Chapter 15 The Autonomic Nervous System

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Chapter 15The Autonomic Nervous System
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I. COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS
SYSTEMS

• A. Somatic nervous system
• motor neurons stimulate skeletal muscles via
  efferent fibers
• sensory neurons of conscious sensation
• respond to stimuli
• send impulses to CNS along afferent fibers
• Somatic motor pathways
• from CNS (spinal cord) to effector ? only one
  single motor neuron
• neuromuscular jxn
• Somatic effector organs skeletal muscles
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COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS
SYSTEMS

• B. Autonomic nervous system
• motor neurons stimulate or inhibit glands,
  cardiac muscle, smooth muscle
• some visceral sensory neurons
• Autonomic motor pathways ? sympathetic and
  parasympathetic (see below)

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COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS
SYSTEMS

• Autonomic nervous system
• Autonomic effector organs
• smooth muscles intestinal, vascular, arrector
  pili
• cardiac muscle
• glands sweat glands, digestive, endocrine

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I. Comparison of SNS and ANS

• Somatic sensory neurons conduct signals from
  special senses and from general senses
• Axons of somatic motor neurons extend all the way
  from CNS to effectors (skeletal muscle)
• All somatic motor neurons release acetylcholine,
  which brings on contraction

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I. Comparison of SNS and ANS

• Autonomic sensory neurons conduct signals from
  interoceptors
• Chemoreceptors
• Mechanoreceptors
• Axons of autonomic motor neurons extend from the
  CNS and synapse with a second autonomic motor
  neuron in an autonomic ganglion
• Preganglionic autonomic motor neurons release
  acetylcholine
• Postganglionic autonomic motor neurons release
  either
• Acetylcholine
• Norepinephrin 

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I. Comparison of SNS and ANS

• ANS branches into two divisions
• Sympathetic division
• Parasympathetic division
•  
• Most organs have dual innervation
• They receive impulses from both sympathetic and
  parasympathetic neurons
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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

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• A. Anatomical Components
• Pre- and postganglionic neurons
• 1. Preganglionic neurons
• Flow from spinal cord to synapse with
  postganglionic neurons
• Thoracolumbar vs. craniosacral
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• 2. Autonomic ganglia
• cell bodies ? where pre- and postganglionic
  neurons synapse
• Thats all well say about this.
• a. sympathetic ganglia (sympathetic trunk ganglia
  or prevertebral ganglia)
• b. parasympathetic ganglia (terminal ganglia)

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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

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• Anatomical Components
• a. Autonomic motor pathways have two neurons
• 1. Preganglionic neurons
• Cell body within CNS
• Axon is myelinated, type B and part of a cranial
  or spinal nerve
• Thoracolumbar vs. craniosacral
• 2. Postganglionic neurons
• Cell body within autonomic ganglion
• Axon is unmyelinated, type C and terminates in a
  visceral effector

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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

• b. Preganglionic neurons
• In sympathetic division cell bodies lie within
  lateral horns of all thoracic segments and the
  first two lumbar segments
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• In parasympathetic division cell bodies lie
  within nuclei of four cranial nerves in the brain
  stem and in lateral horns of the second through
  the fourth sacral segments

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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

• c. Autonomic ganglia
• 2 groups of sympathetic ganglia
• Sympathetic trunk ganglia postganglionc axons
  innervate organs above the diaphragm
• Prevertebral ganglia postganglionic axons
  innervate organs below the diaphragm
• 1 group of parasympathetic ganglion
• Terminal ganglia located close to or entirely
  within visceral organs

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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

• d. Autonomic Plexuses
• Networks of both sympathetic and parasympathetic
  axons in the thorax, abdomen, and pelvis.
• Located in close proximity to blood vessels
• Cardiac plexus
• Pulmonary plexus
• Celiac plexus

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II. ANATOMY OF AUTONOMIC MOTOR PATHWAYS

• e. Postganglionic neurons
• Sympathetic preganglionic neurons synapse with
  postganglionic neurons in one of three ways
• In the first ganglion it reaches
• In a ganglion superior or inferior to the first
  one it reaches
• In a prevertebral ganglion by bypassing the
  sympathetic trunk ganglion
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• Sympathetic preganglionic neurons may synapse
  with many postganglionic  neuron (divergent
  circuit)
• Thus, widespread effects
• Parasympathetic neurons synapse with fewer
  postganglionic neurons near or within the
  effector
• Thus, localized effects

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B. Structure of the Sympathetic Division
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B. Structure of the Sympathetic Division
   Preganglionic axons exit the spinal cord as
part of a spinal nerve through the anterior
root - Preganglionic axons then travel through
the white ramus on their way to the sympathetic
trunk ganglion Postganglionic axons travel
through the gray ramus on their way to
effectors  
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B. Structure of the Sympathetic Division

•    Preganglionic axons exit the spinal cord as
  part of a spinal nerve through the anterior root
• Preganglionic axons then travel through the white
  ramus on their way to the sympathetic trunk
  ganglion
• Postganglionic axons travel through the gray
  ramus on their way to effectors
•   a. Cervical region of sympathetic trunk ganglia
  are subdivided into three ganglia
• i. Superior cervical ganglia
• Serves the head and heart
• ii. Middle cervical ganglia
• Serves the heart
• iii. Inferior cervical ganglia
• Serves the heart

