Transcript Anat3_08_Autonomic_Nervous_System1

Autonomic Nervous System
Dr. Michael P. Gillespie
Autonomic Nervous System
 Auto = self; nomic = law
 The autonomic nervous system (ANS) includes autonomic sensory
neurons, integrating centers in the central nervous system (CNS),
autonomic motor neurons, and the enteric division.
 The ANS is also referred to as the visceral nervous system or
involuntary nervous system.
 It acts as a control system.
 It operates largely without conscious control; however, centers in the
hypothalamus and brain stem do regulate ANS reflexes.
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Flow of nerve impulses in the ANS
 (1) Autonomic sensory neurons in visceral organs and
blood vessels propagate into (2) integrating centers in
the CNS. Then, impulses in (3) autonomic motor
neurons propagate to various effector tissues, thereby
regulating the activity of smooth muscle, cardiac
muscle, and many glands. (4) The enteric division is a
specialized network of nerves and ganglia forming an
independent nerve network within the wall of the
gastrointestinal tract.
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Functions of ANS
 The ANS affects heart rate, digestion, respiratory rate,
salivation, perspiration, pupillary dilation, micturition
(urination), and sexual arousal.
 Most autonomous functions are involuntary.
 Some ANS actions can work with some degree of
conscious control:
 Breathing
 Swallowing
 Sexual arousal
 Heart rate
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Divisions of the ANS
 The ANS is classically divided into two subsystems:
the parasympathetic nervous system (PSNS) and
sympathetic nervous system (SNS).
 For some functions these systems operate
independently and for others they operate cooperatively.
 In many cases the PSNS and SNS have opposite actions
with one activating a physiological response and the
other inhibiting it.
 The enteric nervous system is also considered to be a
part of the ANS.
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Afferent and Efferent
 ANS functions can be divided into sensory (afferent)
and motor (efferent) subsystems.
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Somatic Nervous System
 The somatic nervous system includes both sensory and motor neurons.
 Sensory neurons convey input from receptors for somatic senses (tactile, thermal, pain,
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proprioceptive) and special senses (sight, hearing, taste, smell, equilibrium).
These sensations are normally consciously perceived.
Somatic motor neurons innervate skeletal muscles to produce both voluntary and involuntary
movements.
When a somatic motor neuron stimulates a muscle, it contracts; the effect is excitation.
If it fails to stimulate a muscle it becomes paralyzed.
A few skeletal muscles, such as those in the middle ear, are controlled by reflexes and cannot
be contracted voluntarily.
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Autonomic Sensory Neurons
 The main input to the ANS comes from autonomic
(visceral) sensory neurons. These neurons are
primarily associated with interoceptors (monitor the
internal environment).
 Most of the time, these signals are not consciously
perceived; although, intense activation of
interoceptors may produce conscious sensation.
 Pain sensations from damaged viscera and angina
pectoris (chest pain) form inadequate blood flow to
the heart can produce conscious sensation.
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Autonomic Motor Neurons
 Autonomic motor neurons regulate visceral activities by either
increasing (exciting) or decreasing (inhibiting) activities in the effector
tissues (cardiac muscle, smooth muscle, and glands).
 Examples of autonomic motor responses include: changes in the
diameter of the pupils, dilation and constriction of blood vessels,
adjustment of the rate and force of the heartbeat.
 Unlike skeletal muscle, tissue innervated by the ANS often continue to
function to some extent even if their nerve supply is damaged.
 The heart continues to beat when it is removed for transplantation,
smooth muscle lining the GI tract contracts rhythmically on its own,
and glands produce some secretions in the absence of ANS control.
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Two Divisions of ANS Output
 Unlike the somatic output (motor), the output portion
of the ANS has two divisions: sympathetic division
and parasympathetic division.
 Most organs have dual innervation (both PSNS and
SNS innervation).
 In some organs, nerve impulses from one division
stimulate the organ to increase its activity (excitation)
and impulses from the other division decrease its
activity (inhibition).
