are typically myelinated earlier than motor fibers in the CNS.
4. Myelination begins at birth: Incorrect. Myelination begins during the second trimester of fetal development and continues after birth.

The floor of the inferior horn of the lateral ventricle is formed by the hippocampus, which is a key structure involved in memory formation and spatial navigation. The hippocampus is located in the medial temporal lobe and forms part of the limbic system. The inferior horn of the lateral ventricle, which extends into the temporal lobe, is closely related to the hippocampus.

Here’s why the other options are incorrect:

1. Amygdaloid nucleus: The amygdala is involved in emotions and memory, but it is not located in the floor of the inferior horn of the lateral ventricle. It is found in the temporal lobe, but more anterior and medial compared to the hippocampus.
2. Caudate nucleus: The caudate nucleus is part of the basal ganglia and is not involved in forming the floor of the inferior horn of the lateral ventricle. It is located more laterally in the brain.
3. Corpus callosum: The corpus callosum is a large bundle of nerve fibers that connects the two hemispheres of the brain, but it does not form the floor of the inferior horn of the lateral ventricle. It lies above the lateral ventricles.
4. Septum pellucidum: The septum pellucidum is a thin membrane separating the two lateral ventricles, but it does not form the floor of the inferior horn. It lies more medially and does not have the same structural role as the hippocampus in this region.

The globus pallidus (label E) sends inhibitory signals to the thalamus and other regions of the brain, controlling motor function.

The cingulum is an association fiber that connects different cortical regions within the same cerebral hemisphere. It runs beneath the cingulate gyrus and plays a role in integrating information across different areas of the limbic system, such as the hippocampus and cingulate cortex.

Why the other options are incorrect:

1. External capsule:
   • The external capsule contains projection fibers, which connect the cerebral cortex to lower brain structures, rather than linking regions within the same hemisphere.
2. Internal capsule:
   • The internal capsule is made up of projection fibers, which connect the cerebral cortex with subcortical structures like the thalamus, brainstem, and spinal cord.
3. Corpus callosum:
   • The corpus callosum consists of commissural fibers, which connect corresponding areas of the left and right hemispheres, rather than within the same hemisphere.
4. Fornix:
   • The fornix is primarily involved in limbic system connections, linking the hippocampus to the mammillary bodies, but it is classified as a projection fiber, not an association fiber.

The inferior horn of the lateral ventricle is located in the temporal lobe and is bordered by several key structures. The roof of the inferior horn is primarily formed by:

1. Tail of the caudate nucleus – Runs along the lateral wall and forms part of the roof.
2. Stria terminalis – A white matter tract following the tail of the caudate nucleus, also contributing to the roof.
3. Tapetum of the corpus callosum – A layer of white matter fibers that contributes to the superior part of the roof.
4. Amygdala – Located near the anterior end of the inferior horn, contributing to the superior border.

Why is “Pes hippocampus” the Correct Answer?

• The pes hippocampus is part of the hippocampus, which lies in the floor of the inferior horn of the lateral ventricle, not the roof.
• Since the question asks for a structure that does not form the roof, pes hippocampus is the correct choice.

Why the Other Options Are Incorrect?

❌ Amygdala – Forms the anterior part of the roof near the temporal pole.

❌ Tapetum of corpus callosum – White matter fibers forming part of the roof and lateral wall of the inferior horn.

❌ Stria terminalis – Runs along the tail of the caudate nucleus and contributes to the roof.

❌ Tail of caudate nucleus – Forms part of the roof along with the stria terminalis.

Explanation:

The cerebellum is the key structure responsible for the maintenance of muscle tone and equilibrium. It plays a crucial role in:

1. Muscle Tone Regulation
   • The cerebellum receives proprioceptive input from the muscles and joints to maintain baseline muscle tone.
   • The vestibulocerebellum (flocculonodular lobe) helps adjust tone for balance and posture.
2. Equilibrium and Balance
   • The vestibulocerebellum receives input from the vestibular nuclei to regulate posture and eye movements, maintaining balance.
   • Damage to this area leads to ataxia, vertigo, and difficulty maintaining posture.
3. Coordination of Movements
   • The spinocerebellum adjusts limb movements for smooth motor execution.
   • The cerebrocerebellum fine-tunes voluntary movement precision.

Why the Other Options Are Wrong:

1️⃣ Midbrain ❌

• The midbrain contains the tectum, tegmentum, and cerebral peduncles, which are involved in motor control, vision, and auditory processing, but it does not directly regulate muscle tone and equilibrium.

2️⃣ Substantia nigra ❌

• Part of the basal ganglia, involved in dopamine production and voluntary movement modulation.
• Dysfunction leads to Parkinson’s disease, affecting movement initiation rather than tone and balance.

3️⃣ Pons ❌

• The pons contains relay nuclei that connect the cerebellum to the brain and spinal cord, but it does not directly maintain muscle tone or equilibrium.

4️⃣ Medulla oblongata ❌

• The medulla regulates autonomic functions (breathing, heart rate) and houses the vestibular nuclei, which contribute to balance, but it is not the primary regulator of tone and equilibrium.

✅ Dorsal column

Explanation:

Anterior cord syndrome is caused by damage to the anterior spinal cord, usually due to occlusion of the anterior spinal artery (ASA). Since the dorsal columns are supplied by the posterior spinal arteries, they are spared in this condition.

Structures Affected in Anterior Cord Syndrome:

• Corticospinal tract (motor function) → Paralysis below the lesion (bilateral weakness)
• Lateral spinothalamic tract (pain & temperature sensation) → Loss of pain & temperature below the lesion
• Anterior spinothalamic tract (crude touch & pressure) → May be affected, but often partially spared due to collateral supply

Structures Spared in Anterior Cord Syndrome:

• Dorsal columns (fine touch, proprioception, vibration) → Remain intact because they are supplied by the posterior spinal arteries

Why the Other Options Are Wrong:

1️⃣ Corticobulbar tract ❌

• The corticobulbar tract controls cranial nerve motor function and is located in the brainstem, NOT the spinal cord.
• It is not affected in anterior cord syndrome.

2️⃣ Corticospinal tract ❌

• The corticospinal tract is located anteriorly and is affected in anterior cord syndrome, leading to bilateral paralysis below the lesion.

3️⃣ Anterior spinothalamic tract ❌

• This tract carries crude touch and pressure.
• While it is located anteriorly, it may be partially spared due to collateral blood supply but is not fully spared like the dorsal column.

4️⃣ Lateral spinothalamic tract ❌

• The lateral spinothalamic tract is affected, causing loss of pain and temperature sensation below the lesion.

The medial wall of the cerebral hemisphere consists of structures that are part of the medial aspect of the brain, mainly seen in a midsagittal section. These include:

1️⃣ Cuneus → Located in the medial occipital lobe, involved in visual processing.
2️⃣ Paracentral lobule → Located on the medial surface of the frontal and parietal lobes, responsible for motor and sensory functions of the lower limb.
3️⃣ Precuneus → Found on the medial parietal lobe, involved in sensorimotor integration, memory, and self-awareness.
4️⃣ Corpus callosum → A commissural fiber tract connecting the two hemispheres, visible on the medial surface.

However, the insula is not part of the medial wall.

• The insula (insular cortex) is a deep cortical structure buried within the lateral sulcus (Sylvian fissure).
• It is covered by the frontal, parietal, and temporal opercula and is not visible on a midsagittal section of the brain.
• It plays a role in visceral functions, pain perception, and emotional processing.

Why the Other Options Are Incorrect:

❌ 1. “Cuneus” – Incorrect

• Located in the medial occipital lobe, part of the visual cortex.
• Clearly visible in a midsagittal section.

