Lecture 7

Lecture 7 - The Nervous Systems: The Peripheral Nervous...

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Unformatted text preview: The Nervous Systems: The Peripheral Nervous System Efferent Division Chapter 7 NPB 101. Autumn 2008 Brain Central nervous system (CNS) Spinal cord Peripheral nervous system (PNS) Afferent division Efferent division Sensory stimuli Visceral stimuli Somatic nervous system Autonomic nervous system Motor neurons Sympathetic nervous system Parasympathetic nervous system Skeletal muscle Smooth muscle Cardiac muscle Glands Effector organs (made up of muscle and gland tissue) (Input to CNS from periphery) (Output from CNS to periphery) Fig. 5-1, p. 132 Major sub-divisions of the nervous system Peripheral Nervous System: Efferent Division The central nervous system (CNS) regulates effector organs such as muscles and glands through the efferent division of the PNS. The autonomic nervous system is one peripheral branch of of the PNS that provides involuntary control of smooth muscle, cardiac muscle, some endocrine glands, most exocrine glands and adipose (fat) tissue. The somatic nervous system is a second branch of the PNS that provides voluntary control of skeletal muscle. We have encountered many neurotransmitter types while discussing the CNS and the afferent branch of the PNS but the efferent branch has only two neurotransmitters- acetyl choline and norepinephrine. The Somatic Nervous System Most efferents of the somatic nervous system (motor neurons) originate (have cell bodies) in the ventral horn of the spinal cord. A few cell bodies of motor neurons that innervate muscles in the head originate in the brain stem. Motor neurons have axons that project directly to skeletal muscles where they release the neurotransmitter acetyl choline (Ach) resulting in excitation and contraction of muscle cells. Motor neurons can only excite skeletal muscle cells. Inhibition of muscle contraction is achieved through inhibitory synaptic input to motor neuron cell bodies from the CNS. Input to motor neurons comes through spinal reflexes or via descending pathways from the brain to spinal cord. One motor neuron branches and innervates several muscle fibers (motor unit). Several motor neurons may innervate a muscle but each fiber only receives input from one motor neuron. Neuromuscular Junction This is where the branches of the motor neuron form a junction with the muscle fibers. The axon at this point loses its myelin sheath. The axon terminal forms a terminal button (bouton) that fits into a depression in the muscle fiber. These junctions have been called synapses and motor end plates, but here is referred to as a neuromuscular junction. The motor end plate is the portion of the muscle fiber membrane that lies under the axonal bouton. The neurotransmitter at a neuromuscular junction is acetyl choline. Picture of motor end plate here....
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This note was uploaded on 01/06/2010 for the course NPB idk taught by Professor Wingfield during the Spring '09 term at UC Davis.

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Lecture 7 - The Nervous Systems: The Peripheral Nervous...

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