Learning Objectives:
Describe the anatomical differences between the sympathetic and parasympathetic nervous systemsDescribe the differences in the neurotransmitters and their receptors between the two systemsDescribe how the sympathetic and parasympathetic systems differ in their regulation of the major organ systemsUnderstand the nature of sympathetic and parasympathetic tone
Autonomic Nervous System(Involuntary or Visceral Nervous System)
I. Function --OverviewII. AnatomyIII. Neurotransmitters and receptorsIV. Specific Organ Effects
I. Function-- Overview
Autonomic nervous system controlsinvoluntary functions:
•arterial pressure•gastrointestinal motility•gastrointestinal secretion•urinary bladder emptying•sweating•body temperature•pupilary dilation and constriction
Striking feature of the ANS is the rapidity andintensity with which it can change visceral functions (3-5 seconds)
nervous system
Peripheralnervous system
Centralnervous system
Autonomicnervous system
Somaticnervous system
Parasympatheticnervous system
Sympatheticnervous system
Autonomicnervous system
Somaticnervous system
Peripheral nervous system
Innervates heart, blood vessels, visceral organs, glands,and virtually all other organs with smooth muscle;regulates function of these organs in amanner beyond conscious (involuntary or automatic) control
Nerves innervating the skeletal muscles;activity is under conscious (voluntary) control
Parasympatheticnervous system
Sympatheticnervous system
Autonomic nervous system
“rest and digest” “Fight or flight”
ANATOMY
ANS is activated by centers located in spinal cordbrain stem and hypothalamus
ANS often operates by visceral reflexes:subconscious sensory signals from visceral organs
can enter the spinal cord, brainstem orhypothalamus and then return subconsciousreflex responses directly back to the visceral
organ to control its activities
Autonomic nerves are composed of two neuron relays.
Preganglionic neurons have their cell bodies in the spinal cordand their activity is controlled by higher brain centersand spinal reflexes.
Postganglionic neurons send their axons directly to theeffector organ.
Preganglionic neuron Postganglionic neuron organ
ANATOMY
Spinal cord ganglia
Sympathetic Nervous System
1) preganglionic nerves leave spinal cord at the thoracic and lumbar levels2) preganglionic axons are short and myelinated3) postganglionic axons are long and unmyelinated4) ganglia are located near the spinal cord
Sympathetic nervous system.
Sympathetic nervous system.
Parasympathetic Nervous System
1) Nerves leave spinal cord at cranial and sacral levels• cranial nerves innervate head, neck, thorax,
and abdomen• sacral division forms the pelvic nerve and innervates the
remainder of the intestines, bladder andreproductive organs
2) Preganglionic axons are myelinated and extremely long3) Postganglionic axons are unmyelinated and short4) Postsynaptic ganglia located near the effector organ
Parasympathetic nervous system
Parasympathetic nervous system
cranial
sacral
Neurotransmitters and receptors
Next…………...
Parasympathetic Postganglionic axons release acetylcholine
Sympathetic Postganglionic axonsrelease norepinephrine
accept axons on sweat glands, piloerector muscles of the hairs, and some blood vessels which release acetylcholine
ALL PREGANGLIONC AXONS USE ACETYLCHOLINEAS THEIR NEUROTRANSMITTER
BUT…………….
