The Autonomic Nervous System

The Autonomic Nervous System


-preganglionic fibers are myelinated and long -postganglionic fibers short and unmyelinated SYMPATHETIC

-ganglia mostly near the spinal cord (paravertebral chain) except for some which are prevertebral and some lie near organs innervated -preganglionic fibers are

myelinated but shorter -postganglionic fibers are long and unmyelinated PARASYMPATHETIC -cell bodies of preganglionic nerons

exit spinal cord at cranial and sacral levels SYMPATHETIC -cell bodies of preganglionic fibers

exit at thoracic and lumbar levels PARASYMPATHETIC -Neurotransmitter:

preg.neuronAch postg.neuronAch SYMPATHETIC -Neurotransmitter: preg.neuronAch postg.neuronNE

-Adrenal Medulla chromaffin cellsEpinephrine Autonomic Regulation of peripheral organs Generally the two branches stimulate opposing responses in effector organs but there are some

EXCEPTIONS when similar responses are produced Balance exists between the two so that inhibition of one leads to increases in response mediated by the other Some organs have only one type of innervation such as spleen and vasculature (sympathetic)

A sympathetic preganglionic neuron may synapse with many postganglionic neuronsdiffuse responses Parasympathetic preganglionic neurons usually only have single synapses with postganglionic neurons discrete, localized responses

Activation of outflow Parasympathetic- Sympathetic conservation of

energy, maintenance of function during periods of lesser activity fight, flight or fright response

essential for life response to stress conditions Parasympathetic

-Reduces heart rate and BP -Activates GIT -Emptying of bladder and rectum -Activation of lacrimal, mucus and salivary

cells -Constriction of bronchial tree -Pupillary constriction Sympathetic -Elevation of heart rate

and BP -Redirection of blood flow to skeletal muscles from skin -Dilation of pupils and bronchioles -Piloerection

Neurotransmission Neurotransmitters in the ANS After release: NTS synaptic cleft specific receptors of postganglionic cells or cells of the effector organ message delivery response

Nerve terminals then have mechanisms to degrade and reuse (reuptake) NTS for rapid termination of message Neurotransmitter Receptors in the ANS CHOLINERGIC RECEPTORS

Acetycholine (Ach) action differs depending on the type of receptor it interacts with Ach action is mimicked by nicotine in some organs and mimicked by muscarine in others nicotinic cholinergic receptors muscarinic cholinergic receptors

Nicotinic: Ligand-gated ion channels (+) allows entry of sodium and calcium ions Muscarinic: G protein-coupled receptors (+) activate G proteins to induce downstream effects

Insert Brody Fig 8-10 p.98 *Nicotinic Cholinergic Receptors Primary action of Ach at Para- and Sympganglia are mediated by activation of ganglionic NICOTINIC receptors (similar to that in the CNS and immune cells but different from that in the skeletal muscle at the NMJ)

These different types of nicotinic receptors allow for selective action (+ or -) of different agonist and antagonist *Muscarinic Cholinergic Receptors Mediates responses to Ach at the parasympathetic neuroeffector junction

Subtypes M1 to M5: M1autonomic ganglia- modulates effects of nicotinic receptor activation M2 heart M3 glands, smooth muscles M4, M5? All types CNS

ADRENERGIC RECEPTORS NE and Epi can activate more than one type of adrenergic receptor receptors (1,2, and 3 subtypes) 1 (3 subtypes) and 2 (3 subtypes)

Somati c Parasympathetic Sympathetic ACh

N ACh N AC h


Functional Responses mediated by the ANS Functional Reponses Most organs are innervated by both

cholinergic and adrenergic systems therefore responses of organs are due to interplay between these two HOWEVER, an organ is usually under the PREDOMINANT control of one division Functional Responses

Organs innervated by both systems: Organs innervated only by sympathetic branch: Heart

Eye Bronchial tree GIT Urinary Bladder Reproductive organs Blood vessels

Spleen Piloerector muscles Functional Responses The responses in each organ are mediated by the particular muscarinic cholinergic OR adrenergic receptors present

Functional Responses Usually, the two divisions mediate physiologically opposing responses such that if one inhibits an effect, the other enhances it.

Sites of Drug Action in Neurotransmission Process

synthesis storage release reuptake degradation

Drugs Acting on Autonomic Nerves and Receptors GANGLIONIC BLOCKERS Interferes with transmission from preganglionic to postganglionic neurons Inhibits BOTH divisions of the ANS

Parasympathetic Sympathetic Ganglionic Blocker

(-) ACh Ganglionic Blocker (-) ACh N


INHIBITORS OF NEUROTRANSMITTER RELEASE Inhibitors of biosynthesis of Norepinephrine (NE) and Epinephrine (Epi) Inhibitors of biosynthesis of Acetylcholine (Ach)

Inhibitors of exocytotic release of NE from postganglionic sympathetic nerve terminals Inhibitors of exocytotic release of Ach from all types of cholinergic nerve fibers: PROMOTERS OF NEUROTRANSMITTER RELEASE

Sympathetic ACh Nicotine Tyramine, Ephedrine amphetamine

+ + N

NE Parasympathetic ACh Nicotine

+ Black widow Spider venom N ACh

+ M DRUGS THAT INTERFERE WITH NEUROTRANSMITTER STORAGE The neurotransmitters are taken up into

storage vesicles by specific energy-dependent pumps in the vesicle membrane inhibits uptake of NE into vesicles prevents packing of Ach into storage vesicles DRUGS THAT AFFECT THE DURATION OF ACTION OF NEUROTRANSMITTER

NE 1. imipramine, cocaine- block NE reuptake in the nerve terminal increases synaptic concentration of NEenhancement of adrenergic transmission 2. Paragyline (inhibits MAO) and

tolcapone (inhibits COMT) higher amounts of NE in peripheral tissue Acethylcholine inhibited by physostigmine, edrophonium, and other drugs enhances magnitude and duration of effects of cholinergic stimulation


Adrenergic receptor stimulators 1.NE 2.Epi 3.Phenylephrine 4.Clonidine 5.Isoproterenol 6.Dobutamine

7.Terbutaline Cholinergic receptor stimulators 1.Alkaloid muscarine, betanechol(+) muscarinic receptors 2.Alkaloid nicotine(+) micotinic receptors

DRUGS THAT BLOCK AUTONOMIC RECEPTORS Adrenergic receptor blockers 1.Phentolamine 2.Prazosin 3.Yohimbine 4.Propranolol 5.Metoprolol

Cholinergic receptor blocker 1.Atropine competitive blocker at muscarine receptors 2.trimetaphaninhibits nicotinic cholinergic receptors in ganglia

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