Download Organization of the Autonomic Nervous System LEARNING

Organization of the Autonomic Nervous System
LEARNING OBJECTIVES:
At the end of lecture, students should be able to:
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Define Autonomic Nervous System.
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Know divisions of the ANS into Sympathetic & Parasympathetic Systems.
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Identify levels of autonomic control.
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Compare somatic and autonomic systems.
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Compare Sympathetic & Parasympathetic Systems.
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Know applied aspect related to the topic.
The Autonomic Nervous System and Visceral Sensory Neurons:
The Autonomic Nervous System
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Innervates smooth muscle, cardiac muscle, and glands.
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Regulates visceral functions
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Heart rate, blood pressure, digestion, urination
The general visceral motor division of the PNS
COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS
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Somatic motor system:
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One motor neuron extends from the CNS to skeletal muscle
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Axons are well myelinated, conduct impulses rapidly
Autonomic nervous system:
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Chain of two motor neurons
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Preganglionic neuron
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Postganglionic neuron
Conduction is slower due to thin or unmyelinated axons.
DIVISIONS OF THE AUTONOMIC NERVOUS SYSTEM
Sympathetic and parasympathetic divisions
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Innervate mostly the same structures
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Cause opposite effects
Sympathetic – “fight, flight, or fright”
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Activated during exercise, excitement, and emergencies
Parasympathetic – “rest and digest”
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Concerned with conserving energy
ANATOMICAL DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC
DIVISIONS
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Issue from different regions of the CNS.
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Sympathetic:
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Also called thoracolumbar division.
Parasympathetic:
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also called craniosacral division.
ANATOMICAL DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS
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Length of postganglionic fibers
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Sympathetic – long postganglionic fibers
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Parasympathetic – short postganglionic fibers.
Branching of axons
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Sympathetic axons – highly branched
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Influences many organs
Parasympathetic axons – few branches
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Localized effect.
NEUROTRANSMITTERS OF AUTONOMIC NERVOUS SYSTEM
Neurotransmitter released by preganglionic axons:
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Acetylcholine for both branches (cholinergic)
Neurotransmitter released by postganglionic axons:
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Sympathetic – most release NOREPINEPHRINE (adrenergic).
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Parasympathetic – release ACETYLCHOLINE .
ANATOMICAL DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS
THE PARASYMPATHETIC DIVISION
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Cranial outflow
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Comes from the brain.
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Innervates organs of the head, neck, thorax, and abdomen.
Sacral outflow
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Supplies remaining abdominal and pelvic organs.
CRANIAL OUTFLOW
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Preganglionic fibers run via:
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Oculomotor nerve (III)
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Facial nerve (VII)
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Glossopharyngeal nerve (IX)
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Vagus nerve (X)
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Cell bodies located in cranial nerve nuclei in the brain stem
PARASYMPATHETIC NERVOUS SYSTEM; OUTFLOW VIA THE VAGUS
NERVE (X)
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Fibers innervate visceral organs of the thorax and most of the
abdomen
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Stimulates - digestion, reduction in heart rate and blood pressure
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Preganglionic cell bodies
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Located in dorsal motor nucleus in the medulla
Ganglionic neurons
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Confined within the walls of organs being innervated
PARASYMPATHETIC NERVOUS SYSTEM: SACRAL OUTFLOW
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Emerges from S2-S4
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Innervates organs of the pelvis and lower abdomen
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Preganglionic cell bodies
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Located in visceral motor region of spinal gray matter
Form splanchnic nerves
THE SYMPATHETIC DIVISION
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Basic organization:
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Issues from T1-L2
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Preganglionic fibers form the lateral gray horn
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Supplies visceral organs and structures of
superficial body regions
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Contains more ganglia than the parasympathetic
division.
SYMPATHETIC NERVOUS SYSTEM:
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Larger of the two systems
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Function is to prepare the body for an emergency
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Consists of efferent outflow from the spinal cord, two
ganglionated sympathetic trunks, important branches and,
plexuses and regional ganglia.
Internal structure of the autonomic nervous system is made up of a
series of two neurons:
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PREGANGLIONIC NEURON - arises in the central nervous
system from spinal cord segments T1 to L1 or L2 (the lower
limit varies). This neuron synapses on a cell body of a
postganglionic neuron.
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POSTGANGLIONIC NEURON - arises in a sympathetic
ganglion and travels peripherally to act on smooth muscles,
cardiac muscles or glands.
THE PATH OF THE NEURONS ARE:
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Intermediolateral cell column in gray matter of spinal cord
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ventral root of spinal nerve
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spinal nerve (intercostal nerve in this case)
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white communicating ramus
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sympathetic chain. Preganglionic neuron can travel
up and down the sympathetic chain to synapse in
adjacent ganglia or synapse on the ganglion that it
enters.
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postganglionic neuron leaves the ganglion by way of
gray communicating ramus to reenter the spinal
nerve (intercostal in this case) or, in thorax by way of
a splanchnic nerve to supply structures in the abdominal cavity. The postganglionic neurons
from the middle cervical ganglion, the stellate ganglion and ganglia T2-T4 enter the cardiac
plexus and from there to the heart.
Sympathetic Trunk Ganglia
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Located on both sides of the vertebral column
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Linked by short nerves into sympathetic trunks
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Joined to ventral rami by white and gray rami communicantes
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Fusion of ganglia  fewer ganglia than spinal nerves
PREVERTEBRAL GANGLIA
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Unpaired, not segmentally arranged
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Occur only in abdomen and pelvis
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Lie anterior to the vertebral column
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Main ganglia
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Celiac, superior mesenteric, inferior mesenteric, inferior hypogastric ganglia
SYMPATHETIC PATHWAYS TO THE HEAD
SYMPATHETIC PATHWAYS TO THORACIC ORGANS
SYMPATHETIC PATHWAYS TO THE ABDOMINAL ORGANS
SYMPATHETIC PATHWAYS TO THE PELVIC ORGANS
THE ROLE OF THE ADRENAL MEDULLA IN THE SYMPATHETIC DIVISION
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Major organ of the sympathetic nervous system
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Secretes great quantities epinephrine (a little norepinephrine)
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Stimulated to secrete by preganglionic sympathetic fibers
VISCERAL SENSORY NEURONS
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General visceral sensory neurons monitor:
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Stretch, temperature, chemical changes, and
irritation
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Cell bodies are located in the dorsal root ganglia
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Visceral pain – perceived to be somatic in origin
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Referred pain
Visceral Reflexes
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Visceral sensory and autonomic neurons
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Participate in visceral reflex arcs
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Defecation reflex
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Micturition reflex
CENTRAL CONTROL OF THE ANS
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Control by the brain stem and spinal cord
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Reticular formation exerts most direct influence
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Medulla oblongata
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Periaqueductal gray matter
Control by the hypothalamus and amygdala
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Hypothalamus – the main integration center of the ANS
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Amygdala – main limbic region for emotions
Control by the cerebral cortex