Autonomic Division: Homeostatic balancing

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Autonomic Division Homeostatic balancing
Figure 11-1 Homeostasis and the autonomic
division
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Somatic and Autonomic Nervous Systems

• Somatic
• Skeletal muscle
• Conscious and unconscious movement
• Skeletal muscle contracts
• One synapse
• Acetylcholine
• Receptor molecules nicotinic

• Autonomic
• Smooth and cardiac muscle and glands
• Unconscious regulation
• Target tissues stimulated or inhibited
• Two synapses
• Acetylcholine by preganglionic neurons and ACh or
  norepinephrine by postganglionic neurons
• Receptor molecules varies with synapse and
  neurotransmitter

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Fig. 16.1
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Physiology of ANS

• Neurotransmitters primary substances produced by
  neurons of ANS
• Acetylcholine released by cholinergic neurons
• Norepinephrine released by adrenergic neurons
• Certain cells have receptors that combine with
  neurotransmitters causing a response in the cell
• Cholinergic bind acetylcholine. Have two
  different forms nicotinic and muscarinic
• Nicotinic all receptors on postganglionic
  neurons, all skeletal muscles, adrenal glands
• Muscarinic all receptors on parasympathetic
  effectors, receptors of some sweat glands
• Adrenergic receptors bind norepinephrine/epinephri
  ne
• Alpha and beta receptors.These are further
  subdivided into categories. a1 and b1 usually
  have opposite affects than a2 and b2

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Fig. 9.6
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Sympathetic (Thoracolumbar) Division

• Preganglionic cell bodies in lateral horns of
  spinal cord T1-L2 thoracolumbar
• Preganglionic axons pass through ventral roots to
  white rami communicantes to the retroperitoneal
  sympathetic chain ganglia.

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Parasympathetic (Craniosacral) Division

• Preganglionic cell bodies in nuclei of brainstem
  or lateral parts of spinal cord gray matter from
  S2-S4
• Preganglionic axons from brain pass to terminal
  ganglia through cranial nerves III, VII, IX and X
• Preganglionic axons from sacral region pass
  through pelvic nerves to terminal ganglia
• Terminal ganglia located near organ innervated or
  embedded in wall of organ

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Functional Generalizations of ANS

• Dual innervation to most organs with sympathetic
  and parasympathetic having the opposite effects.
• Either division alone or both working together
  can coordinate activities of different
  structures.
• Sympathetic prepares body for physical activity
  or flight-or-fight response. But also important
  at rest. Blood vessel walls receive only
  sympathetic stimulation, so at rest, sympathetic
  is responsible for maintenance of blood pressure.
• In general, parasympathetic more important for
  resting conditions SLUDD salivation,
  lacrimation, urination, digestion, defecation

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Location of ANS Receptors
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Fig 9.11
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Adrenergic Stimulation

• Causes both excitation inhibition depending on
  tissue
• Because of different subtypes of receptors for
  same NT
• 2 major subtypes are ? ? adrenergic receptors
• Each has own subtypes ?1, ?2 ?1, ?2

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Organs With Dual Innervation

• Most visceral organs receive dual innervation
  (supplied by both Symp Parasymp)
• While 2 branches are usually antagonistic, such
  as their effects on heart rate
• Or cooperative (produce different effects that
  work together to cause desired effect) such as
  with sexual response in males
• Erection - due to parasympathetic stimulation
  (vasodilation of penile blood vessels
• Ejaculation - due to sympathetic stimulation of
  smooth muscle

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Autonomic Reflexes

• Parasympathetic reflex via vagus lowers heart
  rate.
• Sympathetic reflex via cardiac accelerator nerves
  (sympathetic) cause heart rate to increase.

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Organs Without Dual Innervation

• Regulation achieved by increasing or decreasing
  firing rate
• Adrenal medulla, arrector pili muscle, sweat
  glands, most blood vessels receive only
  sympathetic innervation

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Sympathoadrenal System

• The adrenal medulla, located in adrenal gland on
  top of kidney, appears to be a modified
  collateral ganglion
• Its secretory cells appear to be modified
  postganglionics
• That release 85 epinephrine (Epi) 15
  norepinephrine (Norepi) into blood in response to
  preganglionic stimulation
• Stimulated during mass activation

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Control of the ANS by Higher Brain Centers

• Medulla most directly controls activity of ANS
• It has centers for control of cardiovascular,
  pulmonary, urinary, reproductive, digestive
  systems
• Hypothalamus has centers for control of body
  temperature, hunger, thirst can regulate
  medulla
• Limbic system is responsible for visceral
  responses that reflect emotional states
• Cerebral cortex cerebellum also influence ANS

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Responses to Exercise (Fight or Flight Response)

• Increased heart rate and force of contraction
• Blood vessel dilation in skeletal and cardiac
  muscles
• Dilation of air passageways
• Energy sources availability increased
• Glycogen to glucose
• Fat cells break down triglycerides
• Muscles generate heat, body temperature increases
• Sweat gland activity increases
• Decrease in nonessential organ activities