Parasympathetic Signaling Flashcards
Where do pre-ganglionic parasypathetic neurons originate?
Cranial nerve nuclei and sacral spinal cord segments S2-S4
How do pre- and post-ganglionic parasympathetic neurons interact?
Pre-ganglionic parasympathetic neurons release ACh onto nicotinic ACh receptors in parasympathetic ganglia located near the effector organ
Physiologic effects - Cardiovascular
Decreased heart rate and AV conduction rate (M)
Decreased blood pressure (M)
Do blood vessels receive parasympathetic innervation?
No! Blood vessel tone is sympathetic only; vessels contain muscarinic receptors that are innervated, i.e. can be activated by agonists but NOT by activation of the PNS
Physiologic effects - Respiratory
Bronchial muscle contraction (M)
Stimulation of glands (M)
Physiologic effects - GI tract
Increased motility (M) Increased secretion (M)
Physiologic effects - GU
Contraction of detrusor muscle (M) - promotes voiding
Physiologic effects - Eye
Miosis (pupil constriction) (M)
Accomodation (focus for near vision) (M)
How is acetylcholine synthesized?
Choline is taken up by the neuron via active transport through the choline transporter (CHT); this uptake is blocked by hemicholinium
Choline acetyl transferase (ChAT) catalyzes the conversion of choline to ACh
How is ACh inactivated?
ACh is enzymatically metabolized by AChE in the synaptic cleft to choline and acetate
Nicotinic AChR - What type is it?
Ligand-gated ion chanel (ionotropic); permeable to Na+, Ca2+
Effects of nicotine at nAChR
Increases blood pressure, heart rate, vasoconstriction
Increased GI motility
CNS: Euphoria, Arousal, Relaxation
How is ACh stored?
ACh is stored within vesicles by the VAT transporter; this process is inhibited by vesamicol
Muscarinic receptor coupling
M1 and M3 - Gq coupled
M2 and M4 - Gi coupled
