chapter 14

major functions of spinal cord and spinal nerves

structural and functional link between brain and rest f body (sensory input from body and motor commands from brain), spinal reflexes (fast reaction to stimuli)

spinal reflexes

responses that do not involve the brain

spinal cord

extends inferiorly from brains medulla through vertebral canal, typcal adlt spinal cord ¾ in diameter, 16-18 inches in length. shorter than vertebral column.

spinal cord anatomy

contains five parts: cervical, thoracic, lumbar, sacral, coccygeal

and two widened regions with greater number of neurons: cervical enlargement, lumbar enlargement.

cervical part

continuous with medulla oblongata

thoracic part

contains neurons for thoracic spinal nerves

lumbar part

short segment with neurons for lumbar spinal nerves

sacral part

contains neurons for sacral spinal nerves

coccygeal part

is the most inferior tip f the cord

cervical enlargement

neurons innervating the upper limbs

lumbar enlargement

neurons innervating lower limbs

nerve

cable like bundle of axons

epinerium

connecive tissue around the nerve

perineurium

onective tissue around the fascicle

endoneurium

connective tissue around around axon

how many spinal nerves

31 pairs

how many cervical nerves

8

how many lumbar nerves

5

how many thoracic nerves

12

how many sacral nerves

5

how many cccygeal nerves

1

rootlets

merge to form roots

posterior root

of spinal nerve contains sensory neurons

posterior root gangelion

of spinal erve contains cell bodies of hese neurons

anterior root

contains motor neurons

spinal nerve

forms where the root joins.

mixed nerves

sensory and motor neurons in each spinal nerve

cauda equina

roots of lumbar, sacral, coccygeal spinal nerves extend inferiorly rom conus medullris and form a structure called

vertebral column

houses the spinal cord. each spinal neve exits through an interertebral foramen

intervertebral foramen

where each spinal nerve exits in the vertebral clumn

spinal cord meninges

embranes tha protect and encapsulate the spialcord within vertebral canal

epidural space

outermost space surrounding the cord. between dur mater and periosteum; contains areoar tissue and adipose tissue and blod vessels

dura mater

outer structure urrounding cord, omposed of dense. irregular conective tissue

subdural space

2nd outermost space. potential space between dura and arachnoid mater

arachnoid mater

has fibers penetrating te subarachnod space, which contains erebral spino fluid

pia mater

adheres to surface of spinal cord

denticulate ligaments

suspend and anchor the chrd laterall. extensions of a mater

lumbar puncture

procedure for otaining CSF for medical diagnosis

needle passes through skin, back, muscles,ligamentum flavum, epidural space and dural mater

gray matter

made of neurons cell bodies, dendites, and unmyelinated axons; and glial cells

posterior horns of gray mater

house axons of sensory (somatic and viscral) neurons and cell bodies of interneurons

anterior hornsof gray mater

house cell bodies of somatic motor neurons which innervate skeletal muscle

lateral horns

house cel bodies of autonomic motor eurons

somatic sensory nuclei

recieves signals from skin, muscles and joints

visceral sensory nuclei

recieves signals from blood vessels, viscera

somatic motor neuclei

innervate skeletal muscle

autonomic nuclei

inervate smooth muscle, heart and glands

gray commisure

horizontal band of gray matter surrounding central canal. contins mylinated axons connecting left and rght gray matter.

regions of white mater

posterior funiculus, lateral funiculus, anterior funiculus

posterior funiculus

contains sensory tracts

fasciculi

axon bundles

lateral funiculus

contains sensory andmotor tracts

anterior funiculus

left and right are connected by white commisure. contains senory and motor tracts

sensory pathway

ascend toward brain

motor pathways

descend from brain

nervous system pathways

there is left and right tract. each pathway is made of a chain of two or more neurons

cell locations

axons are in spinal cord tracts. cell bodies are in ganglia

general sense receptors

sensory input transmitted through spinal cord orignates from. somatic sensory and visceral sensory receptors

tactile receptors

somatic sensory. detect characteristic of an object

proprioceptors

somatic sensory. detect stretch in joints, muscles, tendons

viceral sensory receptors

detect changes in an organ

somatosensory pathways

carry sigals from skin , muscle, joints

viscrosensor pathways

carry signals from viscera. use a series of neurons o relay signl to brain- primary, secondary, tertiary

primary neuron (posterior funiculus medial lemniscus pathway)

