Resting Membrane Potential and Action Potentials

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the plasma membrane of a cell when it is not actively sending a signal. This potential is crucial for the function of excitable cells such as neurons and muscle cells.

• Key Contributors: The sodium-potassium pump, ion channels, and selective permeability of the cell membrane maintain the resting potential.

• Typical Value: For most neurons, the resting membrane potential is approximately -70 mV.

• Equation: The Nernst equation can be used to calculate the equilibrium potential for a particular ion:

• Example: The resting potential is essential for the transmission of nerve impulses.

Action Potentials

An action potential is a rapid change in membrane potential that travels along the membrane of excitable cells, such as neurons and muscle fibers.

• All-or-None Principle: Action potentials are triggered only if the membrane potential reaches a certain threshold; otherwise, no action potential occurs.

• Graded Potentials: These are changes in membrane potential that vary in magnitude and do not follow the all-or-none principle. They can summate to trigger an action potential.

• Hyperpolarization and Action Potentials: Prolonged opening of chloride channels or potassium channels can cause hyperpolarization, making the neuron less likely to fire an action potential.

• Relative Refractory Period: After an action potential, a stronger stimulus is required to generate another action potential due to the efflux of potassium ions ().

• Equation: The Hodgkin-Huxley model describes the ionic basis of action potentials:

• Example: Action potentials are responsible for the transmission of signals in nerves and muscles.

Specialized Cells and Structures

• Pacemaker Cells: These muscle cells can spontaneously generate action potentials without external input, crucial for maintaining the heartbeat.

• Endothelial Cells: These cells line blood vessels and interact with other cell types to regulate blood flow and maintain the blood-brain barrier.

• Purkinje System: Specialized cardiac fibers that conduct electrical impulses rapidly through the heart.

Sensory Receptors and Cranial Nerves

• Purely Sensory Cranial Nerve: The optic nerve is an example of a cranial nerve that is purely sensory, responsible for vision.

• Referred Pain in Myocardial Infarction: Pain from the heart attack can be felt in areas such as the jaw, due to shared neural pathways.

• Somatosensory Cortex Representation: The brain allocates more space to the upper lip, eyes, and hands, reflecting their sensitivity.

• Free Nerve Endings for Temperature and Pain: These are responsible for detecting changes in temperature and pain.

• Tonic Receptors: These receptors are activated during prolonged or continuous stimuli, such as heightened sensitivity to light after entering a dark room.

Table: Types of Sensory Receptors

Additional info: The above notes expand on the brief points in the source material to provide a comprehensive overview suitable for General Chemistry students, including definitions, examples, and equations relevant to membrane potentials and action potentials.