Download The Autonomic Nervous System

Introduction to
Neurology
Tada Obert
Department of Livestock & Wildlife Management
Midlands State University
Content
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The Vertebrate Nervous System
 Structure and function of the CNS
Brain
 Spinal cord
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Structure and function of the PNS
 The Autonomic Nervous System (ANS)
 The sympathetic nervous system
 The parasympathetic nervous system
 The Somatic Nervous System (SNS)
Divisions of the Nervous System
Organization of Nervous Systems
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There is great diversity in nervous system organization
among animals; some even lack nervous systems (e.g.,
sponges).
Vertebrate nervous systems are highly centralized and
cephalized
Vertebrate nervous systems are structurally and functionally
diverse, however, they all have distinct central and
peripheral elements and a high degree of cephalization.
Because vertebrate nervous systems are so complex, it is
useful to group them into functional components: the
peripheral nervous system and the central nervous system.
Structure & function of CNS
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Nervous systems perform the three overlapping functions of
sensory input, integration, and motor output
1. Sensory input is the conduction of signals from sensory
receptors to integration centers of the nervous system.
2. Integration is a process by which information from sensory
receptors is interpreted and associated with appropriate
responses of the body.
3. Motor output is the conduction of signals from the
processing center to effector cells (muscle cells, gland cells) that
actually carry out the body's response to stimuli.
The signals are conducted by nerves, threadlike extensions of
nerve cells wrapped in connective tissue.
Structure & function of CNS
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These functions involve both parts of the nervous system:
1. Central nervous system (CNS)
 Comprised of the brain and spinal cord; responsible for
integration of sensory input and associating stimuli with
appropriate motor output
2. Peripheral nervous system (PNS)
 Consists of the network of nerves extending into different
parts of the body that carry sensory input to the CNS and
motor output away from the CNS
Central Nervous System
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Provide basis for the complex behaviors of vertebrates by
bridging the sensory and motor functions of the peripheral
nervous system.
Consists of the spinal cord, which is located inside the vertebral
column and receives information from skin and muscles and
sends out motor commands for movement;
Consists also the brain, which carries out complex integration
for homeostasis, perception, movement, intellect and emotions.
Both are covered with meninges, protective layers of connective
tissue.
In the brain, white matter is in the inner region and gray matter
is in the outer region.
This orientation is reversed in the spinal cord.
CNS cont’d
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Cerebrospinal fluid fills the ventricles in the brain and the central canal of
the spinal cord;
 functions in circulation of hormones, nutrients, and white blood cells
and in absorption of shock, which cushions the brain.
The spinal cord integrates simple responses to certain stimuli (reflexes)
and carries information to and from the brain.
 The patellar (knee-jerk) reflex is one of the simplest and involves only
two neurons.
 A stretch receptor in the quadriceps muscle is stimulated by stretching
of the patellar tendon;
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this activates a sensory neuron that carries the information to the spinal
cord where it synapses with a motor neuron;
if an action potential is generated in the motor neuron, it travels back to
the quadriceps, which contracts and causes the forward knee jerk.
Quick Review
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The PNS consists of
 sensory neurons running from stimulus receptors that
inform the CNS of the stimuli
 motor neurons running from the CNS to the muscles and
glands - called effectors - that take action.
The CNS consists of the
 spinal cord and
 the brain
The peripheral nervous system is subdivided into the
 sensory-somatic nervous system and the
 autonomic nervous system
Peripheral Nervous System
Structure & function of Peripheral
NS
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Sensory division, which brings information from sensory
receptors to the CNS
Motor division, which carries signals from the CNS to
effector cells
The two basic functions of a nervous system are to:
 Control responses to external environment
 Maintain homeostasis by coordinating internal organ
functions
The sensory neurons contributes to both functions by
carrying stimuli from the external environment and
monitoring the status of the internal environment.
The Motor Neurons
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Has two separate divisions:
1. The somatic nervous system's neurons carry signals to skeletal
muscles in response to external stimuli;
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includes reflexes (automatic responses to stimuli) and,
often considered "voluntary" because it is subject to conscious control.
2. The autonomic nervous system controls primarily "involuntary,"
automatic, visceral functions of smooth and cardiac muscles and
organs of the gastrointestinal, excretory, cardiovascular, and endocrine
systems.
 Divided into a parasympathetic division that enhances activities
that gain and conserve energy, &
 a usually antagonistic sympathetic division that increases energy
expenditures.
The Autonomic Nervous System
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The ANS has two subdivisions, the
 sympathetic nervous system and the
 parasympathetic nervous system.
The ANS consists of sensory neurons and motor neurons that
run between the CNS (esp. the hypothalamus & medulla
oblongata) and various internal organs such as the heart, lungs,
viscera, & glands.
 responsible for monitoring conditions in the internal
environment and bringing about appropriate changes.
 contraction of both smooth muscle and cardiac muscle is
controlled by motor neurons of the ANS.
