Medical Science 2025 Paper I 50 marks Compulsory Describe

Q1

(a) Describe the formation, course and branches of ulnar nerve. Which muscles do each of the branches supply ? Why is ulnar nerve called the "musician's nerve" ? 10 marks (b) Name the nerves and their branches that supply the sole of the foot stating the specific area of their distribution. Explain in brief what is Morton's metatarsalgia. 10 marks (c) Classify jaundice according to its aetiology. Make a tabular representation of the blood, urinary and stool findings observed in different types of jaundice. 10 marks (d) Describe the process of generation and conduction of nerve impulses in humans. Add a note on saltatory conduction. 7+3=10 marks (e) With the help of a suitable diagram, explain the innervation and functions of muscle spindle. 10 marks

हिंदी में प्रश्न पढ़ें

(a) अंतःप्रकोष्ठिका तंत्रिका के निर्माण, मार्ग और शाखाओं का वर्णन कीजिए। प्रत्येक शाखा कौन-कौन सी पेशियों का संभरण करती है ? अंतःप्रकोष्ठिका तंत्रिका को "संगीतज्ञ की तंत्रिका" क्यों कहते हैं ? 10 अंक (b) उन तंत्रिकाओं तथा उनकी शाखाओं के नाम बताइए जो पैरों के तलवे का संभरण करती हैं। प्रत्येक तंत्रिका किस विशिष्ट भाग में वितरित रहती है, यह स्पष्ट रूप से उल्लेखित कीजिए। मॉर्टन प्रपदिकाति की संक्षेप में व्याख्या कीजिए। 10 अंक (c) हेतुकी के अनुसार कामला को वर्गीकृत कीजिए। विभिन्न प्रकार के कामला में रक्त, मूत्र तथा मल में पाई जाने वाली विशेषताओं को तालिकाबद्ध रूप में प्रस्तुत कीजिए। 10 अंक (d) मनुष्यों में तंत्रिका आवेगों की उत्पत्ति तथा चालन की प्रक्रिया का वर्णन कीजिए। साथ ही, प्रवल्गीय चालन पर एक टिप्पणी लिखिए। 7+3=10 अंक (e) उपयुक्त आरेख की सहायता से पेशीय तर्कु के तंत्रिकाप्रेरण तथा कार्यों को समझाइए। 10 अंक

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Directive word: Describe

This question asks you to describe. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'describe' demands comprehensive, structured exposition of anatomical structures, physiological processes and pathological classifications. Allocate approximately 2 minutes per mark: spend ~20% on (a) ulnar nerve anatomy, ~20% on (b) plantar innervation with Morton's metatarsalgia, ~20% on (c) jaundice classification with table, ~20% on (d) nerve impulse conduction with saltatory note, and ~20% on (e) muscle spindle with diagram. Begin each sub-part with a brief anatomical/physiological context, present the core content systematically, and conclude with clinical relevance where applicable.

Key points expected

  • (a) Ulnar nerve: origin from medial cord (C8-T1), course through axilla, arm, cubital tunnel (Guyon's canal at wrist), branches in forearm (muscular, palmar cutaneous, dorsal cutaneous) and hand (superficial and deep terminal), muscle supply (flexor carpi ulnaris, medial FDP, intrinsic hand muscles), and 'musician's nerve' explanation (fine motor control of fingers for instruments like guitar, piano)
  • (b) Plantar innervation: medial plantar nerve (calcaneal, plantar digital branches—medial 3½ toes, lumbricals, abductor hallucis, flexor digitorum brevis, flexor hallucis brevis) and lateral plantar nerve (calcaneal, muscular, plantar digital branches—lateral 1½ toes, quadratus plantae, abductor digiti minimi, adductor hallucis, interossei); Morton's metatarsalgia as interdigital neuroma between 3rd-4th metatarsal heads
  • (c) Jaundice classification: pre-hepatic (hemolytic), hepatic (hepatocellular), post-hepatic (obstructive/cholestatic); table with bilirubin (unconjugated vs conjugated), urine bilirubin (absent vs present), urobilinogen (increased vs decreased/absent), stool color (normal/pale vs acholic)
  • (d) Nerve impulse: resting membrane potential (-70mV, Na+/K+ pump), depolarization (Na+ influx), repolarization (K+ efflux), hyperpolarization, refractory period; saltatory conduction—myelin sheath, nodes of Ranvier, jumping of action potentials, faster conduction with energy efficiency
  • (e) Muscle spindle: structure (intrafusal fibers—nuclear bag and chain, sensory Ia and II endings, gamma motor neurons), diagram showing fusiform shape, innervation (afferent: Ia to spinal cord, II; efferent: gamma motor neurons), functions (length monitoring, stretch reflex, proprioception, alpha-gamma co-activation)

