Autonomic Nervous system

Dr. Sumera Gul

Associate Professor

Department of Physiology

Wah Medical College

Learning Objectives

• At the end of the lecture the students should be able to:

• Explain the general organization and physiological anatomy of ANS

• Elucidate the different, neurotransmitters, receptors and effector organs of ANS

• Discuss various functions of ANS

• Describe autonomic reflexes

• Explain the various drugs effecting ANS

What do you know about Autonomic Nervous system?

Autonomic Nervous System

• “Auto” = self

• “Nomos” = law

• By definition it is entirely a motor(efferent) system & autonomous in the sense that most of its functions are carried out below conscious level, hence it is independent of volitional control, thus enjoys some degree of autonomy

Autonomic Nervous System

• Controls visceral functions

• Very rapid and prompt

• Intense

• Subconscious

• Since it is not under conscious control, how much would be cortical representation?

General Organization

Afferent Visceral Neurons

Activation centers

Spinal cord, brain stem, hypothalamus

Limbic system.

Efferent autonomic signals

Sympathetic , Parasympathetic and ???

Somatic Autonomic

cutaneous receptors chemoreceptorsproprioceptors baroreceptorsspecial senses mechanoreceptors

may become conscious unconscious

excitatory for skeletal excitatory or inhibitory formuscles cardiac muscle, smooth

muscles, and glands

single motor neuron two motor neurons

Overview of Autonomic Pathways

Preganglionic neuron

• 1. First autonomic motor neurons

• 2. Cell body located in gray matter of spinal cord or brain

• 3. Passes from the CNS in a spinal or cranial nerve

• 4. Axon terminates in a ganglion

Overview of Autonomic Pathways

Ganglion

• 1. Collection of nerve cell bodies located in a specific

site outside the CNS

• 2. Cell bodies give rise to postganglionic neurons

Overview of Autonomic Pathways

Postganglionic neuron

• 1. Second of the two autonomic motor neurons

• 2. Cell body located in ganglion

• 3. Postganglionic axon passes from the ganglion to the effector

• 4. Peripheral effector is either stimulated or inhibited

Division of Autonomic Nervous System

Sympathetic Nervous System

• 1. Lateral gray horns

• 2. Thoracolumbar outflow (T1-L2)

• 3. Ganglia

a. Sympathetic trunk (paravertebral)

b. Prevertebral (collateral)

c. Adrenal Medulla

• 4. Preganglionic axons short

• 5. Postganglionic axons long

Parasympathetic Nervous System

• 1. Lateral gray horns (S2-4)

• 2. Cranial gray matter

(CN III, VII, IX, X)

• 3. Craniosacral outflow

• 4. Terminal ganglia

• 5. Preganglionic axons long

• 6. Postganglionic axons short

Physiological Effects of ANS

Receptors and Neurotransmitters in ANS

ANS Neurotransmitters

Cholinergic Adrenergic

acetylcholine norepinephrine

all preganglionic neurons most postganglionic

all postganglionic parasympathetic neurons sympathetic neurons

few postganglionic sympathetic neurons

acetylcholinesterase catechol-O-methyl transferase

monoamine oxidase

Nicotinic and Muscarinic receptors Alpha and Beta receptors

•

Neurotransmitters and Receptors

Receptors

-At ganglia: sympathetic and parasympathetic have nicotinic receptors at the post synaptic membrane

-on effector cells: Muscarinic receptors

• Muscarinic receptors : GPCR

• Nicotinic receptors: Ligand gated ion channels

• Alpha and Beta receptors: GPCR

Drugs Affecting Autonomic Nervous System

• adrenergic or sympathomimetic drugs• isoproterenol stimulates both beta1 and beta2 receptors

• albuterol stimulates only beta2 receptors

Some drugs act indirectly by increasing the release of norepinephrine from its storage terminals

• amphetamine

Drugs Affecting Autonomic Nervous System

Some drugs block the effect of norepinephrine and epinephrine

Beta blockers

• beta1 - metoprolol

Alpha blockers/ Antagonists

Drugs Affecting Autonomic Nervous System

Parasympathomimetic drugs• nicotine

• activates nicotinic receptors

Cholinesterase inhibitors• neostigmine

• potentiates the effect of acetylcholine

Antimuscarinic drugs• atropine

• blocks the effect of acetylcholine on effector cells