Locomotor – 2020

• Osteosarcoma is the most common primary malignant bone tumor (excluding multiple myeloma).

• It typically arises in the metaphysis of long bones, especially around the knee joint (distal femur, proximal tibia).

• About 50% of all cases occur in this region.

• It usually affects adolescents and young adults (10–25 years), though a secondary peak is seen in elderly patients with Paget’s disease.

❌ Why the others are wrong

1. 75% occur in adults above 60 years of age → ❌ Incorrect; osteosarcoma is common in children & adolescents, not elderly (except secondary cases with Paget’s disease).

2. Histologically characterized by a mosaic pattern of bone formation → ❌ This description is for Paget’s disease of bone, not osteosarcoma.

3. Mutations in tumor suppressor genes play no role → ❌ Wrong; mutations in RB gene (retinoblastoma) and p53 are strongly implicated in osteosarcoma pathogenesis.

4. Brodie’s abscess is a diagnostic feature on X-ray → ❌ Brodie’s abscess is seen in subacute osteomyelitis, not in osteosarcoma.

The sartorius muscle is a long strap-like muscle, running obliquely across the thigh from the anterior superior iliac spine (ASIS) to the medial surface of the tibia (part of pes anserinus).

• At the hip joint:

  • Flexes thigh

  • Abducts thigh

  • Laterally rotates thigh

• At the knee joint:

  • Flexes leg

  • When the knee is flexed, it also medially rotates the leg (due to its medial insertion).

This combined action allows the “tailor’s position” (cross-legged sitting).

❌ Why the others are wrong

• Option : Mentions lateral rotation of thigh & medial rotation of leg, but misses hip flexion and abduction → incomplete.

• Option : Mentions flexion & abduction at hip, but ignores lateral rotation at hip and medial rotation at knee → incomplete.

• Option : Only flexes the knee → very limited, ignores other major actions.

• Option : “Tailor’s position” is true, but this is more of a functional description than a precise action statement → less appropriate for an anatomy exam.

There are two flexor digitorum muscles:

1. Flexor digitorum superficialis (FDS)

   • Function: flexes PIP joints of medial four fingers.

   • Innervation: Median nerve.

2. Flexor digitorum profundus (FDP)

   • Function: flexes DIP joints.

   • Innervation: Dual

     • Lateral half (index & middle fingers) → Median nerve (anterior interosseous branch).

     • Medial half (ring & little fingers) → Ulnar nerve.

Thus, both median and ulnar nerves are required for complete innervation of the flexor digitorum muscles.

❌ Why the others are wrong

• Median nerve only → correct for FDS and part of FDP, but not entire FDP.

• Median and radial nerve → radial nerve supplies extensors, not flexors.

• Ulnar nerve only → supplies only medial half of FDP, not all.

• Radial nerve only → supplies extensors of wrist/fingers, not flexors.

• 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.

• The saphenous nerve is a purely sensory branch of the femoral nerve.

• It accompanies the great saphenous vein along the medial side of the leg and foot.

• Therefore, it provides sensation to the medial leg, ankle, and medial border of the foot up to the great toe.

• During varicose vein surgery (saphenous vein stripping/ligation), this nerve is at risk → sensory loss in its distribution.

❌ Why the others are wrong

• Common peroneal nerve → affects dorsum of foot & anterolateral leg, not medial border.

• Sural nerve → supplies lateral border of foot and little toe, not medial side.

• Tibial nerve → supplies sole of the foot, not medial border of dorsum.

• Superficial peroneal nerve → supplies most of dorsum of foot, except medial border (saphenous) and web space between 1st–2nd toes (deep peroneal).

• Collagen has a unique triple-helical structure.

• Its basic repeating unit is Gly–X–Y, where:

  • Glycine (the smallest amino acid) is at every third position.

  • X is often proline.

  • Y is often hydroxyproline or hydroxylysine.

• The tiny size of glycine allows the three chains to pack tightly into the stable collagen triple helix.

❌ Why the others are wrong

• Lysine → present in collagen, some residues hydroxylated to hydroxylysine (important for cross-linking), but not every third residue.

• Hydroxyproline → stabilizes collagen helix by hydrogen bonding, but not regularly every third position.

• Glutamate → not a major collagen amino acid in the repeating structure.

• Proline → common at every third/fourth position but not in the invariant every third slot like glycine.

• The ulnar nerve divides in the palm into:

  • Deep branch → motor supply (most intrinsic hand muscles).

  • Superficial branch → cutaneous supply.

• The superficial branch of the ulnar nerve supplies sensation to:

  • Medial one and a half digits (little finger + half of ring finger)

  • Corresponding part of the palm.

❌ Why the others are wrong

• Deep branch of ulnar nerve → purely motor; no cutaneous supply.

• Recurrent branch of median nerve → motor to thenar muscles (opponens pollicis, abductor pollicis brevis, flexor pollicis brevis).

• Palmar cutaneous branch of median nerve → supplies skin of thenar eminence and central palm, not digits.

• Radial nerve → dorsum of hand, lateral 3.5 digits (proximal parts), not medial palm.

• The ultimate goal of health promotion is sustained behavior change (e.g., quitting smoking, adopting healthy diet, exercising).

• Education, supportive environment, and resources can facilitate change, but unless individual behavior is modified, long-term improvement in health does not occur.

• Behavior is therefore considered the single most powerful factor influencing long-term health outcomes.

❌ Why the others are wrong

• Supportive environment → important facilitator (schools, workplaces, policies) but by itself cannot ensure long-term change if behaviors remain unchanged.

• Health education session → increases knowledge but does not always translate into sustained behavior change.

• Funding → provides resources but does not guarantee lifestyle modification.

• Publicity → raises awareness, but alone rarely produces lasting changes without personal behavior adaptation.

• Estrogen normally inhibits osteoclast activity and promotes bone formation balance.

• When estrogen is low (e.g., postmenopausal women), osteoclast activity increases unchecked → accelerated bone resorption → high turnover osteoporosis.

• This explains why postmenopausal osteoporosis is the classic type of high turnover osteoporosis.

❌ Why the others are wrong

• Low calcium and low vitamin D → causes osteomalacia/rickets (defective mineralization), not high turnover osteoporosis.

• Low progesterone → not significantly involved in bone turnover regulation.

• High progesterone → no direct link to osteoporosis.

• High estrogen → protective against bone loss (it suppresses osteoclasts).

• Osteoclasts are multinucleated, bone-dissolving cells derived from monocyte–macrophage lineage.

• Their main role: bone resorption → they secrete acids (to dissolve hydroxyapatite) and enzymes (to degrade collagen and matrix).

• This is the direct process by which bone is broken down, releasing calcium and phosphate into blood.

❌ Why the others are wrong

• Bone demineralization → refers specifically to loss of mineral content, not the complete breakdown of bone matrix (collagen + mineral) as done by osteoclasts.

• Bone remodeling → overall cycle of bone renewal, involving both osteoclasts (resorption) and osteoblasts (formation). Not just breaking.

• Bone mineralization → done by osteoblasts, where calcium and phosphate are deposited into osteoid.

• Bone modeling → shaping of bone during growth, involving both deposition and resorption, not simply breakdown.

• The common peroneal nerve branches into:

  • Deep peroneal nerve → supplies anterior compartment (dorsiflexion + toe extension).

  • Superficial peroneal nerve → supplies lateral compartment (peroneus longus & brevis → eversion).

• Injury →

  • Loss of dorsiflexion (→ foot drop).

  • Loss of eversion (because lateral compartment muscles are paralyzed).

• Plantarflexion and inversion are intact because they depend mainly on the tibial nerve.

