Unit A - Describing the Nerve Impulse and Synapse

Question 1

What is the charge outside of the axon during resting membrane potential?

Answer 1

Positive relative to the inside

Question 2

What is the charge inside of the axon during resting membrane potential?

Answer 2

Negative relative to outside

Question 3

What are the three things that the cell membrane of the axon contains? What is needed for them to work?

Answer 3

1. Non-Voltage Gated Ion Channels - do not require a charge to work (some require chemicals instead)
2. Voltage-Gated Ion Channels - Require a specific charge to work
3. Na+/K+ Pump - Require STP to work

Question 4

At what potential difference is an axon’s resting membrane potential?

Answer 4

-70mV

Question 5

What is the polarization of the axon?

Answer 5

Process of generating a resting membrane potential (the potential to do work).

Question 6

What are the two things that are negatively charged that help achieve polarization? Why do they not go through the cell membrane?

Answer 6

Negatively charged proteins - too large to go through the membrane

Chloride ions - cannot go through the selectively permeable membrane

Question 6

What does the sodium-potassium exchange pump do in the axon?

Answer 6

Uses ATP to pump 3 sodium ions out of the axon and 2 potassium ions into the axon.

uses a single ATP

Question 7

Some ion channels in the axon membrane are ____ ____.

Why?

Answer 7

Always open

To ensure the inside of the axon is negative relative to the outside of the membrane.

Question 7

What is another word for nerve impulses?

Answer 7

Action Potentials

Question 8

When is the nerve impulse/action potential established?

Answer 8

When the axon is depolarizing. (passes the threshold)

Question 9

When a stimulus is applied to an axon, what initially happens to the axon?

Answer 9

It triggers the opening of a few non-voltage gated Na+ gates

Question 10

When no voltage passes through voltage-gated Na+ and K+ gates they remain ____

Answer 10

Closed

Question 11

What is the threshold needed to trigger the action potential?

Answer 11

-55mV

Question 12

What happens when a stimulus occurs but does not reach threshold potential?

Answer 12

Returns to normal without triggering.

Question 13

What happens when the threshold is reached and the action potential is triggered?

What happens to the polarity?

What is the voltage peak?

Answer 13

Voltage-gated NA+ channels open allowing even more NA+ to diffuse into the cell.

Polarity is reversed abruptly (becoming depolarized)

+35mV

Question 14

What happens when peak voltage is reached in a neuron?

Answer 14

• Causes the closing and inactivation of voltage-gated NA+ channels
• Voltage-gated K+ channels open (allowing for K+ to diffuse out)
  *The NA+/K+ pump helps assist the repolarization process.

Question 15

What is the process called of decreasing action potential?

is it fast?

Answer 15

Repolarization - very fast (ms - s)

Question 16

What is the period where repolarization happens? What cannot be done in this interval?

Answer 16

The period is called the refractory period. An impulse cannot be activated during this time.

Question 17

What happens after repolarization has reached the resting potential? Why?

Answer 17

It causes hyperpolarization (lower voltage than resting potential) because the K+ channels close slowly.

Question 18

What happens after hyperpolarization?

Answer 18

The membrane then returns to its resting potential.

Question 19

How does the action potential travel down the axon?

Why doesn’t it go backwards?

Answer 19

As the sodium moves into the axon, it diffuses into other parts of the axon, activating the threshold.

because of the refractory period. (that’s all the detail necessary to know)

Question 20

Where are Action potentials generated?

Answer 20

Where the axon membrane is exposed.

Question 21

what is continuous conduction?

Where does it occur?

Answer 21

Action potentials occur at every location along the membrane.

Unmyelinated neurons.

Question 22

What is faster continuous conduction or saltatory conduction?

Why?

Answer 22

Saltatory conduction

fewer channels open, shorter recovery, and less ion flow

Question 23

What is Saltatory conduction?

Answer 23

Action potentials that “jump” from one node of Ranvier to the next.

Question 24

What is the threshold level?

Answer 24

The size of the stimulus necessary to make a response.

Question 25

What is the all or none response?

Answer 25

Increasing the intensity of stimuli above threshold will not produce an increased nerve impulse, speed, or force of contraction.

Question 26

What are two ways intensity detection is interpreted?

Answer 26

1. Amount of neurons stimulated
2. Increased frequency of action potentials.

Question 27

What is a Synapse?

Answer 27

Small spaces between neurons or between neurons and effectors.

Question 28

What is a Neuromuscular Junction?

Answer 28

They are the specific synapses between a motor neuron and a muscle.

Question 29

What are the seven Steps to fire a synapse.

Answer 29

1. Nerve impulse (action potential) moves along the axon to the end plate (axon terminal/presynaptic) Which has small vesicles containing chemicals called neurotransmitters.
2. The neurotransimitters (ex: acetylcholine) are released from the presynaptic neuron and travel to the post-synaptic neurons via diffusion.
3. Neurotransmitters bind to receptors on the postsynaptic dendrite.
4. An excitatory neurotransmitter, OPENS cheically gated sodium channels → causing depolarization
5. Action potential!
6. The neurotransmitter is eventually deactivated by an enzyme (ex. Cholinesterase), resulting in the closure of cheically gated sodium channels.
7. Post-synaptic neuron begins repolarization. Componenets of neurotransmitter get reabsorbed by presynaptic knob and repackaged in vesicles.

Question 30

What is acetylcholine?

Answer 30

A common excitatory neurotransmitter.

Question 31

What is Cholinesterase?

Answer 31

An enzyme that breaks down acetylcholine (neurotransmitter)

Question 32

What is the difference between excitatory vs. inhibitory Neurotransmitters?

Answer 32

Excitatory - Stimulates an action potential
Inhibitory - prevents an action potential

Question 33

What is summation?

Answer 33

Many different neurons may influence a single neuron. Summation is the outcome of the simultaneous release of two or more excitatory and inhibitory neurotransmitters in a synapse.