Synapses

Question 1

Over time can a synapse switch between being excitatory and inhibitory?

Answer 1

No, each neuron only has one type of connection to other neurons.

These connections never change between excitatory and inhibitory, however the synaptic strength can change.

Question 2

What is the benefit of a chemical synapse over a gap junction?

Answer 2

Chemical allows for the pre synaptic spike to a greater variety of affects on the post synaptic potential.

Question 3

In a chemical synapse, the input to the synapse is called the ______ _______, coming from the axon of a neuron. The output from the synapse, is called the ______ ______, connected to the dendrite of another neuron.

Answer 3

The input to synapse is called terminal bouton.

The output from the synapse called the dendritic spine.

Question 4

What is the name given to the small gap between the terminal bouton and the dendritic spine?

Answer 4

Synaptic cleft

Question 5

What causes the vesicles to move towards the membrane that separates the terminal bouton from the cleft?

Answer 5

Incoming spike causes calcium ions to enter the terminal bouton. The calcium ions carry the vesicles towards to membrane.

Question 6

There is a gate which must be open to allow the ions in the cleft to pass into the dendritic spine. What type of gate is this?

Answer 6

Ligand gate. Neurontransmitters are the key to the ligand gate.

The gate is ion specific.

Question 7

Where are there re-uptake pumps?

Answer 7

Terminal bouton and in the astrocyte

Question 8

Why does calcium come in to the terminal bouton in the presence of a spike?

Answer 8

Spike causes calcium gates to open, calcium wants to move down the concentration gradient and INTO the cell.

Question 9

Random collisions cause the neurotransmitter to unbind from the ligand gates channel. What happens next?

Answer 9

The gates closes.

Question 10

If a neuron is excitatory, all its synapses are _______?

Answer 10

Excitatory

Question 11

If a neuron is inhibitory, all its synapses are _______?

Answer 11

Inhibitory

Question 12

What determines if a synapse is excitatory or inhibitory?

Answer 12

The neurotransmitters.

Excitatory neurotransmitters will open calcium or sodium ligand gated channels at the dendritic spine.

Inhibitory neurotransmitters will open potassium or chlorine ligand gated channels at the dendritic spine.

Question 13

Explain short term plasticity?

Answer 13

Spikes in quick succession can deplete the number of vesicles in the terminal bouton, causing a drop in the post synaptic potential, this is called short term depression.

Alternatively, spikes in quick succession can also cause a build up of calcium ions, resulting an increase in the post synaptic potential, this is called short term facilitation.

Question 14

What expression did Donald Hebb coin in regards to long term plasticity?

Answer 14

Neurons that fire together wire together.

Question 15

What does STDP stand for?

Answer 15

Spike- timing dependent plasticity.

Question 16

What happens if the pre synaptic spike occurs just BEFORE the post synaptic spike is produced?

Answer 16

The synaptic strength increases. The amount by which it strengthens decreases exponentially as the time difference between spikes increases.

This is an example of long term potentiation(LTP).

Question 17

What happens if the pre synaptic spike occurs just AFTER the post synaptic spike is produced?

Answer 17

The synaptic strength decreases. The amount by which it weakens decreases exponentially as the time difference between spikes increases.

This is an example of long term depression (LTD).

Question 18

What type of firing can result in long term plastic affects?

Answer 18

Periodic firing between neurons.

Question 19

There are two groups of neurons, A and B, which are almost identical. The only difference being; the probability of a pre synaptic spike arriving before the post synaptic spike is triggered, is more likely in A than B.

Explain what will have over time to groups A and B in terms of plastic affects within the groups.

Answer 19

Since the probability of A starts ahead of B, is is more likely to strengthen. This will make A even more likely to receive a pre synaptic spike prior to a post synaptic spike leaving. This will increase the probability of A even further, hence widening the gap between A and B in terms of synaptic strength.

Question 20

In the absence of any spikes, what is the conductance of the dendritic spine’s membrane?

Answer 20

zero