Spinal cord and Spinal nerves

spinal cord

CNS

the major communication link between the brain and the PNS

involved with reflex mechanisms and the integration of incoming information

Spinal cord

extends from the medulla oblongata to L₁-L₂

Located within the vertebral canal (formed by the vertebral foramen)

surrounded by meninges

Meninges

Dura, arachnoid, and pia continuous with the brain

Epidural (REAL), Subdural (Potential), Subarachnoid (REAL)

lumbar puncture (spinal tap)

procedure in which cerebrospinal fluid is drawn from the subarachnoid space

done at L3—L4 or L4—L5 level → past the spinal cord

cervical enlargement

region where axons supplying the upper extremities enter or leave the spinal cord

carry sensory and motor

lumbar enlargement

region where axons supplying the lower extremities enter or leave the spinal cord

carry sensory and motor

Cauda equina and conus medullaris extend from

cauda equina

collection of nerve roots that extend from the lumbar enlargement

“horse tail”

conus medullaris

cone shaped end of the spinal cord

anchored to the coccyx by the filum terminale (continuation of the pia mater)

filum terminale

continuation of the pia mater off of the conus medullaris

individual nerve/string

gray matter

deeper and surrounded by the white matter

anterior horns, lateral horns, posterior horns, and central canal

anterior (ventral) horns

contain cell bodies of motor neurons supplying skeletal muscle

lateral horns

contain cell bodies of motor neurons supplying smooth or cardiac muscle

only located at the T1-L2 vertebral levels -sympathetic motor neurons

posterior (dorsal) horns

contain axons of sensory neurons

in spinal cord gray matter

central canal

canal located in the center of the gray matter (continuous with the fourth ventricle of the brain)

filled with cerebrospinal fluid

White matter

highly organized

major structures include ventral columns, dorsal columns, and lateral columns

each column is subdivided into tracts/pathways

spinal tracts

composed of a group of axons that carry a specific type of sensory or motor information

Ascending → sensory carried towards brain

Descending → motor carried away from brain

Spinal nerves

31 pairs

each contains thousands of axons (both motor and sensory)

give rise to peripheral nerves that supply all parts of the body (except the head and some parts of the neck)

Dorsal root

1 of 2 ways that spinal nerves attach to spinal cord

contain axons of unipolar sensory neurons

dorsal root ganglion

cell bodies of unipolar sensory neurons in dorsal root are located here

ventral roots

contain axons of motor neurons

1 of 2 ways the spinal nerves attach to the spinal cord

dorsal rami

contains axons that supply the skin near the midline of the back and deep muscles responsible for movement of the vertebral column

ventral rami

in the thoracic region, they form the intercostal nerves

remaining spinal nerves form the five major plexuses

intercostal nerves

contain axons that supply the intercostal muscles and skin of the thorax

brachial plexus

originates from spinal nerves C5-T1

major branches (nerves) include musculocutaneous, median, ulnar, axillary, and radial

musculocutaneous nerve

sensory function: supplies skin on lateral surface of forearm

median nerve

sensory function: supplies skin of the thumb, index finger, and middle finger, the lateral half of the ring finger, and lateral 2/3 of palm

ulnar nerve

“funny bone”

supplies skin on the little finger, medial ½ of the ring finger, and the medial 1/3 of hand

axillary nerve

sensory function: supplies skin on lateral shoulder

dives into armpit

radial nerve

sensory function: supplies skin on posterior surface of arm and forearm and skin on the posterolateral surface of the hand

lumbosacral plexus

originates from the ventral rami of spinal nerves L1-S4

major branches (nerves) include the obturator, femoral, sciatic, tibial, and fibular nerves

obturator nerve

sensory function: supplies skin on medial surface of thigh (groin)

between the adductor longs and adductor brevis

femoral nerve

sensory function: supplies skin on the anterior thigh and medial leg

sciatic nerve

donor flipped on stomach

composed of the tibial nerve and common fibular nerve

Sensory function: none

tibial nerve

sensory function: supplies skin on the posterior leg, lateral surface of foot, and sole of foot

common fibular nerve

divides to form the superficial fibular nerve and deep fibular nerve

sensory function: supplies skin on lateral portion of knee, skin on anterolateral leg, and dorsum (top) of foot

reflexes

fast, predictable, automatic response to a stimulus that helps the body make rapid adjustments to homeostatic imbalances

-ex: stretch

stretch reflex

occur at the elbow, wrist, ankle, and knee joints

reflex in which muscles contract in response to a stretching force that is being applied to them

receptor: muscle spindle

muscle spindle

receptor of the stretch reflex that monitor changes in the length of a muscle

when muscle is stretched, receptors stretch (lengthen)

“lengthening” results in the generation of an action potential

stretch reflex

action potential from muscle spindle is carried to spinal cord along a sensory neuron that synapses directly with a motor neuron in the anterior horn

motor neurons causes muscle to contract (Shorten) → muscles that oppose contraction will be inhibited (relax)