Impulse Transmission

Question 1

What is a reflex arc?

Answer 1

A reflex arc is the basic functional unit of the nervous system and is the pathway that a reflex takes in the body.

Question 2

What is the threshold potential?

Answer 2

The threshold potential is the minimum amount of stimulus that will result in the firing of an action potential.
Raise membrane potential from -70mV to -55mV

Question 3

What are action potentials?

Answer 3

An action potential is is the rapid depolarization/change in voltage of the membrane polarization from -70mV to +35mV

Question 4

What is membrane resting potential?

Answer 4

The resting potential is -70mV when the cell membrane is at rest and is polarized. The membrane is more permeable to K+ than to Na+ so there is more potassium inside the cell and more sodium outside the cell.

Question 5

How is membrane voltage/potential determined?

Answer 5

The membrane resting potential is determined by the uneven concentration of ion between the extracellular and intracellular fluid and is determined by the permeability of each ion.

Question 6

What is the concentration of ions when the membrane is at rest?

Answer 6

During the resting membrane potential there are more sodium ions (Na+) outside than inside the neuron and more potassium ions (K+) inside. K+ ions leak out of the cell down their concentration gradient through potassium channels leading to a net negative charge inside the cell.

Question 7

What is impulse transmission?

Answer 7

Impulse transmission occurs from ion movement and creates a small temporary shift in the voltage of a neuron’s membrane.

Question 8

Where are Na+ ions, K+ ions, and negative ions in abundance?

Answer 8

Na+ ions are in abundance outside of the cell.
K+ and negative ions are in abundance in the inside of the neuron.

Question 9

What are the six steps of a nerve impulse?

Answer 9

1) A stimulus surpasses the threshold value and disrupts the resting potential.
2) The membrane become permeable to Na+ and the inflow of sodium is transported through proteins called sodium gates/channels.
3) The inflow of Na+ changes the voltage and the membrane gains a positive charge (depolarization)
4) the electrical change causes the Na+ channels to close and the K+ channels/gates to open.
5) K+ move to the outside of the cell through K+ gates which restores the polarity of the membrane (repolarization)
6) The Na/K pump is activated and returns ions to their original concentration.

Question 10

What is depolarization?

Answer 10

Depolarization is when the membrane becomes less negative (more positive)

Question 11

What is repolarization?

Answer 11

Repolarization is the change in membrane potential that returns it to a negative value after the depolarization phase of an action potential has changed the membrane potential to positive value.

Question 12

What is hyperpolarization?

Answer 12

Hyperpolarzation is when the membrane potential becomes more negative at a particular location on the neuron’s membrane during the refractory period.

Question 13

What numbers are commonly associated with membrane resting potential, threshold potential, depolarization, repolarization, and hyperpolarization?

Answer 13

Membrane resting potential: -70mV
Threshold potential: -55mV
Depolarization: -55mV to +40mV
Repolarization: +40mV to -70mV
Hyperpolarization: more negative than -70mV

Question 14

What is the movement of ions during depolarization and repolarization?

Answer 14

Depolarization: Na+ ions in
Repolarization: K+ ions out

Question 15

What are voltage-gated ion channels?

Answer 15

Voltage gated ion channels are integral membrane proteins which are activated by a depolarized membrane potential resulting in a conformational change and allow ions to travel.

Question 16

What is the function of the Na/K pump?

Answer 16

The Na/K pumps (protein) that are responsible for establishing and maintaining the ion distribution and resting potential.

Question 17

What are the first three steps of the sodium potassium pump?

Answer 17

1) ATP is broken down and the phosphate group prompt the pump to undergo a conformational change.
2) 3 sodium ions are released into the extracellular fluid.
3) At the same time, 2 potassium ions prompts another conformational change that returns the pump to its previous configuration and the cycle begins again.

Transmembrane protein

Question 18

What is the movement of ions in the Na/K pump?

Answer 18

Each cycle of the pump causes 3 sodium ions to move out of the cell and 2 potassium ions to move into the cell. Because there is one more positive charge leaving the call than entering, there is a net loss of positive ions which makes the resting potential of the membrane more negative.

Question 19

What are three simplified steps of an action potential?

Answer 19

1) Neurotransmitters bind to receptor proteins on the dendrites of a neuron and causes depolarization.
2) The neuron reaches threshold potential and sodium channels open which allows an influx of of positive ions and initiates the action potential.
3) At its peak, sodium channels close and potassium channels open and potassium flows out of the cell. The loss of positive potassium ions prompt repolarization and the neuron returns to its resting potential.

Question 20

What is saltatory conduction?

Answer 20

The ionic movement in one region of an axon affects the others and they undergo the same changes (sodium rushes in followed by potassium rushing out followed by active transport to restore ionic concentrations). The impulse jumpers between the nodes of Ranvier and speed up the impulse.

Question 21

What is a gate on a protein channel?

Answer 21

The charge of the channel, shape, and size indicate what can cross the cell membrane. The protein channel can have a gate at the top of the channel that only opens at certain conditions and remain closed unless they receive a specific electrical signal.

Question 22

What is the difference between an excitatory and inhibitory neurotransmitter?

Answer 22

An excitatory transmitter promotes the generation of an electrical signal called an action potential in the postsynaptic neuron, while an inhibitory transmitter prevents it. In both cases, neurotransmitters binding to receptors open or close ion channels in the postsynaptic neuron.

Question 23

What are the possible effects of excitatory and inhibitory neurotransmitters?

Answer 23

Excitatory neurotransmitter cause depolarization (decrease in membrane potential). Inhibitory neurotransmitter cause hyperpolarization (increase in membrane potential).