PNS Flashcards
describe the organization of PNS nerve fiber and neurotransmitters involved. *
- originates in the CNS (cranial or sacrial)
- pregang nerve is LONG (releases ACh) at ganglion
- ganglia located close to or in target organ
- postgang nerve has nicotinic receptors and is SHORT (releases ACh)
why is postgang PNS fiber shorter than SNS?
ganglia are located near target organs
- allows discrete activation of tissues than SNS
what R does target tissue express? list the receptors and associated GPCRs
Muscarinic receptors
M135 couple to Gq
M24 couple to Gio
where are M1 receptors expressed?*
vomition center in brainstem (scopolamine = antagonist)
where are M3 receptors expressed and detail the mechanism*
expressed in:
- bronchial tubes, trachea
- urinary bladder
causes smooth muscle contraction - pathway identical to a1
ACh binding to M3 > Gq > + PLC > IP3 > intracellular ca2+ release > binds to calmodulin > ca2+:calmodulin > + MLCK > phos MLC > contraction of smooth muscle
where are M2 receptors expressed and detail the mechanism*
SA node of the heart
activation > decrease HR
activation of M2 causes hyperpol and leading to decreasing calcium ch activation
ACh binding M2 > Gi > inhibit AC > - cAMP > decrease activation PKA > stimulate outward k current > hyperpolization
how can cholinomimetic drugs be used to treat side effect of some surgeries (2)
surgeries > decrease activity of GI tract or bladder
- increasing muscarinic tone can alleviate problem
- muscarinic agonist > increase contraction of smooth muscle
- acetylcholinesterase inhib > enhance normal cholinergic neurotrans
what drug can be used to treat overactive bladder
muscarinic antagonist (Vesicare) can block premature contraction of smooth muscles surrounding the bladder. since the detrusor expresses M3 R
what are some side effects of cholinergic antagonist
dry mouth
difficulty urinating
constipation
in general both PNS and SNS operates all the time but SNS is… vs PNS…
sns is capable of massive response (in emergencies ie fight or flight)
PNS exerts more highly localized control
which organs do not have dual innervation?
vasculature, sweat glands, and smooth muscles of hair follicles are only innervated by SNS
describe ANS control of pupils detail mechanisms involved
SNS: open pupil (relax outer circular muscles) and PNS closes pupil (contract inner circular muscle)
SNS activates a1
PNS activates M3
why must SNS and PNS output be coordinated
- effects of the SNS and PNS generally oppose one another
- coordination occurs on several levels (synaptic, spinal, higher brain regions)
at the synaptic level, how does each system prevent concurrent activation of both SNS and PNS *
axon terminal of SNS adrenergic postgang neurons also expresses inhibitory (M2) muscarinic receptors > ACh released from PNS will bind to the autoreceptors on SNS term and inhibit NE release
similarly, axon terminal of PNS cholinergic postgang neurons also expresses inhib (a2) adrenergic autoR > NE release from SNS postgang will bind to the R and inhib ACh release
describe the component of the reflex arc
consist of a receptor that detects changes in the tissue (ie stretch of bladder) > sensory neurons that carries the signal to the CNS (spinal cord) > the CNS then sends signal > pregang > gang > postgang > effector
what is the name of the smooth muscle that surrounds the urinary bladder
detrusor muscle
describe the urinary bladder reflex that leads to urination (micturition). name the players, detail the coordination of the PNS and SNS that allow for this to happen. show mechanisms/pathways
1) stretch receptor sense mechanical stretch stress of bladder wall when filled
2) stretch causes conformational change in structure of ion ch > depol
3) project to SC > activates pregang PNS > project to postgang > release ACh
3.5) stretch sensor also project signal to micturition center in pons
4) activation of M3 receptors in detrusor muscle cause contraction
SAME TIME:
4) Mic center inhibits SNS neurons that project to the internal sphincter (block SNS a1 mediated contraction >allow relaxation)
4) inhibit motor neurons that project to external sphincter (block contraction > allow relaxation)
how is release of urine regulated? what kind of muscle, what R does these tissue express, what are they innervated by?
by the internal and external sphincters
internal: smooth muscle; express a1 R; innervated by SNS
external: striated muscle; expresses nicotinic R; innervated by voluntary motor neurons
describe the pathway and coordination needed to allow filling of the bladder? name the player detail the mechanism
SNS activity allows filling of bladder
- releases NE from postgang neurons > binds to B3 receptors > inhibit smooth muscle contraction AT SAME TIME: inhibit PNS input to inhibit contraction
- release of NE causes constriction of internal sphincter via a1 R
name drugs and detail function/use and their mechanism for bladder control
muscarinic anta:
vesicare: M3 antagonist
oxytrol: nonspecific musc. anta.
toviaz:
myrbetriq: B3 agonist
proin: a1 agonist
botox: prevent vesicular release of ACh
describe the defacation reflex (similar to how described the urination reflex) compare players and mechanism
- intestinal wall innervated by stretch receptors and surrounded by smooth muscles (like bladder: urination)
- waste retained by sphincter (same as urination: internal = smooth; external = striated)
- filling of colon > activate stretch receptor > activate PNS and causes contraction of smooth muscle surrounding colon and rectum.
- SAME time: sensory neurons project to the higher brain regions to inhibit a1 to block contraction and relax internal sphincter and inhibit motor neurons > relax external sphincter
describe the pathway and coordination needed to allow filling of the intestine? name the player detail the mechanism
- sympathetic nervous system activity allows accumulation of fecal matter
- release NE binds B R inhibit contractility of intestinal smooth msc
- NE binds to a1 of internal sphincter and mediate contraction
- also enhances constriction of external sphincter
