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sarcomere skeletal muscle labeled diagram Z line I band A band

This composite educational graphic illustrates the microanatomy of a skeletal muscle sarcomere. The top section shows a high-magnification optical coherence tomography image of a myofibril, displaying a repeating pattern of light and dark bands. Below, an enlarged diagnostic microscopy view identifies key structural landmarks: the Z lines (dark vertical boundaries), the light I band, the dark central A band, and the M line bisecting the center. The bottom schematic diagram maps these histological features to their molecular components. It specifically highlights the positioning of Titin, a large structural protein that spans from the Z line to the M line. The diagram emphasizes Titin’s functional duality: within the I band, it appears as a coiled 'molecular spring' capable of elongation, whereas within the A band, it is closely associated with myosin filaments, providing structural stability. This visual serves to teach the mechanical properties of sarcomere components during muscle contraction and passive stretch in the context of human physiology and biomechanics.

Atmospheric scanning electron microscopy (ASEM) of mouse gastrocnemius skeletal muscle stained with phosphotungstic acid (PTA). Panels A and B provide low and high magnification views of striated muscle fibers, highlighting bright, filamentous networks distributed across the fiber surfaces. Panel C displays the ultrastructure of a single muscle fiber, demonstrating the sarcomere architecture. Broad bright zones represent the A-bands (white arrows), while dark zones represent the I-bands (black arrows). The Z-lines are visible as faint, thin white lines positioned centrally within the dark I-bands (black arrowheads). Brightly stained structures on the periphery indicate muscle nuclei (white arrowheads). An inset diagram illustrates the sarcomere model, labeling the A-band, I-band, and Z-line for structural correlation. These images illustrate the utility of ASEM in observing wet tissue samples at high resolution, maintaining anatomical relationships without typical dehydration artifacts.

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carpal tunnel anatomy cross section median nerve

This diagnostic grayscale ultrasound image displays a transverse cross-section of the right volar wrist, specifically detailing the carpal tunnel anatomy for preoperative planning. The median nerve (MN) is identified within a yellow outline, presenting with a characteristic honeycomb-like appearance and hypoechoic echogenicity relative to the surrounding fascia. Superior to the carpal tunnel contents, the transverse carpal ligament (TCL) is labeled, appearing as a heterogeneous, hyperechoic band. Medial to the TCL and median nerve (on the right side of the image), the ulnar artery (UA) is visible as an anechoic circular structure, adjacent to the ulnar nerve (UN). The image demonstrates the spatial relationships between these neurovascular structures, which is critical for establishing a 'safe zone' during minimally invasive procedures like thread carpal tunnel release (TCTR). Key anatomical landmarks including the flexor tendons and bony boundaries are visible in the background with varying echogenicity.

Diagnostic ultrasound image of the left wrist in a transverse cross-section, demonstrating the carpal tunnel anatomy for the evaluation of carpal tunnel syndrome. The median nerve (MN) is identified as a superficial hypoechoic, honeycomb-textured structure superior to the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) muscle tendons. To the lateral aspect, the ulnar artery (UA) is visible as an anechoic circular structure. A caliper-based measurement tool outlines the circumference of the median nerve, showing a cross-sectional area (CSA) of 0.11 cm² and a circumference of 1.51 cm. This imaging modality is used clinically to assess for median nerve enlargement, a hallmark of entrapment neuropathy. The anatomical relationship between the nerve and the underlying flexor tendons is clearly labeled, providing context for diagnostic assessment or ultrasound-guided regional anesthesia such as a nerve block.

All questions from all 9 papers have been comprehensively answered above. Here is a quick navigation guide:

