Locomotor – 2019

The triceps brachii has three heads, each with distinct origins:

1. Long head → Infraglenoid tubercle of scapula.

2. Lateral head → Upper half of the posterior surface of the humerus, above the radial (spiral) groove.

3. Medial head → Lower half of the posterior surface of the humerus, below the radial groove.

All three heads converge into a common tendon inserting into the olecranon process of the ulna.

Why not the others?

• Lower half of the anterior surface of humeral shaft → wrong; anterior origins belong to brachialis and biceps, not triceps. ❌

• Upper half of the anterior surface of humeral shaft → wrong; anterior side muscles are flexors. ❌

• Lower half of the posterior surface of humeral shaft → this is the medial head, not the lateral head. ❌

• None of these → incorrect, since the correct option is listed. ❌

🔹 True Continuation of the Femoral Artery

• The femoral artery is the direct continuation of the external iliac artery.

• The external iliac artery becomes the femoral artery after passing deep to the inguinal ligament, not above or strictly at the level of it.

• Because none of the provided options describe this transition accurately, the correct choice is “None of these.” ✅

❌ Why the Other Options Are Wrong

• Internal iliac artery at the level of the inguinal ligament → Wrong, internal iliac supplies pelvis and does not continue as femoral.

• External iliac artery above the inguinal ligament → Wrong, because the femoral begins only after crossing beneath the ligament.

• Internal iliac artery above the inguinal ligament → Wrong vessel entirely.

• External iliac artery at the level of the inguinal ligament → Slightly misleading, because the change happens after passing deep to the ligament, not exactly at the ligament itself.

Thus, none of the listed statements are precisely correct.

• The sarcomere is the basic structural and functional unit of a myofibril.

• It extends from one Z-line (Z-disc) to the next Z-line.

• Within a sarcomere:

  • A band = entire length of thick filament (myosin), includes overlap with thin filaments.

  • I band = only thin filaments (actin), on either side of Z-line.

  • H zone = central lighter part of A band, only thick filaments (no overlap).

  • M line = middle of the H zone, site where thick filaments are linked.

Thus, when asked “between two consecutive Z-lines” → it defines the sarcomere.

Why not the others?

• A band → thick filament region, does not span between Z-lines. ❌

• I band → thin filaments only, doesn’t cover the whole span. ❌

• H zone → central thick-only part, within A band. ❌

• M line → central axis of sarcomere, not the whole unit. ❌

• In skeletal muscle, T-tubules (transverse tubules) are invaginations of the sarcolemma that carry action potentials deep into the muscle fiber.

• The sarcoplasmic reticulum (SR) is a specialized form of smooth endoplasmic reticulum in muscle, dedicated to calcium storage and release.

• At the level of the sarcomere:

  • The terminal cisternae are enlarged sacs of SR that lie on either side of a T-tubule.

  • Together, 2 terminal cisternae + 1 T-tubule = Triad of skeletal muscle.

  • This triad is critical for excitation–contraction coupling, as calcium is released from the cisternae when the T-tubule is depolarized.

Why not the others?

• Lysosome → involved in digestion of waste, not in contraction. ❌

• Golgi apparatus → protein packaging/secretion, not Ca²⁺ storage. ❌

• Rough ER → protein synthesis (ribosomes attached), not relevant. ❌

• Smooth ER → general calcium storage in other cells, but in muscle specifically it’s modified into SR, so the precise term here is sarcoplasmic reticulum. ✅

• The lumbricals are 4 small worm-like intrinsic muscles of the hand.

• Origin: From the tendons of flexor digitorum profundus (FDP) in the palm.

• Insertion: Onto the extensor expansion (dorsal digital expansion) of digits 2–5.

• Actions:

  • Flexion at the metacarpophalangeal (MCP) joints.

  • Extension at the proximal and distal interphalangeal (PIP & DIP) joints.

  • (This combined action = “writing position” of fingers ✍️).

Why not the others?

• Flexor carpi ulnaris → flexes and adducts wrist, no digital attachment. ❌

• Palmaris longus → inserts into palmar aponeurosis, not related to lumbricals. ❌

• Flexor carpi radialis → flexes and abducts wrist, no role in lumbricals. ❌

• Flexor digitorum superficialis (FDS) → inserts on middle phalanges, not lumbrical origin. ❌

• Titin (also called connectin) is the largest known protein in skeletal muscle, with a molecular weight of ~3,000 kDa.

• It spans half of the sarcomere:

  • Anchored at the Z-disc,

  • Extends through the thick filament (myosin),

  • Reaches the M-line.

• Function:

  • Provides elasticity and passive tension,

  • Maintains alignment of myosin in the sarcomere.

Why not the others?

• Actin → thin filament, ~42 kDa, much smaller. ❌

• Myosin → thick filament protein (~520 kDa), large but still much smaller than titin. ❌

• Tropomyosin → regulatory filament protein (~70 kDa). ❌

• Troponin → regulatory protein complex (~70 kDa, 3 subunits), very small. ❌

• In second week of development (week of twos):

  • The blastocyst has trophoblast (cyto- + syncytiotrophoblast) outside and embryoblast (epiblast + hypoblast) inside.

  • Hypoblast forms the exocoelomic (Heuser’s) membrane, lining the blastocoel, creating the primary yolk sac.

  • Soon, a new layer — the extraembryonic mesoderm — develops between the exocoelomic membrane and the cytotrophoblast.

  • Cavities appear in this mesoderm → coalesce to form the extraembryonic coelom (chorionic cavity).

• This layer later differentiates into:

  • Somatopleuric extraembryonic mesoderm → lining cytotrophoblast.

  • Splanchnopleuric extraembryonic mesoderm → covering yolk sac.

Why not the others?

• Extraembryonic membrane and cytotrophoblast → vague, not specific. ❌

• Extraembryonic membrane and syncytiotrophoblast → incorrect, syncytiotrophoblast is outside cytotrophoblast. ❌

• Syncytiotrophoblast and cytotrophoblast → that’s where lacunae form, not extraembryonic mesoderm. ❌

• None of these → incorrect, because the correct relation is well-known. ❌

• Pain transmission pathways rely on primary afferent fibers:

  • A-delta fibers → carry fast, sharp, superficial pain.

  • C fibers → carry slow, dull, burning pain.

• Neurotransmitters involved:

  • Glutamate → major excitatory neurotransmitter; released by A-delta fibers → mediates acute superficial pain.

  • Substance P → released by C fibers, responsible for slow, chronic, deep pain transmission.

Why not the others?

• Vasoactive intestinal peptide (VIP) → involved in autonomic & GI functions, not pain conduction. ❌

• Tryptophan → amino acid precursor for serotonin, not itself a pain neurotransmitter. ❌

• Serotonin (5-HT) → modulates pain at the spinal level but is not the primary neurotransmitter of superficial pain. ❌

• Glycine → inhibitory neurotransmitter in spinal cord/brainstem, not excitatory pain mediator. ❌

• Cyclooxygenase (COX) enzymes:

  • COX-1 → constitutive enzyme, maintains gastric mucosa, renal blood flow, platelet aggregation.

  • COX-2 → inducible enzyme, mediates inflammation, pain, and fever.

• Aspirin (acetylsalicylic acid):

  • Irreversibly inhibits both COX-1 and COX-2.

  • At low doses → mainly COX-1 inhibition (antiplatelet effect).

  • At higher doses → inhibits both, giving analgesic, anti-inflammatory, and antipyretic effects.

Why not the others?

• Paracetamol / Acetaminophen → weak inhibitor of COX in the periphery, acts mainly in the CNS; not a strong COX-1/2 inhibitor. ❌

• Dipyrone (metamizole) → a prodrug with weak COX inhibition, more of an analgesic & antipyretic, not a classical NSAID. ❌

• Antipyrine → older analgesic/antipyretic, weak COX inhibitor, not used commonly now. ❌

🔹 Common Elbow Fracture in Children

• The most common fracture around the elbow in children is a supracondylar fracture of the humerus.

• In these fractures, the distal fragment of the humerus is often displaced posteriorly.

• The sharp edge of the proximal bone fragment may impinge on structures anterior to the elbow.

🔹 Anatomy at Risk

• The brachial artery runs anterior to the distal humerus, just in front of the elbow joint.

• When the distal fragment moves posteriorly, the brachial artery is stretched, compressed, or even torn.

• Median nerve may also be injured along with the artery.

🔹 Clinical Correlation

• Compromise of the brachial artery in such fractures can cause ischemia of the forearm.

• This may lead to Volkmann’s ischemic contracture if not treated promptly.

❌ Why the Other Options Are Wrong:

• Ulnar artery → Branches off the brachial artery further down, near the cubital fossa; not the main vessel at risk in this injury.

• Radial artery → Also a distal branch of the brachial artery; not directly damaged at the fracture site.

• Cephalic artery → No such artery; cephalic is a vein, not an artery.

• Axillary artery → Located proximally in the axilla; too far from the elbow.

• Estrogen plays a crucial role in bone remodeling:

  • It inhibits osteoclast activity (thus reducing bone resorption).

