Anatomy Ch 15

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Anatomy Ch 15
2010-12-07 01:11:19
Anatomy Autonomic Nervous System

Notes from chapter 15 ANS
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  1. Review of Somatic Nervous System
    -Somatic sensory neurons conduct signals from special and general senses

    - Axons of somatic motor neurons extend all the way from the CNS to the effectors (skeletal muscle)

    - All somatic motor neurons release ACh, which brings on contraction - all are excitatory
  2. Autonomic sensory neurons
    -conduct signals from interoceptors - sensory receptors located in blood vessels, visceral organs, muscles, and nervous system that monitor condition in the internal environment

    • Two types of interoceptors
    • - chemoreceptors - chemical balance - monitor blood CO2 level
    • - mechanoreceptors - mechanical - detect the degree of stretch in the walls of organs or blood vessels
  3. Autonomic ganglion
    - axons of myelinated autonomic motor neurons extend from the CNS to the autonomic ganglion. it synapses with a second autonomic motor neuron that extends from th autonomic ganglion to the effector via an unmylinated axon

    - preganglionic autonomic motor neurons release ACh

    - postganglionic autonomic motor neurons release either ACh or Norepinephrine
  4. Dual innervation
    most organs receive impulses from both sympathetic and parasympathetic neurons - in general signals from one division of the ANS will stimulate while signals from the other division will decrease organs activity
  5. Two branches of ANS
    1. Sympathetic division - fight-or-flight division - activities result in increased alertness and metabolic activities in order to prepare the body for an emergency situation

    2. Parasympathetic division - rest-and-digest - activities conserve and restore body energy during times of rest or digesting a meal
  6. Autonomic motor pathways
    • Autonomic motor pathways have two neurons
    • 1) Preganglionic neurons - cell body within the CNS
    • - Axon is myelinated, type B and part of a cranial or spinal nerve

    • 2) Postganglionic neurons - cell body within autonomic ganglion
    • - Axon is unmyelinated, type C and terminates in a visceral effector
  7. Preganglionic neurons
    In sympathetic division - cell bodies lie within lateral horns of all thoracic segments and the first two lumbar segements - also called the thoracolumbar division

    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 - also called the craniosacral division
  8. two major groups of autonomic ganglia
    • 1. Sympathetic ganglia
    • - Sympathetic trunk ganglia : postganglionic axons innervate organs above the diaphram

    - Prevertebral ganglia : postganglionic axons innervate organs below the diaphram

    • 2. Parasympathetic division
    • - Terminal ganglia : located close to or entirely within visceral organs
  9. Postganglionic neurons
    Once sympathetic preganglionic neurons reach the sympathetic trunk ganglion they synapse with postganglionic neurons in one of three way
    • 1. in the first ganglion it reaches
    • 2. in a ganglion superior or inferior to the first one it reaches (travels up or down the sympathetic trunk ganglion)
    • 3. In a prevertebral ganglion by bypassing the sympathetic trunk ganglion

    - sympathetic preganglionic neurons may synapse with many postganglionic neurons (divergent circuit) - widespread effects

    - Parasympathetic neurons synapse with fewer postganglionic neurons near or within the effector - localized effects
  10. Autonomic Plexuses
    networks of both sympathetic and parasympathetic axons in the thorax, abdomen and pelvis

    located in close proximity to bloodvessels

    • 1. cardiac plexus - supplies the heart
    • 2. pulmonary plexus - supplies the bronchial tree
    • 3. celiac or solar plexus - surrounds the celiac trunk
  11. Pathways from spinal cord to sympathetic trunk ganglia
    • 1. preganglionic axons exit the spinal cord as part of a spinal nerve through the anterior root
    • 2. Preganglionic axons then travel through the white ramus communicans (farther from spinal cord - swings out further past the sympathetic trunk ganglion) TYPE B - Myelinated
    • 3. postganglionic axons travel through the grey ramus communicans (close to spinal cord ) TYPE C - Unmyelinated
  12. Splanchnic nerves
    • 1.preganglionic axons that pass through the sympathetic trunk ganglion without synapsing
    • 2. they become part of splanchnic nerves
    • 3. that terminate in the prevertebral ganglia
    • 4. from there they synapse with postganglionic neurons that take the signal to effectors
  13. Classification of autonomic neurons
    • classified as either
    • 1. cholinergic
    • 2. adrenergic
    • depending on type of neurotransmitter released
  14. Cholinergic neurons and receptors
    • - release ACh
    • -include 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
  15. Two types of cholinergic receptors (receive ACh)
    classified by other substances they receive
    1. Nicotinic receptors - only excitatory response (depolarization) - located in plasma membrane and cell bodies of all sympathetic and parasympathetic postganglionic neurons and the NMJ

    2. muscarinic receptors - excitatory or inhibitory response (depolarization or hyperpolarization) - located in the plasma membrane of all effectors innervated by parasympathetic postganglionic neurons

    Acetylcholinesterase - enzyme - breaks down ACh and removes it from synaptic gap so cholinergic neurons have brief outcomes
  16. Adrenergic neurons and receptors
    • adrenergic neurons always release norepinephrine - can be excitatory or inhibitory depending on receptor
    • - includes most sympathetic postganglionic receptors

    adrenergic receptors - bind both norepinephrine and epinephrine - may bring on depolarization or hyperpolarization

    • Types of adrenergic receptors:
    • 1. Alpha 1 & 2
    • 2. Beta 1, 2, & 3

    • Alpha 1 & Beta 1 are excitatory
    • Alpha 2 and Beta 2 are inhimitory
    • Beta 3 is excitatory - thermogenesis - only in babies -found in BAT (Brown Adipose Tissue)

    Adrenergic neurons have prolonged effects because COMT and TAO break down epinephrine and norepinephrien slower than Acetylcholinesterase breaks down ACh
  17. Agonist
    substance that binds to and activates a receptor (minics effects of natural neurotransmitter)
  18. Antagonist
    substance that binds to and blocks a receptor (prevents natural neurotransmitter from exerting its effect)
  19. Autonomic reflexes
    -help regulate blood pressure, digestion, defication, and urination

    • invole a typical components of a reflex arc
    • 1. receptor
    • 2. sensory neuron
    • 3. integratin center
    • 4. motor neurons
    • 5. effector
  20. Autonomic control by higher centers
    Hypothalimus 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 chemical in fluids

    - hypothalamic output influences ANS centers in both the brain stem and the spinal cord
  21. glycogenolysis
    breakdown of glycogen to glucose in the liver - occurs during the parasympathetic response