Spinal Cord and Spinal Nerves Flashcards

spinal cord

part of the CNS
major communication link between the brain and the PNS
involved with reflex mechanisms and the integration of incoming information

spinal cord structure

extends from the medulla oblongata to L1-L2
located within the vertebral canal
surrounded by connective tissue membranes called meninges

vertebral canal

formed by the vertebral foramen of the vertebrae

meninges of the spinal cord

dura mater, arachnoid mater, and pia mater
continuous with the meninges of the brain

lumbar puncture (spinal tap)

procedure in which CSF is drawn from the subarachnoid space
done at L3-L4 or L4-L5

major structures of the spinal cord

cervical enlargement, lumbar enlargement, and conus medullaris

cervical enlargement

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

lumbar enlargement

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

cauda equina

collection of nerve roots that extend from the lumbar enlargement

conus medullaris

cone shaped end of the spinal cord L1-L2
anchored to the coccyx by the filum terminale (continuation of the
pia mater)

What is the spinal cord composed of?

gray matter (neuron cell bodies) and white matter (myelinated axons)

gray matter

major structures include the anterior horns, lateral horns, posterior
horns, and central canal

anterior (ventral) horns

contain cell bodies of motor neurons supplying skeletal muscles

lateral horns

contain cell bodies of motor neurons supplying the smooth and cardiac muscles
only located at the T1-L2 vertebral levels

posterior (dorsal) horns

contain axons of sensory neurons

central canal

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

white matter

highly organized
major structures include the ventral columns, dorsal columns, and
lateral columns

white matter columns

each column is divided into tracts (also called pathways)

white matter tracts

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

sensory information

carried by ascending tracts up to the brain

motor information

carried by descending tracts down to muscles

spinal nerves

there are 31 pairs of spinal nerves associated with the spinal cord
each spinal nerve contains thousands of axons (both sensory and motor)
give rise to peripheral nerves that supply all parts of the body
(except the head and some parts of the neck)
spinal nerves are attached to the spinal cord by way of dorsal roots
and ventral roots
8- cervical
12- thoracic
5- lumbar
5- sacral
1- coccygeal

dorsal roots

contain axons of unipolar sensory neurons
the cell bodes of these unipolar sensory neurons are located in the
dorsal root ganglia

ventral roots

contain axons of motor neurons

rami

go out to the body

What does each spinal nerve split into?

dorsal ramus and ventral ramus

What anchors spinal nerves to the spinal cord?

roots

dorsal rami

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

ventral rami

in the thoracic region ventral rami form intercostal nerves
the ventral rami of the remaining spinal nerves form five major plexuses

intercostal nerves

contain axons that supply the intercostal muscles and skin of the
thorax (in between the ribs)

brachial plexus (axillary region aka armpit)

originates from spinal nerves C5-T1
major branches (nerves) of the brachial plexus include the
musculocutaneous, median, ulnar, axillary, and radial nerves

musculocutaneous nerve

sensory function:
supplies skin on lateral surface of forearm

median nerve

(middle of the "m"; middle of the arm)
sensory function:
supplies skin on the thumb, index finger, and middle finger, the
lateral half of the ring finger, and lateral 2/3 of palm

ulnar nerve

travels behind the medial epicondyle of the humerus on the medial side
"funny bone"
sensory function:
supplies skin on the little finger, medial 1/2 of the ring finger,
and the medial 1/3 of the hand

axillary nerve

lateral branch of upside down "y" that sits beside "m"
sensory function:
supplies skin on lateral shoulder

radial nerve

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

lumbosacral plexus

originates from the ventral rami of spinal nerves L1-S4
major branches (nerves) of the lumbosacral plexus include the
obturator, femoral, sciatic, tibial, and fibular nerves

obturator nerve

located between two muscles
sensory function:
supplies skin on the medial surface of thigh (groin)

femoral nerve

most lateral of the three structures next to eachother
sensory function:
supplies skin on the anterior thigh and medial leg

sciatic nerve

posterior side/ big ass nerve
composed of the tibial nerve and common fibular nerve
sensory function:
none
branches of the sciatic nerve: tibial nerve and common fibular nerve

tibial nerve

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

common fibular nerve

lateral side of the sciatic nerve
divides to form the superficial fibular nerve and deep fibular nerve
(anterior side of lower leg)
sensory function:
supplies skin on lateral portion of knee, skin on anterolateral leg,
and dorsum (top) of foot

reflex

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

stretch reflex

occurs 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
this is how it works...
1. muscles contain receptors called muscle spindles that monitor
changes in the length of a muscle
when a muscle is stretched...
2. muscle spindles will also stretch (lengthen)
3. the lengthening of the muscle spindle results in the generation
of an action potential
4. action potential is carried to the spinal cord along a sensory neuron
5. sensory neuron synapses directly with a motor neuron in the
anterior horn of the spinal cord
6. the motor neuron carries an action potential back to the
stretched muscle causing it to contract (shorten)

tap" reflex

1. tap patellar ligament
stretches the muscle and muscle spindle lengthens
2. generates action potential
3. action potential travels through sensory neuron
4. synapse on motor neuron
5. motor neuron sends action potential to muscle
6. muscle contracts

sensory ascending pathway

1. sensory receptor
2. musculocutaneous nerve (peripheral nerve)
3. ventral ramus
4. spinal nerve
5. dorsal root
6. posterior horn
7. ascending tract
8. thalamus
9. primary somatic sensory cortex
10. somatic sensory association area

motor descending pathway

1. primary motor cortex
2. internal capsule
3. descending tract
4. anterior horn
5. ventral root
6. spinal nerve
7. ventral ramus
8. peripheral nerve (musculocutaneous)
9. muscle