Membrane Potentials, Action Potentials, and Cell Receptors

Flashcards covering membrane potentials, action potentials, refractory periods, electrolyte imbalances, and cell receptor mechanisms including membrane-bound and intracellular receptors, G proteins, alpha and beta receptors, and signal transduction.

Membrane Potential

The electrical potential or electrical difference across the cell membrane.

Excitable Cells

Cells that can generate action potentials or electrical impulses and conduct them along their cell membrane (e.g., nerve fibers, skeletal muscle fibers).

Resting Membrane Potential

The electrical difference or the electrical gradient across the cell membrane in the resting undisturbed state.

Polarized

Positive charges accumulate at one pole, and negative charges accumulate at another pole. In cell membranes, positive charges accumulate on one side and negative charges on the other.

Membrane Potential Comparison

Always compare the inside of the cell membrane to the outside of that same cell membrane.

Typical Membrane Potential Value

Enlarged nerve fibers, skeletal muscle fibers, and some cardiac fibers is typically around minus 90 millivolts.

Cellular Membrane Potential

Each cell throughout your body establishes and tries to maintain its own membrane potential.

Body Fluids

Electrically neutral where the number of cations equals the number of anions in both extracellular and intracellular fluids.

Potassium Leak Channels

The primary contributor to the cell membrane potential that allow potassium to move from inside the cell to outside.

Sodium Leak Channels

The second most important contributor to the membrane potential where sodium diffuses from outside to inside the cell.

Sodium-Potassium Pump

Pumps three sodiums out and two potassiums in, contributing to the membrane potential.

Negatively Charged Proteins

Accumulation of negatively charged proteins just along the inside of the cell membrane also contributes to the cell membrane potential.

Action Potentials

Transmission of electrical impulses along the membranes of excitable cells.

Components of Action Potential

Resting membrane potential, threshold potential, depolarization, and repolarization.

Resting Membrane Potential (Action Potential)

The cell is in the resting undisturbed state (e.g., -90 mV).

Threshold Potential

The point at which voltage-gated sodium channels are opened, leading to an influx of sodium.

Depolarization

Rapid influx of sodium into the cell, causing the membrane potential to become less negative until the voltage gated sodium channels close.

Repolarization

Voltage-gated potassium channels open, allowing potassium to move out of the cell, making the membrane potential more negative and returns it to resting.

Refractory Periods

Built-in protective mechanisms allowing the membrane potential to return to resting and recover before another action potential can occur (absolute, relative, supernormal).

Absolute Refractory Period

The cell is completely resistant to another depolarization.

Relative Refractory Period

An extra strong stimulus may cause another depolarization.

Supernormal Refractory Period

Only a mild stimulus is needed to cause another depolarization (vulnerable period).

Stimuli for Initial Sodium Influx

Chemical, electrical, or mechanical stimuli.

All or None Phenomenon

If the initial stimulus does not cause enough sodium influx to reach threshold, depolarization will not occur; if threshold is reached, depolarization occurs normally.

Action Potential Propagation

Depolarization begins at a single point and propagates bidirectionally across the cell membrane.

Hyperkalemia

Increased extracellular potassium, which decreases the potassium gradient, leading to hypopolarization and rapid repolarization.

Hypokalemia

Decreased extracellular potassium increases the potassium gradient, leading to hyperpolarization and prolonged repolarization.

Impact of Potassium on Action Potential

Changes in potassium concentration primarily affect the resting membrane potential.

Impact of Calcium on Action Potential

Changes in extracellular calcium concentration affect the threshold potential.

Hypocalcemia

Low extracellular calcium, which makes it easier to open voltage-gated sodium channels and move the threshold closer to resting.

Hypercalcemia

High extracellular calcium, which makes it harder to open voltage-gated sodium channels because it moves the threshold away from resting.

Cell Receptor Function

Allow extracellular substances to regulate cell activity through intermediate mechanisms.

Signal Transduction

What happens inside the cell after a receptor is activated.

Agonist

A drug that activates a receptor.

Antagonist

A drug that inhibits a receptor.

Membrane Bound Receptors

Receptors located and incorporated into the cell membrane, usually integrated with intracellular proteins, enzymes, or second messengers.

Intracellular Receptors

Receptors located inside the cell, either in the cytoplasm or the nucleus.

Ligand-Gated Ion Channel

Membrane bound receptor that opens an ion channel in the cell membrane as described by the acetylcholine gated sodium channel.

Benzodiazepines

Open chloride channels.

Guanulate Cyclase

Is an enzyme converts GTP to cyclic GMP that activates protein kinase G to increase excretion by the kidneys.

G Proteins

Complexes composed of an alpha, beta, and gamma subunit; the alpha subunit breaks away and activates cellular activity.

Alpha-One Receptors

G protein receptors found in vascular smooth muscle that, when activated by norepinephrine, lead to vascular smooth muscle contraction.

Beta Receptors

G protein receptors that, when activated by epinephrine or isoproterenol, increase heart rate, conduction speed, and contraction strength (beta-one) or cause bronchiole smooth muscle relaxation (beta-two).

Intracellular Receptors Function

Steroid and thyroid hormones using this mechanism binding to receptors, moving to the nucleus, binding to DNA initiating protein synthesis.

Intracellular Receptors Steps

Receptor activation, transcriptase activation, mRNA delivery, ribosome activation, protein synthesis, and cellular response; process takes a long time but lasts longer.

Vasodilation Substances

Histamine, bradykinin, and prostaglandins uses the same events to bring about vasodilation.