❌ 2. “Paracentral lobule” – Incorrect

• Found medially in the frontal and parietal lobes, controlling lower limb motor and sensory functions.

❌ 3. “Precuneus” – Incorrect

• Located in the medial parietal lobe, involved in higher cognitive functions.

❌ 4. “Corpus callosum” – Incorrect

• A large white matter tract that connects both hemispheres, clearly seen in the medial view.

• Cerebrospinal fluid (CSF) is produced by the choroid plexus and circulates through the ventricles, subarachnoid space, and spinal canal.
• Obstruction of CSF flow leads to accumulation of CSF, causing hydrocephalus.
• Types of hydrocephalus:
  1. Communicating Hydrocephalus – impaired CSF absorption (e.g., post-meningitis scarring).
  2. Non-communicating (Obstructive) Hydrocephalus – blockage in ventricular system (e.g., aqueductal stenosis, tumor).
  3. Normal Pressure Hydrocephalus (NPH) – seen in older adults with gait disturbance, urinary incontinence, and cognitive impairment (Hakim’s triad).

Why the Other Options Are Wrong:

1. Meningitis: ❌
   • Meningitis is infection/inflammation of the meninges but does not directly result from CSF obstruction. However, it can cause hydrocephalus due to scarring.
2. Tuberculosis: ❌
   • TB can cause tuberculous meningitis, which may lead to communicating hydrocephalus, but TB itself is not caused by CSF obstruction.
3. Parkinsonism: ❌
   • Parkinson’s disease is caused by dopaminergic neuron degeneration in the substantia nigra, not by CSF obstruction.
4. Tumor Formation: ❌
   • Tumors can cause CSF obstruction, leading to hydrocephalus, but a tumor itself is not the direct result of CSF obstruction.

The tentorium cerebelli is a dural reflection that separates the cerebrum (specifically the occipital lobes) from the cerebellum. It is a horizontally oriented fold of dura mater that extends from the petrous part of the temporal bone and the transverse sinuses, creating a tent-like structure over the cerebellum.

Why the Other Options Are Wrong:

1. Falx cerebelli:

   • This structure is a small vertical dural reflection that separates the two hemispheres of the cerebellum, not the cerebrum from the cerebellum.

2. Falx cerebri:

   • This is a large, sickle-shaped dural reflection that separates the two cerebral hemispheres, not the cerebrum from the cerebellum.

3. Diaphragma sellae:

   • This is a small horizontal dural fold that covers the pituitary gland in the sella turcica of the sphenoid bone. It has an opening for the passage of the pituitary stalk (infundibulum) but has no role in separating the cerebrum from the cerebellum.

4. None of these:

   • Incorrect because the tentorium cerebelli is indeed the structure that separates the cerebrum from the cerebellum.

The dorsal column-medial lemniscus pathway (DCML) is responsible for fine touch, proprioception, and vibration sense.

• First-order neurons: Carry sensory input from mechanoreceptors (like Pacinian corpuscles for vibration) through the dorsal root ganglion (DRG) into the spinal cord.
• Second-order neurons: Ascend ipsilaterally in the dorsal columns (fasciculus gracilis for lower body, fasciculus cuneatus for upper body) and synapse in the medulla.
• Decussation (crossing over) occurs in the medulla, after which fibers ascend as the medial lemniscus.
• Third-order neurons: Project from the thalamus (VPL nucleus) to the primary somatosensory cortex in the postcentral gyrus (Brodmann area 3,1,2).

Thus, vibration sense travels through the dorsal column pathway.

Why the Other Options Are Incorrect:

1. Anterior spinocerebellar tract ❌
   • The spinocerebellar tracts (anterior and posterior) carry unconscious proprioception to the cerebellum, not vibration.
2. Posterior spinocerebellar tract ❌
   • Also involved in unconscious proprioception, mainly for lower limb coordination, not vibration.
3. Anterior spinothalamic tract ❌
   • The anterior spinothalamic tract carries crude touch and pressure, not vibration.
4. Lateral spinothalamic tract ❌
   • The lateral spinothalamic tract transmits pain and temperature, not vibration.

Hemisection of the spinal cord is known as Brown-Séquard syndrome, which presents with a characteristic pattern of deficits:

1. Ipsilateral UMN signs below the lesion → Due to corticospinal tract damage (✅ True)
2. Ipsilateral loss of dorsal column sensations below the lesion → Due to dorsal column damage (✅ True)
3. Contralateral pain and temperature loss below the lesion → Due to spinothalamic tract damage, which crosses at the spinal cord level (✅ True)
4. Ipsilateral loss of all sensations at the level of the lesion → Due to local nerve root involvement (✅ True)

However, ipsilateral UMN signs do not appear at the level of the lesion. Instead, at the lesion level, there may be lower motor neuron (LMN) signs (flaccid paralysis, atrophy, and areflexia) due to damage to anterior horn cells or ventral roots.

Other options explained:

✔ Ipsilateral UMN signs below the lesion → Occurs due to corticospinal tract damage.
✔ Ipsilateral dorsal column sensory loss below the lesion → Due to dorsal column damage (loss of proprioception, vibration, and fine touch).
✔ Contralateral pain and temperature loss below the lesion → Due to spinothalamic tract damage, which crosses at the spinal level.
✔ Ipsilateral loss of all sensations at the level of the lesion → Due to local nerve root and dorsal horn damage.

Understanding the Ventromedial Nucleus and Satiety Control

• The ventromedial nucleus (VMN) of the hypothalamus plays a key role in inhibiting hunger and promoting satiety.
• It receives input from leptin, a hormone released by adipose tissue that signals fullness.
• Lesions in the ventromedial nucleus lead to hyperphagia (excessive eating) and obesity.

Why the Other Options Are Incorrect

• Supraoptic nucleus – Incorrect

  • The supraoptic nucleus primarily produces antidiuretic hormone (ADH/vasopressin), which regulates water balance.
  • It does not control hunger or satiety.

• Posterolateral nucleus – Incorrect

  • The posterolateral hypothalamic area is involved in sympathetic nervous system activation and arousal, not satiety.

• Paraventricular nucleus – Incorrect

  • The paraventricular nucleus (PVN) regulates autonomic function, stress response, and oxytocin release, but it does not act as the primary satiety center.

• Suprachiasmatic nucleus – Incorrect

  • The suprachiasmatic nucleus (SCN) is the body’s master clock, regulating circadian rhythms based on light input from the retina.
  • It does not control hunger or satiety.

The circle of Willis is an arterial ring located at the base of the brain that provides collateral blood flow between the anterior and posterior circulations. The arteries that form the circle of Willis include:

• Anterior cerebral artery (ACA)
• Anterior communicating artery
• Posterior cerebral artery (PCA)
• Posterior communicating artery
• Internal carotid artery (part of it contributes to the circle)

The middle cerebral artery (MCA), although it is a major branch of the internal carotid artery, does not participate in forming the circle of Willis. Instead, it extends laterally to supply a large portion of the lateral surface of the cerebral hemispheres.

The question asks which structure is NOT supplied by the nerve that passes through the stylomastoid foramen.

🔹 The facial nerve (CN VII) exits the skull via the stylomastoid foramen and supplies muscles of facial expression, but NOT the parotid gland.
🔹 The parotid gland is supplied by the glossopharyngeal nerve (CN IX) via the otic ganglion, NOT the facial nerve.

