Electrophysiology I: Spikes, Graded Potentials and Synaptic Integrations

Question 1

What are the differences between extracellular and intracellular recording?

Answer 1

Extracellular:
- Usually done on live subjects
- Cannot record voltage difference across a membrane
- Spikes in nearby neurons cause local extracellular current flow which can be detected as small transcient voltage changes
- Records spikes not membrane potential (Vm)

Intracellular:
- Can record both spikes and Vm

Question 2

What are graded potentials?

Answer 2

Temporary changes in a membrane voltage created by a stimuli opening a voltage-gated channel

Question 3

What are examples of graded potentials?

Answer 3

• Excitatory postsynaptic potentials
• Inhibitory postsynaptic potentials
• Receptor potentials from sensory transduction

Question 4

What is capacitance?

Answer 4

The ability to store and separate charge

Question 5

How is the cell membrane like an electrical circuit?

Answer 5

• It has a current and charge when there is a flow of ions
• It has resistance dependent on the open and closed ion channels
• Has a capacitance by being able to separate charge between outside and inside cell (Vm)

Question 6

What happens in synaptic transmission?

Answer 6

• An AP in the presynaptic neuron triggers a postsynaptic potential
• Neurotransmitters secreted from the presynapse binds to the R on the post synapse
• Causes the ion channels to open and allows for current to flow
• There is a local change in Vm and causes either de/hyperpolarisation

Question 7

Can AP and PSPs summate?

Answer 7

• AP no
  -PSPs Yes

Question 8

What is synaptic integration?

Answer 8

Where over any given time window, spatial and temporal summation determine the value of Vm

Question 9

What are the differences between AP and Graded spikes?

Answer 9

• AP are larger, faster, cannot summate, active and have an all-or-nothing theory
• Graded spikes are smaller, slower, graded (can have multiple sizes), can summate and are passive

Question 10

What are the two types of summation that affect synaptic integration?

Answer 10

Spatial and Temporal Summation

Question 11

What is Temporal Summation?

Answer 11

Where summation occurs over time

• If 2 presynaptic Ads are fired in rapid succession, PSP due to 2nd AP

Question 12

What is Spatial Summation?

Answer 12

Different presynaptic neurons with synapses are on different spatial locations on the post synaptic neuron can be active simultaneously

Question 13

How can time distance and time constants affect synaptic integration?

Answer 13

• Longer the length distance, it means that spatial summations are more effective as a shorter length causes more leakage
• Longer time constant means it allows the current to decrease and increase more slowly

Question 14

What are the electrical properties of the neuronal membrane that determines summation?

Answer 14

Space constant (lambda): increase with square root of diameter and membrane resistance