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Physiology Exam Questions 11–30 — Simple Answers

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Q11. Importance of the Nervous System. Classifications by Morphological and Functional Features

• Controls and coordinates all body functions
• Maintains homeostasis
• Links the body to the external environment
• Basis of higher mental functions (memory, thinking, speech)

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Q12. Structure of a Neuron. Classifications by Morphological and Functional Features

• Cell body (soma): contains nucleus, Nissl bodies (ribosomes for protein synthesis)
• Dendrites: receive signals (input)
• Axon: carries impulse away from cell body (output); may be myelinated

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Q13. Neuroglia — Functions and Classification

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Q14. Nerve Fibers — Myelinated vs. Unmyelinated. Conduction of Excitation. Fast and Slow Fibers

• Covered by myelin sheath (from Schwann cells in PNS)
• Conduction is saltatory — impulse jumps from node of Ranvier to node
• Fast: ~70 m/s
• Examples: motor nerves, touch, proprioception (Type A fibers)

• No myelin sheath
• Conduction is continuous (slow)
• Slow: ~1 m/s
• Examples: pain (C fibers), autonomic fibers

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Q15. The Olfactory Analyzer

1. Receptor level: Olfactory receptor cells in the nasal mucosa (roof of nasal cavity) — bipolar neurons that detect odorant molecules
2. Conduction level: Axons form olfactory nerve (CN I) → olfactory bulb → olfactory tract
3. Cortical level: Primary olfactory cortex (piriform cortex, uncus of temporal lobe)

• Only sensory system that does not relay through thalamus first
• Directly connected to limbic system → explains emotional link to smell (memory, emotion)
• Receptor cells are replaced every ~30–60 days (neurogenesis)

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Q16. Physiology of Analyzers. General Principles of Organizing Analyzers

1. Peripheral (receptor) section — converts stimulus into nerve impulse
2. Conducting section — afferent nerve pathways carrying impulse to cortex
3. Central (cortical) section — located in cerebral cortex; responsible for perception and analysis

• Adequate stimulus: each receptor responds best to one specific type of stimulus
• Transduction: conversion of stimulus energy into electrical signal
• Coding: information is encoded by frequency, pattern of impulses
• Adaptation: receptors can adapt (decrease response) to a constant stimulus
• Projection: each receptor maps to a specific cortical area

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Q17. Chemical Synapses. Classifications. Electrical Synapses

Chemical Synapse

• Uses neurotransmitters (e.g. acetylcholine, dopamine, GABA)
• Structure: presynaptic terminal → synaptic cleft → postsynaptic membrane
• Mechanism: Action potential → Ca²⁺ enters → vesicles release neurotransmitter → binds receptors → postsynaptic potential

Electrical Synapse

• Connected by gap junctions
• Bidirectional, very fast, no delay
• Less common in adult nervous system
• Found in cardiac muscle, smooth muscle, some CNS neurons

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Q18. A Reflex. Reflex Arc. Mono- and Polysynaptic Arcs. Reflex Ring

1. Receptor
2. Afferent (sensory) nerve
3. Nerve center (in CNS)
4. Efferent (motor) nerve
5. Effector (muscle or gland)

• Only 1 synapse (sensory neuron directly synapses on motor neuron)
• Very fast
• Example: knee-jerk (patellar) reflex

• Has interneurons between sensory and motor neurons
• More complex response
• Example: withdrawal (flexor) reflex

• After the reflex response, information from the effector is sent back to the nerve center via afferent feedback
• This allows correction and fine-tuning of the response (closed-loop control)

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Q19. Classifications of Reflexes. Unconditioned vs. Conditioned Reflexes

• Inborn, genetically determined
• Permanent, stable throughout life
• Do not require learning
• Examples: sucking, swallowing, knee-jerk, pupillary reflex

• Acquired during individual life (learning)
• Require repeated pairing of conditioned + unconditioned stimulus
• Can be extinguished if not reinforced
• Examples: salivation at the sight/smell of food, traffic response

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Q20. The Gustatory (Taste) Analyzer

1. Receptors: Taste buds on papillae of the tongue (fungiform, vallate, foliate papillae); also on soft palate and epiglottis
2. Conducting pathway: CN VII (anterior 2/3 tongue), CN IX (posterior 1/3), CN X (epiglottis) → nucleus tractus solitarius (medulla) → thalamus (VPM nucleus)
3. Cortical area: Insular cortex and lower parietal operculum

• Bitter is most sensitive (protective — detects toxins)
• Taste receptor cells are replaced every ~10 days

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Q21. Inhibition in the CNS. Types of Inhibition

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Q22. Coordination of Body Functions. Nerve Center and Its Properties. Principles of Coordination

• One-way conduction — impulse travels in one direction (due to synapse polarity)
• Synaptic delay — time for chemical transmission (~0.5 ms per synapse)
• Summation — temporal and spatial
• Fatigue — nerve centers fatigue faster than nerve fibers
• Tone — centers have background spontaneous activity
• Plasticity — ability to reorganize after injury
• Sensitivity to hypoxia — highly sensitive to lack of oxygen

