Lec 14: ANS

• ANS consists of motor neurons that:

  1) Innervate smooth and cardiac muscle and glands.

  2) Make adjustments to ensure optimal support for body activities.

  3) Operate via subconscious control.

  4) Have viscera as most of their effectors.
• Differences between the ANS and SNS

  Effectors,

  Efferent pathways,

  Target organ responses to their neurotransmitters

  
• Effectors of Somatic Nervous System


  skeletal muscles

  
• Effectors of Autonomic Nervous System


  Cardiac Muscles,

  Smooth Muscles,

  Glands

  
• Efferent pathways of Somatic Nervous System

  Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector

  
• Axons of the ANS are a two-neuron chain

  -The preganglionic (first) neuron has a lightly myelinated axon

  -The postganglionic (second) neuron extends to an effector organ

  
• Target organ responses to the Somatic Nervous System neurotransmitter

  All somatic motor neurons release Ach, which has an excitatory effect

  
• Target organ responses to the Autonomic Nervous System neurotransmitter

  1) Preganglionic fibers release Ach

  2) Postganglionic fibers release norepinephrine (NE) or Ach and the effect is either stimulatory or inhibitory

  3) ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector

  
• Sympathetic Nervous System

  1) Mobilizes the body during extreme situations (the "fight-or-flight" system)

  - Involves "E activities"- exercise, excitement, emergency, and embarrassment

  - Promotes adjustments during exercise -blood flow to organs is reduced, flow to skeletal muscles and heart is increased

  - Its activity is illustrated by a person who is threatened (Increase in HR, breathing is rapid and deep, skin is cold and sweaty, and the pupils dilate)

  
• Parasympathetic Nervous System

  1) Performs maintenance activities and conserves body energy

  - Involves the "D activities"- digestion, defecation, and diuresis (urination)

  - Its activity is illustrated in a person who relaxes after a meal

  ---BP, HR, and respiratory rates are low

  ---GI tract activity is high

  ---Skin is warm and pupils are constricted

  
• How do the two divisions counterbalance each other's activity?

  Dual innervation of organs

  
• autonomic nervous system anatomy

  1) Sympathetic and parasympathetic division are distinguished by their:

  - Unique origin sites

  - Relative lengths of their fibers

  - Location of their ganglia

  
• ANS Unique origin sites

  1) Sympathetic fibers originate from thoracolumbar region of the spinal cord

  2) Parasympathetic fibers originate from craniosacral regions of the spinal cord

  
• Relative lengths of their fibers in ANS

  1) Sympathetic contains short preganglionic and long postganglionic fibers

  2) Parasympathetic contains long preganglionic and short postganglionic fibers

  
• Location of their ganglia in ANS

  1) Sympathetic ganglia are located close to the spinal cord

  2) Parasympathetic ganglia are located in the visceral effector organs

  
• ANS outflow of Parasympathetic (craniosacral) Division

  1) Cranial outflow

  - Cranial nerves- Occulomotor, Facial, Glossopharyngeal, Vagus, etc.

  --Effector organs- salivary, nasal, and lacrimal glands; heart, lungs, and most visceral organs.

  
  

  2) Sacral outflow

  - S2-S4

  -- Effector organs- large intestine, urinary bladder, ureters, and reproductive organs

  
• ANS outflow of Sympathetic (thoracolumbar) Division

  1) Outflow

  -T1-L2

  -- Preganglionic fibers pass through the white rami communicates and synapse in the chain (paravertebral) ganglia

  --Postganglionic fibers innervate the numerous organs of the body

  
  

  -Effector organs- head and neck, heart, bronchi and lungs, esophagus, stomach, spleen, pancreas, liver, small intestine, kidney, reproductive organs, large intestine, ureter, urinary bladder, etc.

  
• Components of Visceral reflexes

  Receptors,

  Sensory (afferent) Neurons,

  Integration Center,

  Motor (efferent) Neurons: Preganglionic Neuron & Postganglionic Neuron,

  Effector

  
• Visceral reflexes

  Visceral reflexes have the same elements as somatic reflexes

  
• Referred Pain

  1)Pain stimuli arising from the viscera are perceived as somatic in origin

  2)This may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers

  
• ANS Physiology: Neurotransmitters and Receptors

  Ach and norepinephrine (NE) are the two major NTs of the ANS

  -Ach

  -NE

  -NT effects can be excitatory or inhibitory depending upon the receptor type

  
• Ach released by:

  All preganglionic axons,

  All parasympathetic postganglionic axons

  -Ach releasing fibers are called cholinergic fibers

  
• Cholinergic Fibers

  Ach releasing fibers
• NE released by:

  most sympathetic postganglionic axons
• NT effects can be what?

  NT effects can be excitatory or inhibitory depending upon the receptor type
• ANS physiology receptors:

  1) Cholinergic receptors (bind Ach)

  -has 2 types

  2) Adrenergic receptors (bind NE)

  
• Two types of Cholinergic Receptors

  Nicotinic Receptors,

  Muscarinic Receptors

  
• Nicotinic Receptors


  Effect of Ach binding is always stimulatory

  
• Muscarinic Receptors


  Effect of Ach binding can be either inhibitory or excitatory depending on the receptor type on the target organ

  
• Types of Adrenergic Receptors

  1) alpha and beta

  2) Each type has 2-3 subclasses (a1, a2, B1, B2, B3)

  3) Effectors of NE binding to:

  -a receptors are generally stimulatory

  -B receptors are generally inhibitory

  4) A notable exception- NE binding to B receptors of the heart is stimulatory

  
• Alpha Receptors


  Type of Adrenergic receptor that are generally stimulatory

  
• Beta Receptors


  Type of Adrenergic receptors that are generally inhibitory

  
• Effect of drugs: Atropine


  Blocks parasympathetic effects
• Effect of drugs: Neostigmine


  inhibits AchE and is used to treat myasthenia gravis
• Effect of drugs: Tricyclic antidepressants


  Prolong the activity of NE on postsynaptic membranes
• Effect of drugs: Over-the-counter for colds, allergies & nasal congestion

  Stimulates alpha-adrenergic receptors
• Effect of drugs: Beta-blockers


  attach mainly to B1 (Beta1) receptors and reduce HR and prevent arrhythmias
• Antagonistic interactions of the autonomic divisions

  Most visceral organs are innervated by both sympathetic and parasympathetic fibers that precisely control visceral activity

  -Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination.

  -Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes

  
• Sympathetic Tone


  1) Controls BP and keeps the blood vessels in a continual state of partial constriction

  2) This sympathetic tone (vasomotor tone)next card info

  3)Alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension

  
• Vasomotor tone


  1) Constricts blood vessels and causes BP to rise as needed

  2) Prompts vessels to dilate if BP is to be decreased