Lecture 15 Somatic Motor & ANS Flashcards
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
sympathetic
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
Sympathetic
a1 -> constriction of blood vessels
G-protein couples receptors, activate phospholipase C second messenger pathway
beta-adrenergic receptors
sympathetic
B1-> stimulates heart
B2-> bronchodilation
G protein couple receptors, activate cAMP second messenger pathway
postganglionic fibers
parasympathetic
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
