Anatomy Exam 3: Generation and Propagation of Action Potentials

Resting Membrane Potential​: neurons

can rapidly change their membrane potential, highly excitable

Opposite charges _____________; same charges ____________.

attract, repel

potential energy

when opposite charges are separated by a membrane

voltage

the measure of potential energy generated by separated charges - the charge difference across a plasma membrane ​

current

flow of electrical charge (ions) from 1 point to another ​

resistance

hinderance to charge flow ​

Insulator

substance with high electrical resistance

Conductor

substance with low electrical resistance

generating resting membrane potential in the human body

The slight difference in the amount of positive and negative ions on either side of a cellular plasma membrane

two types on ion channels

Leakage (Nongated) Channels, Gated Channels

Leakage (Nongated) Channels

always open

Gated Channels

requires a change in protein shape to open/close the channel ​

3 types of gated channels

Chemically Gated​

Voltage Gated ​

Mechanically Gated

Chemically Gated​

open only with binding of a specific chemical (ex: neurotransmitter) ​

Voltage Gated ​

open/close in response to changes in the membrane potential ​

Mechanically Gated

open/close in response to physical deformation of receptors - ex: sensory receptors for touch/pressure​

two components of an electrochemical gradient

- Chemical concentration gradient - ions move from higher to lower concentration

-Electrical gradient - ions move toward the opposite electrical change ​

Ionic Composition: ECF

has higher concentration of Na+ than ICF ​

Ionic Composition: ICF

has higher concentration of K+ than ECF

Ionic Composition: K+

plays the most important role in membrane potential

Differences in Permeability of the Plasma Membrane: large anionic proteins

impermeable

Differences in Permeability of the Plasma Membrane: Cl-

Quite permeable

Differences in Permeability of the Plasma Membrane: Na+ ​

Slightly permeable

Differences in Permeability of the Plasma Membrane: K+ ​

25x more permeable to Na+

Through the leakage channels, which direction does Na+ move?

into the cell - down its concentration gradient ​

Through the leakage channels, which direction does K+ move?

diffuses out of a cell - down its concentration gradient ​

How is the negative resting membrane potential established?

More K+ diffuses out than Na+ diffuses in - interior of a cell is more negative

Which direction are Na+ and K+ moved through Na+/K+ pumps?

3 Na+ are pumped out of the cell while 2 K+ are pumped into the cell ​

Changes in membrane potential are produced by: ​

-Changes in the concentrations of ions across the membrane​

-Changes in membrane permeability to ions

Graded Potentials

incoming signals with variable strength operating over short distances

Action Potentials

long-distance signals of axons with consistent strength

depolarization

-decrease in membrane potential (moves towards zero and above) ​

-Inside of the membrane becomes less negative than resting membrane potential ​

-Probability of producing impulse increases

hyperpolarization

-increase in membrane potential (away from zero) ​

-Inside of the membrane becomes more negative than resting membrane potential ​

-Probability of producing impulse decreases ​

Why are graded potentials "graded"?

because their magnitude varies directly with stimulus strength ​

Postsynaptic Potential

produced when the stimulus is a neurotransmitter released by another neuron

Action potentials

the principal way neurons send signals over long distances ​

___________ potentials are often initially activated by ______________ potentials.

membrane potential, graded potential

The transition from graded potential to AP often takes place:

at the initial segment of the axon ​

What is the average change in membrane potential for an action potential?

~100 mV​

Activation Gates:

closed at rest; opens with depolarization to allow Na+ to enter ​

Inactivation Gates

open at rest; blocks the channel when it is open to prevent more Na+ from entering the cell ​

All-or-None

action potential either happens completely or does not happen at all

How does an action potential propagate?

Influx of Na+ through the voltage gates in one area of the membrane causes local currents that will depolarize adjacent areas of the membrane in the forward direction

Why is propagation a better term to describe what is happening in an axon than conduction?

AP is regenerated anew at each membrane patch; every subsequent AP is identical to the one that generated initially ​