CHAPTER 9

Autonomic Nervous System (ANS) • Divisions of ANS

– Sympathetic – Parasympatheitc

• Functions of ANS • Control of ANS

Dr. Hameed Al-Sarraf Dept. Physiology [email protected]

Autonomic Nervous System • Nervous system that controls many involuntary functions of the body.

• ANS effects (controls) organs which are under involuntary control.

• Effectors of ANS usually are: – Cardiac Muscle – Glands HEART – Smooth Muscle Many internal Organs

Divisions of ANS

• 1- Sympathetic (Thoracolumbar) Division • 2- Parasympathetic (Craniosacral) Division.

Thoracolumbar

Sympathetic

Sympathetic hain

Sympathetic Chain

Sympathetic Chain

Parasympathetic

Vagus Craniosacral

Parasympathetic

Innervation of Body Organs - In the body there are organs which are innervated by both sympathetic and parasympathetic systems: - Heart - Digestive tract - Pupil of the eye - Salivary glands, etc -There are organs with only sympathetic innervation: - Adrenal medulla - Sweat glands - Most blood vessels

Functions of ANS 1- Sympathetic system: -Mass discharge of sympatheic system prepares the body for activity (

Fight/Flight

).

- Excitation of sympathetic centers will cause: - Increase in heart rate.

- increase in blood pressure, - blood glucose is elevated - increase in the rate of metabolism - mental activity is also raised, - blood is diverted to skeletal muscle.

2- parasympathetic system: usually has opposite effects to those of sympathetic system. Excitation of parasympathetic causes: - decrease in heart rate, - increase blood flow to the digestive system, - increase activity of the digestive system.

Sympathetic Tone

Sympathetic Tone

Sympathetic and Prasympathetic Tone - Normally both symathetic and parasympathetic systems continuously transmit action potentials (signals) at low rate throughout their nerve fibers.

- By doing this the ANS can have both positive and negative effects on its effector organs: e.g control of blood vessel diameter by sympathetics, Fast rate of action potentials Vasoconstriction Sympathetic tone slow rate of action potentials vessel diameter at rest Stop sending action potentials Vasodialatation

Examples of Sympathetic System in Action Mass discharge (activation) of sympathetic system prepares the body for activity

Example 1: Blood flow to muscle in exercise

: Sympathetic nervous system causes blood shift to muscle during exercise by vasoconstriction of blood vessels of all other organs except heart and brain.

Example 2: Liver

: Stimulation of glycogenolysis to produce glucose which will be release into blood to provide muscle with fuel .

Examples of Parasympathetic System in Action Activation of parasympathetics usually has opposite effects to the sympathetics.

Example 1: on gastrointestinal tract

: Para sympathetic system causes increased blood flow, motility and secretion of gastrointestinal tract (e.g. stomach, small intestine)

Example 2: Heart and lungs

: Reduced heart rate and constriction of air tubes (bronchioles) in the lung.

Neurotransmitters of the ANS 1-

Acetylcholine

(

ACh

)- the transmission is said to be

cholinergic

.

- ACh is the transmitter released by: - all preganglionic fibers (in both sympathetic and parasympathetic) - most parasympathetic postganglionic fibers - some sympathetic postganglionic fibers 2-

Norepinephrine

(

noradrenaline

)- the transmission is said to be

adernergic

.

- Norepinephrine is the transmitter released by: - most postganglionic sympathetic fibers, 3-

Non-adernergic non-cholinergic

(

NANC

) - the transmitter is neither ACh nor NE - proposed candidates are: ATP, VIP, and NO.

Preganglionic Postganglionic * Some sympathetics that innervate blood vessels and all sympathetics that supply sweat glands release acetylcholine (ACh) as their neurotransmitter.

Receptors - NE causes excitation to some tissues while it inhibits others. This is due to the presence of different receptors on the target cells.

- There are two types of adernergic receptors: a -adernergic receptors b -adernergic receptors - ACh also has two types of receptors: - Nicotinic - Muscarinic

Adernergic Stimulation 1- Binding of epinephrine or norepinephrine (NE) to a

-receptor

cytoplasmic Ca ++ levels: causes increase in NE a

-receptor

Phospholipase C Second messenger Increase cytoplasmic Ca ++ Inositol triphosphate (IP 3 ) receptor Closed Ca ++ channels Opening Ca ++ channels

Adernergic Stimulation 2- Binding of epinephrine or norepinephrine to b

-receptor

stimulates the production of cyclic adonesine monophosphate (cAMP).

NE b

-receptor

Adenylate cyclase (inactive) ATP Adenylate cyclase (active) cAMP Protein kinase (inactive) Protein kinase (active) Second messenger Catalyse many Reactions in the cell

Nicotinic receptors = n Muscarinic receptors = m

Parasympathetic Cholinergic Stimulation Brain Always excitatory Mainly excitatory but with exceptions ACh n ACh m n ACh somatic ACh n ACh n Adernal Medulla ACh n NE ACh m Parasympathetic

Control of the ANS by Higher Brain Centers Higher Brain Centers

Hypothalamus

Contain centers which control: Medulla Oblongata cardiovascular, pulmonary, urinary, reproductive and digestive system.

Preganglionic Sensory Inputs Postganglionic Effector Organs

Control of ANS by Centers in Brain Brain stem – mainly controls vascular system and respiration.

Hypothalamus Medulla Oblongata -Cardiovascular system ; stimulation of: - posterior hypothalamus causes increase in blood pressure and heart rate , - anterior hypothalamus causes decrease in blood pressure and heart rate.

-Body temperature : - changes in blood temperature in anterior hypothalamus causes several mechanisms to operate for temperature regulation.

Body water secretion of ADH and signals to initiate thirst Feeding – hunger and satiety centers Excitement and rage Endocrine function perifornical nucleus in hypothalamus – neurosecretory substances secretion to anterior pituatory.

Reflex Effects of Sensory Inputs to Brain Centers These receptors are different than cell receptors !

These are sensory receptors Organ Lung Aorta Heart G.I. Tract Type of Receptor Reflex Effect Stretch receptor inhalation is inhibited and heart rate increase Chemoreceptor increase breathing and heart rate Baroreceptor decrease in heart rate Stretch receptor Stretch receptor increase volume of urine excreted and decrease in heart rate feeling of satiety