Adrenal medulla
Stimulation of sympathetic innervation of adrenal medulla causes release of large quantities of epinephrine (80%) and norepinephrine (20%)
Cholinergic receptors
Nicotinic Muscarinic
Ganglionic Skeletalmuscle
NeuronalCNS M1 M3 M5 M2 M4
Adrenergic receptors
1A 1B 1D 2A 2B 2C
Nicotinic receptor Muscarinic receptor
Receptors in the parasympathetic system
Neuroscience, Sinauer Asssoc., Inc
Neuroscience, Sinauer Asssoc., Inc
Adrenergic receptors in the sympathetic system
List of relevant receptors and their messengers
Cholinergic receptors:nicotinic receptor--- ligand-gated ion channelmuscarinic receptor--- G-protein coupled receptor
Adrenergic receptors:alpha (1 and 2) receptors
a1: Gq increase in PI turnovera2: Gi inhibition of adenylate cyclase
beta (1 and 2) receptors 1 2: Gs stimulation of adenylate cyclase
Adrenergic receptors:alpha (1 and 2) receptors
1: Gq increase in PI turnover2: Gi inhibition of adenylate cyclase
beta (1 and 2) receptors 1 2: Gs stimulation of adenylate cyclase
NE and Epi have same potency at 1 receptors receptors are much more sensitive to catecholamines
than a1 receptorsNE and Epi are equipotent at 1 receptors2 receptors are preferentially activated by Epi
1 receptors: vascular smooth muscle, on GI and bladder sphincters, and radial
muscle of the eyecause excitation (contraction)Gq IP3
2 receptorspresynaptic nerve terminals, platelets, fat cells, walls of GI tractcause inhibition (relation, dilitation)inhibition of adenlyate cyclase and decrease in cAMP
1 receptorsSA node, AV node, ventricular muscle of heartproduce excitation (increaes heart rate, contactility, increased conduction
velocitystimulation of adenylate cyclase and increase in cAMP
2 receptorsvascular smooth muscle of skeletal muscle, bronchioles, walls fo Gi tract and
bladderproduce relaxation (dilation of vascular smooth muscle and bronchioles,
relaxation of bladder wall)stimulation of adenylate cyclase and increase in cAMP
Comparison of the Components of thePeripheral Nervous System
Parasympathetic Nervous System
PreganglionicNeuron
Postganglionic
Neuron
Synaptic connection Ganglion near organ At organ
Neuron length Long Short
Neurotransmitter Acetylcholine Acetylcholine
Sympathetic Nervous System
PreganglionicNeuron
PostganglionicNeuron
Synaptic connection
Neuron length
Neurotransmitter
Ganglion near spinal cord At organ
Short Long
Acetylcholine Norepinephrine
Somatic Motor Nervous System
Synaptic connection
Neuron length
Neurotransmitter
At skeletal muscleLong
Acetylcholine
Organs are usually innervated by both systemsin opposing roles
Sympathetic Nervous System Receptors at Target Organs
Organ Action Receptor
Heart heart rate 1 contactility AV node conduction
Vascular smooth constrict blood vessels 1muscle dilates blood vessels
in skeletal muscles
Gastrointestinal motility 2, 2Tract constricts sphincters
Bronchioles dilates bronchiolar 2
pupil dilation 1
smooth muscle
Bladder relaxes bladder wall 2 constricts sphincter
organ action receptorsweat glands sweating muscarinic goose bumps contracts
kidney renin secretion 1
Male genitalia ejaculation
fat cells lipolysis 1
Sympathetic Nervous Con’t
Parasympathetic Action
Organ Action Receptor
Heart heart rate M contractility AV node conduction
Gastrointestinal motility MTract relaxes sphincters
Bronchioles constricts M
Male sex organs erection M
Bladder contracts wall M relaxes sphincter
Pupil constriction M
These drugs block both divisions of the autonomic nervous systemequally.However, the end-organ response may show a predominant adrenergicor cholinergic. Therefore interruption of ganglionic transmission hasthe effect of selectively eliminating the dominant component.
Ganglionic blockers
Sympathetic and Parasympathetic
“tone”
Continual basal activity of the sympathetic and parasympathetic systems allows either branchof the ANS to increase or decrease its activityof a stimulated organ
Sympathetic tone caused by basal secretion from adrenal medulla
Guyton and Hall fig 60-4
Denervation supersensitivity
“Alarm” or “Stress” Response
Large portions of the sympathetic nervous system discharge simultaneously-----this increases the body’s ability to perform vigorous muscle activity
Increased arterial pressureIncreased blood flow to the skeletal muscles with concurrent decrease
blood flow to GI tract, kidneysIncreased metabolismIncreased blood glucose concentrationIncreased glycoglysis in liver and muscleIncreased muscle strengthIncreased mental activityIncreased rate of blood coagulation
Autonomic Reflexes
cardiovascular reflexesgastrointestinal reflexesbladder emptyingsweatingblood glucose concentrationsexual reflexes
Enteric Nervous System
Gastrointestinal tract nervous systemMyenteric plexus (auberbach’s)meissner’s plexus (submucosal)
Sympathetic and Parasympathetic systemsinteract with the Enteric System
Acetylcholine most often excites andNorepinephrine inhibits
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