Autonomic Nervous System (ANS)

• Divisions of ANS– Sympathetic – Parasympatheitc

• Functions of ANS

• Control of ANS

CHAPTER 9

Dr. Hameed Al-SarrafDept. Physiologyhameed_alsarraf@hotmail.com

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

– Smooth Muscle

– Glands

• 1- Sympathetic (Thoracolumbar) Division

• 2- Parasympathetic (Craniosacral) Division.

Divisions of ANS

Sympathetic

Sympathetic Chain

Sympathetic Chain

Parasympathetic

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 ANS1- 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 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,

Sympathetic tone

slow rate of action potentials vessel diameter at rest

VasoconstrictionFast rate of action potentials

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 willbe release into blood to provide muscle with fuel.

Activation of parasympathetics usually has opposite effects to the sympathetics.

Examples of Parasympathetic System in Action

Example 1:

on gastrointestinal tract:Parasympathetic 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- 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.

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

Sympathetic andParasympathetic innervationof Effectors.

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:

- -adernergic receptors- -adernergic receptors

- ACh also has two types of receptors:

- Nicotinic - Muscarinic

Adernergic Receptors

1- Binding of epinephrine or norepinephrine (NE) to -receptor causes increase in cytoplasmic Ca++ levels:

-receptor

NE

receptor

Mem

bran

e

Phospholipase C

Inositol triphosphate (IP3)

Closed Ca++ channels Opening Ca++ channels

Increase cytoplasmic Ca ++

End

opla

smic

Ret

icul

um

Adernergic Receptors

2- Binding of epinephrine or norepinephrine to -receptor stimulates the production of cyclic adonesine monophosphate (cAMP).

-receptor

NE

Mem

bran

e

Adenylate cyclase (inactive)

Adenylate cyclase (active)

ATP cAMP

Protein kinase(inactive)

Cyt

opla

sm

Protein kinase(active)

Catalyse manyReactions in thecell

Control of the ANS by Higher Brain Centers

Higher Brain Centers

Medulla Oblongata

Sensory Inputs

Effector Organs

Hypothalamus

Contain centers which control:

cardiovascular, pulmonary, urinary, reproductive anddigestive system.

Control of ANS by Centers in Brain

Brain stem – mainly controls vascular system and respiration.

Hypothalamus-

-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- perifornical nucleus in hypothalamus- Endocrine function – neurosecretory substances secretion to anterior pituatory.

Reflex Effects of Sensory Inputsto Brain Centers

Organ Type of Receptor Reflex Effect

Lung Stretch receptor inhalation is inhibited and heart rate increase

Aorta Chemoreceptor increase breathing and heart rate

Baroreceptor decrease in heart rateHeart Stretch receptor increase volume of urine excreted

and decrease in heart rateG.I. Tract Stretch receptor feeling of satiety