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B. Structure of the Sympathetic Division

• b. Thoracic region of sympathetic trunk ganglia
  serves the heart, lungs, bronchi, skin
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• c. Lumbar regions of sympathetic trunk ganglia
  serve liver, stomach, pancreas, intestine,
  kidneys
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• d. Sacral regions of sympathetic trunk ganglia
  serve urinary bladder, reproductive organs,
  kidney, part of large intestine and rectum
• Some thoracic preganglionic axons as well as
  lumbar and sacral preganglionic axons pass
  through the sympathetic trunk without synapsing
• These become part of splanchnic nerves which
  terminate in prevertebral ganglia
• Splanchnic nerves synapse with postganglionic
  neurons that take the signal to effectors

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C. Structure of the Parasympathetic Division
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C. Structure of the Parasympathetic Division

• C. Structure of the Parasympathetic Division
• Cranial parasympathetic outflow
• Four pairs of terminal ganglia innervate
  structures in the head
• Preganglionic axons that form part of the vagus
  nerve (cranial nerve X) innervate the heart,
  lungs, liver, pancreas, and intestines
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• Sacral parasympathetic outflow
• Preganglionic axons form the pelvic splanchnic
  nerves, which innervate smooth muscle and glands
  in the walls of the colon, ureters, urinary
  bladder, and reproductive organs

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III. ANS Neurotransmitters and
ReceptorsAutonomic neurons are classified as
either cholinergic or adrenergic depending on the
type of neurotransmitter released
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III. ANS Neurotransmitters and Receptors

• A. Cholinergic neurons and receptors
• Cholinergic neurons release acetylcholine
• Includes all sympathetic and parasympathetic
  preganglionic neurons
• Includes all parasympathetic postganglionic
  neurons
• Includes only sympathetic postganglionic neurons
  that innervate sweat glands
• Cholinergic receptors are integral membrane
  proteins in the postsynaptic plasma membrane

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III. ANS Neurotransmitters and Receptors

•    Two types of cholinergic receptors
• a. Nicotinic receptors are located in plasma
  membranes and cell bodies of all sympathetic and
  parasympathetic postganglionic neurons and the
  neuromuscular junction
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• b. Muscarinic receptors are located in the
  plasma membrane of all effectors innervated by
  parasympathetic postganglionic neurons

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III. ANS Neurotransmitters and Receptors

•    Acetylcholine binding with nicotinic
  receptors causes depolarization
• - Acetylcholine binding with muscarinic
  receptors causes either depolarization or
  hyperpolarization, depending on the effector
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• - Acetylcholinesterase quickly removes
  acetylcholine from the synaptic gap and thus
  cholinergic neurons have brief outcomes

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III. ANS Neurotransmitters and Receptors

• B. Adrenergic neurons and receptors
• Adrenergic neurons release norepinephrine
  (noradrenaline)
• Includes most sympathetic postganglionic
  neurons
• Adrenergic receptors bind both norepinephrine and
  epinephrine Two groups of adrenergic receptors
• Alpha
• Beta

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III. ANS Neurotransmitters and Receptors

•    Activation of these receptors may bring on
  depolarization or hyperpolarization
• Adrenergic neurons have prolonged effects

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• V. Physiological Effects of the ANS
• A. Sympathetic responses
• Dominates the parasympathetic division during
  E-situations
• Exercises, Emergency, Excitement, Embarrassment
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• Favors body functions that support vigorous
  physical activity and rapid production of ATP
• Inhibits body functions that support storage of
  energy
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• Fight or Flight responses
• Pupils dilate
• Heart rate and blood pressure increase
• Airways dilate
• Reduced blood flow to kidneys and
  gastrointestinal tract
• Increased blood flow to organs essential for
  fight or flight response
• Release of glucose from glycogen stores
• Reduced non-essential muscular activity

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• V. Physiological Effects of the ANS
• B. Parasympathetic Responses
• Supports body functions that conserve and restore
  body energy during times of rest
• Enhances rest-and-digest activities
• Rest and digest responses
• Salivation
• Lacrimation
• Urination
• Digestion
• Defecation
• Also, decreased heart rate, decreased diameter of
  airways and decreased diameter of pupils

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• V. Integration and Control of Autonomic Functions
• A. Autonomic Reflexes
• Help regulate blood pressure, digestion,
  defecation, and urination
• Involve typical components of a reflex arc
• Receptor
• Sensory neuron
• Integrating center
• Motor neurons
• Effector

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• V. Integration and Control of Autonomic Functions
• B. Autonomic control by higher centers
• Typically, autonomic activities do not involve
  higher brain centers (no conscious perception)
• Hypothalamus is major control center for ANS
• Hypothalamic nuclei have synapses with both
  sympathetic and parasympathetic division of the
  ANS
• Receives sensory input regarding visceral
  functions, olfaction, taste, temperature, and
  levels of chemicals in fluids etc.
• Hypothalamic output influences ANS centers in
  both the brain stem and the spinal cord