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The Autonomic Nervous System and Visceral Reflexes

The Autonomic Nervous System and Visceral Reflexes - The...

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The Autonomic Nervous System and Visceral Reflexes Autonomic Nervous System part of the nervous system that controls the motor systems of cardiac muscles smooth muscles of glands vessels thoracic cavity abdominal cavity piloerector muscles Also called the visceral motor system to distinguish it from the somatic motor system that controls skeletal muscles Autonomic Nervous System carries out its actions involuntarily, without conscious awareness end organ effectors do not depend entirely on the ANS for proper function, but only serve to adjust their activity in accordance to the bodies changing needs. ex: the heart can function if nerves are severed. Visceral Reflexes Reflex arc similar to somatic reflex arch including receptor, efferent neuron to CNS, interneuron, efferent neuron carrying motor signal away from CNS, effector Ex: baroreceptors in controlling decreased blood pressure Divisions of the Autonomic NS ANS has two divisions Sympathetic Parasympathetic Sympathetic extreme responses referred to as “fight or flight” responses involved in emotions of stress, anger, fear Ordinary responses are subtle and hardly noticed, if at all. mild increase in heart rate, breathing rate, increase blood pressure, increased blood flow to muscles Divisions of the Autonomic NS Parasympathetic responses opposite that of sympathetic responses have a calming effect on body functions seen as “resting and digestion” state associated with reduced energy expenditure and normal body maintenance digestion, and waste elimation
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Both systems acting simultaneously on the same target organ produces a state of autonomic tone shifts of predominance determined by mental and physiological states Neural Pathways Sympathetic Division also called thoracolumbar division because they arise from the thoracic and lumbar regions of the cord. has short preganglionic and long postganglionic fibers preganglionic somas are in the lateral horns and nearby regions of the gray matter fibers exit by way of spinal nerves T1-L2 fibers lead to sympathetic chain of ganglia ( paravertebral ganglia) along each side of the cord Paravertebral Ganglia Sympathetic Division preganglionic myelinated fibers travel from spinal nerve to ganglia through white communicating ramus unmyelinated postganglionic fibers leave the ganglion by way of the gray communicating ramus Sympathetic Division Once in paravertebral chain, fiber may take one of three paths May synapse in ganglion with postganglionic neuron, postganglionic neuron sends axon in gray communicating ramus (gray because unmyelinated) back to spinal nerve and out to body organ Axon may pass through sympathetic ganglion without synapsing, exit the ganglion via an autonomic nerve, and synapse in a more distant ganglion in the body cavity, such as celiac or superior mesenteric ganglion (prevertebral ganglia)
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The Autonomic Nervous System and Visceral Reflexes - The...

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