AUTONOMIC NERVOUS SYSTEM Sultan Ayoub Meo, MBBS, PGCMed Ed, M.Phil, Ph.D Professor, Department of Physiology, College of Medicine King Khalid University Hospital, Riyadh, Saudi Arabia
THE NERVOUS SYSTEM • Central Nervous System • Peripheral Nervous System • 1. Central Nervous System • A. Brain • Fore brain: Cerebrum, Diencephalon (Thalamus, Metathalamus, Epithalamus, Hypothalamus and subthalamus • Mid brain • Hind brain: Pons, Medulla oblongata, Cerebellum • Spinal cord
THE NERVOUS SYSTEM 2. Peripheral nervous system: a)Somatic Nervous System: b) Autonomic Nervous System i. Sympathetic nervous system ii. Para sympathetic nervous system
THE NERVOUS SYSTEM The nervous system monitors and controls almost every organ / system through a series of positive and negative feedback loops. The Central Nervous System (CNS): Includes the brain and spinal cord. The Peripheral Nervous System (PNS): Formed by neurons & their process present in all the regions of the body. It consists of cranial nervesarises from the brain & spinal nerves arising from the spinal cord. This again divided into Somatic Nervous system Autonomic nervous system
THE PERIPHERAL NERVOUS SYSTEM The peripheral nervous system is divided into: Somatic nervous system: which controls organs under voluntary control (mainly muscles) Autonomic Nervous System (ANS): It regulates individual organ function and homeostasis and for the most part is not subject to voluntary control. It is also known as the visceral or automatic system.
CHEMICAL DIVISION OF THE ANS • Cholinergic • Nor Adrenergic The neurons that are cholinergic are • Are pre ganglionic neurons • Anatomicallt para syampatheic post ganglionic neuron • Anatomical;lt syampatheic post ganglionic neuron ineervate sweet glands • Anatomically syampatheic neurons that end on blood vessels in skeletal muscles & produce vasodilatation • The remaining post ganglionic sympathetic neurons are nor adrenergic
SOMATIC NERVOUS SYSTEM • The somatic nervous system includes the nerves supplying the skeletal muscles. • Thus the somatic nervous system controls the movements of the body by acting on skeletal muscles.
THE AUTONOMIC NERVOUS SYSTEM • Autonomic nervous system (ANS): • Innervates organs whose functions are not usually under voluntary control. • Effectors include cardiac and smooth muscles and glands. • Effectors are part of visceral organs and blood vessels
THE AUTONOMIC NERVOUS SYSTEM • The Autonomic nervous system is concerned with regulation of visceral or vegetative function. Therefore also called vegetative or involuntary nervous system • The autonomic nervous system (ANS) is a regulatory structure that helps people adapt to changes in their environment. • It adjusts or modifies some functions in response to stress.
THE AUTONOMIC NERVOUS SYSTEM • Anatomical & functional basis ANS is divided into two separate divisions: • Sympathetic systems • Parasympathetic system • Both of these systems consist of myelinated preganglionic fibreswhich make synaptic connections with unmyelinated postganglionic fibres, and then innervate the effector organ • These synapses usually occur in clusters called ganglia.
DIVISION OF THE AUTONOMIC NERVOUS SYSTEM
BASIC ANATOMY OF ANS • Preganglionic neuron: • Cell body in brain or spinal cord • Axon is myelinated type fiber that extends to autonomic ganglion • Postganglionic neuron: • Cell body lies outside the CNS in an autonomic ganglion • Axon is unmyelinated type fiber that terminates in a visceral effector
BASIC ANATOMY OF ANS 2 neurons in the efferent pathway. 1st neuron has its cell body in gray matter of brain or spinal cord. • Preganglionic neuron. • Synapses with 2nd neuron within an autonomic ganglion. • Postganglionic neuron. • Autonomic ganglion has axon which extends to synapse with target tissue.
ANS Neurotransmitters: Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released Cholinergic
ANS Preganglionic autonomic fibers originate in midbrain, hindbrain, and upper thoracic to 4th sacral levels of the spinal cord. Autonomic ganglia are located in the head, neck, and abdomen Presynaptic neuron is myelinated and postsynaptic neuron is unmyelinated Autonomic nerves release NT that may be stimulatory or inhibitory.
Overview of actions LOCATIONS OF AUTONOMIC GANGLIA • Sympathetic Ganglia: • Trunk (chain) ganglia near vertebral bodies • Prevertebral ganglia near large blood vessel in gut • celiac superior mesenteric • inferior mesenteric • Parasympathetic Ganglia: • Terminal ganglia in the wall of organ
Overview of actions AUTONOMIC PLEXUSES • Cardiac plexus • Pulmonary plexus • Celiac plexus • Superior mesenteric • Inferior mesenteric • Hypogastric
SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEM Blue= Para symp; Red symp
THE AUTONOMIC NERVOUS SYSTEM • The ANS is predominantly an efferent system transmittingimpulses from the Central Nervous System (CNS) to peripheral organ systems. • Its effects include: • Control of heart rate and force of contraction • Constriction and dilatation of blood vessels • Contraction and relaxation of smooth muscle • Visual accommodation • Pupillary size and secretions from exocrine and endocrine glands.