❌ Why the others are wrong

• Inability to plantarflex the big toe → tibial nerve (flexor hallucis longus).

• Inability to plantarflex and invert the foot → tibial nerve (gastrocnemius, tibialis posterior).

• Inability to plantarflex the foot → tibial nerve (posterior compartment).

• Inability to invert the foot → mainly tibialis anterior (deep peroneal) and tibialis posterior (tibial nerve); complete inversion loss does not occur with common peroneal injury because tibialis posterior (tibial nerve) still works.

• The deep peroneal (fibular) nerve supplies the anterior compartment of the leg, whose main actions are dorsiflexion of the foot and extension of toes.

• Key muscles it supplies:

  • Tibialis anterior → dorsiflexion & inversion.

  • Extensor hallucis longus → big toe extension.

  • Extensor digitorum longus → toe extension.

  • Peroneus tertius → dorsiflexion & eversion.

So, among the given options, tibialis anterior is the correct choice.

❌ Why the others are wrong

• Peroneus longus & Peroneus brevis → both in the lateral compartment, supplied by the superficial peroneal nerve, not deep.

• Tibialis posterior → in the deep posterior compartment, supplied by the tibial nerve.

• Plantaris → small posterior leg muscle, also supplied by the tibial nerve.

• 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.

This description is classic for a Trendelenburg gait.

• When walking, to lift the left foot off the ground, the right leg becomes the stance limb.

• The right gluteus medius contracts to stabilize the pelvis and prevent it from dropping on the left side.

• If the right gluteus medius is weak (e.g., superior gluteal nerve injury):

  • The pelvis drops on the left

  • The patient compensates by leaning the trunk

  • A limp is seen

Thus, inability to lift the left foot properly points to dysfunction of the right gluteus medius.

❌ Incorrect Options Explained

❌ Left gluteus medius

• Left gluteus medius stabilizes the pelvis when the left leg is the stance limb

• The problem occurs when lifting the left foot, so left side is not the stabilizer

❌ Left gluteus maximus

• Main function: hip extension (e.g., climbing stairs, rising from sitting)

• Does not primarily stabilize the pelvis during single-leg stance

❌ Right gluteus minimus

• Assists gluteus medius, but gluteus medius is the primary stabilizer

• Exam answers typically target gluteus medius

❌ Right gluteus maximus

• Causes difficulty with hip extension

• Leads to a lurching gait, not Trendelenburg gait

• The pelvic girdle is formed by the two hip bones (ossa coxae).

• Each hip bone itself is made of three fused bones:

  1. Ilium

  2. Ischium

  3. Pubis

• These three meet at the acetabulum, where the femur articulates.

• The sacrum and coccyx belong to the axial skeleton, not the girdle itself.

❌ Why the others are wrong

• Ilium, sacrum and coccyx → sacrum & coccyx are not part of the pelvic girdle; they’re part of the vertebral column.

• Hip bone with femur → femur is part of the lower limb, not the girdle.

• Hip bone with sacrum and coccyx → describes the bony pelvis, not just the pelvic girdle.

• Ischium, sacrum and coccyx → again, sacrum & coccyx don’t belong to the girdle.

• The obturator nerve (L2–L4) is the main motor nerve of the medial compartment of the thigh.

• It supplies the adductor muscles (adductor longus, brevis, magnus – part; gracilis; obturator externus).

• Also gives cutaneous innervation to the medial thigh (variable area).

❌ Why the others are wrong

• Tibial nerve → posterior compartment of the leg & foot, not thigh.

• Sural nerve → sensory to posterior-lateral leg and lateral foot.

• Sciatic nerve → supplies posterior thigh (hamstrings) but not the medial thigh.

• Femoral nerve → anterior thigh (quadriceps, sartorius); sensory to anterior and medial leg, not medial thigh.

• Knee extension is performed by the quadriceps femoris (rectus femoris, vastus medialis/lateralis/intermedius).

• Quadriceps are innervated by the femoral nerve (L2–L4). Damage → weak/absent knee extension and reduced patellar reflex.

❌ Why the others are wrong

• Peroneal (common fibular) nerve: Dorsiflexion and eversion of foot; toe extension. Not knee extension.

• Sciatic nerve: Supplies hamstrings (knee flexors); lesion causes weak knee flexion, not extension.

• Tibial nerve: Plantarflexion, toe flexion; intrinsic foot muscles.

• Obturator nerve: Thigh adductors; no primary role in knee extension.

• The quadrangular space is an anatomical passageway at the posterior shoulder.

• Contents:

  • Axillary nerve

  • Posterior circumflex humeral artery and vein

• The axillary nerve (branch of posterior cord of brachial plexus) supplies:

  • Deltoid (arm abduction & extension)

  • Teres minor (lateral rotation)

  • Also gives sensation to the skin over the deltoid (“regimental badge area”).

❌ Why the others are wrong

• Dorsal scapular nerve → innervates rhomboids and levator scapulae, comes directly from C5 root.

• Thoracodorsal nerve → supplies latissimus dorsi, arises from posterior cord, but travels with thoracodorsal artery (not through quadrangular space).

• Long thoracic nerve → supplies serratus anterior, runs on chest wall, not through quadrangular space.

• Nerve to subclavius → from upper trunk, supplies subclavius muscle, located anteriorly, not posteriorly.

• The quadrangular space transmits the axillary nerve and posterior circumflex humeral artery.

• The axillary nerve supplies:

  • Deltoid → main abductor of the arm (beyond 15°) and assists in extension.

  • Teres minor → lateral rotation.

• Damage to the quadrangular space → axillary nerve injury → deltoid paralysis → loss of abduction and extension of the arm.

❌ Why the others are wrong

• Supraspinatus → initiates abduction (first 15°), supplied by suprascapular nerve, not affected here.

• Subscapularis → medial rotator, supplied by upper & lower subscapular nerves.

• Rhomboid major → retracts scapula, supplied by dorsal scapular nerve.

• Infraspinatus → lateral rotator, supplied by suprascapular nerve.

• Dementia (including Alzheimer’s disease) is strongly associated with aging.

• It results from progressive neurodegeneration and is specifically prevalent in the elderly, making it a classical age-related condition.

• Unlike other conditions listed, dementia is not just more severe in old age, it is characteristically common in older people.

❌ Why the others are wrong

• Reproductive health issues → More relevant in younger and middle-aged adults (fertility, pregnancy, STDs).

• Pneumonia → Can occur at any age, though more severe in elderly, but not specifically age-related.

• Tuberculosis → Common in immunocompromised or those with poor living conditions; not age-specific.

• Sexually transmitted diseases → More frequent in younger, sexually active populations.

✅ Correct Answer: Deltoid

• The posterior cord of the brachial plexus gives rise to the axillary nerve, which innervates the deltoid and teres minor.

• Injury to the posterior cord → loss of shoulder abduction beyond 15° (deltoid function).

• That makes deltoid the most directly affected muscle in this case.

❌ Why the Other Options Are Incorrect:

• Pectoralis major → Innervated by medial and lateral pectoral nerves (from medial and lateral cords), not the posterior cord.

• Subclavius → Supplied by the nerve to subclavius, a branch of the upper trunk of the brachial plexus.

• Rhomboid major → Innervated by the dorsal scapular nerve, which comes directly from the C5 root, not the posterior cord.

• Supraspinatus → Innervated by the suprascapular nerve, also from the upper trunk, not the posterior cord.

• The goal of health education is to promote knowledge, attitudes, and skills that lead to positive behavior change, not to enforce habit formation directly.

• “Creating habits” is an outcome of education, but it is not considered one of the core principles guiding health education strategies.

❌ Why the other options are correct principles:

• Learning by doing → Active participation ensures better understanding and retention.

