Locomotor – 2017

• The sarcoplasmic reticulum (SR) is the muscle cell’s modified smooth ER, specialized for calcium storage and release.

• Structurally:

  • It forms longitudinal tubules and terminal cisternae (enlarged ends where calcium is stored).

  • It interacts with transverse (T)-tubules (invaginations of the sarcolemma).

  • Together, they form the triad in skeletal muscle (T-tubule sandwiched between two cisternae).

• Functionally, this setup allows the action potential in the T-tubule to trigger Ca²⁺ release from the SR cisternae → leading to excitation-contraction coupling.

❌ Why the Other Options Are Wrong

• Lysosomes → Digestive organelles, no cisternae or T-tubules.

• Sarcolemma → The plasma membrane of the muscle fiber; it gives rise to T-tubules but does not contain cisternae.

• Smooth endoplasmic reticulum (SER) → Has tubules and cisternae but is not associated with T-tubules; functions in lipid metabolism/detox.

• Rough endoplasmic reticulum (RER) → Has cisternae with ribosomes attached for protein synthesis, but again no T-tubules.

📝 Key Pearl

👉 Sarcoplasmic reticulum + T-tubules = “Triad” system in skeletal muscle (essential for excitation-contraction coupling

• Titin is the largest known protein in humans (~3–4 MDa, with ~34,000 amino acids).

• It extends from the Z-line to the M-line in the sarcomere.

• Functions:

  • Acts as a molecular spring that provides elasticity and stability to the sarcomere.

  • Maintains alignment of myosin filaments during contraction and relaxation.

❌ Why the others are wrong

• Tropomyosin → regulatory protein lying along actin filaments; much smaller.

• Actin → major thin filament protein; smaller than titin (≈42 kDa).

• Troponin → regulatory complex (TnT, TnI, TnC); tiny compared to titin.

• Myosin → thick filament motor protein (≈500 kDa per molecule); large, but still far smaller than titin.

• In blood pressure measurement by auscultatory method (Korotkoff sounds), the stethoscope is placed over the brachial artery in the cubital fossa.

• This location is chosen because:

  • The cuff occludes the brachial artery when inflated.

  • Korotkoff sounds (turbulent blood flow) are best heard directly over the artery being compressed.

• Neither radial nor ulnar arteries are used here, and the stethoscope is not placed above the fossa.

❌ Why the others are wrong

• Radial artery over cubital fossa → radial artery is at the wrist, not cubital fossa.

• None of these → incorrect, since brachial artery at cubital fossa is correct.

• 2.5 cm above the cubital fossa → this refers to placement of the cuff, not the stethoscope.

• Ulnar artery at wrist → not used for BP measurement.

Dystrophin is a key structural protein that links the cytoskeleton of muscle fibers (actin filaments) to the extracellular matrix via the dystrophin–glycoprotein complex. This provides mechanical stability during contraction and relaxation.

• When dystrophin is absent or defective (as in Duchenne and Becker muscular dystrophies), the sarcolemma (muscle cell membrane) becomes fragile.

• Contraction-induced stress leads to microtears in the sarcolemma → leakage of intracellular enzymes like creatine kinase into the blood.

• This explains the high serum CK and progressive muscle weakness in the patient.

❌ Why other options are incorrect:

• Defective cross bridge formation → Caused by actin–myosin interaction problems, but dystrophin is not part of the cross-bridge cycle.

• Defective SERCA pump → Leads to impaired Ca²⁺ reuptake into the SR (seen in some metabolic myopathies), but not in dystrophin mutations.

•  Impaired acetylcholine release → This would be a neuromuscular junction issue (e.g., botulism), unrelated to dystrophin.

•  Reduced binding of calcium to troponin C → Would prevent contraction initiation, but dystrophin has no role in calcium–troponin binding.

• Dystrophin is a large cytoskeletal protein that connects actin filaments of the muscle cytoskeleton to the extracellular matrix via the dystrophin–glycoprotein complex.

• Its role is crucial in stabilizing the sarcolemma during muscle contraction and relaxation.

• Mutations or absence of dystrophin lead to muscular dystrophies such as Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD).

• Without dystrophin, the sarcolemma becomes fragile, leading to repeated injury, degeneration, and progressive weakness.

❌ Why Other Options Are Incorrect:

•  Actin → Actin is a cytoskeletal protein involved in contraction (thin filaments), but it does not anchor the cytoskeleton to the extracellular matrix.

• Myosin → Thick filament motor protein that interacts with actin for contraction, not for attachment to ECM.

• Titin → A giant protein that provides elasticity and stabilizes myosin, but does not link cytoskeleton to ECM.

• Troponin→ Regulatory protein in contraction, binds calcium to initiate actin-myosin interaction, not involved in cytoskeletal attachment.

• Inside the sarcoplasmic reticulum (SR) of skeletal muscle, calcium must be stored efficiently until it is released during contraction.

• The storage protein responsible for this is calsequestrin, which binds large amounts of calcium ions while keeping the free concentration low.

• This helps maintain a steep calcium gradient between the SR and cytosol, ensuring rapid calcium release during excitation–contraction coupling.

❌ Why Other Options Are Incorrect:

• Calbindin → Calcium-binding protein found mainly in intestine and kidney for Ca²⁺ transport.

• Calcineurin → Calcium/calmodulin-dependent phosphatase, involved in T-cell activation and muscle remodeling, not SR storage.

• Calexcitin → A neuronal calcium-binding protein involved in learning and memory, not skeletal muscle SR.

• Calmodulin → Cytosolic calcium-binding protein that activates enzymes (e.g., MLCK), not for SR calcium storage.

Excitation-contraction coupling refers to the process by which an action potential on the muscle membrane (sarcolemma) triggers muscle contraction. The key structure involved in transmitting the action potential from the surface to the interior of the muscle fiber is the T-tubules (transverse tubules). When an action potential travels along the sarcolemma, it enters the T-tubules, which are closely associated with the sarcoplasmic reticulum. This triggers the release of calcium ions from the sarcoplasmic reticulum, ultimately allowing myosin to bind to actin and generate contraction.

Why the others are incorrect:

• The epimysium is excited before excitation of the sarcolemma: The epimysium is connective tissue, not electrically excitable.

• Mitochondria provides the calcium ions for contraction: Mitochondria produce ATP, but calcium comes from the sarcoplasmic reticulum.

• ATP molecules are provided by the sarcoplasmic reticulum: ATP is generated mainly by mitochondria and glycolysis, not the SR.

• The myosin and actin bind because of calcium-calmodulin binding to actin: In skeletal muscle, calcium binds to troponin, not calmodulin.

The correct statement is that the sodium-potassium ATPase pump maintains the concentration difference of ions across the cell membrane.

This pump is an active transport mechanism that pumps 3 sodium ions out of the cell and 2 potassium ions into the cell against their concentration gradients using energy from ATP hydrolysis. By doing this, it establishes and maintains the high extracellular sodium and high intracellular potassium concentrations, which are critical for resting membrane potential, secondary active transport, and cell volume regulation.

Why the other options are incorrect:

• Ions pass through it by diffusion: Incorrect, because ions are moved actively, not by passive diffusion.

• Pumps three sodium into the cell and two potassium out of the cell: The direction is reversed; sodium goes out, potassium goes in.

• It is not inhibited by metabolic poisons: False; inhibitors like ouabain or energy depletion (metabolic poisons) block its activity.

• Has no role in the resting membrane potential of the cell: False; it contributes indirectly by maintaining the ion gradients that generate the resting membrane potential.

In Lambert-Eaton Myasthenic Syndrome (LEMS), autoantibodies are produced against presynaptic voltage-gated calcium channels (VGCCs) at the neuromuscular junction.

These calcium channels are crucial for acetylcholine (ACh) release from the presynaptic terminal. When they are blocked by autoantibodies, the release of ACh is reduced, leading to muscle weakness, especially in the proximal muscles, and autonomic symptoms like dry mouth.

Why the other options are incorrect:

• Acetylcholine channels: These are targeted in myasthenia gravis, not LEMS.

• Sodium channels: Autoantibodies against sodium channels are seen in some forms of periodic paralysis or channelopathies, not LEMS.

• Potassium channels: Not primarily involved in LEMS; autoimmunity against them is rare and usually associated with other syndromes.

• Muscle proteins: These are targeted in some myopathies, but not LEMS.

Slow pain is transmitted by C fibers.

C fibers are unmyelinated, small-diameter nerve fibers that conduct impulses slowly (0.5–2 m/s). They are responsible for dull, burning, aching pain that develops gradually and is poorly localized.

Why the other options are incorrect:

• A-delta fibers: Myelinated fibers that transmit fast, sharp, well-localized pain.

