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