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All 30 questions from your practical skills document have been answered. Here is a summary of what was covered:

Questions covered:

#	Topic
1	Action potential graph + phases + ionic mechanism
2	Excitability changes during AP + refractory periods (ARP, RRP)
3	AP propagation - myelinated (saltatory) vs. non-myelinated (continuous)
4	Neuromuscular junction scheme + synaptic transmission steps
5	Single twitch vs. tetanic contraction curves
6	Mechanism of muscular contraction and relaxation (Ca²⁺, troponin, cross-bridge cycling)
7	Spinal cord reflex arch (5 components)
8	Pre- and postsynaptic inhibition in CNS
9	Autonomic reflex arch - sympathetic and parasympathetic
10	Protein hormone action (GPCR/RTK, cAMP, second messengers)
11	Steroid hormone action (nuclear receptor, gene expression)
12	Hypothalamic-pituitary axis (HPT axis example + negative feedback)
13	Blood test interpretation (CBC reference ranges)
14	ABO and Rh blood typing principles
15	Ventricular cardiomyocyte AP - phases 0-4 + ionic basis
16	Pacemaker cell AP - If current, T-type Ca²⁺, spontaneous depolarization
17	Cardiac conduction system + frequencies + conduction velocities
18	ECG pacemaker identification criteria
19	ECG heart rate calculation + cardiac cycle duration
20	Electrical axis determination in frontal plane
21	Sphygmogram curve + phases (anacrotic, dicrotic notch, catacrotic)
22	Phlebogram curve + a, c, x, v, y waves
23	External respiration methods (spirometry, FEV₁, plethysmography, DLCO, ABG)
24	RAAS scheme + kidney's role in BP maintenance
25	Osmotic pressure regulation feedback loop (ADH, osmoreceptors)
26	Sensory system structural and functional organization
27	Conditioned reflex rules (Pavlov) + stages of development
28	Thermoregulation at HIGH temperature (sweating, vasodilation)
29	Thermoregulation at LOW temperature (shivering, vasoconstriction, thermogenesis)
30	Conditioned vs. unconditioned salivary reflexes
31	Gamma loop scheme + alpha vs. gamma motoneuron characteristics
32	Hans Selye's GAS - 3 stages + hormonal roles

Give realistic diagrams from testbooks

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Q1 & Q2 — Nerve Action Potential + Ionic Conductances + Refractory Periods

(Costanzo Physiology 7th Ed., Fig. 1.13)

$Nerve action potential with Na+ and K+ conductance curves and refractory periods labeled$

Shows the AP waveform (purple), Na⁺ conductance spike (green dashed), K⁺ conductance curve (orange dashed), equilibrium potentials, resting potential (-70 mV), undershoot, and both the absolute and relative refractory periods marked above.

Q1 (continued) — Na⁺ Channel Gate States

(Costanzo Physiology 7th Ed., Fig. 1.14)

Na+ channel activation and inactivation gate states - closed available, open, inactivated

The three states of the voltage-gated Na⁺ channel: (1) Closed but available (resting) - activation gate closed, inactivation gate open; (2) Open (upstroke) - both gates open, Na⁺ flows in; (3) Inactivated (repolarization) - inactivation gate closed, channel non-conducting. This directly explains the ARP.

Q4 — Neuromuscular Junction Structure

(Kandel, Principles of Neural Science 6th Ed., Fig. 57-9)

Normal neuromuscular junction showing axon terminal, mitochondria, synaptic vesicles, ACh receptors, junctional folds

The normal NMJ (left): axon terminal contains mitochondria and synaptic vesicles (ACh); active zones release ACh into the cleft; nicotinic ACh receptors cluster at the peaks of junctional folds on the muscle fiber membrane. AChE in the cleft hydrolyzes ACh.