1. Reciprocal innervation — antagonist muscles are inhibited when agonist is active
2. Common final pathway (Sherrington) — many inputs converge on one motor neuron
3. Dominant focus (Ukhtomsky) — excited center suppresses others and draws their impulses
4. Feedback — output is compared with desired result and corrected

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Q23. Muscle Physiology. Muscle Contraction Modes

• Single twitch — response to one stimulus
• Tetanus — sustained contraction from repeated stimuli (see Q27)

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Q24. Types of Higher Nervous Activity (Pavlov). Temperaments (Hippocrates). Specific Human HNA Types

• Strength (strong/weak)
• Balance (balanced/unbalanced)
• Mobility (mobile/inert)

• Thinker type — 2nd signaling system dominant (abstract thinking, verbal)
• Artistic type — 1st signaling system dominant (concrete imagery, emotions)
• Mixed type — both systems balanced (most people)

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Q25. Characteristics of Human HNA. 1st and 2nd Signaling Systems. Speech

• Present in both animals and humans
• Reality signaled by direct sensory stimuli (sights, sounds, smells)
• Basis of concrete, sensory thinking

• Reality signaled by words (spoken, written, thought)
• Basis of abstract thinking, language, logical reasoning
• Located primarily in left hemisphere (speech centers)

• Broca's area (frontal lobe, left) — motor speech (speaking)
• Wernicke's area (temporal lobe, left) — sensory speech (understanding)
• Arcuate fasciculus — connects Broca's and Wernicke's areas

• Capacity for abstract thinking (only humans)
• Language and speech
• Social conditioning
• Consciousness and self-awareness
• Ability to create conditioned reflexes through words alone

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Q26. Mechanism of Muscle Contraction

1. Action potential arrives at neuromuscular junction
2. ACh released → binds receptors → muscle AP generated
3. AP spreads via T-tubules → reaches sarcoplasmic reticulum
4. Ca²⁺ released from sarcoplasmic reticulum
5. Ca²⁺ binds troponin → tropomyosin shifts → actin binding sites exposed
6. Myosin heads bind actin → form cross-bridges
7. Power stroke — myosin head pivots, pulling actin filament toward center (ATP → ADP + Pi used)
8. ATP binds myosin → cross-bridge detaches → myosin re-cocks
9. Cycle repeats → sarcomere shortens → muscle contracts
10. When stimulus stops → Ca²⁺ pumped back → troponin blocks actin sites → relaxation

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Q27. Single Muscle Contraction. Tetanus (Summation). Serrated and Smooth Tetanus

• Response to one stimulus
• 3 phases: latent period (1–2 ms) → contraction phase → relaxation phase
• Duration ~100 ms

• If a second stimulus arrives before the muscle fully relaxes → contractions add up

• Tetanic force is 4–5× greater than a single twitch
• Optimal frequency for smooth tetanus = when stimuli arrive during contraction phase

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Q28. Optimum and Pessimum Stimulation Frequency. Parabiosis (Vvedensky)

• Frequency of stimulation that produces maximum (strongest) contraction
• Each stimulus arrives during contraction phase of previous twitch → summation is maximal

• Frequency that produces weakest response (paradoxically — too high or too low)
• At very high frequency, stimuli arrive during refractory period → excitation decreases
• Discovered by Vvedensky

• A state between excitation and inhibition produced by applying a local, constant (non-pulsating) irritant to a nerve
• Stages of parabiosis (as irritant intensity increases):

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Q29. Mechanism of Formation of Conditioned Reflexes. Inhibition of Conditioned Reflexes

1. A neutral (conditioned) stimulus (e.g. bell) is repeatedly combined with an unconditioned stimulus (e.g. food)
2. The conditioned stimulus must precede the unconditioned stimulus
3. A temporary connection (cortical arc) forms between two excited cortical zones
4. After enough repetitions, the conditioned stimulus alone triggers the response
5. Requires intact cerebral cortex

• Conditioned stimulus must be presented before unconditioned
• Both stimuli must be significant to the animal
• Absence of strong distracting stimuli

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Q30. The Tactile (Skin) Analyzer

1. Receptors (peripheral level):
   • Meissner's corpuscles — light touch, fingertips
   • Pacinian corpuscles — deep pressure, vibration
   • Merkel's discs — sustained touch, fine detail
   • Ruffini endings — skin stretch, warmth
   • Free nerve endings — pain, temperature, crude touch
2. Conducting pathway:
   • Spinal nerve → dorsal horn → dorsal columns (medial lemniscus pathway) → thalamus (VPL nucleus)
3. Cortical area:
   • Primary somatosensory cortex (postcentral gyrus, parietal lobe — areas 1, 2, 3)
   • Body is mapped as somatotopic map (homunculus) — largest area for hands, lips, face

• Two-point discrimination: ability to distinguish two separate touch points (best at fingertips)
• Adaptation: Meissner's and Pacinian corpuscles adapt fast; Merkel's adapt slowly

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Study tip: For exams, remember each analyzer has 3 levels (receptor → conducting → cortical), reflexes need a 5-part arc, and Pavlov's 4 temperament types match Hippocrates' 4 types.