CHAPTER 16AUTONOMIC NERVOUS SYSTEM

You should read and outline the chapter yourself to best understand the material!!

OBJECTIVES Compare & contrast the characteristics of the somatic

and autonomic nervous system Know the divisions of the autonomic nervous system

and the characteristics of each Know the affect of the sympathetic and

parasympathetic systems for cardiac muscles, glands, ciliary muscle, bronchi, digestive organs, and blood vessels

Know the origination site of the sympathetic neurons Know the origination site of the parasympathetic

neurons Know the location of the adrenergic neurons Know the types & location of the adrenergic receptors Know the location of the cholinergic neurons Know the types & location of cholinergic receptors

COMPARE & CONTRAST SOMATIC AND AUTONOMIC NERVOUS SYSTEM

SOMATIC AUTONOMIC

Cell bodies (somatic motor neurons) in CNS

Cell bodies (preganglionic neurons) in CNS

Axons (somatic motor neurons) in skeletal muscle

Axons (preganglionic neurons) extend to ganglia where they SYNAPSE with postganglionic neuronsAxons of postganglionic neurons extend to smooth muscle, cardiac muscle or glands

Excitory effect Excitory OR inhibitory effect

Voluntary Involuntary

ORGANIZATION OF NERVOUS SYSTEM

Enteric Division

PNS

PNS has both sensory & motor neurons Sensory Neurons – carry action potentials from

periphery to CNS

Motor Neurons – carry action potentials from CNS to periphery

PNS

Motor Neuron

s

Sensory Neuron

s

COMPARISON OF SOMATIC VS AUTONOMIC NERVOUS SYSTEM (TABLE ON PAGE 559)

Characteristic Somatic Nervous System Autonomic Nervous System

Effectors Voluntary (skeletal) muscle Smooth muscle, Cardiac Muscle, Glands

General function Adjustment to external environment.

Adjustment within the internal environment (homeostasis)

Number of neurons from CNS to effector 1 2

Ganglia outside the CNS 0 Chain ganglia, collateral ganglia or terminal ganglia

Neurotransmitter Acetylcholine Acetylcholine, adrenaline, noradrenaline

Effect of nerve damage on the effector

Paralysis and muscle wastage (atrophy)

Effector remains functional but not able to quickly respond to the changing needs of the body.

STRUCTURE OF THE AUTONOMIC NERVOUS SYSTEM

Autonomic Nervous System

Sympathetic Parasympathetic Enteric

Nerve plexus within wall of digestive tract

Sympathetic & Parasympathetic DIFFER:1) Location of

preganglionic neuron cell bodies within CNS

2) Location of their autonomic ganglia

FOR REVIEW

Ganglia – tissue mass made of nerve cells A ganglion is a junction between two neurons in

the Autonomic Nervous System in which storage,release,synthesis and degradation of the neurotransmitters are done.

Nerve Plexus – network of intersecting nerves Preganglionic Neuron Postganglionic Neuron

SYMPATHETIC DIVISION

ANATOMY OF SYMPATHETIC DIVISION

Cell bodies of the preganglionic neurons are in the lateral horns of the spinal cord gray matter between T1 and L2 segments

The axons of the preganglionic neurons exit through the ventral roots of the spinal nerves for a short distance and project to the sympathetic ganglia

Preganglionic Neuron lateral horn T1 thru L2 gray matter exit through ventral root

REVIEW SLIDE

SYMPATHETIC AXON ARE NOW IN THE SYMPATHETIC CHAIN GANGLIA……HOW DO THEY GET OUT?

SYMPATHETIC AXONS EXIT THE SYMPATHETIC CHAIN BY 4 POSSIBLE ROUTES

1) Spinal Nerves Preganglionic axon synapse with postganglionic neurons IN the synaptic chain ganglia

2) Sympathetic Nerves Preganglionic axons enter sympathetic chain and synapse IN a sympathetic chain

ganglion with post ganglionic neurons Postganglionic neurons for sympathetic nerves which supply organs in thoracic cavity

Splanchnic (splangk-nic) nerves Preganglionic axons PASS THROUGH sympathetic chain ganglia and will

form splanchnic nerves and synapse with postganglionic nerves OUTSIDE of the chain in COLLATERAL GANGLIA

Innervation to the Adrenal Gland Preganglionic axons PASS THROUGH the chain AND PASS THROUGH the

Collateral Ganglia and they synapse with cells in the medulla of the adrenal gland

REMEMBER…… THE ADRENAL GLANDS?

PARASYMPATHETIC DIVISION

PARASYMPATHETIC DIVISION Cell Bodies of parasympathetic

preganglionic neurons are located either: Within the cranial nerve nuclei of brainstem Within the lateral parts of the gray matter in the

sacral region of the spinal cord from S2 to S4

Notice in the Parasympathetic Division, the preganglionic axons synapse at the TERMINAL GANGLIA with the postganglionic neurons

Postganglionic neurons travel a short distance to the effectors

ENTERIC NERVOUS SYSTEM

Consists of NERVE PLEXUSES within the wall of the digestive tract

Plexuses have contributions from 3 sources: Sensory neurons that connect

digestive system with CNS ANS motor neurons that connect CNS

to digestive tract Enteric Neurons which are confined to

Enteric Plexuses UNIQUE – enteric neurons are capable of

monitoring and controlling the digestive tract independently of the CNS through local reflexes

REMEMBER…..A nerve plexus is a network of intersecting nerves.

