The Spinal Cord & Peripheral

Nervous System

Lesson 7

Dorsal

Ventral

Horns

Spinal Cord

Dorsal root ganglion (DRG) Sensory input

Ventral root Motor output

Caudal spinal cord Cauda equina ~

Spinal Cord Tracts

Major descending & ascending tracts Motor 1. corticospinal tract

distal muscles only descending tract with overt

effects 1a. Rubrospinal tract

Red nucleus to spinal cord ~

Spinal Cord Tracts Sensory 2. Dorsal column-medial lemniscal tract

touch, vibration, & proprioception axons ascend ipsilaterally synapse then decussate at medulla

3. Spinothalamic tract (anterolateral) pain & temperature decussate at SC entry level ascends contralaterally ~

Medulla

Dorsal column-medial lemniscal path

Spinothalamic path

Corticospinal tract

Dorsal

Ventral

Spinal Cord

Peripheral N. S.

Cranial Nerves - 12 pair Spinal Nerves - 31 pair Somatic Division

Sensory info Body Movement

Autonomic division - Homeostasis regulation ~

Cranial Nerves

From ventral surface numbered anterior posterior

Sensory, motor, or mixed Mnemonic ~

Oh

Oh

Oh

To

Touch

And

Feel

Very

Green

Vegetables

A

H

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Facial

Vestibulococlear

Glossopharangeal

Vagus

Accessory (Spinal)

Hypoglossal

I

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

On

Old

Olympus’s

Towering

Top

A

Famous

Vocal

German

Viewed

Some

Hops

Spinal Nerves

1 pair for each vertebral segment 8 pr. cervical (C1-C8) 12 pr. thoracic (T1-T12) 5 pr. lumbar (L1-L5) 5 pr. sacral (S1-S5) 1 pr coccygeal ~

Spinal Nerves

Thoracic nerves relatively smallback & ribs

Cervical, lumbar, & sacral: large nervesrest of the body

All Interconnect after leaving vertebral canal form 4 major plexuses

cervical, brachial, lumbar, sacral~

Somatic Nervous System Sensory input

receptors DRG dorsal SC Dorsal column-medial lemniscal pathway Spinolthalamic tract

Motor output Lateral SC ventral horns muscles Corticospinal tract Rubrospinal tract ~

Dermatomes

Sensory innervation each spinal nerve has receptive

field Overlap at distal branches

redundancy retain some sensation even if a

complete spinal nerve destroyed ~

The Lateral Pathway

Voluntary movement distal limbs 2 tracts

Corticospinal tractabout 1 million axons

Rubrospinal tractsmall part of pathway ~

Somatic N.S.: Motor Output

Motor N.S. Striate muscle

uninterrupted neurona motor neuron

nerve-dependent Excitatory only at neuroeffector synapse

NT is acetylcholine (ACh)cholinergic

Nicotine = direct agonist (AG) Curare = direct antagonist (ANT) ~

Somatic Motor N. S.

Spinal Cord

Motor Neuron

Effector

ACh

Autonomic N. S.

Homeostasis Effectors

Smooth Muscle Cardiac Muscle Glands ~

Autonomic Subdivisions

Not nerve-dependent Sympathetic

Emergency, flight/fight Parasympathetic

Conservation / vegetative ~

Effector

Ganglion

Preganglionic neuron

Postganglionic neuron

Autonomic N. S.: General Features

Effector

Autonomic N. S.: General Features

ACh

Ganglionic synapse: Nicotinic (nACh) different than neuromuscular

Neuroeffector junction Sympathetic: Norepinephrine Parasympathetic: nACh & mACh ~

Sympathetic vs. Parasympathetic

Sympathetic ganglia near spinal cord interconnected active together long-lasting effects

Parasympathetic ganglia near effector discrete active independently transient effects

Antagonistic regulation ~

Effector Responses

Effector Sympathetic Parasympathetic

Heart Respiration GI Immune system Iris (radial) (sphincter)

Sweat glands no input

Adrenal glands no input ~

Parasympathetic

Post-Pre-

Sympathetic

Adrenal Glands

ACh

Glands

Smooth muscle

NE

Sympathetic Arousal Syndrome

Fight or flight situations Diffuse sympathetic activation

Adrenal glands releases NE into blood maintains sympathetic arousal

Parasympathetic rebound antagonistic regulation ~