Autonomic &�Somatic Nervous Systems.�

Autonomic & �Somatic Nervous Systems.

1. Autonomic & S omatic Nervous Systems. By Syed Abdul Naveed . M.Pharm (Pharmacology). . 1

2. which consists of is divided into that make up which is divided into The Nervous System Sensory nerves Motor nerves Autonomic nervous system Somatic nervous system Central nervous system Peripheral nervous system Sympathetic nervous system Parasympathetic nervous system Enteric nervous system 2

3. Autonomic nervous system The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control (or) responsible for control of involuntary or visceral body functions . The A.N.S composed of efferent neurons that innervates smooth muscle of the viscera, cardiac muscle , vasculators & the exocrine gland ,cardiac output, blood flow & glandular secretion . 3

4. Autonomic nervous system Divisions of the autonomic nervous system: Parasympathetic division Sympathetic division Serve most of the same organs but cause opposing or antagonistic effects. Parasysmpathetic : routine maintenance “rest &digest”. Sympathetic: mobilization & increased metabolism “fight, flight or fright”. Efferent (Motor) Nerve : Carry impulses from cns (brain and spinal cord) to muscle or organ (peripheral tissues). Afferent (Sensory)Nerve : Neuron which transmits impulses from sense organs (bring information from periphery ) to cns 4

5. Introduction (efferent neurons) Efferent (motor)neuron carrier nerve impulse from CNS to the effector organ by way of two types of efferant neurons. First nerve is called P reganglionic neuron and its cell body is located in the CNS. Preganglionic neurons emerge in the brain stem or spinal cord and makes a synaptic connection in the ganglia. The ganglia function as a relay station between a preganglionic neuron and second nerve cell (postganglionic neuron) The postganglionic neuron has a cell body originating in the ganglia and terminates on effector organ. 5

6. Introduction to somatic motor neurons Somatic efferent neurons are involved in the voluntary contol of function such as contraction of the skeletal muscle. Input from sense organs & out put to skeletal muscle. 6

7. Autonomic and Somatic Motor Systems Autonomic motor system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons Somatic motor system One motor neuron extends from the CNS to skeletal muscle Axons are well myelinated , conduct impulses rapidly 7

8. Sympathetic Nervous system (fight, flight or fright) Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2 Preganglionic neuron of the sympathetic system comes from thoracic and lumbar region of the spinal cord and they synapse in the two cord like chain of ganglia that run parallel on each side of the spinal cord. Preganglion neurons are short ,. Postganglion neuros are long Axons of the postganglionic neuron extended from these ganglion to the tissue that they innervate and regulate. The adrenal medulla (large synaptic ganglion receives preganglion fiber from the sympathetic system. The adrenal medulla in response to stimulation secreates epinephrine also know as adrenaline, and lesser amount of norepinephrine in to the blood. 8

9. Ach Ach Ach Ach NE Ach EPI/NE Ach Ach Somatic Sympathetic Sympathetic Sympathetic Para- sympathetic Postganglionic Fiber; Adrenergic Postganglionic Fiber; Cholinergic Adrenal Gland Motor Fiber Sweat Glands Smooth Muscle Cardiac Cells Gland Cells Smooth Muscle Cardiac Cells Gland Cells Skeletal Muscle Preganglionic Fiber; Cholinergic Ganglion Ganglion Ganglion Neurotransmitter released by preganglionic axons Acetylcholine for both branches (cholinergic) Neurotransmitter released by postganglionic axons Sympathetic – most release norepinephrine (adrenergic) Parasympathetic – release acetylcholine 9

10. Role of the Sympathetic Division The sympathetic division is the “fight-or-flight” system Involves E activities – exercise, excitement, emergency, and embarrassment Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased Its activity is illustrated by a person who is threatened Heart rate increases, and breathing is rapid and deep The skin is cold and sweaty, and the pupils dilate 10

11. Sympathetic Division of the ANS 11

12. The Role of the Adrenal Medulla in the Sympathetic Division Adrenalin (also called epinephrine) is produced in the medulla of the adrenal glands. The adrenal glands are located on the top of each kidney. The sympathetic nervous system stimulates the adrenal gland (an effector) to release the hormone adrenalin or epinephrine into the bloodstream. Adrenalin is a modified amino acid hormone. The target tissue for adrenalin is mainly cardiac and skeletal muscle. Adrenalin increases heart rate and blood pressure providing more oxygen to working muscles. It also increases blood sugar levels providing more energy to cardiac and skeletal muscles . 12