  • It stimulates osteoblast survival (promotes bone formation).

👉 In low estrogen states (e.g., postmenopausal women), there is:

• Unopposed osteoclast activity → increased bone resorption

• Bone formation cannot keep up → high bone turnover osteoporosis (postmenopausal osteoporosis).

Why not the others?

• High progesterone → minimal effect on bone metabolism. ❌

• Low calcium & low vitamin D → causes osteomalacia/rickets, not osteoporosis. ❌

• High estrogen → protective, prevents osteoporosis. ❌

• Low progesterone → not a major cause of osteoporosis. ❌

Extension of the leg at the knee joint is performed by the quadriceps femoris muscle group.

• The femoral nerve (L2–L4) supplies the quadriceps. ✅
  → Damage = inability to extend the knee, loss of patellar reflex.

Now why not the others?

• Sciatic nerve → supplies hamstrings & all below knee (posterior thigh & leg), but they mainly flex the knee, not extend. ❌

• Tibial nerve → supplies posterior leg & plantar foot muscles, helps plantarflexion, not knee extension. ❌

• Common peroneal nerve → supplies anterior & lateral leg (dorsiflexion & eversion), not knee extension. ❌

• Obturator nerve → supplies adductors of thigh, role in thigh adduction, not knee extension. ❌

So, loss of knee extension = femoral nerve lesion.

The principles of health education are built on psychology, sociology, and communication science. Classic key principles include:

• Change of behavior → ultimate goal of health education ✅

• Creating habits → reinforcement of healthy practices ✅

• Learning by doing → practical, participatory approach ✅

• Good relations → rapport with community, trust building ✅

👉 But “Knowing customs” is not considered a principle itself. Instead, it is part of understanding the community’s background (a facilitator of health education), not a core principle.

The nuchal ligament (ligamentum nuchae) runs from the external occipital protuberance → spinous process of C7, acting as a midline septum.
Several muscles attach to it:

• Trapezius (major one, though not in options).

• Rhomboid minor also takes part of its origin from the lower end of the ligament.

Now check the options:

• Rhomboid major → Origin: spinous processes of T2–T5, not the nuchal ligament.

• Rhomboid minor → Origin: lower nuchal ligament & spinous processes of C7–T1 ✅

• Latissimus dorsi → Origin: lower thoracic/lumbar vertebrae, iliac crest, ribs, thoracolumbar fascia — not nuchal ligament.

• Levator scapulae → Origin: transverse processes of C1–C4 — not nuchal ligament.

• Teres major → Origin: posterior surface of inferior angle of scapula — not nuchal ligament.

Klumpke’s palsy results from injury to the lower trunk of the brachial plexus (C8–T1 roots), often due to excessive upward traction on the arm (e.g., during delivery or grabbing something while falling).

• It primarily affects the ulnar nerve (and sometimes median), leading to:

  • Paralysis of intrinsic hand muscles (lumbricals + interossei).

  • Imbalance between long flexors/extensors → clawing of the hand.

  • May also be associated with Horner’s syndrome (ptosis, miosis, anhidrosis) if T1 sympathetic fibers are involved.

Now the options:

• Claw hand → Yes, classic finding.

• Waiter’s tip hand → Erb’s palsy (upper trunk, C5–C6).

• Shoulder drop → Accessory nerve injury (CN XI, trapezius).

• Hand of benediction → Median nerve injury (at the wrist or forearm, when trying to make a fist).

• Wrist drop → Radial nerve injury.

The sartorius (the longest muscle in the body) arises from the ASIS and inserts into the upper medial surface of the tibia (pes anserinus).

Its actions:

• Flexes the thigh at the hip

• Laterally rotates the thigh

• Abducts the thigh (weakly)

• Flexes the leg at the knee

This unique combo of actions allows the “tailor’s position” — sitting cross-legged.

Now the options:

• Gracilis → adduction & weak flexion of thigh, medial rotation, not lateral.

• Adductor longus → adduction & medial rotation, not lateral.

• Pectineus → flexion & adduction of thigh, assists in medial rotation.

• Vastus lateralis → extension of the knee, no hip action.

Thus, sartorius is the only one that does both lateral rotation and flexion at the hip.

The serratus anterior originates from the upper 8–9 ribs and inserts along the medial border of the scapula.

Its actions on the scapula are:

• Protraction → pulls scapula forward around the chest wall (like pushing or punching).

• Upward rotation → rotates scapula so the glenoid cavity faces upward (essential for abduction beyond 90°).

• Fixation → holds scapula against thoracic wall (prevents “winging”).

Now the options:

• Depression: done by lower trapezius, pectoralis minor.

• Retraction: done by trapezius (middle fibers) & rhomboids.

• Downward rotation: done by levator scapulae, rhomboids.

• Elevation: done by trapezius (upper fibers), levator scapulae.

So the primary listed action here = Protraction.

The lumbricals are 4 worm-like muscles in the hand that flex the metacarpophalangeal joints (MCP) and extend the interphalangeal joints (IP).

• Lumbricals 1 & 2 (lateral two): supplied by the median nerve.

• Lumbricals 3 & 4 (medial two): supplied by the deep branch of the ulnar nerve.

Now, why the other options are wrong:

• Median + radial: radial nerve does not supply intrinsic hand muscles (except sensation on dorsum).

• Median + musculocutaneous: musculocutaneous ends as lateral cutaneous nerve of forearm, no role in hand muscles.

• Radial + ulnar: radial is excluded (as above).

• Ulnar + musculocutaneous: musculocutaneous irrelevant here.

So the correct functional pair is median + ulnar.

The surgical neck of the humerus is the most common fracture site. The axillary nerve and the posterior circumflex humeral artery wrap around it.

• Axillary nerve damage → paralysis of deltoid and teres minor → loss of shoulder abduction beyond 15° and weak external rotation.

• Also causes loss of sensation over the regimental badge area (skin over deltoid).

Now, ruling out others:

• Radial nerve → injured in mid-shaft humeral fractures (radial groove).

• Musculocutaneous nerve → rarely injured, lies in anterior arm.

• Ulnar nerve → commonly injured at medial epicondyle fracture.

• Median nerve → injured at supracondylar humerus fracture.

Thus, at the neck of humerus, the axillary nerve is at risk.

The sartorius is the “tailor’s muscle,” the longest muscle in the human body.
It performs all three actions together at the hip:

• Flexion of thigh

• Abduction of thigh

• Lateral rotation of thigh

Additionally, it also flexes the knee.

Now, let’s rule out the others:

• Adductor longus → adducts thigh, not involved in abduction or lateral rotation.

• Obturator externus → laterally rotates thigh, but doesn’t flex or abduct.

• Gluteus medius → abducts and medially rotates thigh, not lateral rotation.

• Gracilis → adducts thigh and flexes leg, no role in lateral rotation or abduction.

Thus, the only muscle combining flexion + abduction + lateral rotation is sartorius.

The medial malleolus is the bony prominence you can feel on the inner side of the ankle. It is formed by the inferior end of the tibia.

• Tibia (medial bone of leg): lower end expands to form the medial malleolus → articulates with talus in the ankle joint.

• Fibula (lateral bone of leg): its lower end forms the lateral malleolus.

• Talus & Navicular: tarsal bones of the foot, no malleolus.

• Femur: thigh bone, has condyles and epicondyles, not malleoli.

During collagen synthesis, hydroxylation of proline and lysine residues occurs in the rough endoplasmic reticulum.

• The enzyme prolyl hydroxylase (and lysyl hydroxylase) requires:

  • Ascorbate (Vitamin C) → cofactor

  • Fe²⁺

  • O₂

  • α-ketoglutarate

👉 Hydroxylation stabilizes collagen by forming hydrogen bonds between chains.

🔴 Deficiency of ascorbate → defective hydroxylation → unstable collagen → Scurvy (bleeding gums, poor wound healing, fragile capillaries).

• Calcitriol (active Vit D) → calcium & phosphate metabolism.

• Cholecalciferol (Vit D3 precursor) → inactive form.

• Retinol (Vit A) → vision, epithelial growth.

• Folate (B9) → one-carbon metabolism, nucleotide synthesis.

Inversion of the foot is produced mainly by:

• Tibialis anterior → supplied by deep peroneal nerve

• Tibialis posterior → supplied by tibial nerve

If both deep peroneal + tibial nerves are damaged, both invertors are paralyzed → complete loss of inversion.

• Tibial + common peroneal nerve → ❌ would cause more extensive loss (plantarflexion, dorsiflexion, eversion too), not just inversion.

• Superficial peroneal + sural nerve → ❌ superficial peroneal supplies everters, sural is sensory only.

• Superficial peroneal + tibial nerve → ❌ loss of eversion + plantar flexion, but tibialis anterior (deep peroneal) is intact, so partial inversion still possible.

• Superficial + deep peroneal nerve → ❌ knocks out dorsiflexors + everters, but tibialis posterior (tibial nerve) still inverts.

