Autonomic nervous system
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Autonomic nervous system






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  • (eg, blood vessels, gut wall, urinary bladder)
  • Autonomic responses are coordinated with one another and with behavioral responses and emotions through the hypothalamus in the CNS.
  • between somatic motor neuron and ANS.
  • Autonomicfunctions are involuntaryFirst and second order axonsSynapse outside CNSEffectors include cardiac, smooth muscles and glands.
  • A nerve impulse in the ANS has to travel in along two(2) neurons in series to get from the CNS to effector.
  • muscarinetoxic alkaloid: a toxic substance, found in fly agaric and some other fungi, that affects the nervous system when ingested. Among other effects it dilates the blood vessels, slows the heart rate, constricts the airways, and stimulates the gut.
  • Splanchnic: intestinal: relating to the intestines (technical).

Autonomic nervous system Autonomic nervous system Presentation Transcript

  • Chapter 4: physiology Autonomic Nervous System Girmay F.
  • Out line presentation 1. Introduction 2. Division of ANS  Sympathetic nervous system  Parasympathetic nervous system. 3. Adrenal medulla 4. Neurotransmitters and Receptors in ANS 2
  • Introduction The human internal environments is regulated in large measure by the: • ANS • Endocrine glands and N.B. Integrated activities of these two systems 3
  •  The subdivision of the Peripheral NS that regulates body activities independently (autonomously) and continuously without conscious effort.  ANS innervate  Smooth muscle, Cardiac muscle  Glands (eg, sweat glands, salivary glands) 4
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  •  mediates visceral reflex responses that are involuntary and largely unconscious.  Although survival is possible without an ANS, the ability to adapt to environmental stressors and other challenges is severely compromised. 9
  • The ANS affects the following:  Heart rate, Respiration rate  Digestion, Salivation  Perspiration  Diameter of the pupils  Micturition (urination)  Sexual arousal 10
  •  Basic difference ANS VS SNS  Somatic division:  operates under our conscious (voluntary) control.  Cell bodies of motor neurons reside in CNS  One motor neuron extends from the CNS to skeletal muscle.  Axons are well myelinated, conduct impulses rapidly. 11
  •  Autonomic system:  chains of two motor neurons  1st = preganglionic neuron (in brain or spinal cord)  2nd = ganglionic neuron (cell body in ganglion outside CNS) .   Slower because lightly or unmyelinated. functions are involuntary 12
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  •  Preganglionic neurons :    the first neuron and its cell bodies in CNS Myelinated. Postganglionic neurons:  The second neuron  its cell bodies in the autonomic ganglion  Unmyelinated 15
  •  The nerve impulse transmitted from pre-to-post ganglion occur via Acetyl choline (ACH). N.B 1. Ganglion: the collection of nerve cell bodies in the peripheral nervous system. 2. Nuclei : collection of nerve cell bodies in CNS. 16
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  • Divisions of Autonomic Nervous System  The ANS has two major divisions: the sympathetic and parasympathetic nervous systems.  Sympathetic division (speeds up) • Prepares body for ‘fight or flight’ situations Parasympathetic division (slows down)  • Prepares body for ‘resting and digesting’ activities. 18
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  •  some target organs are innervated by both divisions (Dual innervation), Opposing effects on the same organ.  others are controlled by only one.  It has also Enteric division and has role in digestive tract. 20
  • Sympathetic nervous system 21
  •  You come across a gangster with sharp materials @Gcmhs campus at 8:00 pm on your walk to GCMHs library ………… what happens ??? 1. Heart rate 2. Breathing rate 3. Size of pupil 4. Bronchiole smooth muscle 5. Digestive system 6. Skeletal system 7. Cutaneous circulation 8. Cerebral circulation 22
  • Sympathetic nervous system  mobilization & increased metabolism “fight, flight or fright”.  Involves in activities of exercise, excitement, emergency, and embarrassment.  Non-essential activities are dampened (GI/urinary).  Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased 23
  •  Its activity is illustrated by a person who is threatened  HR increase and breathing is rapid and deep.  The skin is cold and sweaty, and the pupils dilate.  Bronchioles dilate which increasing ventilation, delivering more oxygen to cells. 24
  •  Constriction of visceral & cutaneous blood vessels (blood is shunted to skeletal muscle ).  Liver releases more glucose into blood to provide more readily avail energy  Targets adipocytes for lipolysis. 25
  •  Basic organization  Issues from T1-L2 ( thoraco lumbar division )  Preganglionic fibers form the lateral gray horn.  Supplies visceral organs and structures of superficial body regions.  Contains more ganglia than the parasympathetic division 26
