Resting Membrane Potential

Definition and Contributors

The resting membrane potential is the electrical potential difference across the plasma membrane of a cell at rest. It is essential for the function of excitable cells such as neurons and muscle cells.

• Key Contributors:

  • Sodium-potassium pump: Actively transports Na+ out and K+ into the cell, maintaining concentration gradients.

  • Ion channels: Selective permeability to K+ and Na+ ions.

  • Synaptic transmission: Involves neurotransmitter release, but does not directly affect resting potential.

• Typical Value: Approximately -70 mV in neurons.

Equation

The Nernst equation estimates the equilibrium potential for a particular ion:

where is the equilibrium potential, is the gas constant, is temperature, is the ion charge, is Faraday's constant, and and are the extracellular and intracellular ion concentrations.

Action Potentials and Neural Signaling

All-or-None Principle

The all-or-none principle states that once the threshold is reached, an action potential is generated and propagates without decreasing in size along the axon.

• Application: Ensures reliable transmission of signals in excitable membranes.

Graded Potentials

Graded potentials are changes in membrane potential that vary in magnitude and do not follow the all-or-none law. They occur in dendrites and cell bodies.

• Characteristics: Can be depolarizing or hyperpolarizing, and their amplitude depends on stimulus strength.

Hyperpolarization and Action Potentials

Hyperpolarization occurs when the membrane potential becomes more negative than the resting potential, often due to prolonged opening of chloride channels.

• Action Potentials: Generated when depolarization reaches threshold, typically due to Na+ influx.

Refractory Periods

The absolute refractory period is the time during which a second action potential cannot be initiated, regardless of stimulus strength.

• Relative refractory period: A stronger stimulus can initiate another action potential.

Pacemaker Cells

Pacemaker cells in cardiac muscle spontaneously generate action potentials, regulating heart rhythm.

• Example: The sinoatrial (SA) node in the heart.

Specialized Neural Structures and Functions

Endothelial Cells and Erythrocytes

Endothelial cells line blood vessels and interact with erythrocytes (red blood cells) to maintain blood-brain barrier and vascular integrity.

Motor Coordination

The motor cortex and cerebellum coordinate voluntary movements, especially tracking moving objects or performing fine motor tasks.

Purely Sensory Cranial Nerves

Some cranial nerves are purely sensory, transmitting information from the environment to the brain.

• Example: The optic nerves (cranial nerve II) carry visual information.

Pain Perception and Myocardial Infarction

Pain from a heart attack (myocardial infarction) can be felt in the chest and may radiate to other areas such as the arm or jaw.

Somatosensory Cortex Representation

The somatosensory cortex allocates more space to body regions with higher sensory input, such as the hands and face.

Temperature and Pain Receptors

Free nerve endings detect changes in temperature and pain.

• Thermoreceptors: Respond to changes in temperature.

• Nociceptors: Respond to pain stimuli.

Tonic Receptors

Tonic receptors 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: Key Neural Concepts

Additional info: Academic context and definitions have been expanded for clarity and completeness.