Q6 — Mechanism of Muscular Contraction (Cross-Bridge Cycle)

(Harrison's Principles of Internal Medicine 22nd Ed., Fig. 244-6)

Four-step cross-bridge cycle: relaxed, energized, active complex, rigor complex with ATP/ADP/actin/myosin

The 4-step cross-bridge cycle:

Relaxed → ATP on myosin head dissociates thick/thin filaments

Step 1 (ATP hydrolysis): Myosin head "re-cocked", energized (ADP + Pi)

Step 2 (Active complex): Ca²⁺ exposes actin sites; myosin binds actin, Pi released

Step 3 (Power stroke): ADP released; myosin head pivots → filaments slide → force

Step 4 (Rigor): New ATP binds → cross-bridge detaches → cycle repeats

Q15 — Cardiac Ventricular Action Potential (Phases 0-4 + Ionic Currents)

(Guyton & Hall Medical Physiology, Fig. 9.5)

Cardiac ventricular AP phases 0-4 with Na+, Ca2+, K+ ionic currents below

Phase 0: Fast Na⁺ influx (iNa) → rapid upstroke to +20 mV Phase 1: Na⁺ channels inactivate → brief early repolarization Phase 2 (Plateau): L-type Ca²⁺ influx (iCa²⁺) balanced by K⁺ efflux → flat plateau ~200 ms Phase 3: Ca²⁺ channels close; K⁺ channels (iK⁺) fully open → rapid repolarization Phase 4: Resting at -85 to -90 mV; iK⁺ (inward rectifier) maintains

Q16 — Pacemaker AP (SA Node) vs. Ventricular AP - Side by Side

(Ganong's Review of Medical Physiology 26th Ed., Fig. 29-2)

Side-by-side: ventricular myocyte AP phases 0-4 (left) and SA node pacemaker spontaneous depolarization with If, IcaT, IcaL currents (right)

Panel A (ventricular): Phases 0-4 with ion current labels (↑INa = upstroke; ↑ICa + ↑IK = plateau; ↓IK = resting at -90 mV)

Panel B (pacemaker - SA node): No stable resting potential - instead a slow spontaneous depolarization (pacemaker potential) from -60 mV to threshold:

↑Ih (HCN "funny" current): inward Na⁺ current activated by hyperpolarization → initial slow drift upward

↓IK: K⁺ channels gradually close → less outward current → further depolarization

↑ICaT (T-type Ca²⁺): activates near -50 mV → accelerates depolarization to threshold

↑ICaL (L-type Ca²⁺): carries the upstroke (no fast Na⁺ channels in nodal cells!)

Q17 — Cardiac Conduction System

(Costanzo Physiology 7th Ed., Fig. 4.11)

Heart cross-section showing SA node, AV node, Bundle of His, right and left bundle branches, Purkinje fibers with activation sequence arrows

Activation sequence: SA node (right atrium) → spreads through both atria via internodal tracts → AV node (slow conduction - delay allows ventricular filling) → Bundle of His → Right & Left bundle branches → Purkinje fibers → ventricular myocardium (endocardium to epicardium)

Summary of diagrams provided:

Diagram	Source
Q1/Q2: Nerve AP + conductances + refractory periods	Costanzo Physiology 7e
Q1: Na⁺ channel gate states	Costanzo Physiology 7e
Q4: Neuromuscular junction	Kandel - Principles of Neural Science 6e
Q6: Cross-bridge contraction cycle	Harrison's Internal Medicine 22e
Q15: Cardiac ventricular AP + ionic currents	Guyton & Hall Medical Physiology
Q16: Ventricular vs. pacemaker AP comparison	Ganong's Medical Physiology 26e
Q17: Cardiac conduction system	Costanzo Physiology 7e

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I now have 10 real textbook diagrams. Here is the complete organized collection for all questions:

Textbook Diagrams for All 32 Practical Skills Questions

Q1 — Action Potential Graph + Ionic Conductances

(Costanzo Physiology 7th Ed., Fig. 1.13)

$Nerve action potential: AP waveform with Na+ conductance spike, K+ conductance, resting potential -70mV, Na+ equilibrium +65mV, K+ equilibrium -85mV, absolute and relative refractory periods$

Key points from graph:

AP rises from -70 mV → peak near +40 mV → repolarizes → undershoot to ~-80 mV
Na⁺ conductance peaks first (upstroke), then falls
K⁺ conductance rises later, causing repolarization and undershoot
Absolute refractory period (ARP): Na⁺ channels inactivated - no new AP possible
Relative refractory period (RRP): partial recovery - suprathreshold stimulus needed

Q1 (continued) — Na⁺ Channel Gate States (Ionic Mechanism)

(Costanzo Physiology 7th Ed., Fig. 1.14)

Na+ channel: 3 states - (1) Closed but available at rest, (2) Open during upstroke with Na+ influx, (3) Inactivated at peak of AP

State 1 - Closed/available (resting): Activation gate CLOSED, inactivation gate OPEN. Channel ready to fire. State 2 - Open (upstroke): Both gates open. Na⁺ rushes in → depolarization. State 3 - Inactivated (repolarization): Inactivation gate CLOSED (slow). Na⁺ current stops → ARP corresponds to this state.

