How do neuron cells communicate with other neuron or muscle cells?

Neuron cells communicate with each other by changing the membrane potential

What are the 2 types of membrane potential changes?

The 2 types are: Post-synaptic Potential & Action Potential.

What is a post-synaptic potential?

It is a change in membrane potential of the post synaptic terminal of a chemical synapse; it initiates or inhibits an action potential.

Diagram of a chemical synapse

What are 2 types of postsynaptic potentials?

Excitatory postsynaptic potential (EPSP)Inhibitory postsynaptic potential (IPSP)

What is Excitatory Postsynaptic Potential (EPSP)?

Excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential.

What is depolarization?

Depolarization is a positive-going change in the cells membrane potential, making it more positive (or less negative).

How is the membrane potential excited by Excitatory Postsynaptic Potential (EPSP)?

Neurotransmitters bind to ligand gated ion channels of the postsynaptic neuron and causing influx of Na+ creating a more positive membrane potential.

What ion depolarizes the cell?

Sodium ion (Na+)

What is Inhibitory Postsynaptic Potential (IPSP)?

Inhibitory postsynaptic potential is a postsynaptic potential that makes postsynaptic neuron less likely to generate an action potential.

How does an Inhibitory Postsynaptic Potential (IPSP) prevent the cell from being actived?

Neurotransmitters bind to ligand-gated ion channel and causes influx of anions (Cl-) in the cell.

What are EPSP and IPSP called graded potentials?

Because they can vary in size depending on the strength of the input (stimulus or neurotransmitter)

What is temporal summation?

The addition of postsynaptic potentials (EPSP and IPSP) with time

When does temporal summation occur?

It occurs when postsynaptic neurons receive multiple stimulations within a short period of time.

What is spatial summation?

The addition of several input activating the postsynaptic neuron at different points of contact.

Can temporal and spatial summation occur simultaneously? What does it add to the cell?

Temporal and Spatial summation occur simultaneously and is use to amplify signals.

What happens if EPSP = IPSP?

No change occurs in electrical potential; nothing happens.

What is an Action Potential (AP)?

An action potential is a short-lasting event in which the electrical membrane potential rapidly rises and falls.

Why is Action Potential considered an all-or-none response?

Action potential is not a graded potential (does not depend on strength of input); either the action potential is produced or it is not.

What generates an Action Potential?

Several EPSPs that rises to a certain threshold potential will elicit an action potential.

What is that threshold?

A membrane potential of -55mV.

What happens if the stimulus produces a membrane potential less than -55mV?

No action potential is generated.

What are the components of an Action Potential?

REGION A: Resting membrane potential (RMP)

REGION E: Threshold

REGION B: Depolarization

Peak (END OF DEPOLARIZATION AND GREATEST MAGNITUDE OF DEPOLARIZATION)

REGION C: Repolarization

REGION D: Hyper repolarization

What happens inside the cell during depolarization?

Influx of sodium ion during which the membrane potential becomes more positive.

What are the two parts of depolarization?

Rising Phase part of depolarization that is below 0mV

Overshoot the portion of depolarization that is above 0mV; inside the cell is more positive than the outside of the cell.

What is repolarization?

Influx of potassium ion in which membrane potential becomes more negative.

What is another name for repolarization?

Falling Phase

What is hyper repolarization?

Period where membrane potential becomes more negative than the resting membrane potential.

Describe what occurs from the activation of an action potential to the cell returning to normal membrane potential.

Resting Membrane Potential is -70mV.

Neurotransmitter binds to ligand-gated Na+ channel creating an influx of Na+, the cell depolarizes.

EPSP generates a membrane potential that cross the threshold -55mV (temporal & spatial summation)

Pass -55mV, voltage-gated Na+ channels are activated; Na+ flows in cell (Rising Phase of depolarization)

More voltage-gated Na+ channels are opened (Hodgkin Cycle);

Rapid Na+ conductance allows Na+ to approach its equilibrium potential(Overshoot Phase of Depolarization)

Voltage-gated Na+ channels are closed by Inactivation Gate Plugs (Peak)

Voltage-gated K+ channels are stimulated and K+ exit the cell (Repolarization); cell becomes less positive

As cell become more negative again, voltage-gated K+ channels start to close.

Slow closing of Voltage-gated K+ channels allows K+ to nearly reach its equilibrium potential. (Hyper repolarization)

What 2 gates control voltage-gated Na2+ channels?

It has an activation gate and an inactivation gate

What opens the activation gate of voltage-gated Na2+ channels?

A membrane potential of +40mV

What closes voltage-gated Na2+ channels?

After a certain period of time when activation gate has open, the deactivation gate closes the voltage-gated Na2+ channel

When does the threshold start?

Voltage-gated Na+ channels open

When do we reach the peak of action potential?

Closing of voltage-gated Na+ channels, and opening of voltage-gated K+ channels

When does repolarization occur in action potential?

Voltage-gated K+ channels are open

When does hyper repolarization occur in action potential?

When membrane potential is more negative than resting membrane potential.

What is the Hodgkin cycle?

Positive feedback for sodium voltage-gated sodium channel; when 1 channel open, it influences other sodium channel to open

What is the absolute refractory period?

Period where it is impossible to have another action potential

Why cant another action potential be initiated during the absolute refractory period?

1. Voltage gated Na+ channels are already opened during the rising phase of depolarization

2. Voltage gated Na+ channels are closed by the inactivation gate.

What is the relative refractory period?

Period where another action potential can be generated but may be difficult to accomplish.

Why is it difficult to trigger another action potential during the relative refractory period?

Open voltage-gate K+ channels move the membrane potential farther from resting membrane potential; this requires a greater depolarization to open Na2+ voltage-gated channels.

Name 4 agents that can affect action potential?

LidocaineTetrodotoxin (TTX)CiguatoxinDendrotoxin

How does Lidocaine affect action potential?

Blocks Voltage-gated Na+ channels, no depolarization (no action potential)

How does Tetrodotoxin affect action potential?

Blocks Voltage-gated Na+ channels, no depolarization (no action potential)

How does Ciguatoxin affect action potential?

Lowers threshold for action potential; Voltage-gated Na+ channels may open and elicit action potential.

How does Dentrotoxin affect action potential?

Blocks Voltage-gated K+ channels, prolongs duration of action potential