A comminuted fracture occurs when the bone breaks into multiple fragments (splinters or pieces).

• Usually results from high-energy trauma (e.g., motor vehicle accidents, falls from height).

• These fractures are often unstable and require surgical fixation because the bone pieces cannot realign easily on their own.

• Simple fracture → ❌ bone breaks cleanly into two pieces without fragments.

• Open fracture → ❌ bone pierces through the skin.

• Fracture with unaligned bones (displaced fracture) → ❌ refers to displacement, not fragmentation.

• Closed fracture → ❌ skin remains intact.

The Na⁺/K⁺ ATPase pump actively transports:

• 3 Na⁺ ions out of the cell

• 2 K⁺ ions in to the cell

That means one net positive charge is lost from the inside of the cell per cycle.

• This creates a net outward current, leaving the inside slightly more negative.

• The contribution of this pump to the resting membrane potential (RMP) is relatively small (about –1 to –3 mV), compared to the much larger contribution from K⁺ leak channels.

Among the given options, the closest physiologically correct value is –1 mV.

• –2, –3, –4, –5 mV → ❌ too large; the pump’s effect is minor compared to ion diffusion gradients.

• –1 mV → ✅ realistic contribution to RMP.

The axillary artery is divided into three parts by the pectoralis minor muscle:

1. First part → proximal (medial) to pectoralis minor

2. Second part → posterior (behind) to pectoralis minor

3. Third part → distal (lateral) to pectoralis minor

This anatomical division is important because branches of the artery are grouped according to these three parts.

• Pectoralis major → ❌ lies superficial, does not divide the artery.

• Pectoralis minor → ✅ the landmark that divides the axillary artery.

• Teres minor → ❌ located near shoulder joint, unrelated.

• Teres major → ❌ marks the end of axillary artery (becomes brachial artery) but does not divide it.

• Coracobrachialis → ❌ located in the arm, not dividing the axillary artery.

The medial longitudinal arch of the foot is the higher and more important arch compared to the lateral one.

• Its keystone (the central stone locking an arch in architecture) is the head of the talus.

• This part bears the body weight and distributes it forward (towards forefoot) and backward (towards hindfoot).

• The talus is supported from below by the spring ligament (plantar calcaneonavicular ligament), which prevents it from dropping down.

• Navicular bone → ❌ it is a pillar in the arch, but not the keystone.

• Calcaneal tubercle → ❌ posterior pillar of the arch.

• Talus head → ✅ keystone, central weight-bearing element.

• Medial cuneiform bone → ❌ anterior pillar of the arch.

• Metatarsals → ❌ anterior pillars, help maintain the arch but not keystone.

Inversion and eversion of the foot do not occur at the ankle (talocrural) joint — that joint only allows dorsiflexion and plantarflexion.
Instead, these movements happen at two joints working together:

1. Subtalar joint (between talus and calcaneus) → allows gliding/twisting movements.

2. Transverse tarsal joint (Chopart’s joint) → a compound joint made of:

   • Talonavicular joint

   • Calcaneocuboid joint

Together, they allow the complex motion of inversion (sole turns inward) and eversion (sole turns outward).

• Talocrural + talocalcaneal → ❌ talocrural isn’t for inversion/eversion.

• Subtalar + talocrural → ❌ again, talocrural is dorsiflexion/plantarflexion only.

• Subtalar + transverse tarsal → ✅ correct, these control inversion/eversion.

• Talotibial + talocalcaneal → ❌ talotibial = talocrural, same issue.

• Transverse tarsal + tibiotalar → ❌ same error, ankle joint not involved.

The axillary vein is the main vein of the upper limb that continues as the subclavian vein at the lateral border of the 1st rib.

• It begins at the lower border of teres major by the union of the:

  • Basilic vein (superficial system)

  • Brachial vein (deep system — venae comitantes of the brachial artery)

• It receives tributaries corresponding to the axillary artery branches and also the cephalic vein, but the cephalic vein drains into it later, it does not form it.

• Basilic + brachial → ✅ correct, forms axillary vein.

• Basilic + subclavian → ❌ axillary drains into subclavian, not formed by it.

• Brachial + cephalic → ❌ cephalic joins later, not at formation.

• Basilic + radial → ❌ radial drains into brachial vein, not axillary.

• Basilic + cephalic → ❌ cephalic is a tributary, not a forming vein.

The flexor retinaculum (transverse carpal ligament) forms the roof of the carpal tunnel.

• Laterally (lateral attachment): Tubercle of scaphoid + Ridge of trapezium.

• Medially (medial attachment): Pisiform + Hook of hamate.

This arrangement creates the carpal arch, converting it into a tunnel for the median nerve and the flexor tendons.

• Tubercle of scaphoid & ridge of trapezium → lateral side, not medial.

• Pisiform & trapezoid → trapezoid is not part of carpal tunnel attachment.

• Tubercle of scaphoid & hook of hamate → mixes lateral + medial structures, incorrect.

• Ridge of trapezium & hook of hamate → again lateral + medial mix, wrong.

The deltopectoral triangle (or groove) is a small triangular interval between:

• Deltoid (laterally)

• Pectoralis major (medially)

• Clavicle (superiorly)

🔹 The cephalic vein runs in the deltopectoral groove and pierces the clavipectoral fascia to drain into the axillary vein.

• Subclavian vein → Lies deeper, under clavicle, not in this triangle.

• Brachial vein → Runs with brachial artery in the arm, not here.

• Basilic vein → Medial side of forearm and arm, doesn’t enter deltopectoral groove.

• Axillary vein → Final drainage point but lies deep, not traversing the triangle itself.

Hence, only the cephalic vein is the correct choice.

When taking X-rays of long bones (e.g., humerus, femur, tibia, radius–ulna), radiologists need two views at right angles to each other to avoid missing fractures or displacements.

• AP view → Shows the bone lengthwise in the frontal plane.

• Lateral view → Provides depth and relationship with surrounding structures.

• Oblique views → Usually reserved for joints (e.g., hand, foot, spine), not long bones.

• PA view → More commonly used for chest X-rays, not long bones.

So, the standard imaging for long bones is AP + lateral.

Nerve fibers are classified by Erlanger and Gasser into groups A (α, β, γ, δ), B, and C, based on diameter and conduction velocity.

• A-alpha fibers

  • Largest diameter (13–20 μm)

  • Fastest conduction (80–120 m/s)

  • Function: Somatic motor neurons + proprioception (muscle spindle primary endings, Golgi tendon organs).

• A-beta fibers

  • Diameter: 6–12 μm

  • Conduction: 35–90 m/s

  • Function: Touch and pressure.

• A-gamma fibers

  • Diameter: 5–8 μm

  • Conduction: 10–45 m/s

  • Function: Motor to muscle spindles (intrafusal fibers).

• A-delta fibers

  • Diameter: 1–6 μm

  • Conduction: 5–40 m/s

  • Function: Fast pain, temperature.

• A-epsilon fibers → ❌ Not a recognized standard fiber type.

Thus, A-alpha is the fastest.

• Cartilage is resilient and shock-absorbing because of its extracellular matrix, which is rich in proteoglycans and glycosaminoglycans (GAGs) such as chondroitin sulfate, keratan sulfate, and hyaluronic acid.

• These GAGs are highly negatively charged, attracting large amounts of water molecules → the matrix becomes hydrated, gel-like, and compressible.

• This hydration allows cartilage to act like a shock absorber, resisting compressive forces while remaining flexible.

• Why not others?

  • Non-covalent bonding between GAGs and proteins → helps in structure, but alone doesn’t explain the shock-absorbing property.

  • Regenerative ability of chondrocytes → is actually poor, so not the reason.

  • Ossification of cartilage → makes it rigid, not resilient.

  • All of these → incorrect, since only hydration of GAGs is the real mechanism.

Professor-style Explanation:

• The lateral plate mesoderm splits into two layers:

  • Somatic (parietal) mesoderm → body wall, limbs, dermis, parietal pleura/peritoneum.

  • Splanchnic (visceral) mesoderm → cardiac muscle, smooth muscle of gut, blood vessels, visceral pleura/peritoneum.

• Cardiac muscle specifically develops from the splanchnic mesoderm around the primitive heart tube.

• Why not others?

  • Somatic mesoderm → forms skeletal elements of the limbs, connective tissue of body wall.

  • Paraxial mesoderm → somites → skeletal muscle, dermis, vertebrae.

  • Intermediate mesoderm → kidneys and gonads.

  • Lateral plate mesoderm (general term) is true, but the exam expects the more precise “splanchnic mesoderm.”

• Howship’s lacunae = small resorption bays found on the surface of bone.

• They are created by osteoclast activity when bone is being resorbed.

• Osteoclasts are large, multinucleated cells derived from monocyte/macrophage lineage.

• They release acid + proteolytic enzymes → dissolve mineralized matrix → form these lacunae.

❌ Why the other options are wrong:

• Chondrocytes → found in cartilage lacunae, not bone.

• Osteoprogenitor cells → precursors of osteoblasts, found in periosteum and endosteum.