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Demonstrates precise anatomical knowledge: for (a) correctly identifies C8-T1 roots and all five branches with exact muscle innervation; for (b) accurately maps dermatomal distribution of medial vs lateral plantar nerves; for (c) correctly classifies jaundice types with accurate biochemical markers; for (d) explains ionic basis of each phase with correct numerical values; for (e) distinguishes nuclear bag vs chain fibers with their specific responsesCovers major structures correctly but with minor errors: vague on some branch distributions, confuses medial/lateral plantar territories, or presents jaundice table with one or two incorrect parameters; describes nerve impulse generally without specific ion movementsSignificant factual errors: wrong root values for ulnar nerve, reversed plantar nerve distributions, fundamental misunderstanding of conjugated vs unconjugated bilirubin, or describes muscle spindle as Golgi tendon organ equivalent
Clinical correlation20%10Integrates relevant clinical applications throughout: for (a) explains ulnar claw hand, cubital tunnel syndrome, and precise relevance to Indian classical musicians (sitar, tabla players); for (b) correlates plantar nerve entrapment with diabetic neuropathy patterns in Indian population; for (c) links hemolytic jaundice to G6PD deficiency/thalassemia common in India; for (d) relates demyelinating diseases (GBS, MS); for (e) connects to spasticity and clinical reflex testingMentions common clinical conditions superficially: notes 'ulnar nerve injury' or 'jaundice in hepatitis' without specific Indian context or mechanistic explanation; includes Morton's metatarsalgia definition without epidemiological relevanceLacks clinical correlation entirely or presents irrelevant associations; fails to explain 'musician's nerve' significance; describes jaundice types without any disease examples
Diagram / pathway20%10Produces clear, labeled diagrams for (a) ulnar nerve course with branches, (b) plantar nerve distribution map, (c) well-structured table for jaundice (not a diagram but organized visual), (d) action potential graph with ion channel states, and especially (e) detailed muscle spindle cross-section showing intrafusal fibers, sensory endings, and motor innervation; all diagrams anatomically accurate with proper directional orientationIncludes basic diagrams with some labels; muscle spindle diagram shows general structure but misses gamma motor neuron innervation or confuses afferent/efferent pathways; jaundice table present but poorly formattedDiagrams absent, poorly drawn, or fundamentally incorrect; muscle spindle diagram omitted despite explicit instruction; table for jaundice missing or presented as prose only
Differential / staging20%10Systematically differentiates alternatives: for (a) distinguishes ulnar from median nerve lesions (ape hand vs claw hand); for (b) differentiates Morton's neuroma from stress fracture, plantar fasciitis; for (c) presents clear staging of jaundice progression with discriminating laboratory features; for (d) contrasts continuous vs saltatory conduction with quantitative differences; for (e) distinguishes dynamic vs static nuclear bag fiber responsesMakes some differential points but inconsistently: notes ulnar vs median comparison without functional implications, or describes jaundice types separately without emphasizing distinguishing featuresNo differential approach; fails to distinguish similar conditions; presents information as isolated facts without comparative framework
Management / public-health angle20%10Addresses management where relevant: for (a) mentions surgical decompression for cubital tunnel syndrome; for (b) describes conservative vs surgical management of Morton's neuroma, orthotic interventions; for (c) outlines public health strategies for neonatal jaundice screening (kernicterus prevention), hepatitis B vaccination under India's UIP; for (d) notes implications for nerve conduction studies; for (e) references spasticity management with baclofen, physiotherapy protocolsBriefly mentions treatment options without detail: 'surgery for nerve compression' or 'phototherapy for jaundice' without indication criteria; public health relevance superficialCompletely omits management aspects; no public health perspective despite jaundice being amenable to population-level intervention; answer remains purely descriptive without applied clinical endpoint

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