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NPB.101.Lectures7 - NPB 101. Autumn 2009 The Nervous...

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The Nervous Systems:The Peripheral Nervous SystemEfferent DivisionThe Biological ClockChapter 7, Chapter 18, pp 685-687NPB 101. Autumn 2009
BrainCentralnervoussystem(CNS)SpinalcordPeripheralnervoussystem(PNS)AfferentdivisionEfferentdivisionSensorystimuliVisceralstimuliSomaticnervous systemAutonomicnervous systemMotorneuronsSympatheticnervous systemParasympatheticnervous systemSkeletalmuscleSmooth muscleCardiac muscleGlandsEffector organs(made up of muscleand gland tissue)(Input to CNSfrom periphery)(Output from CNSto periphery)Fig. 5-1, p. 132Major sub-divisions ofthe nervous system
Peripheral Nervous System:Efferent DivisionThe central nervous system (CNS) regulates effector organssuch as muscles and glands through the efferentdivision of the PNS.The autonomic nervous system is one peripheral branch ofof the PNS that provides involuntary control of smoothmuscle, cardiac muscle, some endocrine glands,most exocrine glands and adipose (fat) tissue.The somatic nervous system is a second branch of the PNSthat provides voluntary control of skeletal muscle.We have encountered many neurotransmitter types whilediscussing the CNS and the afferent branch of the PNSbut the efferent branch has only two neurotransmitters- acetyl choline and norepinephrine.
The Somatic Nervous SystemMost efferents of the somatic nervous system (motorneurons) originate (have cell bodies) in the ventralhorn of the spinal cord. A few cell bodies of motorneurons that innervate muscles in the head originatein the brain stem.Motor neurons have axons that project directly to skeletalmuscles where they release the neurotransmitteracetyl choline (Ach) resulting in excitation andcontraction of muscle cells.Motor neurons can only excite skeletal muscle cells.Inhibition of muscle contraction is achieved throughinhibitory synaptic input to motor neuron cell bodiesfrom the CNS.Input to motor neurons comes through spinal reflexes or viadescending pathways from the brain to spinal cord.
One motor neuron branches and innervates several musclefibers (motor unit). Several motor neurons mayinnervate a muscle but each fiber only receives inputfrom one motor neuron.
Neuromuscular JunctionThis is where the branches of the motor neuron form ajunction with the muscle fibers. The axon at thispoint loses its myelin sheath.The axon terminal forms a terminal button (bouton) that fitsinto a depression in the muscle fiber.These junctions have been called synapses and motorend plates, but here is referred to as a neuromuscularjunction. The motor end plate is the portion of themuscle fiber membrane that lies under the axonalbouton.The neurotransmitter at a neuromuscular junction is acetylcholine.
Picture of motor end plate here.Motor neuronsNeuromuscular junctionsTerminal bouton
Axon of motor neuronMyelin sheathAxon terminalTerminal buttonVesicle of acetylcholineAcetylcholinereceptor site

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Term
Spring
Professor
Fuller,Charles/Goldberg,Jack
Tags
motor neurons, motor end plate, Sympathetic input Parasympathetic

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