Lecture 6 - The Autonomic Nervous System

8/3/2019 Lecture 6 - The Autonomic Nervous System

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The Autonomic Nervous System

Hazel Anne L. Tabo


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Efferent (motor) nerves ofthe involuntary system supply allinnervated structures ofthe body (viscera or internal)

While, Skeletal muscles are supplied by somatic nerves.


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Autonomic Nervous System

Peripheral NS

An involuntary system - it consists ofnerves, ganglia, andplexuses that innervate the heart, blood vessels, glands,other visceral organs, and smooth muscle in various tissues.

2 Divisions:

1. Thoracolumbar efferent outflow (Sympathetic)

2. Craniosacral eff. outflow (Parasympathetic)

Enteric NS 3rd division ofPNS; includes myenteric plexus(Auerbachs) and submucosal plexus (Meissners) bothsympathetic and parasympathetic afferent (sensory) nervefibers


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Main Components of Nervous SystemMain Components of Nervous System

31

sp

12

cra


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Autonomic Nervous System

Nucleus nerve cell bodies or soma in the CNS

Ganglion nerve cell bodies or soma in the PNS

ANS is a two-neuron system:

1. Preganglionic neuronOrigin: within the CNS

Termination: within the ganglion

Sympathetic preganglionic fibers: thoracic and lumbarspinal nerves (T1-L2/L3)

Parasympathetic preganglionic fibers: cranial nerves3,7,9,10 and sacral spinal nerves S1-S4

2. Postganglionic neuron

Origin: within the ganglion

Termination: Target organ or structure which itacts upon


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Dorsal nerves afferent nerves

Ventral nerves efferent nerves


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Length of nerve fibers (axons)

Sympathetic Parasympathetic

Preganglionic fibers Short Long

Postganglionic fibers Long Short

Main neurotransmitter Norepinephrine Acetylcholine


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Neurohumoral transmission

Nerves transmit their impulses across most

synapses and neuroeffector junctions through

neurotransmitters (specific chemical agents) Neurotransmitters regulatory agents that

causes neural transmission of impulses

stim

ulatory or inhibitory ne

urotr

ansmitter

s


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Neurotransmitters are released from the

Presynaptic nerve terminals into synaptic cleft

which then activate or inhibit postsynaptic

neuron by binding to specialized receptors.


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Fundamental Steps in the Neurohumoral

Transmission

1. Synthesis of transmitters

2. Storage of transmitters

3. Release of transmitters by nerve action potentials

4. Interaction of the released transmitter withreceptors

of the effector cell

5. Rapid removal of the transmitter

6. Recovery of the effector cell into previous state.


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Sympathetic Outflow

S

P

I

NA

L

N

E

R

V

E

Ganglia

AchNE

Nicotinic

cholinoceptor

Na+

K+

Paravertebral

sympathetic

chain ganglia

Na+

K+

NE

NE

Adrenoceptor

COMTorMAO

Effector organ

Depolarization on

post-synaptic neuron


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Parasympathetic Outflow

S

P

I

NA

L

N

E

R

V

E

Ganglia

AchAch

AchE

Nicotinic

cholinoceptor

Na

+

K+

Paravertebral

sympathetic

chain ganglia

Na+

K+

Muscarinic

cholinoceptor

Effector organ

Depolarization on

post-synaptic neuron

Choline


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Sympathetic Parasympathetic

Preganglionic

neuron

Cholinergic fiber Cholinergic fiber

Ganglion receptor

site

Nicotinic I Nicotinic I

Postganglionic

neuron

E2-Adrenergic fiber Cholinergic fiber

ReceptorSite to

Effector cell

E1 , F1 , F2Adrenergic

fibers

Catecholamines:

Epinephrine;

Norepinephrine,

Serotonin, Dopamine

Muscarinic fiber

[Cholinergic]


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ANS Fiber Classification based on

Neurotransmitter

Cholinergic fiber Adrenergic fiber

Acetylcholine Norepinephrine

1. Preganglionic efferent(motor) autonomic nerve

fibers

2. Parasympathetic

postganglionic fibers3. Somatic nerve fibers in

skeletal muscles

1. Postganglionicsympathetic fibers


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AUTONOMIC RECEPTORS :

GENERAL CLASSES & LOCATION

Cholinergic receptors

Muscarinic 1,2,3,4,5 (M1, M3 GIT; M2 heart)

Nicotinic muscle (NM)

Nicotinic neuronal (NN)

Adrenergic receptors

1, 2 (A1 blood vessels; A2 postganglionicfibers)

1, 2, 3 (B1 heart; B2 lungs) Dopaminergic receptors

Dopamine 1,2,3,4,5,6


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Nerves Fibers and Receptors

Nerve Fibers whose main neurotranmitter is

Acetylcholine (Ach) CHOLINERGIC

Fibers whose main neutrotransmitter is

Norepinephrine (NE) is ADRENERGIC

Adrenergic Receptors (Receives NE)

Muscarinic and Nicotinic Receptors (Receives Ach)


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Factors that modify responses

A. Sensitization by denervation (sympathetic)

at lower amount or level ofdrug, it can

sensitize or stimulate to elicit response.

Effects ofdrugs


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Drugs acting on ANS based on action or

effects on receptors

Receptors Stimulate Depress

Cholinergic receptors in

organs

Cholinergic drugs or

Parasympathomimetics

Cholinergic receptor

blockers

AntimuscarinicNicotinic blockers

Adrenergic receptors Directly-acting

adrenergic drugs or

Sympathomimetics

Adrenergic receptor

blockers (alpha & beta)

Adrenergic neurons Indirectly-actingadrenergic drugs

Adrenergic neuronblockers

Ganglionic receptors Ganglionic stimulants

(low doses of nicotine)

Ganglionic blockers

(high doses of nicotine)

Neuromuscular junction

(in skeletal muscle)

Indirectly-acting

cholinergic drugs

Neuromuscular blockers


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ANS

Organs are connected to pairs ofsympathetic andparasympathetic nerves which oppose each other.

Parasympathetic nerves (on and offpairs) function whenthe body is not stimulated.Postganglionic Receptor: Muscarinic - Acetylcholine

Sympathetic nerves (on and offpairs) function when thebody is stimulated.Postganglionic Receptor: Adrenergic Catecholamines:Epinephrine, Norepinephrine, Serotonin, Dopamine


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A

U

T

O

N

O

M

I

C

N

E

R

V

O

U

S

S

Y

S

T

E

M


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Organ Sympathetic Parasympathetic

Eye Pupil dilation [Mydriasis] Pupil constriction [Miosis];

Improved accommodation

[Ability to focus on nearobjects]

Heart HR; Contractile force;

elec. conduction through AV

node

HR; Contractile force;

elecl conduction through AV

node

Lung Relaxed/opened bronchiolesor airway [bronchodilation]

Constricted/narrowedbronchioles

[bronchoconstriction]

GIT Dec. motility and tone motility and tone

Uterus Contraction Varies with menstrual cycleLiver glycogenolysis glycogen synthesis

Urinary

bladder

Relaxeddetrussor muscle

contracted trigone

sphincter

Contracteddetrussor muscle

relaxed trigone sphincter


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Sources

Manigbas E. Basic Pharmacology.

Guyton AC and JE Hall. 2006. Medical

Physiology 11

th

ed. Pennsylvania USA:E

lsevierSaunders.

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Lecture 6 - The Autonomic Nervous System

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