Neurotransmitters (physiology)

Question 1

Two types of cell to cell communication and the systems involved.

Answer 1

Chemical, endocrine system.
Electrical, nervous system

Question 2

Three mechanisms used for local cell to cell communication

Answer 2

-Gap junctions
-Contact-dependent signals
-Autocrine and paracrine signals

Question 3

What are neurotransmitters?

Answer 3

Chemical messengers which transmit signals across a chemical synapse.

Question 4

What are neuromodulators (3)

Answer 4

• Chemicals released by the neuron.
• Have no effect on their own.
• They modify the effect of neurotransmitters.

Question 5

What is the difference btwn classic and secreted NT? (6)

Answer 5

Classic NT:
- are synthesized in the presynaptic region.
- are stored in vesicles
- are released into synaptic cleft where they bind to specific receptors on the post-synaptic neuron.
Secreted NT:
- are eliminated by the reuptake into the pre-synaptic neuron,
-by diffusing away from the synaptic cleft,
-and/or by specific inactivation.

Question 6

Describe the synaptic neurotransmission (7)

Answer 6

-Action potential arrives at the axon terminal and causes depolarization of the membrane.
-This causes voltage-gated calcium channels to open and allow an influx of calcium inside the neuron.
- Calcium causes the vesicles containing the neurotransmitter ACh to fuse with the membrane and release ACh via exocytosis.
-Ach diffuses in the synaptic cleft and binds to specific receptors in the post-synaptic neuron.
-This opens cation channels and allows the influx of sodium and efflux of potassium and this depolarizes the neuron.
-Depolarization ends as Ach detaches from the receptors and is broken down into acetate and choline by acetylcholinesterase.
-Choline is reabsorbed back into the pre-synaptic neuron to produce ACh.

Question 7

What are the five themes concerning receptors?

Answer 7

1.Each receptor can potentially bind with all subtypes of receptors (e.g. NA on alpha 1,2)
2.There are receptors on pre- and postsynaptic cells.
3.There are two types of receptors:
-Ionotropic receptors- direct ion channels open after engagement by the neurotransmitter.
-Metabotropic receptors- bind to G-proteins which stimulates the production of second messengers and activation of protein kinases which produces a cascade of cellular events.
4.Receptors are found in clusters on postsynaptic membrane close to the endings of neurons that secrete NT specific to them.
5. Prolonged exposure to NT leads to receptors being unresponsive.

Question 8

Name two types of neurotransmitters and how they defer.

Answer 8

Excitatory neurotransmitter-causes depolarisation.
Inhibitory neurotransmitter-causes hyperpolarisation.

Question 9

What type of neurotransmitter is acetylcholine?

Answer 9

It acts as both excitatory and inhibitory.
Excitatory on skeletal muscle, inhibitory in cardiac muscle.

Question 10

Explain the ACh synthesis and recycling.(4)

Answer 10

-Ach is made from choline and acetyl coa.
-Ach from the synaptic cleft is broken down by acetylcholinesterase.
-Choline is then transported back into the presynaptic neuron via the sodium cotransporter.
-Recycled choline is used to make Ach.

Question 11

Two types of postsynaptic potentials

Answer 11

1.Excitatory postsynaptic potential-depolarisation.
2.Inhibitory postsynaptic potential-hyperpolarisation.

Question 12

What do we call the process through which EPSP and IPSP combine?

Answer 12

Summation

Question 13

Two types of summation

Answer 13

Spatial summation
Temporal summation