acetylcholine Flashcards
acetylcholine (ACh)
- first neurotransmitter discovered
- plays crucial role in sympathetic and parasympathetic systems
- plays role in CNS
- responsible for muscle contractions as it is released at neuromuscular junction
botox
interferes with Ach release at nerve terminals, thereby blocking neurotransmission
- prevents fusion of synaptic vesicles with nerve terminal
membrane
- results in muscle weakness or paralysis
cholinergic system
ACh is the neurotransmitter used for communication
- mediates parasympathetic
functions (e.g. inhibits heart);
- released onto muscles leading to muscle contraction (activates)
ACh formation
- acetylcholine = acetyl coenzyme A + choline
- ACh is formed from choline and acetyl coenzyme A (Acetyl CoA).
- this reaction is catalyzed by choline acetyltransferase (ChAT)
acetyl CoA
produced during the 2nd step of aerobic cellular respiration
- pyruvate decarboxylation: conversion of pyruvate, the end product of glycolysis, into acetyl CoA
- occurs in the matrix of the mitochondria
ChAT
- synthesized within the cell body and transported to the nerve terminal
- used as a marker for motor neurons
Vesicular ACh Transporter
(VAChT)
responsible for loading ACh into vesicles
cholinergic cell bodies primarily located in
- Caudate putamen
- Nucleus Accumbens
- Nucleus basalis
- Pedunculopontine Nuclei (PPN)
i. Laterodorsal tegmental nucleus
ii. Pedunculopontine tegmental nucleus - Medial Septum
cholinergic receptor families
- nicotinic acetylcholine receptors
- muscarinic acetylcholine receptors
nicotinic acetylcholine receptors
- ionotropic
- respond to nicotine
- located at neuromuscular junction
mediate fast, excitatory responses - opening of pore, rapid increase in permeability of
Na+ and Ca2+ = depolarization
nicotinic acetylcholine receptors 2
- each nicotinic receptor consists of five subunits
- there are ten a subunits, and four b subunits (functional implications)
- this produces a wide range of nicotinic receptor subtypes;
- receptors on muscle cells look different than
receptors on neurons
nicotinic acetylcholine receptors 3
- when nicotinic receptors are
subjected to continuous agonist exposure, they become
desensitized – the channel will
not open even when agonist
binds - desensitized receptors will
naturally, and spontaneously,
re-sensitize and are able to
respond again
muscarinic acetylcholine receptors
- respond to muscarine
- metabotropic
five types: M1-M5 - M1,M3, M5 activate phospholipase C to increase intracellular Ca2+
- M2, M4 inhibit adenyl cyclase to decrease cAMP
muscarinic acetylcholine receptors 2
- cardiac muscles have M2 receptors meaning stimulation of the parasympathetic system slows heart rate and decreases contraction strength
- smooth muscles have M3 receptors meaning activation results in muscle contractions
muscarinic acetylcholine receptors 3 - M5
- found in hippocampus, hypothalamus and midbrain DA areas
- add to DA neuron excitation mediated by nicotinic receptors
- may be involved in rewarding effects of drugs
