Chapter 15 Autonomic NS

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Autonomic Nervous System
Chapter 15
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Autonomic Nervous System
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Autonomic Nervous System
- Regulate activity of smooth muscle, cardiac
muscle certain glands - Structures
involved General visceral afferent
neurons General visceral efferent
neurons Integration center within the brain -
Receives input from limbic system and other
regions of the cerebrum
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Basic Anatomy of ANS

• Preganglionic neuron
• cell body in brain or spinal cord
• axon is myelinated type B fiber that extends to
  autonomic ganglion
• Postganglionic neuron
• cell body lies outside the CNS in an autonomic
  ganglion
• axon is unmyelinated type C fiber that terminates
  in a visceral effector

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Autonomic vs Somatic NS
Somatic nervous system consciously perceived
sensations excitation of skeletal muscle one
neuron connects CNS to organ
Autonomic nervous system unconsciously perceived
visceral sensations involuntary inhibition or
excitation of smooth muscle, cardiac muscle or
glandular secretion two neurons needed to connect
CNS to organ preganglionic and postganglionic
neurons
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Somatic/Autonomic Nervous System
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Sympathetic Division of the ANS
Sympathetic Ganglia Trunk(chain) ganglia- near
vertebral column on either side Prevertebral(colla
teral) ganglia- anterior to vertebral column
close to large abdominal arteries.
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Sympathetic Division Structure

• Sympathetic preganglionic neurons pass to the
  sympathetic trunk. They may connect to
  postganglionic neurons in the following ways
• May synapse with postganglionic neurons in the
  ganglion it first reaches.
• May ascend or descend to a higher of lower
  ganglion before synapsing with postganglionic
  neurons.
• May continue, without synapsing, through the
  sympathetic trunk ganglion to a prevertebral
  ganglion and synapse with postganglionic neurons.
• May pass through sympathetic trunk ganglion and a
  prevertebral ganglion and then extend to
  chromaffin cell of adrenal medulla.

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Pathways of Sympathetic Fibers
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Parasympathetic Division of the ANS
Parasympathetic Ganglia terminal ganglia close to
or in the wall of organs
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Parasympathetic Division Structure

• Parasympathetic preganglionic neurons synapse
  with postganglionic neurons in terminal ganglia.

• The cranial outflow consists of preganglionic
  axons that extend from the brain stem in four
  cranial nerves.
• The cranial outflow consists of four pairs of
  ganglia and the plexuses associated with the
  vagus nerve (X).
• Ciliary ganglia
• Pterygopalatine ganglia
• Submandidibular ganglia
• Otic ganglia
• The sacral parasympathetic outflow consists of
  preganglionic axons in the anterior roots of the
  2nd through 4th sacral nerves and they form the
  pelvic splanchnic nerve.

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Autonomic Plexuses
Cardiac plexus Pulmonary plexus Celiac (solar)
plexus Superior mesenteric Inferior
mesenteric Hypogastric Renal plexus
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Pathway from Spinal Cord to Sympathetic Trunk
Ganglia

• Preganglionic axons ? anterior root of a spinal
  nerve ? white ramus ? sympathetic trunk ganglion.
• White rami communicantes structures containing
  sympathetic preganglionic axons that connect the
  anterior ramus of the spinal nerve with the
  ganglia of the sympathetic trunk.

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Organization of Sympathetic Trunk Ganglia

• Sympathetic trunk ganglia 3 cervical, 11 or 12
  thoracic, 4 or 5 lumbar, 4 or 5 sacral and 1
  coccygeal.
• Postganglionic neurons from the
• - superior cervical region head and heart.
• - middle cervical ganglion and the inferior
  cervical ganglion heart.
• Thoracic sympathetic trunk- heart, lungs, and
  bronchi.

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Pathways from Sympathetic Trunk Ganglia to
Visceral Effectors

• Axons leave the sympathetic trunk in 4 possible
  ways
• - spinal nerves
• - cephalic periarterial nerves
• - sympathetic nerves
• - splanchnic nerves

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Spinal nerves

• Gray ramus Axons of some postganglionic neurons
  leave the sympathetic trunk by entering a short
  pathway called a gray ramus and merge with the
  anterior ramus of a spinal nerve.
• Gray rami communicantes structures containing
  sympathetic postganglionic axons that connect the
  ganglia of the sympathetic trunk to spinal nerves.

