Download I:\Physio Psych\PSN.shw

Peripheral Nervous System
Physiological Psychology
PSYC370
Thomas E. Van Cantfort, Ph.D.
‚
‚
The brain and spinal cord communicate with the rest of
the body via the cranial nerves and spinal nerves.
These nerves are part of peripheral nervous system,
Ú which convey sensory information to the central
nervous system
Ú and convey messages from the central nervous system
to the body’s muscles and glands.L
Peripheral Nervous System
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
Spinal Nerves
The spinal nerves begin at the junction of the dorsal root
and ventral root of the spinal cord.
‚ The nerves leave the vertebral column and travel to the
muscles or sensory receptors they innervate, branching
repeatedly as they go.L
‚
L
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
L
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
Spinal Nerves
‚
Ú
Let us consider the pathway by which sensory
information enters the spinal cord and motor information
leaves it.
Ú The cell bodies of all axons that bring sensory
information into the brain and spinal cord are located
outside the CNS.
Ú The sole exception is the visual system;
< the retina of the eye is actually a part of the brain.
Ú These incoming axons are referred to as afferent axons
because they bear toward the CNS.L
Ú
Ú
Peripheral Nervous System (continued)
Ú
Ú
Ú
Ú
Ú
The cell bodies that give rise to the axons that bring
somatosenory information to the spinal cord reside in
the dorsal root ganglia, the round swellings of the
dorsal root.
The neurons are of the unipolar type.
< Axonal stalk divides close to the cell body,
< sending one limb into the spinal cord
< and the other limb out to the sensory organ
Note that all of the axons in the dorsal root convey
somatosensory information.L
Peripheral Nervous System (continued)
Cell bodies that give rise to the ventral root are located
within the gray matter of the spinal cord.
< Gray matter are unmyelinated neurons, glial cells,
cell bodies, and dendrites.
< White matter are large concentration of myelinated
axons giving the tissue an opaque white appearance.
The axons of the multipolar neurons leave and the
spinal cord via a ventral root,
which joins a dorsal root to make a spinal nerve.
The axons that leave the spinal cord through the
ventral roots control muscles and glands.
They are referred to as efferent axons, because they
bear away from the CNS.L
Cranial Nerves
Twelve pairs of cranial nerves leave the ventral surface of
the brain.
‚ Most of these serve sensory and motor functions of the
head and neck region.L
‚
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
Cranial Nerves
‚
‚
‚
‚
L
‚
One of them, the tenth, or vagus nerve, regulates the
functions of organs in thoracic and abdominal cavities.
Somatosensory information is received, via the cranial
nerves, from unipolar neurons.
Auditory, vestibular, and visual information is received
via fibers of bipolar neurons.
Olfactory information is received via the olfactory bulbs,
Ú which receive information from the olfactory receptors
in the nose.
The olfactory bulbs are complex structures containing a
considerable amount of neural circuitry; actually, they
are part of the brain.L
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
‚
Autonomic Nervous System
The part of the peripheral nervous system that receives
sensory information from the sensory organs
Ú and that controls movements of the skeletal muscles is
called the somatic nervous system.
‚ The other branch of the peripheral nervous system – the
autonomic nervous system (ANS) – is concerned with
the regulation of smooth muscle, cardiac muscle, and
glands.
Ú Smooth muscles is found in the skin (associated with
hair follicles), in blood vessels, in the eyes (controlling
pupil size and accommodation of the lens),
Ú and in the walls and sphincters of the gut, gallbladder,
and urinary bladder.L
‚
‚
‚
Peripheral Nervous System (continued)
Merely describing the organs innervated by the
autonomic nervous system suggests the function of this
system:
Ú regulation of vegetative processes in the body,
Ú that is the involuntary bodily processes.
The ANS consists of two anatomically separate system,
Ú the sympathetic division
Ú and the parasympathic division.
With few exceptions, organs of the body are innervated
by both of these subdivisions, and each has a different
effect.
Ú For example, the sympathetic division speeds the heart
rate,
Ú whereas the parasympathetic division slows it.
Ú There is reciprocal inhibition between the two
divisions.L
Peripheral Nervous System (continued)
Sympathetic Division of the ANS
The fibers of these neurons exit via the ventral roots.
After joining the spinal nerves, the fibers branch off and
pass into the spinal sympathetic ganglia.
‚ Note that the spinal sympathetic ganglia are connected to
the neighboring ganglia above and below, thus forming
the sympathetic chain.
‚ The axons that leave the spinal cord through the ventral
root are part of the preganglionic neurons.
Ú With one exception, all sympathetic preganglionic axon
enter the ganglia of the sympathetic chain,
Ú but not all of them synapse there.L
‚
The sympathetic division is mot involved in activities
associated with expenditure of energy from reserves that
are stored in the body.
Ú For example, when an organism is excited, the
sympathetic nervous system increases blood flow to
skeletal muscles,
Ú stimulates the secretion of adrenaline (resulting in
increase heart rate and a rise in blood sugar level),
Ú and causes piloerection (goose bumps in humans).
‚ The cell bodies of sympathetic motor neurons are located
in the gray matter of the thoracic and lumbar regions of
the spinal cord.L
‚
‚
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
Some axons leave and travel to one of the other
sympathetic ganglia, located among the internal organs.
‚ All sympathetic preganglionic axons form synapse with
neurons located in one of the ganglia.
‚ The neurons with which they form synapses are called
postganglionic neurons.
‚ In turn, the postganglionic neurons send axons to the
target organs,
Ú such as intestines, stomach, kidney, or sweet glands.
‚ All synapses within the sympathetic ganglia are
cholinergic;
Ú the terminal buttons on the target organs, belong to the
postganglionic axons are noradrenergic.
Ú One exception to this rule is the sweat glands, the
terminal buttons are cholinergic.L
‚
L
Peripheral Nervous System (continued)
Peripheral Nervous System (continued)
Parasympathetic Division of the ANS
‚
‚
‚
The parasympathetic division of the autonomic nervous
system supports activities that are involved with
increases in the body’s supply of stored energy.
These activities include salivation, gastric and intestinal
motility, secretion of digestive juices, and increase blood
flow to the gastrointestinal system.
Cell bodies that give rise to preganglionic axons is the
parasympathetic nervous system are located in two
regions:
Ú In the nuclei of some of the cranial nerves (vagus
nerve)
Ú and the intermediate horn of the gray matter in the
sacral region of the spinal cord.L
Peripheral Nervous System (continued)
M
‚
Parasympathetic ganglia are located in the immediate
vicinity of the target organs;
Ú the postganglionic fibers are therefore relative short.
Ú The terminal buttons of both the preganglionic and
postganglionic neurons in the parasympathetic nervous
system secrete acetylcholine.L