• Osteocytes → mature bone cells, live inside lacunae (but not Howship’s, rather osteocytic lacunae).

• Osteoblasts → bone-forming cells, line bone surfaces, do not occupy Howship’s lacunae.

• The clavicle is the most commonly fractured bone in the body, especially from falls on the outstretched hand or direct trauma.

• The weakest point is at the junction of the medial 2/3 and lateral 1/3, because:

  • Medial 2/3 is rounded and strong (transmits force to axial skeleton).

  • Lateral 1/3 is flattened and weak (articulates with scapula, subject to stress).

  • The sudden change in curvature creates a structural weak spot → fracture site.

❌ Why the other options are wrong:

• Junction of lateral 3/4 with medial 1/4 → not the usual weak point.

• Junction of medial 3/4 with lateral 1/4 → rarely described fracture site.

• Midpoint of clavicle → close, but classically it’s the medial 2/3 & lateral 1/3 junction, not exact midpoint.

• Junction of lateral 2/3 with medial 1/3 → incorrect phrasing; should be medial 2/3 with lateral 1/3.

The great saphenous vein (GSV) is the longest vein in the body, running from the foot to the groin.

Course of GSV:

1. Origin: From the medial side of the dorsal venous arch of the foot.

2. Ankle: Passes anterior to the medial malleolus (this is the key landmark).

3. Leg & Thigh: Ascends along the medial side of the leg and thigh.

   • Lies posterior to the medial condyle of the femur (not anterior).

4. Termination: Pierces the cribriform fascia in the femoral triangle to drain into the femoral vein, but it does so deep to the fascia lata, not superficial.

❌ Why the other options are wrong:

• Posterior to the medial malleolus → That’s the small saphenous vein, not the great.

• Anterior to the medial condyle of tibia/femur → Wrong, it passes posterior to the medial condyle of femur.

• Passes up the lateral side of the leg → That’s the small saphenous vein.

• Joins femoral vein superficial to the fascia lata → Wrong, it pierces fascia lata at the saphenous opening → joins femoral vein deep.

Abduction of the upper limb occurs in stages and involves different muscles at different ranges:

1. 0–15°: Supraspinatus initiates abduction.

2. 15–90°: Deltoid (mainly middle fibers) continues abduction.

3. Above 90° (90–180°): The arm cannot elevate further unless the scapula rotates upward.

   • This scapular upward rotation is produced by trapezius (upper and lower fibers) and serratus anterior working together.

So, after 90°, abduction is not just about the glenohumeral joint anymore — it requires the scapulothoracic joint, hence trapezius and serratus anterior.

❌ Why the other options are wrong:

• Deltoid and levator scapulae: Levator scapulae elevates the scapula, not upwardly rotates it — so it cannot assist in abduction above 90°.

• Deltoid and supraspinatus: Work only up to 90°, not beyond.

• Deltoid and trapezius: Deltoid stops being the prime mover after 90°; trapezius needs serratus anterior for coordinated scapular rotation.

• Trapezius and levator scapulae: Same problem — levator scapulae elevates, doesn’t rotate scapula upward.

• Sartorius → The longest muscle in the human body.

  • It runs obliquely across the thigh, from the anterior superior iliac spine (ASIS) to the medial surface of the tibia (pes anserinus).

  • Function: Flexes, abducts, and laterally rotates the hip + flexes the knee.

❌ Why the other options are wrong:

• Iliacus → A flat muscle filling the iliac fossa, contributes to hip flexion, but is not the longest.

• Psoas major → A long vertical muscle, but shorter than sartorius.

• Vastus medialis → A quadriceps muscle; large and powerful, but not the longest.

• Pectineus → A short, flat muscle of the medial thigh (adductor group).

• The lesser tubercle of the humerus is a small anterior prominence.

• Subscapularis, one of the rotator cuff muscles, inserts into the lesser tubercle.

• Function: It medially rotates the humerus and stabilizes the shoulder joint.

❌ Why the others are wrong:

• Infraspinatus → Inserts on the greater tubercle (middle facet); externally rotates the humerus.

• Teres minor → Inserts on the greater tubercle (inferior facet); externally rotates the humerus.

• Supraspinatus → Inserts on the greater tubercle (superior facet); initiates abduction of the arm.

• Teres major → Inserts on the medial lip of the intertubercular sulcus (NOT on any tubercle).

The femoral canal is the medial compartment of the femoral sheath. Its main purpose is to allow:

• Expansion of the femoral vein during increased venous return (e.g., exercise, pregnancy).

• Passage of lymphatics and a deep inguinal lymph node.

📌 Contents of femoral canal:

1. Lymphatics (from deep inguinal to external iliac nodes)

2. Deep inguinal lymph node (node of Cloquet/Rosenmüller, sometimes present)

3. Loose areolar tissue (to allow vein expansion)

4. Fat

It does NOT contain major vessels (artery/vein) or the femoral nerve.

❌ Why the other options are wrong:

• Femoral artery, vein, and lymphatic vessels → ❌ Artery and vein are in other compartments of the sheath, not the femoral canal.

• Femoral artery → ❌ Lateral compartment, not canal.

• Femoral nerve → ❌ Outside the femoral sheath altogether.

• Femoral vein → ❌ Intermediate compartment, not canal.

The femoral sheath is a funnel-shaped fascial tube located in the upper thigh. It is an extension of abdominal fascia (transversalis and iliac fascia) into the thigh.

• Important point: The femoral sheath does NOT contain the femoral nerve. The femoral nerve lies outside the sheath, lateral to it.

The sheath is divided into three compartments (from lateral → medial):

1. Lateral compartment → Femoral artery (and femoral branch of genitofemoral nerve)

2. Intermediate compartment → Femoral vein

3. Medial compartment (femoral canal) → Contains lymphatics and lymph node of Cloquet (deep inguinal node), plus loose connective tissue.

❌ Why the other options are wrong:

• Femoral nerve, femoral artery, and femoral vein → ❌ Femoral nerve is outside the sheath.

• Femoral vein, femoral artery, and lymphatic vessels → ❌ Wrong order (artery is lateral to vein, not vice versa).

• Femoral vein, femoral artery, and femoral nerve → ❌ Again, nerve not inside sheath, and order incorrect.

• Femoral nerve, femoral artery, femoral vein, and inguinal lymph nodes → ❌ Too many contents; nerve is excluded.

The greater sciatic foramen is a key anatomical passage between the pelvis and gluteal region.

• The piriformis muscle passes through the greater sciatic foramen.

• In fact, the piriformis is so important that it divides the foramen into two regions:

  • Above piriformis → superior gluteal vessels and nerve.

  • Below piriformis → inferior gluteal vessels, pudendal nerve, sciatic nerve, posterior femoral cutaneous nerve, and others.

❌ Why the other options are wrong:

• Obturator externus: Does not pass through the greater sciatic foramen; it passes directly from the obturator membrane to the trochanteric fossa.

• Obturator internus: Passes through the lesser sciatic foramen, not the greater.

• Quadratus femoris: Lies deep in the gluteal region; does not pass through any sciatic foramen.

• Superior and inferior gemelli: These muscles arise from the ischium and attach to tendon of obturator internus; they do not pass through the foramen.

• The nutrient artery of the fibula arises from the peroneal artery (also called the fibular artery).

• This artery is a branch of the posterior tibial artery, and it runs along the medial aspect of the fibula.

• From it, a nutrient branch enters the nutrient foramen (on the posterior surface of the fibula) to supply the medullary cavity and inner two-thirds of the shaft.

❌ Why the other options are wrong:

• Popliteal artery: Supplies branches around the knee (genicular arteries), but not the nutrient artery of the fibula.

• Inferior medial genicular artery: A branch of the popliteal, but it only supplies the knee joint region, not long bone shafts.

• Posterior tibial artery: Main branch of popliteal, gives off the peroneal artery but does not directly supply the fibula’s nutrient artery.

• Anterior tibial artery: Runs in the anterior compartment of the leg to supply anterior muscles and the dorsum of foot, not the fibula shaft.

• An action potential depends on depolarization of the neuronal membrane.

• Depolarization occurs mainly due to influx of sodium (Na⁺) ions, which make the inside of the cell more positive.

• Anything that makes the inside more negative (hyperpolarization) will inhibit action potential.

👉 Chloride (Cl⁻) is a negatively charged ion.

• When chloride ions flow into the cell, the membrane potential becomes more negative (hyperpolarized).

• This moves the membrane potential further away from the threshold required to fire an action potential, thereby inhibiting excitability.

❌ Why the other options are wrong:

• Influx of potassium (K⁺): Potassium normally moves out of the cell during repolarization. Influx of K⁺ (if it happens) would actually depolarize, not inhibit.

• Influx of sodium (Na⁺): This is the main cause of depolarization and initiation of action potential, not inhibition.

• Influx of calcium (Ca²⁺): Calcium influx typically promotes neurotransmitter release and can support depolarization, not inhibit.