• Change of behavior → The central aim of health education is long-term behavior change.

• Good relations → Effective communication between educator and community builds trust.

• Knowing customs → Health education must respect local culture and traditions for success.

• The saphenous nerve (terminal branch of femoral nerve) runs along the medial leg and foot, accompanying the great saphenous vein.

• It provides cutaneous sensation to the medial side of the leg and foot.

❌ Why others are wrong:

• Femoral nerve → stays in the thigh; doesn’t descend with the vein.

• Peroneal nerve → lateral leg; not medial.

• Tibial nerve → deep in posterior leg; runs with posterior tibial artery, not GSV.

• Sural nerve → runs with small saphenous vein, not great.

The femoral nerve arises from the posterior divisions of the ventral rami of L2, L3, and L4 spinal nerves. It supplies the anterior compartment of the thigh, including the quadriceps femoris, sartorius, and pectineus muscles, and provides sensory innervation to the anterior thigh and medial leg via the saphenous nerve.

Why the others are incorrect:

• L4, L5, S1, S2: These segments contribute to the sciatic nerve, not the femoral nerve.

• L2, L3: Insufficient alone; L4 is also required.

• L5, L6, L7: These segments do not exist in humans (L6–L7 are in some animals).

• L5, S1, S2: Form part of the sacral plexus, contributing to the sciatic nerve.

The posterior tibial artery primarily supplies the posterior compartment of the leg and the plantar surface of the foot. Its main branches include the medial plantar artery, lateral plantar artery, and the peroneal (fibular) artery. Additionally, small nutrient branches arise to supply the tibia.

The nutrient artery of the fibula, however, does not originate from the posterior tibial artery; it usually arises directly from the peroneal (fibular) artery or other nearby vessels.

Why the others are incorrect:

• Medial plantar artery: Terminal branch of posterior tibial artery.

• Lateral plantar artery: Terminal branch of posterior tibial artery.

• Peroneal artery: Branch of posterior tibial artery supplying lateral compartment and fibula.

• Nutrient artery of tibia: Small branch from posterior tibial artery to tibial shaft.

Myasthenia gravis is an autoimmune disorder caused by antibodies directed against postsynaptic acetylcholine receptors at the neuromuscular junction. This leads to impaired transmission of nerve impulses to skeletal muscle, resulting in fatigable muscle weakness, commonly affecting the ocular, facial, and proximal limb muscles.

Why the other options are incorrect:

• Caused by Clostridium botulinum: This refers to botulism, not myasthenia gravis.

• Antibodies against presynaptic calcium channels: Seen in Lambert-Eaton myasthenic syndrome, not MG.

• Antibodies against muscles: No; the autoimmune attack targets receptors, not the muscle itself.

• Release of acetylcholine is blocked: Also characteristic of botulism, not MG, where acetylcholine release is normal.

The structure not present in the axilla is the trunks of the brachial plexus.

The brachial plexus is organized into roots, trunks, divisions, cords, and branches:

• Roots and trunks are located in the posterior triangle of the neck.

• Divisions and cords pass into the axilla, along with the axillary artery, axillary vein, fat, and the tail of the breast (which can extend into the axilla).

Why the others are present:

• Tail of the breast: Commonly extends into the axilla.

• Axillary artery & vein: Main vascular structures running through the axilla.

• Fat: Fills the axillary space and provides cushioning.

The clinical scenario describes a child with multiple fractures at birth, bone fragility, and bending of long bones, which strongly suggests Osteogenesis imperfecta (OI). OI is a genetic disorder caused by defective type I collagen synthesis, leading to brittle bones that fracture easily, blue sclera, dentinogenesis imperfecta, and in some cases hearing loss. The bones are often deformed due to repeated fractures and improper collagen structure.

Why the other options are incorrect:

• Osteoporosis: Usually occurs later in life; it is characterized by decreased bone density but not congenital multiple fractures.

• Osteopetrosis: Causes abnormally dense bones due to defective osteoclast activity; bones are brittle but do not bend.

• Rickets: Caused by vitamin D deficiency; mainly affects children but leads to soft bones and deformities like bowing, not spontaneous fractures at birth.

• Osteomalacia: Adult equivalent of rickets; bones soften due to defective mineralization, not collagen defect, and does not typically present at birth.

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.

A claw hand is characterized by hyperextension of the metacarpophalangeal (MCP) joints and flexion of the interphalangeal (IP) joints. This deformity occurs due to ulnar nerve injury, which leads to paralysis of the lumbricals and interossei muscles that normally flex the MCP joints and extend the IP joints. As a result, the fingers assume a “clawed” appearance.

Why the others are incorrect:

• Loss of sensation at the thenar eminence: This occurs with median nerve injury, not specifically a claw hand.

• Pronation of the forearm: Involves muscles innervated by the median nerve; not a feature of claw hand.

• Flexion of the wrist joint: Wrist position is not defining for claw hand; it may vary depending on nerve involvement.

• Loss of supination: Caused by biceps brachii or supinator dysfunction, unrelated to claw hand.

The subscapularis is the prime mover of medial (internal) rotation of the arm. It arises from the subscapular fossa of the scapula and inserts on the lesser tubercle of the humerus. Its contraction rotates the humerus medially and also stabilizes the shoulder joint as part of the rotator cuff.

Why the others are incorrect:

• Infraspinatus: Performs lateral (external) rotation of the arm.

• Supraspinatus: Initiates abduction of the arm.

• Teres minor: Also contributes to lateral rotation of the arm.

• Teres major: Assists in adduction and medial rotation, but is not the prime mover for medial rotation.

The popliteal fossa is a diamond-shaped space at the back of the knee, and its boundaries are formed by specific muscles of the thigh and leg. The gastrocnemius muscle contributes significantly to the inferior (inferolateral and inferomedial) boundaries of the popliteal fossa. Its lateral and medial heads form the lower edges of the fossa, while the hamstring muscles form the superior boundaries.

Why the other options are incorrect:

• Obturator externus: Located in the hip region; does not participate in the popliteal fossa.

• Popliteus muscle: Lies deep within the fossa, forming part of the floor rather than the boundary.

• Quadratus femoris: Located in the gluteal region; not related to the fossa.

• Sartorius: Forms part of the adductor canal and contributes indirectly to the superior medial aspect of the thigh, but not the fossa boundary.

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.

The nerve most likely injured in this scenario is the median nerve.

The median nerve supplies the thenar muscles (abductor pollicis brevis, opponens pollicis, and superficial part of flexor pollicis brevis). When it is injured, especially at the wrist (as in carpal tunnel syndrome), the thenar eminence atrophies, leading to a “flat” appearance of the hand and the ape-hand deformity, characterized by inability to oppose or abduct the thumb. The patient can still extend the thumb because that function is controlled by the radial nerve, but the fine movements of opposition and lateral rotation are lost.

Why the other options are incorrect:

• Radial nerve: Injury causes wrist drop and inability to extend the wrist or fingers, but the thenar muscles remain intact.

• Anterior interosseous nerve: Branch of the median nerve; its injury causes weakness in flexion of the distal phalanges of the thumb and index finger (“pinch sign”) but does not cause ape-hand deformity.

• Ulnar nerve: Injury leads to claw hand due to intrinsic muscle paralysis, but the thenar muscles supplied by the median nerve are preserved.

• Axillary nerve: Supplies deltoid and teres minor; injury causes weakness in shoulder abduction and lateral rotation, unrelated to the hand deformity.

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.