NEUROTRANSMITTERS

Sympathetic & Parasympathetic Nerve Endings secrete one of two neurotransmitters: ACETYLCHOLINE

Nerve that secretes this NT is called a CHOLINERGIC NEURON NOREPINEPHERINE (or EPINEPHERINE)

Nerve that secretes this NT is called an ADRENERGIC NEURON {once believed to secrete adrenaline (aka: epinepherine)}

CHOLINERGIC NEURONS Preganglionic SYMPATHETIC Neurons Preganglionic PARASYMPATHETIC Neurons Postganglionic PARASYMPATHETIC Neurons

ADRENERGIC NEURONS Postganglionic SYMPATHETIC Neurons (most)

NEUROTRANSMITTER “LIKE” SUBSTANCES

The following substances play a role in regulating the ANS, but it is unclear exactly how. They act as neurotransmitters or neuromodulators.

These “chemicals” have also been found (in addition to epi and acety) in the ANS. Nitric oxide Fatty acids

Eicosanoids Peptides

Gastrin Somatostatin Cholecystokinin Vasoactive intestinal peptide Enkephalines Substance P

Monoamines Dopamine Serotonin Histamine

RECEPTORS FOR NEUROTRANSMITTERS

Receptors for acetylcholine and norepinephrine are located in the plasma membrane of certain cells.

Depending on the type of cell, the response to these NT can be excitatory or inhibitory.

There are two types of receptors: CHOLINERGIC RECEPTORS

Receptors to which acetylcholine bind (there are two types) NICOTINIC RECEPTORS MUSCARINIC RECEPTORS

ADRENERGIC RECEPTORS Receptors to which norepinephrine or epinephrine bind

NICOTINIC RECEPTORS (A TYPE OF CHOLINERGIC RECEPTOR)

Respond to the Neurotransmitter: Acetylcholine Located in ALL POSTGANGLIONIC NEURONS in Autonomic ganglia

AND the membranes of ALL SKELETAL MUSCLE CELLS EXCITATORY EFFECT since it results in opening of Na+ channels which

will produce an action potential

MUSCARINIC RECEPTORS (A TYPE OF CHOLINERGIC RECEPTOR)

Respond to the Neurotransmitter: Acetylcholine

LOCATION: found on cells of ALL PARASYMPATHETIC EFFECTORS and some sympathetic effectors

Response: Excitatory or Inhibitory (depending on effector in which receptors are found) ACh binds to muscarinic receptors

in cardiac muscle which will REDUCE heart rate

ACh binds to muscarinic receptors in smooth muscle of stomach INCREASING rate of contraction

ADRENERGIC RECEPTOR

Receptors to which Norepinephrine or Epinephrine bind

LOCATION: Plasma membrane of Effectors innervated by the Sympathetic Division

Stimulated by: Nervous System Epinephrine &

Norepinephrine released from Adrenal Gland

Subdivided into: Alpha (α) Receptors Beta (β) Receptors

GENERALIZATIONS!

BOTH divisions of ANS produce stimulatory & inhibitory effects

Most organs are innervated by BOTH divisions

Usually each division produces an OPPOSITE effect on a given organ

Sympathetic Division produces more GENERALIZED effects than the parasympathetic division

Sympathetic division generally prepares the body for PHYSICAL ACTIVITY

Parasympathetic division is more important in RESTING FUNCTIONS

AFFECT OF SYMPATHETIC & PARASYMPATHETIC SYSTEMS FOR CERTAIN EFFECTORS (PAGE 567)

EFFECTOR Sympathetic ParasympatheticCardiac Muscle Increase rate and force of

contraction (beta)Decreased rate of contraction(m)

Glands:

Adrenal Release epi & norepi (n) None

Pancreas Decrease insulin (alpha) Increase Insulin (m)

Salivary Constrict blood vessels and slight production of thick saliva (alpha)

Dilation of blood vessels and thin, copious saliva (m)

Ciliary Muscle (eye)

Relaxation for far vision (beta) Contraction for near vision (m)

Bronchi Dilated air passage (beta) Constricted air passage (m)

Digestive Organs:

Wall Decreased tone (alpha and beta)

Increased motility (m)

Sphincter Increased tone (alpha) Decreased tone (m)

Blood Vessels Constriction (alpha)Dilation (beta)

none

INFLUENCE OF DRUGS

DRUGS

Direct Acting – bind to ACS receptors to produce an effect Agonists (stimulating agents) – bind to specific

receptors and activate them Antagonists (blocking agents) – bind to specific

receptors and prevent them from being activated

NICOTINE Present in tobacco Nicotine STIMULATES the Postganglionic neuron of

BOTH Sympathetic and Parasympathetic Divisions, its effects VARY

Heart Rate may increase or decrease Heart Rhythm becomes less regular Blood Pressure Increases (due to constriction of Blood

Vessels) Drugs that BLOCK nicotine receptors are called

Ganglionic Blocking Agents, because they block the effect of Ach on neurons Trimethaphancamsylate is used to treat high BP, it blocks the

sympathetic stimulation of blood vessels causing blood vessels to dilate which decrease blood pressure (problem: act on both sym and parasym ganglia, so not the best drug choice to use)

DRUGS THAT BIND TO MUSCARINIC RECEPTORS