Autonomic Nervous System, Lect 5

8/14/2019 Autonomic Nervous System, Lect 5

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15:23 [email protected]


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DefinitionDefinitionThe portion of The portion of

nervous system nervous system

controls most visccontrols most viscfunctions of the bodfunctions of the bod

called thecalled the autonoautono

nervous s stem ANS .nervous s stem ANS .15:23 [email protected]


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DefinitionDefinition

Or it is the motor nervoOr it is the motor nervo

system that controlssystem that controls

glands, cardiac muscleglands, cardiac muscleand smooth muscle.and smooth muscle.



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DefinitionDefinition

It is also called the viscIt is also called the visce

motor system tomotor system to

distinguish it from thedistinguish it from thesomatic motor system somatic motor system

controls the skeletalcontrols the skeletal

muscles.muscles.15:23 [email protected]


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The primary target orgThe primary target org

of the ANSof the ANS

The viscera of the thoraThe viscera of the thoracand abdominal cavities aand abdominal cavities asome structures of the bsome structures of the b

wall, including cutaneouwall, including cutaneoublood vessels, sweat glablood vessels, sweat glaand piloerector muscles.and piloerector muscles.



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ControlControl

Autonomic literallAutonomic literallmeans self-means self-

governed..governed..TheThe ANS usually carries out itANS usually carries out itactions involuntarily, withoutactions involuntarily, withoutconscious intent or awarenesconscious intent or awarenes

contrast to the voluntary natcontrast to the voluntary nat15:23 [email protected]


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ControlControlThis voluntary involuntary distincThis voluntary involuntary distinc

not, however, as clear-cut as it onot, however, as clear-cut as it o

seemed. Some skeletal muscleseemed. Some skeletal muscle

responses are quite involuntary,responses are quite involuntary,as the somatic reflexes, and somas the somatic reflexes, and som

skeletal muscles are difficult orskeletal muscles are difficult or

impossible to control, such as thimpossible to control, such as th

middle-ear muscles.middle-ear muscles.15:23 [email protected]


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ControlControlOn the other hand,On the other hand,

therapeutic uses oftherapeutic uses of

biofeedback show that sobiofeedback show that so

people can learn topeople can learn to

voluntarily control suchvoluntarily control such

visceral functions as bloovisceral functions as bloo15:23 [email protected]


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Visceral effectorVisceral effector

Visceral effectors do noVisceral effectors do no

depend on the ANS todepend on the ANS to

function, but only tofunction, but only toadjust their activity to adjust their activity to

bodys changing needsbodys changing needs15:23 [email protected]


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The heart, for example, gThe heart, for example, gon beating even if allon beating even if allautonomic nerves to it aautonomic nerves to it a

severed, but the ANSsevered, but the ANSmodulates (adjusts) themodulates (adjusts) theheart rate in conditions oheart rate in conditions o

rest or exercise.rest or exercise.15:23 [email protected]


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If the somatic nerves toIf the somatic nerves to

skeletal muscle areskeletal muscle are

severed, the musclesevered, the muscleexhibits flaccid paralysexhibits flaccid paralys

it no longer functions.it no longer functions.15:23 [email protected]


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But if the autonomic neBut if the autonomic ne

to cardiac or smoothto cardiac or smooth

muscle are severed, thmuscle are severed, thmuscle exhibitsmuscle exhibits

exaggerated responseexaggerated responses

denervationdenervation15:23 [email protected]


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striking characteristics

the ANSThe rapidity and intensity.For instance,Within 3 to 5 seconds it can increase the heart

twice normal.Within 10 to 15 seconds the arterial pressure c

doubled.The arterial pressure can be decreased low en

within 10 to 15 seconds to cause fainting. Sweating can begin within seconds, and the ur

bladder may empty involuntarily, also within s15:23 [email protected]


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General OrganizationGeneral Organization

the ANSthe ANSThe autonomic nervous system is ACTIVACTIVmainly by centers located in the spinaspinabrain stem, and hypothalamus.brain stem, and hypothalamus.

Also, portions of the cerebral cortex, esp

of the limbic cortexlimbic cortex, can transmit signthe lower centers and in this way influeautonomic control.



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the ANSthe ANSThe autonomic nervous system also oftoperates by means ofVISCERAL REFLVISCERAL REFLThat is, subconscious sensory signa

from a visceral organ can enter the

autonomic ganglia, the brain stem,the hypothalamus and then returnsubconscious reflex responses direback to the visceral organ to contr

activities.15:23 [email protected]


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the ANSthe ANSThe EFFERENTEFFERENT autonomic signals aretransmitted to the various organs of thethrough two major subdivisions called

The sympathetic nervoussympathetic nervoussystem.system.

Theparasympathetic nerparasympathetic ner

systemsystem15:23 [email protected]


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Physiologic Anatomy of thePhysiologic Anatomy of the

Sympathetic NSSympathetic NS



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Each sympathetic pathwaysympathetic pathway frocord to the stimulated tissue iscomposed oftwo neuronstwo neurons, a

preganglionic neuron and apreganglionic neuron and apostganglionic neuronpostganglionic neuron, in conto only a single neuron in the sk

motor pathway15:23 [email protected]


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Physiologic Anatomy of thPhysiologic Anatomy of th

Parasympathetic Nervous SyParasympathetic Nervous Sy

Parasympathetic fibers leave the Cthrough cranial nerves III, VII, IX, andIII, VII, IX, and

Additional parasympathetic fibers lethe lowermost part of the spinal cord th

the second and third sacral spinalsecond and third sacral spinal nand occasionally the first and fourth sanerves.



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Physiologic Anatomy of thPhysiologic Anatomy of th

Parasympathetic Nervous SyParasympathetic Nervous Sy

About 75 per cent of allparasympathetic nerve fibers arthe vagus nervesvagus nerves (cranial nervpassing to the entire thoracic anabdominal regions of the body.

Therefore, a physiologist speakinthe parasympathetic nervous sy

often thinks mainly of the two v15:23 [email protected]

i i


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Neurotransmitters in tNeurotransmitters in t

ANSANSSympathetic NS

Preganglionic neuron neurotransmitter: Ach

Postganglionic neuron neurotransmitter:

Norepinephrine, Epinephrine

Parasympathetic NS

Preganglionic neuron neurotransmitter: Ach

Postganglionic neuron neurotransmitter: Ach



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SympathSympath

Nervous SNervous S



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ParasympaParasympa

Nervous SNervous S



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Comparison of Somatic andComparison of Somatic and



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Comparison ofComparison of

Sympathetic and ParasympathetSympathetic and Parasympathet



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Effects of Sympathetic anEffects of Sympathetic an

Parasympathetic NSParasympathetic NS


ff f h i


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Eff f S h i


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ff f S h iEff t f S th ti


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Autonomic Nervous System, Lect 5

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