Membrane Potentials

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the cell membrane when the cell is not actively sending a signal. It is primarily determined by the distribution of ions, such as sodium (Na+), potassium (K+), and chloride (Cl-), and the selective permeability of the cell membrane.

• Key Contributors: Sodium-potassium pump, ion channels, and membrane permeability.

• Typical Value: For most animal cells, the resting membrane potential is around -70 mV.

• Equation:

Additional info: This is the simplified Nernst equation for potassium ions; the Goldman-Hodgkin-Katz equation is used for multiple ions.

Action Potentials

An action potential is a rapid change in membrane potential that travels along excitable cells such as neurons and muscle cells. It is initiated when the membrane potential reaches a threshold, causing voltage-gated ion channels to open.

• All-or-None Principle: Action potentials occur fully or not at all once threshold is reached.

• Graded Potentials: These are changes in membrane potential that vary in magnitude and do not necessarily lead to an action potential.

• Hyperpolarization: Occurs when the membrane potential becomes more negative than the resting potential.

• Refractory Period: The period after an action potential during which a neuron cannot fire another action potential.

• Equation:

Pacemaker Cells

Pacemaker cells are specialized muscle cells (such as those in the heart) that can spontaneously generate action potentials without external stimuli.

• Function: Regulate rhythmic activities, such as heartbeat.

Cellular and Tissue Properties

Endothelial Cells and Erythrocytes

Endothelial cells line blood vessels and interact with circulating blood cells, such as erythrocytes (red blood cells).

• Function: Maintain the blood-brain barrier, regulate blood flow, and facilitate exchange of substances.

Sensory Systems

Purely Sensory Cranial Nerve

The cranial nerves are a set of nerves that emerge directly from the brain. Some are purely sensory, such as the optic nerve (vision).

• Example: The optic nerve is an example of a purely sensory cranial nerve.

Referred Pain and Sensory Cortex

Referred pain occurs when pain from one part of the body is perceived as coming from another area. The sensory cortex allocates more space to regions with higher sensitivity, such as the upper lip.

• Example: Pain from a heart attack can be felt in the jaw or arm.

Free Nerve Endings: Temperature and Pain

Free nerve endings are responsible for detecting changes in temperature and pain. They are found throughout the body and respond to various stimuli.

• Function: Detect noxious stimuli and temperature changes.

Tonic Receptors

Tonic receptors are sensory receptors that adapt slowly to stimuli and continue to produce action potentials over the duration of the stimulus.

• Example: Sensitivity to light after entering a dark room.

Summary Table: Membrane Potentials and Sensory Receptors