relays signal from skin to brainstem. peripheral receptor hs axon in spinal nerve,posterior root, spinal cord

secondary neuronposterior funiculus medial lemniscus pathway)

relays signal from medulla to thalamus. cell body in either nucleus cuneatus or nucleus gracilis of medulla, axon decussates and joins medial lemnicus, in thalamus the axon contacts tertary neuron

tertiary neuron(posterior funiculus medial lemniscus pathway))

relays signals to primary somatosensory cortex from thalamus

anterolateral pathway

signals related to crude touch, pressure pain, and temperature with three-neuron chain

primary neuron anterolateral pathway

relays sigals rom skin to spinal cord. axon is in spina nerve and posterior root

secondary neuron anterolateral pathway

relays signal from cord to thalamus.

terrtiary neuron anterolateral pathway

relays from thalamus to cerebro cortex. axon ontacts target neuron in aproriate part of primary somatosensory crtex

posterior funiculus medial lemniscal pathway

sensory input about discriminative touch, concious perception, from proprioceptors

anterolateral

ignals related to crude touch, pressure, pain, and temperature with a 3 neuron chain

spincerebellar pathway

signals about propriception with a two neuron chain.

primary neurons spincerebellar pathway

relays signals from skin to spinal cord. axon is in spinal nerve and posterior root, the axon contacts the secondary neuron in spinal cords posteriorhorn

secondary pathway spincerebellar pathway

relays signals from spinal cord to cerebellum. some axons cross while others remain on the same side, then it ascends to either anterior spinocerbeallar tract or posterior spinocerebellar tract

motor pathways

control effectors uc as skeletal muscles. start in the brain and includes at least 2 neurons: upper motor neuron lower motr neuron

upper motor neuron

in motor cortex. cerbral nucleus or brainstem nucleus; contats lower motor neuron

lower motor neuron

in cranial nerve nucleus or spinal cod anterior horn excites muscle innervates limb muscle skilled movement

direct pathway

pathway between brain and skeletal muscles. begins with upper motor neurons n primary motor cortex, axons course through internal capsule cerebral peduncles, corticospinal tracts. lower motor neurons extends to skeletal muscle

lateral corticospinal tracts

upper motot euron axons decussate within medullas pyramids, axons form hite tractsin lateral funniculi and contact lower motor neurons.

anterior corticospinal tracts

upper motor neurons axons form white tracts in anerior funiculi. decussate at level spinal cord segment nd contact interneurons or or lower motor neurons. lower motor neurons innervate axial skeletal muscle

indirect pathway

upper motor neurons originate in banstem uclei and take compicated route to spinal cord

lateral pathway of indirect pathway

regulates prcise movement and tone in flexor limb muscles

medial pathway

regulates muscle tone and movements of head, neck, proximal limb, trunk.

reticulospinal tracts

heps control reflexes related to posture and balance

tectospinal tracts

regulate orienting responses to visual and audtory stimuli

vestibulopinaltracts

help maintain belance during stting, stadnig and walking

spinalcord injuries

may leave ndividualsaralyzed and unable perceive sensation . steroids can preserve muscle function.

posterior ramus

small branch that innrvates muscles to the skin and the back

anterior ramus

large branch splits into multiple other branches

rami communicates

small branches of autonomic fibers. extend between spinal nerve and the sympathetictrunk ganglion

dermatones

segment of skin supplied by a single spinal nerve. can help localize damage to one or more spinal nerves

nerve plexus

network of interweaving anterior rami of spinal nerves. four main plexus occur bilaterally: cerivical, brachial, lumbar and sacral plexus

intercostal nerves

locate bewteen ribs. receives sensory signals from overlying skin

cervical plexus

anterior rami o C1-C4. branches innervate: anterior neck muscles, skin of neck portions of head and shoulders

brachial plexus

network of fibers extending laterally from neck into axilla. composed of anterior rami, trunk, divisions, cords. cord give rise to 5 major terminal branches

axillary nerve

to deltoid, teres major muscles; sensory nput from superolateral arm

median nerve

to most anterior forearm muscles, thenar muscles and lateral lumbricals; sensory input from palma side and dosal tips of most fingers(not pinkie)

musculocutaneous nerve

to anterior arm musclesensory input from lateral forearm,

radial nerve

to posterior arm muscles; enaory input from posterior arm and forearm and dorsolateral hand

ulnar nerve

to anterior rearm muscles, most intrinsic hand muscle; sensory from palmar and dorsal aspect of two medial finger