---

PHYSIOLOGY LABORATORY SKILLS — Complete Guide

---

1. Preparation of a Neuromuscular Preparation

Aim

Materials

Procedure

1. Pithing: Destroy the brain and spinal cord of the frog by inserting a probe through the foramen magnum (double pith — brain + cord).
2. Skin removal: Cut and remove skin from the lower half of the body, exposing thigh muscles.
3. Expose the sciatic nerve: Carefully separate the thigh muscles along the line of the femur to expose the sciatic nerve running deep in the thigh.
4. Isolate the nerve: Using glass hooks (never metal), trace the sciatic nerve proximally toward the spinal cord and distally to the knee; ligate and cut proximally, leaving a long nerve thread.
5. Isolate the gastrocnemius muscle: Cut the Achilles tendon, tie a thread to its distal end; cut the leg free below the knee, leaving the muscle attached to the bone.
6. Keep moist: Frequently irrigate the preparation with Ringer's solution (NaCl 0.65%, KCl, CaCl₂, NaHCO₃) to keep it viable.
7. Mount on a kymograph lever for recording contractions.

Key Points

• Glass hooks must be used — metal instruments create injury currents that confound results.
• Ringer's solution mimics frog plasma in ionic composition and pH.
• Preparation remains viable for several hours at room temperature.
• The gastrocnemius is chosen because it is easily accessible and produces large, recordable contractions.

Cross Questions

• Q: Why is pithing done before preparation? A: To eliminate reflex activity and prevent pain/movement, allowing clean dissection.
• Q: Why use glass hooks instead of metal? A: Metal touches on nerve can generate electrochemical currents (injury potentials) that artificially stimulate the nerve.
• Q: What is Ringer's solution and why is it used? A: Isotonic saline with KCl, CaCl₂, NaHCO₃ — maintains ionic environment similar to frog tissue fluid, preserving excitability.
• Q: How long does a frog NM preparation remain viable? A: Several hours (2–4 h at room temperature; longer if refrigerated).
• Q: What happens if the nerve is touched with metal forceps? A: Injury currents stimulate the nerve, causing spontaneous contraction and degrading preparation quality.

---

2. Galvani's First Experiment

Principle

Historical Background

Setup & Procedure

1. Prepare a neuromuscular preparation (sciatic nerve–gastrocnemius).
2. Place the preparation on a glass or wax surface (non-conductor).
3. Connect the preparation to an electrostatic machine or Leyden jar via a metal conductor.
4. When a spark is discharged or the metal touches the nerve, the muscle contracts.
5. Repeat with the preparation on metal vs. non-conducting surfaces; contraction occurs only when current can flow.

Key Observations

• Muscle contracts when electricity from external source is applied to the nerve.
• No contraction when the preparation sits on a non-conductor (glass, resin, wax).
• Contraction occurs even when the spark does not directly touch the frog — induction effect.

Galvani's Conclusion

Cross Questions

• Q: What was the accidental discovery in Galvani's lab? A: A charged scalpel near an electrostatic generator sparked; on touching the sciatic nerve, the frog leg twitched — demonstrating electrical excitation of nerve.
• Q: What role did the Leyden jar play? A: It stored static electricity and could deliver a controlled electrical discharge to the preparation.
• Q: What surfaces prevent muscle contraction in this experiment? A: Non-conductors — glass, wax, resin — which break the circuit.
• Q: What is "animal electricity" as proposed by Galvani? A: An intrinsic electrical force residing in the nerve and muscle, analogous to the electricity stored in a Leyden jar.
• Q: How does Galvani's 1st experiment differ from his 2nd? A: 1st uses an external electrical source; 2nd uses only the biological tissues themselves (bimetallic arc generating current from tissue).

---

3. Galvani's Second Experiment

Principle

Setup & Procedure

1. Prepare a neuromuscular preparation.
2. Method A (Bimetallic arc): Connect the nerve and muscle using an arc made of two different metals (e.g., brass hook and iron plate). When the nerve is laid on the metal arc and touches the muscle, a contraction occurs. The electrochemical potential difference between the two metals creates a current that stimulates the nerve.
3. Method B (Injury potential): Lay the nerve across a cut/injured surface of the muscle — the injured region is electronegative relative to the intact surface, creating a demarcation current. The nerve is stimulated and the muscle contracts.

Key Observations

• Contraction occurs without any external electrical device.
• Two different metals produce a stronger effect than two identical metals.
• A nerve laid across a cut muscle also contracts — this is the first demonstration of bioelectric current.

Galvani's Conclusion

Volta's Counterargument

Galvani's Rebuttal

Cross Questions

• Q: What is a demarcation potential (injury current)? A: The electrical potential difference between the cut (injured, electronegative) and intact (electropositive) surface of a muscle/nerve — typically −40 to −60 mV.
• Q: Why do two different metals produce a stronger effect than one? A: Galvanic cell principle — two dissimilar metals in contact with ionic tissue fluid create an electrochemical potential difference (EMF), generating current.
• Q: How did Galvani counter Volta's criticism? A: He connected two nerve-muscle preparations without metal; the nerve of one touched the cut muscle of the other, causing contraction — proving bioelectricity is intrinsic.
• Q: What is the significance of Galvani's 2nd experiment? A: First demonstration of bioelectricity and the concept of resting membrane potential/action potential in nerve and muscle.
• Q: What concept does the injury potential relate to in modern physiology? A: Resting membrane potential — the interior of cells is negative (~−70 mV) relative to the exterior; damage exposes this potential difference.

---

4. Effects on Nerve Fiber by Currents from an Electric Stimulator (Matteucci Experiment) — Secondary Tetanus

Principle

Matteucci Experiment Setup

1. Prepare two neuromuscular preparations (frog sciatic nerve–gastrocnemius).
2. First (primary) preparation: Place on a kymograph; stimulate its nerve electrically with an induction coil — the muscle enters primary tetanus (sustained contraction).
3. Second (secondary) preparation: Lay its sciatic nerve across the contracting gastrocnemius of the primary preparation.
4. Observation: The secondary preparation's muscle also contracts — secondary tetanus — even though no direct electrical stimulus was applied to it.

Key Points

• The primary muscle, during tetanic contraction, generates rhythmic action potentials (bioelectric currents).
• These action currents from the primary muscle act as stimuli on the secondary nerve.
• Demonstrates that muscle action potentials are measurable and biologically effective.
• This experiment laid the groundwork for electromyography (EMG).

Tetanus Physiology

• Primary tetanus: Sustained fusion of twitches from rapid stimulation of the nerve (>50 Hz in frog).
• Secondary tetanus: Reflex contraction in the second preparation driven by action currents emanating from the primary contracting muscle.

