a&p 1 module 4 // spinal cord lecture

25 june 2025

CSF

flows through central canal and provides cushioning/absorbs shock and diffuses nutrients, waste and gas

grey commissures

bands of grey matter around the central canal that allow axons to decussate to other side of the SC and control sensory and motor nuclei that control body functions

horns

protected regions of nuclei in grey matter

posterior horns

somatic and visceral sensory nuclei (receive and relay sensory info from affectors)

anterior horns

somatic motor nuclei (carries outgoing motor commands to effectors)

lateral horns

mostly found in thoracic and lumbar segments and contains visceral motor nuclei

tracts

bundles of myelinated axons in white matter that speed up an action potential

ascending tracts

carries sensory info up to CNS

descending tracts

carries motor info down from CNS to the body (any damaged tracts will result in loss of function of that area and decussation may occur)

1st order neurons

detects stimuli and transmits it to the CNS

2nd order neurons

aid in transporting signal to thalamus (sometimes it goes straight into the cerebellum and sometimes it will have to go through the medulla oblongata to get to the thalamus)

3rd order neurons

carries the rest of the stimuli to cerebral cortex (some may not go through this step)

anterior root

axons of motor neurons that control effectors

posterior root

axons of sensory neurons that affect affecters

spinal ganglia

contain the same cell bodies as the posterior root (sensory neurons) but are found between the pedicles of the vertebrae

posterior ramus

innervates skin and muscles of back

anterior ramus

innervates most of body walls and skin

conus medullaris

tapered portion of SC under lumbar segment

cauda equina

bundle of nerves extending below conus medullaris that innervate pelvic organs and lower limbs

terminal filum

thin thread of fibrous tissue at the tip of conus medullaris that attaches the coccygeal ligament

dura mater

outermost spinal meninge layer that is made up of collagen fibers and is continuous with epineurium (the distal end joins terminal filum in coccygeal ligament)

arachnoid mater

middle spinal meninge made up of arachnoid membrane (weblike layer of simple squamous cells) and arachnoid trabeculae (network of collagen and elastin fibers)

subarachnoid space

space between arachnoid trabeculae and pia mater that is filled with CSF and moves gases, nutrients and waster (lumbar puncture withdraws CSF from here); also houses blood vessels of SC on surface of pia mater

pia mater

innermost spinal meninge that is made up of collagen and elastic fibers and firmly attached to underlying structure of SC

denticulate ligaments

found in the pia mater and anchor it to the dura mater and prevent lateral movement of the SC

epineurium

outermost layer surrounding spinal nerves made up of dense connective tissue

perineurium

middle layer surrounding spinal nerves that surrounds and holds fascicles together

endoneurium

innermost layer surrounding spinal nerves that holds neurons and blood vessels within fascicles

nerve plexus

networks of nerve fibers formed from blended fibers of anterior rami

cervical plexus

innervate scalp behind ear, neck and diaphragm

phrenic nerve

C3-C5; diaphragm

lesser occipital nerve

C2; scalp and sternocleidomastoid

great articular nerve

C2-C3; external ear

transverse cervical nerve

C2-C3; anterior neck and upper sternum

supraclavicular nerve

C3-C4; upper thoracic and sternoclavicular joint and part of sternocleidomastoid

brachial plexus

innervates pectoral girdle, upper back and upper limbs

musculocutaneous nerve

C5-C7; brachialis and bicep brachii

median nerve

C6-T1; flexor muscles of forearm and index & middle finger

ulnar nerve

C8-T1; muscles of forearm, hand and flexor carpi ulnaris & digitorum profundis

axillary nerve

C5-C6; teres minor and deltoid

radial nerve

C5-T1; tricep brachii and extensor carpi radialis

lumbar plexus

innervates some abdominal, pelvic and leg

iliohypogastric nerve

L1; internal oblique, transverse abdominis and glutes

ilioinguinal nerve

L1; internal oblique, transverse abdominis, inner thigh, scrotum, pubis and labia majora

femoral nerve

L2-L4; anterior thigh (quadriceps and medial leg)

obutrator nerve

L2-L3; medial thigh (adductors and gracilis)

genitofemoral nerve

L1-L2; cremaster, pubis, labia majora and upper thigh

lateral femoral cutaneous nerve

L2-L3; anterior and lateral thigh down to the knee

sacral plexus

innervates anterior rami of sacral nerves

sciatic nerve

L4-S3; posterior thigh (hamstrings, adductors, leg and sole of foot)

fibular nerve

lateral side of leg into foot

tibial nerve

posterior leg into sole of foot

reflex

quick, automatic nerve response triggered by a specific stimuli

innate reflex

basic neural reflexes formed before birth (can be genetic) eg. chewing, withdrawals, etc.

acquired reflex

learned motor patterns that can be enhanced through repetition eg. studying

somatic reflex

controls skeletal muscle contractions eg. knee jerk

visceral/autonomic reflex

controls smooth and cardiac muscle and glands

monosynaptic reflex

sensory neuron synapses directly to motor neuron

polysynaptic reflex

sensory neuron synapses to interneuron which synapses to motor neuron

ipsilateral reflex arc

occurs on the same side of the body as the stimulus eg. touching something hot

contralateral reflex arc

occurs on opposite side of the body as the stimulus eg. stepping on a thumbtack