13. Role of the Parasympathetic Division Concerned with keeping body energy use low Involves the D activities – digestion, defecation, and diuresis Its activity is illustrated in a person who relaxes after a meal Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity is high The skin is warm and the pupils are constricted 13

14. Parasympathetic neurons (Rest and Digest) Allow body to function under Rest and digest Pre- ganglionic fiber rises from the cranium(cranium fibers) [III , VII, IX, X]and from sacral region of the spinal cord and synapse in ganglia near or on the effector organ. Cranial outflow III –oculomotor nerve(- pupils constrict) VII -facial nerve –( tears, nasal mucus IX -gloss-pharyngeal nerve(parotid salivary gland) X –vagus nerve(visceral organs of thorax & abdomen): Stimulates digestive glands Increases motility of smooth muscle of digestive tract Decreases heart rate Causes bronchial constriction Sacral outflow (S2-S4) : form pelvic splanchnic nerves Innervates organs of the pelvis and lower abdomen Supply 2 nd half of large intestine Supply all the pelvic (genitourinary) organs Preganglionic fibers are long Postganglionic fibers are short , with a ganglia close or with in the organ. 14

15. Summary of parasympathetic neurons and synapses Preganglionic neurons Long Synapse with postganglionic neurons at ganglia. Release acetylcholine (ACH) to activate nicotinic receptors on postganglionic neurons Postganglionic neurons Short Synapse on the target organ Release acetylcholine (ACH) to activate muscarinic receptors on the target organ 15

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17. INNERVATION BY THE A.N.S DUAL INNERVATION Most organs in the body are innervated by both divisions of the a.n.s . Despite this dual innervation one system usually predominates in controlling the activity of a given organ. Ex: In the heart vagus nerve is the predominant factor for controlling rate. ORGAN RECIVING ONLY SYMPATHETIC INNERVATION The adrenal medulla pilomotor muscle and sweat glands. The control of blood pressure is also mainly a sympathetic activity with essential no participation by the parasympathetic system 17

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20. Enteric neurons It is third division of ANS It is collection of nerve fibers that innervates the GIT, Pancreas and Gall B ladder This system function independently of the CNS and control the motility exocrine and endocrine secretion and micro-circulation of the GIT. It is modulated by both sympathetic and parasympathetic nervous system. 20

21. Neurotransmitter in sympathetic and parasympathetic nervous system 21

22. DIFFERENCES BETWEEN SNS&PNS SNS PNS ORIGIN DORSO-LUMBAR(T 1 TO L 2 OR L 3 ) CRANOI SACRAL(III,VII,IX,X AND S 2- S 4 ) DISTRIBUTION WIDE LIMITED GANGLIA AWAY FROM ORGANS ON/ CLOSE TO THE ORGANS POST GANGLIONIC FIBRES LONG SHORT PRE:POST FIBRES RATIO 1:20 TO 1:100 1:1 TO 1:2 TRANSMITTER NE (MAJOR) Ach (MINOR) Ach STABILITY OF TRANSMITTER NA STABLE Ach (RAPIDLY DESTROYS) IMP FUNCTION TACKLING STRESS & EMERGENCY ASSIMILATION OF FOOD ,CONSERVATION OF ENERGY 22

23. Adrenergic Receptors α 1 - receptors : vasoconstriction, relaxation of gastrointestinal smooth muscle, salivary secretion and hepatic glycogenolysis α 2 - receptors : inhibition of transmitter release (including noradrenalin and acetylcholine release from autonomic nerves), platelet aggregation, contraction of vascular smooth muscle, inhibition of insulin release β 1 - receptors : increased cardiac rate and force β 2 - receptors : bronchi dilatation, vasodilatation, relaxation of visceral smooth muscle, hepatic glycogenolysis and muscle tremor β 3 - receptors : lipolysis. 23