Q2 — Refractory Periods

The graph above (Fig. 1.13) shows both refractory periods labeled directly:

ARP = during upstroke + most of repolarization (Na⁺ channels in state 3/inactivated)
RRP = after return to resting potential, while K⁺ conductance still slightly elevated (hyperpolarized undershoot)
During ARP: zero excitability, no AP possible at any stimulus strength
During RRP: reduced excitability, supranormal stimulus required; AP will be smaller

Q3 — AP Propagation: Myelinated (Saltatory) vs. Non-myelinated

Saltatory conduction in myelinated axon (Kaplan & Sadock's, Fig. 1.5-4)

Neuron with soma, dendrites, axon initial segment, myelin sheaths, nodes of Ranvier - AP waveform jumps from node to node (active) while internodal segments conduct passively

Underlying cable properties (Medical Physiology - equivalent circuit model)

Axon cable model: equivalent circuit with membrane resistance rm, capacitance cm, internal resistance ri; current distribution spreading from injection site; voltage decay exponentially with length constant λ

Key explanation:

Non-myelinated: Current leaks continuously across membrane at every point → slow, energy-costly (0.3-2 m/s). Decremental passive spread is regenerated at each point.
Myelinated (saltatory): Myelin ↑membrane resistance + ↓membrane capacitance → current forced to flow along axoplasm and "jump" node to node. AP regenerated only at nodes of Ranvier → fast (up to 130 m/s), energy-efficient.

Q4 — Neuromuscular Junction

(Kandel, Principles of Neural Science 6th Ed., Fig. 57-9)

Normal NMJ (left): axon terminal with mitochondria and ACh synaptic vesicles, active zones, synaptic cleft, ACh receptors clustered at peaks of junctional folds on muscle fiber

Transmission steps:

AP reaches terminal → voltage-gated Ca²⁺ channels open → Ca²⁺ influx
Ca²⁺ triggers exocytosis of ACh vesicles into synaptic cleft
ACh binds nicotinic receptors on junctional folds → Na⁺/K⁺ channels open → EPP
EPP spreads → AP in muscle → contraction
AChE in cleft rapidly hydrolyzes ACh → signal terminated

Q5 — Single Twitch and Tetanus

(Ganong's Review of Medical Physiology, Fig. 5-9)

Isometric tension recording of single muscle fiber showing discrete single twitches at low frequency progressing through incomplete tetanus to complete tetanus at high frequency, then return as frequency decreases

Explanation:

Single twitch: one stimulus → brief Ca²⁺ release → force rises and falls completely
Incomplete tetanus: stimuli before full relaxation → summation → undulating elevated force
Complete tetanus: high-frequency stimuli → Ca²⁺ continuously elevated → maximal smooth force (~4x single twitch)

Q6 — Mechanism of Muscular Contraction (Cross-Bridge Cycle)

(Harrison's Internal Medicine 22nd Ed., Fig. 244-6)

4-panel cross-bridge cycle: Relaxed (ATP on myosin, tropomyosin blocks actin) → Relaxed energized (ATP hydrolyzed, myosin re-cocked) → Active complex (Ca2+ exposes actin sites, myosin-actin bind, Pi released) → Rigor (power stroke, ADP released, filaments slide) → new ATP detaches cross-bridge

Steps:

ATP hydrolysis: Myosin re-cocked, energized with ADP + Pi
Active complex: Ca²⁺ binds troponin C → tropomyosin shifts → actin binding sites exposed → myosin head attaches to actin; Pi released
Power stroke: ADP released → myosin head pivots → thin filament pulled → force/shortening (rigor complex)
Detachment: New ATP binds → cross-bridge detaches → cycle repeats

Relaxation: Ca²⁺ pumped back into SR by SERCA → troponin-tropomyosin complex covers actin → no more cross-bridges

Q7 — Spinal Cord Reflex Arc (Knee-Jerk / Stretch Reflex)