Why the other options are incorrect (i.e., they ARE supplied by the facial nerve after exiting the stylomastoid foramen):

1. Sublingual gland ✅ (Supplied by CN VII via chorda tympani)
   • Chorda tympani (CN VII) → Joins lingual nerve (CN V3) → Submandibular ganglion → Sublingual gland.
   • This occurs before the facial nerve exits, but since the facial nerve is involved, it is still correct.
2. Buccinator ✅ (Supplied by CN VII after exiting the stylomastoid foramen)
   • Supplied by the buccal branch of the facial nerve.
3. Lacrimal gland ✅ (Supplied by CN VII via greater petrosal nerve)
   • The greater petrosal nerve (branch of CN VII) carries parasympathetic fibers to the pterygopalatine ganglion, which then innervates the lacrimal gland.
4. Orbicularis oculi ✅ (Supplied by CN VII after exiting the stylomastoid foramen)
   • Supplied by the zygomatic branch of CN VII.

The posterior cranial fossa is the deepest part of the skull base and houses structures such as the cerebellum, brainstem, and cranial nerves VII–XII. A fracture involving the posterior cranial fossa would typically affect bones that contribute to its formation, such as the occipital bone, temporal bone (squamous, petrous, and mastoid parts), but not the sphenoid bone, which primarily forms part of the anterior and middle cranial fossae.

Why the other options are incorrect:

1. Occipital bone:
   • The occipital bone forms a major portion of the posterior cranial fossa, including the foramen magnum. Fractures here can affect structures passing through this opening, such as the medulla oblongata and spinal cord.
2. Squamous part of the temporal bone:
   • The squamous part of the temporal bone contributes to the posterior and middle cranial fossae and could be affected by fractures in this region.
3. Petrous part of the temporal bone:
   • The petrous part of the temporal bone is located within the posterior cranial fossa and houses the inner ear structures. A fracture in this region can lead to hearing loss and facial nerve palsy.
4. Mastoid part of the temporal bone:
   • The mastoid part of the temporal bone is also part of the posterior cranial fossa. Fractures here can cause mastoid air cell damage and increase the risk of CSF leakage.

The insula is a structure located deep within the lateral sulcus (also known as the Sylvian fissure) of the brain. It is involved in various functions, including processing sensory information, emotional responses, and autonomic control. The insula plays a role in perception, motor control, and homeostasis, as well as in aspects of consciousness and the processing of emotions.

Here’s why the other options are incorrect:

1. Primary motor cortex: The primary motor cortex is located in the precentral gyrus, which is situated on the lateral surface of the frontal lobe, but not deep in the lateral sulcus.
2. Secondary motor cortex: The secondary motor cortex, also known as the premotor cortex, is located in the frontal lobe, just anterior to the primary motor cortex, and is not located deep in the lateral sulcus.
3. Primary sensory cortex: The primary sensory cortex is located in the postcentral gyrus, in the parietal lobe, and is not located deep within the lateral sulcus.
4. Supplementary motor area: The supplementary motor area is located on the medial surface of the frontal lobe, near the top of the brain, and is not located deep in the lateral sulcus.

The middle cerebral artery (MCA) does not contribute to the blood supply of the midbrain. Instead, the midbrain is primarily supplied by branches of the vertebrobasilar system, including:

1. Posterior cerebral artery (PCA) → Major blood supply to the midbrain.
2. Peduncular branches of PCA → Supply the cerebral peduncles.
3. Posterior choroidal artery (a branch of PCA) → Supplies tectum (superior & inferior colliculi).
4. Superior cerebellar artery (SCA) → Contributes to the midbrain’s dorsolateral regions.
5. Interpeduncular branches of the basilar artery → Supply the ventral midbrain (interpeduncular fossa and surrounding structures).

Why the Middle Cerebral Artery (MCA) is Incorrect:

• The MCA supplies the lateral aspects of the cerebral hemispheres, including:
  • Motor and sensory cortex for face & upper limbs.
  • Broca’s and Wernicke’s areas (speech).
  • Basal ganglia (via lenticulostriate arteries).
• It does not reach the midbrain, making it the correct answer.

Why the Other Options Are Correct Contributors to the Midbrain Blood Supply:

1. Posterior cerebral artery and its peduncular branch (✓) [Correct]
   • PCA is the main supplier of the midbrain, particularly the cerebral peduncles and colliculi.
2. Posterior choroidal artery (✓) [Correct]
   • A branch of PCA, it supplies the tectum, thalamus, and part of the midbrain.
3. Superior cerebellar artery (✓) [Correct]
   • Supplies the dorsolateral part of the midbrain, including portions of the tectum.
4. Interpeduncular branches of the basilar artery (✓) [Correct]
   • These branches supply the ventral midbrain, including the interpeduncular fossa.

The insula is not part of the medial wall of the cerebral hemisphere. Instead, it is located deep within the lateral sulcus, hidden beneath the frontal, parietal, and temporal lobes. The insula is involved in visceral sensation, autonomic control, taste perception, and emotional processing.

Why the other options are incorrect (i.e., they are part of the medial wall):

1. Cuneus:
   • Located in the medial occipital lobe, between the parieto-occipital sulcus and calcarine sulcus.
   • Part of the primary visual cortex (V1).
2. Paracentral lobule:
   • Located in the medial frontal lobe, anterior to the precuneus.
   • It includes the primary motor and sensory areas for the lower limb.
3. Precuneus:
   • Located in the medial parietal lobe, between the paracentral lobule and cuneus.
   • Plays a role in self-awareness, memory, and visuospatial processing.
4. Corpus callosum:
   • A large white matter structure forming the roof of the lateral ventricles.
   • Connects the left and right cerebral hemispheres.

Subcallosal, cingulate and parahippocampal gyri, hippocampal formation, amygdaloid nucleus, mammillary body and anterior thalamic nuclei

The limbic system is a network of interconnected structures that work together to regulate emotions, memory, and motivation. The key components of the limbic system include:

1. Subcallosal gyrus: Involved in emotional processing.
2. Cingulate gyrus: Plays a role in emotion formation and processing, as well as learning and memory.
3. Parahippocampal gyrus: Associated with memory encoding and retrieval.
4. Hippocampal formation: Critical for forming new memories (declarative memory).
5. Amygdaloid nucleus (amygdala): Central to emotional responses, especially fear and aggression.
6. Mammillary bodies: Important for memory formation and recall.
7. Anterior thalamic nuclei: Involved in memory and emotional regulation.

These structures are interconnected and work together to integrate emotional and cognitive processes.

Why the Other Options Are Incorrect:

1. Cingulate gyrus and the uncus
   While the cingulate gyrus is part of the limbic system, the uncus (a part of the parahippocampal gyrus) is not typically listed as a primary constituent of the limbic system. This option is incomplete and does not include other critical limbic structures.
2. Amygdaloid nucleus, red nucleus, and vestibular nucleus
   The amygdaloid nucleus is part of the limbic system, but the red nucleus (involved in motor coordination) and the vestibular nucleus (involved in balance and spatial orientation) are not part of the limbic system. This option incorrectly includes non-limbic structures.
3. Hippocampal formation
   The hippocampal formation is a key component of the limbic system, but this option is incomplete because it does not include other essential limbic structures like the amygdala, cingulate gyrus, or mammillary bodies.
4. Pulvinar of the thalamus and substantia nigra
   The pulvinar of the thalamus is involved in visual processing, and the substantia nigra is part of the basal ganglia and is involved in motor control. Neither of these structures is part of the limbic system. This option is entirely incorrect.

Correct Answer:

The epithalamus is not part of the sub limbic cortex. The sub limbic cortex (limbic system) includes structures like the amygdala, hippocampus, septal nuclei, and parts of the basal ganglia, which are involved in emotion, memory, and behavior. The epithalamus, which includes the pineal gland and habenular nuclei, is not traditionally considered part of the limbic system. Instead, it is more associated with circadian rhythms and some aspects of emotional processing but is not a core component of the limbic system.