24. Cholinergic Receptors The two types of receptors that bind ACh are nicotinic and muscarinic These are named after drugs that bind to them and mimic ACh effects. Nicotinic receptor Nicotinic receptors are found on: Motor end plates (somatic targets) All ganglionic neurons of both sympathetic and parasympathetic divisions The hormone-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always stimulatory. Muscarinic receptor Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers The effect of ACh binding: Can be either inhibitory or excitatory Depends on the receptor type of the target organ 24

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26. Regulation of ANS Autonomic reflexes control most of activity of visceral organs, glands, and blood vessels. Autonomic reflex activity influenced by hypothalamus and higher brain centers, but it is the hypothalamus that has overall control of the ANS. Sympathetic and parasympathetic divisions influence activities of enteric (gut) nervous system through autonomic reflexes. These involve the CNS. But, the enteric nervous system can function independently of CNS through local reflexes. E.g., when wall of digestive tract is stretched, sensory neurons send information to enteric plexus and then motor responses sent to smooth muscle of gut wall and the muscle contracts. Centers of the hypothalamus control: Heart activity and blood pressure Body temperature, water balance, and endocrine activity Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) Reactions to fear and the “fight-or-flight” system 26

27. Levels of ANS Control The hypothalamus is the main integration center of ANS activity Subconscious cerebral input via limbic lobe connections influences hypothalamic function Other controls come from the cerebral cortex, the reticular formation, and the spinal cord 27

28. synapse The junction between two neurons is called a synapse. An action potential cannot cross the synaptic cleft between neurons, and instead the nerve impulse is carried by chemicals called neurotransmitters. These chemicals are made by the cell that is sending the impulse (the pre-synaptic neuron) and stored in synaptic vesicles at the end of the axon. The cell that is receiving the nerve impulse (the post-synaptic neuron) has chemical-gated ion channels in its membrane, called neuroreceptors . These have specific binding sites for the neurotransmitters 28

29. 1 . At the end of the pre-synaptic neuron there are voltage-gated calcium channels. When an action potential reaches the synapse these channels open, causing calcium ions to flow into the cell. 2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane, releasing their contents (the neurotransmitter chemicals) by exocytosis . 3. The neurotransmitters diffuse across the synaptic cleft. 4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the channels to open. In the example shown these are sodium channels, so sodium ions flow in. 5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an action potential.   6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for example the enzyme acetylcholinesterase breaks down the neurotransmitter acetylcholine. The breakdown products are absorbed by the pre-synaptic neuron by endocytosis and used to re-synthesis more neurotransmitter, using energy from the mitochondria. This stops the synapse being permanently on. 29

30. General Features of Peripheral Autonomic Neurotransmission Membrane Depolarization of Pre- or Postganglionic Fiber Calcium Entry into Varicosity Exocytosis of NT Diffusion of NT Across Neuroeffector Junction or Synapse Activation of NT Receptors Depolarization of Postganglionic Fiber or Response of Effector Cell Nerve Impulse 30

31. SYNTHESIS OF NOREPINEPHRINE Nor epinephrine (NE) is the primary neurotransmitter For postganglionic sympathetic adrenergic nerve. It is synthesized inside the nerve axon, stored within vesicles, then released by the nerve when an action potential travels down the nerve. Synthesis of NE: The amino acid tyrosine is transported into the sympathetic nerve axon. Tyrosine (Tyr) is converted to DOPA by tyrosine hydroxylase , (rate-limiting step for NE synthesis). DOPA is converted to dopamine (DA) by DOPA decarboxylase . Dopamine is transported into vesicles then converted to norepinephrine (NE) by dopamine β- hydroxylase (DBH); transport into the vesicle can by blocked by the drug reserpine . 31

32. An action potential traveling down the axon depolarizes the membrane and causes calcium to enter the axon. Increased intracellular calcium causes the vesicles to migrate to the axonal membrane and fuse with the membrane, which permits the NE to diffuse out of the vesicle into the extracellular ( junctional ) space. DBH, and depending on the nerve other secondary neurotransmitters (e.g., ATP), is released along with the NE. The NE binds to the postjunctional receptor and stimulates the effector organ response 32