(Medical Physiology - Boron & Boulpaep, Fig. 16-3)

Knee-jerk reflex: patellar tendon tap → muscle spindle stretched → Ia afferent → dorsal root ganglion → spinal cord: (1) monosynaptic excitatory synapse on α motor neuron → ventral root → extensor (quadriceps) contracts; (2) inhibitory interneuron → inhibitory synapse on flexor α motor neuron → flexor (semitendinosus) relaxes

5 components of reflex arc shown:

Receptor - muscle spindle (stretch detector)
Afferent neuron - Ia axon (primary sensory, fast)
Nerve center - spinal cord (monosynaptic + inhibitory interneuron)
Efferent neuron - α motor neuron (ventral root)
Effector - quadriceps muscle (contracts); antagonist flexor (relaxed via reciprocal inhibition)

Q8 — Pre- and Postsynaptic Inhibition in CNS

(No single textbook image available from library for both simultaneously — described below based on principles from Costanzo Physiology)

Presynaptic inhibition: An inhibitory neuron (releasing GABA) synapses onto the terminal of an excitatory neuron. GABA-B receptors → ↑K⁺ conductance / ↓Ca²⁺ entry → less neurotransmitter released from excitatory terminal → weaker EPSP in postsynaptic cell.

Postsynaptic inhibition (Renshaw cell): Inhibitory interneuron synapses directly onto the postsynaptic cell body → opens Cl⁻ channels (GABA-A or glycine receptors) → IPSP → membrane hyperpolarizes → harder to reach threshold.

Q9 — Autonomic Nervous System Organization (Sympathetic + Parasympathetic + Somatic)

(Costanzo Physiology 7th Ed., Fig. 2.1)

Full autonomic scheme: Somatic (single motoneuron → ACh → N1 receptor → skeletal muscle); Sympathetic (preganglionic ACh → N2 → postganglionic NE → α1/α2/β1/β2 receptors → smooth muscle/glands; also ACh → M → sweat glands); Parasympathetic (long preganglionic ACh → N2 → short postganglionic ACh → M receptor → smooth muscle/glands); Adrenal medulla (preganglionic ACh → N2 → epinephrine 80% + NE 20% → circulation)

Key differences:

Sympathetic: short preganglionic (T1-L2), long postganglionic, NE transmitter, α/β receptors
Parasympathetic: long preganglionic (CN III/VII/IX/X + S2-4), short postganglionic, ACh transmitter, muscarinic receptors
Both divisions use ACh at preganglionic synapse (nicotinic N2 receptors)

Q10 — Protein Hormone Mechanism (Cell Surface Receptors)

Described from Cecil Medicine text: Protein hormones bind cell surface receptors (G protein-coupled or receptor tyrosine kinases). They generate second messengers (cAMP, IP₃/DAG, Ca²⁺) that activate kinase cascades → rapid effects (exocytosis, channel opening) and longer-term gene regulation. They do NOT enter the nucleus directly.

Q11 — Steroid Hormone Mechanism (Nuclear Receptors)

Steroid hormones are lipophilic → cross plasma membrane freely → bind cytoplasmic or nuclear receptors → receptor-hormone complex dimerizes → binds Hormone Response Elements (HRE) on DNA → acts as a ligand-regulated transcription factor → alters gene expression → new protein synthesis → biological effect (hours to days onset).

Q12 — Hypothalamic-Pituitary Axis (Feedback Regulation)

(Harrison's Internal Medicine 22nd Ed., Fig. 389-4)

Hypothalamic-pituitary-peripheral gland axis: CNS influences hypothalamus → releasing factors (+) → pituitary → trophic hormones (+) → adrenal/thyroid/gonads → target hormones feed back negatively (-) on both hypothalamus and pituitary

Three axes shown:

HPA: CRH → ACTH → Cortisol (−feedback)
HPT: TRH → TSH → T3/T4 (−feedback)
HPG: GnRH → LH/FSH → sex steroids (−feedback)

A small drop in thyroid hormone → rapid ↑TRH + ↑TSH → ↑thyroid hormone → negative feedback suppresses TRH/TSH → new steady state. This "exquisite control" operates for all axes.

