Chapter 14: Autonomic Nervous System

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Chapter 14 Autonomic Nervous System

• Comparison between the ANS and SNS
• Parasympathetic and Sympathetic Nervous Systems
• Anatomy and Physiology of the ANS
• Homeostatic Imbalances of the ANS

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Overview of ANS

• Main input to ANS comes from autonomic sensory
  neurons that are associated with interoceptors.
• Chemoreceptors that monitor pH
• Mechanoreceptors that monitor stretch
• Pain receptors produce conscious sensations
• Autonomic motor neurons regulate visceral
  activities.
• Limited conscious control of autonomic responses

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Placement of the ANS
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ANS vs SNS
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SNS and ANS Overlap

• Nearly all spinal and cranial nerves have both
  somatic and autonomic neurons
• Adaptation to internal and external conditions
  need both SNS and ANS
• The ANS speeds heart rate and diverts blood to
  skeletal muscles.

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ANS divisions

• Parasympatheticmaintenance and conservation
• Sympatheticmobilization for activity
• Innervate the same organs
• Produce opposite effects
• Continuously produce fine adjustments

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ANS anatomy

• Origin
• Length of fibers
• Location of ganglia

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Parasympathetic anatomy Cranial outflow

• Occulomotor nerve (III)
• Controls constriction of pupils
• Causes bulging of lens
• Facial nerve (VII)
• Activate nasal and lacrimal glands
• Stimulate submandibular and sublingual salivary
  glands

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Parasympathetic anatomy Cranial outflow

• Glossopharyngeal nerve (IX)
• Stimulates parotid salivary glands
• CN III, VII and IX Jump to trigeminal (V)

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Parasympathetic anatomyCranial outflow

• Vagus nerves (X)
• Input to the neck plexuses
• Serve all organs in the thoracic and abdominal
  cavities
• Numerous branches join plexuses

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Parasympathetic anatomy Sacral outflow

• Originate in lateral gray matter of segments
  S2-S4
• Branch to form pelvic splanchnic nerves and
  hypogastric plexus.

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Sympathetic anatomyThoracolumnar outflow

• Sympathetic division innervates more organs
• Innervates structures in superficial part of the
  somatic nervous system
• Innervates smooth muscles of vessels
• Preganglionic fibers originate in lateral horns
  of T1 to L2
• Ventral root ? white rami communicans ?
  sympathetic trunk ganglion

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Projection of preganglionic neurons

• Synapse with a ganglionic neuron in same trunk
  ganglion
• Ascend or descend in trunk and synapse in another
  ganglion
• Pass through the trunk to synapse in a
  prevertebral ganglion
• Synapse in the adrenal medulla

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Sympathetic pathways

• Postganglionic neurons enter ventral rami via
  gray rami communicantes and then travel to
  effectors.
• Rami communicantes are associated only with the
  sympathetic division
• Pathways to head (T1-T4) ascend to superior
  cervical ganglion

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Sympathetic pathways

• Pathways to the thorax (T1-T6)
• Synapse in the middle and inferior cervical
  ganglia and enter cervical nerves C4 to C8
• Synapse in the nearest trunk ganglion with
  preganglionic cells and then travel directly to
  organ

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Sympathetic pathways

• Pathways to the abdomen (T5-L2)
• Travel in splanchnic nerves and synapse in celiac
  and mesenteric ganglia
• Serve stomach, intestines liver, spleen and
  kidneys

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Sympathetic pathways

• Pathways to the pelvis (T10-L2)
• Travel in lumbar and sacral splanchnic nerves to
  the lumbar and splanchnic trunk ganglia
• Serves distal intestines, bladder and
  reproductive organs

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Sympathetic pathways

• Pathway to the adrenal medulla
• Travels through the celiac ganglion to the
  medullary area of the adrenal gland

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Visceral reflexes

• Visceral sensory neurons signal chemical changes,
  stretch, and irritation of viscera

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Autonomic reflexes

• Receptordistal end of the sensory neuron
• Sensory neuron--projects to CNS
• Integration centerhypothalamus and brain stem
  and spinal cord
• Motor neurons project from CNS through one or two
  synapses
• Effectoreffects on smooth muscle, cardiac
  muscle, and glands.

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Referred pain

• Somatic and visceral sensory fibers travel the
  same pathways
• Visceral sensations can be perceived as somatic
  sensations

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Neurotransmitters and receptors

• Cholinergic neurons release ACh
• Cholinergic receptors
• Nicotinic receptors
• Muscarinic receptors
• Adrenergic neurons release NE and epinephrine
• Adrenergic receptors
• a1 and b1 are excitatory
• a2 and b2 are inhibitory

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Cholinergic neurons and receptors
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Cholinergic neurons and receptors
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Cholinergic neurons and receptors
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Adrenergic neurons and receptors
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Drug effects

• Atropineblocks muscarinic receptors
• Blocks salivation and lung secretions during
  surgery
• Dilate the pupils
• Neostigmine inhibits acetylcholinesterase
• Myasthenia gravis
• Sympathomimetics (Phenylephrine)
• Colds, allergies and nasal congestion
• b2 activators and blockers
• Asthma

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Sympathetic and parasympathetic tone

• Sympathetic or vasomotor tone
• Increase in blood pressure
• Regulate flow of blood
• Parasympathetic tone
• Slows heart
• Regulates activity of digestive system
• Activates glands

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Cooperative effects

• ANS regulation of external genitalia
• Sympathetic coordination
• Thermoregulation
• Renin-angiotensin pathway
• Metabolic effects

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Local and diffuse effects

• Parasympathetic input is local and brief
• Sympathetic input is diffuse and highly
  interconnected
• Some sympathetic input is local
• Sympathetic effects can be prolonged

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Control of ANS function

• Anterior hypothalamus and parasympathetic
  functions
• Posterior hypothalamus and sympathetic functions

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Homeostatic imbalances of ANS

• Hypertensionvasoconstriction
• Raynauds diseaseexaggerated vasoconstriction
• Autonomic dysflexiauncontrolled activation of
  autonomic neurons leads to high arterial blood
  pressure