Neurophysiology; Potentials

Question 1

True or false; temporal and spatial summations can occur simultaneously

Answer 1

True

Question 2

Differentiate temporal summations from spatial summations.

Answer 2

Spatial summations are a result of several neurons supplying the same post-synaptic neuron/effector organ being stimulated at the same time; temporal summation is a result of one nerve fiber being stimulated repeatedly with the subliminal stimuli appearing very closely so that there is summation.

Question 3

Define subliminal stimulus.

Answer 3

One that is below threshhold for conscious perception

Question 4

True or false: in spatial summation, if the nerve fibers are stimulated separately by subliminal stimuli, there is a response

Answer 4

FALSE: In spatial summation, if nerve fibers are stimulated separately by subliminal stimuli, there is no response. But if both are stimulated simultaneously, the signals summate to produce a response

Question 5

True or false: IPSPs can only be hyperpolarizing.

Answer 5

FALSE: IPSPs can also be initially depolarizing only if the equilibrium potential of the anions is below the threshhold required for firing action potential

Question 6

Difference between direct and indirect inhibition.

Answer 6

Direct inhibition a result of IPSP

Indirect inhibition a result of previous discharges by the neuron leading to refractory period and hyperpolarizations

Question 7

Presynaptic inhibition occurs over what type of synapses?

Answer 7

Axo-axonal synapses

Question 8

3 mechanisms of presynaptic inhibition

Answer 8

1. Increase Chlorine (-ve) conductance (via GABA binding to GABA a receptors) = decrease in calcium and therefore neurotransmitter realeased
2. Opening voltage gated Potassium channels (via GABA binding to GABA b receptors) = decrease in calcium
3. Direct inhibition independent of calcium levels

Question 9

How Baclofen treats spasticity in spinal chord injuries.

Answer 9

Acts like GABAb agonist to cause presynaptic inhibition and reduce neurotransmitter released so muscles are not always receiving signal to contract

Question 10

Presynaptic faciliation

Answer 10

Calcium channels kept open for longer to prolong action potential

Question 11

Can neurons inhibit themselves?

Answer 11

Yes. Via negative feedback inhibition by internuncial neuron.

Question 12

Define LATENCY of a synpatic potential?

Answer 12

amount of time it takes for signal to pass from presynaptic to post synaptic neuron

Question 13

Is it EPSPs or IPSPs that are caused by decrease in potassium (+ve) conductance?

Answer 13

EPSPs because slower influx

Question 14

At chemical synapses, the electrical currents generated by the action potential in the pre-synaptic terminal have little effect on the post-synaptic cell because

Answer 14

low resistance of the extra-cellular fluid combined with the relatively high resistance of the post-synaptic membrane means that little current enters the post-synaptic cell.