Why the other options are part of the sub limbic cortex:

1. Thalamus:
   • While the thalamus is not a core part of the limbic system, it has strong connections to limbic structures (e.g., the anterior thalamic nucleus is involved in memory and emotion). However, it is primarily a relay station for sensory and motor signals.
2. Basal ganglia:
   • The basal ganglia, particularly the nucleus accumbens, are closely linked to the limbic system and are involved in reward and motivation.
3. Amygdala:
   • The amygdala is a key component of the limbic system and is central to emotional processing, especially fear and aggression.
4. Septal nuclei:
   • The septal nuclei are part of the limbic system and are involved in reward, pleasure, and emotional regulation.

Gliosis is a process in which astrocytes undergo hyperplasia and hypertrophy in response to CNS injury, ischemia, inflammation, or neurodegeneration. It serves as a repair mechanism in the brain and spinal cord.

• Astrocyte proliferation and hypertrophy → Leads to the formation of a glial scar, which helps contain damage but can inhibit neuronal regeneration.
• Increased expression of glial fibrillary acidic protein (GFAP) → A hallmark of gliosis.

Other options explained:

❌ Myelin sheath → Involves oligodendrocytes (not related to gliosis).
❌ Fibers → Axonal fibers may be affected, but gliosis is an astrocytic response.
❌ Fibroblasts → Present in peripheral tissue repair, but gliosis is a CNS-specific process.
❌ Macrophages → Microglia act as CNS macrophages, but gliosis is distinct from their function.

The auditory pathway is responsible for transmitting sound signals from the cochlea to the auditory cortex. The major relay centers in this pathway include:

✅ Spiral ganglion → First-order neurons located in the cochlea.
✅ Cochlear nuclei → Receive input from the spiral ganglion and send projections bilaterally.
✅ Trapezoid body → A key decussation site for auditory fibers in the brainstem.
✅ Medial geniculate body (MGB) → A relay center in the thalamus for auditory signals.

The superior colliculi, however, are NOT part of the auditory pathway. Instead, they play a role in the visual system, particularly in coordinating eye movements and reflexes.

Other options explained:

❌ Medial geniculate body (MGB) → An essential relay in the thalamus for auditory signals.
❌ Trapezoid body → Important for bilateral hearing processing in the brainstem.
❌ Cochlear nuclei → The first central relay station for auditory input in the brainstem.
❌ Spiral ganglion → The first-order neurons of the auditory pathway located in the cochlea.

The oculomotor nerve nucleus (CN III) is located in the midbrain, specifically at the level of the superior colliculus and Edinger-Westphal nucleus. The midbrain receives its blood supply mainly from the posterior cerebral artery (PCA) and its branches, including the quadrigeminal and paramedian branches.

A lesion in the oculomotor nucleus results in oculomotor nerve palsy, which presents with:

• Ptosis (due to paralysis of the levator palpebrae superioris)
• Mydriasis (pupil dilation due to loss of parasympathetic function)
• Eye deviation “down and out” (due to unopposed action of the lateral rectus and superior oblique)

Since the PCA supplies this region, infarction or ischemia in the PCA territory can damage the oculomotor nerve nucleus, leading to oculomotor palsy.

Why the Other Options Are Incorrect:

1. Basilar artery → ❌ Incorrect
   • The basilar artery supplies the pons, not the midbrain. It mainly gives rise to the pontine arteries, which supply structures like the corticospinal tract and cranial nerve nuclei (like CN VI, VII).
   • Damage to the basilar artery leads to locked-in syndrome but does not affect the oculomotor nucleus.
2. Anterior cerebral artery (ACA) → ❌ Incorrect
   • The ACA supplies the medial aspect of the frontal and parietal lobes, including the motor and sensory cortices of the lower limb.
   • It does not supply the midbrain, making it unrelated to CN III lesions.
3. Middle cerebral artery (MCA) → ❌ Incorrect
   • The MCA supplies the lateral cerebral hemisphere, including the primary motor and sensory cortices, Broca’s and Wernicke’s areas.
   • It does not reach the midbrain, so it cannot cause oculomotor nerve damage.
4. Vertebral artery → ❌ Incorrect
   • The vertebral arteries primarily supply the medulla and form the basilar artery.
   • They do not have a direct supply to the midbrain and thus do not affect the oculomotor nerve nucleus.

Somatosensory Area-I (SI), located in the postcentral gyrus of the parietal lobe (Brodmann areas 3, 1, and 2), is responsible for processing fine touch, proprioception, vibration, and detailed spatial discrimination. When SI is ablated, a person loses precise tactile perception, making it difficult to recognize shapes, textures, and object forms by touch alone.

Why the other options are incorrect:

1. Pain perception:
   • Pain is mainly processed by the spinothalamic tract and Somatosensory Area-II (SII).
   • Since SII remains functional after SI ablation, pain perception is not significantly impaired.
2. Crude touch:
   • Crude touch is carried by the anterior spinothalamic tract and is poorly localized, meaning its perception is less dependent on SI.
   • Affected individuals can still detect touch but lose the ability to distinguish fine details.
3. Proprioception:
   • Proprioception relies on SI for conscious awareness, but subcortical structures like the cerebellum also process it.
   • Thus, proprioception is impaired but not entirely lost.
4. Vibration:
   • Vibration sensation is processed by SI, but other brain areas contribute, making the loss partial rather than complete.

The midbrain (mesencephalon) is characterized by the presence of the cerebral aqueduct (also called the aqueduct of Sylvius), which connects the third ventricle (in the diencephalon) to the fourth ventricle (in the hindbrain). At the level of the superior colliculus, the cerebral aqueduct is a prominent feature, surrounded by the periaqueductal gray matter.

Why the Other Options Are Wrong:

1. Fourth ventricle:
   • The fourth ventricle is located in the hindbrain (pons and medulla), not the midbrain.
2. Red nucleus:
   • The red nucleus is present in the midbrain but is located at the level of the inferior colliculus, not the superior colliculus.
3. Third ventricle:
   • The third ventricle is located in the diencephalon (thalamus and hypothalamus), not the midbrain.
4. Third and fourth ventricle:
   • The third ventricle is in the diencephalon, and the fourth ventricle is in the hindbrain. Neither is located in the midbrain.

The ventral (anterior) spinothalamic tract is responsible for transmitting crude touch and pressure sensations. Damage to this tract would result in loss of crude touch, while fine touch remains intact, as fine touch is conveyed by the dorsal column-medial lemniscus (DCML) pathway.

Sensory Tracts and Their Functions:

1. Ventral (anterior) spinothalamic tract → Crude touch and pressure
2. Lateral spinothalamic tract → Pain and temperature
3. Dorsal column tract (DCML pathway) → Fine touch, vibration, proprioception
4. Spinocerebellar tract → Unconscious proprioception (balance and coordination)
5. Spino-reticular tract → Pain perception and arousal response

Why not the other options?

• Spinocerebellar tract → Involved in unconscious proprioception, not touch sensation.
• Dorsal column tract → Carries fine touch, vibration, and proprioception, but fine touch is intact in this case.
• Lateral spinothalamic tract → Conveys pain and temperature, which are not affected here.
• Spino-reticular tract → Primarily involved in pain modulation and alertness, not touch sensation.

Thus, damage to the ventral (anterior) spinothalamic tract leads to loss of crude touch, making it the correct answer.

The flailing movement of the left upper limb suggests hemiballismus, a condition caused by damage to the contralateral subthalamic nucleus.

