Autonomic nervous system Flashcards
What is the autonomic nervous sytstem?
Efferent system that controls organs whose functions are not usually under voluntary control. Split into sympathetic and parasympathetic nervous system.
What is a reflex?
Rapid predictable involuntary response to a stimulus. Important to autonimic control and may evoke changes in negative feedback (especially visceral organs and blood vessels) or feedforward (fight or flight)
What is the general autonomic nerve pathway for output?
Preganglionic fiber in CNS synapses with cell body of postganglionic in autonomic ganglion which innervates with effector organ or tissue.
What are varicosities?
Small nodules at axon terminals of postganglionic neuron that contain neurotransmitters
Where are the sympathetic cell bodies of preganglionics found?
Thoracic and lumbar regions of spinal cord.
What are the three routes axons of sympathetic preganglionic neurons take after leaving the spinal cord?
- Make a synapse in the sympathetic chain ganglion (bilateral along spinal cord)
- Pass through sympathetic chain ganglion and synapse in the adrenal medulla (modified sympathetic ganglion) to release epinephrine in the blood.
- Pass through sympathetic chain ganglion and synapse in a collateral ganglion (sympathetic ganglion for abdominal cavity)
What is the difference between pre and post ganglionic fibres in the SYMPATHETIC branch?
preganglionic: short, release ACh to nicotinic receptors on post-G neuron
post ganglionic: long, release norepinephrine and sometimes Ach to muscarinic receptors
Where are the parsaympathetic cell bodies of preganglionics found?
Cranial and sacral areas of the CNS.
What is the difference between preganglionic fibres and post ganglionic fibres in the PARASYMPATHETIC branch?
Preganglionic: long, release ACh
Postganglionic: VERY short, release ACh to Muscarinic receptors and occasionally nicotinic recptors.
What are cranial nerves?
Nerves that connect directly from brain to different parts of the head, instead of going to the spinal cord.
What 4 cranial nerves have parasympathetic function?
Oculomotor nerve: controls lens and pupil of the eye
Facial nerve: controls tear glands, salivary glands, nasal glands
Glossopharyngeal nerve: salivary glands
Vagus nerve: contains 70-90% parasympathetic fibres and innervates ALL organs except adrenal medulla.
What is the reflex arc of the vagus nerve?
- Carries sensory information from viscera to integrating centre called Nucleus of the Solitary Tract (NST)
- Sensory information is processed within the NST, which may project axons to higher parts of the brain.
- Vagus nerve carries efferent information to regulate/modulate organ function.
What is the preganglionic-postganglionic divergence trend differences in SNS and PNS?
SNS: PreG neuron branches many times to synapse on many postG neurons (1:10-1:30)
PNS: PreG neuron branches many times to synapse on some post G neurons (1:4)
What is Mass action?
Phenomenon where sympathetic nervous system responds as a unit due to the increased number of divergence from preG to postG neurons.
Why does the SNS have a longer lasting effect than the PNS?
- ACh in PNS is quickly broken down by acetylcholinesterase
- NE is more persistent than ACh because breakdown takes long. Breakdown includes transport back to the neuron, degradation by COMT and MAO, and picked up by blood.
What are the receptors on the SNS vs PNS?
SNS uses Nor-epi receptors: alpha 1/2, beta 1/2/3
PNS uses nicotinic AChR and Muscarinic AChR: M1/2/3/4/5
What is the difference between effects of SNS and PNS activation?
SNS: Fight or flight, strenous activity, threats
PNS: housekeeping, relaxation
What is the difference between the effect of the SNS and PNS on the heart?
SNS: increased rate, increased force of contrcation
PNS: decreased rate, decreased force of contraction
What is the difference between the effect of the SNS and PNS on the eye?
SNS: dilation of pupil
PNS: constriction of pupil, adjustment of eye for near vision
What is the difference between the effect of the SNS and PNS on the pancreas?
SNS: inhibition of pancreatic secretion
PNS: stimulation of pancreatic exocrine secretion
What is the difference between the effect of the SNS and PNS on the salivary glands?
SNS: Stimulation of small volume of thick saliva, rich in mucus
PNS: stimulation of large volume of water saliva, rich in enzymes
What is dual innervation?
When organs have input form both SNS and PNS, isn’t always balanced. May be antagonistic or complimentary.
What is antagonistic dual innervation?
SNS produces one effect, PNS produces the opposite.
(e.g. SNS increases heart rate and innervates pupilary dilator, while PNS decreases heart rate and innervates pupilary constrictor)
What is complimentary dual innervation?
Activation of SNS and PHNS produce similar results.
(e.g. SNS and PNS increase saliva production but different kinds of saliva; PNS responsible for erection, SNS responsible for ejaculation.)
Which parts of the body are not controlled by dual innervation?
Adrenal medulla, sweat glands, smooth muscle of most blood vessels receive only sympathetic innervation.
Which CNS centres contribute to autonomic regulation?
- Limbic system: sensory and emotional responses with autonomic output
- Hypothalamus: major control centre for autonomic output, includes hunger thirst, thermoregulation, emotions and sexuality.
- Brainstem: gives rise to nuclei of cranial nerves that mediate autonomic responses
- Spinal cord: reflexes are integrated in spinal cord
