Lecture 15 Somatic Motor & ANS Flashcards Preview

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Flashcards in Lecture 15 Somatic Motor & ANS Deck (24)
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Somatic motor effectors

skeletal muscles

(efferent division of the PNS)


Autonomic effectors

cardiac muscle, smooth muscle, glands, adipose tissue


Somatic motor division

somatic motor neurons activate skeletal muscles
voluntary (mostly): control of movement posture, breathing


Somatic Motor Pathway

one motor neuron pathway from CNS to muscle(effector)
motor neuron cell bodies located in the ventral gray horn of spinal cord
axons travel through spinal nerves
axon terminals located at the neuromuscular junction


3 components of the neuromuscular junction

axon terminal of motor neuron
synaptic cleft
motor end plate


neuromuscular junction

ACh into the synaptic cleft
nicotinic cholinergic receptors at the motor end plate
binding of ACh open cations channels -> strong EPSP->
exceeds threshold -> muscle AP


Autonomic Division (ANS)

involuntary control of autonomic effectors (visceral organs, blood vessels, etc.)
activated by the hypothalamus, pons&medulla, and spinal cord (autonomic reflexes)
two motor neuron pathway from CNS to effectors: preganglionic and postgagnlionic


Autonomic division ganglionic fibers

preganglionic fibers from CNS to autonomic ganglia
postganglionic fibers from autonomic ganglion to target organ


2 Divisions of the ANS

sympathetic - fight or flight
parasympathetic- rest and digest


Dual innervation of sympathetic and parasympathetic

to target organs, usually antagonistic (opposite)
both systems are active, but parasympathetic dominates during normal maintenance states; sympathetic system dominates during short term stress, exercise, cold, drop in BP


ANS organization
Sympathetic Division

thoracolumbar outflow
short preganglionic, long postganglionic fibers
ganglia located in sympathetic chain and collateral ganglia
adrenal medulla is functionally part of the sympathetic division


In the sympathetic division what do postganglionic neurons secrete

norepinephrine (NE) as the neurotransmitter at target cells


Adrenal medulla's role in the sympathetic division

stimulated directly by preganglionic sympathetic fibers
secretes the hormones epinephrine (E) and norepinephrine (NE)
only stimulated by sympathetic response


where do the preganglionic fibers in the sympathetic division arise from?

the thoracic and lumbar spinal cord


Where do the short preganglionic fibers go to in the sympathetic

go to sympathetic ganglia close to the spinal cord


Parasympathetic division

carinosacral outflow (preganglionic arise from cranial and sacral regions)
long preganglionic, short postganglionic fibers
post ganglionic neurons secrete acetylcholine (ACh) as the neurotransmitter at target cells
terminal ganglia located in or near target organs


Vagus nerbe (cranial nerve X)

is the major parasympathetic nerve to visceral organs


ANS neurotransmitter and receptors
preganglionic fibers

ACh-> nicotinic cholinergic receptors
sympathetic and parasympathetic


Postganglionic fibers

E, NE -> adregergic receptors
most target cells use NE as the neurotransmitter
E is the hormone released form the adrenal medulla
alpha-adrenergic receptors
beta-adrenergic receptors


alpha-adrenergic receptors

a1 -> constriction of blood vessels
G-protein couples receptors, activate phospholipase C second messenger pathway


beta-adrenergic receptors

B1-> stimulates heart
B2-> bronchodilation
G protein couple receptors, activate cAMP second messenger pathway


postganglionic fibers

ACh-> muscarinic cholinergic receptors
G-protein coupled receptors, open or close K+ channels (excitatory or inhibitory)


Sympathetic causes

increase heart rate and contractability (B1)
inhibits digestive tract motility and secretion (a, B2)
vasoconstriction in peripheral blood vessels (a, some B2)
vasodilation in skeletal muscles
bronchiole dilation (B2)
pupil dilation (a)
mobilization of energy reserves (glycogen and lipids)


Parasympathetic causes

decrease in heart rate (no effect on contractility) (B1)
stimulates digestive tract motility and secretion (a,B2)
no effect on blood vessels
bronchiole constriction (B2)
pupil constriction (a)
no metabolic effects