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Chapter 7 The Peripheral Nervous System: Efferent Division Outline • Autonomic nervous system • Somatic nervous System • Neuromuscular Junction Outline • Autonomic nervous system – Anatomy • Pre and post fibers, sympathetic ganglia chain, collateral ganglia, terminal ganglia – Neurotransmitters • Pre = Acetylcholine (ach) • Post = adrenaline (epinepherine) noradrenaline (norepinepherine) – Sympathetic and parasympathetic branches • Dual innervation • Sympathetic dominance “fight or flight” • Parasympathetic dominance “rest and digest” – Receptor types • Cholinergic, muscarinic, nicotinic • Adrenergic. a1 a2 b1 b2 – CNS control PNS: Efferent Division • Communication link by which CNS controls activities of muscles and glands • Two divisions of PNS – Autonomic nervous system (ANS) • Involuntary branch of PNS • Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue – Somatic nervous system • Subject to voluntary control • Innervates skeletal muscle ANS • Autonomic nerve pathway – Extends from CNS to an innervated organ • Ganglion = neuronal cell bodies in the PNS • Nuclei = neuronal cell bodies in the CNS – Two-neuron chain • Preganglionic fiber (synapses with cell body of second neuron) • Postganglionic fiber (innervates effector organ) Sympathetic Nervous System Parasympathetic Nervous System Fibers originate in thoracic and lumbar regions of spinal cord Fibers originate from cranial and sacral areas of CNS Most preganglionic fibers are short Preganglionic fibers are longer Long postganglionic fibers Very short postganglionic fibers Preganglionic fibers release acetylcholine (Ach) Preganglionic fibers release acetylcholine (Ach) Most postganglionic fibers release noradrenaline (norepinephrine) Postganglionic fibers release acetylcholine • • • Most visceral organs innervated by both sympathetic and parasympathetic fibers In general produce opposite effects in a particular organ Dual innervation of organs by both branches of ANS allows precise control over organ’s activity ACh ACh Autonomic effectors Terminal ganglion Nicotinic Muscarinic Cardiac receptor receptor muscle α receptor Sympathetic ganglion chain Nicotinic receptor NE Adrenal Medulla E NE Blood E Smooth muscle β1 receptor E Collateral ganglion NE Nicotinic receptor E β2 receptor ACh KEY Parasympathetic preganglionic fiber Parasympathetic postganglionic fiber Sympathetic preganglionic fiber Sympathetic postganglionic fiber ACh Acetylcholine NE Norepinephrine E Epinephrine Terminal ganglion Nicotinic receptor Most endocrine glands and some endocrine glands Adipose ACh tissue Muscarinic receptor Fig. 7-2, p. 241 ANS • Sympathetic system dominates in emergency or stressful (“fight-or-flight”) situations – Promotes responses that prepare body for strenuous physical activity • Parasympathetic system dominates in quiet, relaxed (“rest-and-digest”) situations – Promotes body-maintenance activities such as digestion Eye Lacrimal gland Nasal mucosa Parotid gland Sympathetic Salivary glands Spinal nerves Sympathetic trunk Liver Splanchino nerves Adrenal gland Parasympathetic Trachea Lung Cranial nerves Heart Stomach Gall bladder Pancreas Spleen Sympathetic preganglionic fiber Sympathetic postganglionic fiber Spinal nerves Kidney Small intestine Colon Parasympathetic preganglionic fiber Parasympathetic postganglionic fiber Rectum Urinary bladder Genitalia Fig. 7-3, p. 237 Table 7-02a p244 ANS • Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system – Most arterioles and veins receive only sympathetic nerve fibers (arteries and capillaries are not innervated) – Most sweat glands are innervated only by sympathetic nerves – Salivary glands are innervated by both ANS divisions but activity is not antagonistic – both stimulate salivary secretion ANS • Adrenal medulla is a modified part of sympathetic nervous system – Modified sympathetic ganglion that does not give rise to postganglionic fibers – Stimulation of preganglionic fiber prompts secretion of hormones into blood • About 20% of hormone release is norepinephrine • About 80% of hormone released is epinephrine (adrenaline) • Broadcast vs. localized Table 7-1 p242 ACh ACh Autonomic effectors Terminal ganglion Nicotinic Muscarinic Cardiac receptor receptor muscle α receptor Sympathetic ganglion chain Nicotinic receptor NE Adrenal Medulla E NE Blood E Smooth muscle β1 receptor E Collateral ganglion NE Nicotinic receptor E β2 receptor ACh KEY Parasympathetic preganglionic fiber Parasympathetic postganglionic fiber Sympathetic preganglionic fiber Sympathetic postganglionic fiber ACh Acetylcholine NE Norepinephrine E Epinephrine Terminal ganglion Nicotinic receptor Most endocrine glands and some endocrine glands Adipose ACh tissue Muscarinic receptor