• A-beta fibers: Large, myelinated fibers that carry touch and pressure, not pain.

• A-alpha fibers: Large, myelinated fibers responsible for motor signals and proprioception, not pain.

• None of these: Incorrect because C fibers are the correct answer.

Rheumatoid arthritis is not included in the group of seronegative spondyloarthropathies.

Seronegative spondyloarthropathies are a group of chronic inflammatory disorders that share features such as axial skeleton involvement, enthesitis, HLA-B27 association, and absence of rheumatoid factor (seronegative status). The classic members include:

• Ankylosing spondylitis

• Reactive arthritis (Reiter’s syndrome)

• Psoriatic arthritis

• Axial spondyloarthritis

• Enteropathic arthritis (associated with IBD)

Now, option breakdown:

• Reactive arthritis – Included in seronegative spondyloarthropathies.

• Ankylosing spondylitis – Classic prototype of this group.

• Rheumatoid arthritis – Not part of this group; it is seropositive for rheumatoid factor/anti-CCP and has different pathogenesis.

• Axial spondyloarthritis – Belongs to this group.

• Psoriatic arthritis – Also included.

When a patient starts treatment, their autonomy and right to make decisions about their own health remain fully intact. Consent is not a one-time event; it is a continuous process. A patient has the right to withdraw consent at any stage, even after treatment has begun.

• Patient cannot withdraw consent – Incorrect. Patients always retain the right to stop treatment.

• Patient’s consent is not taken – Incorrect. Informed consent is a legal and ethical prerequisite before starting treatment.

• Patient cannot leave the treatment – Incorrect. Patients can discontinue treatment if they wish, unless in rare exceptions (e.g., public health laws for infectious disease control).

• Patient is not allowed to take decisions – Incorrect. Unless the patient is legally incompetent, they always retain decision-making authority.

• Patient can withdraw consent anytime – Correct. This reflects respect for autonomy and patient rights in medical ethics.

The defining histological feature of ductal carcinoma in situ (DCIS) is cellular polymorphism. DCIS represents malignant proliferation of epithelial cells confined within the breast ducts, without invasion through the basement membrane. Microscopically, the ducts are filled with atypical cells showing pleomorphism (variation in size and shape), hyperchromatic nuclei, and sometimes necrosis (particularly in the comedo type).

• Cellular polymorphism → Correct. Hallmark finding in DCIS; it reflects atypical malignant cells proliferating within the ductal lumen.

• None of these → Incorrect, since DCIS does have distinct features, and cellular polymorphism is characteristic.

• Hyperplasia → Incorrect. Hyperplasia can be seen in benign proliferative breast disease, not necessarily carcinoma in situ.

• Necrosis → Incorrect. Necrosis (especially central necrosis) may be seen in the comedo type of DCIS, but it is not universal or the defining feature.

• Fibrosis → Incorrect. Fibrosis is usually seen in invasive carcinoma and the stromal response, not in DCIS, which is confined to ducts.

Curare works by inhibiting motor nerve end-plates. Specifically, it acts as a competitive antagonist of nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction. By binding to these receptors without activating them, curare prevents acetylcholine from binding and triggering muscle contraction, resulting in flaccid paralysis.

• Stimulates cells in the anterior horn of the spinal cord → Incorrect. Curare does not act on the spinal cord or motor neurons directly; its action is peripheral at the neuromuscular junction.

• Prevents saltatory conduction of nerve impulses → Incorrect. That mechanism is typical of demyelinating diseases (e.g., multiple sclerosis) or sodium channel blockers, not curare.

• Excites neuromuscular junctions → Incorrect. Curare blocks excitation instead of promoting it.

• Slows conduction of nerve impulses → Incorrect. Nerve conduction velocity is unaffected; the block occurs at the synapse (NMJ), not along the nerve axon.

• Inhibits motor nerve end-plates → Correct. Curare blocks nicotinic receptors at the motor end-plate, preventing depolarization and contraction.

Hairline fractures, also called stress fractures, are tiny cracks in the bone caused by repeated stress or overuse rather than a single traumatic event. They are most commonly seen in limbs, especially in the weight-bearing bones such as the tibia, metatarsals, and fibula in athletes, runners, or military recruits.

• Joints → Incorrect. Fractures occur in bones, not in joints themselves, though joints may be affected secondarily.

• Limbs → Correct. Hairline fractures most often occur in the long bones of the limbs, especially lower limbs.

• Mouth → Incorrect. Stress fractures are not associated with oral bones.

• Skull → Incorrect. Skull fractures can be linear or depressed, but “hairline” fractures in the skull are not the common usage of the term.

• Vertebrae → Incorrect. Vertebrae are prone to compression fractures, especially in osteoporosis, not stress-type hairline fractures.

Glucocorticoids are powerful anti-inflammatory and immunosuppressive agents, but their chronic use comes with significant adverse effects.

• Exaggeration of inflammatory reaction → Incorrect. Glucocorticoids suppress inflammation, they don’t exaggerate it.

• Osteoporosis → Correct. Glucocorticoids decrease osteoblast activity, increase osteoclast activity, and reduce calcium absorption in the gut, leading to bone loss and osteoporosis.

• Alopecia → Not a typical side effect of glucocorticoids. In fact, they can sometimes cause hirsutism (excess hair growth).

• Ototoxicity → Not associated with glucocorticoids. This effect is more common with aminoglycosides and cisplatin.

• None of these → Incorrect, because osteoporosis is indeed a classical side effect.

Leflunomide is a disease-modifying antirheumatic drug (DMARD) that inhibits dihydroorotate dehydrogenase, leading to decreased pyrimidine synthesis and suppression of T-cell proliferation. Its adverse effects are well-documented.

• Cytotoxicity → Correct, because leflunomide suppresses immune cell proliferation, giving it a cytostatic effect.

• Alopecia → Also correct; hair loss is a common adverse effect due to inhibition of rapidly dividing cells.

• Ototoxicity → Not typically associated with leflunomide; this is more a feature of aminoglycosides and cisplatin.

• Nephrotoxicity → Not a classical side effect of leflunomide; drugs like cyclosporine or aminoglycosides are more nephrotoxic.

• All of these → Incorrect, because not all the listed options are seen with leflunomide. The correct side effect from the list is alopecia.

Methotrexate is an antimetabolite and folate antagonist used in cancer chemotherapy and autoimmune diseases. Its most important and common side effect is myelosuppression due to inhibition of DNA synthesis in rapidly dividing cells, particularly bone marrow.

• Myelosuppression → Correct. This occurs because methotrexate inhibits dihydrofolate reductase, impairing thymidylate and purine synthesis, leading to suppression of bone marrow cell proliferation.

• Ototoxicity → Typically seen with drugs like aminoglycosides and cisplatin, not methotrexate.

• Pulmonary fibrosis → More commonly associated with bleomycin, busulfan, and amiodarone. Methotrexate can rarely cause interstitial pneumonitis, but pulmonary fibrosis is not its classical hallmark side effect.

• Anaphylactic reaction → Not a typical adverse effect of methotrexate; hypersensitivity reactions are rare.

• None of these → Incorrect because one of the listed options (myelosuppression) is correct.

Cyclones are classified as meteorological disasters, since they are caused by atmospheric and weather-related phenomena such as wind systems, pressure changes, and temperature differences over oceans and coastal regions. Meteorological disasters include events like storms, hurricanes, tornadoes, floods, and droughts.

• Meteorological → Correct, because cyclones originate from atmospheric disturbances.

• Accident → Refers to man-made events (e.g., industrial accidents, transport crashes).

• Telluric and tectonic → Related to Earth’s crust movements (e.g., earthquakes, volcanic eruptions).

• Atomic explosion → A man-made disaster related to nuclear events, not natural.

• Topological → Refers to disasters linked with land structures like landslides, avalanches, or soil erosion, not atmospheric events.

Health promotion and education involve planned stages that help individuals and communities adopt healthier behaviors and sustain them. The recognized stages generally include sensitization (making people aware of health issues), education (providing knowledge and skills), publicity (wider dissemination of information to the public), and community transformation (achieving lasting behavioral and cultural change at the community level).

Legislation, however, is not considered a stage of health promotion and education. It falls under health protection or policy-level interventions, where governments and authorities enforce laws such as anti-smoking regulations, seatbelt use, or food safety standards. While legislation plays an important role in improving health outcomes, it is not part of the structured stages of health education itself.

• Sensitization → the first step, creating awareness.

• Education → providing necessary knowledge and motivation.

• Publicity → spreading health messages to a wide audience.

• Community transformation → sustained behavior change at the societal level.

• Legislation → belongs to health protection, not education stages.

