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Topic 25 (Autonomic Nervous System)

Topic 25 (Autonomic Nervous System) - BIOL 255 Topic 25...

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10/8/12 1 BIOL 255 Topic 25: Autonomic Nervous System Topic 25 Outline Comparison of the Somatic and Autonomic Nervous Systems Overview of the Autonomic Nervous System Parasympathetic Division Sympathetic Division CNS Control of Autonomic Function Autonomic Nervous System • The autonomic nervous system (ANS) is a complex system of nerves that govern involuntary actions. The ANS works constantly with the somatic nervous system (SNS) to regulate body organs and maintain normal internal functions. Autonomic Nervous System The ANS and SNS are part of both the central nervous system and the peripheral nervous system. The SNS operates under our conscious control. The ANS functions are involuntary and we are usually unaware of them. Comparison of Somatic and Autonomic Nervous Systems Both the SNS and the ANS use sensory and motor neurons. In the SNS, somatic motor neurons innervate skeletal muscle fibers, causing conscious voluntary movement. ANS motor neurons innervate smooth muscle fibers, cardiac muscle fibers, or glands. ANS motor neurons can either excite or inhibit cells in the viscera. Comparison of Somatic and Autonomic Nervous Systems
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10/8/12 2 Comparison of Somatic and Autonomic Nervous Systems SNS—single lower motor neuron axon extends uninterrupted from the spinal cord to one or more muscle fibers ANS—two-neuron chain innervates muscles and glands Two-Neuron Chain in ANS The first neuron in the ANS pathway is the preganglionic neuron. Its cell body is in the brain or spinal cord. • A preganglionic axon extends to the second cell body housed within an autonomic ganglion in the peripheral nervous system. The second neuron in the pathway is called a ganglionic neuron. • A postganglionic axon extends from its cell body to effector (target) cells. Components of the Autonomic Nervous System Two-Neuron Chain in ANS Neuronal convergence— axons from numerous preganglionic cells synapse on a single ganglionic cell Neuronal divergence— axons from one preganglionic cell synapse on numerous ganglionic cells Divisions of Autonomic Nervous System Parasympathetic division— conservation of energy and replenishment of nutrient stores ( rest-and-digest ) Sympathetic division— preparation of body for emergencies ( fight-or-flight ); increased activity of this division results in increased alertness and metabolic activity Comparison of Parasympathetic and Sympathetic Divisions
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10/8/12 3 Anatomic Differences Between Parasympathetic and Sympathetic Neurons Parasympathetic Division • Termed craniosacral division because preganglionic neurons are housed within nuclei in the brainstem and within lateral gray regions of the S2–S4 spinal cord segments Ganglionic neurons are found in either terminal ganglia close to the target organ, or intramural ganglia in the wall of the target organ Four Cranial Nerves of Parasympathetic Division 1. Oculomotor (CN III) 2. Facial (CN VII) 3.
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