The 1987 ACR (American College of Rheumatology) criteria for the diagnosis of rheumatoid arthritis include:

1. Morning stiffness (lasting at least 1 hour before maximal improvement).

2. Arthritis of three or more joint areas (simultaneous soft tissue swelling or fluid).

3. Arthritis of hand joints (at least one area in wrist, MCP, or PIP).

4. Symmetrical arthritis (not asymmetrical).

5. Rheumatoid nodules.

6. Serum rheumatoid factor.

7. Radiographic changes (hand/wrist erosions, juxta-articular osteopenia).

Diagnosis = 4 or more of the above criteria, with persistence for ≥6 weeks.

❌ Why Wrong Options Are Actually Included:

• Rheumatoid nodules → Part of criteria.

• Morning stiffness → Very classic feature, included.

• Serum rheumatoid factor → Included.

• Arthritis of three or more joint areas → Included.

• The Nernst equation calculates the equilibrium potential (diffusion potential) for a single ion across a semipermeable membrane, based on:

  • The concentration gradient of that ion (inside vs. outside).

  • The charge (valence, z) of the ion.

  • The temperature and the universal gas constant (R).

Formula:

Ex=RTzFln⁡([X]outside[X]inside)E_x = \frac{RT}{zF} \ln \left( \frac{[X]_{outside}}{[X]_{inside}} \right)Ex​=zFRT​ln([X]inside​[X]outside​​)

• This describes the electrical potential at which there is no net movement of that ion.

❌ Why the Other Options Are Incorrect:

• Facilitated diffusion → Transport process, not directly explained by Nernst.

• Counter transport (antiport) → Secondary active transport, not Nernst.

• Concentration of multiple ions → That’s described by the Goldman-Hodgkin-Katz equation, not Nernst.

• Co-transport (symport) → Also secondary active transport, not related to Nernst.

The base of the 2nd metacarpal cannot be palpated in the anatomical snuffbox.

The anatomical snuffbox is a triangular depression on the lateral aspect of the dorsum of the hand, visible when the thumb is extended. Its boundaries are formed by the tendons of the abductor pollicis longus and extensor pollicis brevis (laterally) and extensor pollicis longus (medially).

Palpable bony landmarks within the snuffbox:

• Scaphoid: forms the floor medially; commonly palpated and clinically tested for tenderness in scaphoid fractures.

• Trapezium: lies laterally, near the base of the thumb.

• Radial styloid process: forms the proximal boundary.

• Base of 1st metacarpal: can be palpated at the lateral border of the snuffbox.

The base of the 2nd metacarpal, however, is more medial and distal, outside the boundaries of the anatomical snuffbox, and cannot be felt in this depression.

The breast lymphatic drainage is crucial for understanding the spread of malignancies.

• Primary drainage:

  • About 75% of lymph from the breast drains into the axillary lymph nodes.

  • Within the axilla, the pectoral (anterior) group is the first to receive lymph from the upper outer quadrant of the breast, which is the most common site for breast tumors.

• Other nodes:

  • Subscapular nodes: drain the posterior thoracic wall and scapular region.

  • Deltopectoral nodes: along the cephalic vein, drain lateral upper limb.

  • Supraclavicular nodes: receive lymph from deeper structures, often involved in later stages of cancer.

  • Parasternal nodes: medial breast quadrants, near internal thoracic vessels.

Why pectoral nodes are correct:

• Tumors in the upper outer quadrant first drain into the pectoral nodes along the lateral thoracic vessels before reaching central or apical nodes.

Other options are incorrect because:

• Subscapular, supraclavicular, deltopectoral, and parasternal nodes are either secondary or drain different regions of the breast/limb/chest wall.

The flexor retinaculum (transverse carpal ligament) forms the roof of the carpal tunnel. Structures that pass deep to it (inside the carpal tunnel) include:

🔹 Tendons:

• 4 tendons of flexor digitorum superficialis (FDS)

• 4 tendons of flexor digitorum profundus (FDP)

• Tendon of flexor pollicis longus (FPL)

🔹 Nerve:

• Median nerve

🔹 Other:

• Tendon of flexor carpi radialis passes in a separate compartment within the retinaculum.

Why the other options are incorrect:

• Median artery: ❌ No such artery; likely a distractor.

• Ulnar artery: ❌ Passes superficial to the flexor retinaculum along with the ulnar nerve.

• Cutaneous branch of median nerve: ❌ The palmar cutaneous branch arises proximal to the flexor retinaculum and runs superficial, which is why sensation over the thenar eminence is preserved in carpal tunnel syndrome.

• Radial artery: ❌ Lies outside the carpal tunnel, lateral to the flexor carpi radialis tendon.

✅ Key fact: The contents of the carpal tunnel are remembered as:
“9 tendons + 1 nerve” → FDS (4) + FDP (4) + FPL (1) + median nerve.

Calcium absorption primarily occurs in the duodenum and jejunum, not the terminal ileum. It happens via two mechanisms:

1. Active, transcellular transport:

   • Regulated by calcitriol (active form of vitamin D₃)

   • Involves calcium-binding proteins like calbindin

   • Occurs mainly in the duodenum

2. Passive, paracellular transport:

   • Occurs throughout the small intestine

   • Driven by the electrochemical gradient

   • Less significant than active transport

Why the other options are incorrect:

• Is enhanced by phytate: Phytates (found in grains) inhibit calcium absorption by forming insoluble complexes.

• Occurs in the terminal ileum: Terminal ileum is primarily involved in vitamin B₁₂ and bile salt absorption, not calcium.

• Is independent of protein: Protein can slightly enhance calcium absorption; it is not independent.

• Is enhanced by parathyroid hormone directly: PTH indirectly increases calcium absorption by stimulating renal production of calcitriol, which then promotes intestinal absorption; it does not act directly on the gut.

Carpal tunnel syndrome (CTS) occurs when the median nerve is compressed as it passes through the carpal tunnel at the wrist. The carpal tunnel is a narrow passage formed by carpal bones and the flexor retinaculum.

Clinical features of median nerve compression in CTS include:

• Numbness, tingling, and pain in the thumb, index, middle, and lateral half of the ring finger

• Weakness of thenar muscles, leading to difficulty with thumb opposition

• Symptoms often worse at night or with repetitive wrist movements

Why the other options are incorrect:

• Ulnar nerve: Passes through the Guyon canal, not the carpal tunnel; affects the medial hand and little finger.

• Radial nerve: Supplies the dorsal hand and extensor muscles; not involved in CTS.

• Axillary nerve: Supplies the deltoid and teres minor; unrelated to wrist or hand sensory/motor function.

• Median and ulnar nerves together: Only the median nerve is affected in classic CTS; the ulnar nerve is spared.

The Sartorius muscle is a long, strap-like muscle that originates from the anterior superior iliac spine (ASIS) and inserts on the medial surface of the tibia. Its actions include:

• Flexion of the thigh at the hip

• Abduction of the thigh at the hip

• Lateral rotation of the thigh at the hip

• It also flexes the knee and medially rotates the leg when the knee is flexed.

Because the patient cannot flex, abduct, or laterally rotate the thigh, this indicates dysfunction of the Sartorius muscle.

Why the other options are incorrect:

• Gracilis: Primarily adducts the thigh and flexes the knee; does not laterally rotate.

• Obturator externus: Laterally rotates the thigh but does not flex or abduct.

• Adductor longus: Mainly adducts the thigh; does not flex or laterally rotate.

• Gluteus medius: Abducts and medially rotates the thigh; does not contribute to lateral rotation.

Collagen type I constitutes about 90% of the organic matrix of bone. It forms a strong fibrillar framework that provides tensile strength to the bone and acts as a scaffold for the deposition of hydroxyapatite crystals, which give the bone its hardness.