The ability to extend the knee depends on the quadriceps femoris muscle group, which is supplied by the femoral nerve (L2–L4). Damage to this nerve leads to paralysis of the quadriceps, resulting in an inability to extend the knee and difficulty with walking, especially climbing stairs or rising from a seated position.

The tibial nerve supplies the posterior compartment of the leg and plantar foot muscles, which are responsible for plantarflexion, toe flexion, and intrinsic foot movements, not knee extension.
The sciatic nerve is a large mixed nerve of the posterior thigh, but it primarily supplies the hamstring muscles, which are knee flexors, not extensors.
The fibular (common peroneal) nerve supplies the muscles of the anterior and lateral compartments of the leg, involved in dorsiflexion and eversion, not knee extension.
The obturator nerve innervates the adductor muscles of the thigh, responsible for adduction, but not extension of the knee.

In a fracture of the midshaft of the humerus, the radial nerve is most commonly injured. This is because the radial nerve runs in the spiral (radial) groove of the humerus along its midshaft. Injury to this nerve leads to wrist drop due to paralysis of wrist extensors, along with sensory loss over the dorsum of the hand.

The median nerve lies more anteriorly in the arm and is not in close contact with the humeral shaft, so it is not typically injured in midshaft fractures.
The musculocutaneous nerve runs in the anterior compartment of the arm, supplying the flexors of the arm, and is also not in direct relation to the humeral shaft.
The ulnar nerve passes behind the medial epicondyle of the humerus, so it is more commonly injured in fractures involving the medial epicondyle rather than the midshaft.
“None of these” is incorrect because one of the listed options (radial nerve) is indeed affected.

The quadriceps femoris is a large extensor muscle group in the anterior compartment of the thigh. It consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. All of them insert into the patella via the quadriceps tendon and play a key role in extending the knee.

Biceps femoris, however, is not part of this group. Instead, it belongs to the hamstrings, located in the posterior compartment of the thigh. Its main actions are flexion of the knee and extension of the hip, which are opposite to the extensor function of the quadriceps.

Vastus medialis, rectus femoris, vastus intermedius, and vastus lateralis are all genuine components of the quadriceps, so these options are correct members and cannot be the answer.

Biceps femoris stands out because it lies in a completely different muscle compartment, has a different innervation (sciatic nerve), and serves a different function.

The trapezius is a large, triangular, superficial back muscle that extends from the occipital bone and nuchal ligament down to the spinous processes of the thoracic vertebrae and inserts on the clavicle, acromion, and spine of the scapula. Its fibers act differently depending on the region:

• Upper fibers → elevate (shrug) the shoulders and extend the neck.

• Middle fibers → retract the scapula.

• Lower fibers → depress the scapula.

When all fibers act together, they rotate the scapula upward, important in raising the arm above the head.

Option breakdown:

• Depression of the shoulders → Partially true but not the main defining action; only the lower fibers contribute.

• Flexion of the neck → Incorrect. Trapezius does not flex the neck; sternocleidomastoid does.

• Extension of the neck → Partially true for the upper fibers, but not the hallmark function tested here.

• Rotation of the arm → Incorrect. Rotation of the arm is performed by the rotator cuff muscles, not trapezius.

• Shrugging of the shoulders → Correct. This is the most characteristic and clinically tested action of trapezius (upper fibers).

In a postfixed brachial plexus, the plexus is shifted downward, meaning its contribution extends more caudally than usual.

Normally, the brachial plexus arises from C5 to T1.

• In a prefixed plexus, it shifts upward: C4 to C8.

• In a postfixed plexus, it shifts downward: C6 to T2.

Why each option is right or wrong:

• C2 to C5 → incorrect; this would be too high and would not supply the upper limb.

• C6 to T2 → correct; this is the classic root range for a postfixed brachial plexus.

• C5 to T1 → incorrect; that’s the normal root value.

• T4 to T11 → incorrect; this is the intercostal nerve range, not brachial plexus.

• L4 to S5 → incorrect; this represents lumbosacral plexus, not brachial plexus.

n a double-blind method in randomized control trials (RCTs), both the doctor and the patient do not know which treatment is being given. This helps eliminate observer bias (doctor’s expectations influencing results) and subject bias (patient’s expectations influencing response).

Why the correct option is right

• Both the doctor and the patient don’t know about the drug → This is the true definition of a double-blind study. Neither the treating physician nor the patient knows whether the subject is receiving the actual treatment or a placebo, ensuring unbiased outcomes.

Why the other options are wrong

• Doctor knows about the drug given but the patient doesn’t → This is a single-blind trial, not double-blind.

• Doctor, patient and the administer do not know about the drug → This describes a triple-blind trial, which extends blinding to data analysts/administrators.

• None of these → Incorrect, since the correct description is provided among the options.

• Doctor and the patient don’t know about the drug but the administer does → This is often still called a double-blind, since the person administering may need to know for safety, but technically it is not fully blinded if the administer knows.

The hip joint is closely related to several neurovascular structures:

• Posterior dislocation of the hip (most common type, often due to dashboard injuries in car accidents) pushes the femoral head backward and medially.

• The sciatic nerve runs just posterior to the hip joint, making it highly vulnerable in this type of dislocation. Injury can cause weakness in hamstrings, foot drop, and sensory loss in the posterior thigh and most of the leg/foot.

Why the other options are wrong

• Femoral nerve → Lies anteriorly in the femoral triangle; more at risk in anterior hip dislocations, not posterior.

• Obturator nerve → Lies medially, primarily affected in pelvic fractures, not typical hip dislocation.

• Median nerve → Runs in the upper limb, unrelated to the hip joint.

• All of them → Incorrect, because only the sciatic nerve has a direct anatomical relation at risk here.

Botulinum toxin (produced by Clostridium botulinum) is one of the most potent toxins known. It prevents exocytosis of acetylcholine vesicles from presynaptic nerve terminals by cleaving SNARE proteins (such as synaptobrevin, SNAP-25, syntaxin), which are essential for vesicle fusion.

• Without acetylcholine release, the postsynaptic muscle fiber cannot depolarize, leading to flaccid paralysis.

• Clinically, it causes botulism (descending paralysis, cranial nerve palsies, respiratory failure) and is also used in controlled doses for therapeutic and cosmetic purposes (e.g., Botox).

Why the other options are wrong

• Blocks the uptake of acetylcholine → No such mechanism; acetylcholine is not “taken up” but released.

• Decreases the formation of acetylcholine → That would involve inhibition of choline acetyltransferase, which botulinum toxin does not do.

• Increases the release of acetylcholine → Opposite effect; this is the action of black widow spider toxin (α-latrotoxin).

• Breaks down the acetylcholine → That is the action of acetylcholinesterase enzyme, not botulinum toxin.

Osteoporosis is by far the most prevalent bone disease worldwide. It is characterized by low bone mass and microarchitectural deterioration, leading to increased bone fragility and risk of fractures (especially hip, vertebrae, and wrist). It is particularly common in postmenopausal women and the elderly due to estrogen deficiency and age-related bone loss.

Why the other options are wrong

• Osteogenesis imperfecta → A rare genetic disorder (“brittle bone disease”) caused by defects in type I collagen. Not nearly as common as osteoporosis.

• Achondroplasia → The most common cause of dwarfism, but still a rare congenital condition compared to osteoporosis.

• Melorheostosis → Extremely rare sclerosing bone dysplasia with “candle-wax” appearance on X-ray.

• All of these → Incorrect, because osteoporosis overwhelmingly surpasses the others in prevalence.

Lymphocytic mastopathy, also called diabetic mastopathy, is a rare but recognized benign breast condition. It is most often seen in long-standing type 1 diabetes mellitus (though occasionally in type 2). Histologically, it is characterized by:

• Dense keloid-like fibrosis

• Prominent periductal and perivascular lymphocytic infiltrates

Clinically, it presents as firm, irregular, painless breast masses that can mimic carcinoma, but biopsy confirms its benign nature.

Why the other options are wrong

• Benign lumps: This is too vague and nonspecific; not directly associated with diabetes.

• Mastitis: Usually linked to lactation and infection, not diabetes.

• Gynecomastia: Seen in males due to hormonal imbalance (estrogen/testosterone ratio), liver disease, or drugs — not diabetes.

• All of them: Incorrect because diabetes is specifically associated with lymphocytic mastopathy, not all the listed conditions.

Fibrocystic changes represent the most common benign breast condition, especially in women of reproductive age. Importantly, they are considered non-proliferative because they involve cyst formation, fibrosis, and adenosis without epithelial proliferation. These changes generally do not increase the risk of breast cancer (or only minimally, in some subtypes).

Key histologic features include:

• Cyst formation (often “blue dome cysts”)

• Stromal fibrosis

• Adenosis without atypia

Why the other options are wrong

• Ductal epithelial hyperplasia: This is a proliferative lesion without atypia and does slightly increase the risk of breast cancer.