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Sympathetic Nervous System
 The sympathetic division is often called the fight-or-flight division.
 Sympathetic activities result in increased alertness and metabolic
activities in order to prepare the body for an emergency situation.
 Physical activity and emotional stress can trigger sympathetic
activities.
 Effects of sympathetic stimulation: rapid heart rate, faster breathing
rate, dilation of pupils, dry mouth, sweaty but cool skin, dilation to
blood vessels to organs involved in combating stress (heart and skeletal
muscles), constriction of blood vessels to organs not involved in
combating stress (GI tract and kidneys), and release of glucose from
the liver).
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Parasympathetic Division
 The parasympathetic division is often referred to as the
rest-and-digest division because its activities conserve
and restore body energy during times of rest or
digesting a meal.
 The majority of the nerve output is directed towards
smooth muscle and glandular tissue of the
gastrointestinal and respiratory tracts.
 The parasympathetic division conserves energy and
replenishes nutrients.
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Comparison of Somatic and Autonomic
Nervous Systems
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Comparison of Somatic and Autonomic
Nervous Systems
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Two-neuron Efferent Pathway
 The ANS differs from the somatic nervous system in that it requires a
sequential two-neuron efferent pathway.
 The preganglionic neuron will synapse with a postganglionic neuron
before innervating the target organ.
 The first of the two motor neurons is called the preganglionic
neuron. The cell body is located in the brain or spinal cord. It exits
the CNS as part of a cranial or spinal nerve.
 It synapses with a postganglionic neuron in an autonomic ganglion,
which is the second neuron in the autonomic pathway. The
postganglionic neuron is located entirely in the PNS.
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Preganglionic Neuron
 Sympathetic Division
 Thoracolumbar division [cell bodies in the lateral horns
of the 12 thoracic segments and the first two (sometimes
three) lumbar segments]
 Thoracolumbar outflow [axons]
 Parasympathetic Division
 Craniosacral division [cell bodies in the nuclei of four
cranial nerves (III, VII, IX, & X) and the lateral gray
matter of the second through fourth sacral segments]
 Craniosacral outflow [axons]
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Structure of the Sympathetic Division
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Structure of the Parasympathetic Division
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Adrenergic and Cholinergic Receptors
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Autonomic Ganglia
 Sympathetic ganglia
 Parasympathetic ganglia
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Sympathetic Ganglia
 Sympathetic ganglia – sites of synapse between
sympathetic preganglionic and postganglionic
neurons.
 Sympathetic trunk ganglia (also called vertebral chain
ganglia or paravertebral ganglia). Lie in a vertical row on
either side of the vertebral column. Extend from the
base of the skull to the coccyx. Innervate organs above
the diaphragm (head, neck and heart).
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Superior, middle, and inferior cervical ganglia.
 Prevertebral (collateral) ganglia. Lie anterior to the
vertebral column. Innervate organs below the
diaphragm.
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Celiac ganglion, superior mesenteric ganglion, inferior
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mesentericDr.ganglion,
aorticorenal ganglion, and renal
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Parasympathetic Ganglia
 Parasympathetic ganglia – sites of synapse between
preganglionic parasympathetic neurons and
postganglionic neurons in the terminal (intramural)
ganglia.
 Terminal ganglia in the head have specific names:
ciliary ganglion, pterygopalatine ganglion,
submandibular ganglion, and otic ganglion.
 The remaining terminal ganglia do not have specific
names.
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Postganglionic Neuron
 Axons of preganglionic neurons pass to sympathetic trunk ganglia and
synapse with postganglionic neurons.
 A single sympathetic preganglionic fiber has many axon collaterals and
may synapse with 20 or more postganglionic neurons. This divergence
explains why many sympathetic responses affect almost the entire body
simultaneously.
 After exiting their ganglia, the postganglionic axons typically terminate
in several visceral effectors.
 Axons of preganglionic neurons of the parasympathetic division pass to
terminal ganglia near or within a visceral effector.