Why the other options are incorrect:

• Elastin: Present in elastic tissues like arteries and ligaments; negligible in bone.

• Collagen type II: Found mainly in cartilage, not bone.

• Collagen type III: Present in reticular fibers of soft tissues, skin, and blood vessels; minor in bone.

• Fibronectin: Glycoprotein involved in cell adhesion and matrix organization; present but not the major structural protein of bone.

Foot eversion is primarily controlled by the fibularis (peroneus) longus and brevis muscles, which are innervated by the superficial branch of the common peroneal nerve. Damage to the common peroneal nerve, particularly its superficial branch, leads to weakness or inability to evert the foot.

Other nerves in the options:

• Sural nerve: Sensory nerve; does not control motor function for eversion.

• Medial plantar nerve: Branch of the tibial nerve, supplies medial plantar muscles, involved in toe movements and sensation on the medial sole.

• Medial calcaneal nerve: Sensory branch of the tibial nerve, innervates skin of heel.

• Tibial nerve: Supplies posterior compartment of the leg (plantar flexors), inversion of the foot, and plantar muscles, not eversion.

The tibia, also known as the shin bone, is the larger and more medial of the two long bones in the leg. Its distal end expands medially to form the medial malleolus, which is a prominent bony projection felt on the inner aspect of the ankle. This structure is crucial for:

• Stabilizing the ankle joint by articulating with the talus.

• Serving as an attachment point for ligaments such as the deltoid ligament.

Other bones in the options:

• Talus: Forms the main ankle articulation but does not have a malleolus; it articulates with the tibia and fibula.

• Fibula: Forms the lateral malleolus, not medial.

• Navicular bone: Tarsal bone in the midfoot, no malleoli.

• Femur: Thigh bone, ends distally in the medial and lateral condyles, not involved in malleoli formation.

Collagen synthesis involves several key steps, one of which is the post-translational hydroxylation of specific proline and lysine residues in the procollagen molecule. This hydroxylation is crucial for:

• Stabilizing the triple helical structure of collagen via hydrogen bonding.

• Allowing glycosylation and proper extracellular secretion of collagen.

Ascorbate (Vitamin C) acts as a cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase, donating electrons to maintain the iron atom in the enzyme in its active reduced state. Without vitamin C, these hydroxylation reactions fail, leading to unstable collagen. This underlies scurvy, characterized by fragile blood vessels, bleeding gums, poor wound healing, and defective connective tissue.

❌ Why other options are incorrect:

• Cholecalciferol (Vitamin D3) / Calcitriol: Regulate calcium and phosphate homeostasis, unrelated to collagen hydroxylation.

• Folate: Cofactor in one-carbon metabolism and DNA synthesis.

• Retinol (Vitamin A): Involved in vision, epithelial maintenance, and growth.

The nipple serves as a reliable surface landmark for thoracic anatomy and procedures:

• Intercostal space: It usually lies at the level of the 4th intercostal space, though slight variations can occur depending on age, sex, and body habitus.

• Lateral position: Positioned lateral to the mid-clavicular line, roughly at the apex of the breast in females.

• Clinical relevance: This position helps in identifying underlying structures such as the heart (especially the apex of the left ventricle) and guides breast examinations, thoracentesis, and chest tube placement.

❌ Why other options are incorrect:

• 3rd intercostal space or 2nd intercostal space: Too high; corresponds to upper thoracic structures rather than the breast.

• 3rd intercostal space lateral to mid-clavicular line: Higher than typical nipple level.

• 6th intercostal space: Too low; closer to the lower border of the breast.

• The acromioclavicular (AC) joint is stabilized by:

  1. Acromioclavicular ligament → holds the clavicle to the acromion.

  2. Coracoclavicular ligament (trapezoid + conoid parts) → provides strong support between coracoid process and clavicle.

• In a shoulder separation due to a fall or blow to the shoulder (especially with clavicle fracture near the acromion):

  • First, the acromioclavicular ligament is torn.

  • If severe, the coracoclavicular ligament also ruptures → clavicle becomes displaced upwards (“step deformity”).

❌ Why Other Options Are Incorrect:

• Coracoclavicular ligament (alone) → Damaged in more severe cases, but classic separation involves both AC and CC ligaments.

• Costoclavicular ligament → Stabilizes clavicle to 1st rib; not involved in AC separation.

• Sternoclavicular ligament → Stabilizes medial clavicle to sternum; unrelated to lateral end fracture/separation.

• Glenohumeral coracoid ligament → (Coracohumeral ligament) stabilizes humeral head; not part of AC joint injury.

• ATP is required for the detachment of the myosin head from actin and provides energy for the power stroke during muscle contraction.

• Calcium ions (Ca²⁺) bind to troponin C, which shifts tropomyosin away from the actin-binding sites, allowing myosin heads to attach.

• Together, ATP (for cycling and energy) and Ca²⁺ (for exposing sites) make strong and instantaneous binding of myosin to actin possible.

❌ Why the Other Options Are Incorrect:

• Magnesium ions only → Needed only as a cofactor for ATPase activity, not sufficient for binding.

• Calcium ions only → Exposes binding sites but without ATP, myosin cannot detach/re-cock properly for cycling.

• ATP and magnesium ions → Drives energy release but without calcium, the actin sites stay blocked.

• ATP only → Energy is available, but without calcium, the actin-binding sites remain covered.

Chondroitin sulfate is a type of glycosaminoglycan (GAG), which are long, unbranched polysaccharides composed of repeating disaccharide units.

• Each disaccharide unit of chondroitin sulfate consists of:

  • N-acetylgalactosamine (GalNAc) – an amino sugar

  • Glucuronic acid (GlcA) – a uronic acid

• These units are often sulfated at various positions, giving chondroitin sulfate its negative charge and contributing to the resilience of cartilage and connective tissues.

• Functions:

  • Provides structural support in cartilage

  • Contributes to resistance against compression

  • Plays a role in extracellular matrix organization

❌ Why other options are wrong:

• Glucuronic acid + iduronic acid: This is found in dermatan sulfate and heparin, not chondroitin sulfate.

• N-acetylglucosamine + iduronic acid or glucuronic acid: These combinations are characteristic of heparan sulfate or keratan sulfate, not chondroitin sulfate.

• N-acetylgalactosamine + iduronic acid: This is seen in dermatan sulfate, not chondroitin sulfate.

Vitamin D exists in several forms, and understanding their sources and activity is key:

• Cholecalciferol (Vitamin D3):

  • Made in the skin when 7-dehydrocholesterol is exposed to UVB rays from sunlight.

  • Also found in dietary sources such as fatty fish, egg yolk, and liver.

  • Inactive in this form; it requires hydroxylation in the liver (to 25-hydroxyvitamin D) and then in the kidney (to 1,25-dihydroxyvitamin D, calcitriol) to become active.

• Ergocalciferol (Vitamin D2):

  • Derived from plants and fungi; can be consumed in diet or supplements.

  • Less potent than cholecalciferol in raising serum 25(OH)D levels.

• Calcitriol (1,25-dihydroxyvitamin D):

  • The active hormonal form of vitamin D.

  • Not made in skin or consumed directly; produced in the kidney from calcidiol.

• Calciferol:

  • General term sometimes used for vitamin D compounds, not specific to the form made in skin.

• Cholesterol:

  • Precursor for vitamin D synthesis but not itself vitamin D.

❌ Why other options are wrong:

• Calcitriol: Active form, not made directly in skin or diet.

• Ergocalciferol: Plant/fungal source only; skin does not produce it.

• Calciferol: Non-specific term; does not indicate the physiologically relevant form.

• Cholesterol: Precursor molecule, not the vitamin form.