ANS (cont’d)
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The actions of the ANS are largely involuntary;
 contrast to those of the sensory-somatic system.
Also differs from the sensory-somatic system in using two groups
of motor neurons to stimulate the effectors instead of one.
The first, the preganglionic neurons, arise in the CNS and run to a
ganglion in the body.
 They synapse with postganglionic neurons, which run to the
effector organ (cardiac muscle, smooth muscle, or a gland).
The Sympathetic Nervous System (SNS)
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The preganglionic motor neurons of the sympathetic system
arise in the spinal cord.
They pass into sympathetic ganglia which are organized into
two chains that run parallel to and on either side of the spinal
cord.
Sympathetic NS cont’d
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The preganglionic neuron may do one of three things in the
sympathetic ganglion:
 synapse with postganglionic neurons which then re-enter the
spinal nerve and ultimately pass out to the sweat glands and the
walls of blood vessels near the surface of the body.
 pass up or down the sympathetic chain and finally synapse with
postganglionic neurons in a higher or lower ganglion
 leave the ganglion by way of a cord leading to special ganglia
(e.g. the solar plexus) in the viscera.
 it may synapse with postganglionic sympathetic neurons
running to the smooth muscular walls of the viscera.
The Sympathetic Nervous System
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The neurotransmitter of the preganglionic sympathetic
neurons is acetylcholine (ACh).
It stimulates action potentials in the postganglionic
neurons.
The neurotransmitter released by the postganglionic
neurons is noradrenaline
The action of noradrenaline on a particular gland or
muscle is excitatory is some cases, inhibitory in others.
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The release of noradrenaline
 stimulates heartbeat
 raises blood pressure
 dilates the pupils
 dilates the trachea and bronchi
 stimulates the conversion of liver glycogen into glucose
 shunts blood away from the skin and viscera to the skeletal
muscles, brain, and heart
 inhibits peristalsis in the gastrointestinal (GI) tract
 inhibits contraction of the bladder and rectum
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In short, stimulation of the sympathetic branch of the
autonomic nervous system prepares the body for
emergencies: for "fight or flight".
Activation of the sympathetic system is quite general
because
 a single preganglionic neuron usually synapses with
many postganglionic neurons;
 the release of adrenaline from the adrenal medulla into
the blood ensures that all the cells of the body will be
exposed to sympathetic stimulation even if no
postganglionic neurons reach them directly.
The Parasympathetic Nervous System
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The main nerves of the parasympathetic system are the
tenth cranial nerves, the vagus nerves.
They originate in the medulla oblongata.
Preganglionic parasympathetic neuron synapses with just
a few postganglionic neurons, which are located near - or
in - the effector organ, a muscle or gland.
Acetylcholine (ACh) is the neurotransmitter at all the preand many of the postganglionic neurons of the
parasympathetic system.
Parasympathetic stimulation causes
slowing down of the heartbeat
 lowering of blood pressure
 constriction of the pupils
 increased blood flow to the skin and viscera
 peristalsis of the GIT
In short, the parasympathetic system returns the body
functions to normal after they have been altered by
sympathetic stimulation.
 In times of danger, the sympathetic system prepares the
body for violent activity.
 The parasympathetic system reverses these changes when
the danger is over.
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Parasympathetic effect on Inflammation
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The vagus nerves also help keep inflammation under control.
Inflammation stimulates nearby sensory neurons of the vagus.
When these nerve impulses reach the medulla oblongata, they
are relayed back along motor fibers to the inflamed area.
The acetylcholine from the motor neurons suppresses the release
of inflammatory cytokines from macrophages in the inflamed
tissue.
Sensory-Somatic Nervous System
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The sensory-somatic system consists of
 12 pairs of cranial nerves and
 31 pairs of spinal nerves.
See Handout
The Cranial Nerves
Nerves
Type
Function
I
Olfactory
sensory
olfaction (smell)
II
Optic
sensory
vision
(Contain 38% of all the axons connecting to the brain.)
III
Oculomotor
motor*
eyelid and eyeball muscles
IV
Trochlear
motor*
eyeball muscles
V
Trigeminal
mixed
Sensory: facial and mouth sensation
Motor: chewing
VI
Abducens
motor*
eyeball movement
VII
Facial
mixed
Sensory: taste
Motor: facial muscles and
salivary glands
VIII
Auditory
sensory
hearing and balance
IX
Glossopharyngeal
mixed
Sensory: taste
Motor: swallowing
X
Vagus
mixed
main nerve of the
parasympathetic nervous system (PNS)
XI
Accessory
motor
swallowing; moving head and shoulder
XII
Hypoglossal
motor*
tongue muscles
*Note: These do contain a few sensory neurons that bring back signals from the muscle spindles in the muscles they control.
Spinal Nerves