Lecture 4 Autonomic Nervous System

8/9/2019 Lecture 4 Autonomic Nervous System

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Lecture 4

THE AUTONOMIC NERVOUS SYSTEM

1. Organization of the Autonomic Nervous System (ANS)

Central components

hypothalamus

brain stem

spinal cord

Peripheral components

sympathetic nerves

parasympathetic nerves


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2. The Peripheral Autonomic nervous system

Sympathetic nervous system

coordinates the bodys responses to stress

nerve fibers emerge from the spinal

segments T1-L2

preganglionic nerve cells are located in the

interomedial lateral nuclei (IML)

postganglionic cells are located in ganglia

near the spinal cord


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neurotransmitters:

- preganglionic fibers: acetylcholine (Ach)

- postganglionic fibers: norepinephrine

(NE)

- exceptions: sweet glands, piloerector

muscle and a few blood vessels also

called adrenergic fibers

receptors that NE activates

- E receptors

E1, E2

F receptors (greater sensitivity to

isoproterenol)

F1, F2


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Parasympathetic nervous system

coordinates the bodys more vegetativeactivities such as digestion

nerve fibers exit from the brain stem and

sacral level of the spinal cord

preganglionic fibers have long axons

ganglia are near or in target organs

neurotransmitters:

preganglionic fibers: acetylcholine

postganglionic fibers: acetylcholine

also called cholinergic fibers


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Autonomic neurons release their

neurotransmitter from enlarged areas

known as varicosities

The varicosities of autonomic

neurons are found along the distal

end of the postganglionic axon

Action potential arriving at varicosity

opens voltage-gated Ca2+

channels, causing exocytosis ofsynaptic vesicles

Any NE transported back into axon

can be metabolized by monoamine

oxidase (MAO) or taken back into

synaptic vesicles for re-release


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receptors that Ach activates:

nicotinic receptors located on thepostganglionic neurons

muscarinic receptors

M1, M2

located on target cells

Reciprocal regulation of bodily organs bysympathetic and parasympathetic systems

reciprocal regulation at effector organse.g. blood pressure

heart

blood vessels


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antagonistic actions are controlled at the

site of the target organ- E2 on presynaptic terminals of

cholinergic neurons

NE E2 Ach

- M2 on presynaptic terminals of

adrenergic neurons

Ach M2 NE


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3. Actions of the ANS on organs

Heart Sympathetic fibers: increase the overall

activity of the heart

by increasing the rate and the force of heart

contraction

Parasympathetic fibers: the opposite effects

Lungs

Bronchial muscles

Bronchial glands

Blood vessels


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effects on target organs


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Gastrointestinal system

stomachmotility and tone

sphincters

secretion

intestinemotility and tone

sphincters

secretion

Intrinsic eye muscles iris muscles

ciliary muscle

Blood vessels: coronary, skeletal muscle, etc


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4. Function of the adrenal Medulla

Release norepinephrine (20%) and epinephrine(EP, 80%) into circulating blood

Stimulated by sympathetic nerves

Similar effects as sympathetic stimulation exceptof 5-10 times longer

Differences of EP from NE

greater effect on heart (F receptor effects)

weak constriction of the blood vessels inthe muscles

greater metabolic effect (5-10 times)


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Importance of the adrenal medulla

supports the sympathetic system and

provides a safety factor

can stimulate the structures that are not

innervated by sympathetic fibers

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Lecture 4 Autonomic Nervous System