Cross Questions

• Q: What generates the secondary tetanus? A: Action currents (bioelectric potentials) from the rhythmically contracting primary muscle stimulate the nerve of the secondary preparation.
• Q: What frequency of stimulation induces tetanus in frog muscle? A: ~30–50 Hz (stimuli so rapid that individual twitches fuse into a sustained contraction).
• Q: What is the difference between incomplete and complete tetanus? A: Incomplete tetanus — twitches partially fuse; complete tetanus — full fusion into smooth sustained contraction with no visible individual twitches.
• Q: What modern diagnostic technique is based on the principle of Matteucci's experiment? A: Electromyography (EMG) — recording electrical activity from contracting muscles.
• Q: What happens if Ringer's solution dries out during the experiment? A: Excitability is lost; the preparation becomes non-responsive and secondary tetanus does not occur.

---

5. Summation of Stimuli

5a. Successive (Temporal) Summation

1. Connect the nerve of the preparation to an electrical stimulator with adjustable inter-stimulus interval.
2. Determine the threshold stimulus (minimum for a visible twitch).
3. Apply two sub-threshold stimuli with a very short interval (<2–3 ms).
4. Observe: the muscle contracts even though each stimulus alone is sub-threshold.

• Only possible within the relative refractory period (summation window).
• Does not occur during the absolute refractory period.
• Demonstrates graded (local) potentials can summate in nerve membranes.

---

5b. Spatial Summation

1. Apply two pairs of electrodes at different points on the nerve simultaneously.
2. Each pair delivers a sub-threshold stimulus simultaneously.
3. The muscle contracts, even though neither pair alone was sufficient.

Cross Questions

• Q: What is a sub-threshold stimulus? A: A stimulus intensity below the minimum needed to produce an action potential.
• Q: Why doesn't summation occur during the absolute refractory period? A: During the absolute refractory period, Na⁺ channels are inactivated (closed); no stimulus, regardless of strength, can initiate another action potential.
• Q: What is the "all-or-none" law and how does it relate to summation? A: The all-or-none law applies to action potentials (once threshold is reached, full AP fires). Summation operates at the subthreshold (graded potential) level to reach threshold.
• Q: Give an example of spatial summation in the CNS. A: Multiple excitatory postsynaptic potentials (EPSPs) from different presynaptic neurons converging on one motor neuron simultaneously.
• Q: What is temporal summation in CNS synaptic transmission? A: Rapid repetitive firing by the same presynaptic neuron produces EPSPs that summate before decay, eventually reaching threshold.

---

6. Determination of Reflex Time (Türck's Experiment)

Principle

Equipment

Procedure (Classic Türck's Method — Spinal Frog)

1. Spinalize the frog: Remove the brain (spinal frog retained — retains spinal reflexes).
2. Suspend the frog vertically by its jaw.
3. Dip the toe/foot into warm acidic water (dilute H₂SO₄) or warm water of measured temperature.
4. Record the time from immersion to the moment the leg withdraws (flexion reflex).
5. Repeat at different water temperatures/stimulus strengths.
6. Longer stimulus → shorter reflex time (stronger = faster irradiation to more interneurons).

Key Observations

• Stronger stimulus → shorter reflex time (more motoneurons recruited rapidly).
• Weaker stimulus → longer reflex time (more summation needed to reach threshold).
• Irradiation: Very strong stimuli produce bilateral flexion (irradiation to contralateral cord).
• Reflex time is always longer than simple nerve conduction time — the extra time = synaptic delay × number of synapses.

Components of Reflex Time

Cross Questions

• Q: What is synaptic delay and what causes it? A: ~0.3–0.5 ms at each synapse; caused by time for vesicle fusion, neurotransmitter diffusion across the synaptic cleft, and receptor activation.
• Q: Why does increasing stimulus strength reduce reflex time? A: Stronger stimulus recruits more afferent fibers simultaneously, activating more interneurons faster, reaching motoneuron threshold sooner.
• Q: What is the difference between reflex time and reaction time? A: Reflex time is purely spinal/brainstem (involuntary); reaction time includes cortical processing (voluntary).
• Q: What phenomenon occurs when a very strong stimulus is used in Türck's experiment? A: Irradiation — bilateral flexion, spread of excitation to many cord segments.
• Q: What is the simplest reflex arc and how many synapses does it have? A: The monosynaptic stretch reflex (knee jerk) — 1 synapse (Ia afferent → α-motor neuron).

---

7. Dynamometry

Aim

Equipment

Procedure

1. Subject grips the dynamometer tightly with dominant hand, arm extended.
2. Squeeze maximally — record reading in kg or N.
3. Repeat with non-dominant hand.
4. Repeat after sustained repeated efforts to demonstrate fatigue.
5. Record readings at equal intervals (every 10 seconds for 5–10 repetitions).

Normal Values

• Adult male: 40–60 kg (dominant hand)
• Adult female: 25–40 kg (dominant hand)

Key Observations

• Dominant hand is typically ~10% stronger.
• Progressive decrease in readings demonstrates muscle fatigue.
• Recovery of strength after rest demonstrates fatigue reversal.

Factors Affecting Muscle Strength

1. Age — peaks at 25–35 years, declines after 50.
2. Sex — males > females (testosterone effect on muscle bulk).
3. Training — athletes have higher grip strength.
4. Fatigue — lactic acid accumulation, ATP depletion.
5. Body position and arm position.
6. Motivation and psychological state.

Fatigue Mechanism

• Depletion of ATP and creatine phosphate.
• Accumulation of lactic acid (H⁺ ions inhibit actomyosin ATPase).
• Accumulation of inorganic phosphate (Pi) inhibits cross-bridge formation.
• K⁺ accumulation in T-tubules disrupts excitation-contraction coupling.

Cross Questions

• Q: What is the physiological basis of muscle fatigue? A: ATP depletion, lactic acid/H⁺ accumulation reducing ATPase activity, Pi accumulation, K⁺ imbalance in T-tubules.
• Q: Where does fatigue first occur in the neuromuscular system? A: The neuromuscular junction (NMJ) — due to depletion of acetylcholine vesicles.
• Q: What is ergography? A: Use of an ergograph to measure repetitive work done by muscles — plots fatigue curve (decreasing lift height over time).
• Q: Differentiate central and peripheral fatigue. A: Central fatigue — failure at CNS level (reduced motor drive, motivation); peripheral fatigue — failure at muscle fiber level.
• Q: Define motor unit and explain its role in graded muscle contraction. A: A single α-motor neuron + all muscle fibers it innervates; graded contraction achieved by recruiting more motor units (spatial summation) or increasing firing rate (temporal summation).

---

8. Study of the Patellar Tendon Reflex (Knee Jerk)

Reflex Arc

• Receptor: Muscle spindle (annulospiral endings) in quadriceps femoris
• Afferent: Ia sensory fibers → posterior root → L2–L4 spinal cord
• Centre: Anterior horn of spinal cord (L3–L4) — monosynaptic
• Efferent: α-motor neurons → femoral nerve → quadriceps
• Effector: Quadriceps femoris (extends the leg)

Procedure

1. Patient seated with legs dangling freely.
2. Strike the patellar tendon (just below the patella) with a reflex hammer.
3. Observe extension of the knee (quadriceps contraction).
4. Assess amplitude and symmetry bilaterally.

Grading (0–4+)

Clinical Significance

• Diminished/absent: Lower motor neuron lesion, L3–L4 root compression, peripheral neuropathy (diabetes, Guillain-Barré).
• Exaggerated: Upper motor neuron lesion (stroke, multiple sclerosis, spinal cord injury above L4).