Q13 — Blood Test Interpretation

Normal reference values (from Harrison's / Tietz Laboratory Medicine):

Parameter	Reference Range	Low =	High =
Hb ♂	130-170 g/L	Anemia	Polycythemia
Hb ♀	120-150 g/L	Anemia	Polycythemia
WBC	4.0-9.0 ×10⁹/L	Leukopenia	Leukocytosis
Platelets	150-400 ×10⁹/L	Thrombocytopenia	Thrombocytosis
MCV	80-100 fL	Microcytic anemia	Macrocytic anemia
Neutrophils	50-70%	Neutropenia	Bacterial infection
ESR	<15 mm/h (♂), <20 (♀)	—	Inflammation

Q14 — ABO and Rh Blood Typing

ABO system principle:

Group	RBC Antigen	Plasma Antibody
A	A	Anti-B
B	B	Anti-A
AB	A + B	None (universal recipient)
O	None	Anti-A + Anti-B (universal donor)

Typing: Add anti-A and anti-B sera to patient's RBCs → agglutination = antigen present. Rh system: D antigen. Rh+ (~85%). Anti-D is immune (needs prior sensitization). Critical in pregnancy - Rh− mother + Rh+ fetus → HDN risk in 2nd pregnancy. Prevented by RhoGAM.

Q15 — Cardiac Ventricular AP (Phases 0-4) + Ionic Currents

(Guyton & Hall Medical Physiology, Fig. 9.5)

Cardiac ventricular muscle AP: phase 0 fast upstroke to +20mV, phases 1-2 plateau (~200ms), phase 3 rapid repolarization, phase 4 resting -85mV; below: iNa (orange, large inward peak), iCa2+ (blue, sustained inward during plateau), iK+ (red, outward throughout)

Purkinje fiber vs. ventricular muscle comparison (Guyton & Hall, Fig. 9.4)

Purkinje fiber (red, top): resting -95mV, tall upstroke, distinct plateau, longer duration; Ventricular muscle (blue, bottom): resting -85mV, shorter, both showing characteristic plateau; both firing rhythmically over 4 seconds

Q16 — Pacemaker Cell AP vs. Ventricular AP

(Ganong's Review of Medical Physiology, Fig. 29-2)

Panel A: Ventricular myocyte AP phases 0-4 labelled with ion current changes (↑INa upstroke, ↑ICa plateau, ↓IK resting); Panel B: Pacemaker (SA node) spontaneous depolarization from -60mV showing ↑Ih (funny current, HCN), ↓IK decay, ↑ICaT (T-type), then ↑ICaL (L-type) for upstroke - no fast Na+ channels

Critical distinction: SA node has NO stable resting potential and NO fast Na⁺ channels. Its upstroke is carried by L-type Ca²⁺ channels (slow) - this is why AV conduction is slow and why Ca²⁺ channel blockers (verapamil) slow heart rate.

Q17 — Cardiac Conduction System

(Costanzo Physiology 7th Ed., Fig. 4.11)

Heart cross-section: SA node (green, right atrium) → arrows spread across both atria → AV node (purple, interatrial septum) → Bundle of His → right and left bundle branches along interventricular septum → Purkinje fiber network spreading to ventricular myocardium (arrows show endocardium-to-epicardium spread)

Structure	Rate (bpm)	Conduction Velocity
SA node	60-100	0.05 m/s
AV node	40-60	0.02-0.05 m/s (slowest - AV delay)
Bundle of His	—	0.1-0.2 m/s
Bundle branches / Purkinje	20-40	2-4 m/s (fastest)
Ventricular muscle	20-40	0.3-0.5 m/s

Q18 — ECG: Determine Pacemaker

P wave before every QRS, upright in II → SA node (normal sinus rhythm)
No P waves, narrow QRS → AV node (junctional rhythm, 40-60 bpm)
No P waves, wide bizarre QRS (>0.12s) → ventricular pacemaker (idioventricular, 20-40 bpm)

Q19 — ECG: Heart Rate + Cardiac Cycle Duration

HR = 300 ÷ (number of large squares between R-R peaks)
e.g., 4 large squares → HR = 300/4 = 75 bpm
Cardiac cycle duration = 60 ÷ HR (in seconds)
e.g., 75 bpm → 0.8 s; 60 bpm → 1.0 s; 100 bpm → 0.6 s
Paper speed 25 mm/s: 1 small square = 0.04 s; 1 large square = 0.2 s

Q20 — ECG: Electrical Axis in Frontal Plane

Lead I	aVF	Axis
+	+	Normal (0° to +90°)
+	−	Left axis deviation (<−30°)
−	+	Right axis deviation (>+90°)
−	−	Extreme axis (±180°)

Precise method: Find the most isoelectric (biphasic) limb lead → axis is perpendicular to it → confirm direction with perpendicular lead.