33. Synthesis of epinephrine Epinephrine is synthesized from norepinephrine within the adrenal medulla, which are small glands associated with the kidneys. Preganglionic fibers sympathetic adrenergic nerves synapse within the adrenals. Activation of these fibers releases acetylcholine, which binds to postjunctional nicotinic receptors in the tissue. This leads to stimulation of NE synthesis within adenomedullary cells, but unlike sympathetic neurons, there is an additional enzyme (phenyl ethanolamine-N- methyltransferase ) that adds a methyl group to the NE molecule to form epinephrine. The epinephrine is released into the blood perfusing the glands and carried throughout the body. 33

34. Synthesis of acetylcholine Acetylcholine Synthesis Acetyl- CoA is synthesized from pyruvate by mitochondria within cholinergic nerves.  This acetyl- CoA combines with choline that is transported into the nerve axon to form acetylcholine ( ACh ). The enzyme responsible for this is choline acetyltransferase . The newly formed ACh is then transported into vesicles for storage and subsequent release similar to what occurs for NE. After ACh is released, it is rapidly degraded within the synapse by acetylcholineesterase , to form acetate and choline . 34

35. COTRANSMISSION Release of More Than One Neurotransmitter from the Same Nerve Terminal Cotransmitter B Synergistic or Opposite Actions Cotransmitter A 35

36. Many Examples of NANC Neurotransmitters 36

37. Many Examples of NANC Neurotransmitters 37

38. MODULATION OF NEUROTRANSMISSION Modulation of Neurotransmisson Presynaptic/ Prejunctional Modulation Postsynaptic/ Postjunctional Modulation Presynaptic/ Prejunctional Inhibition Presynaptic/ Prejunctional Facilitation Postsynaptic/ Postjunctional Inhibition Postsynaptic/ Postjunctional Facilitation 38

39. MODULATION OF NEUROTRANSMISSION From Nerve Terminal Being Modulated (e.g., Autoinhibitory Feedback) From Postsynaptic/ Postjunctional Site (e.g., Trans- synaptic/ Transjunctional Inhibitory Feedback) From Nearby Nerve Terminal (Cross- talk) From Remote Site via Circulation (e.g., Renin Release) Sources of Modulators of Neurotransmission 39

40. Neuromodulation and presynaptic interactions As well as functioning directly as neurotransmitters, chemical mediators may regulate: - presynaptic transmitter release - neuronal excitability. Both are examples of  neuromodulation  and generally involve second messenger regulation of membrane ion channels. Presynaptic receptors may inhibit or increase transmitter release, the former being more important. Inhibitory  presynaptic autoreceptors  occur on noradrenergic and cholinergic neurons, causing each transmitter to inhibit its own release ( autoinhibitory feedback ). Many endogenous mediators (e.g. GABA, prostaglandins, opioid and other peptides), as well as the transmitters themselves, exert presynaptic control (mainly inhibitory) over autonomic transmitter release . 40

41. Mechanisms of Neuromodulation 41

42. SOMATIC NERVOUS SYSTEM The somatic nervous system, or voluntary nervous system, is part of the peripheral nervous system that regulates body movement through control of skeletal (voluntary) muscles and also relates the organism with the environment through the reception of external stimuli, such as through the senses of vision, hearing , taste, and smell. The somatic nervous system controls such voluntary actions as walking and smiling through the use of efferent motor nerves, in contrast with the function of the autonomic nervous system, which largely acts independent of conscious control in innervating cardiac muscle and exocrine and endocrine glands. It is the somatic nervous system that allows individuals to receive sensory information and consciously react to environmental changes. 42

43. Overview of somatic nervous system The somatic nervous system consists of cranial and spinal nerves that innervate skeletal muscle tissue and are more under voluntary control (as well as the sensory receptors ). The somatic nervous system includes all the neurons connected with muscles ,skin , and sense organs. The somatic nervous system processes sensory information and controls all voluntary muscular systems within the body, with the exception of reflex arcs. The somatic nervous system consists of efferent nerves responsible for sending brain signals for muscle contraction. In humans, there are 31 pairs of spinal nerves and 12 pairs of cranial nerves. The 31 pairs of spinal nerves emanate from different areas of the spinal cord and each spinal nerve has a ventral root and a dorsal root. The ventral root has motor (efferent) fibers that transmit messages from the central nervous system to the effectors, with the cell bodies of the efferent fibers found in the spinal cord gray matter. The dorsal root has sensory (afferent) fibers that carry information from the sensory receptors to the spinal cord The 12 pairs of cranial nerves transmit information on the senses of sight, smell, balance, taste, and hearing from special sensory receptors . They also transmit information from general sensory receptors in the body, largely from the head. This information is received and processed by the central nervous system and then the response travels via the cranial nerves to the skeletal muscles to control movements in the face and throat, such as swallowing and smiling . 43