The axillary lymph nodes are divided into several groups based on their anatomical position:

1. Pectoral (anterior) nodes → along the lateral thoracic vessels, drain most of the anterior thoracic wall and breast.

2. Subscapular (posterior) nodes → along the subscapular vessels, drain the posterior thoracic wall and scapular region.

3. Lateral (humeral) nodes → along the lateral thoracic vessels, drain the upper limb.

4. Central nodes → located centrally in the axilla, embedded in adipose tissue. These nodes receive lymph from the pectoral, subscapular, and lateral groups.

5. Apical nodes → at the apex of the axilla, receive lymph from central nodes and some directly from the breast.

So, the central nodes act as a collecting station for the pectoral, lateral, and subscapular nodes before lymph is directed toward the apical nodes.

❌ Why the other options are wrong:

• Subscapular nodes only → incomplete; central nodes receive from multiple groups, not just subscapular.

• Lateral axillary nodes only → again incomplete; they also receive from pectoral and subscapular nodes.

• Apical nodes only → apical nodes receive from central nodes, not the other way around.

• Pectoral nodes only → same issue; central nodes are a hub for multiple groups.

Parathyroid hormone (PTH) is secreted by the chief cells of the parathyroid gland in response to low plasma calcium levels.
Its main effect is to increase plasma calcium concentration by:

1. Bone → stimulates osteoclast activity indirectly (via osteoblast signaling), increasing bone resorption and calcium release.

2. Kidneys → increases Ca²⁺ reabsorption in the distal tubule, while decreasing phosphate reabsorption (phosphaturia).

3. Intestine → indirectly increases Ca²⁺ absorption by stimulating calcitriol (active vitamin D) synthesis in kidneys.

Thus, overall: ↑ Calcium, ↓ Phosphate.

❌ Why the other options are wrong:

• Sodium → regulated mainly by aldosterone and kidney tubular mechanisms, not PTH.

• Phosphate → PTH actually lowers plasma phosphate by increasing its urinary excretion.

• Potassium → regulated by aldosterone and renal handling, no major role for PTH.

• Magnesium → PTH has a small effect to increase Mg²⁺ reabsorption, but the major and most tested mineral increased is calcium.

• Calcitonin is a hormone secreted by the parafollicular cells (C cells) of the thyroid gland.

• Its main function is to lower blood calcium levels when they are too high.

• It does this by:

  1. Inhibiting osteoclast activity → reduces bone resorption.

  2. Promoting calcium deposition in bone.

  3. Increasing urinary calcium excretion.

Thus, calcitonin acts as a calcium-lowering hormone, opposing the effects of parathyroid hormone (PTH).

❌ Why the other options are wrong:

• Increases plasma calcium concentration → This is the role of PTH and calcitriol (active vitamin D), not calcitonin.

• Increases plasma calcitriol concentration → PTH stimulates calcitriol synthesis in kidneys; calcitonin does not.

• Decreases plasma magnesium concentration → Calcitonin doesn’t affect magnesium directly; magnesium homeostasis is largely regulated by kidneys.

• Increases plasma potassium concentration → Not related to calcitonin at all; potassium is regulated by renal handling and aldosterone.

• The bicipital groove (also called the intertubercular sulcus of the humerus) is a deep groove between the greater tubercle (lateral) and the lesser tubercle (medial).

• The tendon of the long head of the biceps brachii runs inside this groove, enclosed by a synovial sheath, before it enters the shoulder joint capsule and attaches to the supraglenoid tubercle of the scapula.

• The short head of biceps brachii originates from the coracoid process, so it never enters the bicipital groove.

• Triceps brachii (long or short head) → both insert into the olecranon, not the groove.

• Deltoid → inserts into the deltoid tuberosity of humerus, not the groove.

❌ Why the other options are wrong:

• Short head of triceps brachii → No such muscle; triceps has long, medial, and lateral heads, not short.

• Long head of triceps brachii → Passes posterior to humerus, not in the groove.

• Deltoid → Inserts laterally, not related to groove.

• Short head of biceps brachii → Originates at coracoid, no relation to groove.

• A comminuted fracture is when the bone breaks into multiple fragments or is splintered.

• This usually occurs after high-energy trauma (e.g., road traffic accidents, gunshot injuries).

• Because of the splintering, it can be difficult to treat and often requires surgical fixation (plates, rods, or external fixation).

❌ Why the other options are wrong:

• An open fracture → This means the bone communicates with the outside through the skin, also called a compound fracture. Not the same as comminuted.

• A fracture with unaligned bones → That is called a displaced fracture.

• A closed fracture → The opposite of open fracture (skin intact). Not necessarily splintered.

• A simple fracture → Usually refers to a clean break into two parts, without fragmentation.

Glycine is the most abundant amino acid in collagen, making up about one-third of its amino acid content. In the triple-helix structure of collagen, every third residue is glycine. This regular spacing is essential because glycine is the smallest amino acid, with a single hydrogen atom as its side chain. Its small size allows the three collagen alpha chains to pack tightly together in the triple helix without steric hindrance.

This triple-helix is stabilized by interchain hydrogen bonds, and the repeating sequence is typically Gly-X-Y, where X and Y are often proline and hydroxyproline, respectively.

Why the other options are incorrect:

• Histidine ❌
  Not particularly abundant in collagen and does not significantly contribute to the triple-helix structure.

• Proline ❌
  While proline and hydroxyproline are important for collagen stability and give rigidity to the helix, they are not the most abundant amino acids. Proline is often found in the X or Y positions of the Gly-X-Y repeat.

• Arginine ❌
  Not a major component of collagen and plays no significant structural role in the helix.

• Lysine ❌
  Lysine and its hydroxylated form hydroxylysine are involved in cross-linking collagen fibrils, which strengthens the matrix, but they are not the most abundant and are not central to the triple helix formation.

The flexor digitorum longus (FDL) is a deep muscle of the posterior compartment of the leg. It functions to flex the lateral four digits and assists in plantar flexion of the ankle. This muscle is innervated by the tibial nerve, a branch of the sciatic nerve, which supplies all the muscles of the posterior compartment of the leg (both superficial and deep groups).

Why the other options are incorrect:

• Deep peroneal nerve ❌
  This nerve supplies muscles in the anterior compartment of the leg, such as tibialis anterior, extensor hallucis longus, and extensor digitorum longus, not the posterior compartment.

• Superficial peroneal nerve ❌
  Supplies the lateral compartment muscles like fibularis longus and brevis, not the deep posterior compartment.

• Common peroneal nerve ❌
  This is a branch of the sciatic nerve, but it splits into the deep and superficial peroneal nerves, neither of which supply the FDL.

• Sciatic nerve ❌
  Although the tibial nerve arises from the sciatic nerve, the sciatic nerve itself does not directly innervate the FDL.

The suprascapular nerve arises from the upper trunk of the brachial plexus (C5–C6) and innervates two key muscles of the rotator cuff:

• Supraspinatus

• Infraspinatus

The infraspinatus muscle is responsible for lateral rotation of the arm and stabilization of the shoulder joint.

Why the other options are incorrect:

• Teres minor ❌
  This muscle is innervated by the axillary nerve, not the suprascapular nerve.

• Pectoralis major ❌
  Innervated by the medial and lateral pectoral nerves, depending on the region (clavicular or sternocostal head).

• Pectoralis minor ❌
  Also innervated by the medial pectoral nerve.

• Teres major ❌
  Supplied by the lower subscapular nerve, not the suprascapular nerve.

The common peroneal nerve (also called the common fibular nerve) is the most commonly injured nerve in the lower limb due to its superficial location around the neck of the fibula, where it is prone to trauma or compression.

