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Chapter 7 The Peripheral Nervous System: Efferent Division

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

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Chapter 7 The Peripheral Nervous System: Efferent Division

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  1. Chapter 7 The Peripheral Nervous System: Efferent Division

  2. Outline • Autonomic nervous system • Somatic nervous System • Neuromuscular Junction

  3. 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. a1a2 b1b2 • CNS control

  4. 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

  5. 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)

  6. 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

  7. ACh ACh Autonomic effectors Terminal ganglion Nicotinic receptor Muscarinic receptor Cardiac muscle α receptor Sympathetic ganglion chain NE Adrenal Medulla E NE Blood E Smooth muscle Nicotinic receptor β1 receptor E Most endocrine glands and some endocrine glands NE Collateral ganglion Nicotinic receptor E β2 receptor Adipose tissue ACh ACh Terminal ganglion Nicotinic receptor Muscarinic receptor KEY Parasympathetic preganglionic fiber Parasympathetic postganglionic fiber Sympathetic preganglionic fiber Sympathetic postganglionic fiber Acetylcholine ACh NE E Norepinephrine Epinephrine Fig. 7-2, p. 241

  8. 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

  9. Eye Lacrimal gland Nasal mucosa Parotid gland Sympathetic Parasympathetic Salivary glands Trachea Lung Cranial nerves Sympathetic trunk Heart Spinal nerves Liver Stomach Splanchino nerves Spleen Gall bladder Sympathetic preganglionic fiber Adrenal gland Pancreas Sympathetic postganglionic fiber Spinal nerves Parasympathetic preganglionic fiber Kidney Parasympathetic postganglionic fiber Colon Small intestine Rectum Urinary bladder Genitalia Fig. 7-3, p. 237

  10. Table 7-02a p244

  11. 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

  12. 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

  13. Table 7-1 p242

  14. ACh ACh Autonomic effectors Terminal ganglion Nicotinic receptor Muscarinic receptor Cardiac muscle α receptor Sympathetic ganglion chain NE Adrenal Medulla E NE Blood E Smooth muscle Nicotinic receptor β1 receptor E Most endocrine glands and some endocrine glands NE Collateral ganglion Nicotinic receptor E β2 receptor Adipose tissue ACh ACh Terminal ganglion Nicotinic receptor Muscarinic receptor KEY Parasympathetic preganglionic fiber Parasympathetic postganglionic fiber Sympathetic preganglionic fiber Sympathetic postganglionic fiber Acetylcholine ACh NE E Norepinephrine Epinephrine Fig. 7-2, p. 241

  15. 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

  16. 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

  17. Autonomic Neurotransmitter Receptors • Adrenergic receptors – bind to norepinephrine and epinephrine • G protein coupled • Alpha (α) receptors - Ca second messenger system - a1= stimulates cyclic amp, sympathetic tissues, vessel constriction, contraction of smooth muscle, constrictor - a2 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

  18. Table 7-3 p246

  19. 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

  20. Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems

  21. 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 • Anatomy • Motor neurons • Continuous to effector • Voluntary • Final common pathway • ALS = Amyotropic lateral sclerosis, death of motor neurons

  22. 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

  23. 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

  24. Axons of two efferent motor neuron Muscle fibers innervated by red motor neuron Muscle fibers innervated by red motor neuron Spinal cord (section) Axon terminals Axon terminals Terminal buttons Neuro- muscular junction Muscle Muscle fibers Muscle fibers Terminal button Neuromuscular junction Fig. 7-4, p. 251

  25. Axon terminal of motor neuron Action potential propagation in motor neuron Myelin sheath 1 Terminal button Voltage-gated Na+ channel Vesicle of acetylcholine Voltage-gated Ca2+ channel Action potential propagation in muscle fiber Plasma membrane of muscle fiber Ca2+ Na+ 2 8 8 6 7 Na+ 7 6 3 K+ Acetylcholinesterase 9 4 5 Acetylcholine-gated receptor-channel (for nonspecific cation traffic) Na+ Motor end plate Contractile elements within muscle fiber Fig. 7-5, p. 252

  26. Comparison of Somatic and Autonomic Nervous System

  27. 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

  28. 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

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