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Comparison of Sympathetic And
Parasympathetic Divisions of ANS
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Effects of Sympathetic And Parasympathetic
Divisions of ANS
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Effects of Sympathetic And Parasympathetic
Divisions of ANS
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Autonomic Plexuses
 Thorax
 Cardiac plexus – innervates the heart
 Pulmonary plexus – innervates the bronchial tree
 Abdomen and Pelvis
 Celiac (solar) plexus [largest plexus]– innervates the stomach, spleen,
pancreas, liver, gallbladder, kidneys, adrenal medulla, testes, & ovaries
 Superior mesenteric plexus – innervates the small and large intestines
 Inferior mesenteric plexus – innervates the large intestine
 Hypogastric plexus – innervates the pelvic viscera
 Renal plexus – innervates the renal arteries within the kidneys and
ureters
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Postganglionic Neurons in the Sympathetic
Division
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Autonomic Plexuses in the Thorax, Abdomen,
and Pelvis
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Sympathetic Trunk Ganglia
 Cervical Portion
 Thoracic Portion
 Lumbar Portion
 Sacral Portion
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Pathways from Sympathetic
Ganglia to Visceral Effectors
 Spinal nerves (31 pairs) – innervate visceral effectors of the skin of the neck, trunk,
and limbs including sweat glands, smooth muscle in blood vessels, arrector pili
muscles.
 Gray rami communicantes – structures containing sympathetic postganglionic axons
that connect the ganglia of the sympathetic trunk to the spinal nerves.
 Cephalic periarterial nerves – innervate visceral effectors of the skin of the face
(sweat glands, smooth muscle of blood vessels, arrector pili muscles. Innervates
visceral effectors of the head (smooth muscle of the eye, lacrimal glands, pineal
gland, nasal mucosa, and salivary glands.
 Sympathetic nerves – innervates visceral effectors in the thoracic cavity including
the heart and lungs.
 Splanchnic nerves – innervates the organs of the abdominopelvic cavity.
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Sacral Parasympathetic Outflow
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Parasympathetic Division of the
ANS
 Preganglionic neurons originate from the cranial
nerves III, VII, IX, & X as well as the sacral spinal
nerves S2-4.
 The presynaptic neuron usually synapses with 4-5
postsynaptic neurons, all of which supple a single
visceral effector.
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Enteric Division
 Plexuses
 Myenteric plexus
 Submucosal plexus
This system controls motility and secretory functions of
the gastrointestinal tract.
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Cholinergic Neurons
 Cholinergic neurons – acetylcholine Ach
 Cholinergic neurons include:
 All sympathetic and parasympathetic preganglionic
neurons
 Sympathetic postganglionic neurons that innervate
most sweat glands
 All parasympathetic postganglionic neurons
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Cholinergic Receptors
 Cholinergic receptors bind with acetylcholine
 Two types
 Nicotinic receptors
 Muscarinic receptors
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Adrenergic Neurons and
Receptors
 Release noripinephrine (noradrenalin)
 Most sympathetic postganglionic neurons are
adrenergic.
 Two types:
 Alpha receptors
 Beta receptors
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Cholinergic and Adrenergic Neurons in the
Autonomic Nervous System
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Autonomic Tone
 Autonomic tone is a balance between sympathetic and
parasympathetic activity.
 Autonomic tone is regulated by the hypothalamus.
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Sympathetic Responses
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Stress ↑sympathetic system ↑fight-or-flight response.
↑ production of ATP
Dilation of pupils
↑heart rate and blood pressure
Dilation of airways
Constriction of blood vessels that supply the kidneys and gastrointestinal tract
↑blood supply to the skeletal muscles, cardiac muscle, liver and adipose tissue
↑glycogenolysis ↑blood glucose
↑lipolysis
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Parasympathetic Responses
 Rest-and-digest response
 Conserve and restore body energy
 ↑digestive and urinary function
 ↓Body functions that support physical activity
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Integration and Control of Autonomic
Functions
 Direct innervation – brain stem and spinal cord
 Hypothalamus is the major control and integration
center of the ANS
 It receives input from the limbic system
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