Fig. 7-2, p. 241 Autonomic Neurotransmitter Receptors • Tissues innervated by autonomic nervous system have one or more of several different receptor types for postganglionic chemical messengers – Alter tissue/cell response instead of chemical message – Alter the distribution (localized – varicosity, broadcast – adrenal medulla) – Cholinergic receptors – bind to ACh • Nicotinic receptors – found on postganglionic cell bodies of all autonomic ganglia – nicotine • Muscarinic receptors – found on effector cell membranes – Mushroom poison – Adrenergic receptors – bind to norepinephrine and epinephrine • Alpha (α) receptors • Beta (β) receptors Autonomic Neurotransmitter Receptors – Cholinergic receptors – bind to ACh • Nicotinic receptors – found on postganglionic cell bodies of all autonomic ganglia – Nicotine – Respond to Ach, opens Na and K channels, triggers AP • Muscarinic receptors – found on effector cell membranes – – – – Mushroom poison Smooth muscle, cardiac muscle, glands 5 subtypes G protein linked Autonomic Neurotransmitter Receptors – Adrenergic receptors – bind to norepinephrine and epinephrine • G protein coupled • Alpha (α) receptors - Ca second messenger system - a 1= stimulates cyclic amp, sympathetic tissues, vessel constriction, contraction of smooth muscle, constrictor - a 2 blocks cyclic amp, decreases smooth muscle contraction in the digestive tract, inhibitory to the effector organ • Beta (β) receptors - cyclic amp - b1 Found in the heart, increases contractility and rate - b2 Found in the arterioles and airways, dilator Table 7-3 p246 Autonomic Agonists and Antagonists • Agonists – Bind to same receptor as neurotransmitter – Elicit an effect that mimics that of neurotransmitter • Antagonists – Bind with receptor – Block neurotransmitter’s response Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems • Somatic nervous system – Anatomy • Motor neurons • Continuous to effector • Voluntary • Final common pathway • ALS = Amyotropic lateral sclerosis, death of motor neurons Outline • Neuromuscular junction – Anatomy • Muscle fiber, terminal button • “motor end plate” – Ach release • Presynaptic vesicular • Postsynaptic intracellular – Ach activation of end plate potentials • Activation of nicotinic receptors • Inflow of sodium and potassium • Ap propagated along the muscle fiber – Ach breakdown • AChe Somatic Nervous System • Consists of axons of motor neurons of motor neurons that originate in spinal cord or brain stem and end on skeletal muscle • Motor neuron releases neurotransmitter, Ach, which stimulates muscle contraction • Motor neurons are final common pathway by which various regions of CNS exert control over skeletal muscle activity – These areas of CNS include spinal cord, motor regions of cortex, basal nuclei, cerebellum, and brain stem Outline • Neuromuscular junction – Anatomy • Muscle fiber, terminal button • “motor end plate” – Ach release • Presynaptic vesicular • Postsynaptic intracellular – Ach activation of end plate potentials • Activation of nicotinic receptors • Inflow of sodium and potassium • Ap propagated along the muscle fiber – Ach breakdown • AChe Axons of two efferent motor neuron Spinal cord (section) Axon terminals Muscle fibers innervated by red motor neuron Muscle fibers innervated by red motor neuron Axon terminals Terminal buttons Muscle Neuromuscular junction Muscle fibers Muscle Terminal Neuromuscular fibers button junction Fig. 7-4, p. 251 Axon terminal of motor neuron Myelin sheath Action potential propagation in motor neuron 1 Terminal button Voltage-gated Vesicle of Na+ channel acetylcholine Voltage-gated Ca2+ channel Plasma membrane of muscle fiber 8 Action potential propagation in muscle fiber 8 Ca2+ Na+ 2 6 7 Acetylcholinesterase Acetylcholine-gated receptor-channel (for nonspecific cation traffic) 7 6 3 4 5 K+ Na+ 9 Na+ Motor end plate Contractile elements within muscle fiber Fig. 7-5, p. 252 Comparison of Somatic and Autonomic Nervous System Neuromuscular Junction • Acetylcholinesterase – Inactivates ACh – Ends end-plate potential and the action potential and resultant contraction • Neuromuscular junction is vulnerable to chemical agents and diseases – Black widow spider venom causes explosive release of ACh – Botulism toxin blocks release of ACh – Curare blocks action of ACh at receptor sites – Organophosphates prevent inactivation of ACh – Myasthenia gravis inactivates ACh receptor sites Neuromuscular conditions and compounds • ALS – Lou Gehrig’s Disease • death of motor neurons – Black widow venom • Explosive release of Ach • Paralysis of the diaphram – Botulinum toxin • Inhibits Ach release – Curare • Ach receptor blocker (chloinergic) – Organophosphates • Ache inhibition – Mysanthia Gravis • Autoimmune, body attacks Ach receptors