Autonomic Nervous System Flashcards
PNS divided into
ANS and somatic
ANS divided into
SNS and PNS
Somatic nervous system divided into
Sensory (afferent) and motor (efferent)
Effectors of Somatic System
skeletal muscles
ANS effectors
cardiac, smooth muscle, glands
Efferent pathways of somatic system
thick, heavily myelinated, somatic motor fiber makes pathway from CNS to muscle
Efferent pathway of ANS
2 neuron chain
preganglionic- thin, lightly myelinated preganglion axon
ganglionic neuron has unmyelinated postganglionic axon that extends to effector organ
Somatic NT effects
all somatic motor neurons release ACh- always stimulatory
ANS NT Effects
PREganglionic fibers release ACh
POSTganglionic fibers release NE or ACh at effectors
effect is either stim/inhibitory depending on receptor
SNS fibers
originates in thoracolumbar (T1-L2) region of SC
short pre and long post
ganglia close to spinal cord
PNS fibers
Origin in craniosacral spinal cord
long pre and short post
ganglia in visceral effector organs
sympathetic neurons produce ? of the spinal cord
lateral horns
Upon entering sympathetic trunk ganglion, preganglionic fiber may do one of following:
1) synapse with ganglionic neuron within same ganglion
2) ascend or descend sympathetic trunk to synapse in another trunk ganglion
3) pass through trunk ganglion and emerge without synapsing
T1-T4 fibers
cardiac accelerator fibers
Pathways with synapses in adrenal medulla
some preganglionic fibers pass directly to medulla without synapsing- stimulates medullary cells to secrete NE and epi into blood
Cholinergic fibers
release ACh
all ANS preganglionic axons and all PNS postganglionic axons
Adrenergic Fibers
release NE
most sympathetic postganglionic axons
Nicotinic Receptors
- end plates of SKELETAL muscle cells, all ganglionic neurons, hormone producing cells of adrenal medulla
- always stimulatory
Muscarinic Receptors
- found on all effector cells stimulated by postganglionic cholinergic fibers (parasympathetic target organs)
- effect either inhibitory or excitatory (depends on organ)
B1 receptors
- heart, kidneys, adipose
- NE increases HR contractility, stimulates renin release
B2 receptors
- lungs, most other sympathetic organs
- NE effects mostly inhibitory- dilates BV and bronchioles, relax smooth muscle walls of digestive/urinary organs/uterus
A1 receptors
- blood vessels, almost all sympathetic target organs except heart
- NE constricts BV and visceral organ sphincters, pupil dilation
A2 receptors
- membrane or adrenergic axon terminals; pancrease; platelets
- inhibits NE release from adrenergic terminals, inhibits insulin secretion, promotes blood clotting
Atropine
- anticholinergic; blocks muscarinic receptors
- prevents salivation, dilate pupils
Neostigmine
- inhibits acetylcholinesterase
- reverses NMBs, used to treat MG
alpha blocker drugs
interfere with vasomotor fibers, used to treat HTN
PNS vs SNS length of effects
PNS- short lived
SNS- long lasting (NE inactivated more slowly than ACh)
Main integrative center of ANS activity
hypothalamus
