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DEPARTMENT OF PHYSIOLOGY - PREFINAL PAPER II ANSWERS

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I. ESSAY QUESTION (10 Marks)

Q1. Case: 58-year-old male - unsteadiness walking, slurred speech, difficulty with fine tasks, unable to perform finger-nose test, intention tremors.

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(a) Structure of Brain Involved (1M)

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(b) Anatomical and Physiological Parts with Functional Divisions (1M)

• Superior peduncle (brachium conjunctivum) - mainly efferent
• Middle peduncle (brachium pontis) - afferent from pons
• Inferior peduncle (restiform body) - afferent from spinal cord and vestibular

1. Granular layer - granule cells, Golgi II cells, mossy fiber synapses
2. Purkinje cell layer - output cells (always inhibitory)
3. Molecular layer - parallel fibers, basket cells, stellate cells

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(c) Functions of the Cerebellum (2M)

1. Coordination of movement - controls rate, range, force, and direction (collectively: synergy)
2. Planning and execution of voluntary movement (pontocerebellum)
3. Maintenance of posture and equilibrium (vestibulocerebellum)
4. Coordination of head and eye movements
5. Motor learning - adaptation and error correction
6. Regulation of muscle tone - prevents hypotonia
7. Integrates sensory information from spinal cord, motor commands from cortex, and vestibular information

The cerebellum acts as a comparator - it compares intended movement (efference copy from cortex) with actual movement (proprioceptive feedback) and corrects errors. - Costanzo Physiology 7th Ed.

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(d) Afferent and Efferent Connections (2M)

• Output arises from deep cerebellar nuclei (Purkinje cells are inhibitory on these nuclei)
• Dentate nucleus → via superior peduncle → contralateral thalamus (VL nucleus) → motor cortex (controls fine skilled movement)
• Interposed nuclei (globose + emboliform) → red nucleus → rubrospinal tract + thalamus
• Fastigial nucleus → vestibular nuclei and reticular formation (controls balance)

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(e) Physiological Basis of Intention Tremor and Ataxia (2M)

• Occurs during voluntary (goal-directed) movement, increasing in amplitude as the limb approaches its target
• Due to loss of error-correction mechanism of the pontocerebellum
• The cerebellum normally dampens oscillations using proprioceptive feedback; without this, the limb overshoots and then corrects, creating rhythmic oscillations perpendicular to the direction of movement
• Differs from resting tremors of Parkinson's disease (which occur at rest and diminish with movement)
• In cerebellar disease, the dentate nucleus fails to modulate motor cortex output via the thalamus, causing uncontrolled tremor

• Cerebellar ataxia = lack of coordination due to errors in rate, range, force, and direction of movement
• Manifestations:
  • Dysmetria - overshooting (past-pointing) or undershooting of target (positive finger-nose test)
  • Dysdiadochokinesia - inability to perform rapid alternating movements
  • Rebound phenomenon - inability to stop a movement when resistance is suddenly removed
  • Gait ataxia - broad-based, staggering, "drunken" gait
  • Dysarthria - slurred, scanning, explosive speech (cerebellar dysarthria)
• Mechanism: Loss of synergy - the smooth sequencing and timing of agonist/antagonist muscle activation is lost due to failure of the cerebellum to compare intended vs. actual movement

Costanzo Physiology 7th Ed., p.114

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(f) Other Clinical Tests Done for This Patient (2M)

1. Gait assessment - broad-based ataxic gait; Romberg test (negative = cerebellar ataxia; positive = sensory ataxia)
2. Tandem walking - walking heel-to-toe in a straight line
3. Finger-nose test - already mentioned; also heel-shin test for lower limb coordination
4. Dysdiadochokinesia test - rapid alternating movements (pronation/supination)
5. Rebound test (Stewart-Holmes sign)
6. Pendular knee reflex - hypotonia causes pendular (swinging) knee jerks
7. Nystagmus assessment - cerebellar nystagmus (direction-changing)
8. MRI brain/cerebellum - to identify structural lesion (infarct, tumor, degeneration)
9. CT scan brain - if acute hemorrhage suspected
10. Neurological examination - assess cranial nerves, speech (dysarthria), eye movements
11. Blood tests - alcohol levels, thyroid function, vitamin B12, paraneoplastic antibodies
12. Assessment of speech - cerebellar dysarthria (slurred, scanning speech)

