UNIT 3 SPINAL CORD & NERVES

posterior median sulcus

on posterior side

anterior median fissure

deeper groove on anterior side

conus medullaris

thin, conical spinal cord below lumbar enlargement

filum terminale

thin thread of fibrous tissue at end of conus medullaris that attaches to coccygeal ligament

cauda equina

nerve roots extending below conus medullaris

dorsal root

contains axons of sensory neurons

dorsal root ganglia

contain cell bodies of sensory neurons

ventral root

contains axons of motor neurons

cranial meninges

surrounds the brain

spinal meninges

start at foramen magnum

dura mater

tough, fibrous outer layer

the epidural space

between dura mater and walls of vertebral canal, epidural injection site

arachnoid mater

middle meningeal layer

subarachnoid space

area underneath arachnoid mater, filled with CSF

cerebrospinal fluid (CSF)

shock absorber, medium for exchange

spinal tap

procedure to withdraw CSF by needle in lumbar region

pia mater

innermost layer, binds to neural tissue

denticulate ligaments

anchors spinal cord, prevents lateral movement

sensory nuclei

receives and relays sensory info from peripheral receptors

motor nuclei

issue motor commands to peripheral effectors

posterior grey horns

contain somatic and visceral sensory nuclei

anterior gray horns

contain somatic motor nuclei

lateral gray horns

(thoracic & lumbar only) visceral motor nuclei

posterior white columns

lies between posterior gray horns

anterior white columns

lies between anterior gray horns

lateral white columns

lies between anterior & posterior gray horns

ascending tracts

carry sensory info to the brain

descending tracts

carry motor commands to the spinal cord

white ramus

travels to sympathetic ganglion → sympathetic div. or ANS

grey ramus

unmyelinated/innervates smooth muscles & glands of body wall and limbs

dorsal ramus

somatic & visceral motor of skin & skeletal muscles of the back/ S & V sensory

ventral ramus

somatic & visceral motor of ventral & lateral surface, body wall & limbs, S & B sensory

dermatomes

specific bilateral region of skin monitored by spinal nerves

cervical plexus & its major nerve

C1-C5, phrenic nerve - controls diaphragm

brachial plexus & the trunks and cords

C5-T1, trunks and cords are named relative to the axillary artery

(roots→trunks→divisions→cords→

branches)

major nerves of the brachial plexus

musculocutaneous nerve, axillary nerve, ulnar nerve, median nerve, radial nerve

lumbar plexus & nerves

T12-L4

femoral nerve, obturator nerve, genitofemoral nerve

sacral plexus & nerves

L4-S4

sciatic nerve (tibial nerve & fibular nerve), gluteals, pudendal nerve

neuronal pools

functional groups of interconnected neurons (interneurons)

divergence

spreads stimulation to many neurons or neuronal pools in CNS

ex. sensory info entering CNS

convergence

brings input from many sources to a single neuron, many neurons can have the same effect

ex. controlling the diaphragm

serial processing

moves information on single line - step by step

ex. pain relay

parallel processing

moves same information along several paths simultaneously

reverberation

positive feedback mechanism, functions until inhibited, complicated

ex. maintain consciousness

neural reflexes

rapid, automatic responses to specific stimuli to preserve homeostasis

steps of neural reflexes

1. arrival of stimulus, activation of receptor

2. activation of sensory neuron

3. information processing by postsynaptic cell

4. activation of motor neuron

5. response of peripheral effector

innate reflexes

basic neural reflexes formed before birth

ex. blinking, swallowing

acquired reflexes

rapid, automatic learned motor patterns

ex. brake pedal, sports

somatic reflexes

involuntary control of muscular system

visceral reflexes

control systems other than muscular system

cranial reflexes

occurs in brain

spinal reflexes

occurs in spinal cord

monosynaptic reflexes

sensory neuron synapses directly onto motor neurons

patellar reflex

postural reflexes

many stretch reflexes, helps maintain normal upright posture

polysynaptic reflex

at least 1 interneuron between sensory neuron and motor neuron

tendon reflex

prevents tearing or breaking of tendons

withdrawal (flexor) reflex

move body part away from stimulus

ex. pulls hand away from hot stove

reciprocal inhibition

antagonistic muscle must be inhibited

crossed extensor reflexes

straightens other leg to receive body weight

babinski sign (plantar reflex)

normal in infants, may indicate CNS damage in adults