Autonomic Nervous System Touqeer Ahmed PhD 3 rd March, 2017 Atta-ur-Rahman School of Applied Biosciences National University of Sciences and Technology
Nervous System Divisions The peripheral nervous system is subdivided into afferent division: bring information from the periphery to the CNS. Afferent neurons provide sensory input to modulate the function of the efferent division efferent division: carry signals away from the brain and spinal cord to the peripheral tissues The efferent portion of the peripheral nervous system is further divided into two major functional subdivisions Somatic: involved in the voluntary control of functions such as contraction of the skeletal muscles essential for locomotion Autonomic systems: Regulates everyday requirements of vital bodily functions without the conscious participation of the mind
Autonomic Nervous System Role of the CNS in the control of autonomic functions: ANS is a motor system but it does require sensory input from peripheral structures to provide information on the state of affairs in the body. This feedback is provided by streams of afferent impulses, originating in the viscera and other autonomically innervated structures that travel to integrating centers in the CNS, such as the hypothalamus, medulla oblongata, and spinal cord. These centers respond to the stimuli by sending out efferent reflex impulses via the ANS
Autonomic Nervous System
Autonomic Nervous System
Anatomy of the ANS 1. Efferent neurons: The ANS carries nerve impulses from the CNS to the effector organs by way of two types of efferent neurons. The first neuron is called a preganglionic neuron, and its cell body is located within the CNS. Preganglionic neurons emerge from the brainstem or spinal cord and make a synaptic connection in ganglia (an aggregation of nerve cell bodies located in the peripheral nervous system and functions as relay stations). The postganglionic euron has a cell body originating in the ganglion. It is generally nonmyelinated and terminates on effector organs, such as smooth muscles of the viscera, cardiac muscle, and the exocrine glands.
Anatomy of the ANS 2. Afferent neurons: The afferent neurons (fibers) of the ANS are important in the reflex regulation of system (for example, by sensing pressure in the carotid sinus and aortic arch) and in signaling the CNS to influence the efferent branch of the system to respond.
Anatomy of the ANS 5. Enteric neurons: The enteric nervous system is the third division of the ANS. It is a collection of nerve fibers that innervate the gastrointestinal (GI) tract, pancreas, and gallbladder, and it constitutes the brain of the gut. This system functions independently of the CNS and controls the motility, exocrine and endocrine secretions, and microcirculation of the GI tract. It is modulated by both the sympathetic and parasympathetic nervous systems.
Autonomic Nervous System
Autonomic Nervous System Sympathetic Nervous System Parasympathetic Nervous System
Functions of the sympathetic nervous system Although continually active to some degree (for example, in maintaining the tone of vascular beds), the sympathetic division has the property of adjusting in response to stressful situations, such as trauma Fear Hypoglycemia Cold and exercise. Effects of stimulation of the sympathetic division: increase heart rate and blood pressure mobilize energy stores of the body increase blood flow to skeletal muscles and the heart while diverting flow from the skin and internal organs. sympathetic stimulation results in dilation of the pupils and the bronchioles it also affects GI motility and the function of the bladder
Functions of the Parasympathetic nervous system The parasympathetic division is involved with maintaining homeostasis within the body. To accomplish this, it maintains essential bodily functions, such as digestive processes and elimination of wastes. The parasympathetic division is required for life. It usually acts to oppose or balance the actions of the sympathetic division and is generally dominant over the sympathetic system in rest and digest situations. The parasympathetic never discharges as a complete system. If it will, it will produce massive, undesirable, and unpleasant symptoms, such as involuntary urination and defecation. Discrete parasympathetic fibers are activated separately and the system functions to affect specific organs, such as the stomach or eye.
Autonomic Nervous System Neurotransmitters Muscarinic and Nicotinic Receptors
Autonomic Nervous System (Receptors) Muscarinic receptors: M1 M5 M2 is present in heart M3 is present in glands, smooth muscles and endothelium Nicotinic receptors (present in NMJ and CNS) Adrenergic receptors: α and β Receptors α are mainly present in blood vessels β are present in heart and lungs
Differences between sympathetic and parasympathetic nervous systems.
Somatic Nervous System Somatic nervous system: The efferent somatic nervous system differs from the autonomic system in that a single myelinated motor neuron, originating in the CNS, travels directly to skeletal muscle without the mediation of ganglia. Somatic nervous system is under voluntary control, whereas the autonomic system is involuntary. Responses in the somatic division are generally faster than those in the ANS.
Drugs Acting on The Autonomic Nervous System
Drugs Acting on The Autonomic Nervous System Antimuscarinic drugs (e.g. Atropine and scopolamine) Cholinergic blockers are beneficial in a variety of clinical situations such as, dilation of pupil, antispasmodic in GIT, antidote for the overdoses of cholinesterase inhibitor insecticides and antisecretory. Used as antisecretory agent to block secretions in the upper and lower respiratory tracts prior to surgery. Because they do not block nicotinic receptors, the antimuscarinic drugs have little or no action at skeletal neuromuscular junctions. Ganglionic blockers (e.g. Mecamylamine): The drugs produce complex and unpredictable responses, making it impossible to achieve selective actions. Therefore, ganglionic blockade is rarely used therapeutically. However, ganglionic blockers often serve as tools in experimental pharmacology. Mecamylamine is primarily used to lower blood pressure in emergency situations. Neuromuscular Blocking Drugs: (Tubocurarine) Neuromuscular blockers are clinically useful during surgery for producing complete muscle relaxation, without having to employ higher anesthetic doses to achieve comparable muscular relaxation. Adrenergic Blocking Drugs (Propanolol and atenolol) Drugs that block adrenoceptors profoundly affect blood pressure. Blockade of these receptors reduces the sympathetic tone of the blood vessels, resulting in decreased peripheral vascular resistance.