Action potential

More dendrites =

More integration

The neural membrane is selectively

porous: chooses what molecules go through

Where is the neural membrane

on the axon

Potential meaning

electric charge

Resting membrane potential

• state of electrical charge when it is not altered by an electrical charge.

• -70mV

what is the measured voltage inside the cell compared to outside

-70mV

What are ions

They are + and - charged particles. + ion lost an electron and a negative ion gained an electron

What are the ions involved in potential?

Na⁺, Cl^-, K⁺ and protein anions

What keeps the RMP potential negative?

• Concentration

• Diffusion

• Electrostatic pressure

• Differential permeability to ions

• They cancel out.

Concentrations of ions inside and outside the cell.

More sodium and Cl^- ions outside of the cell

More ions of potassium and protein anions are inside the cell.

Diffusion definition and what it means for the ions.

• movement from High to low concentration

• K+ moves from inside to outside the cell

• Cl- wants to move from outside the cell to inside the cell

• Na+ wants to move from outside the cell to inside the cell

Electrostatic pressure

• opp attract:

• similar repel

• K+ is attracted inside the cell

• Na is attracted inside the cell

• Cl is attracted to the outside the cell

Permeability for ions

• The membrane is very permeable to K+

• The membrane is relatively impermeable to Na

• The membrane is permeable to Chlorine ions

What do these ions travel through?

• ion channels

• Some channels are specific to ions

• More K+ leaked channels than Na+; K can move more freely.

Types of ion channels

1. Leaked ion channels: always open.

2. Voltage-gated channels: change in potential

3. ligand-gated channels: binding of neurotransmitters

What keeps concentrations constant?

Sodium potassium pump

What does the sodium potassium pump do, and how does it do it?

• pumps 3 Na+ and 2K + in

• Uses ATP/ energy

Action Potential

• a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific cell rapidly rises and falls.

• Caused by a stimulus or a chemical

• causes depolarization: separation of charges is close to 0. changes in membrane potential to be more positive (+)

• Starts when the threshold is crossed at -60mV

Small changes in membrane potential caused by neurotransmitters are called

Post synaptic potentials

Steps of action potential

1. Sodium channels open: Na+ rushes in also due to diffusion. Increases EP up to +40mV

2. Potassium channels open; K+ starts to leave the cell close to the peak of the action potential

3. At +40mV Na+ is inactive, and sodium channels become inactive. K+ continues to exit

4. Overshooting RMP (hyperpolarizing) Potassium channels gradually regain the ability to open again.

Repolarization

repolarize the cell. Reduce the charge back to the resting membrane potential

Hyperpolarization

The cell becomes more negative than the resting membrane potential.

in myelinated axons, the action potential jumps between ———-. The process is called ————-

nodes of Ranvier. saltatory conduction.

time between depolarization and hyperpolarization

2-5 milliseconds

Refractory periods and what are they responsible for

Rate of neural firing being related to intensity of stimulation. his is the period, during and after the action potential, during which, another action potential

cannot be generated.

• Absolute refractory period

• Relative Refractory period

Absolute refractory period

• From depolarization to the end of repolarization

• it is absolutely not possible to induce a new action potential

• sodium channels are inactivated

Relative refractory period

it is possible to induce a new action potential but it takes more strength (more energy or electricity)

All or none law

action potential are full or not at all. No small action potential or half potential.

Where is an action potential first generated?

Axon hillock