  • Parasympathetic Division  Cranial outflow  Supplies the visceral structure in the head, neck and face via the oculomotor, facial and glossophryngeal nerves.   Thorax and upper abdomen via vagus nerves. Sacral outflow  Supplies pelvic organ via the pelvic branches of the second to fourth sacral spinal nerves. 27
  •  Cranial Outflow Preganglionic fibers run via:    Facial nerve (VII)  Glossopharyngeal nerve (IX)   Oculomotor nerve (III) Vagus nerve (X) Cell bodies located in cranial nerve nuclei in the brain stem. 28
  •  oculomotor nerve  ciliary ganglion  Ciliary muscle, accommodation for near vision  Pupillary constrictor of iris(sphincter), miosis (contraction of pupil). 29
  •  Facial nerve  Submandibular and sublingual glands via Submandibular ganglion     Lacrimal gland via Pterygopalatine ganglion . Glands of nasal cavity, mouth, and palate Glossopharyngeal nerve Parotid gland via otic ganglion 30
  •  Outflow via the Vagus Nerve (X)  Fibers innervate visceral organs of the thorax and most of the abdomen.  Stimulates - digestion, reduction in heart rate and blood pressure.  Preganglionic cell bodies   Located in dorsal motor nucleus in the medulla. Ganglionic neurons  Confined within the walls of organs being innervated. 31
  •  Sacral Outflow  Emerges from S2-S4  Innervates organs of the pelvis and lower abdomen  Preganglionic cell bodies   Located in visceral motor region of spinal gray matter. Form pelvic splanchnic nerves. 32
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  • SNS VS PNS  Sympathetic 1. Thoracolumbar  Parasympathetic 1. Craniosacral 2. Short preganglionic and long 2. Long preganglionic and short post ganglionic neurons. 3. Sympathetic axons – highly branched , Influences many organs 4. Location of Ganglia: Close to postganglionic fibers 3. Parasympathetic axons – few branches , Localized effect. 4. Location of ganglia: In the visceral effector organs the spinal cord 34
  • SNS VS PNS cont’d…  Neurotransmitter released by preganglionic axons   Acetylcholine for both branches (cholinergic) Neurotransmitter released by postganglionic axons  Sympathetic – most release norepinephrine (adrenergic).  Parasympathetic – release acetylcholine . 35
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  • Adrenal medulla  Major organ of the sympathetic nervous system.  Secretes great quantities epinephrine (a little norepinephrine)  Stimulated to secrete by preganglionic sympathetic fibers. 40
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  • Neurotransmitters & Receptors in ANS 1. Neurotransmitter  chemical messengers produced by the cell bodies of neuron and have role in communication between neurons and neuron, muscle coordination.  Neurotransmitters are released by the presynaptic cell. 43
  •  Bind to specific receptors in the postsynaptic cell membrane.  Binding has either an excitatory or an inhibitory effect on the effector, depending on the specific receptor.  Acethylcholine(ACh) and Norepinephrine( NE) are the major neurotransmitters in autonomic nervous system. 44
  • A. Both the preganglionic and postganglionic axons in the parasympathetic division release acetylcholine and thus are called Cholinergic. B. The preganglionic axon and a few postganglionic axons in the sympathetic division are also cholinergic(blood vessels of skeletal muscle and sweat gland). 45
  • C. Most of the postganglionic axons of the sympathetic division release Norepinephrine and are called Adrenergic. D. The postganglionic chromaffin cells at the adrenal medulla secrete Adrenaline(epinephrine). 46
  •  Acetylcholine   ALL parasympathetic postganglionic neurons   ALL preganglionic neurons Blood vessels of muscle and sweat gland. ACH is rapidly hydrolyzed by a membrane-associated Acetylcholinesterase in the synaptic cleft.  Effects are short and localized. 47
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  •  Norepinephrine (= Noradrenalin):  Most sympathetic postganglionic neurons  Exceptions: Sweat glands (Acetylcholine), Renal arteries (Dopamine).  Epinephrine (= Adrenaline): – Adrenal medulla upon sympathetic impulses 49
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  • 2. Receptors A. Cholinergic Receptors:  Receptor for Ach.  classified as nicotinic, muscarinic.  Muscarinic (M): at the target organ named after activation by Muscarine (poison of Amanita muscaria). 51
  •  Hetrotrimeric G protein-coupled  CNS, gastric mucosa: M1  Cardiac: M2   Glandular/Smooth muscle: M3 The effect of ACh binding:  Can be either inhibitory or excitatory.  Depends on the receptor type of the target organ 52
  • Nicotinic (N) receptors  All ganglionic neurons of both sympathetic and parasympathetic  At the neuromuscular junction  The hormone-producing cells of the adrenal medulla  The effect of ACh binding to nicotinic receptors is always stimulatory  named after activation by Nicotine. 53
  •  The effect of ACh binding to nicotinic receptors is always stimulatory (excitatory ).  Stimulation of muscarinic receptors produces a longer lasting effect than does stimulation of nicotinic receptors.  The effects produced by the PS division center on relaxation, food processing and energy absorption. 54
