Download ANPS 019 Black 11-02-11

SPINAL CORD AND SPINAL NERVES
November 2, 2011
SPINAL CORD CIRCUITRY
1. Peripheral receptors bring in sensory information from body to spinal cord –somatic from
skin/muscle, visceral from organs
2. Sensory neuron enters dorsal part of spinal cord to synapse on gray matter neuron (very
particular) pseudounipolar structure
3. Information integration by interneurons (not required)
4. Motor neurons exit ventral part of spinal cord
5. Effector (muscle, gland) responds
SPINAL NERVE:
Has both sensory and motor components
Dorsal nerve root: sensory
Ventral nerve root: motor
Spinal nerve Trunk: BOTH
Arrows indicate direction of information flow
Green indicates autonomic outflow to viscera
ANATOMY OF THE SPINAL CORD
Ventral root: motor/efferent axons
Dorsal Root: sensory/afferent axons
Dorsal root ganglion: cell body of afferent
Spinal nerve: sensory + motor axons
SPINAL NERVES LEAVE THE SPINAL CORD IN SMALL SPACES BETWEEN THE VERTEBRAE
WHY POSITION MATTERS:
Partial crushing of the vertebral column leads to compression of the spinal cord, but symptoms will vary
depending on which part of spinal cord is injured
Epidural: sensory is deadened, but still have motor
Dorsal ganglia: cell bones of sensory neurons
COMPOSITION OF A PERIPHERAL NERVE
Nerves contain both (sensory and motor axons and both somatic and autonomic fibers
Also myelinated or unmyelinated
Motor axons: myelinated=fast
CONNECTIVE TISSUE
COMPONENTS OF A PERIPHERAL NERVE
Epineurium:
-outer layer
Perineurium:
-middle layer
-divides nerve into fascicles (axon bundles)
Endoneurium:
-inner layer
-surrounds individual axons
ANATOMY OF THE SPINAL CORD
Gray matter: area containing neuron cell bodies, dendrites, synapses
Central canal: ventricles of spinal cord
GRAY MATTER ANATOMY:
Somatic and visceral sensory areas are separated
Somatic: movement of arms and legs
GRAY MATTER CONSISTS OF COLUMNS OF CELLS
Columns of cells: sends out axons at different levels
ANATOMY OF THE SPINAL CORD:
White matter: myelinated axon tracts:
-ascending sensory info
-descending motor info
WHITE MATTER ANATOMY
The white matter has:
Ascending tracts carrying sensory info to the cortex and descending tracts carrying motor info from the
cortex
The spinal cord does not look exactly alike at all levels:
More gray matter in cervical and lumbar enlargements because more motor neurons to innervate arm
and leg
More white matter at the cervical level because of all motor axons descending and all sensory axons
ascending
*C-spine injuries damage motor neurons going down and sensory going up
SPINAL CORD SEGMENTS
31 pairs of spinal nerves:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Cervical Enlargements: Upper extremity
Lumbar Enlargement: Lower extremity
DERMATOMES
A topographic map of the body
Region of skin innervated by the fibers of 1 spinal never
-Arm: cervical
-Leg: lumbar
Spinal cord lies in dural sac (within CSF fluid)
Spinal segments do not coincide with vertebral level
Spinal cord ends at L1 vertebra as the conus medullaris
The spinal nerves below this level form the cauda equine “horse’s tail”
The conus medullaris is anchored to Dura via the filum terminale
Axons that extend beyond the end of the spinal nerves travel long distances before innervating
something
LUMBAR PUNCTURE TO OBTAIN CSF
The cauda equine is located in a sac (Dura) filled with fluid (CSF). Since there is no spinal cord, CSF can be
drawn from here
Some peripheral nerves (eg sciatic nerve) are formed from the union of branches of several spinal
nerves = plexus
NERVE PLEXUSES
Complex, interwoven networks of nerve fibers
Formed from blended fibers of adjacent spinal nerves
Four major plexuses:
1. Cervical
2. Brachial
3. Lumbar
4. Sacral
Lumbar and Sacral are often combined as lumbosacral
CERVICAL PLEXUS
Innervates neck, thoracic cavity, diaphragm muscles (to breath)
BRACHIAL PLEXUS
Innervates pectoral girdle and upper limbs
LUMBAR AND SACRAL PLEXUSES
Innervate pelvic girdle and lower limbs
CRANIAL NERVES:
1. Head and neck
2. Diaphragm
3. Deltoids, biceps
4. Wrist extenders
5. Triceps
6. Hand
THORACIC NEVERS
1. Chest muscles
2. Ab muscles
LUMBAR NERVES
1. Leg muscles
SACRAL NERVES
1. Bowel, Bladder
2. Sexual function