BackMembrane Potentials and Signal Transmission in Neurons
Study Guide - Smart Notes
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Membrane Potentials and Signal Transmission
Types of Electrical Signals in Neurons
Neurons communicate using electrical signals that result from changes in membrane potential. There are two main types of signals:
Graded potentials: Small, localized changes in membrane potential that vary in size and decay with distance from the stimulus.
Action potentials: Large, rapid changes in membrane potential that propagate along the axon without decreasing in size.
Key Terminology: Membrane Potential Changes
Membrane potential refers to the voltage difference across a cell's plasma membrane. The following terms describe changes in membrane potential during neuronal signaling:
Term | Description | Membrane Potential Change | State |
|---|---|---|---|
Polarized | Inside of membrane is negative (about -70 mV) | Resting potential | Cell at rest |
Depolarization | Inside of membrane becomes less negative | Temporary decrease in membrane potential | Signal initiation |
Repolarization | Inside of membrane becomes more negative | Return to resting potential | Signal recovery |
Hyperpolarization | Inside of membrane becomes more negative than resting potential | Temporary increase in membrane potential | Inhibitory state |
Graphical Representation of Membrane Potential Changes
The graph below illustrates how membrane potential changes over time during an action potential. The Y-axis represents membrane potential (mV), and the X-axis represents time (ms).
Polarization: The neuron is at its resting potential (about -70 mV).
Depolarization: The membrane potential rapidly rises, becoming less negative (up to +30 mV).
Repolarization: The membrane potential returns toward the resting value.
Hyperpolarization: The membrane potential temporarily becomes more negative than the resting potential before stabilizing.
Example
If a neuron's membrane potential changes from -90 mV to -10 mV, this is described as depolarization, because the inside of the membrane becomes less negative.
Definitions of Key Terms
Membrane potential: The electrical potential difference across a cell's plasma membrane.
Resting potential: The stable, negative charge of a neuron when it is not transmitting a signal (typically around -70 mV).
Depolarization: A decrease in membrane potential (the inside becomes less negative).
Repolarization: The process of returning the membrane potential to its resting value after depolarization.
Hyperpolarization: An increase in membrane potential (the inside becomes more negative than the resting potential).
Equations
The membrane potential can be estimated using the Nernst equation for a single ion:
Where:
= equilibrium potential for the ion
= universal gas constant
= temperature in Kelvin
= charge of the ion
= Faraday's constant
= concentration of the ion outside the cell
= concentration of the ion inside the cell
Summary Table: Membrane Potential Changes
Process | Direction of Change | Effect on Neuron |
|---|---|---|
Depolarization | Less negative | Excitatory, may trigger action potential |
Repolarization | More negative (toward resting) | Restores resting state |
Hyperpolarization | More negative than resting | Inhibitory, reduces likelihood of firing |
Additional info: The notes have been expanded to include definitions, equations, and context for membrane potential changes in neurons, suitable for college-level Anatomy & Physiology students.
