0-1 Chapter 15 - Autonomic Nervous System Flashcards Preview

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1

Autonomic Nervous System

•portion of the nervous system that operates in comparative secrecy
•it manages a multitude of unconscious processes responsible for the body’s homeostasis

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autonomic nervous system (ANS)

a motor nervous system that controls glands, cardiac muscle, and smooth muscle
carries out actions involuntarily–without our conscious intent or awareness

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visceral motor system

autonomic nervous system (ANS)

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primary organs of the ANS

•viscera of thoracic and abdominal cavities
•some structures of the body wall
–cutaneous blood vessels
–sweat glands
–piloerector muscles

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denervation hypersensitivity

exaggerated response of cardiac and smooth muscle if autonomic nerves are severed

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visceral reflexes

unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors and somewhat slower responses

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visceral reflex arc

–receptors–nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli
–afferent neurons –leading to the CNS
–interneurons–in the CNS
–efferent neurons –carry motor signals away from the CNS
–effectors–that make adjustments

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Visceral Reflex to High BP

high blood pressure detected by arterial stretch receptors (1), afferent neuron (2) carries signal to CNS, efferent (3) signals travel to the heart (4), heart slows reducing blood pressure

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Divisions of ANS

•two divisions innervate same target organs
–may have cooperative or contrasting effects
sympathetic division
parasympathetic division

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sympathetic division

prepares body for physical activity –exercise, trauma, arousal, competition, anger, or fear
•increases heart rate, BP, airflow, blood glucose levels, etc
•reduces blood flow to the skin and digestive tract

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parasympathetic division

calms many body functions reducing energy expenditure and assists in bodily maintenance
•digestion and waste elimination
•“resting and digesting” state

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autonomic tone

normal background rate of activity that represents the balance of the two systems according to the body’s changing needs

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parasympathetic tone

•maintains smooth muscle tone in intestines
•holds resting heart rate down to about 70 –80 beats per minute

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sympathetic tone

keeps most blood vessels partially constricted and maintains blood pressure

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balance between sympathetic and parasympathetic

sympathetic division excites the heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect

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Neural Pathways

ANS has components in both the central and peripheral nervous systems
–control nucleus in thehypothalamus and other brainstem regions
–motor neurons in the spinal cord and peripheral ganglia
–nerve fibers that travel through the cranial and spinal nerves

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somatic motor pathway

–a motor neuron from the brainstem or spinal cord issues a myelinated axon that reaches all the way to the skeletal muscle

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autonomic pathway

–signal must travel across two neurons to get to the target organ
–must cross a synapse where these two neurons meet in an autonomic ganglion

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presynaptic neuron

the first neuron has a soma in the brainstem or spinal cord

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postganglionic neuron

synapses with a postganglionic neuron whose axon extends the rest of the way to the target cell

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ANS –two neurons from CNS to effectors

•presynaptic neuron whose cell body is in CNS
•postsynaptic neuron cell body in peripheral ganglion

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Sympathetic Nervous System

also called the thoracolumbar division because it arises from the thoracic and lumbar regions of the spinal cord
relatively short preganglionic and long postganglionic fibers

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preganglionic neurosomas

in lateral horns and nearby regions of the gray matter of spinal cord
–fibers exit spinal cord by way of spinal nerves T1 to L2
–lead to nearby sympathetic chain of ganglia (paravertebral ganglia)

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sympathetic chain of ganglia

•series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels
•usually 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal ganglion
•sympathetic nerve fibers are distributed to every level of the body

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preganglionic fibers are

small myelinated fibers that travel form spinal nerve to the ganglion by way of the white communicating ramus (myelinated)

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postganglionic fibers leave the ganglion by way

of the gray communicating ramus (unmyelinated)
•forms a bridge back to the spinal nerve

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postganglionic fibers extend

postganglionic fibers extend the rest of the way to the target organ

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after entering the sympathetic chain, the preganglionic fibers may follow any of three courses

some end in ganglia
some travel up or down the chain
some pass through the chain without synapsing

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nerve fibers leave the sympathetic chain by

spinal, sympathetic, and splanchnic nerves

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spinal nerve route

•some postganglionic fibers exit a ganglion by way of the gray ramus
•returns to the spinal nerve and travels the rest of the way to the target organ
•most sweat glands, piloerector muscles, and blood vessels of the skin and skeletal muscles