spinal cord test 4- rileys

functions of spinal cord

conduction, neural integration, locomotion, reflexes

conduction

nerve fibers conduct sensory and motor information up and down the spinal cord

neural integration

spinal neurons receive input from multiple sources, integrate it, and execute appropriate output (e.g., bladder control)

Locomotion

spinal cord contains central pattern generators: groups of neurons that coordinate repetitive sequences of contractions for walking

refelxes

involuntary, responses to stimuli

- vital to posture, coordination, and protection

spinal cord

cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull

segment

part of the spinal cord supplied by each pair of spinal nerves

cervical enlargement

nerves to upper limb

lumbar enlargement

nerves to pelvic region and lower limbs

medullary cone

cord tapers to a point inferior to lumbar enlargement

cauda equina

bundle of nerve roots that occupy the vertebral canal from L2 to S5

meninges

three fibrous membranes that enclose the brain and spinal cord

dura matter

surrounds spinal cord and is separated from vertebrae by epidural space

arachnoid matter

adheres to dura and is seperated from pia by fibers spanning the subarachnoid space that is filled with cerebral spinal fluid

pia matter

delicate membrane that follows contours of spinal cord and continues inferiorly as fibrous terminal filum that fuses with dura to coccygeal ligament

gray matter

neuron cell bodies, dendrites, and unmyelinated axons

- site of info processing and synaptic integration

white matter

abundantly myelinated axons

Carry signals from one part of the CNS to another

gray commissure

connects right and left sides

- has central canal lined with ependymal cells filled with CSF

lateral horn (gray matter)

contains neurons of sympathetic nervous system

columns/funiculi (white matter)

three pairs of these white matter bundles

- posterior, lateral, anterior on each side

-tracts/ fasciculi divsions of each column

ascending tracts

carry sensory info up

descending tracts

carry motor info down

Decussation

crossing in the midline that occurs in many tracts so that brain senses and controls contralateral side of the body

contralateral

when the origin and destination of a tract are on opposite sides of the body

ipsilateral

when the orgin and destination of a tract are on the same side of the body and does not decussate

sensory signals travel across ___

3 neurons

- first order: detect stimulus and transmit signal to spinal cord or brainstem

- second order: continues to the thalamus at the upper end of the brainstem

- third order: carries the signal the rest of the way to sensory region of cerebral cortex

descending tracts involve ____

2 motor neurons

- upper motor neuron: starts in cerebral cortex or brainstem and terminates on lower motor neuron

- lower motor neuron: nuerosoma is in brainstem and spinal cord

Corticospinal Tracts

carry signals from cerebral cortex for precise fine movement

pyramids

ridges on anterior surface of medulla formed from fibers of this system

- most fibers decussate in lower medulla

nerve

cord like organ composed of numerous nerve fibers bound together by connective tissue

nerve fibers in PNS

surrounded by Schwann cells that form neurilemma and myelin sheath around axon

endoneurium

loose connective tissue external to neurilemma

perineurium

layers of overlaping squamous cels that wrap fascicles: bundle of nerve fibers

epineurium

dense irregular connective tissue that wraps entire nerve

sensory afferent nerves

carry signals from sensory receptors to the CNS

motor efferent nerves

carry signals from cns to muscles and glands

mixed nerves

consist of both afferent and efferent fibers

ganglion

cluster of neurosomas outside the CNS

- enveloped in an endoneurium continuous with that of the nerve

31 pairs of spinal nerves

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

posterior branch

dorsal

root is sensory input to spinal cord

Posterior root ganglion

contains the neurosomas of sensory neurons carrying signals to spinal cord

anterior ventral root

is motor output out of spinal cord

anterior ramus

In thoracic region, it gives rise to intercostal nerve

In other regions, anterior rami form plexuses

posterior ramus

innervates the muscles and joints in that region of the spine and the skin of the back

menigeal branch

reenter the vertebral canal and innervates the meninges vertebrae and spinal ligaments

Cervical Plexus (C1-C5)

supplies neck and phrenic nerve to the diaphragm

Brachial Plexus (C5-T1)

supplies upper limb and some of shoulder and neck

median nerve

carpal tunnel syndrome

Lumbar Plexus (L1-L4)

Supplies abdominal wall, anterior thigh, and genitalia

Sacral Plexus (L4-S4)

supply lower limbs, sciatic nerve: lower limb

coccygeal plexus (S4-Co1)

supplies a small area of skin in coccygeal region

somatosensory function

carry sensory signals from bones joints muscles and skin

proprioception

brain receives info about body position and movements from nerve endings in muscles tendons and joints

Dermatome

a specific area of skin that conveys sensory input to a spinal nerve

dermatome map

a diagram of the cutaneous regions innervated by each spinal nerve

dermatones are need to

anesthetize 3 successive spinal nerves to produce a total loss of sensation in one dermatome