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Cephalic Periarterial Nerves

• Some sympathetic preganglionic neurons that enter
  the sympathetic trunk ascend to the superior
  cervical ganglion where they synapse with
  postganglionic neurons. Some of these leave the
  sympathetic trunk by forming cephalic
  periarterial nerves.
• Serve visceral effectors in the skin of the face
  and head.

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Sympathetic Nerves

• Some axons of the postganglionic neurons leave
  the trunk by forming sympathetic nerves.
• Innervate the heart and lungs.

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Splanchnic Nerves

• Some sympathetic preganglionic axons pass through
  the sympathetic trunk without terminating in it.
  Beyond the trunk they form nerves called
  splanchnic nerves which extend to prevertebral
  ganglia.
• T5-T9 or T10- Greater splanchnic nerve.
• T10-T11- Lesser splanchnic nerve.
• L1-L4- Lumbar splanchnic nerve.

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Cranial Parasympathetic Outflow

• The cranial outflow has four pairs of ganglia and
  are associated with the vagus nerve.
• Ciliary ganglia-
• Pterygopalatine ganglia-
• Submandibular ganglia-
• Otic ganglia-
• Vagus nerve carries nearly 80 of the total
  craniosacral flow.

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Sacral Parasympathetic Outflow

• Consists of S2-S4.
• Pelvic splanchnic nerves

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Neurotransmitters and Receptors
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Adrenergic and Cholinergic Receptors
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Sympathetic vs. Parasympathetic
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Physiological Effects of the ANS

• Most body organs receive dual innervation
• innervation by both sympathetic parasympathetic
• Hypothalamus regulates balance (tone) between
  sympathetic and parasympathetic activity levels
• Some organs have only sympathetic innervation
• sweat glands, adrenal medulla, arrector pili mm
  many blood vessels
• controlled by regulation of the tone of the
  sympathetic system

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Sympathetic Responses

• Dominance by the sympathetic system is caused by
  physical or emotional stress -- E situations
• emergency, embarrassment, excitement, exercise
• Alarm reaction flight or fight response
• dilation of pupils
• increase of heart rate, force of contraction BP
• decrease in blood flow to nonessential organs
• increase in blood flow to skeletal cardiac
  muscle
• airways dilate respiratory rate increases
• blood glucose level increase
• Longer lasting than parasympathetic due to
  lingering of NE in synaptic gap and release of
  norepinephrine by the adrenal gland

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Parasympathetic Responses

• Enhance rest-and-digest activities
• Mechanisms that help conserve and restore body
  energy during times of rest
• Normally dominate over sympathetic impulses
• SLUDD type responses salivation, lacrimation,
  urination, digestion defecation and 3
  decreases--- decreased HR, diameter of airways
  and diameter of pupil
• Paradoxical fear when there is no escape route or
  no way to win
• causes massive activation of parasympathetic
  division
• loss of control over urination and defecation

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Sympathetic vs. Parasympathetic
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Autonomic Reflexes

• Autonomic reflexes occur over autonomic reflex
  arcs. Components of reflex arc
• sensory receptor
• sensory neuron
• integrating center
• motor neurons (pre postganglionic)
• visceral effectors
• Unconscious sensations and responses
• changes in blood pressure, digestive functions
  etc
• filling emptying of bladder or defecation

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Control of Autonomic Functioning

• Hypothalamus is major control center
• input emotions and visceral sensory information
• smell, taste, temperature, osmolarity of blood,
  etc
• output to nuclei in brainstem and spinal cord
• posterior lateral portions control sympathetic
  NS
• increase heart rate, inhibition GI tract,
  increase temperature
• anterior medial portions control
  parasympathetic NS
• decrease in heart rate, lower blood pressure,
  increased GI tract secretion and mobility

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Autonomic vs Somatic NS - Review

• Autonomic nervous system
• unconsciously perceived visceral sensations
• involuntary inhibition or excitation of smooth
  muscle, cardiac muscle or glandular secretion
• two neurons needed to connect CNS to organ
• preganglionic and postganglionic neurons

• Somatic nervous system
• consciously perceived sensations
• excitation of skeletal muscle
• one neuron connects CNS to organ

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Autonomic vs Somatic NS - Review
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Autonomic Dysreflexia

• Exaggerated response of sympathetic NS in cases
  of spinal cord injury above T6
• Certain sensory impulses trigger mass stimulation
  of sympathetic nerves below the injury
• Result
• vasoconstriction which elevates blood pressure
• parasympathetic NS tries to compensate by slowing
  heart rate dilating blood vessels above the
  injury
• pounding headaches, sweating warm skin above the
  injury and cool dry skin below
• can cause seizures, strokes heart attacks