• Lobular hyperplasia: Again, this involves proliferation of lobular cells, so it is not non-proliferative.

• Papilloma: This is a benign intraductal proliferative lesion that can present with nipple discharge.

• None of these: Incorrect, because fibrocystic changes are indeed the classic non-proliferative lesion.

Sesamoid bones in the hand are almost always found at the metacarpophalangeal (MCP) joint of the thumb. More precisely, they are located at the distal portion of the first metacarpal, where it articulates with the base of the proximal phalanx.

So the correct answer here is indeed: Distal portion of the first metacarpal.

Why this is correct

• At the MCP joint of the thumb (the knuckle), there are usually two sesamoid bones, embedded within the tendons of the flexor pollicis brevis and adductor pollicis.

• Functionally, they increase leverage, reduce tendon wear, and allow smooth movement of the thumb during gripping and pinching.

• Radiographically, they appear just distal to the first metacarpal head, at the base of the proximal phalanx.

Why the other options are wrong

• Distal portion of second metatarsal: Sesamoid bones are found under the first metatarsal head (big toe), not the second.

• Coronoid process of ulna: A fixed bony projection, not a sesamoid.

• Lunate bone of wrist: A carpal bone, not sesamoid.

• Proximal portion of first metacarpal: Sesamoids are not at the carpometacarpal joint but distally at the MCP joint.

Claw hand is a classic deformity resulting from ulnar nerve injury, particularly at the wrist.

🔹 Muscles Affected by Ulnar Nerve Damage:

• Medial two lumbricals (to 4th and 5th digits)
• All interossei (palmar and dorsal)
• Adductor pollicis
• Hypothenar muscles
• Part of flexor digitorum profundus (to digits 4 and 5)

🔹 Why the Hand Claws:

 Lumbricals and interossei normally:

• Flex the MCP joints
• Extend the PIP and DIP joints

With ulnar nerve injury:

• Unopposed action of the long finger extensors → Hyperextension at MCP joints
• Unopposed flexor digitorum profundus (still intact) → Flexion at PIP and DIP joints

This results in clawing of the 4th and 5th fingers, especially noticeable when the ulnar nerve is injured distally at the wrist.

❌ Why the Other Options Are Incorrect:

• Axillary nerve
  → Innervates deltoid and teres minor; damage leads to loss of shoulder abduction, not claw hand

• Median nerve
  → Injury causes ape hand or hand of benediction, not claw hand

• Radial nerve
  → Injury leads to wrist drop, not clawing

• Musculocutaneous nerve
  → Affects forearm flexors and lateral forearm sensation, not hand muscles

The knee joint has a special mechanism called the “locking mechanism” that stabilizes it in full extension. To begin flexion, the joint must first be “unlocked” — a process that involves rotating the femur laterally (on the fixed tibia).

🔹 The Popliteus Muscle:

• Origin: Lateral condyle of the femur (and lateral meniscus)
• Insertion: Posterior surface of the tibia (above soleal line)

• Action:

  • Laterally rotates the femur on the tibia when the foot is fixed (i.e., in weight-bearing)

  • This “unlocks” the knee, allowing flexion to begin

  • Also assists in medial rotation of the tibia when the limb is not weight-bearing

Because of its oblique orientation, popliteus is ideally positioned to initiate knee flexion by reversing the locking mechanism.

❌ Why the Other Options Are Incorrect:

• Quadriceps femoris
  → Extends the knee and helps in locking, not unlocking

• Plantaris
  → Assists in plantarflexion and flexion of the knee, but does not unlock it

• Gastrocnemius
  → Flexes the knee and ankle (via plantarflexion), but not involved in unlocking

• Biceps femoris
  → Flexes and laterally rotates the leg, but it does not unlock the knee joint

🔹 Boundaries of the Popliteal Fossa:

Superomedial boundary:

• Semimembranosus

• Semitendinosus

These two muscles lie medially, coming from the ischial tuberosity and descending to insert near the medial aspect of the tibia. They form the upper medial border of the fossa.

Superolateral boundary:

• Biceps femoris (long head)

Inferomedial boundary:

• Medial head of gastrocnemius

Inferolateral boundary:

• Lateral head of gastrocnemius
  (+ sometimes plantaris)

❌ Why the Other Options Are Incorrect:

• Quadratus femoris and semitendinosus
  → Quadratus femoris is located much higher and does not contribute to the popliteal fossa

• Semimembranosus and the lateral head of gastrocnemius
  → Lateral head is on the inferolateral side, not superomedial

• Semimembranosus and biceps femoris
  → Biceps femoris is lateral, not part of the medial boundary

• Semitendinosus and biceps femoris
  → Again, biceps femoris is superolateral, not superomedial

🔹 Clinical Features of Klumpke’s Palsy

• Claw hand deformity:

  • Hyperextension at MCP joints

  • Flexion at PIP and DIP joints

  • Due to paralysis of lumbricals and interossei

❌ Why the Other Options Are Incorrect:

• Hand of benediction
  → Seen in median nerve injury, especially when trying to make a fist (inability to flex 2nd and 3rd digits)

• Shoulder drop
  → Seen in accessory nerve injury (CN XI), affecting trapezius

• Wrist drop
  → Seen in radial nerve palsy, due to paralysis of forearm extensors

• Waiter’s tip hand
  → Seen in Erb’s palsy (C5–C6 upper trunk injury), not Klumpke’s

The sartorius muscle is a long, strap-like muscle that originates from the anterior superior iliac spine (ASIS) and inserts into the medial surface of the tibia (part of the pes anserinus group). It crosses both the hip and knee joints.

🔹 Actions of Sartorius:

• Flexion of the thigh at the hip joint

• Lateral rotation of the thigh

• Abduction of the hip

• Flexion of the leg at the knee

• Assists in placing the lower limb in a cross-legged position

This unique combination of movements reflects its oblique path across the thigh.

❌ Why the Other Options Are Incorrect:

• Adductor longus
  → Primarily adducts the thigh; it does not perform lateral rotation or flexion at the hip

• Vastus lateralis
  → One of the quadriceps muscles, acts only on the knee joint to extend the leg, not the hip

• Pectineus
  → Adducts and flexes the thigh, may assist in medial rotation, not lateral

• Gracilis
  → Adducts the thigh and flexes the leg at the knee, but does not laterally rotate the thigh

Inversion of the foot refers to the movement in which the sole of the foot turns medially, toward the opposite foot. This action is primarily produced by muscles that:

• Pass medial to the subtalar joint axis
• Insert medially on the foot
• Pull the foot medially and upward

🔹 Tibialis Anterior:

• Origin: Lateral surface of the tibia and interosseous membrane

• Insertion: Medial cuneiform and base of the 1st metatarsal

• Action:

  • Dorsiflexes the ankle

  • Inverts the foot

Tibialis anterior is the main dorsiflexor and primary inverter of the foot.

❌ Why the Other Options Are Incorrect:

• Flexor digitorum longus
  → Assists plantarflexion and toe flexion, minor role in inversion, but not primary

• Fibularis tertius
  → Dorsiflexes and everts the foot, not inverter

• Fibularis longus
  → Plantarflexes and everts the foot, inserts laterally

• Fibularis brevis
  → Also everts and plantarflexes, not involved in inversion

Erb’s palsy (also called Erb–Duchenne palsy) is caused by injury to the upper trunk of the brachial plexus, specifically the C5 and C6 nerve roots.

🔹 Clinical Appearance:

• Arm hangs by the side (loss of abduction – deltoid/supraspinatus)

• Medially rotated arm (loss of infraspinatus)

• Extended elbow and pronated forearm (loss of biceps)

• This gives the classic “waiter’s tip” or “policeman’s tip” posture

❌ Why the Other Options Are Incorrect:

• Abducted shoulder
  → Incorrect; shoulder is adducted due to loss of abduction muscles

• C3–C5 nerve roots are involved
  → Wrong; C5 and C6 are involved — C3 and C4 contribute to phrenic nerve

• Flexed elbow
  → No; elbow is extended due to loss of biceps and brachialis

• Laterally rotated arm
  → Incorrect; arm is medially rotated due to paralysis of lateral rotators (e.g., infraspinatus)

🔹 Primary Actions of the Serratus Anterior:

1. Protraction of the scapula

   • Pulls the scapula anteriorly and around the thoracic cage (as in punching or pushing forward)

2. Upward rotation of the scapula

   • Important during abduction of the arm above 90°, working with the trapezius to rotate the scapula upward

3. Stabilization of the scapula

   • Holds the scapula tightly against the thoracic wall

   • Prevents winging of the scapula

❌ Why the Other Options Are Incorrect:

• Retraction
  → Performed by rhomboids and middle fibers of trapezius, pulling the scapula toward the spine

• Downward rotation
  → Carried out by levator scapulae, rhomboids, and pectoralis minor

• Depression
  → Mainly by lower trapezius, pectoralis minor, and gravity

• Elevation
  → Achieved by levator scapulae, upper trapezius, and rhomboids

Plasma calcium levels are tightly regulated by three key hormones:

1. Parathyroid Hormone (PTH)
   – Secreted in response to low calcium
   – Increases calcium levels by:

   • Stimulating bone resorption (osteoclast activity)

   • Increasing renal calcium reabsorption

   • Stimulating production of calcitriol (active Vitamin D)

2. Calcitriol (Vitamin D₃)
   – Enhances intestinal absorption of calcium
   – Works synergistically with PTH

3. Calcitonin
   – Secreted by parafollicular (C) cells of the thyroid gland
   – Released when plasma calcium levels rise
   – Lowers blood calcium by:

   • Inhibiting osteoclast activity (reducing bone resorption)

   • Promoting calcium deposition into bone

Thus, calcitonin serves as a protective hormone to prevent hypercalcemia.

