Sept 24th: Communication: Neurons and the Action Potential

What is the resting membrane potential?

• The voltage (millivolt) difference between intracellular and extracellular fluid

• we have this because ions are not evenly distributed

Which cells have an RMP

ALL CELLS HAVE A RESTING MEMBRANE POTENTIAL, but the actual voltage may vary

What is the RMP of a neuron

-70 mV

What two factors affect cells membrane potential

1. conc. gradient of different ions across the membrane

2. the permeability of the membrane to those ions

What is the function of the Na+-K+ ATPase and its role in the maintenance of the resting membrane potential?

Function: To actively move three sodium ions out of the cell and two potassium ions into the cell using energy from ATP

Role: Maintains conc. gradient of Na+ and K+

How do mechanically gated ion channel open?

Opens when: the membrane is stretched

How do chemically gated ion channels open?

Opens when: a chemical (ligand) binds

How do voltage gated ion channels open?

Opens when: a cell’s voltage changes

Label the neuron

What are the Four Functional Zones of a Neuron

Structure + purpose

1. Input Zone: Dendrites and cell body (receives incoming signals)

2. Trigger Zone: Axon hillock (initiates the action potential if threshold is met)

3. Conducting Zone: Axon (transmits the electrical impulse over a distance)

4. Output Zone: Axon terminals (releases neurotransmitters to communicate with target cells)

What is depolarization

cell becomes more +

What is repolarization

cell returns to the RMP

What is the threshold

the minimum voltage that will initiate an action potential

What is hyperpolarization

a membrane potential that is more negative than the RMP

The — the stimulus = the — the graded potential

larger

larger

What are the properties of an action potential

what channel?

what direction?

threshold magnitude?

amplitude?

where does it occur?

Refractory period?

• voltage-gated channels

• travel down axon (one way)

• all or none (threshold)

• same amplitude

• occurs in axon

• has refractory period to prevent overlapping signal or backward signal

What are properties of graded potential?

what channel does it open?

size of amplitude?

direction?

where does it occur?

refractory period?

• mechanically-gated or chemically-gated channels

• size varies

• can be depolarizing or repolarizing (both directions)

• occurs in input zone (dendrite and soma)

• no refrac. period= multiple graded potentials can sum up