• Influx of bicarbonate (HCO₃⁻): While theoretically a negatively charged ion entering could hyperpolarize, bicarbonate is not a major regulator of action potential under physiological conditions. Chloride is the physiologically relevant inhibitory ion (through GABA_A receptor activation).

Vitamin D plays a central role in maintaining calcium and phosphate homeostasis, which is crucial for:

• Bone mineralization

• Neuromuscular function

• Cell signaling

How Vitamin D Regulates Calcium and Phosphorus:

1. Increases intestinal absorption of calcium and phosphate by upregulating calcium-binding proteins.

2. Stimulates bone resorption in conjunction with parathyroid hormone (PTH) when calcium is low, releasing both calcium and phosphate.

3. Promotes renal reabsorption of calcium and excretion of phosphate, balancing serum levels.

The active form of Vitamin D is calcitriol (1,25-dihydroxycholecalciferol), synthesized in the kidneys under PTH influence.

❌ Why the Other Options Are Incorrect

• Vitamin B:
  ❌ Involved in energy metabolism and nervous system function, not mineral regulation.

• Glycogen:
  ❌ A storage form of glucose, not related to calcium or phosphate homeostasis.

• Vitamin C:
  ❌ Important for collagen synthesis and immune function, but not directly involved in calcium/phosphorus regulation.

• Insulin:
  ❌ Regulates glucose metabolism, not calcium or phosphate levels directly.

The gluteus medius is a key hip abductor and pelvic stabilizer during walking.

• It functions primarily during the stance phase of gait.

• When the opposite foot is lifted (e.g. during swing phase), the gluteus medius on the stance leg contracts to keep the pelvis level.

• If the gluteus medius is weak or paralyzed (e.g., due to superior gluteal nerve injury), the pelvis drops on the opposite side — a condition called a Trendelenburg gait, commonly perceived as limping.

❌ Why the Other Options Are Incorrect

• Gluteus maximus:

  • Important for hip extension (e.g., standing up from sitting, climbing stairs), but not critical for pelvic stabilization during normal walking.

• Semitendinosus & Semimembranosus:

  • These are hamstring muscles, involved in knee flexion and hip extension, not in lateral pelvic stability during gait.

• Rectus abdominis:

  • A trunk flexor. Has no direct role in leg movement or gait stabilization.

From the 18th to 20th century, the significant decline in mortality rates was primarily driven by preventive measures, not cures or treatments.

Key contributors to improved survival included:

• Public health interventions:

  • Clean water supply

  • Improved sanitation

  • Waste disposal systems

  • Quarantine practices

• Vaccination:

  • For smallpox, diphtheria, and later other infectious diseases.

• Improved nutrition and living standards:

  • Better food distribution, housing, and hygiene awareness.

• Health education:

  • Knowledge of handwashing, safe childbirth practices, etc.

While medical treatments were limited before antibiotics (introduced mid-20th century), preventive strategies drastically reduced mortality, especially from infectious diseases like cholera, tuberculosis, and typhoid.

❌ Why the Other Options Are Incorrect

• Diseases:
  ❌ Incorrect. Diseases caused mortality, not its decline.

• All of these:
  ❌ Incorrect. While prevention is correct, the other choices are not. “All” includes incorrect factors.

• Carelessness:
  ❌ Incorrect. Carelessness typically contributes to increased mortality, not its reduction.

• None of these:
  ❌ Incorrect. Prevention clearly did cause a decline in mortality, so this is false.

The great saphenous vein is the longest vein in the body and is a superficial vein of the lower limb. It plays a critical role in venous drainage and is often harvested for coronary artery bypass grafting (CABG).

Course Overview:

• Begins at the medial end of the dorsal venous arch of the foot.

• Ascends anterior to the medial malleolus.

• Travels along the medial side of the leg and thigh.

• Passes posterior to the medial condyle of the femur.

• Remains superficial to the deep fascia (fascia lata) throughout its course.

• Finally pierces the fascia lata at the saphenous opening to drain into the femoral vein.

❌ Why the Other Options Are Incorrect

• Posterior to medial malleolus:
  ❌ Incorrect. The great saphenous vein passes anterior to the medial malleolus. The small saphenous vein passes posterior to the lateral malleolus.

• Posterior to medial epicondyle of femur and tibia:
  ❌ Incorrect. While it does pass posterior to the medial condyle of the femur, there is no “epicondyle” of the tibia, and grouping the femur and tibia together here is anatomically imprecise.

• Anterior to medial epicondyle of femur and tibia:
  ❌ Incorrect. Again, epicondyles of the tibia don’t exist, and the vein runs posterior to the femoral medial condyle, not anterior.

• None of these:
  ❌ Incorrect. The last option (superficial to fascia lata) is correct.

The short head of the biceps femoris originates from the linea aspera on the femur and does not cross the hip joint, unlike other hamstrings. This means its flexion of the leg (at the knee) is not affected by the position of the hip.

• When the thigh is flexed, the long head of biceps femoris, semitendinosus, and semimembranosus (all crossing both hip and knee) are in a shortened position, reducing their ability to further shorten and produce strong flexion at the knee.

• But the short head, being a one-joint muscle, functions more effectively during knee flexion regardless of hip position.

This is an example of the length-tension relationship in muscle physiology.

❌ Why the Other Options Are Incorrect

• Semitendinosus: Crosses both hip and knee; its ability to flex the knee decreases when the hip is already flexed.

• Adductor longus: A hip adductor; does not contribute to knee flexion.

• Long head of biceps femoris: Like other true hamstrings, it crosses both joints and its flexion force at the knee is reduced when the hip is flexed.

• Semimembranosus: Also a hamstring muscle that crosses both hip and knee joints; less efficient in flexed hip position.

Raising the arm above shoulder level (beyond 90°) involves scapular rotation, not just movement at the glenohumeral joint.

• The serratus anterior, supplied by the long thoracic nerve, is crucial for upward rotation of the scapula.

• This muscle anchors the scapula to the thoracic wall and allows it to rotate so that the glenoid fossa tilts upward, permitting full arm elevation.

• Damage to the long thoracic nerve (e.g., during trauma, surgery, or backpack injury) causes winging of the scapula and an inability to raise the arm above shoulder level.

❌ Why the Other Options Are Incorrect

• Pectoralis major:

  • A powerful adductor and medial rotator of the humerus.

  • Does not assist in raising the arm above the shoulder.

• Deltoid:

  • Abducts the arm from 15° to 90°.

  • Damage here prevents shoulder abduction, but not specifically lifting above shoulder level, which needs scapular movement.

• Supraspinatus:

  • Initiates abduction (first 15°).

  • It’s important for starting the movement but not responsible for lifting beyond shoulder level.

• Infraspinatus:

  • A lateral rotator of the arm.

  • Not involved in shoulder elevation.

In adults, a transverse midshaft fracture of both radius and ulna is considered unstable and requires surgical fixation to restore proper anatomy, alignment, and rotation — especially to preserve forearm supination and pronation.

• Open Reduction and Internal Fixation (ORIF) with plates is the gold standard for:

  • Midshaft fractures of both radius and ulna

  • Transverse or oblique fractures

  • Ensuring rigid fixation and early mobilization

  • Restoring radial bow and interosseous membrane integrity

This approach minimizes complications such as malunion or loss of forearm rotation.

❌ Why the Other Options Are Incorrect

• All of these:

  • Not correct, because only ORIF with plating is the recommended treatment in this case. The other methods are not standard for this fracture in adults.

• Close reduction and slab:

  • Suitable for temporary immobilization or in children, not definitive for adult midshaft fractures.

• Open reduction and nail:

  • Intramedullary nailing is not typically used for radius and ulna midshaft fractures in adults. It is more common for long bones like the femur or tibia.

• Close reduction and plaster cast:

  • Conservative management like casting is not appropriate for adult midshaft fractures of both bones due to high instability.

Nerve conduction velocity (NCV) refers to the speed at which an electrical impulse travels along a nerve. It is influenced by axon diameter and myelination, both of which enhance conduction speed.

• Larger axon diameter = faster conduction

  • Due to reduced internal resistance to ion flow along the axoplasm.

  • Think of it like water flowing through a wide pipe — there’s less resistance.

• Myelin sheath = saltatory conduction

  • Myelin insulates the axon and forces action potentials to jump between Nodes of Ranvier, greatly increasing speed.

❌ Why the Other Options Are Incorrect

• Decrease in diameter of axon:

  • Smaller diameter means greater internal resistance, resulting in slower conduction.

• All of these:

  • Incorrect because only the increase in diameter improves conduction. The others impair it.

• Decrease in thickness of myelin sheath:

  • Thinner myelin results in less effective insulation and slower conduction.

• Demyelination of axon:

  • Seen in diseases like Multiple Sclerosis, this leads to severe reduction in conduction velocity or even conduction block.

The subclavius muscle originates from the first rib at its junction with the costal cartilage and inserts on the groove on the inferior surface of the lateral to middle third of the clavicle. Its function is to stabilize the clavicle and protect underlying neurovascular structures.