• Hemiballismus is characterized by sudden, involuntary, violent flinging movements of the proximal limbs, usually affecting one side of the body.
• It results from damage to the subthalamic nucleus, which normally inhibits excessive movement via the indirect pathway of the basal ganglia.
• A right-sided subthalamic lesion would cause left-sided hemiballismus.

Why not the other options?

• Hypothalamus → Regulates autonomic and endocrine functions, not voluntary movement control.
• Globus pallidus → Damage here can cause movement disorders, but not hemiballismus. The globus pallidus is more associated with Parkinsonism or dystonia.
• Spinal cord → Lesions here cause weakness or sensory deficits, not flailing movements.
• Midbrain → Damage here affects cranial nerves (e.g., oculomotor nerve in Weber’s syndrome) and dopaminergic pathways (e.g., Parkinson’s disease), but does not typically cause hemiballismus.

Thus, the subthalamus (subthalamic nucleus) is the correct answer, as its lesion leads to hemiballismus.

The confluence of sinuses (torcular Herophili) is located at the internal occipital protuberance and serves as a meeting point for several dural venous sinuses. The sinuses that drain into the occipital confluence include:

✔ Superior sagittal sinus – Drains from the superior portion of the brain.
✔ Straight sinus – Formed by the inferior sagittal sinus and the great cerebral vein (of Galen).
✔ Occipital sinus – Runs along the internal occipital crest and drains into the confluence.
✔ Transverse sinuses – Receive blood from the confluence and continue laterally toward the sigmoid sinuses.

The inferior petrosal sinus does not drain into the confluence of sinuses. Instead, it runs along the inferior border of the petrous part of the temporal bone, connecting the cavernous sinus to the internal jugular vein.

Why the Other Options Are Incorrect?

❌ Straight sinus

• Drains into the confluence of sinuses, carrying blood from the deep venous system (inferior sagittal sinus and great cerebral vein of Galen).

❌ Superior sagittal sinus

• Drains into the confluence of sinuses, receiving blood from the superior cerebral veins.

❌ Occipital sinus

• Drains into the confluence of sinuses, running along the internal occipital crest.

❌ Transverse sinus

• Receives drainage from the confluence of sinuses and carries blood toward the sigmoid sinus and eventually the internal jugular vein.

The visual cortex is located in the occipital lobe, which is primarily supplied by the posterior cerebral artery (PCA). The PCA arises from the basilar artery and provides blood to:

• The occipital lobe (including the primary visual cortex).
• The inferior temporal lobe.
• Portions of the thalamus and midbrain.

A posterior cerebral artery occlusion can lead to contralateral homonymous hemianopia with macular sparing due to partial dual blood supply from the middle cerebral artery (MCA) to the macula.

Why the Other Options Are Incorrect?

❌ “The internal carotid artery has no branches other than cerebral arteries.”

• The internal carotid artery (ICA) does give off branches other than the cerebral arteries, such as:
  • Ophthalmic artery (supplies the eye).
  • Anterior choroidal artery.
  • Posterior communicating artery (part of the Circle of Willis).
• Thus, this statement is incorrect.

❌ “The posterior inferior cerebellar artery (PICA) is a branch of the basilar artery.”

• The PICA arises from the vertebral artery, not the basilar artery.
• The anterior inferior cerebellar artery (AICA) and superior cerebellar artery (SCA) are branches of the basilar artery.

❌ “The anterior cerebral artery occlusion may lead to aphasia if the left hemisphere is affected.”

• Aphasia (language impairment) typically results from middle cerebral artery (MCA) occlusion, as the MCA supplies Broca’s and Wernicke’s areas in the dominant hemisphere (usually the left).
• The anterior cerebral artery (ACA) mainly supplies the medial frontal and parietal lobes, affecting lower limb motor and sensory functions, not speech centers.

❌ “The internal capsule is supplied by the lenticulostriate arteries, branches of the anterior cerebral artery.”

• The lenticulostriate arteries are actually branches of the middle cerebral artery (MCA), not the anterior cerebral artery (ACA).
• These small arteries supply the internal capsule and basal ganglia.
• Damage to these arteries (e.g., in hypertensive stroke) can lead to lacunar infarcts, causing pure motor hemiparesis.

The supranuclear facial nerve pathway refers to the upper motor neuron (UMN) control of the facial nerve (CN VII), which originates in the motor cortex and projects to the facial nucleus in the pons.

• The upper face (forehead and eyes) receives bilateral cortical input, meaning it is supplied by both hemispheres.
• The lower face (mouth and jaw) receives only contralateral cortical input from the opposite hemisphere.

Thus, a right supranuclear lesion (UMN damage) will affect the contralateral (left) lower facial muscles while sparing the left upper facial muscles due to bilateral innervation.

Why the Other Options Are Wrong:

1. Right lower facial motor loss – Incorrect. Since the facial nucleus on the right side is still functioning, the right side of the face remains unaffected.
2. Left upper facial motor loss – Incorrect. The upper facial muscles receive bilateral innervation, so they are still functional despite the right-sided damage.
3. Right upper facial motor loss – Incorrect. The upper face on the right receives innervation from both hemispheres, so a right-sided lesion will not affect the right upper face.
4. Upper and lower facial motor loss – Incorrect. A supranuclear (UMN) lesion spares the upper face, while a nuclear or infranuclear (LMN) lesion would cause complete ipsilateral facial paralysis (as seen in Bell’s palsy).

The internal cerebral vein is a major deep venous structure in the brain. It is formed by the union of the thalamostriate vein and the choroidal vein near the interventricular foramen (of Monro).

Once formed, the internal cerebral veins run posteriorly and join with the basal veins of Rosenthal, eventually contributing to the formation of the great cerebral vein (of Galen), which drains into the straight sinus.

Other options explained:

❌ Anterior cerebral vein and striate vein → These do not directly contribute to the formation of the internal cerebral vein.
❌ Superior cerebral vein and the great cerebral vein → The superior cerebral veins drain into the superior sagittal sinus, not forming the internal cerebral vein.
❌ Superficial cerebral vein and the basal vein → Superficial cerebral veins drain the cortex, while the basal vein (of Rosenthal) is separate and later joins the internal cerebral vein.
❌ Superficial and deep middle cerebral vein → These veins drain into different sinuses and do not contribute to the internal cerebral vein.

The cerebellum contains four deep nuclei embedded in its white matter, from lateral to medial: dentate, emboliform, globose, and fastigial nuclei. The fastigial nucleus is the most medial of these nuclei and is located near the midline, close to the vermis. It is involved in maintaining balance and posture through connections with the vestibular and reticular systems.

Why not the other options?

1. Emboliform nucleus: Located lateral to the globose nucleus and medial to the dentate nucleus.
2. Globose nucleus: Located medial to the emboliform nucleus but still lateral to the fastigial nucleus.
3. Dentate nucleus: The largest and most lateral of the cerebellar nuclei, involved in planning and coordination of voluntary movements.
4. Putamen: Part of the basal ganglia, not a cerebellar nucleus, and therefore unrelated to this question.

Understanding Wernicke’s Area and Its Function

• Wernicke’s area is located in the superior temporal gyrus of the dominant hemisphere (usually the left hemisphere in right-handed individuals).
• It is primarily responsible for language comprehension, including understanding spoken and written words.
• A lesion here results in Wernicke’s aphasia, which is characterized by:
  ✅ Fluent but meaningless speech (word salad)
  ✅ Poor comprehension of spoken and written language
  ✅ Difficulty repeating words or sentences
  ✅ Unawareness of language deficits (anosognosia)

Why the Correct Answer is Right

✅ “Inability to understand written or spoken words” is correct because:

• Wernicke’s area is essential for processing and understanding language.
• A lesion here causes receptive aphasia, meaning the patient cannot comprehend speech or text but can still produce fluent speech.

