Transcript The Spinal Cord

The Spinal Cord
General Info
• Long, slender bundle of nerve tissue that
extends approx. 17 inches from the base
of the brain to the 1st or 2nd lumbar
vertebrae
• Emerges from foramen magnum at base
of skull and passes through the vertebral
canal
• Provides a two-way connection between
brain and peripheral nerves
Protective Coverings
• Protected by bone of
vertebral column, fluid
that provides a liquid
cushion, and several
layers of membrane
called meninges
• Meninges extend
beyond inferior end of
spinal cord, providing
a region for sampling
of spinal fluid
• Shape of a cylinder slightly flatted on anterior and
posterior surfaces
• 31 segments each give rise to a pair of nerves by
way of spinal roots
• Two areas slightly enlarged to serve
appendages, cervical enlargement and
lumbosacral enlargement
• There are two grooves, one located on each the
anterior (antierior median fissure) and posterior
surface (posterior median sulcus)
• After its terminal tip, or conus medullaris, the
spinal cord branches into spinal nerves referred
to as the cauda equina (horse’s tail)
Gray Matter
• Consists of unmyelinated fibers
• Located in the center of spinal cord in a
pattern that resembles the letter “H”
• The projections are referred to as horns
• The horizontal portion is called the gray
commissure; in its center is the central
canal which carries CSF
• Anterior horns contain cell bodies of motor
neurons
• Posterior horns contain terminal ends of sensory
neurons, while their cell bodies lay outside in
clusters called ganglia
• Lateral horns contain neurons of autonomic
nervous system
White Matter
• Made up of myelinated fibers
• Divided into anterior, posterior, and lateral
columns
• Each column contains bundles of fibers
called nerve tracts
Functions of Spinal Cord
• Communication between brain and
peripheral nerves
• Also functions as a reflex center,
eliminating the need for transmission of
impulses all the way to the brain to speed
up processing
Conduction Pathways
• Ascending tracts travel toward brain,
posterior horns and posterior columns
• Descending tracts travel away from brain,
anterior horns and anterior columns
• Having separate pathways avoids “traffic
jams” of action potentials
Reflexes
• Reflex – extremely rapid way of responding to
an emergency situation
• Involves a small number of neurons, happens
without conscious thought
• Reflex arc is a conduction pathway for a reflex
action
• Involves a receptor, a sensory neuron, one or
more association neurons (reflex center), motor
neurons, and effectors that carry out the
response
Reflex Arc
• Association neurons are also connected to
other pathways which explains why pain is
often felt after the motor response has
already occurred
• Other examples of reflexes include the
withdrawal reflex, startle reflex, pupillary
response, coughing, and sneezing