❌ Why the Other Options Are Incorrect

• Anterior surface of lateral 2/3rd of clavicle: Incorrect surface. Subclavius inserts on the inferior, not anterior, surface.

• Posterior surface of lateral 2/3rd of clavicle: The posterior surface is related to muscles like trapezius, not subclavius.

• Inferior surface of medial 1/3rd of clavicle: While the surface is correct, the location is wrong. Subclavius does not insert medially; it inserts more laterally.

• Sternal head: This is not part of the clavicle at all—refers instead to the manubrium, not relevant to the subclavius.

The subclavius muscle originates from the first rib at its junction with the costal cartilage and inserts on the groove on the inferior surface of the lateral to middle third of the clavicle. Its function is to stabilize the clavicle and protect underlying neurovascular structures.

❌ Why the Other Options Are Incorrect

• Anterior surface of lateral 2/3rd of clavicle: Incorrect surface. Subclavius inserts on the inferior, not anterior, surface.

• Posterior surface of lateral 2/3rd of clavicle: The posterior surface is related to muscles like trapezius, not subclavius.

• Inferior surface of medial 1/3rd of clavicle: While the surface is correct, the location is wrong. Subclavius does not insert medially; it inserts more laterally.

• Sternal head: This is not part of the clavicle at all—refers instead to the manubrium, not relevant to the subclavius.

The skeletal system, particularly the limbs, has a well-orchestrated timeline and morphological process during embryonic development. This includes limb bud formation, apical ectodermal ridge (AER) activity, mesenchymal proliferation, chondrification, ossification, and joint formation.

Let’s explore each option:

✅ Option A: Fingers and toes formation occur due to death of apical ectodermal ridge cells by apoptosis

✔️ Correct

• Apical ectodermal ridge (AER) is a thickened ectodermal structure that plays a vital role in limb outgrowth and patterning.

• Apoptosis (programmed cell death) in the AER and surrounding tissues (especially in the interdigital zones) is responsible for separating digits (fingers and toes).

• Failure of this apoptosis results in syndactyly (webbed fingers or toes).

• This process occurs around weeks 6–8 of development.

📚 Reference: Larsen’s Human Embryology, 5th edition; Moore’s The Developing Human

❌ Option B: Upper limbs develop two days after lower limbs

❌ Incorrect

• It’s the opposite:

  • Upper limb buds appear first, around day 24–26.

  • Lower limb buds follow approximately 1–2 days later, around day 28.

• This is consistent with the cranio-caudal gradient of embryonic development.

❌ Option C: Limb development starts in second week of development

❌ Incorrect

• The second week is focused on bilaminar disc formation, implantation, and early trophoblast development.

• **Limb buds do not appear until the 4th week, specifically by day 24–28.

• Thus, limb development starts in the late 4th week, not the 2nd week.

❌ Option D: None of these

❌ Incorrect

• This is a trap option.

• Option A is correct, so “None of these” is wrong.

❌ Option E: Joints development starts in fourth week of development

❌ Incorrect

• Joint formation begins later, after chondrification of limb mesenchyme.

• This usually starts around the 6th week when interzones form between cartilage models, which later become joints.

• By 8th week, joint cavities begin to appear.

Prevention, cure and rehabilitation from the disease in the older adults” captures the full scope of geriatrics, which includes:

• Prevention:
  • Immunizations, fall prevention, nutritional counseling
  • Management of polypharmacy and minimizing iatrogenic risks
• Cure:
  • Diagnosing and treating acute and chronic conditions like hypertension, diabetes, arthritis, dementia
• Rehabilitation:
  • Restoring function after illness, injury, or hospitalization (e.g., after a stroke or fracture)

This holistic approach is central to geriatric care and distinguishes it from other adult medicine.

❌ Why the Other Options Are Incorrect:

• Option 1: Cure and rehabilitation of the elderly
  🔺 Misses prevention, which is crucial in aging populations.
• Option 2: Prevention and rehabilitation of the elderly
  🔺 Misses treatment/cure, which is vital for managing chronic illnesses.
• Option 3: Diagnosis of illness of the elderly
  🔺 Too narrow—geriatrics is not limited to diagnosis; it includes management and long-term care.
• Option 4: Management of the illness of the elderly
  🔺 Also incomplete—it omits prevention and rehabilitation, which are equally important.

• A splint is non-invasive, readily available, and allows initial stabilization of the fracture.
• It helps:
  • Immobilize the arm
  • Prevent further injury
  • Reduce pain and swelling
• Especially important in:
  • Initial emergency management
  • Field settings
  • Pre-operative care if surgery is indicated later
• Midshaft humerus fractures often heal well with conservative treatment like splinting and functional bracing (unless there’s a complication such as nerve injury or displacement).

❌ Why the Other Options Are Incorrect:

• Locking plate fixation:
  🔧 Requires open surgery, general anesthesia, and is typically reserved for:
  • Comminuted fractures
  • Non-union
  • Cases involving vascular or nerve compromise
  • But not first-line for a simple midshaft fracture.
• Pain relief medication only:
  💊 While essential for symptom management, it doesn’t address bone alignment or stabilization.
  So, it’s inadequate as a stand-alone treatment.
• Intramedullary nail:
  🧬 This is invasive surgery often used in femoral or tibial fractures, and less frequently in humerus due to:
  • Risk to shoulder joint
  • Radial nerve injury
  • Reserved for complex or failed conservative cases
• External fixation:
  ⚙️ Used mainly in open fractures, polytrauma, or when there’s severe soft tissue damage.
  It is not the safest or easiest in a typical midshaft humerus fracture.

To understand this question, let’s briefly review the ultrastructure of skeletal muscle, especially the sarcomere, which is the functional unit of striated muscle fibers.

🧬 Structure of the Sarcomere:

• A sarcomere extends from one Z line to another.
• It contains thick filaments (myosin) and thin filaments (actin) arranged in a very precise pattern.

🔹 A Band:

• The A band is the dark band of the sarcomere.
• It represents the entire length of the myosin filaments.
• It may overlap with actin filaments, but myosin is always present in the A band.

🔹 I Band:

• The I band is the light band, containing only actin (thin filaments)—no myosin.
• So, myosin cannot be present in the I band.

❌ Why the Other Options Are Incorrect:

• It contains titin:
  ✖️ Titin is a large elastic protein that connects the Z line to the M line and helps stabilize the myosin filament, but myosin filament itself doesn’t “contain” titin—titin is associated with it.
• Isotropic to light:
  ✖️ “Isotropic” means light-passing, which refers to the I band (which lacks myosin).
  The myosin-containing A band is anisotropic—i.e., dark under polarized light.
• It is a structural protein:
  ✖️ Myosin is a motor protein, not just structural.
  It plays an active role in muscle contraction by binding to actin and hydrolyzing ATP.
• It is present in I band:
  ✖️ I band contains only actin, not myosin.

To answer this question correctly, we need to understand the anatomy and functional roles of the radius and ulna, especially at the midshaft level where a fracture could interrupt the ability of the forearm to rotate.

🦴 Functional Anatomy of the Forearm:

• The radius and ulna are the two long bones of the forearm.
• At rest, the radius and ulna lie parallel, but during supination and pronation, the radius rotates over the ulna.
• The proximal and distal radioulnar joints, with the interosseous membrane between the bones, allow this rotation.
• A midshaft fracture of both bones disrupts the alignment and integrity of this rotation mechanism.

👉 So, damage at this site primarily affects the ability to supinate and pronate the forearm.

❌ Why the Other Options Are Incorrect:

• Wrist extension: Controlled mainly by the posterior forearm muscles (extensor carpi radialis longus/brevis, extensor carpi ulnaris), innervated by the radial nerve, and not directly impaired by midshaft fractures unless there’s a nerve injury (which isn’t mentioned).
• Elbow flexion: Mainly done by biceps brachii and brachialis—this action uses muscles from the arm, not the mid-forearm.
• Wrist flexion: Done by flexor carpi radialis and ulnaris, which originate from the medial epicondyle of the humerus, not the midshaft of radius or ulna.
• Elbow extension: Carried out by the triceps, which are also located in the arm—not affected by fractures in the mid-forearm

To understand where the triad is located in skeletal muscle, you need to understand muscle fiber structure and how it coordinates excitation-contraction coupling.

🧬 What is the Triad?

The triad in skeletal muscle consists of:

• 1 transverse (T) tubule
• 2 terminal cisternae of the sarcoplasmic reticulum (SR)

These three structures come together to form a “triad” at specific points along the muscle fiber.

🏗️ Where is it located?

• The T tubules penetrate the muscle fiber and wrap around the myofibrils at the A-I junction—that is, between the A band (dark band) and I band (light band) of the sarcomere.
• The terminal cisternae of the sarcoplasmic reticulum lie on either side of the T-tubule at this junction.

⟶ This specific arrangement ensures that electrical signals quickly lead to calcium release from the sarcoplasmic reticulum, triggering muscle contraction.

