The Autonomic Nervous System Course Coordinator Jamaluddin Shaikh, Ph.D. School of Pharmacy, University of Nizwa Lecture-12 October 22, 2011

Organization of Nervous System Peripheral Central Afferent Efferent Autonomic Somatic Enteric Sympathetic Parasympathetic

General Organization and Functions of the Nervous System CNS 1) Brain and 2) Spinal cord PNS 1) Afferent (sensory) neurons, which carry nerve impulses into the CNS from sensory end organs in peripheral tissues 2) Efferent (motor) neurons, which carry nerve impulses from the CNS to effectors cells in peripheral tissues. Peripheral efferent system 1) somatic nervous system. The effectors cells innervated by the somatic nervous system are skeletal muscle cells. 2) autonomic nervous system. The autonomic nervous system innervates three types of effectors cells: (a) smooth muscle, (b) cardiac muscle, and (c) exocrine glands

Central Nervous System

Peripheral Nervous System

Peripheral Nervous System

Peripheral Nervous System

Anatomical Differences Between Somatic and Autonomic Nervous Systems Axon of a somatic motor neuron leaves the CNS and travels without interrupting innervated effector cell Two neurons are required to connect the CNS and a effector cell of the autonomic nervous system: 1) the preganglionic neuron and 2) the postganglionic neuron, whose cell body is within the ganglion, travels to the effector cell

Autonomic Nervous System Ganglia is an aggregation of nerve cell bodies located in the peripheral nervous system Sympathetic division: preganglionic neurons are short, postganglionic neurons are long Parasympathetic division: preganglionic neurons are long, postganglionic neurons are short

Autonomic Nervous System, continued… Preganglionic neurons of sympathetic division: cell bodies in thoracic and lumbar regions of the spinal cord Preganglionic neurons of the parasympathetic division: cell bodies in the brainstem and in the sacral region of the spinal cord

Autonomic Neurotransmitters Two PNS neurotransmitters: acetylcholine (Ach) norepinephrine (NE) Synthesized and stored primarily in the nerve terminals Released by nerve impulse Neurotransmission in the PNS occurs at three major sites: (1) preganglionic synapses in both parasympathetic and sympathetic ganglia (2) parasympathetic and sympathetic postganglionic neuro effector junctions, and (3) all somatic motor end plates on skeletal muscle ACh is the transmitter released at all of these sites Neurons that release ACh are called cholinergic neurons.

Autonomic Neurotransmitters, continued… NE is the transmitter released at most sympathetic postganglionic neuroeffector junctions The sympathetic postganglionic neurons that innervate the sweat glands are cholinergic Neurons that release this substance are called adrenergic or noradrenergic neurons Drugs that mimic the actions of ACh are termed cholinomimetic, and those that mimic epinephrine and/or NE are adrenomimetic

Autonomic Neurotransmitters, continued… The receptors with which ACh and other cholinomimetic drugs interact are called cholinoreceptors The receptors with which NE, and epinephrine drugs combine are called adrenoceptors Drugs that antagonize the actions of ACh are known as cholinoreceptor antagonists Drugs that antagonize the action of NE are known as adrenoceptor antagonists

Transmission of the Nerve Impulse The axons branch many times on entering the effector tissue, forming a plexus among the innervated cells The vesicles are intimately involved in the release of the transmitter into the synaptic or neuroeffector cleft in response to an action potential Following release, the transmitter must diffuse to the effector cells, where it interacts with receptors on these cells to produce a response

Functions of the Sympathetic Nervous System Sympathetic division has the property of adjusting in response to stressful situations, such as trauma, fear, hypoglycemia, cold, or exercise Effects of stimulation of the sympathetic division: Effect of sympathetic output is to increase heart rate and blood pressure, to mobilize energy stores of the body, and to increase blood flow to skeletal muscles and the heart. It also affects gastrointestinal motility and the function of the bladder

Functions of the Parasympathetic Nervous System The parasympathetic division maintains essential bodily functions, such as digestive processes and elimination of wastes, and is required for life It usually acts to oppose or balance the actions of the sympathetic division

Steps in the Neurochemical Transmission Steps in the normal transmission process: 1. Synthesis of the transmitter 2. Storage of the transmitter 3. Release of the transmitter by a nerve action potential 4. Interaction of the released transmitter with receptors on the effector cell membrane and the associated change in the effector cell 5. Rapid removal of the transmitter from the vicinity of the receptors 6. Recovery of the effector cell to the state that preceded transmitter action

Synthesis and Storage of ACh

Synthesis and Storage of NE

Receptors on the Autonomic Effector Cells The receptors for ACh and related drugs and for NE and related drugs are different ACh will not interact with receptors for NE, and NE will not interact with receptors for ACh These receptors are selective not only for their respective agonists but also for their respective antagonist drugs