AUTONOMIC NERVOUS SYSTEM AND SPECIAL SENSES

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AUTONOMIC NERVOUS SYSTEM AND SPECIAL SENSES
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AUTONOMIC NERVOUS SYSTEM

• functions
• responsible for maintaining a nearly constant
  internal environment
• acts on all effectors other than _________
  muscles
• coordinates cardiovascular, respiratory,
  digestive, urinary and reproductive functions
• adjusts internal water, electrolyte, nutrient and
  dissolved gas concentrations in body fluids
• activated by spinal cord, brain stems reticular
  formation, hypothalamus and cerebral cortex
• travel through spinal and cranial nerves

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ANS - TWO MOTOR NEURONS

• 1. preganglionic myelinated neurons
• cell body in the ___________ horn of the spinal
  cord or in the brain stem
• 2. postganglionic unmyelinated neurons
• cell body lies outside the CNS
• synapses onto the effector - smooth muscle,
  cardiac muscle or glands

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ANS VERSUS SOMATIC MOTOR NERVOUS SYSTEM

• origin
• Somatic
• spinal cord, ventral horn
• ANS
• spinal cord, lateral horn or brain stem
• innervation
• Somatic
• skeletal muscle
• ANS
• smooth and cardiac muscle, glands

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ANS VERSUS SNS

• motor neurons
• SNS
• one - thick, heavily myelinated A fibers
• ANS
• 1. preganglionic - heavily myelinated, thin
• 2. postganglionic - thinner, unmyelinated
• response to stimulation
• SNS
• always stimulatory
• ANS
• stimulatory or inhibitory

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ANS VERSUS SNS

• neurotransmitter
• SNS
• ____________
• ANS
• ______________
• voluntary or involuntary
• SNS
• can be voluntary
• ANS
• generally involuntary

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SYMPATHETIC DIVISION SUMMARY

• vasoconstriction of blood vessels to skin
• increases sweating
• increases heart rate
• increases blood pressure
• inhibits gastrointestinal secretion and movements
• increases metabolism
• vasodilation of pupils

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PARASYMPATHETIC DIVISION SUMMARY

• controls focusing of eyes
• constriction of pupils
• stimulates intestinal secretions
• decreases heart rate
• increases contractions in the intestinal tract
• allows for urinary bladder and rectal emptying

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SYMPATHETIC DIVISION - ANATOMY

• origin
• spinal cord between T1- and L2
• also called thoracolumbar division
• preganglionic neurons leave ventral root of
  spinal cord and enter one of a series of
  interconnected ganglia
• called paravertebral or sympathetic chain ganglia

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SYMPATHETIC DIVISION - PATHWAYS

• exception - only one in the ANS
• preganglionic neuron to adrenal medulla
• passes thru prevertebral ganglia and synapses
  directly on the adrenal medulla
• no postganglionic neuron

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PARASYMPATHETIC DIVISION - ANATOMY

• origin
• two areas
• 1. brain stem
• 2. spinal cord S2 to S4
• called craniosacral division
• brain stem origin
• cranial nerves III, VII, IX
• X- vagus
• latin for wandering
• 90 of all parasympathetic fibers
• no ganglion, synapse on the effector

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ANS NEUROTRANSMITTERS

• Cholinergic fibers
• release ACh
• all preganglionic neurons of both divisions
• all postganglionic neurons of the Parasympathetic
  division
• Adrenergic fibers
• release NE
• all postganglionic neurons of the Sympathetic
  division

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PHYSIOLOGY OF NOREPINEPHRINE

• formation of NE
• tyrosine --gt DOPA --gt dopamine --gt
  norepinephrine --gt epinephrine (in adrenal
  medulla)
• effect of NE
• lasts a few seconds
• ACh last 20 milliseconds

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PHYSIOLOGY OF NOREPINEPHRINE

• fate of norepinephrine after it is released
• a. 50 - 80 taken up by active transport into the
  synaptic bulbs
• b. some diffuses away
• c. some is destroyed by one of two enzymes
• MAO - monoamine oxidase
• MAO inhibitors - antidepressant
• COMT- catechol-O-methyl transferase

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ACh or Cholinergic RECEPTORS

• 1. Muscarinic
• Muscarine
• poison from a mushroom activates these receptors
• ACh receptors at the effector
• ACh binding can be stimulatory or inhibitory
• 2. Nicotinic
• - nicotine
• toxin (50 mg) obtained from tobacco leaves
• ACh binding always stimulatory
• ACh receptors
• a. ACh receptors on the adrenal medulla
• b. ACh receptors on the postganglionic neuron at
  the synapse between pre- and postganglionic
  neurons
• c. ACh receptors on skeletal muscle

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ADRENERGIC RECEPTORS

• beta-1 -- excitation
• beta-2 -- inhibition
• most common beta
• alpha-1 -- excitation
• most common alpha
• alpha-2 -- inhibition

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SYMPATHETIC CONTROL ONLY

• adrenal medulla - stimulates secretion
• arrector pili - stimulates contraction
• sweat glands - stimulates secretion
• kidneys - releases renin
• adipose tissue - fatty acid release
• most blood vessels - stimulates vasoconstriction

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DUAL CONTROL - ANTAGONISTIC

• eye
• salivary glands
• heart
• respiratory system
• digestive system
• sphincters
• level of activity
• secretory glands
• liver

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DUAL CONTROL - ANTAGONISTIC

• urinary bladder
• sphincters
• contraction

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PARASYMPATHETIC SUMMARY ACTIONS

• short-term control
• ACh is quickly destroyed
• gastrointestinal tone
• paradoxical fear reaction
• massive activation of the Parasympathetic system
• loss of control over urination or defecation

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SYMPATHETIC SUMMARY ACTIONS

• long-term control
• NE is inactivated slowly
• adrenal medulla releases EP and NE which act
  longer
• vasomotor tone

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ADRENAL MEDULLA

• stimulated by cholinergic fibers of the
  sympathetic division
• modified postganglionic neuron
• hormones
• EP -- 80
• NE -- 20
• dopamine -- trace
• effects
• same as those caused by direct sympathetic
  stimulation plus effects other cells
• effect lasts 10 times longer

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EP VS NE

• EP has a greater effect on
• increasing cardiac activity
• increasing metabolism
• dilating bronchioles
• NE has a greater effect on increasing
• constriction of blood vessels
• blood pressure

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ADRENERGIC MIMICING DRUGS

• epinephrine and norepinephrine
• amphetamine
• causes release of NE from storage vesicles in SNS
• tricyclic antidepressants
• prolongs activity of NE
• used to treat depression

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ADRENERGIC BLOCKING DRUGS

• reserpine
• blocks synthesis and storage of NE
• used as a tranquilizer
• beta blockers - propanolol and metoprolol
• decrease heart rate and force of contraction

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CHOLINERGIC STIMULATING DRUGS

• ACh
• cannot be used, broken down too quickly
• muscarinic
• pilocarpine
• increases the diameter of the canal of schlemm
• nicotinic - nicotine
• excites both sympathetic and parasympathetic
  nervous systems
• stimulates skeletal muscle in somatic nervous
  system

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CHOLINERGIC INHIBITING DRUGS

• atropine
• blocks ACh on muscarinic but not nicotinic
  receptors
• derived from nightshade plant
• uses
• dilates pupils (bella donna)
• dries mucous membranes of respiratory tract prior
  to general anaesthetics
• antidote to nerve gas