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  • B. Adrenergic receptors: respond to norepinephrine/epinephrine  Subdivided in to α and β.  α Adrenergic receptors  α receptors are located postsynaptically at sympathetic neuroeffector junctions of many organs.  In general, alpha receptors mediate excitation or increased activity of the effector cells.  Vascular smooth muscle is an important site of alpha receptors. 56
  •  They are subdivided into two types:  1  Located in the vascular smooth muscle of the skin and splanchnic regions, the gastro intestinal(GI) and bladder sphincters, and the radial muscle of the iris.  Produce excitation( e. g. contraction or constriction). 57
  •  2  Are located in presynaptic nerve terminals, platelets, fat cells and pancreatic islets.  Effects  platelet aggregation  Vasoconstriction  inhibition of norepinephrine release and of insulin secretion.  Often produce inhibition ( e. g. relaxation or dilation). 58
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  •  β adrenergic receptors  are also located postsynaptically at sympathetic neuroeffector junctions of many organs.  In general, beta receptors mediate relaxation or Decreased activity of the effector cells. Thus, Blood vessels dilate and Uterine smooth muscle relaxes in response to activation of beta receptors. 60
  •  A notable exception – NE binding to  receptors of the heart is stimulatory.  There are three known types of beta receptor, designated β1, β2 and β3.  β1-Adrenergic receptors : are located mainly in the heart.  Produce excitation ( e. g. increased HR, increased conduction velocity, increased contractility). 61
  •  β2-Adrenergic receptors: are located on the vascular smooth muscle of skeletal muscle, bronchial smooth muscle, and in the wall of GI tracts and bladder.  Produce relaxation( e.g. dilation of vascular smooth muscle, dilation of bronchioles, relaxation of the bladder wall.  β3- adrenergic Receptors are located in fat cells. 62
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  • Rhythm disturbances are a major concern with drugs that activate the beta1 receptor. 64
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  •  Alpha receptor activation leads to smooth muscle contraction  Activation of beta 1 leads to smooth muscle contraction(especially in heart).  Activation of beta 2 receptors lead to smooth muscle relaxation. 66
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  • Dual Innervation  Most of viscera receive nerve fibers from both parasympathetic and sympathetic divisions.  Both divisions do not normally innervate an organ equally.  Antagonistic effects  oppose each other 68
  •  Exerted through dual innervation of same effector    Heart rate decreases (parasympathetic) Heart rate increases (sympathetic) Exerted because each division innervates different cells  pupillary dilator muscle (sympathetic) dilates pupil  constrictor pupillae (parasympathetic) constricts pupil 69
  •  Cooperative effects seen when 2 divisions act on different effectors to produce a unified effect    parasympathetics increase salivary serous cell secretion sympathetics increase salivary mucous cell secretion ANS cooperation is best seen in control of the external genitalia 71
  •  Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris.  Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females  Some effectors receive only sympathetic  adrenal medulla, arrector pili muscles, sweat glands and many blood vessels. 72
  • Summary Effector Organ Nicotinic receptor α,β1 β2 receptors Sympathetic Preganglionic Postganglionic ACh Noradrenaline Effector Organ Nicotinic receptor Muscarinic receptors Parasympathetic Preganglionic Postganglionic ACh ACh 73
  • Summary Cont. Nicotinic receptor Adrenalin (80%) Noradrenalin (20%) ACh Adrenal gland Skeletal muscle Somatic ACh Nicotinic receptor 74
  • Receptor Location Response α1 Widespread, found in most tissues Excitation, stimulation of metabolism α2 Sympathetic neuroeffector junctions Parasympathetic neuroeffector Junctions Inhibition of effector cell Heart, kidneys, liver, adipose tissue* Stimulation, increased energy consumption Adrenergic Receptors β1 β2 Cholinergic Receptors Nicotinic Muscarinic Smooth muscle in vessels of heart and skeletal muscle; smooth muscle layers in the intestines, lungs, and bronchi Inhibition of neurotransmitter release Inhibition, relaxation All autonomic synapses between preganglionic and ganglionic neurons; neuromuscular junctions of the SNS Stimulation, excitation; muscular contraction All parasympathetic neuroeffector junctions; cholinergic sympathetic neuroeffector junctions Variable Adrenergic and Cholinergic Receptors of the ANS 75
  • Recall  Describe the main functions of ANS.  Distinguish the division of the ANS  Appreciate the difference between the sympathetic nervous and parasympathetic nervous system.  Identify the neurotransmitters and its receptors in ANS. 76