Nervous System Physiology Part 3

Question 1

What does Unidirectional transmission of signals involve?

Answer 1

Involves the release of chemical messengers from one neuron to affect another.

Question 2

What event arrives at the axon terminal of the presynaptic neuron?

Answer 2

Action potential

Question 3

What type of channels open in the presynaptic neuron membrane upon arrival of the action potential? What ion passes through these channels?

Answer 3

Voltage-gated Ca2+channels open.
Ca2+calcium ions) pass through the channels

Question 4

Where does Ca{2+}enter after the voltage-gated channels open?

Answer 4

The presynaptic neuron (specifically, the axon terminal).

Question 5

What do Ca2+ signals trigger within the presynaptic neuron?

Answer 5

signals the neurotransmitter vesicles.

Question 6

What happens to the neurotransmitter vesicles as a result of the Ca$^{2+}$ signal?

Answer 6

Vesicles move to the membrane and dock.

Question 7

How are neurotransmitters released from the presynaptic neuron into the synaptic cleft?

Answer 7

Via exocytosis.

Question 8

What do neurotransmitters do once they are released into the synaptic cleft?

Answer 8

Neurotransmitters bind to receptors on the postsynaptic cell.

Question 9

What is initiated in the postsynaptic cell upon neurotransmitter binding?

Answer 9

A graded potential (which may or may not lead to an action potential).

Question 10

Many receptors on postsynaptic membranes at chemical synapses are specialized to

Answer 10

open ion channels, converting chemical signals to electrical signals.

Question 11

What do neurotransmitter receptors do for graded potentials?

Answer 11

Neurotransmitter receptors mediate graded potentials.

Question 12

What are graded potentials?

Answer 12

Graded potentials are local changes in membrane potential that vary in strength.

Question 13

What does the strength of a graded potential depend on?

Answer 13

• The strength of a graded potential depends on the amount of neurotransmitter released and how long it remains in the

Question 14

Where does Graded Potential occur and where does Action Potential occur?

Answer 14

• Graded Potential: Usually dendrites and cell body
• Action Potential: Trigger zone through axon

Question 15

Types of gated ion channels involved in graded potential and action potential

Answer 15

Graded Potential: Mechanically, chemically, or voltage-gated channels
* Action Potential: Voltage-gated channels

Question 16

Ions involved in graded potential and action potential

Answer 16

Graded Potential: Usually Na ion K ion Cl ion
* Action Potential: Na ion and K iona

Question 17

Type of signal used in graded potential and action potential

Answer 17

Graded Potential: Depolarizing (e.g., Na$^+) or hyperpolarizing (e.g., K^+$ or Cl$^-$)
* Action Potential: Depolarizing

Question 18

Strength of signal in graded potential and that of action potential

Answer 18

Graded Potential: Depends on initial stimulus; can be summed
* Action Potential: All-or-none phenomenon; cannot be summed

Question 19

What initiates the signal in graded potential and action potential

Answer 19

Graded Potential: Entry of ions through channels
* Action Potential: Threshold stimulus graded potential at the trigger zone

Question 20

Unique characteristics of graded potential and action potential

Answer 20

Graded Potential:
* No minimum level required to initiate
* Two signals coming close together in time can summate
* Initial stimulus strength is indicated by frequency of a series of action potentials
* Action Potential:
* Threshold stimulus required to initiate
* Refractory period: two signals too close together in time cannot summate

Question 21

What can increase the amplitude of graded potential?

Answer 21

Stimulus responses can summate to increase the amplitude of the graded potential.

Question 22

What is the difference between temporal and spatial summation?

Answer 22

Temporal Summation: Increased frequency of stimuli from a single presynaptic neuron can add together.
* Spatial Summation: Stimuli from multiple sources (different presynaptic neurons) arriving at the same time can add together.

Question 23

What are the two main types of postsynaptic potentials?

Answer 23

Excitatory Postsynaptic Potentials (EPSPs)
* Inhibitory Postsynaptic Potentials (IPSPs)

Question 24

At excitatory synapses, what happens when neurotransmitters bind to the postsynaptic membrane? What is the result?

Answer 24

Neurotransmitter binding depolarizes the postsynaptic membrane.

Question 25

What type of ion channels are opened during an EPSP? What ions flow and in what direction?

Answer 25

Opens chemically gated channels that allow simultaneous Na$^+$ and K$^+$ fluxes. * Each channel allows Na$^+$ and K$^+$ to diffuse simultaneously through the membrane but in opposite directions. * Na$^+$ influx is greater than K$^+$ efflux, resulting in a net depolarization.

Question 26

EPSP Effect on Membrane Potential: What is the typical change in membrane potential during an EPSP?

Answer 26

The membrane potential depolarizes, moving toward 0 mV from the resting potential (e.g., -70 mV).

Question 27

What do most inhibitory neurotransmitters cause in the postsynaptic membrane? How do they achieve this?

Answer 27

Most inhibitory neurotransmitters hyperpolarize the postsynaptic membrane by making the membrane more permeable to K$^+$ or Cl$^-$.

Question 28

If K$^+$ channels open during an IPSP, in which direction does K$^+$ move? What effect does this have on the membrane potential?

Answer 28

If K$^+$ channels open, K$^+$ moves out of the cell. This causes the inside of the membrane to become more negative, resulting in hyperpolarization.

Question 29

If Cl$^-$ channels open during an IPSP, in which direction does Cl$^-$ move? What effect does this have on the membrane potential?

Answer 29

If Cl$^-$ channels open, Cl$^-$ moves into cell. In either case (depending on the initial membrane potential and Cl$^-$ concentration), the charge on the inner face of the membrane becomes more negative (hyperpolarization) or it stabilizes the membrane potential preventing depolarization.

Question 30

What is the typical change in membrane potential during an IPSP?

Answer 30

The membrane potential hyperpolarizes, moving toward a more negative value (e.g., -90 mV) from the resting potential (e.g., -70 mV).