❌ Why the Other Options Are Incorrect:

• Aldosterone
  → Regulates sodium and potassium balance, not calcium

• Parathyroid hormone (PTH)
  → Increases when calcium is low, not high

• Calcitriol
  → Activated in response to low calcium or PTH stimulation, not directly secreted due to high calcium

• Vasopressin (ADH)
  → Regulates water retention and plasma osmolality, not calcium levels

🔹 Innervation of the Lumbricals:

• Lumbricals 1 & 2 (lateral two):

  • Innervated by the median nerve

  • These are unipennate muscles (arising from one tendon)

• Lumbricals 3 & 4 (medial two):

  • Innervated by the ulnar nerve

  • These are bipennate muscles (arising from two tendons)

Thus, two nerves are responsible for lumbrical innervation:
→ Median and ulnar nerves

❌ Why the Other Options Are Incorrect:

• Radial and ulnar nerve
  → The radial nerve is mainly motor to the extensor muscles in the posterior compartment and sensory to parts of the hand; it does not supply intrinsic hand muscles

• Median and musculocutaneous nerve
  → Musculocutaneous nerve innervates anterior arm muscles, not intrinsic hand muscles

• Median and radial nerve
  → Radial nerve has no motor function in the hand

• Ulnar and musculocutaneous nerve
  → Again, musculocutaneous is irrelevant to hand muscle innervation

🔹 Role of the Subclavius Muscle:

• Anchors and depresses the clavicle
• Protects underlying neurovascular structures by acting as a buffer between the broken bone ends and deeper tissues
• Acts like a “shock absorber”, limiting the displacement of the fractured clavicle downward toward the brachial plexus and subclavian vessels

❌ Why the Other Options Are Incorrect:

• Trapezius
  → Acts on the scapula, and though it may contribute to postural support, it does not lie beneath the clavicle to protect nerves

• Pectoralis major
  → Covers the anterior chest but is not interposed between the clavicle and the underlying neurovascular bundle

• Deltoid
  → Covers the shoulder and upper arm, not the subclavian region

• Sternocleidomastoid (SCM)
  → Inserts on the medial clavicle, but it’s a superficial neck muscle and not positioned to shield nerves under the midshaft of the clavicle

The shoulder joint (glenohumeral joint) is a ball-and-socket synovial joint, allowing a wide range of motion. However, its mobility comes at the expense of stability — the glenoid cavity is shallow and provides minimal bony support.

This makes muscular support crucial, and the rotator cuff muscles are the most important stabilizers of this joint.

🔹 Rotator Cuff Muscles (SITS):

1. Supraspinatus
   – Initiates abduction

2. Infraspinatus
   – Lateral rotation

3. Teres minor
   – Lateral rotation

4. Subscapularis
   – Medial rotation

Together, these muscles:

• Hold the head of the humerus firmly within the glenoid cavity

• Provide dynamic stability during shoulder movements

• Resist dislocating forces

❌ Why the Other Options Are Incorrect:

• Deltoid muscle
  → Major abductor of the arm, but does not stabilize the head of the humerus within the glenoid cavity

• Teres major muscle
  → Involved in adduction and medial rotation, but not a rotator cuff muscle; it plays a minimal role in joint stability

• Trapezius muscle
  → Acts on the scapula, not directly on the glenohumeral joint

• Pectoralis major muscle
  → A powerful adductor and medial rotator of the arm, but it does not stabilize the shoulder joint itself

The musculocutaneous nerve innervates the three primary flexor muscles of the forearm at the elbow:

1. Biceps brachii – strong supinator and flexor of the forearm

2. Brachialis – main pure flexor of the forearm

3. Coracobrachialis – flexes and adducts the arm at the shoulder

After supplying these muscles, the musculocutaneous nerve continues as the lateral cutaneous nerve of the forearm, providing sensory innervation to the lateral forearm

❌ Why the Other Options Are Incorrect:

• Radial nerve
  → Innervates extensor muscles of the arm and forearm, not flexors

• Median nerve
  → Supplies most anterior forearm muscles, but not the main elbow flexors (like biceps and brachialis)

• Ulnar nerve
  → Supplies flexor carpi ulnaris and part of flexor digitorum profundus in the forearm, but not the elbow flexors

• Lateral cutaneous nerve of the forearm
  → This is the terminal sensory branch of the musculocutaneous nerve; it does not have motor function

The axillary nerve is a branch of the posterior cord of the brachial plexus. It:

• Emerges through the quadrangular space

• Winds posteriorly around the surgical neck of the humerus

• Innervates the deltoid and teres minor muscles

• Provides sensation to the skin over the deltoid (regimental badge area)

❌ Why the Other Options Are Incorrect:

• Median nerve
  → Runs medially in the arm, commonly injured in supracondylar fractures or carpal tunnel syndrome, not at the surgical neck

• Radial nerve
  → Passes in the radial groove of the humerus (midshaft), not near the surgical neck

• Musculocutaneous nerve
  → Innervates the anterior arm (biceps, brachialis); not located near the humeral neck

• Ulnar nerve
  → Courses posterior to the medial epicondyle; injured in fractures near the elbow, not the shoulder

🔬 Electromyography (EMG):

• A test that measures the electrical activity of muscles

• In myasthenia gravis, repetitive nerve stimulation shows a decremental response in muscle action potentials (i.e., the amplitude drops progressively)

• This reflects fatigability, a hallmark of the disease

• EMG can also help differentiate MG from other neuromuscular disorders

❌ Why the Other Options Are Incorrect:

• Computed tomography scan (CT scan)
  → May be used to detect a thymoma (often associated with MG) but not diagnostic of the disease itself

• Romberg test
  → Used to assess proprioception and balance, often in dorsal column or vestibular disorders, not MG

• Pinprick test
  → A sensory test for assessing pain perception, unrelated to neuromuscular transmission

• Nerve conduction test
  → Evaluates the speed of signal transmission in nerves, useful in peripheral neuropathies, but less specific for MG than EMG

Inferior gluteal artery is a branch of the internal iliac artery, located in the gluteal region (buttocks). Its primary supply is to the muscles of the gluteal region, posterior thigh, and external genitalia. It does not send branches to the knee joint

❌ Why the Other Options Are Incorrect:

• Lateral femoral circumflex artery: This artery is a branch of the deep femoral artery (profunda femoris artery). It gives off descending branches that contribute to the genicular anastomosis around the knee joint. So, it does supply the knee joint.

• Popliteal artery: This is the main artery in the popliteal fossa (behind the knee). It gives off several crucial branches directly supplying the knee joint, known as the genicular arteries (superior medial, superior lateral, inferior medial, inferior lateral, and middle genicular arteries). So, it does supply the knee joint.

• Femoral artery: While the femoral artery itself is the major artery of the thigh, it gives rise to branches like the deep femoral artery, which in turn gives off the lateral femoral circumflex artery. Some direct branches of the femoral artery in the lower thigh (e.g., descending genicular artery) also contribute to the knee’s blood supply. So, indirectly and directly, the femoral artery system does supply the knee joint.

• Anterior tibial artery: This artery is a continuation of the popliteal artery after it passes through the interosseous membrane. It gives off recurrent branches (e.g., anterior and posterior tibial recurrent arteries) that ascend to contribute to the genicular anastomosis around the knee joint. So, it does supply the knee joint.