44. Motor Pathway of Somatic Nervous System Somatic division: Cell bodies of motor neurons reside in CNS (brain or spinal cord) Their axons (sheathed in spinal nerves) extend all the way to their skeletal muscles 44

45. Nerve Signal Transmission The nerve signals in the efferent somatic nervous system involves a sequence that begins in the upper cell bodies of motor neurons (upper motor neurons) within the precentral gyrus (primary motor cortex). Stimuli from the precentral gyrus are transmitted from upper motor neurons and down the corticospinal tract, via axons to control skeletal (voluntary) muscles. These stimuli are conveyed from upper motor neurons through the ventral horn of the spinal cord, and across synapses to be received by the sensory receptors of alpha motor neuron (large lower motor neurons) of the brainstem and spinal cord. Upper motor neurons release a neurotransmitter , acetylcholine , from their axon terminal knobs, which are received by nicotinic receptors of the alpha motor neurons. In turn, alpha motor neurons relay the stimuli received down their axons via the ventral root of the spinal cord. These signals then proceed to the neuromuscular junctions of skeletal muscles. From there, acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors (Nicotinic acetylcholine receptors) of muscles, thereby relaying the stimulus to contract muscle fibers 45

46. Sensory neurons General visceral sensory neurons monitor: Stretch, temperature, chemical changes, and irritation Cell bodies are located in the dorsal root ganglia Pain Receptors. Thermo receptor Mechanoreceptor Chemoreceptor Photoreceptor Hearing and balance 46

47. Pain Receptors Throughout body; except brain Respond to chemical released by damaged cells Important to recognize Danger Injury Disease Thermoreceptors In skin, body core, hypothalamus Detect variations in body temperature 47

48. Mechanoreceptors Skin, skeletal muscle, and inner ears Sensitive to Touch Pressure Stretching of muscles Sound motion Chemo receptors Chemoreceptors pick up chemical reception in nose and mouth Smell – olfactory bulb Taste – taste buds Salty Bitter Sour Sweet 48

49. Photoreceptors Eyes Sensitive to Light Vision Cornea Helps focus light Filled with aqueous humor Iris Back of cornea Colored part of eye Pupil Tiny muscles regulate the size Regulates amount of light Lens Small muscles change its shape to focus on object near and far away Behind lens eye filled with vitreous humor Retina Has photoreceptors No photoreceptors where optic nerve passes through the back of the eye; blind spot Two types Rods – black and white Cones – color 49

50. Hearing and Balance Hearing Ear Two Functions Hearing Detecting Positional change to movement. Cochlea Hammer, Anvil, Stirrup Tymapnum Auditory canal Sound Balance Semicircular Canals 3 canals that form half circles Filled with fluid and hairs that detect motion of head in relation to gravity 50

51. Differences Between somatic & Autonomic Nervous System Differences Somatic Autonomic No of neurons in efferent path way 1 2 Neurotransmitter / receptor at neuron target synapse Ach/nicotinic Ach/ Muscarinic (or) N.E/ Alpha or beta Target tissue Skeletal muscle Smooth & cardiac muscle, some endocrine & exocrine Glands , some adipose tissue. Neurotransmitter released from Axon terminals Varicosities & axon terminals Effects on target tissue Excitatory only, Muscle contracts. Excitory or inhibitory. Peripheral components found outside the cns Axons only Preganglionic axons, ganglia, postganglionic neurons. Summary of functions Posture & movement Visceral functions , including Movement in internal organs & secretion , control of metabolisium . 51

52. References GOODMAN & GILMAN'S THE PHARMACOLOGICAL BASIS OF THERAPEUTICS (11th Ed.) . PHARMACOLOGY BY H.P.RANG, M.M.DALE(6 th Ed.). ESSENTIALS OF MEDICAL PHARMACOLOGY BY KD.TRIPATHI(5 th Ed.) LIPPINCOTT’S ILLUSTRATED REVIEWS PHARMACOLOGY. 52

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