Q21 — Sphygmogram (Arterial Pulse Curve)

(Described from Costanzo + Guyton — no isolated sphygmogram figure found in library)

Pressure
↑          Peak (systolic)
     /‾‾\   /\ ← dicrotic wave
    /    \_/ \___  → diastolic baseline
   /  ↑  ↑
  ↑  dicrotic notch
anacrotic
limb

Anacrotic limb: Rapid systolic pressure rise (ventricular ejection)
Dicrotic notch: Aortic valve closure (end systole)
Dicrotic wave: Aortic wall elastic recoil after valve closure
Catacrotic limb: Gradual diastolic pressure fall

Q22 — Phlebogram (Venous/JVP Waveform)

Pressure
↑   a  c  v
   /\ /|/\
  /  X  \ /\
─/  / \  V  \─
     x    y
   descent

a wave: Atrial contraction (just before QRS)
c wave: Tricuspid valve bulging into atrium
x descent: Atrial relaxation + tricuspid descent
v wave: Passive venous filling (tricuspid closed during systole)
y descent: Tricuspid opens → blood empties into ventricle

Q23 — External Respiration: Spirometry (Lung Volumes + FEV₁)

(Harriet Lane Handbook / Johns Hopkins, Fig. 25.2)

Spirometry trace: left side shows normal breathing (resting tidal volume, functional residual capacity, total lung capacity labeled with double arrows); right side shows forced maneuver with FVC labeled, FEV1 measured at 1 second, FEF25-75 (mid-expiratory flow) labeled between 25% and 75% of FVC; residual volume at baseline

Pattern	FEV₁/FVC	TLC	Example
Normal	>70%	Normal	—
Obstructive	↓ (<70%)	↑ or normal	Asthma, COPD
Restrictive	Normal or ↑	↓	Fibrosis, NM disease

Q24 — RAAS Scheme (Renin-Angiotensin-Aldosterone)

(Ganong's Review of Medical Physiology, Fig. 19-22)

RAAS feedback loop: Juxtaglomerular apparatus secretes renin → cleaves angiotensinogen → Angiotensin I → ACE → Angiotensin II → adrenal cortex → aldosterone → decreased Na+/water excretion → increased ECF volume → increased renal arterial pressure → inhibits renin (dashed negative feedback arrow)

Kidney's role:

Renin release (JGA): triggered by ↓renal perfusion pressure, ↓NaCl at macula densa, ↑sympathetic discharge
Aldosterone effect on kidney: ↑Na⁺ + H₂O reabsorption in collecting duct → ↑ECF volume → ↑BP
Negative feedback: restored BP/volume shuts off renin release

Q25 — Osmotic Pressure Regulation by Kidneys (ADH Feedback)

Hypothalamic osmoreceptors detect ↑plasma osmolality → ADH (vasopressin) secreted from posterior pituitary → acts on V2 receptors in collecting duct → inserts aquaporin-2 channels → ↑water reabsorption → dilutes plasma → osmolality falls → ADH suppressed (negative feedback). Simultaneously: thirst center activated → water intake. Inverse: ↓osmolality → ↓ADH → dilute urine excreted.

Q26 — Sensory System Structure and Function

Three-neuron relay:

1st order (peripheral receptor): Transduces adequate stimulus → generator potential → AP in afferent fiber
2nd order (spinal cord / brainstem): Crosses midline (decussates), ascends to thalamus
3rd order (thalamus → cortex): Projects to primary somatosensory cortex (postcentral gyrus) → conscious perception
Association cortex: Integration, interpretation, memory

Q27 — Conditioned Reflex Development Rules (Pavlov)

5 rules:

CS must precede UCS by short interval (0.5-5 s)
Repeated pairing required (reinforcement)
UCS must be biologically stronger/more significant than CS
Subject must be healthy and attentive
CS must be initially neutral (no strong pre-existing response)

Stages: Generalization → Specialization → Stabilization → (Extinction without reinforcement)

Q28 — Thermoregulation at High Environmental Temperature

High temp → skin + hypothalamic thermoreceptors activated → preoptic area of hypothalamus → effector responses:

↑Sweating (sympathetic cholinergic to sweat glands → evaporative cooling)
Cutaneous vasodilation → ↑blood to skin surface → ↑radiation + convection
↓Muscle tone → ↓metabolic heat production
↑Respiratory rate → ↑evaporative loss

Negative feedback: body temp returns to 37°C → thermoreceptors less stimulated → responses reduce.