Jendrassik Maneuver

Cross Questions

• Q: What is the receptor for the patellar reflex? A: Muscle spindle (intrafusal fibers); specifically the primary (annulospiral) endings of Ia fibers.
• Q: Why is the patellar reflex monosynaptic? A: The Ia afferent fiber synapses directly on the α-motor neuron in the anterior horn — only one central synapse.
• Q: What does a brisk (hyperreflexia) patellar reflex indicate? A: UMN lesion (corticospinal tract damage) — loss of descending inhibition on the spinal reflex arc.
• Q: Explain the Jendrassik maneuver. A: Pulling interlocked hands apart while the reflex is being tested increases descending excitatory drive on γ-motor neurons, raising spindle sensitivity, amplifying reflex.
• Q: What nerve roots mediate the patellar reflex? A: L2, L3, L4 (main contribution L3–L4).

---

9. Brachial (Triceps) Extensor Reflex

Reflex Arc

• Receptor: Muscle spindle in triceps brachii
• Afferent: Ia fibers → C6–C8 dorsal root
• Centre: C6–C8 anterior horn — monosynaptic
• Efferent: Radial nerve → triceps brachii
• Response: Extension of the forearm (elbow extension)

Procedure

1. Patient's arm supported at ~90° flexion at elbow.
2. Strike the triceps tendon just above the olecranon process (or strike examiner's finger placed on the tendon).
3. Observe extension of the forearm.

Biceps Reflex (for comparison)

• Receptor: Biceps muscle spindle
• Afferent: C5–C6
• Strike the biceps tendon at the antecubital fossa
• Response: Flexion of elbow

Clinical Significance

• Absent triceps reflex: C7 root lesion, radial nerve palsy.
• Absent biceps reflex: C5–C6 root lesion (e.g., Erb's palsy).
• Exaggerated: UMN lesion.

Cross Questions

• Q: Which nerve mediates the triceps reflex? A: Radial nerve (C6–C8, predominantly C7).
• Q: What root level is specifically tested by the triceps reflex? A: C7.
• Q: How do you differentiate LMN from UMN lesion using reflex findings? A: LMN lesion → hyporeflexia/areflexia, muscle wasting, fasciculations; UMN lesion → hyperreflexia, clonus, Babinski's sign, no wasting.
• Q: What is inversion of reflexes? A: A reflex is absent at the expected spinal level (LMN lesion at that level) but reflexes below are exaggerated (due to loss of descending inhibition from UMN lesion at same level) — e.g., C5–C6 lesion → absent biceps jerk, brisk triceps jerk.
• Q: What is the brachioradialis reflex and its root value? A: Elbow flexion on striking the brachioradialis tendon; C5–C6.

---

10. Definition of the Achilles Reflex (Ankle Jerk)

Reflex Arc

• Receptor: Muscle spindle in gastrocnemius/soleus
• Afferent: Ia fibers → S1–S2 dorsal root
• Centre: S1–S2 anterior horn — monosynaptic
• Efferent: Tibial nerve → gastrocnemius + soleus
• Response: Plantar flexion of the foot

Procedure

1. Patient kneeling on a chair/bench, feet hanging free, or patient seated with foot dorsiflexed.
2. Strike the Achilles tendon (calcaneal tendon) with a reflex hammer.
3. Observe plantar flexion of the foot.

Clinical Significance

• Absent: S1–S2 root lesion, sciatic nerve lesion, peripheral neuropathy (diabetes most common), hypothyroidism (delayed relaxation), Guillain-Barré.
• Exaggerated: UMN lesion.
• Delayed relaxation of Achilles reflex is a classic sign of hypothyroidism.

Cross Questions

• Q: Which nerve root primarily mediates the Achilles reflex? A: S1 (with contribution from S2).
• Q: What is the clinical significance of a delayed Achilles reflex relaxation? A: Classic sign of hypothyroidism — slow relaxation due to reduced ATP-dependent calcium uptake by sarcoplasmic reticulum in hypothyroid muscles.
• Q: Why is the Achilles reflex absent in peripheral neuropathy? A: Damage to peripheral sensory or motor fibers (Ia afferents or motor efferents) interrupts the reflex arc.
• Q: How is the Achilles reflex used in diagnosing S1 radiculopathy vs. peripheral neuropathy? A: S1 radiculopathy → unilateral absent ankle jerk, dermatomal sensory loss, may have positive SLR; peripheral neuropathy → bilateral, distal, with glove-stocking sensory loss.
• Q: What is clonus and when is it seen? A: Rhythmic involuntary contractions elicited by sustained dorsiflexion of the foot; indicates severe UMN lesion with markedly enhanced stretch reflex.

---

11. Statokinetic Reflexes

Definition

Types

A. Static Reflexes (Tonic Reflexes)

1. Local static reflexes: Stretch reflexes maintaining limb position.
2. Segmental static reflexes: Tonic neck reflexes, tonic labyrinthine reflexes.
3. General static reflexes: Righting reflexes.

B. Statokinetic (Phasic) Reflexes

Key Statokinetic Reflexes

• Receptor: Otolith organs (utricle, saccule) — sense gravity and linear acceleration.
• Response: Changes in limb extensor tone with changes in head position.
• Supine → increased extensor tone; Prone → decreased extensor tone.

• Receptor: Neck muscle proprioceptors.
• Response: Rotation of head to right → right limbs extend, left limbs flex.

• Receptor: Vestibular, visual, tactile inputs.
• Response: Restore normal head and body orientation when displaced.
• Example: Head righting reflex — head brought to normal position when tilted.

• Triggered by rotation.
• Slow phase: Eyes deviate opposite to rotation (vestibular input).
• Fast phase: Rapid eye movement back to center.
• Post-rotational nystagmus reverses when rotation stops.

Practical Demonstration (Lab)

1. Subject sits in a rotating chair (Barany chair).
2. Rotate 10 times in 20 seconds, stop suddenly.
3. Observe post-rotational nystagmus (eyes beat opposite to rotation direction).
4. Subject also feels sensation of rotation — demonstrates vestibuloocular reflex.

Cross Questions

• Q: What organs are responsible for sensing linear vs. angular acceleration? A: Otolith organs (utricle/saccule) → linear acceleration; Semicircular canals → angular acceleration.
• Q: What is the Romberg test and what does it assess? A: Patient stands with feet together, eyes open then closed; if swaying increases with eyes closed (Romberg positive) → proprioceptive or vestibular deficit (not cerebellar).
• Q: Explain the mechanism of nystagmus during rotation. A: Endolymph in semicircular canals lags behind rotation, deflecting cupula → excites hair cells → VOR causes slow eye movement opposite to rotation; fast correction saccade brings eyes back.
• Q: What is the difference between physiological and pathological nystagmus? A: Physiological nystagmus is a normal VOR response during/after rotation; pathological nystagmus occurs at rest and indicates vestibular disease or cerebellar pathology.
• Q: What role does the cerebellum play in statokinetic reflexes? A: Coordinates timing, amplitude, and smooth execution of postural adjustments; lesion leads to ataxia, past-pointing, rebound nystagmus.

