Unit 2 Membrane Potential

Membrane potential

The electrical difference (voltage) across a cell membrane caused by unequal distribution of ions between the intracellular and extracellular fluids.

Cause of membrane potential

It results from selective permeability of the membrane to certain ions (mainly K⁺ and Na⁺) and the activity of ion pumps.

Potassium concentration

has a higher concentration inside the cell

Sodium concentration

has a higher concentration outside the cell

Potassium movement

moves out of the cell through leak channels.

Sodium movement

moves into the cell through leak channels.

Potassium Membrane potential

The inside becomes very negative until equilibrium is reached (around -90 mV).

Sodium Membrane potential

The inside becomes very positive until equilibrium is reached (around +60 mV).

Factors affecting membrane potential

Ion concentration gradients, membrane permeability to specific ions, and the activity of ion pumps.

Types of ion transport

Sodium-potassium pump (active), sodium leak channels, and potassium leak channels.

Sodium-potassium pump

Uses ATP to move 3 Na⁺ out and 2 K⁺ in per cycle, maintaining ionic gradients and negative resting potential.

Resting membrane potential

The stable electrical charge across the cell membrane at rest (typically about -70 mV in neurons).

Neuron use of membrane potentials

use changes in membrane potential to send and receive electrical signals

Dendrite

Branching extensions of the neuron that receive input signals from other neurons.

Soma (cell body)

Contains the nucleus and organelles; integrates incoming signals from dendrites.

Axon

Long fiber that carries electrical impulses (action potentials) away from the cell body.

Myelin sheath

Fatty insulation around axons that speeds up the conduction of electrical impulses.

Axon terminal (synapse)

End of the axon where neurotransmitters are released to communicate with other neurons or target cells.

Integration region of neuron

Axon hillock — where incoming signals are processed and an action potential is triggered if threshold is reached.

Output region of neuron

Axon terminals — where the neuron sends information to another cell via neurotransmitter release.

Input region of neuron

Dendrites and cell body — where the neuron receives information.