Physiology of autonomic nervous system

Comparison of Somatic and Autonomic Nervous System

Somatic Skeletal muscle Conscious and

unconscious movement Skeletal muscle

contracts One synapse Acetylcholine

Autonomic Smooth and cardiac muscle

and glands Unconscious regulation

Target tissues stimulated or inhibited

Two synapses Acetycholine by

preganglionic neurons and ACh or norepinephrine by postganglionic neurons

Autonomic nervous system

Chain of two motor neurons Preganglionic neuron Postganglionic neuron

Conduction is slower due to thinly or unmyelinated axons

Pre-ganglionic

Ganglion

Post-ganglionic

Comparison of ANS & PNS

Figure 15.2

Compare the one motor neuron of the somatic motor division with the two neuron chain of the autonomic nervous system

Somatic and Autonomic Nervous System

Divisions of ANS There are two division of the ANS

Parasympathetic Sympathetic Metasympathetic

Generally the two divisions have chains of two motor neurons that innervate same visceral organs but cause essentially opposite effects

If one division stimulates certain smooth muscle to contract or a gland to secrete, the other division inhibits that action

Through this process of duel innervation the two systems counterbalance each other

Divisions of ANS Both the sympathetic

and parasympathetic divisions issue from the brain and spinal cord

Two neuron pathways are shown for both divisions

Solid lines indicate pre-ganglionic axons while broken lines indicate post-ganglionic axons

Where they come from

Parasympathetic:craniosacral

Sympathetic:thoracolumbar

N

αβ

SympatheticACh

NE

Nicotine

Tyramine, Ephedrineamphetamine

+

+

Divisions of the Autonomic Nervous System

Sympathetic – “fight, flight, or fright” Activated during exercise,

excitement, and emergencies Parasympathetic – “rest and digest”

Concerned with conserving energy

Functions of the Functions of the Autonomic Nervous Autonomic Nervous SystemSystem

Sympathetic activitiesSympathetic activities

““E situations”E situations” ExerciseExercise EmergencyEmergency ExcitementExcitement EmbarrassmentEmbarrassment

Functions of the Functions of the Autonomic Nervous Autonomic Nervous SystemSystem

Parasympathetic activitiesParasympathetic activities Stimulated by: Stimulated by:

Quiet periodsQuiet periods Paradoxical fearParadoxical fear

Produces “rest-and-digest” responseProduces “rest-and-digest” response Supports body functions that conserve and restore Supports body functions that conserve and restore

body energy body energy Reduce body functions that support physical activityReduce body functions that support physical activity

SLUDD

Function of the Sympathetic Nerve Sympathetic nervous system prototypically

“fight” or “flight”.

Associated with increased

energy expenditure,

cardiopulmonary adjustments for intense activity,

blood flow adjustments for maximum energy expenditure.

SNS - Fight & Flight ReactionYou’re walking alone at night and all the sudden you hear

an unfamiliar noise near by… In a matter of seconds, your heart rate increases dramatically, blood vessels in your skeletal muscles dilate, blood vessels in the visceral muscles constrict, digestion is ceased, your liver ramps up glucose release, your pupils dilate, salivary production decreases, sweat increases.

Sympathetic

Preganglionic cell bodies in lateral horns of spinal cord T1-L2

Sympathetic Trunk Ganglia

Located on both sides of the vertebral column

Linked by short nerves into sympathetic trunks

Joined to ventral rami by white and gray rami communicantes

Fusion of ganglia fewer ganglia than spinal nerves

Sympathetic Pathways to Periphery

Figure 15.9

Sympathetic Pathways to the Head

Figure 15.10

Sympathetic Pathways to Thoracic Organs

Figure 15.11

Parasympathetic Nervous System

If that noise turns out to be the result of wind, then the body is returned to “pre-noise” state.

This is the job of the parasympathetic nervous system.

Autonomic Nervous System• Parasympathicus• Wind down, relaxation,

digestion• Dominated by

Acetylcholine

• Sympathicus • Fight & Flight Reaction• Dominated by

Noradrenaline (Adrenaline)

• Fear, exercise, rage

Different Lengths of their Fibers

Sympathetic is the opposite with short preganglionic and long postganglionic fibers Parasympathetic division has long preganglionic and short postganglionic fibers

Anatomical Differences in Sympatheticand Parasympathetic Divisions

Figure 15.4a

Divisions of ANS Therefore, all

sympathetic ganglia lie near the spinal cord and vertebral column, and all parasympathetic ganglia lie far from the CNS, in or near the organs innervated

Parasympathetic

Parasympathetic Division

The parasympathetic division is most effective in non-stressful situations

This division is chiefly concerned with keeping body energy use as low as possible, even as it directs body processes such as digestion and elimination

Resting and digesting division

N

M

ACh

ACh

Parasympathetic

Nicotine+

Black widowSpider venom

+

Parasympathetic Nervous System: Sacral Outflow

Emerges from S2-S4

Innervates organs of the pelvis and lower abdomen

Preganglionic cell bodies Located in visceral motor region of

spinal gray matter Form splanchnic nerves

Sacral Outflow The sacral outflow

arises from neurons located in the lateral horn of the spinal cord at S2 - S4

The axons of these neurons run in the ventral roots of the spinal nerves to the ventral rami

Sacral Outflow

From the ventral rami the neurons branch to form the pelvic splanchnic nerves

Most neurons synapse in the intramural ganglia located in the walls of the distal large intestine, urinary bladder and reproductive organs

Neurotransmitters and Neuroreceptors

Acetylcholine and Norepinephrine

All preganglionic neurons are cholinergic

Parasympathetic post ganglionic neurons are cholinergic

Sympathetic post ganglionic neurons are adrenergic except

Sympathetics innervating sweat glands, blood vessels in skeletal muscle, and piloerection muscles are cholinergic

Cholinergic Receptors

The two types of receptors that bind ACh are nicotinic and muscarinic

These are named after drugs that bind to them and mimic ACh effects

Acetylcholine Nicotinic receptors

Nm (muscular-type or N2): skeletal muscle

Nn (neuron-type, or N1): autonomic ganglia, CNS

Muscarinic receptors Postganglionic parasympathetic and a few

sympathetic sites, CNS (also autonomic gang.)

Receptor subtypes: M1-5

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