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II. SHORT ANSWER QUESTIONS (5 Marks each)

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Q2. Brown-Séquard Syndrome (5M)

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Q3. Autonomic Function Tests (5M)

1. Heart Rate Response to Valsalva Maneuver (Valsalva ratio)
   • Patient blows into manometer to 40 mmHg for 15 seconds
   • Normal: reflex bradycardia after release (ratio >1.21)
   • Abnormal: loss of reflex bradycardia = parasympathetic dysfunction
2. Heart Rate Response to Deep Breathing (R-R variation)
   • 6 deep breaths per minute; measure R-R interval variation on ECG
   • Normal variation: >15 beats/min (E:I ratio >1.2)
   • Reduced = early parasympathetic failure
3. Heart Rate Response to Standing (30:15 ratio)
   • Maximum HR at beat 15 after standing: minimum HR at beat 30
   • Normal ratio >1.04
   • Tests baroreceptor reflex - parasympathetic component

1. Blood Pressure Response to Standing (Postural Hypotension)
   • Fall in systolic BP >20 mmHg or diastolic >10 mmHg on standing = sympathetic failure
2. Blood Pressure Response to Sustained Handgrip
   • 30% maximum voluntary contraction for 5 minutes
   • Normal: diastolic BP rise >16 mmHg
   • Blunted = sympathetic dysfunction
3. Cold Pressor Test
   • Hand immersed in ice water for 1 minute
   • Normal: BP rises 20/15 mmHg due to sympathetic activation

1. Thermoregulatory Sweat Test - assess distribution of sweating
2. Sympathetic Skin Response (SSR) - galvanic skin response
3. Quantitative Sudomotor Axon Reflex Test (QSART)

• Cocaine test (tests sympathetic integrity)
• Methacholine test (tests parasympathetic supersensitivity)
• Pharmacologic Tests of Autonomic Function - Adams and Victor's Neurology, 12th Ed.

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Q4. Regulation of Food Intake by Hypothalamus (5M)

• Located in the lateral hypothalamic area (LHA)
• Stimulation → eating (hyperphagia)
• Destruction → anorexia, starvation
• Neurons contain orexin (hypocretin) and Melanin-concentrating hormone (MCH) - orexigenic

• Located in the ventromedial nucleus (VMN) of hypothalamus
• Stimulation → cessation of eating
• Lesion → hyperphagia and obesity (VMH syndrome)
• Normally inhibits the feeding center

• Arcuate nucleus - key integrating center; contains:
  • NPY/AgRP neurons (orexigenic - stimulate feeding)
  • POMC/CART neurons (anorexigenic - inhibit feeding)
• Paraventricular nucleus - responds to CRH, TRH; anorexigenic
• Dorsomedial nucleus - role in feeding rhythmicity

Guyton & Hall, Textbook of Medical Physiology; Medical Physiology (Medical Physiology textbook)

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Q5. Theories of Colour Vision (5M)

• Proposed by Thomas Young (1801), elaborated by Helmholtz
• Three types of cone photoreceptors with different spectral sensitivities:
  • S-cones (Blue) - peak at ~430 nm
  • M-cones (Green) - peak at ~530 nm
  • L-cones (Red) - peak at ~560 nm
• Any color is perceived by the ratio of stimulation of these three cone types
• Example (from Guyton & Hall): Orange light (580 nm) stimulates Red:Green:Blue = 99:42:0 → perceived as orange
• White light stimulates all three approximately equally
• Color blindness results from absence/defect of one cone type:
  • Missing green cones = deuteranopia (red-green color blind)
  • Missing red cones = protanopia
  • Missing blue cones = tritanopia

• Proposed that color vision operates in three opponent channel pairs:
  • Red vs. Green
  • Blue vs. Yellow
  • Black vs. White (luminance)
• Colors in each pair are mutually inhibitory (cannot see "reddish-green" or "bluish-yellow")
• Explains color afterimages: staring at red produces green afterimage
• Explains unique hues and color opponency in retinal ganglion cells and LGN
• Now confirmed: retinal ganglion cells and LGN cells show opponent responses