Why the Other Options Are Incorrect

• “Inability to produce fluent speech” – Incorrect

  • Speech production is controlled by Broca’s area, located in the frontal lobe.
  • In Wernicke’s aphasia, speech is fluent but nonsensical, not absent or effortful.

• “Inability to appreciate the texture of objects” – Incorrect

  • Texture perception is controlled by the somatosensory cortex (parietal lobe), not Wernicke’s area.

• “Inability to read or write” – Incorrect

  • While reading comprehension is affected, writing ability depends on multiple regions, including the angular gyrus and Broca’s area.
  • Pure alexia (inability to read) occurs due to left occipitotemporal damage, not isolated Wernicke’s area damage.

• “Inability to interpret sounds” – Incorrect

  • Primary auditory processing occurs in the primary auditory cortex (Heschl’s gyrus, temporal lobe), not Wernicke’s area.
  • Wernicke’s area specifically processes language, not basic sound perception.

The Pharyngotympanic tube (also known as the Eustachian tube) connects the middle ear (tympanic cavity) to the nasopharynx (the upper part of the throat, behind the nose). Its primary function is to equalize air pressure on both sides of the eardrum, allowing the tympanic membrane to vibrate properly for sound conduction.

lesion in the non-dominant hemisphere (typically the right hemisphere in right-handed individuals) commonly results in hemineglect syndrome, also known as contralateral neglect syndrome.

• This condition is characterized by neglect of the contralateral (left) side of the body and space.
• The patient fails to respond to stimuli on the left side and may even ignore the left side of their own body.
• This occurs due to damage to the parietal association cortex of the non-dominant hemisphere, which is responsible for spatial awareness and attention.
• The right hemisphere is dominant for spatial perception, so damage leads to severe neglect of the left side.

Why the Other Options Are Incorrect:

❌ 1. “Sensory loss” – Incorrect

• A lesion in the primary somatosensory cortex (S1) of either hemisphere can cause sensory deficits, but neglect syndrome is specific to the non-dominant hemisphere.

❌ 2. “Abnormal speech” – Incorrect

• Speech abnormalities (aphasias) occur due to lesions in the dominant hemisphere (usually left), affecting Broca’s or Wernicke’s areas.
• The non-dominant hemisphere is more involved in emotional and tonal aspects of speech (prosody), not core language function.

❌ 3. “Visual disturbances” – Incorrect

• Lesions in the visual cortex (occipital lobe) or optic radiations can cause visual field defects (hemianopia), but this is not specific to the non-dominant hemisphere.

❌ 4. “Loss of perception of language” – Incorrect

• Language comprehension and production are primarily controlled by the dominant hemisphere (left in most people).
• The non-dominant hemisphere contributes to understanding tone and emotion in speech, but it does not lead to a major loss of language perception.

The oculomotor nerve (CN III) is responsible for both accommodation (focusing on near objects) and the light reflex (pupillary constriction in response to light).

Functions of CN III in Accommodation & Light Reflex:

1. Accommodation Reflex (Near Vision Adjustment)
   • The ciliary muscles contract, causing the lens to become more convex to focus on near objects.
   • This is controlled by parasympathetic fibers from CN III via the Edinger-Westphal nucleus and the ciliary ganglion.
2. Pupillary Light Reflex
   • Direct & consensual light reflex (pupil constriction in response to light) is mediated by CN III through its parasympathetic fibers.
   • Pathway:
     • Afferent limb: Optic nerve (CN II) detects light.
     • Efferent limb: Oculomotor nerve (CN III) carries parasympathetic signals from the Edinger-Westphal nucleus to the sphincter pupillae muscle via the ciliary ganglion, causing pupil constriction.

Why the Other Options Are Incorrect:

1. V (Trigeminal nerve) ❌
   • CN V is responsible for facial sensation and mastication, not for accommodation or the light reflex.
2. IV (Trochlear nerve) ❌
   • CN IV controls the superior oblique muscle, which moves the eye downward and inward, but it does not control pupil size or lens accommodation.
3. II (Optic nerve) ❌
   • The optic nerve (CN II) is the afferent limb of the pupillary light reflex, meaning it detects light but does not control the pupil or accommodation.
   • The efferent limb (pupil constriction) is mediated by CN III.
4. VI (Abducens nerve) ❌
   • CN VI controls the lateral rectus muscle, which moves the eye laterally (abduction).
   • It is not involved in the pupillary reflex or lens accommodation.

The trigeminal nerve (CN V) is the primary sensory nerve of the face, responsible for touch, pain, temperature, and proprioception. The sensory nucleus of the trigeminal nerve is divided into three parts:

1. Principal (Chief) Sensory Nucleus – Located in the pons, responsible for fine touch and proprioception.
2. Spinal Trigeminal Nucleus – Extends from the pons to the medulla, responsible for pain and temperature sensations.
3. Mesencephalic Nucleus – Located in the midbrain, responsible for proprioception of jaw muscles.

Damage to the sensory nucleus of the trigeminal nerve leads to loss of touch sensation on the face, particularly from CN V1 (ophthalmic), CN V2 (maxillary), and CN V3 (mandibular) divisions.

Why the Other Options Are Incorrect?

❌ Nucleus of facial nerve (CN VII)

• The facial nerve (CN VII) is primarily motor and controls facial expression muscles.
• It does not mediate touch sensation on the face (which is the function of CN V).

❌ Nucleus of hypoglossal nerve (CN XII)

• The hypoglossal nucleus controls tongue movements and has no role in facial touch sensation.

❌ Motor nucleus of trigeminal nerve (CN V)

• This nucleus controls mastication muscles and does not handle sensory functions.

❌ Nucleus of abducens nerve (CN VI)

• The abducens nucleus controls lateral eye movement (via the lateral rectus muscle) and has no role in touch sensation.

• The oculomotor nerve (CN III) controls most of the extraocular muscles, including the medial rectus, which is responsible for moving the eye medially (adduction).
• Damage to CN III leads to:
  • Lateral deviation (down and out position) due to unopposed action of the lateral rectus (CN VI) and superior oblique (CN IV).
  • Pupil dilation (mydriasis) due to loss of parasympathetic fibers controlling the sphincter pupillae.
  • Loss of accommodation due to impaired ciliary muscle function.
• Common causes of oculomotor nerve palsy:
  • Diabetes mellitus (ischemic neuropathy)
  • Aneurysm (posterior communicating artery)
  • Uncal herniation (compresses CN III)

Why the Other Options Are Wrong:

1. Pons ❌
   • The pons contains the nuclei of CN V, VI, VII, and VIII, but not CN III.
   • CN VI (abducens) lesion would cause medial deviation, not lateral deviation.
2. Midbrain ❌ (Partially correct but not the best answer)
   • The oculomotor nucleus is in the midbrain, but the question asks for the directly involved structure.
   • The direct answer is CN III (oculomotor nerve itself), not the midbrain.
3. Medulla Oblongata ❌
   • The medulla contains CN IX, X, XI, and XII nuclei, not CN III.
   • Medullary lesions cause issues with swallowing, voice, and tongue movement, not eye movement.
4. Trochlear Nerve (CN IV) ❌
   • CN IV controls the superior oblique muscle, which helps in downward and inward movement of the eye.
   • A trochlear nerve lesion causes vertical diplopia and difficulty looking downward, but not lateral deviation with mydriasis.

• Posterior spinal artery: This artery is a branch of the vertebral artery or sometimes the posterior inferior cerebellar artery (PICA). It supplies the posterior third of the spinal cord.

