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