Conduction Velocity and Membrane Potentials

These flashcards cover key concepts of conduction velocities, the role of myelination, action potentials, and related physiological mechanisms.

Group A fibers

Largest diameter, myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints, transmitting at 150 m/s (~300 mph).

Group B fibers

Intermediate diameter, lightly myelinated fibers, transmitting at 15 m/s (~30 mph).

Group C fibers

Smallest diameter, unmyelinated fibers, transmitting at 1 m/s (~2 mph).

Conduction Velocity

The speed at which an action potential travels along an axon.

Local anesthetics

Chemical agents that block voltage-gated Na+ channels to inhibit action potential propagation.

Homeostatic Imbalance

Condition that disrupts normal physiological functioning, possibly affecting AP impulse propagation.

Multiple Sclerosis (MS)

An autoimmune disease that damages myelin sheaths in the CNS, primarily affecting young adults.

Demyelination

The process of losing the myelin sheath insulating a nerve fiber.

Resting membrane potential

The electrical charge difference across a neuron's membrane at rest, typically around -70 mV.

Continuous conduction

Slow conduction that occurs in nonmyelinated axons.

Saltatory conduction

Rapid conduction that occurs in myelinated axons due to jumping of action potentials between nodes of Ranvier.

Myelin sheath

A fatty layer that insulates axons, preventing leakage of charge and increasing conduction speed.

Action Potential (AP)

A rapid change in voltage across a neuron's membrane; all-or-nothing response.

Depolarization

A decrease in membrane potential; the inside of the membrane becomes less negative relative to the outside.

Hyperpolarization

An increase in membrane potential; the inside of the membrane becomes more negative.

Graded potential

Small changes in membrane potential that occur over short distances.

Electrical current

Flow of electrical charge (ions) between two points.

Voltage-gated channels

Ion channels that open or close in response to changes in membrane potential.

Chemically gated channels

Ion channels that open only when a specific chemical binds to them.

Mechanically gated channels

Ion channels that open or close in response to physical deformation.

Scleroses

Hardened lesions formed from the destruction of myelin sheaths in the CNS.

Threshold voltage

The level of membrane depolarization needed to trigger an action potential.

Na+ influx

The movement of sodium ions into a neuron, crucial for depolarization during an action potential.

K+ efflux

The movement of potassium ions out of a neuron, contributing to repolarization after an action potential.

Polarized membrane

A membrane that has a charge difference across it; generally negative inside relative to outside.

Ohm's Law

A fundamental principle relating voltage, current, and resistance in electrical circuits.

Electrochemical gradient

The combined effect of electrical and chemical gradients on ion movement across a membrane.

Insulator

A substance with high electrical resistance that impedes charge flow.

Conductor

A substance with low electrical resistance that facilitates charge flow.

Resting neuron

A neuron at rest with a typical membrane potential of -70 mV.

Action potential propagation

The process of transmitting an action potential along the length of an axon.

Na+/K+ pumps

Molecular machines in the axon membrane that restore ionic conditions after repolarization.

Voltage difference

The potential between two points that influences the direction of ion movement.

Local currents

Currents created by ion movement that lead to depolarization of adjacent membrane areas.

Charge leakage

Loss of electrical charge across the 'leaky' plasma membrane, decreasing voltage with distance.

Membrane permeability

The ability of the membrane to allow ions to pass through; changes can alter membrane potential.

Impulse propagation factors

Axon diameter and degree of myelination that influence the speed of action potential conduction.

Threshold potential

The specific level of depolarization required to initiate an action potential.

Neurotransmitter

Chemical messengers that bind to receptors and can cause opening of chemically gated channels.

Resting state

The baseline state of a neuron before any stimulation occurs.

Membrane potential changes

Variations in charge across a cell membrane due to ion concentrations and permeability.

Long-distance signals

Action potentials that transmit information along axons to distant targets.

Short-distance signals

Graded potentials that operate over brief distances and do not travel far.

Voltage-gated Na+ channels

Channels that are crucial for the rapid depolarization phase of action potentials.

Positive feedback cycle

A feedback mechanism where the increase in one quantity leads to further increase in the same quantity.

Sodium channels

Ion channels that facilitate Na+ influx during depolarization phases of action potentials.

Potassium channels

Ion channels that allow K+ efflux and play a role in repolarization.

Ion flow

Movement of ions across the membrane contributing to the electrical changes.

Voltage drop

The reduction of voltage along an axon; impacts conduction velocity.

Na+ influx exceeds K+ efflux

Condition necessary for depolarization to trigger action potentials.

Decreases in membrane potential

Changes that lead to increased likelihood of generating an action potential.

Increased Na+ channels

Response seen in demyelinated axons, which can lead to cycles of relapse in diseases like MS.

Sodium-potassium pump

A mechanism that restores the original conditions of Na+ and K+ concentrations after an action potential.

Conduction types

Continuous and saltatory conduction, which depend on myelination.