Lecture9ANS_062746

Lecture9ANS_062746 - The Autonomic Nervous System November...

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The Autonomic Nervous System November 18, 2010
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Divisions of the Nervous System Nervous system is divided into two parts: Central nervous system (CNS) Brain and spinal cord Peripheral nervous system (PNS) Somatic nervous system Consists of peripheral nerve fibers that send sensory information to the CNS and the motor nerve fibers that project to skeletal muscle Autonomic nervous system
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Autonomic Nervous System Divided into three parts: Sympathetic nervous system Parasympathetic nervous system Enteric nervous system Controls smooth muscle of the viscera (internal organs) and glands
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Autonomic Nervous System Because the neurons of the PNS conduct impulses away from the CNS, they are referred to as efferent neurons Unlike somatic motor neurons, which conduct impulses along a single axon from the spinal cord to the neuromuscular junction, autonomic motor control involves two neurons in a pathway
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General Organization of the Autonomic Nervous System The preganglionic neuron is located in either the brain or the spinal cord (grey matter) The preganglionic neuron projects to an autonomic ganglion (collection of cell bodies outside the CNS The postganglionic neuron then projects to the target organ
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Smooth muscle is a major target of the ANS Smooth muscle is located in all internal contractile organs, except the heart Under the microscope, it has the following features: Small cells Unstriated (no stripes) Contains actin and myosin (that’s how it contracts!) Less organized than skeletal muscles (doesn’t have bands—no sarcomeres)
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Smooth muscle In order to contract, the cells contain actin and myosin Even though the filaments are essentially the same in smooth muscle as they are in skeletal and cardiac muscle, the way they are arranged is different. Some regulatory proteins also differ, and there are specific smooth muscle isoforms of actin and myosin Smooth muscle does not contain the protein troponin; calmodulin takes on this regulatory role in smooth muscle Actin filaments attach to other actin filaments via dense bodies (act much like Z-lines in striated muscle)
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Smooth Muscle Contraction Ca2+ ions enter the cells from ECF and from intracellular stores Series of biochemical reactions occur Myosin cross bridges are phosphorylated and bind to actin
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Single-Unit vs. Multi-Unit Smooth Muscle Multiunit smooth muscle organs Each smooth muscle cell acts relatively independently of other smooth muscle cells in the organ In this sense multiunit smooth muscle is like skeletal muscle Found in large blood vessels, large airways of the lungs, ciliary muscle, iris of the eye, arrector pilae This type of smooth muscle tends to have fewer gap junctions between cells, making each cell operated independently Multiunit smooth muscle tends to have higher innervation (by the ANS) ratios than in visceral smooth muscle ( neurogenic )
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Single-Unit vs. Multi-Unit Smooth Muscle
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This note was uploaded on 04/12/2011 for the course BIOL 1020 taught by Professor Staff during the Spring '11 term at North Texas.

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Lecture9ANS_062746 - The Autonomic Nervous System November...

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