Why it is the most commonly injured:

• It winds laterally around the fibular neck, where it is subcutaneous and vulnerable.

• Common causes of injury include:

  • Fibular fractures

  • Tight casts or splints

  • Prolonged leg crossing or squatting

• Damage to this nerve leads to:

  • Foot drop (inability to dorsiflex)

  • Loss of eversion of the foot

  • Sensory loss over the dorsum of the foot

Why the other options are incorrect:

• Femoral nerve ❌
  Injury is less common. It lies deep in the inguinal region and is protected. Injuries usually occur due to pelvic trauma or surgical complications.

• Saphenous nerve ❌
  This is a purely sensory branch of the femoral nerve. While it can be injured during varicose vein surgeries or knee procedures, it’s not the most commonly affected nerve.

• Obturator nerve ❌
  This nerve supplies the medial thigh muscles. Injuries are rare and typically occur during pelvic surgery or childbirth, not trauma to the limb.

• Tibial nerve ❌
  It is deep and well protected in the popliteal fossa and leg, making it less likely to be injured compared to the superficial course of the common peroneal nerve.

The teres minor is one of the four rotator cuff muscles (alongside supraspinatus, infraspinatus, and subscapularis), and it plays a role in lateral rotation of the arm and stabilizing the humeral head in the glenoid cavity.

• It originates from the lateral border of the scapula and inserts onto the greater tubercle of the humerus.

• Its sole motor innervation is from the axillary nerve, which arises from the posterior cord of the brachial plexus (C5–C6 roots).

• The axillary nerve passes through the quadrangular space along with the posterior circumflex humeral artery and gives motor branches to deltoid and teres minor.

Let’s examine why the other options are incorrect:

• Suprascapular nerve ❌
  Supplies supraspinatus and infraspinatus, but not teres minor.

• Spinal part of accessory nerve ❌
  This nerve (cranial nerve XI) innervates sternocleidomastoid and trapezius, not shoulder girdle muscles like teres minor.

• Pectoral nerve ❌
  These include medial and lateral pectoral nerves, which supply pectoralis major and minor, not teres minor.

• Subscapular nerve ❌
  The upper and lower subscapular nerves supply subscapularis (both) and teres major (lower only), not teres minor.

Parathyroid hormone (PTH) plays a central role in calcium homeostasis. It is secreted in response to low serum calcium levels and acts on multiple organs to raise calcium levels in the blood — but directly on only bones and kidneys.

Here’s how it works:

• Bone:
  PTH stimulates osteoclast activity indirectly via osteoblasts, increasing bone resorption. This releases calcium and phosphate into the bloodstream.

• Kidneys:
  PTH:

  • Increases calcium reabsorption in the distal tubules, preventing its excretion.

  • Decreases phosphate reabsorption in the proximal tubules, helping prevent calcium-phosphate precipitation in blood.

  • Stimulates production of active vitamin D (calcitriol) via 1-alpha-hydroxylase, which acts on the intestine indirectly.

Let’s rule out the other options:

• Kidney ❌
  It is one of the correct sites, but not the only one. Bone is equally important.

• Bone ❌
  Also only partially correct. PTH acts directly on both bone and kidney.

• Intestine ❌
  PTH does not act directly on the intestine. The intestinal effect (increased calcium absorption) is indirectly mediated by calcitriol (activated vitamin D), which is synthesized in the kidney under PTH stimulation.

• Skeletal muscle ❌
  PTH has no direct action on skeletal muscle related to calcium homeostasis.

The pectoralis major is a large, fan-shaped muscle of the anterior chest wall and serves as a powerful adductor and medial rotator of the arm at the shoulder joint. It has two heads — the clavicular and sternocostal — both inserting into the lateral lip of the intertubercular sulcus of the humerus.

• Adduction: It pulls the arm toward the body’s midline.

• Medial rotation: It rotates the arm inward, especially when combined with the action of other medial rotators like subscapularis.

Let’s now evaluate the incorrect options:

• Teres major ❌
  While it does medially rotate and adduct the arm, it is less powerful than pectoralis major and is considered a helper muscle in these movements.

• Pectoralis minor ❌
  This muscle acts on the scapula, not the arm. It helps stabilize and draw the scapula anteriorly and inferiorly.

• Subscapularis ❌
  This is a rotator cuff muscle that medially rotates the arm, but adduction is not its primary action. It also helps hold the humeral head in the glenoid cavity.

• Teres minor ❌
  This is a lateral rotator of the arm and a part of the rotator cuff. It performs the opposite function of medial rotation.

The median nerve supplies most of the flexor muscles in the forearm (except flexor carpi ulnaris and half of flexor digitorum profundus) and some thenar muscles in the hand.

• Flexor carpi radialis is a superficial flexor muscle of the forearm and is innervated by the median nerve. Injury to the median nerve impairs wrist flexion on the radial side and reduces grip strength due to involvement of other forearm flexors and thenar muscles.

Now let’s analyze the incorrect options:

• Triceps brachii ❌
  This is a posterior arm muscle innervated by the radial nerve, not the median nerve.

• Biceps brachii ❌
  Innervated by the musculocutaneous nerve, this muscle is involved in forearm flexion and supination.

• Supinator ❌
  Although it is a forearm muscle, it is innervated by the deep branch of the radial nerve.

• Brachialis ❌
  Mainly innervated by the musculocutaneous nerve, with a small lateral portion occasionally supplied by the radial nerve—not the median nerve.

The sarcolemma is the thin, specialized cell membrane that surrounds each skeletal muscle fiber. It plays a crucial role in the initiation and conduction of action potentials, as well as in maintaining the integrity of the muscle cell. The sarcolemma is located just beneath the endomysium and surrounds the sarcoplasm (cytoplasm of muscle cell), enclosing the myofibrils within.

Let’s break down each option:

• Sarcolemma ✅
  This is the correct answer. It is the plasma membrane of a muscle fiber and is essential for electrical signal conduction and muscle fiber integrity.

• Actin ❌
  Actin is a thin filament protein involved in muscle contraction. It is found within the myofibrils but does not enclose the muscle fiber.

• Myofibril ❌
  These are bundles of contractile proteins (actin and myosin) inside the muscle fiber. Each muscle fiber contains many myofibrils — they are internal components, not membranes.

• Sarcomere ❌
  The sarcomere is the structural and functional unit of contraction, composed of actin and myosin arranged in a repeating pattern within myofibrils. It is inside the myofibril, not a covering membrane.

• Myosin ❌
  Myosin is the thick filament protein involved in contraction and found inside the sarcomere. Like actin, it is a contractile protein, not a membrane.

The deltoid muscle, a thick, triangular muscle covering the shoulder, is the primary abductor of the arm from 15° to 90°. Its innervation is a high-yield anatomical point, especially in clinical scenarios involving shoulder trauma.

Here’s the breakdown:

• Axillary nerve ✅
  This is the correct answer. The axillary nerve arises from the posterior cord of the brachial plexus (C5–C6). It passes through the quadrangular space and innervates the deltoid and teres minor muscles. It also provides sensation over the lateral shoulder (regimental badge area). Damage to this nerve (e.g., surgical neck fracture of the humerus or incorrect intramuscular injection) can lead to deltoid atrophy and loss of arm abduction.

Now let’s go through the incorrect options:

• Accessory nerve ❌
  The spinal accessory nerve (CN XI) innervates the sternocleidomastoid and trapezius, not the deltoid.

• Dorsal scapular nerve ❌
  This nerve innervates the rhomboids and levator scapulae, not the deltoid.

• Thoracodorsal nerve ❌
  This innervates the latissimus dorsi, not the deltoid.