• Combines both theories:
  • Stage 1 (Receptor level): Trichromatic - three cone types as per Young-Helmholtz
  • Stage 2 (Neural processing): Opponent channels as per Hering - at level of bipolar/ganglion cells and lateral geniculate nucleus

• Ishihara plates test red-green color blindness
• Farnsworth-Munsell 100 Hue Test for detailed color vision assessment
• X-linked inheritance of red-green color blindness

Guyton & Hall Textbook of Medical Physiology - COLOR VISION chapter

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Q6. Case: 35-year-old woman - weight gain, lethargy, cold intolerance, constipation, dry skin, slow reflexes, puffy face, low T3/T4, increased TSH.

1. Calorigenic/Thermogenic effect: T3/T4 increase basal metabolic rate (BMR) by stimulating Na+/K+ ATPase activity, increasing oxygen consumption in virtually all tissues. This is why hypothyroidism causes cold intolerance and lethargy.
2. Protein, carbohydrate, and fat metabolism: T3/T4 stimulate protein synthesis (anabolic at normal levels), increase glucose absorption from gut, enhance lipolysis and gluconeogenesis. They also regulate lipid metabolism - hypothyroidism causes hypercholesterolemia due to reduced LDL receptor expression.

• Thyroid hormone production follows the HPT (Hypothalamic-Pituitary-Thyroid) axis:
  • Hypothalamus secretes TRH → stimulates anterior pituitary to secrete TSH
  • TSH stimulates thyroid to produce T3 and T4
  • T3/T4 exert negative feedback on both hypothalamus and pituitary
• In primary hypothyroidism: damaged thyroid gland cannot produce adequate T3/T4
• Low T3/T4 → reduced negative feedback on pituitary thyrotrophs
• Pituitary thyrotrophs become hyperactive → TSH production markedly elevated
• This is the compensatory attempt to stimulate the failing thyroid
• Additionally, low T3/T4 → increased TRH from hypothalamus → further stimulates TSH release
• TSH is therefore a very sensitive and early marker of thyroid dysfunction

• Drug of choice: Levothyroxine sodium (T4 analogue)
• Starting dose: 25-50 mcg/day (start low in elderly/cardiac patients)
• Target: normalize TSH (0.5 - 4.0 mIU/L)
• Monitoring: TSH every 6-8 weeks until stable, then annually
• Note: T4 is peripherally converted to active T3

Goodman & Gilman's Pharmacological Basis of Therapeutics - Thyroid Hormone Replacement

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Q7. Dignity and Diversity in Management of Patients (5M)

• Dignity: The inherent worth of every patient as a person; treating patients with respect, privacy, and compassion regardless of condition
• Diversity: Recognition that patients come from varied cultural, ethnic, religious, linguistic, socioeconomic, and gender backgrounds that influence their healthcare needs

• Patients have the right to make informed decisions about their care
• Informed consent must account for language barriers and cultural beliefs
• Use interpreters when needed; never use family members as interpreters for sensitive matters

• Understanding cultural beliefs about illness, diet, and treatment
• Religious considerations (e.g., Jehovah's Witnesses refusing blood transfusion; halal/kosher dietary requirements)
• Gender preferences for healthcare providers

• Equal quality care regardless of race, religion, gender, sexual orientation, socioeconomic status, or disability
• Avoiding stereotyping and bias in clinical decision-making

• Maintaining dignity during physical examination (adequate draping, private rooms)
• Protecting patient information (HIPAA/hospital regulations)

• Plain language, avoiding medical jargon
• Active listening; acknowledging patients' concerns
• Respectful address (using patient's preferred name)

• Preventing unnecessary exposure during examination and procedures
• Knocking before entering; asking permission before touching
• Providing adequate pain relief - pain undermines dignity

• Culturally sensitive care improves patient adherence and trust
• Reduces health disparities in minority populations
• Patient-centered care leads to better health outcomes and satisfaction

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Q8. Tests for Ovulation (5M)

• Temperature rises 0.2-0.5°C after ovulation due to progesterone's thermogenic effect
• Temperature chart shows a biphasic pattern (low in follicular phase, high in luteal phase)
• Retrospective confirmation of ovulation