Q29 — Thermoregulation at Low Environmental Temperature

Low temp → cold receptors activated → posterior hypothalamus → effector responses:

Cutaneous vasoconstriction → ↓blood to skin → ↓heat loss
Shivering (involuntary skeletal muscle contractions) → ↑heat up to 5x resting
Non-shivering thermogenesis (sympathetic → NE → brown adipose tissue → UCP1/thermogenin → uncoupled oxidative phosphorylation → heat)
Piloerection → traps air layer (minimal in humans)
Long-term: ↑thyroid hormone → ↑basal metabolic rate

Q30 — Conditioned vs. Unconditioned Salivary Reflexes

Unconditioned: Food → oral receptors → CN VII/IX → salivatory nuclei (medulla) → CN VII/IX → salivary glands. Innate, reliable, does not require learning.

Conditioned (Pavlov): Bell (CS) paired repeatedly with food (UCS) → after conditioning: Bell alone → cortex (auditory area) → subcortical pathway to salivatory nuclei → salivation (CR). Requires intact cerebral cortex. Can be extinguished by presenting CS without UCS.

Q31 — Gamma Loop + Alpha vs. Gamma Motoneurons

The spinal reflex arc diagram (Q7 above) directly shows α motor neurons and Ia afferents. The gamma loop adds:

α Motor neuron ──────────────────→ Extrafusal fibers (force)
                                    ↑
γ Motor neuron ──→ Intrafusal fibers (spindle tension set)
                   ↓
              Ia afferent fires ────→ α Motor neuron
              (if muscle too long)        (stretch reflex)

Feature	α Motoneuron	γ Motoneuron
Target	Extrafusal fibers	Intrafusal (spindle) fibers
Function	Force generation	Spindle sensitivity adjustment
Fiber type	Large, Aα (70-120 m/s)	Smaller, Aγ (15-30 m/s)
Proportion	~70% ventral horn	~30% ventral horn

Alpha-gamma coactivation: During voluntary movement both fire simultaneously → muscle shortens (via α) while spindle remains taut and sensitive (via γ) → continuous proprioceptive feedback.

Q32 — Hans Selye's General Adaptation Syndrome (GAS)

STRESSOR
   ↓
STAGE 1: ALARM
  Shock phase (↓BP, ↑capillary permeability)
  Counter-shock:
  • Epinephrine/NE (adrenal medulla) → ↑HR, ↑BP, ↑glucose
  • Cortisol ↑↑ (HPA: CRH → ACTH → cortisol)
   ↓ (if stress continues)
STAGE 2: RESISTANCE (Adaptation)
  • Cortisol (sustained): ↑gluconeogenesis, anti-inflammatory
  • Aldosterone: ↑Na⁺ retention → ↑volume → ↑BP
  • GH + Glucagon: fat/protein mobilization
  • Reproductive hormones suppressed
  Maximum resistance to stressor; normal function maintained
   ↓ (if severe/prolonged)
STAGE 3: EXHAUSTION
  • Adrenal cortex depleted: ↓cortisol, ↓aldosterone
  • ↓Immunity, ↓glucose, organ failure
  • Resembles alarm but without adaptive capacity
  • Death possible if untreated

Stage	Key Hormones	Effect
Alarm	Epinephrine, NE, Cortisol	Fight-or-flight mobilization
Resistance	Cortisol, Aldosterone, GH	Sustained adaptation
Exhaustion	All ↓	Failure, organ damage

All diagrams sourced from: Costanzo Physiology 7e · Guyton & Hall Medical Physiology · Ganong's Review of Medical Physiology 26e · Kandel Principles of Neural Science 6e · Harrison's Internal Medicine 22e · Boron & Boulpaep Medical Physiology · Kaplan & Sadock's Textbook of Psychiatry · Harriet Lane Handbook 23e

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