PARASYMPATHETIC NERVOUS SYSTEM • The preganglionic outflow of the parasympathetic nervous system arises from • Cell bodies of the motor nuclei of the cranial nerves III, VII, IX and Xin the brain stem • Second, third and fourth [S2-S4] sacral segments of the spinal cord. It is therefore also known as the cranio-sacral outflow
PARASYMPATHETIC NERVOUS SYSTEM • The cranial nerves III, VII and IX affect the pupil and salivary gland secretion • Vagus nerve (X) carries fibres to the heart, lungs, stomach, upper intestine and ureter • The sacral fibres form pelvic plexuses which innervate the distal colon, rectum, bladder and reproductive organs.
PARASYMPATHETIC NERVOUS SYSTEM • The parasympathetic nervous system has "rest and digest" activity. • In physiological terms, the parasympathetic system is concerned with conservation and restoration of energy, as it causes a reduction in heart rate and blood pressure, and facilitates digestion and absorption of nutrients, and consequently the excretion of waste products • The chemical transmitter at both pre and postganglionic synapses in the parasympathetic system is Acetylcholine (Ach).
Overview of actions PARASYMPATHETIC RESPONSE Enhance “rest-and-digest” activities Mechanisms that help conserve and restore body energy during times of rest • Normally dominate over sympathetic impulses • SLUDD type responses: salivation, lacrimation, urination, digestion & defecation 3 “Decreases”decreased HR,diameter of airways and diameter of pupil • Paradoxical fear when there is no escape route or no way to win causes massive activation of parasympathetic division – loss of control over urination and defecation
Overview of actions ORGANS INNERVATED BY SYMPATHETIC NS Structures innervated by each spinal nerve: Sweat glands, arrector pili, blood vessels to skin & skeletal mm. Thoracic & cranial plexuses supply:Heart, lungs, esophagus & thoracic blood vessels Plexus around carotid artery to head structures Splanchnic nerves to prevertebral ganglia supply: GIT from stomach to rectum, urinary & reproductive organs
SYMPATHETIC NERVOUS SYSTEM • Cell bodies of the sympathetic preganglionic fibres are in the lateral horns of the spinal segments T1-L2,called thoraco-lumbar outflow. • The preganglionic fibres travel a short distance in the mixed spinal nerve and then branch off as white rami (myelinated) to enter the sympathetic ganglia. • These are mainly arranged in two paravertebral chains which lie anterolateral to the vertebral bodies and extend from the cervical to the sacral region. They are called the sympathetic ganglionic chains.
SYMPATHETIC NERVOUS SYSTEM • The short preganglionic fibres which enter the chain make a synapse with a postsynaptic fibre either at the same dermatomal level, or at a higher or lower level • The longer postganglionic fibres usually return to the adjacent spinal nerve via grey rami (unmyelinated) and are conveyed to the effector organ.
SYMPATHETIC NERVOUS SYSTEM FEAR, FLIGHT OR FIGHT • The sympathetic system enables the body to be prepared for fear, flight or fight • Sympathetic responses include an increase in heart rate, blood pressure and cardiac output • Diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal muscle • Increased pupil size, bronchiolar dilation, contraction of sphincters and metabolic changes such as the mobilisation of fat and glycogen.
FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM Frequently referred to as the fear, flight or fight system It has a stimulatory effect on organs and physiological systems, responsible for rapid sensory activity (pupils in the eye) and movement (skeletal muscle). It diverts blood flow away from the GIT and skin via vasoconstriction. Blood flow to skeletal muscles, lungs is not only maintained, but enhanced (by as much as 1200%), in case of skeletal muscles.
FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM Bronchioles dilate, which allows for greater alveolar oxygen exchange. It increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles. Sympathetic nerves dilate the pupil and relax the lens, allowing more light to enter the eye.
Overview of actions SYMPATHETIC RESPONSE Dominance by the sympathetic system is caused by physical or emotional stress “E situations” Emergency, Embarrassment, Excitement, Exercise Alarm reaction = flight or fight response: • Dilation of pupils • Increase heart rate, force of contraction & BP • Decrease in blood flow to nonessential organs • Increase in blood flow to skeletal & cardiac muscle • Airways dilate & respiratory rate increases • Blood glucose level increase
ADRENALINE & NOR ADRENALINE • Adrenaline and noradrenaline are both cate-cholamines • Both synthesized from the essential amino acid phenylalanine by a series of steps, which includes the production of dopamine. • The terminal branches of the sympathetic postganglionic fibres have varicosities or swellings, giving them the appearance of a string of beads. • These swellings form the synaptic contact with the effector organ, and are also the site of synthesis and storage of noradrenaline.
ADRENALINE & NOR ADRENALINE • On the arrival of a nerve impulse, noradrenaline is released from granules in the presynaptic terminal into the synaptic cleft. • The action of noradrenaline is terminatedby diffusion from the site of action, re-uptake back into the presynaptic nerve ending where it is inactivated by the enzyme Monoamine Oxidase in mitochondria or metabolism locally by the enzyme Catechol-O-Methyl-Transferase.
Overview of actions RECEPTORS • The parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter. • The ACh acts on two types of receptors, the muscarinic and nicotonic choloinergic receptors. • Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of the postganglionic nerve. • The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.
Overview of actions TYPES OF MUSCARINIC RECEPTORS The three main types of muscarinic receptors: M1 muscarinic receptors: located in the neural system. M2 muscarinic receptors: located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the SA and AV node. Note, they have no effect on the contractile forces of the ventricular muscle.
Overview of actions TYPES OF MUSCARINIC RECEPTORS M3 muscarinic receptors: located at many places in the body, such as the smooth muscles of the blood vessels, as well as the lungs, which means that they cause vasoconstriction & bronchioconstriction and. They are also in the smooth muscles of the GIT, which help in increasing intestinal motility and dilating sphincters. M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body.