❌ Why the Other Options Are Incorrect:

• I band: This is the light region with only actin filaments; triads do not align here.
• M band: Located at the center of the A band; contains proteins anchoring thick filaments—no T-tubules or SR cisternae here.
• A band: Contains thick (myosin) filaments; triads are not located in the middle of it, but at its edge.
• Z line: The boundary of the sarcomere; T-tubules do not penetrate here.

Vitamin D is not active in the form we ingest it. It must undergo two hydroxylation steps—first in the liver, then in the kidney—to become biologically active.

🧬 Step-by-step Activation of Vitamin D:

• Cholecalciferol (Vitamin D₃)
  → This is the inactive form obtained from the skin (via UV light) or diet.
• 25-hydroxycholecalciferol (Calcidiol)
  → Formed in the liver through hydroxylation of cholecalciferol.
  → This is the major circulating form, used to assess vitamin D levels in blood.
  → Still inactive.
• 1,25-dihydroxycholecalciferol (Calcitriol)
  → Formed in the kidney by another hydroxylation.
  → This is the biologically active form of vitamin D.
  → Regulates calcium and phosphate absorption in the gut, bone remodeling, and kidney reabsorption of calcium.

❌ Why the Other Options Are Incorrect:

• 25-hydroxycholecalciferol: Intermediate form; not the biologically active hormone.
• Riboflavin: Vitamin B2, unrelated to vitamin D metabolism.
• Cholecalciferol: Inactive precursor form of vitamin D₃.
• Niacin: Vitamin B3, used in NAD⁺/NADP⁺ metabolism; unrelated to vitamin D activation.

🔹 Superior Gluteal Artery

• Largest branch of the posterior division of the internal iliac artery.

• Leaves the pelvis via the greater sciatic foramen above the piriformis.

• Supplies gluteus medius, gluteus minimus, tensor fasciae latae, and also contributes to collateral circulation around the hip joint.

🔹 Relevance When Cruciate Anastomosis Is Cut Off

• The cruciate anastomosis normally ensures collateral flow around the femur.

• If all vessels of the cruciate anastomosis are cut, the superior gluteal artery still provides an alternative route via its branches to the gluteal region, which indirectly contribute to femoral supply through muscular and capsular branches.

• This makes it the remaining source of arterial supply to the proximal femur in this scenario. ✅

❌ Why the Other Options Are Wrong

• Inferior gluteal artery → Major contributor to the cruciate anastomosis; if cruciate is cut off, this is also lost.

• Medial circumflex femoral artery → Normally the dominant supplier of the femoral head/neck, but in this scenario, its contribution is assumed lost due to the cruciate being cut off.

• Lateral circumflex femoral artery → Also part of cruciate anastomosis, hence excluded.

• First perforating artery → Another contributor to cruciate anastomosis; also excluded here.

• Supination is the movement that turns the palm upward or forward (like holding a bowl of soup). Two main muscles are responsible for this action:
• Biceps brachii – the primary supinator, especially when the elbow is flexed
• Supinator – acts mainly when the elbow is extended

Let’s now break this down by muscle innervation and why loss of supination points to a specific nerve injury.

🦴Muscles Involved in Supination:

🔹Biceps brachii

• Innervation: Musculocutaneous nerve
• Function: Flexion and powerful supination (especially when the elbow is flexed)

🔹 Supinator muscle

• Innervation: Radial nerve (specifically deep branch/posterior interosseous)
• Function: Assists in supination when the elbow is extended

🧠 Which Nerve Is Most Likely Damaged?

Since loss of supination implies that both major supinators are impaired, but especially when elbow flexion is involved, biceps brachii is critical. That leads us to the musculocutaneous nerve, which innervates biceps brachii.

Therefore, damage to the musculocutaneous nerve causes significant loss of supination, especially in flexed positions.

❌ Why the Other Options Are Incorrect:

• Radial nerve: Innervates supinator muscle, but not biceps. Its damage would cause partial loss of supination, not complete, especially when the elbow is bent (since biceps would still function).
• Median nerve: No role in supination; primarily controls forearm flexors and thenar muscles.
• Ulnar nerve: Controls most hand muscles and some forearm flexors; has no role in supination.
• Brachial nerve: This is not a named nerve in human anatomy (possibly a distractor or misnamed for the brachial plexus).

To answer this question, we need to know which muscles insert into the greater and lesser tubercles of the humerus, and the primary functions of each.

🦴 Anatomy of the Humerus Tubercles:

🔹 Greater Tubercle

• Lateral projection on the proximal humerus
• Serves as the insertion point for three rotator cuff muscles:
  • Supraspinatus
  • Infraspinatus
  • Teres minor

🔹

Lesser Tubercle

:

• Anterior projection on the proximal humerus
• Serves as the insertion point for:
  • Subscapularis (the only rotator cuff muscle inserting here)

❌ Why Deltoid is Correct (NOT attached):

The deltoid muscle inserts into the deltoid tuberosity of the shaft of the humerus — not the tubercles.

It plays a major role in abduction of the arm (15°–90°) but does not attach to either the greater or lesser tubercles.

✅ Why the Other Options Are Incorrect (They are attached):

• Subscapularis → Inserts into the lesser tubercle
• Teres minor → Inserts into the greater tubercle
• Infraspinatus → Inserts into the greater tubercle
• Supraspinatus → Inserts into the greater tubercle

The axillary nerve is a key peripheral nerve of the upper limb, arising from the posterior cord of the brachial plexus (C5–C6). It travels through the quadrangular space in the shoulder region and innervates specific muscles and skin.

✅ Muscles Innervated by the Axillary Nerve:

• Deltoid: Primary abductor of the arm (15°–90°)
• Teres minor: Part of the rotator cuff, helps with lateral rotation of the arm

The deltoid is the major muscle responsible for lifting the arm away from the body (abduction), especially from 15 to 90 degrees. Damage to the axillary nerve results in:

• Weakness or loss of arm abduction
• Atrophy of the deltoid muscle (flattened shoulder appearance)
• Loss of sensation over the deltoid region (regimental badge area)

❌ Breakdown of Incorrect Options:

• Supraspinatus:
  → Innervated by the suprascapular nerve, not the axillary nerve.
  → Initiates arm abduction (first 15°), but not primarily affected in axillary nerve injury.
• Pectoralis major:
  → Supplied by medial and lateral pectoral nerves, involved in adduction and internal rotation.
• Infraspinatus:
  → Also innervated by the suprascapular nerve, helps in lateral rotation.
• Teres major:
  → Supplied by the lower subscapular nerve, assists in adduction and medial rotation of the humerus.

✅ Key Principles of Health Education:

• Knowing the customs:
  ➤ Understanding the cultural, religious, and social context of a community helps tailor health messages appropriately.
• Good human relations:
  ➤ Building trust and rapport ensures people are open to learning and adopting healthy behaviors.
• Learning by doing:
  ➤ Active participation reinforces concepts better than passive learning. E.g., practicing handwashing improves retention compared to just hearing about it.
• Motivation:
  ➤ A motivated individual is more likely to change behavior and retain knowledge.

❌ Why “Trial” is Incorrect:

• Trial is not considered a core principle of health education.
• It refers to trying something temporarily, which aligns more with marketing or behavior change models like the Transtheoretical Model (e.g., trial stage before adoption), not with the principles that guide teaching and communication in health education.

❌ Why the Other Options Are Correct Principles:

• Knowing the customs → ensures relevance of health messages
• Good human relations → improves communication and receptivity
• Learning by doing → enhances engagement and understanding
• Motivation → drives behavior change

The femoral nerve (L2–L4) is the primary nerve supplying the anterior compartment of the thigh. It is responsible for motor innervation to the quadriceps femoris, iliacus, sartorius, and pectineus, which are involved in knee extension and hip flexion.

It also gives rise to the saphenous nerve, which is purely sensory and supplies the anteromedial leg and foot.

🔍 How This Matches the Clinical Scenario:

• Motor loss in anterior thigh → weakness in knee extension due to quadriceps dysfunction
• Sensory loss in medial and anterior leg → indicates saphenous nerve involvement, a branch of the femoral nerve

Thus, damage to the femoral nerve explains both motor and sensory deficits described.

❌ Why the Other Options Are Incorrect:

• Radial nerve:
  ➤ Supplies posterior arm and forearm (e.g., triceps, wrist extensors), not the thigh or leg.
• Popliteal nerve:
  ➤ Not a nerve per se; it refers to the popliteal fossa, through which the sciatic nerve divides into tibial and common fibular nerves.
• Sciatic nerve:
  ➤ Supplies posterior thigh and entire lower leg, not the anterior thigh or medial leg specifically.
• Obturator nerve:
  ➤ Innervates medial thigh muscles (adductors) and gives limited sensory innervation to the medial thigh, not the anterior thigh or leg.

Intramuscular (IM) injections are commonly given to deliver medication deep into muscles, allowing it to be absorbed quickly into the bloodstream. For safety and effectiveness, specific muscles are preferred due to:

• Muscle size
• Blood supply
• Distance from major nerves and vessels

🦾 Deltoid Muscle:

• Location: Upper arm (shoulder region)
• Landmark: About 2.5–5 cm (1–2 inches) below the acromion process
• Advantages: Easily accessible, good blood supply, and well-tolerated by patients

It is especially common for vaccinations (e.g., flu, tetanus), where small-volume injections (≤1 mL in adults) are required.

