Neuromuscular junction and synaptic transmission

Question 1

What is the most common type of voltage gated calcium channel and where is it found? What is it similar to in structure?

Answer 1

L type
Is found in muscles, neurones and lungs
Similar to Na+ volatage gates channel

Question 2

Name a substance that inhibits the calcium channel

Answer 2

DHP

Question 3

Describe the inactivation of voltage gates calcium channels

Answer 3

Inactivated more slowly that Na channels

Inactivation is calcium dependant- when Ca is high in cell it inactivates

Question 4

Describe how neurotransmitter is released at the synapse.

Answer 4

• Action potentials cause depolarisation to threshold to open VOCC
• Ca moves in and binds with synaptotagmin
• Synaptotagmin brings vesicle close to membrane and activates snare complex
• Snare complex creates fusion pore to allow neurotransmitter release

Question 5

Describe how action potential in muscle is propagated at nACh receptors.

Answer 5

• 2 ACh binding to nACh receptor
• Pore opens and allows Na and K to flow
• More Na flows in than K out because cells potential is further from the equilibrium potential of Na than K
• When depolarisation reaches threshold adjacent voltage gated sodium channels open
• Depolarisation spreads along t- tubules

Question 6

What two drugs will stop action potentials being propagated in the muscle- so causing paralysis

Answer 6

• Tubocurarine (from curare family) competitively blocks nACh receptors so ACh cannot bind to cause it to open
• Succinyl choline binds to nACh receptor to keep it open. This causes continual depolarisation, causing voltage gated sodium channels to remain inactivated and so further action potentials (and so muscle contraction) cannot occur

Question 7

What is myasthenia gravis?

Answer 7

Autoimmune destruction of nACh receptors causing profound muscle weakness, fatigue and poor coordination, droopy eyelids

Question 8

What is multiple sclerosis?

Answer 8

Autoimmune destruction of myelin sheath, meaning less saltatory conduction, voltage operated sodium channels can be expressed the whole way along axon when, myelin sheath lost.

Question 9

Can the CNS or PNS regenerate?

Answer 9

PNS can CNS cannot

Question 10

Where are muscarinic ACh receptors found? Describe their function.

Answer 10

At motor end plates of parasympathetic nervous system, eg in sweat gland, heart, lungs and smooth muscle.
They are GPCRs, because of this their action is much slower

Question 11

What is the general mechanism of fast synaptic transmission?

Answer 11

The neurotransmitter receptor is a channel protein which opens on ligand binding

Question 12

What neurotransmitters are used and what ions are allowed to move for excitatory synapses?

Answer 12

Ach

Na/ Ca

Question 13

What neurotransmitters are used and which ions are allowed to move for inhibitory synapses?

Answer 13

Glycine, GABA

K+/Cl- (causing hyperpolarisation)

Question 14

What two types of slow synaptic transmission is there describe how they work and their characteristics?

Answer 14

• Direct G- protein gating
  G protein activated, this moves along plasma membrane and activates channel protein. It is localised and faster.
• Gating vis intracellular messenger
  G protein activates enzyme/ second messenger which activates signal cascade. Final kinase/ messenger activates ion channel. Slower but moves through out cell and amplifies signal due to cascade.