12.8- Physiological Events in the Neuron Segments

Question 1

What are the three types of chemically gated channels in the receptive segment of the neuron?

Answer 1

Cation, K+, and Cl-

Question 2

How long do graded potentials last?

Answer 2

While the Na+ channels are open and until the ion current ceases.

Question 3

The degree of change is dependent on what?

Answer 3

The degree of magnitude.

Question 4

Depolarization

Answer 4

The change of membrane potential in the positive direction.

Question 5

Hyperpolarization

Answer 5

When chemical gated channels allow K+ to flow out of the cell or Cl- to enter the cell. Making the cell more negative than prior compared to the IF.

Question 6

Postsynaptic potentials that result in the cell becoming move positive are called?

Answer 6

Excitatory Postsynaptic potentials- aka depolarization- Na+ rushing into cells and K+ out.

Question 7

Postsynaptic potentials that result in the cell becoming less positive are called?

Answer 7

Inhibitory postsynaptic potentials- aka hyperpolarization- K+ out of the cell or Cl- into cell.

Question 8

Spacial summation

Answer 8

two or more presynaptic neurons stimulating the postsynaptic neuron and creating summation.

Question 9

Temporal summation

Answer 9

Summation cause by only one presynaptic neuron firing rapidly to stimulate the postsynaptic neuron.

Question 10

How is summation triggered by the initial segment?

Answer 10

The voltage gated channels must be stimulated by a minimum level of membrane potential. This is how the axon hillock “decides” if it will allow an action potential to extend down the axon. This threshold is -55 mV, a change of 15 mV from it’s original -70mV.

Question 11

Threshold membrane potential

Answer 11

Minimum voltage change needed to cause a potential.

Question 12

Subthreshold value

Answer 12

Any voltage that is generated but not sufficeintly to cause a potential.

Question 13

All-or-none law

Answer 13

Law that says the minimum voltage must be reached to cause any potential, and that if a potential is released it will be completely. There are no weak or strong potentials.

Question 14

What two process make up an action potential?

Answer 14

Depolarization and repolarization

Question 15

What is depolarization the result of?

Answer 15

The opening of voltage gated Na+ channels allowing a rapid influx of Na+ into the cell.

Question 16

What is repolarization?

Answer 16

The opening of voltage gated K+ channels and the subsequent movement of K+ out of the cell.

Question 17

Nerve impulse

Answer 17

The propagation of an action potential down the axolemma.

Question 18

What happens during hyper polarization?

Answer 18

The K+ channels stay open longer than they need to to create the -70 mV resting potential creating a charge more negative than the RMP. Usually around -80 mV.

Question 19

refractory period

Answer 19

The period of time after depolarization when an axon is not yet ready to generate another action potential, or greater than normal stimulation is required to cause another action potential.

Question 20

Absolute refractory period

Answer 20

Period after depolarization when no amount of stimulation will cause another depolarization.

Question 21

What does repolarization do to the voltage gated Na+ channels?

Answer 21

Causes them to go into a resting state instead of an inactive state. During the time while this is the case, the absolute refractory period is in effect.

Question 22

Relative refractory period

Answer 22

Period of time after depolarization when larger the normal stimulus is required to cause another depolarization.

Question 23

Where does continuous conduction happen?

Answer 23

Unmyelinated axons.- Voltage gated channels open and close along the entire length of the axon.

Question 24

Where does saltatory conduction happen?

Answer 24

In myelinated axons.- Voltage gated channels only open and close in the neurofibril nodes between myelin sheaths.