Autonomic Nervous System

AUTONOMIC NERVOUS SYSTEM The Autonomic nervous system consists of efferent neurons that conduct impulses from CNS to smooth muscles, cardiac muscles and glands. It is involuntary in nature. It regulates the activity of smooth muscles, GIT, sweat glands, adrenal glands and some endocrine glands. Main function of ANS is to maintain the optimal internal environment of the body. COMPOSITION OF ANS ANS has two divisions – sympathetic and parasympathetic system. Both divisions send impulses exactly of opposite type to the same organ. FUNCTIONS z z z z z

Sympathetic activity involves the expenditure of energy and parasympathetic activity involves the conservation of energy. The system governs the activities of cardiac and smooth muscles, endocrine glands, sweat glands and digestive glands. It regulates the composition of body fluids and temperature by acting on respiration, circulation and glands. It regulates the movement of GIT It regulates the size of pupil, accommodation for near vision and dilatation of blood vessels.

SYMPATHETIC N.S. SITE Preganglionic fibers

Postganglionic fibers

Forms the Thoracolumbar outflow Pass to the paravertebral sympathetic ganglia Pass to the postganglionic neurons in the sympathetic chain. Pass to viscera in the various sympathetic nerves.

PARASYMPATHETIC N.S. Forms the Craniosacral outflow Fm brain and spinal cord to the parasympathetic ganglia located near the effector organs

Supplies visceral structures in the head (oculomotor nerve Facial nerve, glossopharyngeal nerve)

Some preganglionic fibers pass directly to the postganglionic neurons in the paravertebral ganglia— z Superior mesenteric z Inferior mesenteric Preganglionic fibers Postganglionic fibers Neurotransmitter between postganglionic fibers and effector cells

Short Long Adrenaline

Long Short Acetylcholine

AUTONOMIC NERVOUS SYSTEM

SOMATIC NERVOUS SYSTEM

Neurons of autonomic nervous system innervate all the organs except skeletal muscles.

Neurons of somatic nervous system innervate only skeletal muscles.

Involuntary

Voluntary

The axon of one efferent neuron extends from the CNS and synapses with another neuron in a ganglia.

The axon of one efferent neuron extends from CNS and synapses directly on skeletal muscle fibers.

Action may be excitatory or inhibitory

Always excitatory

Neurotransmitter is acetylcholine or noradrenaline

Neurotransmitter is acetylcholine

Preganglionic fibers are myelinated

Myelinated

Postganglionic fibers are nonmyelinated

Myelinated

Peripheral plexus formation is present

Peripheral plexus formation is absent

NOTE:25% of the parasympathetic nerve fibers are in the vagus nerve. In both sympathetic and parasympathetic system the main neurotransmitter released between pre and post ganglionic fibers is acetylcholine. CHOLINERGIC NEUR Neurons which secrete acetylcholine at the nerve endings. Includesz Preganglionic autonomic endings z Postganglionic parasympathetic endings z Postganglionic sympathetic endings which innervate sweat glands, skeletal muscle blood vessels z Neuromuscular junction ADRENERGIC NEURONS Neurons which secrete norepinephrine at nerve endings

Includes 1. Spinal cord 2. Adrenal medulla 3. Parts of brain- cerebral cortex, hypothalamus, cerebellum 4. Postganglionic sympathetic nerve endings other then supplied by cholinergic neurons. NICOTINC RECEPTORS AND MUSCARINIC RECEPTORS

MUSCARINIC RECEPTORS LOCATION Heart, smooth muscles, Exocrine glands.

NICOTINIC RECEPTORS Autonomic ganglia.

Action

Causes Release of Decreased heart rate, neurotransmitter in brain contractility of heart. Increase secretion of the glands. Relaxes the smooth muscles.

Onset of action

Slow

rapid

Duration

Prolonged

Short

Antagonists Atropine

EFFECTOR ORGAN EYES Iris muscle Ciliary muscle Heart SA node Atria

Hexamethonium / tubocurarine

SYMPATHETIC RESPONSE

PARASYMPATHETIC RESPONSE

Dilates pupil (contracts radial muscle) relaxation

Constrict pupil (contracts sphincter muscle) contracts

Increases HR Increases contractibility and conduction

Decrease HR Decrease conduction

AV node and conduction Ventricles Lungs Bronchial glands Bronchial muscles Salivary glands Stomach and intestine Motility , tone sphincters Pancreas Exocrine glands Endocrine glands Liver Gall bladder Fat URINARY BLADDER Detrusor muscle sphincter ARTERIOLES Coronary Skin Skeletal muscle Abdominal viscera kidney

Increase conduction velocity Increase contractibility and conduction

Decrease conduction velocity Decrease contractibility

Inhibits secretion (α1) Stimulates (β2)

Stimulates secretion

Relaxes

Constricts

Stimulates secretion Decrease motility Constricts sphincters Inhibits secretions

Stimulates Increase motility Relaxes sphincter Stimulates secretions

Inhibits secretion Inhibits insulin and glucagon secretion Gluconeogenesis, glycogenolysis Relaxes Breakdown of fat Relaxes constricts

Increase insulin and glucagon secretion Glycogen synthesis

Constricts Constricts Constricts Constricts Constricts

Dilates Dilates Dilates Dilates Dilates

Veins

Constricts

Uterus

Pregnant- contracts

Contracts

Variable

Non pregnant- relax Skin Pilomotor muscle Sweat glands

Contracts Localized

Generalized

Multiple Choice Questions: 1. False about ANS is a) Sympathetic NS forms the thoracolumbar outflow b) Preganglionic fibers of sympathetic NS are short c) Postganglionic fibers of parasympathetic NS are short d) Neurotransmitter in parasympathetic NS is adrenaline 2. Cholinergic neurons present in all except a) Preganglionic autonomic endings b) Post ganglionic parasympathetic endings c) Adrenal medulla d) Neuromuscular junction 3. Stimulation of sympathetic NS causes a) Dilatation of pupil b) Decrease heart rate c) Inhibits motility of GIT d) Increase Insulin secretion 4. Sympathetic stimulation on heart does not cause a) Increase heart rate b) Increase contractility c) Increase AV conduction time d) Increase conduction time 5. Parasympathetic stimulation causes all except a) Stimulate saliva secretion b) Constricts bronchial muscle c) Dilates pupil d) Dilates arterioles