---

12. Danini-Aschner Reflex (Oculocardiac Reflex)

Definition

Reflex Arc

• Receptor: Mechanoreceptors in the globe and extraocular muscles
• Afferent: Ophthalmic branch (V1) of the trigeminal nerve (CN V) → trigeminal nucleus in brainstem
• Centre: Reticular formation → dorsal vagal nucleus
• Efferent: Vagus nerve (CN X) → SA node of the heart
• Response: Bradycardia (slowing of heart rate)

Procedure

1. Record baseline pulse rate for 1 minute.
2. Apply gentle, firm pressure on both closed eyes (using thumb and index finger) for 20–30 seconds.
3. Count pulse rate during pressure.
4. Normal response: Pulse slows by 5–13 beats/minute.
5. Release pressure — pulse returns to baseline.

Clinical Significance

• Used diagnostically to evaluate vagal tone.
• May terminate some supraventricular tachycardias (SVT).
• Exaggerated response → hyperactive vagal tone.
• Absent response → atropinized patient (vagal blockade) or autonomic neuropathy.
• Danger: Excessive pressure can cause asystole in susceptible individuals.
• Common trigger during strabismus surgery — anesthesiologists must monitor.

Cross Questions

• Q: What is the afferent limb of the Danini-Aschner reflex? A: Trigeminal nerve (ophthalmic branch, V1).
• Q: What is the efferent limb? A: Vagus nerve (CN X) to the SA node.
• Q: What drug blocks this reflex? A: Atropine (muscarinic blocker at the SA node).
• Q: By how much does the pulse decrease normally? A: 5–13 beats/minute (>20 bpm decrease is considered exaggerated).
• Q: What are the dangers of this reflex? A: Excessive pressure or high vagal tone → severe bradycardia, asystole, cardiac arrest. Risk is highest in children during strabismus surgery.
• Q: What other cardiovascular effects can eyeball pressure cause? A: ECG changes including junctional rhythm and even asystole in extreme cases.

---

13. The Effect of Adrenaline on the Pupil of the Frog's Eye

Principle

Procedure

1. Prepare two frogs.
2. Remove the eyeball or observe the intact eye.
3. Apply 1:1000 adrenaline (epinephrine) solution to one eye (experimental).
4. Apply normal saline to the other eye (control).
5. Observe the pupil diameter in both eyes at intervals (5, 10, 15 minutes).

Observation

• Adrenaline eye: Pupil dilates (mydriasis) — iris dilator muscle (radial fibers) contracts.
• Control eye: No change.

Mechanism

• Adrenaline activates α₁-adrenergic receptors on the iris dilator muscle.
• This causes contraction of dilator pupillae → pupillary dilation.
• The sphincter pupillae (constrictor) receives parasympathetic (muscarinic) innervation and is not directly activated.

Human Pharmacology Comparison

Cross Questions

• Q: What receptor does adrenaline act on in the iris? A: α₁-adrenergic receptors on the iris dilator muscle.
• Q: Why does adrenaline cause dilation, not constriction? A: Dilator pupillae expresses α₁ receptors (sympathetic); constrictor pupillae expresses muscarinic receptors (parasympathetic). Adrenaline primarily activates α₁ in the iris.
• Q: What is Horner's syndrome? A: Interruption of sympathetic supply to the eye → miosis (small pupil), ptosis (drooping lid), anhidrosis on same side of face.
• Q: How does the pupillary light reflex work? A: Light → retinal ganglion cells → pretectal nucleus → bilateral Edinger-Westphal nucleus → ciliary ganglion → constrictor pupillae (CN III, muscarinic) → miosis.
• Q: Why is frog eye used instead of mammalian eye in this experiment? A: Frog eyes are easily accessible, iris pigmentation allows visual observation of pupil changes, and adrenergic pharmacology of frog iris is well characterized.

---

14. Esthesiometry (Tactile Discrimination)

Aim

Equipment

Procedure

1. Subject's eyes are closed.
2. Apply both points of the esthesiometer simultaneously to the skin surface.
3. Gradually decrease the distance between points; ask the subject after each application if they feel one or two points.
4. Record the minimum distance at which 2 points are correctly identified (2-point discrimination threshold).
5. Repeat on different body regions.

Normal Two-Point Discrimination Values

Mechanism

• High density of receptors + small receptive fields → fine discrimination (fingertips).
• Low density + large receptive fields → poor discrimination (back).
• Receptors involved: Meissner's corpuscles (fine touch), Merkel's disks (pressure/form), both in superficial dermis with small, well-defined fields.

Clinical Relevance

• Increased threshold → peripheral neuropathy, posterior column lesion (dorsal column-medial lemniscal pathway damage), thalamic lesion.
• Posterior column pathway (dorsal columns) carries fine touch, proprioception, vibration.

Cross Questions

• Q: What is the receptor responsible for fine tactile discrimination at fingertips? A: Meissner's corpuscles (rapidly adapting, superficial) and Merkel's discs (slowly adapting, superficial).
• Q: Why are fingertips better at two-point discrimination than the back? A: Fingertips have a higher density of mechanoreceptors with smaller receptive fields and greater cortical representation (larger area in somatosensory homunculus).
• Q: What spinal cord pathway carries two-point discrimination signals? A: Dorsal column-medial lemniscal pathway (ipsilateral dorsal columns → nucleus gracilis/cuneatus → contralateral thalamus → somatosensory cortex).
• Q: What clinical condition causes impaired two-point discrimination with preserved pain sensation? A: Dorsal column (posterior column) lesion — e.g., tabes dorsalis (syphilis), multiple sclerosis, vitamin B12 deficiency (subacute combined degeneration).
• Q: What is Weber's two-point compass test? A: Method of applying two calibrated points simultaneously to skin to measure the discrimination threshold — named after Ernst Heinrich Weber who first systematically described spatial tactile discrimination.

---

15. Determination of Visual Acuity

Aim

Equipment

Procedure

1. Place subject 6 meters from the Snellen chart in good illumination.
2. Test each eye separately (occlude the other eye).
3. Subject reads the smallest line where ≥50% of letters are correctly identified.
4. Record as a fraction: Snellen notation = testing distance / distance at which a normal eye reads that line.

Snellen Notation

• 6/6 (or 20/20 in feet): Normal visual acuity — reads at 6 m what normal eye reads at 6 m.
• 6/12: Reads at 6 m what normal reads at 12 m → halved acuity.
• 6/60: Very poor acuity (legal blindness threshold varies by country).
• 6/6 or better (6/5, 6/4): Supernormal acuity.

Visual Angle

• The standard letter subtends 5 minutes of arc (each stroke = 1 minute) at the designated distance.
• Minimum angle of resolution (MAR) of normal eye = 1 minute of arc.

Factors Affecting Visual Acuity

• Refractive errors (myopia, hyperopia, astigmatism) — corrected with lenses.
• Illumination (dim light → reduced acuity, rods replace cones).
• Pupil size (too large or too small reduces acuity).
• Macular/foveal health (cones densest at fovea → best acuity).
• Age (presbyopia).

