THE AUTONOMIC - PowerPoint Presentation

Slide1

THE AUTONOMICNERVOUS SYSTEM

LECTURE 12

CH 9 Slide2

Neural Control of Involuntary Effectors

The autonomic nervous system helps regulate cardiac, smooth muscle and glands

Impulses are conducted from the CNS to a

second autonomic neuron. And then the second neuron innervates the involuntary effector.Slide3

Visceral Effector Organs

The autonomic nervous system regulates all the organs.

Common features of organs regulated

autonomically: 1) a built-in muscle tone – they maintain a resting ‘tone’

2) denervation hypersensitivity – they may become more

sensitive to regulation when nerves are damaged

3) They may contract without autonomic input

4) The autonomic system is like an accelerator or brakeSlide4

Divisions of the Autonomic Nervous System

Sympathetic

-

thoracolumbar division – preganglionic fibers exit spinal cord at spinal nerves T1-L2 - synapse with paravertebral ganglia (sympathetic chain)Slide5

Fig. 9.2 The Sympathetic Chain of Paravertebral GangliaSlide6

Sympathetic Neuron PathwaysSlide7

Sympathetic Division

Divergence

– preganglionic fibers branch out to postganglionic fibers at different levels of the chain

Convergence – a postganglionic neuron can receive info frommany pre-

ganglionic

nerves.

Mass activation

– all postganglionic sympathetic neurons

can be activated simultaneously for fight or flightSlide8

Sympathetic Collateral (

prevertebral

) Ganglia

These are placeswhere pre-

ganglionic

neurons

synapse

if they do not

synapse in the

paravertebral

chain; they form

splanchnic

nerves

E.G. celiac, superior, mesenteric, inferior mesenteric ganglia

which innervate digestive, urinary, reproductiveSlide9

Note

: dual innervation of organs

by both systemsSlide10

Adrenal Glands

Two functionally different glands: medulla and cortex

Medulla

– originates from neural crest; innervated by preganglionic sympathetic fibers which trigger the secretion of epinephrine into the bloodCortex – secretes steroid hormonesSympathoadrenal system

–

stimulation of adrenal

medulla by mass activation of

sympathetic nervous systemSlide11

QuestionWhat happens to blood vessels of the digestive tract during sympathetic activation?

What happens to skeletal muscles?

Lungs?Slide12

Parasympathetic Division

Craniosacral

Division

Preganglionic fibers originate in the brain (midbrain, pons, medulla) and in sacrum; they extend to terminal ganglia, which are inside the organs they stimulate.Terminal ganglia supply postganglionic fibers to synapse with effector cells.Slide13

Functions of the Autonomic Nervous System

Sympathetic

:

Fight or flightEpinephrine/norepi released from postganglionic neuronsCan be regulated as a

“mass system” or finely

tuned

Purpose: increase ATP

Parasympathetic

Rest and digest

Acetylcholine released from postganglionic neurons

Not activated as a whole

Opposite of sympatheticSlide14

Adrenergic and Cholinergic Synaptic Transmission

Sympathetic and parasympathetic –

preganglionic neurons release Acetylcholine

Sympathetic postganglionic neurons release epi [adrenergic]

Parasympathetic

postganglionic

neurons release Ach [cholinergic]

Exception

:

some sympathetic fibers to skeletal muscle and sweat glands release

AChSlide15

Response to Adrenergic Stimulation

Both excitatory and inhibitory

effects can be produced in different tissues by the same neurotransmitter because different tissues have different receptors.

α

(alpha)

-adrenergic receptors

stimulate a rise in cytoplasmic Calcium

α

1

– causes

vasoconstriction by increasing Ca2+

α

2

–

they are activated by

norepi

, but then cause a negative

feedback

reduction

in epi levels

(p. 254)

clonidine (drug) -

α

2

receptors in the brain

 lowers

sympathoadrenal

system

β

(beta)

-adrenergic receptors

stimulate the production of

cAMP

in the target cell.

β

1

– increase heart rate;

β

2

– vasodilation;

bronchodilationSlide16

Response to Cholinergic Stimulation

The effects of

ACh

depend on the nature of the ACh receptor:Nicotinic – located in CNS and neuromuscular junction and in autonomic ganglia; always excitatory; always cause an inflow of Na+

Muscarinic

– located in visceral organs; excitatory or inhibitory; G-protein coupled and can activate different membrane enzymes. Subtypes of muscarinic receptors existSlide17

The effects of

ACh

depend

on nature of the Ach receptor

:

Nicotinic

–always

excitatory; always cause an inflow of Na+

Muscarinic

–excitatory

or inhibitory;

Subtypes existSlide18

Other Autonomic Neurotransmitters

Non-adrenergic, non-cholinergic

Nitric oxide

– causes vasodilation of penis, causes vasodilation of cerebral arteries (parasympathetic); sometimes called a paracrine regulator

VIAGRA

blocks the breakdown

of cyclic GMPSlide19

Antagonistic Effects

“Antagonistic” means the two systems produce opposite effects.

Example: the heart –

epi speeds it up/ACh slows itSlide20

Complementary and Cooperative Effects

Complementary

– both systems produce similar effects

e.g. salivary glands – Cooperative

– systems produce different effects that work together to promote a single action

.

e.g. erection of the penis/clitoris – arousal is parasympathetic/orgasm is sympathetic

e.g. urinary bladder -

Slide21

Organs Without Dual Innervation

Some organs receive only sympathetic innervation:

Adrenal medulla

Arrector pili

Sweat glands

Blood

vessels

of skin

Regulation is achieved by increases or decreases in firing rate of sympathetic fibers.

E.g.

During

exercise, increased sympathetic activity dilates blood vessels in the muscles and stimulates sweat glands (which secrete

bradykinin

to stimulate dilation of surface blood vessels)Slide22

Control of the Autonomic Nervous System by Higher Brain Centers

Medulla oblongata

Hypothalamus

Limbic system (contains the cingulate gyrus, hypothalamus, fornix, hippocampus, amygdala) – emotional control of autonomic activation (fainting, blushing, racing heartbeat)

Cerebellum – control of motion sickness

, nausea