Synaptic transmission and neural integration

Question 1

What is synaptic transmission

Answer 1

A typically fast process of transferring information between neurons or between neurons and muscle fibres.

Question 2

Synaptic transmission occurs between neurons through either what two things

Answer 2

Chemical synapses or electrical synapses

Question 3

What is the ionic mechanism of End-plate potentials

Answer 3

Transient opening of ion channels permeable to both Na+ and K_

Question 4

End-plate potential is always supathreshold, what does this mean?

Answer 4

Once triggered, AP is transmitted along the muscle fibres

Question 5

What are the three key features of a chemical synapse

Answer 5

Specifity, complexity and plasticity

Question 6

a key feature of a chemical synapse

What is specificity?

Answer 6

Special neurotransmitters have specific effects on postsynaptic membrane.

Question 7

a key feature of a chemical synapse

What is complexity?

Answer 7

Type, time, course, strength, location and timing etc

Question 8

a key feature of a chemical synapse

What is plasticity

Answer 8

Changes in synaptic structure and function associated with development, aging, learning etc.

Question 9

What are the two main types of chemical synapses in the CNS

Answer 9

Excitatory and inhibitory

Question 10

Why do we need chemical synapses

Answer 10

• At a chemical synapses, depolarisation at the presynaptic terminal causes the release of a neurotransmitter which diffuses across the synaptic cleft and binds to receptors in the postsynaptic membrane.
• The binding usually initiates an opening of a channel associated with the receptor, and a current in the postsynaptic cell.

Question 11

What are excitatory synapses

Answer 11

Depolarisation of the postsynaptic membrane called the Excitatory Postsynaptic Potential (EPSP)

Question 12

What are inhibitory synapses

Answer 12

Hyperpolarisation of the postsynaptic membrane called the Inhibitory Postsynaptic Potential (IPSP)

Question 13

What are the main neurotransmitters involved in the production of EPSPs

Answer 13

Glutamic acid and acetylcholine.

Question 14

What is the ionic mechanism of EPSPs

Answer 14

The opening of channels selective for Na+, K+ and sometimes Ca2+.

Question 15

What are the main neurotransmitters involved in the production of IPSPs

Answer 15

Mainly gamma-aminobytyric acid (GABA) or glucine.

Question 16

Wh

Question 16

What is the ionic mechanisms of IPSPs

Answer 16

Often through the opening of K+ channels which hyperpolarises the cell membrane (moves RMP away from threshold)

Question 16

What are the two types of mechanisms used to gate ion channels by neurotransmitters.

Answer 16

Direct gating and indirect gating

Question 17

What is direct gating

Answer 17

Where the transmitter binds to the receptor/ion channel complex, causing the pore to open and ions to pass through, depolarising and hyperpolarising the cell membrane.

Question 18

What is indirect gating

Answer 18

Where the transmitter binds to receptors (such as G-protein-coupled), also known as metabotropic receptors) activating the biochemical pathway which involves a G-protien.

Question 19

Role of G proteins in indirect gating

Answer 19

G-proteins are membrane-enclosed proteins which bind GPT when activated by membrane receptor. This leads to the production of second messengers such as cAMP.

Protein kinases activated by the second messenger phosphorylate specific ion channels, causing them to open or close and thus, the membrane potential changes.

Question 20

Is direct or indirect gating faster/longer lasting

Answer 20

Direct gating is faster on oniset and short-lasting.
Indirect gating effects are slower in onset and longer-lasting

Question 21

What are the two classifications of neurotransmitters

Answer 21

Small molecule neurotransmitters (classical neurotransmitters) and neuropeptides (neuromodulators)

Question 22

What are classical neurotransmitters

Answer 22

Usually fast and often act indirectly on postsynaptic receptors.

Question 23

What classifies under classical neutrotransmitters

Answer 23

• amino acids (glutamate, GABA, glycine)
• Acetylcholine
• Biogenic amines (dopamine, norepinephrine, serotonin 5-HT)

Question 24

What are neuropeptides

Answer 24

Large molecule chemicals with indirect (metabotropic) action, or modulatory action on the effects of other neurotransmitters. They tend to exert slow and usually a more diffuse action.

Question 25

There are dozens of neuropeptides identified to be involved in the communication between neurons, what are some examples?

Answer 25

• enkephalin
• substance P
• Neuropeptide Y (NPY)

Question 26

What are the factors determining synaptic action

Answer 26

• type of neurotransmitter/neuromodulator
• type of neurotransmitter receptor/channel complex expressed in the postsynaptic membrane
• amount of neurotransmitter receptor present in the postsynaptic membrane - synaptic plasticity: long term potentiation (LTP) or long term depression (LTD)

Question 27

What are the three ways to cause neurotransmitter inactivation (and recovery)

Answer 27

1. diffusion away from synapse
2. enzymatic degradation in the synaptic cleft
3. reuptake for most of the aminoacids and amines and recycling.

Question 28

What is excitotoxicity

Answer 28

• increased release of neurotransmitters
• example: glutamate
• leads to increases Ca2+ accumulation
• activates enzymes that kills the cell