🔹 What Actually Happens in Myasthenia Gravis:

• Acetylcholine (ACh) is produced in normal amounts by motor neurons

• However, autoantibodies bind to or destroy the postsynaptic nicotinic ACh receptors, preventing effective stimulation of skeletal muscles

• This results in muscle weakness and fatigability, especially in muscles that are repeatedly used (e.g., extraocular muscles)

❌ Why the Other Options Are Incorrect:

• Dopamine
  → Deficient in Parkinson’s disease, not myasthenia gravis

• Acetylcholine
  → Normal production; problem lies in receptor availability, not neurotransmitter level

• Epinephrine and Norepinephrine
  → Involved in the autonomic nervous system, not the neuromuscular junction of voluntary muscle

The common fibular nerve (also called common peroneal nerve) is one of the two terminal branches of the sciatic nerve, the other being the tibial nerve. The sciatic nerve is the largest nerve in the body and arises from the lumbosacral plexus, specifically from L4, L5, S1, S2, and S3

The common fibular nerve receives fibers from L4, L5, S1, and S2

Hence, the correct root value of the common fibular nerve is L4 to S2.

❌ Why the Other Options Are Incorrect:

• L5 to S2
  → Incomplete; L4 also contributes

• L5 to S4
  → Includes S3 and S4, which do not contribute to the common fibular nerve

• L2 to S4
  → Includes roots not related to the sciatic nerve (e.g., L2–L3)

• L2 to L4
  → These are the roots for the femoral and obturator nerves, not the common fibular

The common peroneal nerve (also called the common fibular nerve) is one of the two terminal branches of the sciatic nerve. After branching off, it winds laterally around the neck of the fibula, just below the knee — a position that makes it highly susceptible to injury, especially from blunt trauma to the lateral knee, as in this football injury.

❌ Why the Other Options Are Incorrect:

• Superficial fibular nerve
  → A branch of the common peroneal nerve, but lies further down the leg and wouldn’t be directly affected at the fibular neck

• Deep fibular nerve
  → Also a branch of the common peroneal nerve, involved in dorsiflexion, but is distal to the site of injury

• Sciatic nerve
  → Proximal to the knee; not affected by trauma to the fibular neck

• Tibial nerve
  → Follows the posterior leg and does not wind around the fibula; unaffected by lateral knee injuries

Inversion of the foot involves turning the sole medially. This movement requires combined action of muscles from two compartments of the leg:

🔹 Muscles Involved in Inversion:

1. Tibialis anterior

   • Located in the anterior compartment

   • Innervated by the deep peroneal (fibular) nerve

2. Tibialis posterior

   • Located in the deep posterior compartment

   • Innervated by the tibial nerve

These two muscles are the primary invertors of the foot, and both must function properly for inversion to occur.

❌ Why the Other Options Are Incorrect:

• Tibial and common peroneal nerve
  → Common peroneal branches into superficial and deep; damage to it affects more than just inversion, and doesn’t isolate the key invertor (tibialis anterior) specifically.

• Superficial peroneal and tibial nerve
  → Superficial peroneal nerve supplies evertors (peroneus longus/brevis); not involved in inversion.

• Superficial peroneal and sural nerve
  → Both are sensory or evertor-related, not involved in inversion.

• Superficial and deep peroneal nerve
  → Superficial → evertors, deep → invertor (tibialis anterior), but inversion also needs tibialis posterior, which is innervated by the tibial nerve, not included here.

🔹 Structures in the Anterior Compartment of the Arm:

✅ Muscles:

• Biceps brachii
• Brachialis
• Coracobrachialis

✅ Nerve:

• Musculocutaneous nerve
  → Innervates all muscles in the anterior arm

✅ Vessels:

• Brachial artery

The radial nerve is a branch of the posterior cord of the brachial plexus

It travels in the radial (spiral) groove of the humerus, in the posterior compartment

It supplies the triceps brachii and extensor muscles of the forearm

Although it passes anteriorly at the elbow, it is not a component of the anterior arm compartment

❌ Why the Other Options Are Incorrect:

• Musculocutaneous nerve
  ✅ This is part of the anterior compartment. It innervates biceps brachii, brachialis, and coracobrachialis.

• Biceps brachii
  ✅ A major flexor of the forearm and supinator, clearly located in the anterior compartment.

• Brachial artery
  ✅ This large artery travels in the anterior arm and supplies all structures in the anterior compartment.

• Coracobrachialis
  ✅ A muscle of the anterior compartment, innervated by the musculocutaneous nerve, and assists in flexion and adduction of the arm.

Dupuytren’s contracture is a progressive, fibroproliferative disease of the palmar fascia (aponeurosis) that results in permanent flexion of one or more fingers due to thickening and shortening of fibrous tissue.

🔹 Key Features:

• Most commonly affects the 4th and 5th digits (ring and little fingers)

• Caused by fibrous degeneration and thickening of the ulnar side of the palmar aponeurosis

• Over time, nodules form and fibrous cords develop, pulling the fingers into flexion at the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints

• Painless but progressive, often bilateral, more common in men over 40

❌ Why the Other Options Are Incorrect:

• “Caused by fibrous degeneration on radial side of the palmar aponeurosis”
  Radial side involvement (thumb and index finger) is rare

• “It causes flexion of 1st digit at metacarpophalangeal joint”
   The thumb is rarely involved; the condition mainly affects the 4th and 5th digits

• “It causes extension of 4th and 5th digits at metacarpophalangeal joint”
   It causes flexion, not extension

• “Is a disease of interphalangeal joints of thumb”
   Again, the thumb is usually spared; and the disease affects the palmar fascia, not the joint per se

Foot drop is characterized by an inability to dorsiflex the foot, resulting in a slapping gait or high-stepping gait to prevent the toes from dragging during walking.

🔹 Common Peroneal (Fibular) Nerve:

• A branch of the sciatic nerve

• Wraps around the neck of the fibula, where it is superficial and prone to injury

• Divides into:

  • Deep peroneal nerve → supplies anterior compartment (dorsiflexors of the foot)

  • Superficial peroneal nerve → supplies lateral compartment (evertors)

✅ Damage to the common peroneal nerve results in:

• Foot drop due to paralysis of tibialis anterior

• Sensory loss over the dorsum of the foot (except medial side)

❌ Why the Other Options Are Incorrect:

• Femoral nerve
  → Supplies the anterior thigh (quadriceps); involved in knee extension, not foot movement

• Superficial fibular nerve
  → Supplies evertors and skin of dorsum of foot, but not primary dorsiflexors

• Sciatic nerve
  → Proximal cause of foot drop is possible, but less common than isolated common peroneal nerve injury

• Saphenous nerve
  → A sensory branch of the femoral nerve; has no motor function, thus not involved in foot drop

Skeletal muscle tissue is organized in three concentric layers of connective tissue, each surrounding a different level of muscle structure:

🔹 1. Endomysium

• A delicate connective tissue layer

• Surrounds each individual muscle fiber

• Contains capillaries, nerves, and extracellular matrix

• Made primarily of reticular fibers (type III collagen)

🔹 2. Perimysium

• Thicker connective tissue

• Surrounds a fascicle (a bundle of muscle fibers)

• Provides pathways for larger blood vessels and nerves

🔹 3. Epimysium

• Outermost layer

• Dense irregular connective tissue

• Encloses the entire muscle

• Continuous with the tendon

❌ Why the Other Options Are Incorrect:

• Perimysium
  → Wraps fascicles, not individual muscle fibers

• Sarcoplasmic reticulum
  → A specialized organelle inside the muscle fiber; stores calcium, not connective tissue

• Terminal cisternae
  → Enlarged ends of the sarcoplasmic reticulum; not part of any connective wrapping

• Epimysium
  → Surrounds the entire muscle, not individual fibers

🔹 T-tubules (Transverse Tubules):

• Invaginations of the sarcolemma
• Penetrate into the muscle fiber at regular intervals
• Run perpendicular to the muscle fiber’s length
• Located at the junction of the A and I bands
• Carry action potentials from the surface deep into the fiber, ensuring synchronous contraction of the myofibrils

❌ Why the Other Options Are Incorrect:

• Pili
  → Not an anatomical term in muscle histology

• Terminal cisternae
  → Enlarged sacs of the sarcoplasmic reticulum, not part of the sarcolemma; store and release calcium

• Sarcoplasmic reticulum
  → Specialized endoplasmic reticulum in muscle fibers, stores Ca²⁺, but is not an indentation of the sarcolemma

• Lamellae
  → Refers to layers of bone matrix, not muscle structure

The axillary artery is a continuation of the subclavian artery and begins at the lateral border of the first rib, continuing until the lower border of the teres major, where it becomes the brachial artery.

