Physiology of the sympathetic and parasympathetic nervous system Dr. Moizuddin Khan Associate Professor of Physiology Dr.Beenish Mukhtar Lecturer of Physiology

Objectives Upon completion of this lecture, students should be able to understand: The anatomy of somatic and autonomic nervous system Sympathetic and parasympathetic nerves Pre and post ganglionic neurons Functions of sympathetic and parasympathetic nerves in head & neck, chest, abdomen and pelvis Neurotransmitters release at pre and post ganglionic sympathetic / parasympathetic nerves endings Various responses due to stimulation of the sympathetic / parasympathetic nervous system

Peripheral Nervous System Somatic NS Permits voluntary action Control activity of skeletal muscles (writing your name). Autonomic NS Permits Involuntary functions Control of blood vessels, Glands & internal organs e.g.:- bladder, stomach, heart. The two systems are anatomically separated form each other, but functionally they work with each other in an integrated manner

Divisions of Autonomic Nervous System Anatomically Functionally Cranial Thoracolumber Sacral outflow outflow outflow Sympathetic N.S. Parasympathetic N.S. Thoraco –lumber Cranio – sacral T1 to L3 III –VII- IX- X S2 to S5

The autonomic reflex arc The reflex arc The autonomic reflex arc The somatic reflex arc Receptor Mostly in viscera Mostly in skin Afferent identical Center Lateral horn cells Anterior horn cells Efferent 2 neuron, relay in autonomic ganglia outside the CNS. One neuron, supply the effector organ directly. Effector organs Smooth , cardiac muscles skeletal

The ANS is most important in two situations: 1- In emergencies that cause stress and require us to "fight" or take "flight" (run away). 2- In no emergencies that allow us to "rest" and "digest".

Functional Division of Autonomic Nervous System Parasympathetic NS Sympathetic NS

Sympathetic nervous system The sympathetic nervous system has a thoracolumbar outflow (T1-L3) The sympathetic connecting the spinal cord with different visceral effectors consists of 2 neurons, pre- and post ganglionic neurons. Sympathetic Trunk Ganglia

Functions of sympathetic nervous system during stress (mass discharge) Dilates the pupil. Increases all properties of the heart. Dilates the bronchioles. Constriction of skin blood vessels. Shift of blood flow from skin & splanchnic areas to heart, CNS and skeletal muscles. Increases glycogenolysis in the liver. Elevates blood glucose & free fatty acid level.

8- Contraction of splenic capsule. 9- Increases the secretion of adrenaline & noradrenaline from the adrenal medulla. 10- Increases mental activity. 11- Increases sweat secretion. 12- Reinforcing the alert, aroused state by stimulation of reticular formation by catecholamine.

Parasympathetic Nervous System Activities directed toward conserving and restoring energy that allow us to "rest" and "digest" The parasympathetic nervous system has a craniosacral outflow. Prepares the body for recovery & repair. Its activity continues and even increase during sleep & rest.

Important Functions : 1- Pupillary constriction & accommodation. 2- Stimulation of GIT secretion & peristalsis 3- Secretion of watery saliva 4- Decrease heart properties 5- Constriction of bronchioles 6- Secretion of tears 7- Stimulation of emptying mechanism of the rectum and urinary bladder micturation & defecation. 8- Nerve of erection.

Comparison between sympathetic & parasympathetic systems Origin Thoracolumber outflow (T1-L3) Craniosacral outflow III, VII, IX, X S2,3,4 Preganglionic fibers --Short, from spinal cord to sympathetic chain. -- Synapse & activates many postganglionic fibers. Long , from brain or spinal cord to ganglia in effector organ. --Synapse & activates few postganglionic fibers. Solitary innervation - Smooth muscles of cutaneous blood vessels. - Pilomotor muscles Sweat glands - Lacrimal glands Post- ganglionic fibers Long, from sympathetic chain to the effector organ Short, because ganglia are embedded in effector organ Functionally -- catabolic -- prepare the body for vigorous muscle activity (fight & flight) --Action is wide spread -- Anabolic -- Concerned with vegetative aspects of day to day living -- action is localized and discrete

