Synaptic signalling

Question 1

What is the postsynaptic density?

Answer 1

Where the membrane appears thicker and receptors are located

Question 2

What is the presynaptic active zone?

Answer 2

Where vesicles fuse, can be seen down a microscope

Question 3

What is a Grays type I synapse

Answer 3

Asymmetrical
Has thicker postsynaptic density
Usually excitatory
e.g. glutamate

Question 4

What is a Grays type II synapse

Answer 4

Symmetrical
Thickness is equal
Usually inhibitory
e.g. glycine or GABA

Question 5

What is an axodendritic synapse?

Answer 5

Synapse onto dendrite of neurone

Question 6

What is an axosomatic synapse?

Answer 6

Synapse onto soma of neurone

Question 7

What is an axoaxonic synapse?

Answer 7

Synapse onto an axon of the neurone

Question 8

Why is the point of synaptic contact important?

Answer 8

Closer to axon hillock = greater influence on action potential generation
Inhibitory synapses are often on soma or axon hillock
This is the best position to control neuron activity

Question 9

Are axodendritic synapses effective?

Answer 9

No
Input may not spread down dendrite to reach soma or axon hillock
Yes
Could amplify excitatory input
Increasing likelihood of action potential at axon hillock

Question 10

What happens if the dendrite has no channels?

Answer 10

Passive spread of depolarisation

Large input required

Question 11

How many synapses does a typical neuron have?

Answer 11

1000-10,000

Question 12

What is synaptic integration of information?

Answer 12

The integration of multiple synaptic inputs

Question 13

What does SEPSP stand for?

Answer 13

A small excitatory post synaptic potential

Question 14

What is an SEPSP?

Answer 14

A small excitatory post synaptic potential is a small change in Em, smaller than threshold value

Question 15

Why will multiple synaptic inputs trigger an action potential?

Answer 15

Combined size of SEPSP will be greater than threshold

Question 16

What is spatial summation?

Answer 16

Summing of post synaptic potentials generated at separate synapses

Question 17

What is an SIPSP?

Answer 17

A small inhibitory post synaptic potential

Question 18

When are EPSPs most effective?

Answer 18

When they coincide

Question 19

How can one EPSP trigger an action potential in the post synaptic neurone?

Answer 19

Synaptic input at a high frequency

Question 20

What is temporal summation?

Answer 20

Summing of post synaptic potentials generated at same synapse, if they occur in rapid succession

Question 21

Outline neuronal communication

Answer 21

Receive messages from connected neurones
Integrate all inputs
Send a frequency-encoded message

Question 22

What is the purpose of frequency coding?

Answer 22

Action potentials are all-or-nothing
Can’t differ in amplitude
Communication therefor via frequency

Question 23

Frequency of action potential firing is directly related to…

Answer 23

…the intensity of the stimulus

Question 24

Signalling is described as being…

Answer 24

…frequency-modulated

Question 25

What happens when a stimulus is at threshold?

Answer 25

Just strong enough to trigger an action potential

Question 26

What happens when a stimulus is at sustained threshold level?

Answer 26

A 2nd action potential fires This is delayed Time taken = sum of absolute refractory period and relative refractory period

Question 27

What happens with a supra-threshold stimulus?

Answer 27

Multiple action potentials fire An action potential fires in relative refractory period Only absolute refractory period limits action potentials firing

Question 28

How frequently can action potentials fire?

Answer 28

200-300 times a second