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The two primary functions of the spinal cord include:
1) communication between receptors and brain (sensory information) and between
brain and effectors (motor information). White matter spinal tracts.
2) acts as reflex center (association neurons in gray matter)
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I. Cross section of spinal cord
A. Cross-sectional Anatomy of spinal cord.
Nervous reflex pathway (Receptor-sensory neuron-association neuron-motor neuron-effector)
is imposed on structures of spinal cord
posterior root of spinal nerve with ganglion -sensory input, from receptors,
to association neurons
gray matter (association neurons)-decision making part of spinal cord
white matter (myelinated neurons going vertically, also known as spinal tracts)-carry
information to/from brain)
anterior root of spinal nerve-motor output to effectors
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B. Cross section of vertebral column (protective structures)
structures and fluids provide protection.
Vertebrae bone
Epidural Space – filled with adipose provides cushion
Dura mater – tough protective layer
Arachnoid mater
Subarachnoid space -filled with CerebroSpinal Fluid providing nutrient/gas transport.
( CSF is made from blood plasma and is similar in composition to it.)
Pia mater
Spinal Cord (gray and white matter=neural tissue)
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II. Gross Anatomy of spinal cord
- Extends from the foramen magnum to L1 or L2.
cervical and lumbar enlargements (plexuses)contain the cell bodies of the many spinal nerves to the limbs.
Cauda equina: The lumbar and sacral spinal nerve roots travel inferiorly through the vertebral canal. This is because the vertebral column is longer than the spinal cord. They leave the canal at their respective intervertebral foramina. These nerve roots collectively resemble a “horse’s tail”.
Ascending and descending white matter tracts carry information to/away from brain, respectively
III. Spinal Nerve Structure:
similar to that of a muscle, with fascicles and membranes.
1) axon
2) myelin sheath around axon
3) Endoneurium: surrounds each myelinated axon.
4) Perineurium: forms each fascicle ( a group of myelinated axons)
5) Epineurium: tough fibrous sheath surrounding the nerve, enclosing
all of the fascicles.
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III. Spinal Nerves Function:
They supply all parts of the body except the head and some parts
of the neck.
All are mixed nerves, having both motor and sensory neurons.
They originate as the anterior and posterior roots meet laterally and
just distal to the posterior root ganglion.
Plexuses: These branching networks of the spinal nerves found at spinal cord.
Usually associated with appendages.
A
web activity
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Professor Thomas M. Lancraft
Human Anatomy Courses
at St. Petersburg College
St. Petersburg/Gibbs Campus
6/2006