Sympathetic Tone The sympathetic division controls blood pressure and keeps the blood vessels in a continual state of partial constriction This sympathetic tone (vasomotor tone): Constricts blood vessels and causes blood pressure to rise as needed Prompts vessels to dilate if blood pressure is to be decreased Alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension

Parasympathetic Tone Parasympathetic tone: Slows the heart Dictates normal activity levels of the digestive and urinary systems The sympathetic division can override these effects during times of stress Drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention

Effects of Sympathetic Activation Sympathetic activation is long-lasting because Norepinephrin…… Is inactivated more slowly than ACh Is an indirectly acting neurotransmitter, using a second-messenger system And epinephrine are released into the blood and remain there until destroyed by the liver

Balance Between The Two Is Responsible For Maintaining A Stable Internal Environment.

CNS control of the ANS 15.17

Neurotransmitters & Receptors of the ANS All preganglionic fibers of ANS release and all parasympathetic postganglionic fiber release acetylcholine (ACh) (cholinergic). MOST sympathetic postganglionic fibers release norepinephrine (adrenergic), except at sweat glands and some blood vessels in skeletal muscles where they release Ach.  All cholinergic receptors on the postganglionic neurons of sympathetic and parasympathetic systems, and on the adrenal gland are nicotinic  All cholinergic receptors on effector cells are muscarinic

1. Cholinergic Receptors They are named after the drugs that bind to them: A. Muscarinic (G-ptotein coupled) Receptors (bind muscarine) B. Nicotinic (ligand-gated) Receptors (bind nicotine) Muscarine (Mushroom) Nicotine (Tobacco) M1 M2 M3 M4 M5 Blocker: Atropine blocks M receptors and is used to inhibit salivary and bronchial secretion before surgery.

2. Adrenergic Receptors Adrenergic receptors bind to norepinephrine and epinephrine α1-receptors: their activation usually produces excitation (most target tissues) α2-receptors: their activation usually produce inhibition (digestive organs) β1-receptors:. They cause an excitatory response (mainly in heart). β2-receptors: their activation in general causes inhibition (blood vessels and airways). β3-receptors: ???

Functions of Adrenergic Receptors Alpha ( α-) Receptor Beta (β-) Receptor Vasoconstriction Vasodilation ( β2 Iris dilation Cardioacceleration (β1 Intestinal sphincter contraction Increased myocardial strength (β1) Bladder sphincter contraction Glycogenolysis (β2) Pilomotor contraction

Effects of Sympathetic and Parasympathetic Stimulation on Specific Organs

Effects of Sympathetic and Parasympathetic Stimulation on Specific Organs

Function of the Adrenal Medullae Stimulation of the sympathetic nerves to the adrenal medullae causes large quantities of epinephrine and norepinephrine to be released into the circulating blood, and these two hormones in turn are carried in the blood to all tissues of the body. On the average, about 80 per cent of the secretion is epinephrine and 20 per cent is norepinephrine

Epinephrine causes almost the same effects as those caused by norepinephrine, but the effects differ in the following respects: First, epinephrine, because of its greater effect in stimulating the beta receptors, has a greater effect on cardiac stimulation than does norepinephrine. Second, epinephrine causes only weak constriction of the blood vessels in the muscles, in comparison with much stronger constriction caused by norepinephrine this difference is of special importance because norepinephrine greatly increases the total peripheral resistance and elevates arterial pressure whereas epinephrine raises the arterial pressure to a lesser extent but increases the cardiac output more.

A third difference between the actions of epinephrine and norepinephrine relates to their effects on tissue metabolism. Epinephrine has 5 to 10 times as great a metabolic effect as norepinephrine. Epinephrine can increase the metabolic rate of the whole body often to as much as 100 per cent above normal, in this way increasing the activity and excitability of the body. It also increases the rates of other metabolic activities, such as glycogenolysis in the liver and muscle, and glucose release into the blood.

Thank You