Incorrect options:

1. Posterior communicating artery is a branch of the middle cerebral artery: Incorrect. It arises from the internal carotid artery, not the middle cerebral artery.
2. Pontine arteries are branches of the internal carotid artery: Incorrect. Pontine arteries are branches of the basilar artery, not the internal carotid.
3. Posterior inferior cerebellar artery (PICA) is a branch of the basilar artery: Incorrect. PICA is a branch of the vertebral artery.
4. Ophthalmic artery is a branch of the middle cerebral artery: Incorrect. The ophthalmic artery arises from the internal carotid artery.

• The lenticulostriate arteries are small, deep penetrating arteries that arise from the middle cerebral artery (MCA).
• These arteries supply critical deep structures, including:
  ✔ Posterior limb of the internal capsule – Contains the corticospinal tract (motor pathway) and somatosensory fibers.
  ✔ Putamen – Part of the basal ganglia, involved in movement regulation.
  ✔ Globus pallidus – Plays a role in voluntary movement control.
  ✔ Caudate nucleus (head) – Important for motor processes and cognitive function.

Clinical Relevance:

• Lacunar infarcts due to hypertensive microangiopathy commonly affect the lenticulostriate arteries, leading to pure motor strokes (contralateral hemiparesis) due to damage to the corticospinal tract in the posterior limb of the internal capsule.

Why the Other Options Are Wrong:

1. Anterior limb of the internal capsule ❌
   • Supplied by the medial striate arteries (from anterior cerebral artery, ACA), not the lenticulostriate arteries.
2. Whole internal capsule ❌
   • The internal capsule has multiple blood supplies:
     • Anterior limb → Medial striate arteries (ACA).
     • Genu → Internal carotid & lenticulostriate arteries (MCA).
     • Posterior limb → Lenticulostriate arteries (MCA) (Correct answer).
3. Inferior limb of the internal capsule ❌
   • The internal capsule does not have an “inferior limb.” The correct anatomical terms are anterior limb, genu, and posterior limb.
4. Both anterior and inferior limb of internal capsule ❌
   • The anterior limb is supplied by the medial striate arteries, not the lenticulostriate arteries.
   • Again, there is no “inferior limb” in the internal capsule.

✅ Proprioceptors

Explanation:

The cerebellum plays a crucial role in coordinating muscle movement, maintaining balance, and fine-tuning motor control. To perform these functions, it receives sensory feedback about muscle movement and body position, primarily from proprioceptors.

What Are Proprioceptors?

• Proprioceptors are specialized sensory receptors located in muscles, tendons, and joints that provide information about body position, movement, and muscle tension.
• These signals are transmitted to the cerebellum via the spinocerebellar tracts (posterior and anterior spinocerebellar pathways).

How Does the Cerebellum Use This Information?

• Adjusts movement coordination based on real-time feedback.
• Ensures smooth, precise motion by fine-tuning motor activity.
• Plays a role in balance and posture control.

Why the Other Options Are Wrong:

1️⃣ Caudate ❌

• The caudate nucleus is part of the basal ganglia, which is involved in motor planning and cognitive functions but does not send direct movement feedback to the cerebellum.

2️⃣ Putamen ❌

• The putamen is another part of the basal ganglia, responsible for regulating voluntary movements and motor learning, but it does not provide proprioceptive feedback to the cerebellum.

3️⃣ Macula ❌

• The macula (of the inner ear) is involved in vestibular function (balance and spatial orientation) but not in muscle movement feedback.
• While the vestibular system does interact with the cerebellum, it primarily deals with balance rather than direct muscle movement control.

4️⃣ Basal ganglia ❌

• The basal ganglia help in initiating and modulating voluntary movements but do not provide real-time proprioceptive feedback to the cerebellum.
• The basal ganglia influence movement indirectly through the thalamus and cortex, while the cerebellum receives direct proprioceptive input.

The inferior colliculi are part of the auditory pathway in the midbrain. They are located in the tectum of the midbrain and play a critical role in processing auditory information. The inferior colliculi receive input from the cochlear nuclei and superior olivary complex and send projections to the medial geniculate body of the thalamus, which then relays auditory information to the auditory cortex. Damage to the inferior colliculi can result in auditory disturbances, such as difficulty localizing sounds or processing auditory information.

Why the Other Options Are Wrong:

1. Lateral geniculate body:
   • The lateral geniculate body is part of the visual pathway, not the auditory pathway. It relays visual information from the retina to the visual cortex.
2. Superior colliculi:
   • The superior colliculi are involved in visual processing and coordinating eye movements, not auditory function.
3. Superior brachium:
   • The superior brachium (also called the brachium of the superior colliculus) is a pathway that connects the superior colliculus to the lateral geniculate body. It is related to visual processing, not auditory function.
4. Medial geniculate body:
   • While the medial geniculate body is part of the auditory pathway, it is located in the thalamus, not the midbrain. Damage to this structure would also cause auditory disturbances, but the question specifically asks about structures in the midbrain.

Axons are specialized structures of neurons designed for transmitting action potentials over long distances. They originate from the axon hillock, which is a specialized region of the soma. However, axons lack Nissl substance (rough endoplasmic reticulum and ribosomes), which is why this statement is false.

Why is “Nissl substance is present” false?

• Nissl substance (composed of rough ER and ribosomes) is found in the soma and dendrites but not in the axon.
• The axon hillock and initial segment of the axon lack Nissl substance, making them distinct from the soma and dendrites.
• Since axons do not have ribosomes or rough ER, they rely on the soma for protein synthesis, which is why they require axonal transport to receive necessary proteins.

Why the Other Options Are True:

1. “Transmit action potential” ✅ (True)

   • The primary function of the axon is to transmit action potentials from the soma to the axon terminals, where neurotransmitters are released to communicate with other neurons or muscles.

2. “Axons can arise from dendrites” ✅ (True)

   • While most axons arise from the axon hillock, in some neurons (like pseudounipolar neurons in the dorsal root ganglion), an axon may arise directly from a dendritic process.

3. “Axons can arise from soma” ✅ (True)

   • In most neurons, the axon originates directly from the soma (cell body), specifically from a specialized region called the axon hillock.

4. “Axons can arise from hillock” ✅ (True)

   • The axon hillock is the specialized structure of the neuron where the axon begins and where action potentials are initiated.

The nucleus ambiguus is a motor nucleus located in the medulla oblongata. It supplies the soft palate, pharynx, and larynx via the glossopharyngeal (CN IX) and vagus (CN X) nerves. Specifically:

• It provides motor innervation to the muscles of the pharynx and larynx, which are involved in swallowing and speech.
• It also contributes to the parasympathetic innervation of the heart via the vagus nerve.

Why the Other Options Are Wrong:

1. Facial nucleus:
   • The facial nucleus supplies the muscles of facial expression, not the soft palate or pharynx.
2. Trochlear nucleus:
   • The trochlear nucleus supplies the superior oblique muscle of the eye, which controls eye movement, not the soft palate or pharynx.
3. Abducens nucleus:
   • The abducens nucleus supplies the lateral rectus muscle of the eye, which controls lateral eye movement, not the soft palate or pharynx.
4. Trigeminal nucleus:
   • The trigeminal nucleus is involved in sensory and motor functions of the face, including mastication, but it does not supply the soft palate or pharynx.

The reward and punishment centers of the brain are primarily located within the limbic system, which plays a crucial role in emotion, motivation, reinforcement learning, and behavior regulation. The key structures involved in this system include:

• Nucleus accumbens (dopamine-mediated reward pathway)
• Amygdala (processing emotions like fear and pleasure)
• Hippocampus (memory and learning reinforcement)
• Hypothalamus (regulates pleasure, stress responses, and homeostasis)

These centers are critical for motivation, addiction, learning, and decision-making.

