L7: Cholinergic Transmission Flashcards
What is the definition of a synapse?
It is the functional connection between a neuron and a second cell (neuron or muscle or glands)
What is the structure of a synapse?
is formed of 3 parts:
a) Presynaptic portion→ transmits impulse towards the synapse
b) Postsynaptic portion→ transmits impulse away from the synapse.
c) Synaptic cleft →is full of interstitial fluid which separates the nerve ending from the next neuron or effector organ.
What is the definition of the electrical synapse?
Is a gap junction between the presynaptic membrane
and postsynaptic membrane.
Is the electrical synapse common or rare?
Rare
What is the function of electrical synapses?
It allows direct transmission of the electrical depolarization waves from the presynaptic to the postsynaptic neuron
What is the definition of chemical synapses?
It is a junction between the presynaptic and postsynaptic membrane which is chemically mediated.
Are chemical synapses common or rare?
Common
What is the function of chemical synapses?
A chemical substance is released at the nerve endings which allows the transmission of nerve impulses from one neuron to another neuron.
What are the types of chemical transmitters?
-Types of chemical transmitters:
chemical transmitters released by autonomic nerve endings include :
a) acetylcholine. b) noradrenaline
What are the types of nerve endings?
a) Cholinergic nerve fibers: secrete acetylcholine.
b) Adrenergic nerve fibers: secrete noradrenaline
What are the sites of the release of acetylcholine?
a) All preganglionic sympathetic and parasympathetic nerve endings.
b) Preganglionic sympathetic nerve fibers to the suprarenal medulla.
c) All postganglionic parasympathetic nerve ending.
d) Sympathetic postganglionic fibers supplying skeletal ms blood vessels and sweat glands.
e) Somatic motor nerve ending to skeletal muscle (motor endplate).
f) Some synapses at CNS (brain and spinal cord).
How is ach biosynthesized?
Ach is formed by a reaction between choline and acetyl CoA as follow;
ATP
Acetyl CoA + choline ——————— > acetylcholine + CoA
NB:-
- CAT (choline acetyltransferase)
- ATP and glucose are required to form acetyl CoA.
Where is ach stored?
- Ach is stored inside the nerve terminals in minute vesicles
- Each vesicle contains more than one thousand Ach molecules (5000-10000 molecules)
- Some molecules of Ach are found free in the cytoplasm.
How is ach released?
The arrival of action potential (depolarization) to nerve ending → open Ca2+ channels →↑ed Ca2+ influx to inside nerve endings → interact with the vesicles adjacent to the membrane causing them to fuse with the membrane → rupture of vesicles emptying their contents outside the nerve fibers by exocytosis
- Released Ach which passes rapidly over the gap (10-30 nm) between nerve terminals → Ach binds to receptors on the effector organs.
What is the mechanism of action of ach?
Ach binds with its receptors on the postsynaptic membrane which might be;
i) Ligand-gated ion channels → Na+ and Ca2+ influx → depolarization (stimulation) or K+ and Cl_ influx → hyperpolarization (inhibition).
ii) G-protein coupled receptors → activate membrane enzymes such as adenyl cyclase → formation of 2nd messenger called cyclic AMP from ATP → intracellular signal