Cross Questions

• Q: Why is the Snellen chart read at 6 meters? A: At 6 m, parallel rays entering the eye require minimal accommodation, simulating infinity.
• Q: What does 6/12 visual acuity mean? A: The patient reads at 6 m what a normal person can read at 12 m — their acuity is half of normal.
• Q: Which part of the retina gives the best visual acuity? A: The fovea centralis of the macula — highest cone density (~150,000 cones/mm²), each cone has its own ganglion cell.
• Q: What is the Snellen minimum letter design based on? A: Each letter subtends 5 minutes of arc total; each limb (stroke) subtends 1 minute of arc.
• Q: What is a pinhole test and why is it used? A: Viewing through a small pinhole eliminates refractive error by restricting light to axial rays — improvement in acuity with pinhole suggests a correctable refractive error.

---

16. Definition of the Field of View (Visual Field Testing / Perimetry)

Aim

Equipment

Normal Visual Field Extent (Monocular)

Procedure (Arc Perimeter)

1. Subject positions head on chin rest, fixes gaze on central fixation point.
2. A white object (5 mm diameter) is moved from the periphery along meridians every 30°.
3. Subject signals when the object first appears.
4. Plot isopters on a chart.
5. Identify the blind spot (physiological scotoma at ~15° temporal to fixation — corresponds to optic disc with no photoreceptors).

Confrontation Visual Field Test

1. Examiner faces patient at arm's length, both fix on each other's eye.
2. Examiner moves fingers from periphery — tests all 4 quadrants of each eye.

Clinical Field Defects

Cross Questions

• Q: What is the blind spot and what causes it? A: Area of no vision ~15° temporal to fixation — corresponds to the optic disc, which has no photoreceptors.
• Q: What visual field defect suggests a pituitary macroadenoma? A: Bitemporal hemianopia (loss of both temporal fields) — due to compression of decussating fibers at the optic chiasm.
• Q: What is homonymous hemianopia? A: Loss of the same half of the visual field in both eyes (e.g., both left halves lost in right optic tract lesion).
• Q: Explain the Goldmann perimeter and what it measures. A: A bowl-shaped perimeter with a movable light stimulus of variable size/intensity; maps static and kinetic visual fields.
• Q: What is a scotoma? A: An area of absent or reduced vision within the visual field, surrounded by normal vision.

---

17. Definition of Color Perception

Aim

Equipment

Procedure (Ishihara Test)

1. Show each plate at ~75 cm in good daylight illumination.
2. Subject reads the number or traces the path (for illiterates) seen in the plate.
3. Normal vision reads hidden numbers; color-blind individuals see different/no numbers.
4. Record errors per plate — classify type of deficiency.

Normal Color Vision

• Trichromacy: 3 cone types — L (red/564 nm), M (green/534 nm), S (blue/420 nm).
• Normal individuals correctly read all Ishihara plates.

Color Deficiency Classification

• Sex-linked recessive inheritance for red-green defects → more common in males (8%) than females (<0.5%).

Mechanism

• Ishihara plates use dots of varying color and luminance arranged to form numbers visible only if certain cone pigments are functioning.
• Color-blind persons rely on luminance contrast and miss chromatic contrast patterns.

Cross Questions

• Q: What is the genetic basis of red-green color blindness? A: X-linked recessive; genes for M and L cone opsins are on the X chromosome.
• Q: Why are more males affected by color blindness than females? A: Males are hemizygous for X chromosome — one copy of a defective gene causes the condition; females need two defective copies.
• Q: What are the three types of cones and their peak sensitivities? A: S cones (420 nm, blue), M cones (534 nm, green), L cones (564 nm, red).
• Q: What is the Young-Helmholtz trichromatic theory? A: Color vision based on 3 types of cone receptors with different spectral sensitivities; all colors are perceived by the brain as combinations of these three signals.
• Q: What is the opponent-process theory of color vision? A: Color is processed in opponent pairs: red-green, blue-yellow, black-white; supported by ganglion cell and LGN responses.

---

18. Determination of Hearing Acuity

Aim

Equipment

A. Whisper Test

1. Examiner stands 60 cm behind subject (subject's eye covered).
2. Examiner whispers numbers after full exhalation.
3. Subject repeats what is heard.
4. Normal: Hears whisper at 60 cm.

B. Watch Tick Test

1. Hold a ticking watch near the ear; note maximum distance at which tick is heard.
2. Compare both ears.

C. Audiometry

• Pure-tone audiogram: Tests air and bone conduction thresholds at frequencies 250–8000 Hz.
• Normal threshold: ≤25 dB HL.
• Degree of loss: 26–40 mild, 41–55 moderate, 56–70 moderately severe, 71–90 severe, >90 profound.

Normal Hearing

• Frequency range: 20–20,000 Hz.
• Most sensitive: 1000–4000 Hz (speech range).
• Threshold of hearing: 0 dB (by definition).
• Threshold of pain: ~120–140 dB.

Cross Questions

• Q: What is presbycusis? A: Age-related bilateral sensorineural hearing loss — first affects high frequencies (4000–8000 Hz) due to loss of basal turn hair cells.
• Q: What is the range of human hearing? A: 20–20,000 Hz; most sensitive at 1000–4000 Hz.
• Q: What is a pure-tone audiogram? A: Graph plotting hearing threshold (dB) vs. frequency (Hz); determines degree, type, and configuration of hearing loss.
• Q: What structure in the cochlea is responsible for frequency discrimination? A: The basilar membrane — high frequencies → base (narrow, stiff); low frequencies → apex (wide, flexible). Tonotopic organization.
• Q: What causes noise-induced hearing loss? A: Destruction of outer hair cells (OHCs), particularly at 4000 Hz (corresponds to resonance frequency of ear canal) — irreversible sensorineural loss.

---

19. Comparison of Bone and Air Conduction (Rinne and Weber Tests)

Principle

• Air conduction (AC): Ear canal → tympanic membrane → ossicles → oval window → cochlea.
• Bone conduction (BC): Vibrations transmitted directly through skull bones → cochlea.

A. Rinne Test

1. Strike a 512 Hz tuning fork, place base on mastoid process (bone conduction).
2. When patient no longer hears it, immediately move fork to just outside external auditory meatus (air conduction).
3. If still heard → Rinne Positive (Normal or SNHL): AC > BC.
4. If not heard → Rinne Negative (Conductive HL): BC > AC.

B. Weber Test

1. Strike 512 Hz tuning fork, place base on midline of forehead.
2. Ask: "In which ear do you hear the sound louder?"
3. Lateralizes to better ear in unilateral SNHL.
4. Lateralizes to poorer (affected) ear in unilateral conductive HL.
5. No lateralization in normal hearing or symmetrical loss.

