Human Physiology: Chapter 9 (Autonomic Nervous System)

Dual Innervation

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Parasympathic division

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Sympathetic Division

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Autonomic nervous system

- innervates organs whose functions organs whose functions are not under voluntary control - Effects include cardiac and smooth muscles, glands (usually a part of visceral organs and blood vessels)

Adrenal medulla

- located in adrenal gland, like a modified collateral ganglion (innervated by preg) - secretory cells = modified postg - produces (85% Epi, 15% Norepi)

Smooth muscles

- somewhat independent of innervation - maintain resting tone(tension) in absence of nerve stimulation - denervation hypersensitivity

Divisions of the ANS?

1. sympathetic 2. parasympathetic

Preganglionic neuron

1st neuron has its cell body in gray matter of brain/spinal cord

What is the NT for preganglionic fibers of sympathetic and parasympathetic nervous system?

ACh Chollinergic transmission

denervation hypersensitivity

ANS input/nerve is cut and the target tissue is more sensitive to stimulants

Similarity between sympathetic and parasympathetic?

Both consist of preganglionic neurons that originate in the CNS and postganglionic neurons that originate outside of CNS in ganglia

How are most visceral organs innervates?

Dual innervation, innervated by both parasympathetic and sympathetic fibers Thus, effects can be antagonistic, complementary, cooperative

Where do cranial nerves III, VII, IX synapse?

Ganglia in the head

What regulates medulla?

Hypothalamus

Where do preganglionic fibers synapse for parasympathetic?

In terminal ganglia/parasympathetic ganglia located next to or within organs innervated

How are organs without dual innervation regulated?

Increasing or decreasing tone or firing of sympathetic sympathetic fibers

Describe autonomic neurons

Involves two neurons in efferent pathway - Preganglionic neuron - Postganglionic neuron 1st neuron synapses with a 2nd neuron within autonomic ganglion can release excitatory or inhibitory NT unlike somatic (excitatory)

How are smooth muscles somewhat autonomous?

Many types of smooth/cardiac muscles are spontaneously active & contract rhythmically without ANS input - ANS input simply increases or decreases intrinsic activity - contract in response to depolarization initiated by muscles in absence of nerve stimulation

Do parasympathetic fibers travel within spinal nerves?

No, thus they do not innervate blood vessels, sweat glands, skeletal muscles

Describe the preganglionic fibers of the vagus nerve

Nuclei from medulla contribute preG that are very long - some fibers branch off from main trunk to innervate organs

Parasympathetic division = craniosacral division

Preganglionic neurons originate in the brain and in the sacral level of the spinal cord midbrain, medulla, pons, S1-S2

Sympathetic division = thoracolumbar division

Preganglionic neurons originate in the thoracic and lumbar levels of the spinal cord T1-L2

Effects of Fight or Flight response?

Release norepinephrine (stress) from postganglionic fibers and epinephrine (adrenaline) from adrenal medulla Mass activation prepares for intense activity (heart rate increases, bronchioles dilate, blood glucose increases)

Effects of parasympathetic nervous system?

Rest & digest - No mass activation, instead separate stimulation of parasympathetic nerves that can slow heart beat, increase digestion activity, dilate blood vessels - Releases ACh from postG at synapse with effector

Synapses en passant (synapse in passing)

The axons of postganglionic ANS have numerous swellings or varicosities that allow the axons to release NT along its length as opposed to just the axon terminal

Which cranial nerve has the most parasympathetic fibers?

Vagus X - innervates heart,lungs,esophagus,stomach,pancreas,liver,small intestine, upper half of large intestine

Sympathoadrenal system

adrenal medulla + mass activation of SNS

Organs without dual innervation?

adrenal medulla, arrector pili muscles in the skin, sweat glands, blood vessels

How does the ANS regulate our physiology?

by regulating organs, organ systems, & smooth muscles & glands, cardiac muscle

ANS control by medulla?

control most activity of ANS location center for control of cardiovascular, pulmonary, urinary, reproductive, digestive systems

Mass activation of all postganglionic neurons (increase SNS activity in response to fight/flight)

divergence + convergence

catecholamines

dopamine, epi, norepi DERIVED FROM AMINO ACID TYROSINE

Sympathetic ganglia/Paravertebral ganglia

double row of sympathetic ganglia located on either side of spinal cord join and form a chain of ganglia that parallel on each side of spinal cord

Difference between Epi and Norepi?

epi has CH3 or additional methyl group

Which postganglionic sympathetic fibers aren't Adergonic?

fibers that innervate blood vessels in the skeletal muscles and sweat glands are cholinergic

Sympathetic nervous system

fight or flight & stress reactions

Postganglionic neuron

has an axon that extends from autonomic ganglion to effector organ, where it synapses with target tissue

Where are autonomic ganglia located?

head,neck,abdomen

Where do cranial nerves X synapse?

in terminal ganglia in wide spread regions of the body - preg fibers innervate heart, lungs, gastrointestinal tract

What do preganglionic parasympathetic fibers from the sacral level innervate?

lower half of large intestine, the rectum, urinary and reproductive tracts

Where do preganglionic autonomic fibers originate?

midbrain, hindbrain, and upper thoracic to 4th sacral levels of the spinal cord

Preganglionic/Postganglionic neuron

myelinated/unmyelinated

Which cranial nerves contain parasymapthetic preganglionic fibers?

oculomotor III, facial VII, glossopharyngeal IX, vagus X

Collateral ganglion

outlying postganglionic do not synapse in paravertebral ganglion but with preganglionic fibers of splanchnic nerves - postg from collateral innervate digestive, uterinary, reproductive organs

Where do sympathetic preganglionic synapse with postganglionic?

paravertebral ganglia or the symapthetic chain of ganglia

Convergence

postganglionic receive synaptic input from large number of preganglionic fibers

Divergence

preganglionic fibers synpase with numerous postganglionic located in chain of ganglia at different levels

nonshivering theromgenesis

requires sympathoadrenal system

Cerebral cortex and limbic system?

responsible for visceral responses that are characteristic of emotional reactions

Parasympathetic nervous system

rest & digest reactions

How is ANS controlled by higher brain centers?

sensory input is sent to brain centers where information is integrated and respond by modifying the activity of preganglionic autonomic neurons

Structure of postganglionic parasympathetic neuron?

short axon that innervates target

Antagonistic effect of dual innervation?

sympathetic and parasympathetic counteract each other - heart rate

Cooperative effect of dual innervation?

sympathetic and parasympathetic produce different effects that work together to achieve desired effect - micturition, erection

Complementary effect of dual innervation?

sympathetic and parasympathetic produce similar effects - salivary gland secretion

Adergonic transmission

transmission of norepinephrine has both excitatory and inhibitory effects ie: postganglionic fibers of sympathetic nervous system