Graded Potentials & Action Potentials

Question 1

What are Gated Ion Channels?

Answer 1

• Different from ion leak channels
• Opened or closed depending on the conditions of the environment (i.e., mechanically, chemically or voltage-gated)

Question 2

What does it mean when the membrane is Polarized?

Answer 2

there is a potential difference (inside and outside the cell have a different net charge)
polarization refers to the resting state of the cell membrane, where the inside of the cell is negatively charged relative to the outside

Question 3

What does it mean when a membrane is Depolarized?

Answer 3

potential becomes less negative (closer to 0)
the inside of the cell less negative compared to the outside

Question 4

What does it mean to Overshoot?

Answer 4

reversal of membrane potential polarity (i.e., inside of the cell becomes positive relative to the outside).

Question 5

What does it mean for the membrane to be Repolarized?

Answer 5

When a membrane is repolarized, it means that the membrane potential is returning to its resting state after being depolarized

Question 6

What are Graded Potentials?

Answer 6

Graded potentials are local changes in the membrane potential of neurons in response to stimuli. They occur when ion channels open, allowing ions to flow across the membrane and causing a temporary change in the membrane potential, which can either depolarize or hyperpolarize the cell.

Graded potentials vary in size depending on the strength of the stimulus and decay over short distances.

Question 7

How do graded Potentials Work?

Answer 7

Electrical signal decreases with distance, therefore signal can only travel a few millimeters

Summation can take place if another stimulus arrives before the graded potential has diminishe

Can initiate action potentials

Question 8

What are Action Potentials?

Answer 8

• Large alterations in membrane potential (up to 100 mV) - DEPOLARIZATION
• Very rapid (1-4 ms), may repeat at frequencies of several hundred per second
• Communicate over large distances
• Fixed size and duration
• ALL OR NOTHING

Question 9

What are Voltage-Gated Ion Channels?

Answer 9

Vary by which ion they conduct (i.e., K+, Na+, Cl-, Ca2+).

• K+ and Na+ can reversibly change in shape in response to changes in membrane potential

Question 10

When are Voltage Gated Channels Closed?
When are they Open?

Answer 10

• Channels closed: when membrane potential is negative (i.e., resting)
• Channels open: during depolarization

Question 11

Do Na+ or K+ channels open first?

Answer 11

• Na+ channels respond faster to changes in membrane voltage (i.e., they open and close before K+ channels)
• Inactivation gate limits Na+ flux shortly after depolarization opens it

Question 12

How do Action Potentials Initiate?

Answer 12

1. The membrane potential is at its resting value of ~-70 mV.
2. When NT bind to receptors on a dendrite, they depolarize the neuron
3. Once the membrane potential reaches its threshold (-55mV), Na+ ions enter the cell and depolarize to a + value

Note: For an AP to be generated, a depolarizing stimulus is required (i.e., presence of neurotransmitter). This causes local opening of voltage-gated Na+ channels, Na+ influx and local depolarization.

Question 13

What happens once peak membrane potential is reached during an Action Potential?

Answer 13

4. Peak membrane potential is reached, Na+ channels close. Voltage-gated K+ channels open, causing K+ flux out of the cell.
5. Cell begins to repolarize.
6. Return to (-) resting membrane potential closes Na+ and K+ channels but K+ channels are slower; therefore, K+ permeability is greater than resting level, causing hyperpolarization.
7. Resting membrane potential is restored

Question 14

What is the Positive Feedback Mechanism During an AP?

Answer 14

During an action potential (AP), positive feedback occurs when the depolarization of the cell membrane opens voltage-gated sodium channels, allowing an influx of sodium ions, which further depolarizes the membrane and opens more sodium channels. This cascade of events rapidly increases the membrane potential towards its peak, leading to the generation of the action potential.

Question 15

What is the Negative Feedback Mechanism During an AP?

Answer 15

During an action potential (AP), the negative feedback mechanism involves the repolarization phase, where the opening of voltage-gated potassium channels allows the efflux of potassium ions, leading to the restoration of the resting membrane potential. This repolarization counteracts the depolarization caused by sodium influx during the AP, helping to restore the membrane potential to its resting state and prevent sustained depolarization.

Question 16

How does Increasing the strength of the stimulus past threshold affect the action potential?

Answer 16

Increasing the strength of the stimulus past threshold does not
result in “bigger” action potentials

Question 17

How do Action potentials Propagate in Unmyelinated Fibres?
1

Answer 17

In unmyelinated fibers, action potentials propagate relatively slowly compared to myelinated fibers because each action potential depolarizes the membrane along the entire length of the axon

Question 18

How do Action potentials Propagate in Unmyelinated Fibres?
2

Answer 18

Question 19

How do Action potentials Propagate in Unmyelinated Fibres?
3

Answer 19

Question 20

How do Action potentials Propagate in Myelinated Fibres?

Answer 20

Saltatory conduction allows for fast and efficient transmission of electrical signals along myelinated axons, conserving energy and ensuring rapid communication within the nervous system.

Question 21

What are the stimuli that cause threshold potential, cause Na+ channels to open and the propagation of an action potential?

Answer 21

1. Receptor Potential
2. Synaptic Potentials
3. Pacemaker Potentials

Question 22

What are Receptor Potentials?

Answer 22

Produced at the peripheral endings of afferent neurons (or separate receptor cells) in response to a stimulus

Question 23

What are Synaptic Potentials?

Answer 23

Produced in the post-synaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal

Question 24

What are Pacemaker Potentials?

Answer 24

Spontaneously occurring changes in membrane potentials that occurs in specialized cells