Combining Results

Cross Questions

• Q: Why does the Weber test lateralize to the affected ear in conductive hearing loss? A: Masking noise from the environment reaches the normal ear via air conduction, but not the affected ear (conductive block), so BC signal appears louder in the quiet (affected) ear.
• Q: What is a false Rinne negative? A: In severe unilateral sensorineural deafness, the tuning fork on the mastoid of the deaf ear is "heard" by the contralateral healthy cochlea via cross-cranial transmission, falsely suggesting conductive HL.
• Q: What does a 512 Hz tuning fork assess? A: Mid-frequency hearing — most sensitive for detecting clinically significant hearing loss affecting speech understanding.
• Q: Define conductive vs. sensorineural hearing loss. A: Conductive HL: defect in external ear canal, tympanic membrane, or ossicular chain — prevents sound from reaching cochlea. Sensorineural HL: defect in cochlear hair cells, cochlear nerve, or central auditory pathways.
• Q: What is the Schwabach test? A: Comparison of BC duration of the patient vs. the examiner (assumed normal hearing); patient's BC > examiner's BC in conductive HL; patient's BC < examiner's in SNHL.

---

20. Development of Conditioned Reflexes in Humans

Principle

Pavlov's Classic Setup

• UCS: Food → UCR: Salivation
• CS: Bell/light → initially no salivation
• CS + UCS repeated → after several pairings → CS alone → CR (salivation)

Human Laboratory Demonstration

1. Shine a bright light (UCS) in the eye → pupil constricts (UCR).
2. Sound a buzzer (CS) simultaneously with the light.
3. After 10–20 pairings, sound the buzzer alone.
4. Observation: Pupil constricts to the buzzer alone (CR).

1. Show/smell a lemon (UCS) → salivation (UCR).
2. Pair with a visual cue (CS: colored card).
3. After pairings, CS alone elicits salivation.

1. Electric shock (UCS) → GSR/skin conductance change (UCR).
2. Tone (CS) paired repeatedly.
3. Tone alone → GSR (CR).

Properties of Conditioned Reflexes

• Acquisition: Repeated CS-UCS pairing builds the CR.
• Extinction: CS presented repeatedly without UCS → CR gradually disappears.
• Spontaneous recovery: After extinction + rest, CR reappears when CS given.
• Generalization: Stimuli similar to CS also elicit CR.
• Discrimination: Differential reinforcement allows distinguishing CS+ from CS-.

Neural Basis

• CR formation involves strengthening of synapses (long-term potentiation, LTP) in the cerebral cortex (primarily) and amygdala/hippocampus.
• Pavlov called cortical neurons "analyzers" that form "temporary connections."
• CR can be extinguished by cortical inhibition.

Differences: Conditioned vs. Unconditioned Reflexes

Cross Questions

• Q: What is the difference between classical (Pavlovian) and operant (Skinnerian) conditioning? A: Classical conditioning associates two stimuli (CS-UCS); operant conditioning associates a behavior with its consequence (reinforcement/punishment).
• Q: What is extinction of a conditioned reflex? A: Gradual disappearance of the CR when the CS is repeatedly presented without reinforcement (UCS).
• Q: What brain structures are critical for forming conditioned fear responses? A: Amygdala (emotional conditioning), hippocampus (contextual conditioning), prefrontal cortex (extinction).
• Q: What is long-term potentiation (LTP) and its role in learning? A: Activity-dependent strengthening of synaptic transmission; requires NMDA receptor activation, calcium influx, and AMPA receptor insertion — the cellular basis of associative learning.
• Q: What is second-order conditioning? A: After CS1→UCR is established, a new CS2 is paired with CS1 (not directly with UCS); CS2 alone then elicits CR — a conditioned reflex built on a conditioned reflex.

---

Quick Reference Summary Table

---

---

How to Use This Guide

1. Aim — What the experiment demonstrates
2. Principle/Mechanism — The physiology behind it
3. Procedure — Step-by-step protocol
4. Key Observations & Results — What you see and record
5. Clinical/Physiological Significance — Why it matters
6. Cross Questions (5 per lab) — Most likely exam viva questions with model answers

---

High-Priority Cross Question Topics (Most Frequently Asked in Exams)

---

🧪 PHYSIOLOGY LAB SKILLS — Simple Language Guide

---

1. Preparation of a Neuromuscular Preparation

What is this?

Why a frog?

How to do it — Step by Step

1. Kill the frog (called "pithing") — insert a needle through the base of the skull to destroy the brain and spinal cord. This stops all movement and pain.
2. Remove the skin from the lower half of the body.
3. Find the sciatic nerve — it runs deep in the thigh muscle. Carefully expose it using glass hooks (NOT metal — metal can accidentally stimulate the nerve).
4. Free the nerve — cut it at the top, leaving it long.
5. Separate the gastrocnemius muscle — cut the Achilles tendon, tie a thread to it, cut the leg free below the knee.
6. Keep it wet with Ringer's solution — a special liquid similar to frog body fluid.
7. Attach the preparation to a recording machine (kymograph).

Why glass hooks?

What is Ringer's solution?

---

Cross Questions (Simple Q&A)

---

2. Galvani's First Experiment

What is this?

The Story

How it Works

1. Prepare a frog neuromuscular preparation.
2. Place it on a glass or wax surface (non-conducting).
3. Touch the nerve with a metal connected to an electrostatic machine or Leyden jar (stores electricity).
4. Result: The muscle contracts (kicks).
5. On non-conducting surfaces (glass, resin) — NO contraction. On conducting surfaces — contraction occurs.

What did Galvani conclude?

---

Cross Questions

---

3. Galvani's Second Experiment

What is this?

Simple Explanation

Two Ways to Do It

• Connect the nerve to the muscle using two different metals (e.g., brass hook + iron plate).
• Two different metals in contact with body fluids create a small current (like a battery).
• This current stimulates the nerve → muscle contracts.

• Place the nerve across the cut surface of a muscle.
• The cut (injured) area is electrically negative, the intact area is positive.
• This difference in charge stimulates the nerve → muscle contracts.
• No external electricity needed!

What this proved

Volta vs. Galvani argument

---

Cross Questions

---

4. Matteucci Experiment — Secondary Tetanus

What is this?

Simple Analogy

How to Do It

1. Take two frog neuromuscular preparations.
2. First preparation: Stimulate its nerve electrically → muscle contracts continuously = primary tetanus (like a strong sustained cramp).
3. Second preparation: Lay its nerve gently on top of the first preparation's contracting muscle.
4. Result: The second preparation's muscle also starts contracting = secondary tetanus — even though it was never directly stimulated!

Why does this happen?

What is Tetanus?

Modern Significance

---

Cross Questions

---

5. Summation of Stimuli

Simple Idea

---

5a. Successive Summation (Temporal Summation)

1. Find the threshold (minimum) stimulus strength for a muscle twitch.
2. Reduce to sub-threshold (below threshold — no twitch happens).
3. Apply two sub-threshold stimuli very quickly (within 2–3 ms apart).
4. Result: Muscle twitches — even though each stimulus alone was too weak!

---

5b. Spatial Summation

• Apply two pairs of electrodes at different points on the nerve.
• Each pair gives a sub-threshold stimulus simultaneously.
• Result: Muscle contracts — even though neither pair alone was sufficient.

---

Cross Questions

---

6. Reflex Time — Türck's Experiment

What is this?