To better describe its anatomical relations and branches, the axillary artery is divided into three parts, using the pectoralis minor muscle as the landmark:

🔹 Divisions of the Axillary Artery:

1. First Part – Proximal to pectoralis minor

   • Has 1 branch: Superior thoracic artery

2. Second Part – Posterior (deep) to pectoralis minor

   • Has 2 branches: Thoracoacromial artery and Lateral thoracic artery

3. Third Part – Distal to pectoralis minor

   • Has 3 branches: Subscapular artery, Anterior circumflex humeral artery, Posterior circumflex humeral artery

❌ Why the Other Options Are Incorrect:

• Teres major
  → Landmark for when the axillary artery becomes the brachial artery, but does not divide it into three parts

• Coracobrachialis
  → Related to the musculocutaneous nerve, but not used to divide the artery

• Pectoralis major
  → Lies superficially over the axillary artery but does not serve as a landmark for dividing it

• Teres minor
  → Found in the shoulder region, not related to the axillary artery

🔹 Keystone of the Arch:

• The head of the talus acts as the keystone — just like the top wedge stone in an architectural arch.

• It receives the body’s weight from the tibia and distributes it anteriorly to the navicular and posteriorly to the calcaneus.

❌ Why the Other Options Are Incorrect:

• Medial cuneiform bone
  → Part of the arch but located distally, not the keystone

• Metatarsals
  → Form the anterior end of the arch, but do not support it centrally

• Calcaneal tubercle
  → Forms the posterior end (heel) of the arch; acts as a pillar, not the keystone

• Navicular bone
  → Lies just in front of the talus; helps receive the talar head but isn’t the central wedge

Inversion (turning the sole medially) and eversion (turning the sole laterally) occur primarily at joints in the hindfoot and midfoot, not at the ankle (talocrural) joint, which only allows dorsiflexion and plantarflexion.

🔹 Main Joints Involved in Inversion and Eversion:

1. Subtalar Joint

• Articulation: Talus and Calcaneus

• Type: Plane synovial joint

• Allows gliding and rotation crucial for inversion and eversion

2. Transverse Tarsal Joint (also called Chopart joint)

• Made up of two joints:

  • Talonavicular joint

  • Calcaneocuboid joint

• Works with the subtalar joint to allow complex rotation and tilting of the foot

❌ Why the Other Options Are Incorrect:

• Subtalar and talocrural joint
  → Talocrural (ankle) joint only allows plantarflexion/dorsiflexion, not inversion/eversion

• Talotibial and talocalcaneal
  → “Talotibial” refers to the ankle joint; again, not involved in inversion/eversion

• Talocrural and talocalcanial joint
  → “Talocalcanial” is another name for the subtalar joint, but talocrural is still not involved in inversion/eversion

• Transverse tarsal and tibiotalar joint
  → Tibiotalar = talocrural, which doesn’t contribute to inversion/eversion

Function of Posterior Cruciate Ligament: Prevents posterior displacement of the tibia and hyperflexion of the knee.

🩺 Clinical Correlation:

A posterior dislocation of the tibia typically results from:

• Dashboard injury (e.g., knee hits dashboard in a car accident)

• Falling hard on a flexed knee

In such cases, the PCL is torn, since it’s the main restraint against backward movement of the tibia.

❌ Why the Other Options Are Incorrect:

• Medial meniscus
  → A cartilage pad; commonly torn with twisting injuries, not directly damaged by posterior displacement.

• Anterior cruciate ligament (ACL)
  → Prevents anterior displacement of the tibia, not posterior.

• Tibial collateral ligament (MCL)
  → Stabilizes the medial side of the knee against valgus stress; not primarily involved in posterior tibial stability.

• Lateral meniscus
  → Also a shock-absorbing cartilage; not directly responsible for restraining posterior tibial movement.

Axillary vein is formed by the union of the basilic vein and the brachial veins (which are paired and accompany the brachial artery)

This union occurs at the lower border of the teres major muscle

❌ Why the Other Options Are Incorrect:

• Brachial vein and cephalic vein
  → Cephalic joins later; it does not form the axillary vein

• Basilic vein and radial vein
  → Radial vein is a deep forearm vein; it contributes to brachial veins, not directly to axillary vein

• Basilic vein and subclavian vein
  → Subclavian vein is the continuation of the axillary vein; it doesn’t form it

• Basilic vein and cephalic vein
  → Cephalic joins later; not part of axillary vein formation

📌 Attachments of the Flexor Retinaculum:

🔹 Medially (ulnar side):

• Pisiform (a sesamoid bone in the tendon of flexor carpi ulnaris)

• Hook of hamate

🔹 Laterally (radial side):

• Tubercle of scaphoid

• Ridge of trapezium

Why the Other Options Are Incorrect:

• Tubercle of scaphoid and ridge of trapezium → These are the lateral attachments, not medial.

• Pisiform and trapezoid → Trapezoid is a deep central carpal bone, not involved in retinaculum attachment.

• Ridge of trapezium and hook of hamate → One lateral and one medial bone; incorrect pairing.

• Tubercle of scaphoid and hook of hamate → Also a mismatched pair (lateral and medial).

The deltopectoral triangle (also called the clavipectoral triangle) is an anatomical space found just below the clavicle.

Within this triangle, the cephalic vein pierces the clavipectoral fascia to drain into the axillary vein.

❌ Why the Other Options Are Incorrect

Axillary vein

• Lies deep and medial to the deltopectoral triangle

• The cephalic vein drains into it, but it does not pass through the triangle itself

Basilic vein

• Ascends on the medial side of the forearm and arm

• Joins the brachial vein to form the axillary vein

• Does not traverse the deltopectoral triangle

Brachial vein

• Paired deep veins accompanying the brachial artery

• Located in the deep compartment, not superficial enough to pass through the triangle

Subclavian vein

• Located superior to the clavicle

• Receives the axillary vein but does not pass through the triangle

The cubital lymph nodes (also called supratrochlear lymph nodes) are superficial lymph nodes located in the cubital fossa, specifically just above the medial epicondyle of the humerus, along the basilic vein.

These nodes receive lymph from:

• The medial side of the hand and forearm

• Associated skin and superficial tissues

❌ Why the Other Options Are Incorrect:

Just medial to the radial nerve

• The radial nerve is a deep structure in the lateral arm

• Not associated with superficial lymph nodes

Just lateral to the brachial artery

• The brachial artery is deep and medial in the cubital fossa

• Cubital nodes are superficial and medial, not lateral

At the medial border of the brachioradialis

• The brachioradialis is a lateral forearm muscle

• Cubital lymph nodes lie medially, not near this muscle

Just above the lateral epicondyle

• No lymph nodes are typically located here

• This area is related more to tennis elbow than lymphatic structures

Howship’s lacunae (also called resorption bays) are shallow depressions or pits found on the surface of bones undergoing resorption. These are created by the activity of osteoclasts, which are the bone-resorbing cells of the skeletal system.

❌ Why the Other Options Are Incorrect:

Osteoblasts

• Bone-forming cells

• Located on the surface of newly formed bone, not within resorption pits

Osteocytes

• Mature bone cells

• Reside in lacunae within bone matrix (not Howship’s lacunae)

Osteoprogenitor cells

• Precursor cells that differentiate into osteoblasts

• Found in the periosteum and endosteum, not in resorption bays

Chondrocytes

• Found in cartilage, not bone

• Reside in cartilage lacunae, not Howship’s lacunae

The most common site of fracture of the clavicle is at the junction of the medial two-thirds and the lateral one-third. This is a biomechanically vulnerable transition zone between the strong, thick medial portion and the thinner, flatter lateral portion of the clavicle.

🔹 Why This Area Is Vulnerable:

• The medial two-thirds of the clavicle are convex anteriorly and structurally stronger.

• The lateral one-third is concave anteriorly, thinner, and weaker.

• This junction is where the change in curvature and cross-sectional strength creates a natural stress concentration point.

• Most commonly fractured due to falling on an outstretched hand (FOOSH) or direct trauma to the shoulder.

❌ Why the Other Options Are Incorrect:

• The mid-point of the clavicle
  → Close, but not the precise fracture site. The actual fracture zone is slightly medial to the midpoint.

• Junctions involving three-fourths and one-fourth divisions
  → These are not anatomically relevant divisions and do not correspond to the typical stress zone of the clavicle.

• Junction of lateral two-thirds with medial one-third
  → Also not correct — that location is more lateral than the usual fracture zone.

🔹 Anatomical Course of the Great Saphenous Vein:

1. Origin:

   • Arises from the medial end of the dorsal venous arch of the foot

2. Course:

   • Passes anterior to the medial malleolus (landmark for cannulation)

   • Ascends medial side of the leg and thigh

   • Passes posterior to the medial condyle of the femur (not anterior!)

   • Pierces the cribriform fascia of the fascia lata

   • Joins the femoral vein at the saphenous opening, but deep to the fascia lata, not superficial to it

3. Termination:

   • Drains into the femoral vein in the femoral triangle

❌ Why the Other Options Are Incorrect:

• Joins the femoral vein superficial to the fascia lata
  It pierces the fascia lata at the saphenous opening and joins the femoral vein deep to it.

