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Anatomy & Physiology: Nervous System and Sensory Pathways

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  • Cranial Nerve I (Olfactory)

    Type: Sensory. Originates from olfactory epithelium through cribriform plate to olfactory bulb. Function: smell. Unique as the only sense that bypasses the thalamus first.

  • Cranial Nerve II (Optic)

    Type: Sensory. Path: retina → optic chiasm → thalamus → occipital cortex. Function: vision. Crossing at chiasm allows visual field processing.

  • Cranial Nerve III (Oculomotor)

    Type: Motor. Origin: midbrain → superior orbital fissure. Functions: eye movement, pupil constriction via parasympathetic fibers.

  • Sensory vs Motor Cranial Nerves

    Sensory: I, II, VIII. Motor: III, IV, VI, XI, XII. Mixed: V, VII, IX, X.

  • Parasympathetic Cranial Nerves

    Cranial nerves III, VII, IX, and X carry parasympathetic fibers controlling rest and digest functions.

  • Spinal Nerves Overview

    31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal. All are mixed nerves with sensory and motor fibers.

  • Dorsal vs Ventral Roots

    Dorsal root: sensory (afferent) fibers entering spinal cord. Ventral root: motor (efferent) fibers exiting spinal cord.

  • Phrenic Nerve

    Originates from C3–C5 cervical plexus. Innervates diaphragm and is essential for breathing.

  • Brachial Plexus Major Nerves

    Includes axillary (shoulder abduction), musculocutaneous (elbow flexion), median (forearm flexors, grip), ulnar (hand muscles), and radial (arm extension) nerves.

  • Lumbar Plexus Functions

    Formed by L1–L4 ventral rami. Controls thigh muscles and sensation. Major nerves: femoral (knee extension) and obturator (thigh adduction).

  • Sacral Plexus and Sciatic Nerve

    Formed by L4–S4 ventral rami. Supplies lower limb. Sciatic nerve is largest, splitting into tibial (plantar flexion) and common fibular (dorsiflexion) nerves.

  • Brain Development Vesicles

    Neural tube forms forebrain (telencephalon, diencephalon), midbrain, and hindbrain (metencephalon, myelencephalon).

  • Gray vs White Matter

    Gray matter contains neuron cell bodies for processing; white matter contains myelinated axons for communication.

  • Cerebral Cortex Functions

    Responsible for conscious thought, voluntary movement, memory, language, and sensory perception.

  • Primary Motor Cortex

    Located in frontal lobe; controls voluntary movement with a motor homunculus mapping body regions.

  • Broca's Area

    Located in frontal lobe, usually left hemisphere; responsible for speech production.

  • Thalamus Function

    Acts as sensory relay station for all sensory afferent fibers to the cerebral cortex; involved in motor signals and memory.

  • Hypothalamus Role

    Maintains homeostasis by controlling autonomic nervous system and hormone release; main ANS control center.

  • Reticular Formation

    Maintains cortical arousal (RAS), filters sensory input, and controls motor pathways; damage can cause coma.

  • Cerebellum Function

    Coordinates movement by comparing intended vs actual movement using input from motor cortex, brainstem, and sensory receptors.

  • Sensory Receptor Types by Stimulus

    Mechanoreceptors (touch), thermoreceptors (temperature), photoreceptors (light), chemoreceptors (chemicals), nociceptors (pain).

  • Sensory Receptor Types by Location

    Exteroceptors (external stimuli), interoceptors (internal organs), proprioceptors (body position).

  • Pain Fiber Types

    Fast pain: A-delta fibers (sharp). Slow pain: C fibers (dull). Pain modulated by endorphins at thalamus.

  • Autonomic Nervous System Divisions

    Parasympathetic: rest & digest, decreases heart rate, increases digestion. Sympathetic: fight/flight, increases heart rate and energy.

  • Parasympathetic vs Sympathetic Differences

    Origin: craniosacral vs thoracolumbar. Fiber length: long preganglionic vs short preganglionic. Ganglia location: near organ vs near spinal cord.

  • Taste Pathway Cranial Nerves

    Taste signals carried by cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) to medulla, thalamus, then gustatory cortex.

  • Phototransduction Process

    Light activates rhodopsin → transducin → PDE → cGMP decreases → Na⁺/Ca²⁺ channels close → photoreceptor hyperpolarizes.

  • Rods vs Cones

    Rods: dim light, peripheral vision, sensitive, no color. Cones: bright light, high resolution, color vision.

  • Visual Pathway to Brain

    Retina → optic nerve → optic chiasma (nasal fibers cross) → optic tract → thalamus → optic radiations → primary visual cortex.