Week 9 - Spinal Cord and Spinal Nerves

Descending tracts

Carry motor signals to body

Pacinian corpuscles

Deep pressure/vibration

CN IX (9) Glossopharyngeal

Taste, swallowing

CN XII hypoglossal

Tongue movement

Spinal cord (Conduction)

Transmits signals up and down; connects brain and body

Spinal cord neural integration

Processes input and produces appropriate output

Spinal cord locomotion

Central pattern generators control repetitive movement (walking)

Spinal cord reflexes

Rapid, involuntary responses to stimuli

Cervical enlargement

Supplies upper limbs

Dorsal funiculus

Sensory (ascending)

Ventral funiculus

Motor (descending)

Ascending tracts

Carry sensory info to brain

Third-order neuron

Thalamus → cortex

Upper motor neuron

Starts in brain → spinal cord

Lower motor neuron

Spinal cord → muscle

Nerve

Bundle of axons with connective tissue

Endoneurium

Wraps individual fibers

Perineurium

Wraps fascicles

Epineurium

Wraps entire nerve

Dorsal root

Sensory (afferent)

Cervical plexus

Head/neck (C1-C5)

Brachial plexus

Arms (C5-T1)

Lumbar plexus

Lower abdomen/legs (L1-L4)

sacral plexus

Lower limbs (L4-S4), gives sciatic nerve

Stretch reflex

Muscle contracts when stretched

Flexor reflex

Withdrawal from pain

Crossed extensor reflex

Opposite limb stabilizes

Tendon reflex

Prevents muscle damage from stretch

Sensory (afferent) division

Carries signals to CNS

Optic chiasm

Crossing of optic nerves

Lateral geniculate nucleus

Thalamus relay for vision

Visual cortex

Processes vision

Baroreceptors

Detect blood pressure

Vagus nerve role

Lowers heart rate

Free nerve endings

Pain/temp

Merkel discs

Light touch

Meissner corpuscles

Light touch/texture

Muscle spindles

Detect stretch

Golgi tendon organs

Detect tendon tension

Corticospinal tract

Controls voluntary movement

Autonomic nervous system

Controls organs/glands

Sympathetic division

Fight or flight

Parasympathetic division

Rest and digest

Parasympathetic effects

↓HR, ↑digestion, energy conservation

CN I Olfactory Nerve

Olfactory (smell)

CN III Oculomotor

Eye movement, pupil

CN V (5) Trigeminal Nerve

Face sensation, chewing

CN VI (6) Abducens

Lateral eye movement

CN VII (7) Facial nerve

Facial expression, taste

CN VIII (8) Vestibulocochlear

Hearing, balance

CN X (10) Vagus Nerve

Organs, parasympathetic

CN XI (11) Spinal Accessory

Neck muscles

Gustation

Taste

Taste buds

Detect chemicals

Olfaction

Smell

Auditory pathway

Sound → eardrum → ossicles → cochlea → nerve

Semicircular ducts

Detect rotation

Saccule & utricle

Detect position/linear movement

Spinal cord location

Foramen magnum → vertebral canal → ends at L1

Number of spinal nerves

31 pairs

Lumbosacral enlargement

Supplies lower limbs and pelvis

Medullary cone

Tapered end of spinal cord

cauda equina

Bundle of nerve roots below L2

Gray matter

Contains neuron cell bodies, dendrites

White matter

Myelinated axons forming tracts

Lateral funiculus

Sensory + motor (MIX)

Decussation

Crossing of nerve fibers

First-order neuron

Detects stimulus → spinal cord

Second-order neuron

Spinal cord → thalamus

Schwann cells

Produce myelin in PNS

Ventral root

Motor (efferent)

Dorsal root ganglion

Contains sensory neuron cell bodies

Ganglion

Cluster of neuron cell bodies in PNS

Somatic reflex

Fast, involuntary, predictable response

Optic nerve

CN II carries vision signals

Visceral sensory division

Signals from organs

Receptor

Detects stimulus

Ruffini corpuscles

Pressure/stretch

Pain pathway

Skin → spinal cord → thalamus → cortex

Somatic motor division

Controls skeletal muscle

Autonomic tone

Baseline activity of both systems

Sympathetic effects

↑HR, ↑BP, bronchodilation, ↓digestion

CN II: Optic Nerve

Optic (vision)

CN IV (4) Trochlear

Eye movement

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