• Anterior to the medial condyle of the tibia and femur
   It passes posterior to the medial condyle of the femur.

• Passes up the lateral side of the leg
   That describes the small saphenous vein. The great saphenous runs medially.

• Posterior to the medial malleolus
  It passes anterior to the medial malleolus. The posterior tibial artery and tibial nerve pass posteriorly.

The quadriceps femoris is a powerful group of four muscles located in the anterior compartment of the thigh. It includes Rectus femoris, Vastus lateralis, Vastus medialis and Vastus intermedius

🔹 Primary Action:

All four heads converge into the quadriceps tendon, which inserts onto the patella, and via the patellar ligament, onto the tibial tuberosity. Their main function is to:

• Extend the knee joint

• Rectus femoris also crosses the hip joint, so it assists in hip flexion as a secondary function.

❌ Why the Other Options Are Incorrect:

Adduction at the hip

• Performed by adductor muscles (e.g., adductor longus, brevis, magnus)

• Located in the medial compartment, not affected by quadriceps paralysis

Extension of the hip

• Performed mainly by the gluteus maximus and hamstrings

• Quadriceps does not participate in hip extension

Flexion at the knee

• Carried out by posterior thigh muscles (hamstrings)

• Quadriceps is an extensor, not a flexor

Medial rotation of the knee

• Involves semimembranosus, semitendinosus, gracilis, and sartorius

• Quadriceps do not perform this action

🔷 Phases of Upper Limb Abduction:

1. 0–15°:

   • Performed primarily by the supraspinatus (initiates abduction)

2. 15–90°:

   • Mainly by the middle fibers of the deltoid

3. Above 90° (90°–180°):

   • Requires upward rotation of the scapula

   • Carried out by the trapezius and serratus anterior

🔹 Why Trapezius and Serratus Anterior Are Correct:

• These muscles work together to rotate the scapula upward:

  • Upper trapezius pulls the acromion upward

  • Lower trapezius pulls the scapular spine downward

  • Serratus anterior pulls the inferior angle laterally and forward

• This coordinated action allows the glenoid cavity to face upward, facilitating continued abduction.

❌ Why the Other Options Are Incorrect:

Deltoid and levator scapulae

• Deltoid helps up to 90°

• Levator scapulae elevates scapula; does not contribute to upward rotation

Trapezius and levator scapulae

• Again, levator scapulae rotates scapula downward, opposing abduction beyond 90°

Deltoid and supraspinatus

• Both act on the humerus, not on scapular rotation

• Effective only up to 90°, not beyond

Deltoid and trapezius

• Deltoid does not help beyond 90°

When considering the formation of bones and cartilage of the limbs (upper and lower), we’re referring to the appendicular skeleton, which has a different embryological origin compared to the axial skeleton (skull, vertebrae, ribs).

🔹 Lateral Plate Mesoderm — Limb Bones:

• The lateral plate mesoderm splits into:

  • Parietal (somatic) layer

  • Visceral (splanchnic) layer

• The parietal/somatic layer gives rise to:

  • Bones and connective tissue of the limbs

  • Sternum

  • Parts of the body wall

Limb development begins with limb bud formation, where mesenchyme derived from the lateral plate mesoderm condenses to form cartilage models, which then ossify to become bones.

❌ Why the Other Options Are Incorrect:

Paraxial mesoderm

• Forms somites, which contribute to:

  • Axial skeleton(vertebrae, ribs, base of skull)

  • Skeletal muscle and dermis

• Does not form limb bones, although limb muscles do come from here (myotome)

Intermediate mesoderm

• Develops into the urogenital system

• No contribution to limb skeleton

Endoderm

• Forms gut tube and internal linings — not involved in musculoskeletal development

Ectoderm

• Forms epidermis and nervous system

• Does not form bones or cartilage. However, it interacts with mesoderm to pattern limb development

A humeral shaft fracture, especially distal to the deltoid tuberosity, is most likely to injure the radial nerve. This is due to the anatomical course of the radial nerve in the radial (spiral) groove of the humerus. A fracture at or near the mid-to-distal third of the humeral shaft puts the nerve at risk because the bone and nerve are in direct contact at this level.

🧠 Clinical Consequences of Radial Nerve Injury:

• Wrist drop: Paralysis of wrist and finger extensors

• Sensory loss: Over the posterior arm, forearm, and dorsum of the hand (particularly the first dorsal web space)

❌ Why the Other Options Are Incorrect:

• Axillary nerve: Runs around the surgical neck, not the shaft — injured in surgical neck fractures

• Median nerve: Travels along the medial arm, typically injured at the elbow, not the shaft

• Ulnar nerve: Passes behind the medial epicondyle, vulnerable in elbow fractures, not mid-shaft

• Musculocutaneous nerve: Lies between biceps and brachialis, not in contact with the humerus

The radial nerve is the most commonly injured nerve in midshaft fractures of the humerus, particularly distal to the deltoid tuberosity. This is because it travels in close contact with the bone within the radial (spiral) groove of the humerus.

❌ Why the Other Options Are Incorrect:

Axillary nerve

• Winds around the surgical neck of the humerus, not the shaft.

• Injured in fractures at the surgical neck, not shaft fractures.

Median nerve

• Travels medially with the brachial artery.

• More likely injured at the elbow (supracondylar fractures) or in carpal tunnel syndrome, not humeral shaft fractures.

Ulnar nerve

• Passes posterior to the medial epicondyle of the humerus.

• Typically injured in medial epicondyle fractures, not in shaft fractures.

Musculocutaneous nerve

• Pierces the coracobrachialis and runs between biceps and brachialis.

• Rarely injured in humeral fractures.

The sartorius muscle is the longest muscle in the human body, named from the Latin word sartor, meaning “tailor” — because it helps bring the leg into the tailor’s sitting position (cross-legged).

❌ Why the Other Options Are Incorrect:

Pectineus

• Much shorter than sartorius

Vastus medialis

• Powerful knee extensor, but not nearly as long as sartorius

Psoas major

• Not as long as sartorius, and doesn’t span both hip and knee joints

Iliacus

• Flat muscle in the iliac fossa

• Shorter and more localized

The lesser tubercle of the humerus is located on the anterior surface of the proximal humerus. It serves as the insertion point for one specific rotator cuff muscle — the subscapularis.

❌ Why the Other Options Are Incorrect:

Supraspinatus

• Inserts on the superior facet of the greater tubercle

Infraspinatus

• Inserts on the middle facet of the greater tubercle

Teres minor

• Inserts on the inferior facet of the greater tubercle

Teres major

• Inserts on the medial lip of the intertubercular sulcus, not the lesser tubercle

The greater tubercle of the humerus serves as the insertion point for three of the four rotator cuff muscles.

The infraspinatus muscle:

• Originates from the infraspinous fossa of the scapula (just below the spine of the scapula)

• Inserts on the middle facet of the greater tubercle of the humerus

❌ Why the Other Options Are Incorrect:

Subscapularis

• Inserts on the lesser tubercle of the humerus

• Performs medial rotation, not lateral

Teres major

• Inserts on the medial lip of the intertubercular sulcus, not the greater tubercle

• Functions in medial rotation and adduction

Supraspinatus

• Inserts on the superior facet of the greater tubercle

• Initiates abduction of the arm (first 15°)

• Does not perform lateral rotation

Latissimus dorsi

• Inserts on the floor of the intertubercular sulcus of the humerus

• Performs extension, adduction, and medial rotation

• Does not insert on the greater tubercle

🏗️ Formation of the Femoral Sheath:

The sheath is formed by a downward prolongation of two fascial layers from the abdomen:

1. Fascia transversalis — contributes to the anterior wall of the sheath

2. Fascia iliaca — contributes to the posterior wall

Together, they enclose the femoral artery and vein in a protective sleeve, allowing them to glide during hip movements.

❌ Why the Other Options Are Incorrect:

The processus vaginalis

• This is an embryological structure related to testicular descent, not involved in femoral sheath formation.

The pectineus fascia

• This covers the pectineus muscle, which lies posterior to the femoral sheath.

• It does not contribute to the sheath itself.

The psoas fascia and the fatty layer of the superficial fascia

• The psoas fascia surrounds the psoas major muscle; it does not form the sheath.

• The fatty layer (Camper’s fascia) is superficial and unrelated to the femoral sheath’s deep location.

The fascia lata and the membranous layer of the superficial fascia

• Fascia lata is the deep fascia of the thigh, lying below the femoral sheath.

• Membranous layer (Scarpa’s fascia) is superficial and does not extend into the femoral sheath.