Simple Analogy

What Makes Up Reflex Time?

• Sensor detects stimulus (e.g., pain/heat)
• Signal travels up the sensory nerve to the spinal cord
• A tiny delay at each synapse (0.3–0.5 ms per junction)
• Signal travels down the motor nerve to the muscle
• Muscle takes a moment to start contracting

How to Do It (Spinal Frog Method)

1. Remove only the frog's brain — keep the spinal cord intact (spinal frog, still has reflexes).
2. Hang the frog by its jaw.
3. Dip the toe into dilute acid or warm water — time how long before the leg pulls away.
4. Try different temperatures/acid strengths.

Key Finding

• Stronger stimulus → shorter reflex time (more nerve fibers activated quickly).
• Weaker stimulus → longer reflex time (takes more time to summate to threshold).
• Very strong stimuli → both legs withdraw (irradiation — signal spreads to the other side of spinal cord).

Typical Reflex Times (Human)

• Simple monosynaptic reflex (knee jerk): ~25–30 ms
• Polysynaptic reflex: >50–100 ms
• Voluntary reaction time: ~150–250 ms (much longer — needs brain)

---

Cross Questions

---

7. Dynamometry

What is this?

How to Do It

1. Hold the dynamometer tightly and squeeze as hard as you can.
2. Record the number shown (in kg).
3. Do it with the dominant hand, then the non-dominant hand.
4. Repeat squeezing every 10 seconds to demonstrate fatigue (watch the numbers go down).

Normal Values

• Adult men: 40–60 kg
• Adult women: 25–40 kg
• Dominant hand is ~10% stronger

What is Muscle Fatigue?

• ATP runs low — less energy for muscle fibers
• Lactic acid builds up — makes muscles feel sore and work poorly
• Phosphate accumulates — interferes with muscle contraction mechanism
• Potassium leaks out of muscle cells — disrupts electrical signaling

What affects grip strength?

• Age (peaks at 25–35 years)
• Sex (males > females)
• Training
• Tiredness/fatigue
• Dominant hand

---

Cross Questions

---

8. Patellar Tendon Reflex (Knee Jerk)

What is this?

Simple Story of What Happens

1. Hammer taps the patellar tendon.
2. This stretches the quadriceps muscle (front of thigh).
3. Muscle spindles (tiny sensors inside the muscle) detect the stretch.
4. Signal shoots to the spinal cord (L3–L4 level).
5. Signal bounces straight back to the muscle (only 1 synapse — very fast!).
6. Quadriceps contracts → leg extends (kicks).

Why is it Monosynaptic?

Grading (How Strong is the Reflex?)

• 0 = No response (absent)
• 1+ = Very weak
• 2+ = Normal
• 3+ = Brisk/exaggerated
• 4+ = Very brisk with clonus (repeated jerking)

What Abnormal Findings Mean

• Absent/reduced: Nerve damage (diabetes, disc problem at L3–L4)
• Exaggerated: Brain or spinal cord damage above L4 (stroke, MS)

Jendrassik Maneuver

---

Cross Questions

---

9. Brachial Extensor (Triceps) Reflex

What is this?

Simple Story

1. Tap triceps tendon above the elbow (olecranon).
2. Triceps muscle spindles detect the stretch.
3. Signal goes to spinal cord at C7 level.
4. Signal returns → triceps contracts → elbow extends.

How to Test

• Support the patient's arm at ~90° elbow flexion.
• Strike the triceps tendon just above the olecranon.
• Watch for elbow extension.

Clinical Meaning

• Absent triceps reflex = C7 nerve root problem or radial nerve damage.
• Exaggerated = UMN damage.

Biceps Reflex (Related)

• Strike biceps tendon in elbow crease.
• Elbow flexion occurs.
• Root level: C5–C6.

---

Cross Questions

---

10. Achilles Reflex (Ankle Jerk)

What is this?

Simple Story

1. Tap the Achilles tendon.
2. Calf muscle (gastrocnemius/soleus) spindles detect stretch.
3. Signal goes to S1 spinal cord level.
4. Signal comes back → calf muscles contract → foot points down.

How to Test

• Patient kneels on a chair with feet hanging.
• Tap the Achilles tendon with a reflex hammer.
• Watch foot flex downward.

Clinical Meaning

• Absent: S1 nerve root problem, sciatic nerve damage, diabetic neuropathy (very common!), Guillain-Barré syndrome.
• Delayed relaxation: Sign of underactive thyroid (hypothyroidism) — a classic finding!
• Exaggerated: UMN damage.

---

Cross Questions

---

11. Statokinetic Reflexes

What is this?

Simple Analogy

Key Sensors Involved

• Otolith organs (utricle + saccule): Detect gravity and straight-line movement (like in a car going forward or backward).
• Semicircular canals: Detect rotational movement (like spinning in a chair).
• Eyes + Proprioceptors: Support the vestibular information.

Key Reflexes

• Slow phase: Eyes move opposite to your last rotation direction (vestibular system still "thinks" you're spinning).
• Fast phase: Eyes snap back to center (brain corrects).

Lab Demonstration (Barany Chair)

1. Sit in a rotating chair, spin 10 times in 20 seconds, stop suddenly.
2. Observe your eyes moving rhythmically = post-rotational nystagmus.
3. You also feel you're still spinning — shows how vestibular system works.

---

Cross Questions

---

12. Danini-Aschner Reflex (Eye-Heart Reflex)

What is this?

Simple Story

1. Gentle pressure on the eyes activates pressure receptors in the eyeball.
2. Signal travels up the trigeminal nerve (V1) to the brainstem.
3. In the brainstem, it connects to the vagus nerve.
4. Vagus nerve slows the heart (SA node).
5. Result: Heart rate drops by 5–13 beats per minute.

How to Do the Test

1. Count pulse for 1 minute (baseline).
2. Press gently on both closed eyes for 20–30 seconds.
3. Count pulse again during pressure.
4. Release — pulse returns to normal.

Normal Response

Clinical Uses

• Tests vagal tone (how strong is the parasympathetic system?).
• Was once used to stop fast heart rhythms (SVT).
• Occurs during eye surgery — anesthesiologists must watch for it!

Danger!

What drug blocks it?

---

Cross Questions

---

13. Effect of Adrenaline on the Frog's Eye Pupil

What is this?

Simple Explanation

• Dilator muscle (like spokes of a wheel) — enlarges pupil — controlled by sympathetic nerves (adrenaline).
• Constrictor/sphincter muscle (like a ring) — shrinks pupil — controlled by parasympathetic nerves.

How to Do It

1. Take two frogs — one for experiment, one as control.
2. Put adrenaline (1:1000 solution) drops on one eye.
3. Put normal saline on the other eye (control).
4. Observe pupil size every 5 minutes.

Result

• Adrenaline eye: Pupil gets BIGGER (dilation = mydriasis).
• Control eye: No change.

Why?

Drug Comparison Table (Simple)

---

Cross Questions

---

14. Esthesiometry (Touch Sensitivity Test)

What is this?