Quick Navigation Guide

Paper	Key Topic Areas Covered
Aug 2024 (Short)	Intrinsic hand muscles, Axilla, Adductor magnus, MLA foot, Shoulder abduction, Popliteal fossa, Uric acid/Gout, Cori cycle, Osteomyelitis pathogenesis, Osteosarcoma morphology, Pott's spine, RA clinical features, Ibuprofen, DMARDs, Sarcomere diagram
Aug 2024 (Clinical)	Carpal tunnel syndrome (median nerve C6-T1, LOAF muscles), Gluteal injection nerve injury (sciatic/peroneal), E-C coupling, NMJ transmission, Myasthenia gravis, Fatigue
Feb 2025 (Short)	Cubital fossa, Brachial plexus diagram, Knee ligaments (8), Adductor compartment, Ankle movements, Axillary artery branches, ATP sources, PTH/Calcitriol, Leprosy, Fracture types/healing, Pyogenic osteomyelitis, Gout, Aspirin, Allopurinol, Isometric vs isotonic
Feb 2025 (Clinical)	Eversion of foot, Carpal tunnel (formation + contents), E-C coupling (detailed), Excitation-contraction
March 2023 (Short)	MLA, Erb's point, Shoulder abduction, Clavicle peculiarities, Popliteal fossa, Deltoid, Creatine phosphate, Calcitriol, Leprosy causative agent, Fracture healing, DMD, Osteomyelitis types, Aspirin, Lepromatous leprosy WHO treatment, End plate potential
March 2023 (Clinical)	Ankle lateral ligament (ATFL, CFL, PTFL), Ankle movements, Carpal tunnel/Ape hand, NMJ transmission, Muscle fiber types, Nerve injury classification, Strength-duration curve
Internal 2024 (Short)	Axilla, Popliteal fossa, Lower limb bones, Plantar aponeurosis, Median nerve, Shoulder ligaments, Creatine phosphate, Cori cycle, Osteomyelitis, Pathology (osteomyelitis, Pott's, RA, osteoclastoma), Allopurinol, Leprosy drugs, Isotonic vs isometric
Internal 2024 (Clinical)	Brachial plexus injury/Ulnar nerve, Inguinal triangle, Myasthenia gravis, E-C coupling + NMJ, ATP/Ca²⁺ role, Muscle fiber types
Other exam (anatomy)	Lymphatic drainage of breast, 1st CMC joint, Radial nerve formation, Osteomyelitis pathogens, Calcium homeostasis hormones, Knee joint (OA case), Supracondylar humerus/Volkmann's, Brachial artery branches

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These are the same 9 images as your previous question - all questions have already been fully answered above. However, I notice image 9 contains a May/June 2022 paper (Paper-I: Basic concepts, genetics, integumentary and autonomic nervous system) which has some different topics not covered yet. Let me answer those now.

KATHMANDU UNIVERSITY - May/June 2022

Paper I: Basic Concepts, Genetics, Integumentary & Autonomic Nervous System

Section B - Short Answer Questions

ANATOMY

1. Well-Labelled Diagram of Thin Skin

Thin skin (covers most of the body except palms and soles) has 4 layers (unlike thick skin which has 5):

SURFACE
─────────────────────────────────
Stratum corneum     (dead, keratinized cells)
─────────────────────────────────
Stratum granulosum  (keratohyalin granules)
─────────────────────────────────
Stratum spinosum    (prickle cells, desmosomes)
─────────────────────────────────
Stratum basale      (stem cells, melanocytes)
─────────────────────────────────
DERMIS (papillary → reticular)
─────────────────────────────────
Subcutaneous tissue (hypodermis)

Thin skin characteristics vs thick skin:

Feature	Thin Skin	Thick Skin
Layers	4 (no stratum lucidum)	5 (includes stratum lucidum)
Hair follicles	Present	Absent
Sebaceous glands	Present	Absent
Sweat glands	Few	Many
Location	Most of body	Palms, soles, fingertips

BIOCHEMISTRY

2. Define and Classify Lipids [1+2=3]

Definition: Lipids are heterogeneous group of naturally occurring organic compounds that are soluble in non-polar (organic) solvents (chloroform, ether) but insoluble in water. They contain C, H, O (and sometimes N, P, S).

Classification:

A. Simple lipids (esters of fatty acids + alcohol):

Fats (triglycerides/triacylglycerols): Glycerol + 3 fatty acids
Waxes: Long-chain alcohol + fatty acid

B. Compound (complex) lipids (simple lipid + additional group):

Phospholipids: Glycerophospholipids (lecithin, cephalin, plasmalogen) + Sphingomyelin
Glycolipids (cerebrosides, gangliosides): Lipid + carbohydrate
Lipoproteins: Lipid + protein (chylomicrons, VLDL, LDL, HDL)

C. Derived lipids (hydrolysis products):

Fatty acids (saturated, unsaturated)
Sterols (cholesterol, bile acids, steroid hormones, vitamin D)
Fat-soluble vitamins (A, D, E, K)
Ketone bodies

3. Prokaryotic Replication with Diagram [3]

Prokaryotic DNA Replication (e.g., E. coli):

Key features:

Circular, double-stranded DNA
Single origin of replication: oriC (origin of replication chromosome)
Bidirectional (two replication forks move in opposite directions)
Semiconservative (each new molecule has one old + one new strand)

Steps:

Initiation: DnaA protein binds oriC → DNA helicase (DnaB) unwinds the double helix → single-strand binding (SSB) proteins stabilize
Primer synthesis: Primase (DnaG) synthesizes short RNA primers
Elongation:
- DNA Pol III (main enzyme): 5'→3' synthesis; 3'→5' exonuclease (proofreading)
- Leading strand: continuous synthesis
- Lagging strand: Okazaki fragments (discontinuous)
Removal of primers: DNA Pol I (5'→3' exonuclease) removes RNA primers, fills gaps
Joining: DNA ligase seals nicks between Okazaki fragments

oriC
 ↓
→→→→→→→→ (leading)
←←←←←←←← (lagging, Okazaki fragments)

MICROBIOLOGY

4. Differentiating Characters Between Bacteria and Viruses [3]

Feature	Bacteria	Viruses
Size	0.2-10 μm	20-300 nm (smaller)
Cell type	Prokaryotic	Acellular (not true cells)
Genetic material	DNA AND RNA (both)	DNA OR RNA (not both)
Cell wall	Present (peptidoglycan)	Absent (protein coat = capsid)
Ribosomes	Present (70S)	Absent
Replication	Binary fission (independent)	Only inside host cell
Metabolism	Independent (have own enzymes)	Obligate intracellular parasite
Response to antibiotics	Susceptible	Not susceptible
Response to antivirals	Not susceptible	Susceptible
Examples	S. aureus, E. coli	HIV, Influenza, SARS-CoV-2

5. Causative Agent of Leprosy and Classification [1+2]

Causative agent: Mycobacterium leprae

Acid-fast bacillus (AFB)
Obligate intracellular parasite (Schwann cells and macrophages)
Cannot be cultured in vitro (grown in armadillo footpad)
Slow growing (doubling time ~12-13 days)
Optimal temperature: 27-30°C (peripheral nerves - cooler areas)

Classification: (See previous detailed answer - Ridley-Jopling: TT, BT, BB, BL, LL; WHO: PB vs MB)

PATHOLOGY

6. Difference Between Apoptosis and Necrosis [2]

Feature	Apoptosis	Necrosis
Mechanism	Programmed cell death (active, energy-dependent)	Uncontrolled cell death (passive)
Cause	Physiological or pathological signals	Pathological (ischemia, toxins, trauma)
ATP required	Yes	No
Cell size	Shrinks (condensation)	Swells (oncosis)
Nucleus	Karyorrhexis → apoptotic bodies	Karyolysis, pyknosis, karyorrhexis
Membrane	Intact (blebbing)	Disrupted (contents leak)
Inflammation	No (anti-inflammatory; phagocytosed cleanly)	Yes (DAMPs released → inflammation)
Morphology	Apoptotic bodies (phagocytosed by macrophages)	Cell ghosts, calcification, abscess
Examples	Embryogenesis, thymic selection, CD8+ T cell killing	MI, infarction, gangrene
Caspases	Activated (caspase cascade)	Not activated

7. Types of Cell Adaptations with Examples [2]

Cell adaptations = reversible changes in cell size, number, phenotype, or function in response to stress.

Adaptation	Definition	Example
Hypertrophy	↑ cell size (not number)	Cardiac hypertrophy in hypertension; skeletal muscle in exercise
Hyperplasia	↑ cell number	Endometrial hyperplasia (estrogen); liver regeneration after resection
Atrophy	↓ cell size/number	Disuse atrophy (limb in cast); denervation atrophy; starvation
Metaplasia	Change from one differentiated cell type to another	Squamous metaplasia of bronchial epithelium in smokers; Barrett's esophagus (squamous → columnar)
Dysplasia	Abnormal cell growth (pre-neoplastic)	Cervical dysplasia (CIN); not a true adaptation but related

8. Difference Between Acute and Chronic Inflammation [2]

Feature	Acute Inflammation	Chronic Inflammation
Onset	Rapid (minutes-hours)	Slow (weeks-months-years)
Duration	Short (days)	Long (weeks to years)
Primary cells	Neutrophils	Macrophages, lymphocytes, plasma cells
Exudate	Serous, fibrinous, purulent	Less prominent; more fibrosis
Vascular changes	Prominent (vasodilation, increased permeability)	Less prominent
Tissue destruction	Variable	More prominent (granuloma formation)
Fibrosis	Absent/minimal	Prominent
Examples	Lobar pneumonia, appendicitis, abscess	TB, RA, Crohn's, silicosis
Outcome	Resolution, organization, abscess, chronicity	Healing by fibrosis, amyloidosis
Granuloma	Absent	May be present (TB, sarcoidosis)

PHARMACOLOGY

9. Plasma Half-Life; Zero Order and First Order Kinetics [2+2]

Plasma Half-life (t½):

