Autonomic Nervous System (ANS) Divisions of ANS –Sympathetic –Parasympatheitc Functions of ANS Control of ANS CHAPTER 9 Dr. Hameed Al-Sarraf Dept. Physiology

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 HEART Many internal Organs

1- Sympathetic (Thoracolumbar) Division 2- Parasympathetic (Craniosacral) Division. Divisions of ANS

Sympathetic Thoracolumbar Sympathetic hain

Sympathetic Chain

Parasympathetic Craniosacral Vagus

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 Fast rate of action potentials VasoconstrictionVessel diameter at rest Slow rate of action potentials

Sympathetic Tone Stop sending action potentials VasodilatationVessel diameter at rest Slow rate of action potentials

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 Vasoconstriction Fast 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 will be 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: 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 - 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. (in both sympathetic and parasympathetic)

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

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 Stimulation 1- Binding of epinephrine or norepinephrine (NE) to  -receptor causes increase in cytoplasmic Ca ++ levels:  -receptor NE receptor Membrane Phospholipase C Inositol triphosphate (IP 3 ) Closed Ca ++ channels Opening Ca ++ channels Increase cytoplasmic Ca ++ Endoplasmic Reticulum Second messenger

Adernergic Stimulation 2- Binding of epinephrine or norepinephrine to  -receptor stimulates the production of cyclic adonesine monophosphate (cAMP).  -receptor NE Membrane Adenylate cyclase (inactive) Adenylate cyclase (active) ATPcAMP Protein kinase (inactive) Cytoplasm Protein kinase (active) Catalyse many Reactions in the cell Second messenger

Cholinergic Stimulation Nicotinic receptors = n Muscarinic receptors = m Brain ACh Adernal Medulla NE ACh somatic Parasympathetic Sympathetic n n n n n m m Always excitatory Mainly excitatory but with exceptions

Control of the ANS by Higher Brain Centers Higher Brain Centers Medulla Oblongata Sensory Inputs Preganglionic Postganglionic Effector Organs Hypothalamus Contain centers which control: cardiovascular, pulmonary, urinary, reproductive and digestive 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. Medulla Oblongata

Reflex Effects of Sensory Inputs to Brain Centers OrganType of ReceptorReflex Effect LungStretch receptor inhalation is inhibited and heart rate increase Aorta Chemoreceptor increase breathing and heart rate Baroreceptor decrease in heart rate Heart Stretch receptor increase volume of urine excreted and decrease in heart rate G.I. TractStretch receptor feeling of satiety These receptors are different than cell receptors ! These are sensory receptors