Learning Objectives: Describe the anatomical differences between the sympathetic and parasympathetic...

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