Time taken for plasma concentration of a drug to fall by 50%
Formula: t½ = 0.693 / Ke (Ke = elimination rate constant)
Also: t½ = (0.693 × Vd) / CL (Vd = volume of distribution, CL = clearance)
Clinical importance:
- Determines dosing frequency
- After 4-5 half-lives: steady state achieved
- After 4-5 half-lives: drug essentially eliminated (97%)

First-Order Kinetics:

Rate of elimination is proportional to plasma drug concentration
A constant fraction of the drug is eliminated per unit time
t½ is constant (independent of dose)
Most drugs follow this (therapeutic doses)
Graph: exponential decline in plasma concentration vs time
Example: paracetamol, most antibiotics

Zero-Order Kinetics:

Rate of elimination is constant regardless of plasma concentration (saturation kinetics)
A constant amount eliminated per unit time
t½ is NOT constant (increases with dose)
Enzymes saturated - small dose increase → disproportionate rise in levels (toxic!)
Examples: Alcohol (ethanol), Phenytoin (at high doses), Aspirin (high doses)

10. Cholinergic Drugs - Uses and Adverse Effects [2+1+1]

Cholinergic drugs = drugs that mimic or enhance acetylcholine (ACh) activity

Classification:

Direct: Bind muscarinic/nicotinic receptors
- Muscarinic agonists: Pilocarpine, Bethanechol, Carbachol
- Nicotinic agonists: Nicotine (not therapeutic)
Indirect (AChE inhibitors): Inhibit acetylcholinesterase → ↑ ACh
- Reversible: Neostigmine, Pyridostigmine, Physostigmine, Donepezil
- Irreversible: Organophosphates (nerve agents, insecticides)

Uses:

Glaucoma (Pilocarpine - constricts pupil, opens trabecular meshwork)
Myasthenia gravis (Neostigmine, Pyridostigmine - increase NMJ ACh)
Atony of GI/bladder after surgery (Bethanechol)
Alzheimer's disease (Donepezil, Rivastigmine, Galantamine)
Reversal of non-depolarizing NMJ blockers (Neostigmine)
Glaucoma, xerostomia (Pilocarpine)

Adverse Effects (SLUDGE = muscarinic excess):

S - Salivation (excessive)
L - Lacrimation
U - Urination (incontinence)
D - Defecation/Diarrhea
G - GI cramps
E - Emesis (vomiting)
Also: Bradycardia, bronchoconstriction, miosis, sweating

PHYSIOLOGY

11. Four Differences Between Parasympathetic and Sympathetic Nervous System [2]

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar (T1-L2/L3)	Craniosacral (III, VII, IX, X; S2-S4)
Preganglionic fiber	Short	Long
Postganglionic fiber	Long	Short
Ganglion location	Paravertebral chain / prevertebral	In/near the target organ (terminal ganglia)
NT at postganglionic	Noradrenaline (adrenergic)	Acetylcholine (cholinergic)
NT at preganglionic	ACh (nicotinic)	ACh (nicotinic)
Heart rate	↑ (tachycardia)	↓ (bradycardia)
Pupils	Dilated (mydriasis)	Constricted (miosis)
Bronchi	Dilated	Constricted
GI motility	↓	↑
Urinary bladder	Relaxation (urinary retention)	Contraction (micturition)
Adrenal medulla	Innervated (releases adrenaline)	Not innervated
Function overall	"Fight or flight"	"Rest and digest"

CLINICAL BASED QUESTIONS (from last exam in image 9)

Clinical Anatomy - Mrs. Shrestha (Knee Osteoarthritis)

a. Articulating bones of knee joint:

Distal end of femur (medial + lateral condyles)
Proximal end of tibia (medial + lateral condyles)
Patella (with femur - patellofemoral joint)

b. Extracapsular and Intracapsular Ligaments:

Extracapsular:

Patellar ligament (ligamentum patellae)
Medial (tibial) collateral ligament
Lateral (fibular) collateral ligament
Oblique popliteal ligament
Arcuate popliteal ligament

Intracapsular (within capsule, covered by synovium):

Anterior cruciate ligament (ACL) - prevents anterior tibial glide
Posterior cruciate ligament (PCL) - prevents posterior tibial glide

c. Muscles producing movements:

Flexion: Biceps femoris, semitendinosus, semimembranosus, gastrocnemius, popliteus, gracilis, sartorius
Extension: Quadriceps femoris (rectus femoris, vastus medialis, lateralis, intermedius)

Clinical - Raju Shah (Supracondylar Fracture + Volkmann's)

a. Muscular attachments of supracondylar ridges of humerus:

Medial supracondylar ridge:

Medial head of triceps
Coracobrachialis (distal)

Lateral supracondylar ridge:

Brachioradialis
Extensor carpi radialis longus (ECRL)
Lateral head of triceps

b. Volkmann's Ischaemic Contracture:

Caused by compartment syndrome following supracondylar fracture of humerus in children
Brachial artery kinking/injury → ischaemia of anterior forearm compartment
Ischaemia → fibrosis of flexor muscles (FDS, FDP, FPL)
Classic posture: Forearm pronated, wrist flexed, fingers flexed at IP joints (characteristic contracture deformity)
Treatment: Emergency fasciotomy (if acute); late: Z-plasty, tendon lengthening

c. Branches of brachial artery:

Profunda brachii (deep brachial artery)
Superior ulnar collateral artery
Inferior ulnar collateral artery
Nutrient artery to humerus
Radial artery (terminal branch at cubital fossa)
Ulnar artery (terminal branch at cubital fossa)

Clinical Physiology - Myasthenia Gravis (Rani Maiya)

a. What is Myasthenia Gravis? Autoimmune disease caused by antibodies against nicotinic acetylcholine receptors (nAChR) at the neuromuscular junction.

Antibodies block/destroy nAChR → reduced end plate potential → fatigable muscle weakness
Hallmarks: Fluctuating, fatigable weakness (worse with activity, better with rest); bilateral ptosis and diplopia (ocular muscles first)
Associated with thymic hyperplasia or thymoma
Diagnosis: Anti-AChR antibodies, Tensilon (edrophonium) test, repetitive nerve stimulation (decremental response)
Treatment: Pyridostigmine (AChE inhibitor), immunosuppression (steroids, azathioprine), thymectomy, plasma exchange/IVIG in crisis

b. Neuromuscular Transmission + E-C Coupling: (Full answers given above in previous response)

Clinical Physiology - Asthma Patient (ATP/Ca²⁺ and Type I vs Type II Muscle Fibers)

a. Role of ATP and Ca²⁺ in skeletal muscle contraction: (Full answer given above)

b. Type I vs Type II Muscle Fibers:

Feature	Type I (Slow, Red)	Type II (Fast, White)
Speed	Slow twitch	Fast twitch
Color	Red	White/pale
Myoglobin	High	Low
Mitochondria	Many	Few
Metabolism	Aerobic/oxidative	Anaerobic/glycolytic
Fatigue resistance	High (fatigue-resistant)	Low (fatigues quickly)
Force	Low	High
Glycogen content	Low	High
Capillary density	High	Low
ATPase isoform	Slow myosin ATPase	Fast myosin ATPase
Best for	Endurance, posture	Sprinting, power
Examples	Soleus, postural back muscles	Extraocular muscles, gastrocnemius

Type IIa = intermediate (fast oxidative); Type IIx/IIb = fast glycolytic

Newborn Brachial Plexus Injury (Klumpke's/Erb's)

Scenario: Traction on neck during vaginal delivery.

Name of palsy: Erb's palsy (upper brachial plexus injury - C5, C6)

Mechanism: Widening of angle between head and shoulder (forcible lateral neck flexion away from shoulder)
Nerves affected at Erb's point: C5, C6 (upper trunk of brachial plexus)
Position ("Waiter's tip"):
- Shoulder: adducted, internally rotated
- Elbow: extended
- Forearm: pronated
- Wrist: flexed
Muscles paralyzed: Deltoid, supraspinatus, infraspinatus, teres minor, biceps, brachioradialis, supinator

(If lower trunk C8,T1 = Klumpke's palsy → claw hand, intrinsic wasting ± Horner's syndrome)

QUICK REFERENCE SUMMARY

All questions across all 9 papers now fully answered. The most frequently recurring topics across all papers are:

Topic	Appeared in
Carpal tunnel syndrome / Median nerve	Aug 2024, Feb 2025, March 2023, Internal 2024
E-C coupling	Aug 2024, Feb 2025, Internal 2024
NMJ transmission	Aug 2024, March 2023, Internal 2024
Osteomyelitis	Aug 2024, Feb 2025, Internal 2024
Pott's spine/disease	Aug 2024, Internal 2024
Allopurinol mechanism	Feb 2025, Internal 2024
Red vs white muscle fibres	Aug 2024, March 2023, Internal 2024
Knee joint ligaments	Feb 2025, March 2023, Internal 2024
ATP + Ca²⁺ in muscle	Feb 2025, Internal 2024
Creatine phosphate	March 2023, Internal 2024

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