• Subscapular nerve ❌
  Both upper and lower subscapular nerves innervate the subscapularis, and the lower also supplies the teres major—but not the deltoid.

The cubital fossa is a triangular depression located on the anterior aspect of the elbow. Its boundaries are well-defined and are important for understanding the anatomical layout of structures like the brachial artery and median nerve.

Let’s examine each option:

• Base ⟶ Imaginary line between two condyles ✅
  This is correct. The superior boundary (base) of the cubital fossa is indeed formed by an imaginary line connecting the medial and lateral epicondyles of the humerus.

• Medially ⟶ Palmaris longus ❌
  This is incorrect. The medial boundary of the cubital fossa is formed by the lateral border of pronator teres, not palmaris longus. Palmaris longus lies more superficially and distally in the forearm and does not contribute to the boundary of the cubital fossa.

• Floor ⟶ Brachialis and supinator ✅
  This is correct. The floor is indeed formed by the brachialis muscle medially and the supinator laterally.

• Apex ⟶ Meeting point of lateral and medial boundaries ✅
  This is correct. The apex is located inferiorly where the brachioradialis (lateral) and pronator teres (medial) converge.

• Laterally ⟶ Brachioradialis ✅
  This is correct. The lateral boundary of the cubital fossa is formed by the medial border of the brachioradialis muscle.

📘 Aα fibers are the fastest-conducting nerve fibers in the human body.

They are:

• Heavily myelinated

• Largest in diameter

• Responsible for motor innervation of skeletal muscle (extrafusal fibers)

• Crucial for proprioception from muscle spindles and Golgi tendon organs

Their speed is essential for immediate motor responses and reflexes like the knee-jerk reflex or postural adjustments.

❌ Why the Other Options Are Incorrect:

• Aβ fibers: Conduct pressure and touch—fast but slower than Aα.

• Aγ fibers: Supply muscle spindle intrafusal fibers—important for tone, but slower.

• AΔ fibers: Carry fast pain and cold sensations—smaller diameter and slower.

• C fibers: Unmyelinated and slowest—carry dull pain, warmth, and postganglionic autonomic signals.

The triceps brachii is a three-headed muscle of the posterior arm responsible primarily for extension of the forearm at the elbow joint. It has three heads:

• Long head originates from the infraglenoid tubercle of the scapula

• Lateral head originates from the posterior surface of the humerus, superior to the radial groove

• Medial head originates from the posterior surface of the humerus, inferior to the radial groove

• All three converge to insert via a common tendon into the olecranon process of the ulna

✅ Why Clavicle is the Correct Answer:

• The clavicle is not involved in the origin or insertion of any head of the triceps brachii.

• It serves as an attachment site for other muscles like pectoralis major, deltoid, trapezius, and sternocleidomastoid, but not triceps.

❌ Why the Other Options Are Incorrect:

• Scapula:
  ✅ The long head of triceps originates from the infraglenoid tubercle of the scapula.

• Humerus:
  ✅ The lateral and medial heads originate from the posterior humerus.

• Ulna:
  ✅ The insertion site of the triceps brachii is the olecranon process of the ulna.

• None of these:
  ❌ This would imply that all listed bones are involved with triceps brachii, which is false due to the clavicle.

This patient’s presentation — progressive bone pain, hearing loss, orthopnea, pedal edema, bony sclerosis on radiograph, and elevated serum alkaline phosphatase (ALP) — is highly suggestive of Paget’s disease of bone, also called osteitis deformans.

✅ Why Paget’s Disease is Correct:

Paget’s disease is a chronic disorder of abnormal bone remodeling:

• Initially, there’s excessive osteoclastic bone resorption

• Followed by disorganized osteoblastic bone formation, producing structurally weak and sclerotic bone

• Most common in elderly men

• Bone pain, skull involvement (→ hearing loss due to nerve compression), and long bone deformities are common

• Alkaline phosphatase is elevated due to increased osteoblastic activity

• Heart failure (orthopnea, pedal edema) can occur in advanced disease due to high-output cardiac failure from increased vascularity of bone

❌ Why the Other Options Are Incorrect:

• Vitamin D deficiency:
  ❌ Causes osteomalacia/rickets, presents with hypocalcemia, low phosphate, and looser zones on X-rays. Does not cause sclerosis or hearing loss, and ALP may be mildly elevated, but not to this extent with bony sclerosis.

• Renal osteodystrophy:
  ❌ Seen in chronic renal failure, with secondary hyperparathyroidism. Affects the whole skeleton uniformly, not focal sclerosis. Labs typically show elevated phosphate, low calcium, and very high PTH, which is not described here.

• Metastatic adenocarcinoma:
  ❌ Can cause focal sclerosis (esp. prostate cancer), but usually not with such symmetrical sclerosis in characteristic locations (sacroiliac, vertebrae, tibia). ALP may be raised, but hearing loss and deformity are not typical.

• Osteoporosis:
  ❌ Causes bone thinning, not sclerosis. It is usually silent until fracture, and ALP is normal. There is no bone pain unless a fracture occurs.

Deficiency of vitamin D leads to a condition known as rickets in children and osteomalacia in adults. Both involve impaired mineralization of bone matrix, resulting in soft bones.

Why Vitamin D is the Correct Answer:

• Vitamin D plays a critical role in calcium and phosphate homeostasis. It enhances calcium and phosphate absorption from the gut, both of which are essential for the proper mineralization of osteoid (the unmineralized, organic portion of the bone matrix).

• When vitamin D is deficient, there is insufficient calcium and phosphate, leading to poor mineralization, causing bones to become soft and pliable.

• In children, this manifests as rickets with bowing of legs, delayed closure of fontanelles, and other skeletal deformities.

• In adults, it presents as osteomalacia, with bone pain and increased risk of fractures.

Why the Other Options Are Incorrect:

• Vitamin E:
  While important as an antioxidant, vitamin E deficiency primarily affects neuromuscular function, not bone mineralization.

• Vitamin A:
  Plays a role in bone remodeling and growth, but its deficiency or excess affects bone turnover, not mineralization directly.

• Vitamin C:
  Necessary for collagen synthesis, which forms the organic matrix of bone. Its deficiency causes scurvy, leading to defective collagen formation and weakened connective tissue—not specifically soft bones from mineral deficiency.

• Vitamin B (non-specific):
  Refers to a group of vitamins (B1, B2, B3, etc.), none of which are directly involved in the mineralization of bone. Deficiencies cause neurological and hematological disorders, not soft bones.

The infraspinatus muscle is a posterior scapular muscle and one of the four rotator cuff muscles. Its primary function is lateral (external) rotation of the arm at the shoulder joint.

✅ Infraspinatus – Correct

• Origin: Infraspinous fossa of the scapula

• Insertion: Greater tubercle of the humerus

• Innervation: Suprascapular nerve (C5–C6)

• Action: Powerful lateral rotator of the shoulder; stabilizes the shoulder joint as part of the rotator cuff

• Clinical Note: Injury to the suprascapular nerve may weaken lateral rotation.

❌ Subscapularis

• Inserts on the lesser tubercle of the humerus

• Medial rotator of the arm

• Part of the rotator cuff, but functions opposite to infraspinatus

❌ Teres minor

• Also a lateral rotator, but less powerful than infraspinatus

• Also inserts on the greater tubercle

• Works synergistically with infraspinatus

• Innervated by the axillary nerve

❌ Teres major

• Not a rotator cuff muscle

• Inserts on the medial lip of the intertubercular sulcus of humerus

• Medial rotator and adductor of the arm

• Innervated by lower subscapular nerve

❌ Supraspinatus

• Initiates abduction of the arm (first 15°)

• Does not contribute to rotation

• Innervated by the suprascapular nerve