Communication between Excitable Cells

Question 1

Definition of axodendritic

Answer 1

Synapse between axon and dendrite

Question 2

Definition of axosomatic

Answer 2

Synapse between axon and cell body

Question 3

Definition of axoaxonic

Answer 3

Synapse between axon and axon

Question 4

Definition of miniature endplate potentials (MEPPs)

Answer 4

Small endplate potentials that occur randomly in the presence of random vesicle release

Question 5

Definition of excitatory postsynaptic potentials (EPSPs)

Answer 5

Subthreshold events, determine if a neuron will reach threshold to fire an action potential or not
Add to generate depolarization

Question 6

Definition of inhibitory postsynaptic potentials (IPSPs)

Answer 6

Subthjreshold events, determine if a neuron will reach threshold to fire an action potential or not
Add to generate hyperpolarization

Question 7

Definition of temporal summation

Answer 7

1 presynaptic neurone releases neurotransmitters many times over a short time frame to exceed threshold

Question 8

Definition of spatial summation

Answer 8

Many presynaptic neurons release neurotransmitters together to exceed threshold

Question 9

What happens in a sub threshold post synaptic response

Answer 9

If depolarized insufficiently, threshold not exceeded, no AP

Endplate potential rises and falls

Question 10

What happens in a supra threshold postsynaptic response

Answer 10

Many small depolarizing events = influx of Na+
If that exceeds threshold, AP!
Increase no of open VGNC
Depolarization also activates Ca2+ channels, causes plateau

Question 11

Propagation of action potential

Answer 11

Inwards flow of +ve charge due to influx of Na+
Flows in, around and out and dissipates with distance
If threshold exceeded in other parts of the post synaptic membrane, more NaK and Ca channels open,

Question 12

Order of events in synaptic transmission

Answer 12

Presynaptic action potential
Depolarization of synaptic terminal
Opening of voltage gated Ca2+ channels
Ca2+ entry and fusion of vesicles with membrane
Transmitter release (reuptake/degredation/passive diffusion)
ACh receptor activation, cation channels open
Activation of NaK channels

Question 13

What events reduce vesicle release from presynaptic membrane and what are the effects of this?

Answer 13

Low calcium
High magnesium
Curare

Result in sub threshold miniature endplate potentials (MEPPs)

Question 14

What are MEPPs

Answer 14

Vary in size, occur at random
Generated by random vesicle release
As they themselves don’t exceed threshold, as distance from depolarization increases, signal dissipates

Question 15

Describe the knee jerk reflex

Answer 15

Knee is whacked with a hammer

Muscle spindle in extensor muscle sends impulse through afferent sensory neurone and bifurcates in the spinal cord
Signal to inhibitory interneuron releases an inhibitory post synaptic potential (IPSP), inhibits the flexor

Other bifurcation releases an excitatory post synaptic potential (EPSP), excites the extensor

Question 16

What are EPSPs and IPSPs

Answer 16

Subthreshold events, determine if a neuron will reach threshold to fire an action potential or not
EPSPs add to generate depolarization
IPSPs add to generate hyperpolarization

Question 17

How do EPSPs and IPSPs relate to each other

Answer 17

They can cancel each other out

If there are enough EPSPs, they can cancel out IPSPs and generate action potentials

Question 18

Effects of IPSPs on frequency coding

Answer 18

Prevent EPSPs from generating AP

Question 19

What is temporal summation

Answer 19

1 presynaptic neurone releases neurotransmitters many times over a short time frame to exceed threshold and generate AP

Question 20

What is spatial summation

Answer 20

Many presynaptic neurons release neurotransmitters together to exceed threshold and generate AP