IV. SPINAL CORD AND SPINAL NERVES
A. General function
Carry messages to and from brain, spinal reflexes
B. Location
Vertebral foramen; foramen magnum to about L2
C. Spinal Nerves
-Cauda equina
Inferior spinal nerves resembling a horse’s tail
D. Cervical & Lumbar Enlargements
E. Meninges
Protective membranes of CNS. Meninx is singular.
1. Dura mater
Outermost membrane, dense.
-Epidural space
Most epidural anesthetics are given at L2
2. Arachnoid
Middle spider web-like layer
-Subarachnoid space
Location of CSF
3. Pia mater
Innermost delicate layer
F. Gray Matter
1. Central Canal
Contains CSF
2. Posterior (dorsal) horns/Anterior (ventral) horns
Dorsal is sensory pathway, ventral is motor pathway
3. Dorsal/Ventral nerve fibers
G. White Matter
1. Columns (Anterior, Posterior, Lateral)
2. Ascending tracts (sensory) {Cross}
3. Descending Tracts (motor) {Cross} U.M.N.– Upper motor neurons
H. Spinal Reflex Arc
1. Definition ofreflex
Automatic, stereotyped reaction to a stimulus such that a particular stimulus always elicits a particular response.
2. Receptor
3. Sensory (afferent) neuron
4. Spinal cord
5. Motor (efferent) neuron L.M.N.
6. Effector
7. Somatic, Autonomic Reflexes
Somatic reflexes have skeletal muscle as effectors, autonomic reflexes have smooth muscle, cardiac muscle or glands as effectors.
8. Monosynaptic
9. Polysynaptic
a. Ipsilateral (Flexor)
Also known as withdrawal reflex
b. Contralateral (Crossed Extensor)
I. Spinal Nerves
31 pair, Spinal nerves are mixed with sensory and motor pathways.
1. Dorsal and Ventral Roots
Near the spinal cord, the spinal nerve splits into a dorsal root which carries sensory information in to the spinal cord and a ventral root which carries motor information out of the spinal cord.
2. Dorsal and Ventral Rami
Branching of spinal nerve once it emerges from intervertebral foramen.
3. Plexuses
Network of adjacent spinal nerves
a. Cervical (C1-C4-5)
1. Phrenic Nerve
Innervates diaphragm
b. Brachial (C5-T1)
1. Radial
Innervates arm and forearm extensors
2. Musculocutaneous
Innervates elbow flexors
3. Ulnar
Innervates flexors of wrist, fingers medial side
4. Median
Innervates flexors of wrist, fingers lateral side
c. Lumbar (T12/L1-L4)
1. Femoral
Innervates thigh flexors and knee extensors
d. Sacral (L4-S4)
1. Sciatic
Innervates posterior thigh, leg and foot