Why the other options are incorrect:

1. Hypothalamus:
   • While the hypothalamus is part of the limbic system and plays a role in regulating emotions and drives, the broader limbic system is responsible for reward and punishment mechanisms.
2. Midbrain:
   • The midbrain contains the ventral tegmental area (VTA), which contributes to dopaminergic reward circuits, but it is part of the broader limbic system network.
3. Pons:
   • The pons is primarily involved in motor control, sleep regulation, and autonomic functions, but it is not a primary site for reward and punishment processing.
4. Medulla oblongata:
   • The medulla oblongata is mainly involved in autonomic control of vital functions (e.g., heart rate, respiration) and does not play a major role in motivation and behavior.

The middle layer of the meninges refers to the arachnoid mater. The spinal arachnoid mater terminates at the level of S2, where the dural sac ends. This marks the inferior limit of the subarachnoid space, which contains cerebrospinal fluid (CSF). Tumors arising from arachnoid cells, such as meningiomas, may occur at this level.

Other options:

1. L4: Incorrect; while the spinal cord itself ends at L1-L2, the arachnoid and dural sac continue to S2.
2. S1: Incorrect; the arachnoid does not terminate here.
3. S3: Incorrect; the arachnoid terminates before this level.
4. L5: Incorrect; it is below the spinal cord but above the termination of the arachnoid.

The Circle of Willis is a circulatory anastomosis at the base of the brain that provides collateral blood supply in case of arterial blockage. It consists of arteries that primarily supply the cerebrum, not the cerebellum.

Arteries that form the Circle of Willis:

1. Anterior cerebral artery (ACA)
2. Anterior communicating artery (AComA)
3. Internal carotid artery (ICA) (contributes indirectly)
4. Posterior cerebral artery (PCA)
5. Posterior communicating artery (PComA)

Since the superior cerebellar artery (SCA) is a branch of the basilar artery and primarily supplies the cerebellum and midbrain, it is not part of the Circle of Willis.

Why the Other Options Are Incorrect?

✔ Anterior cerebral artery (ACA)

• Forms the anterior part of the Circle of Willis and supplies the medial frontal and parietal lobes.

✔ Anterior communicating artery (AComA)

• Connects the two anterior cerebral arteries (ACA) and helps complete the circle.

✔ Posterior communicating artery (PComA)

• Connects the internal carotid artery (ICA) to the posterior cerebral artery (PCA), helping maintain collateral circulation.

✔ Middle cerebral artery (MCA)

• Although the MCA is a major cerebral artery, it is not considered part of the Circle of Willis because it does not contribute to the anastomotic ring.

Since the question asks for the artery that is NOT part of the Circle of Willis, and the superior cerebellar artery (SCA) is not involved in cerebral circulation, it is the correct answer.

The genu of the internal capsule primarily contains the corticobulbar tract, which carries motor signals from the cortex to the cranial nerve nuclei controlling the muscles of the face, tongue, pharynx, and larynx. An infarct in the genu can result in dysarthria (difficulty in articulating speech) due to weakness in the orofacial and laryngeal muscles.

Why not the other options?

• Visual impairment → Associated with optic radiation lesions (in the posterior limb of the internal capsule or occipital lobe).
• Agitation → More related to frontal lobe or limbic system damage, not the genu of the internal capsule.
• Confusion → Typically linked to diffuse cortical dysfunction, not a localized infarct in the internal capsule.
• Auditory deficits → Result from damage to the auditory pathway (medial geniculate body, auditory cortex, or brainstem structures), not the internal capsule.

Thus, an infarct of the genu of the internal capsule most commonly leads to dysarthria due to corticobulbar tract involvement.

The vagus nerve (CN X) plays a crucial role in autonomic control of the respiratory system by innervating:
✔ The larynx and pharynx (via the recurrent laryngeal nerve) → important for maintaining an open airway.
✔ The lungs via parasympathetic fibers, regulating bronchoconstriction and secretion.
✔ The diaphragm indirectly, by influencing autonomic control of breathing.

Effects of Vagus Nerve Damage on Respiration:

• Hoarseness or loss of voice (if the recurrent laryngeal nerve is affected).
• Impaired airway protection, leading to aspiration risk.
• Dysregulation of autonomic breathing control.
• Severe bilateral vagus nerve damage can lead to respiratory failure.

Why the Other Options Are Incorrect?

❌ Trochlear nerve (CN IV)

• Controls the superior oblique muscle, affecting eye movement, not respiration.

❌ Optic nerve (CN II)

• Responsible for vision; does not control breathing.

❌ Abducens nerve (CN VI)

• Controls the lateral rectus muscle for eye abduction; no role in respiration.

❌ Oculomotor nerve (CN III)

• Controls eye movement and pupil constriction; does not influence breathing.

The olfactory nerve (Cranial Nerve I) does not originate from the brainstem. It arises from the olfactory epithelium in the nasal cavity and sends its axons directly to the olfactory bulb, bypassing the brainstem entirely.

The other nerves mentioned—facial nerve (Cranial Nerve VII), vestibulocochlear nerve (Cranial Nerve VIII), abducens nerve (Cranial Nerve VI), and nervus intermedius (a part of Cranial Nerve VII)—originate from the pontomedullary junction, a region at the junction between the pons and medulla oblongata in the brainstem.

The cerebellar hemispheres are primarily responsible for coordinating voluntary movements of the ipsilateral limbs. A lesion in one hemisphere results in ipsilateral motor deficits, including tremors, ataxia, dysmetria, and hypotonia.

Correct Answer: Person Falls to the Right

Why is “Person Falls to the Right” the Correct Answer?

• Cerebellar hemispheric lesions cause ipsilateral deficits because cerebellar output affects motor pathways that decussate twice (once in the cerebellum and again in the corticospinal or rubrospinal tracts).
• If the right cerebellar hemisphere is damaged, the patient will exhibit poor coordination and balance on the right side and is likely to fall to the right.
• Patients with cerebellar lesions commonly experience ipsilateral ataxia, dysmetria, and difficulty maintaining balance while standing or walking.

Why Are the Other Options Incorrect?

1. Negative Romberg Sign

   • The Romberg test is used to assess proprioception, not cerebellar function.
   • A positive Romberg sign (loss of balance when the eyes are closed) suggests sensory ataxia due to dorsal column dysfunction (e.g., vitamin B12 deficiency, tabes dorsalis).
   • Cerebellar ataxia occurs regardless of vision, so the Romberg test is typically negative in cerebellar lesions.
   • Incorrect because cerebellar dysfunction does not affect proprioception.

2. Tremors in the Right Hand

   • While cerebellar lesions can cause intention tremors, they occur on the ipsilateral side of the lesion.
   • If the lesion is in the left cerebellar hemisphere, tremors will be in the left hand.
   • Incorrect because the question does not specify which cerebellar hemisphere is affected.

3. Swaying Left to Right with Eyes Closed

   • A patient with a cerebellar lesion sways even with eyes open.
   • If the Romberg sign were positive, it would indicate sensory ataxia, not cerebellar dysfunction.
   • Incorrect because cerebellar ataxia is not dependent on visual input.

4. Decreased Muscle Tone in the Right Upper and Lower Limbs

   • Cerebellar lesions can cause hypotonia, but isolated hypotonia without ataxia is uncommon.
   • The primary symptoms of cerebellar hemisphere lesions are coordination deficits, not just muscle tone reduction.
   • Incorrect because hypotonia alone is not a primary diagnostic feature.