❌ Why the Other Options Are Incorrect:

• Psoas major / minor
  ➤ Deep muscles in the posterior abdominal wall — not easily accessible, and surrounded by critical structures like the lumbar plexus.
• Intrinsic muscles
  ➤ These refer to small muscles confined to a specific region (e.g., intrinsic hand or foot muscles). Not suitable for injections due to small size.
• Extrinsic muscles
  ➤ A broad term for muscles that originate in one area and act on another (e.g., forearm muscles acting on the hand). Again, not a practical or safe injection site.

To understand this scenario, let’s break it down:

• The knee joint allows flexion and extension.
• The primary extensors of the knee are the quadriceps femoris muscles.
• If a patient has restricted movement at the knee and resistance to extension, the most likely culprit is injury or dysfunction in the quadriceps group.

🦵 Quadriceps Femoris Muscle Group:

• Composed of: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius.
• Function: Extends the knee (straightens the leg).
• Clinical correlation: Injury, bruising, or strain to these muscles (common in falls, especially on the knee) can limit extension, cause pain, or muscle imbalance.

❌ Why the Other Options Are Incorrect:

• Flexors
  ➤ Non-specific. If meant as knee flexors, these do the opposite of extension, so injury here would limit bending, not straightening.
• Popliteus
  ➤ Unlocks the knee from full extension (initiates flexion). Dysfunction here would cause locking, not resistance to extension.
• Soleus
  ➤ Acts on the ankle, not the knee. It’s a plantarflexor of the foot.
• Hamstrings
  ➤ Flex the knee and extend the hip. Injury to them limits knee flexion, not extension. Damage here would cause difficulty bending the knee.

The iliac crest is the curved superior border of the ilium, forming the top of the pelvic bone. It serves as an important attachment site for several abdominal and gluteal muscles.

The iliac crest is anatomically divided into:

• External lip (lateral side)
• Intermediate area
• Internal lip (medial side)

Each of these zones anchors different muscles.

🔍 Gluteus Maximus:

• It is the largest and most superficial muscle of the gluteal region.
• Functions: Hip extension, lateral rotation, and rising from sitting.
• Origin Points Include:
  • Posterior gluteal line
  • Sacrum & coccyx
  • Sacrotuberous ligament
  • ✅ External lip of iliac crest

The external lip provides a broad and superficial surface — ideal for the powerful action of the gluteus maximus.

❌ Why the Other Options Are Incorrect:

• Lateral slope – Not a standard anatomical term used in reference to iliac crest subdivisions.
• Intermediate area – Provides attachment for internal oblique.
• Internal lip – Provides attachment for transversus abdominis.
• Medial slope – Again, not a recognized anatomical term for iliac crest regions.

This clinical scenario involves:

• Trauma to the posterior triangle of the neck, and
• Inability to raise the hand to comb hair, i.e., difficulty in shoulder abduction above 90°.

🔍 Step-by-step clinical reasoning:

The posterior triangle of the neck is a region bounded by:

• Anteriorly: Posterior border of sternocleidomastoid
• Posteriorly: Anterior border of trapezius
• Inferiorly: Middle third of the clavicle

One of the key structures that passes superficially through this triangle is the spinal accessory nerve (cranial nerve XI).

The spinal accessory nerve innervates two muscles:

• Sternocleidomastoid: turns the head
• Trapezius: elevates the shoulder and helps in abducting the arm beyond 90° by rotating the scapula

But here’s the catch: raising the hand to comb hair requires:

• Initiation of abduction (0–15°) → Supraspinatus (suprascapular nerve)
• Continued abduction (15–90°) → Deltoid (axillary nerve)
• Overhead abduction (90–180°) → Trapezius and serratus anterior (spinal accessory and long thoracic nerves)

In this case, posterior triangle trauma likely injures the spinal accessory nerve, impairing trapezius, leading to:

• Difficulty elevating the shoulder
• Weak overhead abduction

But note: the deltoid is the most likely muscle directly responsible for the “combing hair” issue since that movement involves active abduction from 15° to 90° — the functional range of deltoid.

Moreover, deltoid is innervated by the axillary nerve, which wraps around the surgical neck of the humerus but may also be injured indirectly due to trauma in this region.

Thus, in a clinical setting, the inability to abduct the arm actively to shoulder height suggests a deltoid muscle problem.

❌ Why the Other Options Are Incorrect:

• Levator scapulae: Elevates scapula; no major role in arm abduction or overhead activities.
• Latissimus dorsi: Extends, adducts, and medially rotates the humerus; used in climbing or rowing, not abduction.
• Teres major: Adduction and medial rotation of the arm; does not abduct the arm.
• Serratus anterior: Used in overhead abduction >90°, but isolated injury would not prevent reaching up unless paired with trapezius damage (also note: not in posterior triangle).

This clinical vignette describes a lower limb nerve injury with clear motor and sensory deficits. Let’s dissect it piece by piece:

🔍 Key Clinical Findings:

• Weak knee extension ➝ Points toward the quadriceps femoris muscle group, which is the primary extensor of the knee.
• Loss of function of the quadriceps compartment ➝ Again reinforces that the anterior thigh muscles are affected.
• Loss of sensation over the anteromedial thigh and medial side of the calf ➝ This sensory territory is supplied by the femoral nerve and its saphenous branch.

The femoral nerve (L2–L4) is the main nerve of the anterior thigh compartment and supplies:

• Motor: Quadriceps femoris, sartorius, pectineus (partly), iliacus
• Sensory: Anterior thigh and medial leg via saphenous nerve

Thus, damage to the femoral nerve would result in:

• Weakness or paralysis of knee extension
• Loss of patellar reflex
• Sensory loss in the described areas

❌ Why the Other Options Are Incorrect:

• Obturator nerve
  • Innervates adductor muscles (medial compartment of thigh)
  • No involvement in knee extension or medial leg sensation.
• Superior gluteal nerve
  • Supplies gluteus medius, minimus, and tensor fasciae latae
  • Controls hip abduction
  • Not related to knee function or leg sensation.
• Sciatic nerve
  • Innervates the posterior thigh, leg, and foot muscles
  • While sensory to most of the leg and foot, not responsible for anterior thigh or medial leg sensation.
  • Motor loss would affect hamstrings, not quadriceps.
• Inferior gluteal nerve
  • Supplies gluteus maximus
  • Responsible for hip extension, not knee extension
  • No sensory role in the thigh or leg.

✅ Achondroplasia

• Correct statement: It is the most common cause of disproportionate (short-limb) dwarfism.
• It is due to a mutation in the FGFR3 gene, which inhibits endochondral ossification, affecting long bone growth.
• Patients have normal intelligence, a normal-sized trunk, and shortened limbs.

❌ Incorrect Options Explained:

• Osteopetrosis is characterized by lesser bone mass
  → Incorrect. Osteopetrosis, or “marble bone disease”, is actually characterized by abnormally dense but brittle bones due to defective osteoclast-mediated bone resorption.
• Thanatophoric dysplasia is harmless
  → Incorrect. The word “thanatophoric” means “death-bearing”. This severe form of skeletal dysplasia is lethal in the perinatal period due to respiratory failure from a small thoracic cavity.
• Osteoporosis is marked by denser bone
  → Incorrect. Osteoporosis is a condition of reduced bone mass and microarchitectural deterioration, leading to fragility and fractures. Bones are less dense, not more.
• Osteopetrosis is brittle bone disease
  → Incorrect. Brittle bone disease is another name for osteogenesis imperfecta, not osteopetrosis. While osteopetrosis bones can fracture easily, the underlying pathophysiology and cause are different.

The knee joint is a complex synovial hinge joint composed of both intracapsular and extracapsular structures. Understanding which structures lie within the joint capsule—but outside the synovial membrane—is essential in anatomy and clinical practice.

✅ Why Popliteus tendon is correct:

• The popliteus muscle originates from the posterior surface of the tibia and inserts into the lateral condyle of the femur.
• Its tendon enters the knee joint capsule and runs deep to the lateral meniscus.
• Although it’s within the fibrous capsule, it lies outside the synovial membrane, which makes it intracapsular but extrasynovial.

This is a classic example of a structure being anatomically within the joint capsule but not bathed in synovial fluid.

❌ Why the other options are incorrect:

• Patellar ligament:
  • It is a continuation of the quadriceps tendon and is extracapsular (outside the joint capsule).
• Tibial collateral ligament (medial collateral ligament):
  • This ligament is extracapsular and also blends with the joint capsule and the medial meniscus, but it is not within the capsule itself.
• Biceps femoris tendon:
  • Inserts on the head of the fibula and is completely outside the joint capsule. It is extracapsular.
• Oblique patellar ligament:
  • A reinforcement of the joint capsule derived from the semimembranosus tendon. It is extracapsular and posterior, but not intracapsular.