Download The Peripheral Nervous System and Reflex Activity

The Autonomic Nervous System
Chapter 14
Introduction
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The stability of our internal environment
depends largely on the autonomic
nervous system
Autonomic nervous system(ANS) receives
signals from visceral organs
The ANS makes adjustments as necessary
to ensure optical support for body system
Overview of the ANS
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The autonomic nervous system differs in
– Effectors
– Efferent pathways
– Target organ
Effectors of ANS
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The somatic nervous system stimulates
skeletal muscles
The ANS innervates cardiac and smooth
muscles and glands
Efferent Pathways and Ganglia
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In the somatic system
– Cell bodies are within the central nervous
system
– Axons extend to the muscles they serve
– Somatic motor fibers are thick, heavily
myelinated Type A fibers that conduct
impulses rapidly
Efferent Pathways and Ganglia
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In the autonomic nervous system
– The motor unit is a two neuron chain
– The cell body of the first neuron, the
preganglionic neuron, resides in the brain or
spinal cord
– Its axon, the preganglionic axon, synapses
with the second motor neuron, the postganglionic neuron, in an autonomic ganglion
outside the central nervous system
– The postganglionic axon then extends to the
effector organ
Efferent Pathways and Ganglia
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Axons of most preganglionic neurons run from the
CNS to synapse in a peripheral autonomic ganglion
with a postganglionic neuron
Efferent Pathways and Ganglia
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Axons of postganglionic neurons run from the
ganglion to the effectors (cardiac and smooth muscle
fibers and glands)
Efferent Pathways and Ganglia
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Preganglionic axons are lightly myelinated
thin fibers
Postganglionic axons are even thinner and
are unmyelinated
Conduction though the autonomic chain is
slower than through the somatic motor
Many pre and postganglionic fibers are
incorporated into spinal or cranial nerves
for most of their course
Efferent Pathways and Ganglia
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Autonomic ganglion are motor ganglia
containing the cell bodies of motor
neurons
They are sites of synapse and information
transmission from pre to postganglionic
neurons
The presence of intrinsic ganglionic cells,
analogous to interneurons, suggests that
certain intergrative functions may occur
there
Neurotransmitter Effects
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All somatic motor neurons release
acetylcholine at their synapses with
skeletal muscle fibers
The effect is always excitatory, and if
stimulation reaches threshold, the
skeletal muscle contacts
Neurotransmitter Effects
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Neurotransmitters released onto visceral
effector organs by postganglionic
autonomic fibers include
– Norepinephrine secreted by most sympathetic
fibers
– Acetylcholine released by parasympathetic
fibers
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Depending on the receptors present on the
target organ its response to these neurotransmitters may be either excitation or
inhibition
Divisions of ANS
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There are two division of the ANS
– Parasympathetic
– Sympathetic
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Generally the two divisions serve the same
visceral organs but cause essentially
opposite effects
If one division stimulates certain smooth
muscle to contract or a gland to secrete,
the other division inhibits that action
Through this process of duel innervation
the two systems counterbalance each other
Divisions of ANS
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The sympathetic part mobilizes the body
during extreme situations (such as fear,
exercise or rage)
The parasympathetic division allows us to
unwind as it performs maintenance
activities and conserves body energy
Role of Parasympathetic Division
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The parasympathetic division is most
effective in non-stressful situations
This division is chiefly concerned with
keeping body energy use as low as
possible, even as it directs body processes
such as digestion and elimination
Resting and digesting division
Role of Sympathetic Division
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Its activity is evident when we are excited
or find ourselves in emergency or
threatening situations (frightened)
Pounding heart, rapid deep breathing, cold
sweaty skin and dilated eyes are signs
Also changes in brain wave patterns
Its function is to provide the optimal
conditions for an appropriate response to
some threat (run / see / think)