The Peripheral Nervous System: Efferent Division Chapter 7.
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Transcript of The Peripheral Nervous System: Efferent Division Chapter 7.
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The Peripheral Nervous System:Efferent Division
Chapter 7
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Objectives
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PNS: Efferent Division
• System by which CNS communicates and controls muscles and glands
• Autonomic and somatic systems
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Overview of Nervous System
octc.kctcs.edu
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Autonomic Nervous System
• System of motor neurons that innervates smooth and cardiac muscle and glands
• Involuntary nervous system
• General visceral motor system
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Characteristics• Effectors
– Cardiac and smooth muscle– Glands
• Efferent Pathway– Involves two neurons
• Ganglia– Preganglionic neuron > preganglionic axon > ganglionic neuron
> postganglionic axon > effector
• Neurotransmitter– Norepinephrine, acetylcholine– Excitatory, inhibitory– All preganglionic neurons release acetylcholine
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Divisions of ANS• Sympathetic
– Fight or flight– Norepinephrine– Cholinergic fibers
• Parasympathetic– Rest and digest– Acetylcholine– Adrenergic fibers
• Dual innervation– Counterbalance– Tonic activity
• Ongoing activity of both divisions
becomehealthynow.com
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Parasympathetic Division
• Anatomically simpler
• Craniosacral origin– Cranial nerves III, VII, IX, X
• Oculomotor• Facial• Glossopharyngeal• vagus
– Splanchnic nerves S2 - S4
anatomy.med.umich.edu
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Sympathetic Division
• Anatomically more complex– Innervates more organs
• Thoracolumbar origins– T1 – L2
• Sympathetic chain (A)– Paravertebral ganglia
wps.aw.com
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Paravertebral Ganglia
• Synapse within same chain ganglion
• Ascend or descend then synapse in chain ganglion
• Pass through chain ganglion without synapsing– Collateral ganglia
anatomy.med.umich.edu
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Receptor Types
• Initiate tissue specific response
• Cholinergic receptors– Acetylcholine receptors
• Nicotinic– Opens nonspecific ion channels in postganglionic cell– Action potential results– Excitatory
• Muscarinic– Activate secondary messengers via G proteins– Cardiac and smooth muscles, exocrine and few endocrine glands– Excitatory of inhibitory
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Receptor Types• Adrenergic receptors– Norepinephrine and epinephrine receptors
• Alpha1 – Most sympathetic tissues– Activates IP3/Ca2+ secondary messenger pathway– Excitatory
• Alpha2 – Digestive organs– Inhibitory (inhibits cAMP)
• Beta1– Heart– Activates cAMP– Excitatory
• Beta2 – Smooth muscle of small vessels– Activates cAMP– inhibitory
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Somatic Nervous System
• Motor neurons supply skeletal muscle
• Single neuron with cell bodies in ventral horn of spinal cord
• Release acetylcholine– Only excitatory
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Neuromuscular Junction• Junction of motor axon with a muscle cell– Only one junction per muscle cell
• Motor end plate– Specialized area on muscle cell for synapse– High concentration of cholinergic receptors– Open nonspecific ion channels
• Na+ rushes in producing an end-plate potential
• Action potential on muscle cell– EPP opens ion channels in adjacent membrane– Threshold is reached and an action potential propagates
away from the motor end plate
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Acetylcholinesterase
• Enzyme that inactivate Ach– Ensures that muscles only contract when needed
• Please look at chemicals and disease associated with the neuromuscular junction