Download The Peripheral and Autonomic Nervous Systems

The Peripheral and
Autonomic Nervous
Systems
The PNS
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Links the central nervous system with
the rest of the body
All sensory information and motor
commands are carried by axons of the
PNS
The sensory and motor axons are
bundled together into peripheral nerves
or nerves and clusters of cell bodies or
ganglia.
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The PNS includes cranial nerves and
spinal nerves
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There are 12 pairs of cranial nerves with
connect to the brain not to the spinal cord.
There are 31 pairs of spinal nerves:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1
coccygeal.
 Each pair monitors a region of the body surface
known as a dermatome.
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Nerve Plexuses
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A complex, interwoven network of
nerves is called a nerve plexus.
The three large plexuses are the
cervical plexus, the brachial plexus, and
the lumbosacral plexus.
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The latter can be divided into the lumbar
plexus and sacral plexus.
Reflexes
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A reflex is an automatic involuntary
motor response to a specific stimulus
A reflex arc is the “wiring” of a single
reflex.
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There are five steps in a reflex arc
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1. Arrival of a stimulus and activation of a
receptor
2. Activation of a sensory neuron
3. Information processing
4. Activation of a motor neuron
5. Response by an effector
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Monosynaptic reflex
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Simplest reflex arc in which a sensory
neuron synapses directly on a motor
neuron that acts as the processing center.
The stretch reflex regulates skeletal muscle
length and muscle tone.
The patellar reflex is an example of a
stretch reflex.
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Polysynaptic reflexes
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Have at least one interneuron between the
sensory afferent and the motor efferent,
Take longer
Produce more complicated responses
The flexor reflex is a withdrawal reflex
affecting the muscles of a limb
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The brain can either facilitate or inhibit
reflex motor patterns based in the spinal
cord.
The Autonomic Nervous
System
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The ANS coordinates cardiovasclar,
respiratory, digestive, excretory and
reproductive functions.
Preganglionic neurons in the CNS send
axon to synapse on ganglionic neurons
in autonomic ganglia outside the CNS
The axons of the postganglionic fibers
innervate cardiac muscle, smooth
muscles, glands, and adipose tissues.
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Preganglionic fibers from the thoracic
and lumbar segments form the
sympathetic division (fight or flight)
Preganglionic fibers leaving the brain
and sacral segments form the
parasympathetic division (the rest and
digest)
The Sympathetic Division
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The sympathetic division consists of
preganglionic neurons between
segments T1 and L2, ganglionic neurons
in ganglia near the vertebral column,
and specialized neurons in the adrenal
gland.
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Preganglionic fibers entering the adrenal
glands synapse within the adrenal medullae.
During sympathetic activation these endocrine
organs secrete epinephrine and
norepinephrine into the bloodstream
In a crisis, the entire division responds,
producing increased alertness, a feeling of
energy and euphoria, increased
cardiovascular and respiratory activity and
elevation in muscle tone.
Sympathetic symptoms.
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Stimulates sweat gland activity
Reduces circulation to the skin
Accelerates blood flow to muscles
Releases stored lipids
Accelerates heart rate
Dilates respiratory passagewats
Reduces blood flow to viscera
Dilates pupils
The Parasympathetic
Division
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The effects produced by the
parasympathetic division center on
relaxation, food processing and energy
absorption.
They are usually brief and restricted to
specific sites.
Include: increased digestive secretions,
constrict pupils, decrease heart rate,
increase smooth muscle activity
digestive tract.
Relationship between the
parasympathetic and
sympathetic divisions
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The sympathetic division has
widespread impact, reaching visceral
and somatic structure throughout the
body.
The parasympathetic division innervates
only visceral structures serviced by
cranial nerves or lying within the
abdominopelvic cavity.
Aging and the Nervous
System
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Age related changes include:
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A reduction of brain size and weight
A reduction of the number of neurons,
Decreased blood flow to the brain
Changes in synaptic organization of The
brain
Intracellular and extracellular changes in
CNS neurons.