Simple Analogy

Equipment

How to Do It

1. Subject closes eyes.
2. Apply both points of the esthesiometer to skin at the same time.
3. Gradually reduce the distance between the two points.
4. Ask: "Do you feel one or two points?"
5. Note the minimum distance where they correctly say "two."
6. Test different body parts.

Results — How Close Can Points Be and Still Feel Like TWO?

Why Fingertips Are Better

Clinical Use

• Peripheral nerve damage
• Spinal cord injury (dorsal column damage)
• Vitamin B12 deficiency

---

Cross Questions

---

15. Determination of Visual Acuity

What is this?

How to Do It

1. Stand or sit 6 meters (20 feet) from the Snellen chart.
2. Cover one eye.
3. Read the smallest line of letters you can see clearly.
4. Record the result as a fraction — e.g., 6/6.

What Does the Fraction Mean?

• The top number = how far away you are from the chart (always 6 m in this test).
• The bottom number = how far away a normal eye can read that same line.

• 6/6 = You read at 6 m what a normal person reads at 6 m → Normal.
• 6/12 = You read at 6 m what a normal reads at 12 m → Half of normal vision.
• 6/60 = You read at 6 m what a normal person could read from 60 m → Very poor vision.
• 6/5 or 6/4 = Better than normal (some people have super sharp vision).

Why 6 Meters?

Where Does Best Vision Come From?

What Reduces Acuity?

• Nearsightedness (myopia) — can't see far
• Farsightedness (hyperopia) — can't see close
• Astigmatism — blurry at all distances
• Cataract — cloudy lens
• Retinal disease

---

Cross Questions

---

16. Definition of the Field of View (Visual Field Testing)

What is this?

Simple Analogy

How to Do It (Basic Method — Confrontation Test)

1. Cover one eye.
2. Look straight at the examiner's nose.
3. Examiner slowly moves a finger in from the edge of your peripheral vision.
4. Tell the examiner when you first see the finger.
5. Test all four directions (up, down, left, right).

With a Perimeter (Arc Perimeter)

• Rest your chin on a support.
• Fix gaze on a central point.
• A white dot is moved along arcs from the outside inward.
• Mark where you first see it at each angle.
• The result is plotted on a visual field chart (like a map of your vision).

Normal Field Extent (One Eye)

• Outward (temporal): 90°
• Inward (nasal): 60°
• Upward: 50°
• Downward: 70°

Blind Spot

Common Field Defects and What They Mean

---

Cross Questions

---

17. Definition of Color Perception

What is this?

Equipment

How Color Vision Works

• Red cones (long wavelength, ~564 nm)
• Green cones (medium wavelength, ~534 nm)
• Blue cones (short wavelength, ~420 nm)

Types of Color Blindness

Why Are More Males Color Blind?

• Males affected: ~8%
• Females affected: <0.5%

Ishihara Test

• 38 plates shown at 75 cm in good daylight.
• Patient reads numbers seen in dot patterns.
• Color blind people miss or read different numbers.

---

Cross Questions

---

18. Determination of Hearing Acuity

What is this?

Simple Tests

• Stand 60 cm behind the patient (so they can't lip-read).
• Whisper numbers softly after breathing out.
• Patient repeats what they hear.
• Normal: Can hear a whisper from 60 cm.

• Hold a ticking watch next to the ear.
• Move it away gradually — note how far the patient can still hear it.
• Compare left and right ears.

• Patient wears headphones.
• Different sound frequencies (250–8000 Hz) are played at different loudness levels.
• Patient presses a button when they hear the sound.
• Results plotted on a graph (audiogram).
• Normal hearing: Can detect sounds up to 25 dB (decibels) or quieter.

Human Hearing Range

• Frequency: 20–20,000 Hz
• Most sensitive range: 1000–4000 Hz (this is the speech range — why we can hear people talking so well)
• Threshold of hearing: 0 dB (the quietest sound a normal ear can detect)
• Threshold of pain: ~120–140 dB

How Does the Ear Detect Different Pitches?

• High-pitched sounds vibrate the narrow, stiff base.
• Low-pitched sounds vibrate the wide, flexible apex. This is called tonotopic organization (different tones activate different locations).

---

Cross Questions

---

19. Bone vs. Air Conduction (Rinne & Weber Tests)

What is this?

1. Air conduction (AC): Sound waves → ear canal → eardrum → tiny ear bones (ossicles) → cochlea. This is the normal way.
2. Bone conduction (BC): Vibrations travel directly through the skull bones → directly to the cochlea, bypassing the eardrum and ossicles.

---

A. Rinne Test

1. Strike a 512 Hz tuning fork (makes it vibrate/hum).
2. Press the base (handle) on the mastoid bone behind the ear — patient hears via bone conduction.
3. When the patient says they no longer hear it, move the vibrating fork to just outside the ear canal — tests air conduction.
4. Ask: "Can you still hear it now?"

• Still hears it after moving to the ear canal = Rinne Positive = AC > BC = Normal ✓
• Cannot hear it after moving = Rinne Negative = BC > AC = Conductive hearing loss (problem in outer/middle ear)

---

B. Weber Test

1. Strike the tuning fork.
2. Place the handle on the middle of the forehead.
3. Ask: "Do you hear it in the middle, or more in one ear?"

• Hears equally both sides = Normal (or same loss in both ears)
• Hears louder in the better ear = Sensorineural hearing loss (nerve/cochlea damage) on the worse side
• Hears louder in the worse ear = Conductive hearing loss (eardrum/bone problem) on that side

---

Combining the Two Tests — Summary Table

---

Cross Questions

---

20. Development of Conditioned Reflexes in Humans

What is this?

The Famous Pavlov Example

• Ring a bell (just a noise, dog doesn't care) → Show food → Dog salivates (automatic)
• Repeat this many times: bell + food together
• Eventually: Ring bell ALONE → Dog salivates (even without food!)
• The dog has "learned" that bell = food coming

Human Lab Demonstrations

1. Flash bright light in eye → pupil constricts (automatic response).
2. Play a buzzer sound at the same time as the light — repeat 10–20 times.
3. Eventually: Play buzzer alone → pupil constricts (conditioned!).

1. Look at / smell a lemon → mouth waters (automatic).
2. Show a colored card at the same time — repeat many times.
3. Eventually: Show colored card alone → mouth waters (conditioned!).

1. Mild electric shock to hand → sweating/skin conductance change (automatic).
2. Play a tone with the shock — repeat many times.
3. Eventually: Tone alone → sweating occurs (conditioned!).

What Can Happen to a Conditioned Reflex?

Why Is This Important?

• Explains how habits and fears are formed.
• Basis of phobias (fear conditioned to specific triggers).
• Basis of behavioural therapy (extinction used to treat phobias).
• Explains placebo effect.

Brain Structures Involved

• Cerebral cortex: Main site for forming conditioned reflexes.
• Amygdala: Fear conditioning (learns what is dangerous).
• Hippocampus: Context learning (remembers where and when).
• Long-term potentiation (LTP): The cellular mechanism — synapses get stronger with repeated activation.

---

Cross Questions

---

🔑 MASTER CHEAT SHEET — One Line Each