Autonomic Nervous System (ANS)
• Divisions of ANS– Sympathetic – Parasympatheitc
• Functions of ANS
• Control of ANS
CHAPTER 9
Dr. Hameed Al-SarrafDept. [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
– 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