• Measured on Day 21 (in a 28-day cycle)
• Level >3 ng/mL (or >10 ng/mL for optimal ovulation) confirms ovulation
• Most reliable biochemical test for confirming ovulation

• Ovulation occurs 24-36 hours after the LH surge
• Urine LH testing started Day 11, continued until surge detected
• Positive result predicts imminent ovulation (used in fertility treatment)
• Blood LH measurement gives earlier detection

• Serial ultrasound to track dominant follicle growth (>18-20 mm pre-ovulation)
• Post-ovulation: collapsed follicle + free fluid in pouch of Douglas
• Gold standard for timing ovulation in assisted reproduction

• Done in mid-luteal phase
• Shows secretory changes (coiled glands, stromal edema) if ovulation occurred
• Historical test; not commonly used now

• Pre-ovulation: Spinnbarkeit (stretchy, clear mucus) and ferning pattern on glass slide
• Post-ovulation: mucus becomes thick and cellular

• Increased cornification index around ovulation due to estrogen peak

• Peaks just before LH surge (Pre-ovulatory estradiol surge)

• Elevated Day 3 FSH (>10-12 IU/L) indicates diminished ovarian reserve

Tietz Textbook of Laboratory Medicine, 7th Ed.; Kaplan & Sadock's; Berek & Novak's Gynecology

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Q9. Functions of the Middle Ear (5M)

1. Hydraulic lever ratio: Area of tympanic membrane (~55 mm²) vs. oval window (~3.2 mm²) = ratio ~17:1 (force amplification)
2. Ossicular lever ratio: Malleus arm is longer than incus arm = lever advantage ~1.3:1
3. Combined amplification: ~17 × 1.3 = ~22-fold pressure amplification (~27 dB gain)
4. Buckling of tympanic membrane: Adds further mechanical advantage

• Loud sounds (>70-80 dB) trigger contraction of Stapedius muscle (CN VII) and Tensor tympani (CN V)
• Stiffens ossicular chain → attenuates loud sounds by 10-15 dB
• Protects inner ear from acoustic trauma
• Also reduces masking of speech by low-frequency environmental noise

• Middle ear connects to nasopharynx via Eustachian tube
• Opens during swallowing/yawning → equalizes pressure on both sides of tympanic membrane
• Maintains optimal vibration of tympanic membrane

• Acts as a buffer against barotrauma
• Reduces bone-conducted sound
• Round window membrane (secondary tympanic membrane) allows fluid movement in cochlea

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Q10. 50-year-old Male - Increased Frequency of Micturition (5M)

• Bladder fills: sympathetic (L1-L2) via hypogastric nerve activates β3 receptors → detrusor relaxation; α1 receptors → internal urethral sphincter contraction (storage)
• Micturition reflex: Parasympathetic (S2-S4) via pelvic nerve → muscarinic (M3) receptors on detrusor → contraction; internal sphincter relaxes → voiding
• Higher centers: Pontine micturition center (PMC) coordinates; frontal cortex provides voluntary control
• Somatic control: External sphincter via pudendal nerve (S2-S4)

• Enlarged prostate compresses urethra → increased outlet resistance
• Detrusor muscle hypertrophies to overcome resistance
• Eventually detrusor becomes irritable → involuntary contractions → urgency/frequency
• Incomplete emptying → residual urine → recurrent infection → further frequency

• Urine R/E and culture (rule out UTI)
• Fasting blood glucose (rule out DM)
• PSA (Prostate Specific Antigen) - rule out prostate cancer
• Serum creatinine (renal function)
• Ultrasound abdomen/pelvis - prostate size, residual urine, hydronephrosis
• Urodynamic studies - detrusor function
• Cystoscopy if hematuria present

• Alpha-1 blockers (tamsulosin, alfuzosin) - relax smooth muscle of prostate/bladder neck → improve flow
• 5-alpha reductase inhibitors (finasteride, dutasteride) - reduce prostate size (for large prostates)
• Anticholinergics/Beta-3 agonists for OAB symptoms
• Surgical: TURP (Transurethral Resection of Prostate) for refractory cases

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