Receptor Mechanism I

Question 1

What causes super fast responses?

Answer 1

Chemicals binding to a receptor that instantaneously creates an ion path
Binding of a chemical transmitter causes an ion path to open

Question 2

What is the ligand gated ion channel receptor superfamily? How do they work?

Answer 2

The binding of two molecules of the activating agonist causes an instantaneous opening of an ionic path that allows ions to follow depending on their electrochemical gradient
Each ligand gated ion channel receptor is made up of 5 similar proteins (a pentamer)
Each of these proteins constitutes some amino acids that form the pore of the channel
These similar proteins can diversify a lot in their composition
The hydrophobic parts of the ligand gated ion channel proteins are the ones within membrane

Question 3

What agonists are part of the ligand gated ion channel receptor superfamily?

Answer 3

There are four agonist (and their receptors)
Acetylcholine—> Nicotinic cholinoreceptor
5-HT—–> 5HT\/3
y amino butyric acid (GABA)—–> GABA\/A
Glycine—–> Glycine

Question 4

How do ion channels work? What are some examples?

Answer 4

Receptor activation allows ion flow 
The ligand molecules that bind cause a kink in the proteins opening it up
In total each functional receptor has 20 transmembrane domains because each protein has 4 
Examples include:
Nicotinic depolarises (Na/Ca influx)
5HT\/3 depolarises (Na/Ca influx)
GABA\/A hyperpolarises (chloride influx)
Glycine hyperpolarises (chloride influx)

Question 5

What are the different types nicotinic receptors?

Answer 5

Stimulation of nicotinic AChR in skeletal muscle contracts muscle quickly
The nicotine type acetylcholine receptors:
Skeletal muscle- N\/1 or N\/M
molecular composition of the pentamer is a1-e-a1-b1-d (adult) or a1-y-a1-b1-d (foetal)
CNS and autonomic ganglia- N\/2 or N\/N
combination of a2 to a8 and b2 to b4 make up the nervous receptors

Question 6

What happens when the nicotinic receptor fails in other words, what is Myasthenia Gravis?

Answer 6

An autoimmune disease
Muscle nicotinic AChRs become degraded 
Targets the a1 subunit
Thus neuronal nicotinic AChRs unaffected
Results in:
Muscle weakness and fatigue 
Drooping eyelids
Difficulty swallowing or talking
Exertion is difficult

Question 7

What happens when GABA\/A receptors are stimulated?

Answer 7

Stimulation of GABA\/A receptors in neurones inhibits activity quickly
Inhibitory nerves release GABA (gamma-aminobutyric acid) or glycine
The ligand gated ion channels allow chloride ions (Cl-1) to enter
This is hyper-polarisation