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9.16 Autonomic nervous
system
By Hassan Ajame
Objectives..
Content objective:
students will show understanding of
the autonomic nervous system, its characteristics and
contents.
Language objective:
students will demonstrate their
understanding of the section through answering questions
about the autonomic nervous system at the end of the
presentation.
The autonomic nervous system (ANS)
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Part the (PNS) in which it functions continuously but
unconsciously and autonomously.
Main purpose is to regulate the functions of certain
internal organs such as:
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Heart rate
Bloodpressure
Breathing rate
Body temperature
The system also regulates the actions of smooth muscles,
cardiac muscles and certain glands to control their
visceral functions.
Sympathetic and parasympathetic divisions
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The (ANS) includes 2 divisions, sympathetic and
parasympathetic divisions.
Sympathetic division: prepares the body for threatening,
stressful and emergency situations and is responsible for
the “fight or flight” response.
Parasympathetic division: works by counterbalancing the
effects of the sympathetic division and tries to bring back
the body into a resting state after it goes through the
sympathetic division by decreasing its effects.
Sympathetic and parasympathetic divisions cont.
Sympathetic division:
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It's preganglionic fibers appear in the gray matter of
spinal cord.
When sympathetic division occurs, axons move from the
spinal cord and through ventral roots of the spinal
nerves to the thoracic and lumbar segments.
The axons then leave the spinal nerves into a chain of
sympathetic ganglia and within it synapses with second
neurons and then return to the spinal nerves.
Sympathetic and parasympathetic divisions cont.
Parasympathetic division:
● Originating from the brainstem region of the
spinal cord, preganglionic fibers lead their
way into the cranial and sacral nerves to the
ganglia in the viscera.
● From there the postganglionic fibers travel
from the ganglia and straight into muscles and
glands.
Autonomic nerve fibers
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The ANS consists of 2 motor neurons
The cell body of one neuron is located in the spinal cord
and brain and the second extends to a visceral effector.
The Preganglionic fiber is the axon within the cell body
that is located in the brain and spinal cord in which it
travels through the CNS and synapse with the neurons
within an autonomic ganglion.
The Postganglionic fiber is the axon within the second
cell body that run from the ganglion to the effector
organ.
Autonomic neurotransmitters
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Preganglionic fibers can also be called cholinergic
fibers because they secrete acetylcholine.
Postganglionic fibers secrete norepinephrine and are
therefore called adrenergic fibers.
These postganglionic neurotransmitters cause the effects
of the sympathetic and parasympathetic divisions leading
to the effector organs.
Control of autonomic activity
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The autonomic nervous system is mainly controlled by the
brain and spinal cord.
Medulla oblongata: receives sensory impulses from the viscera on
vagus nerve fibers to stimulate motor responses in muscles and
glands through the use of autonomic nerve pathways.
Hypothalamus: regulates body temperature, hunger, thirst, and
electrolyte balance through autonomic pathways similarly to the
medulla.
Limbic system/cerebral cortex: controls and regulates emotional
activity or stress also through autonomic pathways.
Quiz..
1. What are the 2 divisions in the autonomic nervous system?
2. What are the 2 types of autonomic nerve fibers?
3. The sympathetic division prepares the body for stressful
and emergency situations. True or False?