Human Anatomy and Physiology - Chapter 11 Part B: Fundamentals of Nervous System & Membrane Potentials

Comprehensive vocabulary flashcards covering membrane potentials, gated ion channels, action potentials, refractory periods, and nerve fiber classifications from Chapter 11 Part B.

Leakage channels

Nongated membrane ion channels that are always open, allowing specific ions like $\text{K}^+$ or $\text{Na}^+$ to pass continuously.

Chemically gated channels

Membrane ion channels (also called ligand-gated channels) that open only upon the binding of a specific chemical, such as a neurotransmitter.

Voltage-gated channels

Membrane ion channels that open and close directly in response to changes in membrane potential.

Mechanically gated channels

Membrane ion channels that open and close in response to physical deformation of sensory receptors.

Resting membrane potential

The potential difference across the plasma membrane of a resting neuron, typically around $-70\,\text{mV}$ (ranging from $-40\,\text{mV}$ to $-90\,\text{mV}$), where the inside is negatively charged relative to the outside.

Depolarization

A decrease in membrane potential where the inside of the membrane becomes less negative (moving toward zero and above), increasing the probability of producing a nerve impulse.

Hyperpolarization

An increase in membrane potential where the inside becomes more negative than resting state (moving away from zero), decreasing the probability of producing a nerve impulse.

Graded potentials

Short-lived, localized changes in membrane potential that operate over short distances and decay over distance.

Receptor potential

A specific type of graded potential (also known as a generator potential) generated in the receptors of sensory neurons.

Postsynaptic potential

A localized graded potential generated in a neuron following neurotransmitter release across a synapse.

Action potential

A brief reversal of membrane potential with a voltage change of approximately $100\,\text{mV}$ that does not decay over distance and serves as the principal method of long-distance neural communication.

Activation gate

A voltage-sensitive gate on a $\text{Na}^+$ channel that is closed at rest and opens upon depolarization to allow $\text{Na}^+$ entry into the cell.

Inactivation gate

A voltage-sensitive gate on a $\text{Na}^+$ channel that is open at rest and automatically blocks the channel shortly after opening to prevent further $\text{Na}^+$ influx.

Threshold

The critical membrane potential level ($-55\,\text{mV}$ to $-50\,\text{mV}$) at which positive feedback opens all voltage-gated $\text{Na}^+$ channels to initiate an action potential.

Repolarization

The phase in an action potential where voltage-gated $\text{Na}^+$ channels inactivate and voltage-gated $\text{K}^+$ channels open, restoring internal negative electrical conditions.

All-or-None phenomenon

The property of action potentials stating that an impulse either fires completely or does not happen at all once threshold is reached.

Absolute refractory period

The timeframe from the opening of $\text{Na}^+$ channels until their resetting, during which a neuron cannot respond to another stimulus, enforcing one-way AP transmission.

Relative refractory period

The period following repolarization where most $\text{Na}^+$ channels have reset but some $\text{K}^+$ channels remain open, requiring an exceptionally strong stimulus to trigger an action potential.

Continuous conduction

Slow action potential propagation occurring along nonmyelinated axons as each successive segment depolarizes and repolarizes.

Saltatory conduction

Rapid action potential propagation in myelinated axons, occurring about $30\times$ faster because electrical signals jump between myelin sheath gaps.

Multiple sclerosis

An autoimmune disease affecting young adults in which immune cells attack myelin sheaths in the central nervous system, reducing them to hardened lesions called scleroses.

Group A fibers

Large-diameter, heavily myelinated somatic sensory and motor fibers serving skin, muscles, and joints, transmitting impulses at speeds up to $150\,\text{m/s}$.

Group B fibers

Intermediate-diameter, lightly myelinated nerve fibers that transmit visceral sensory and autonomic motor impulses at speeds of about $15\,\text{m/s}$.

Group C fibers

Smallest-diameter, unmyelinated nerve fibers that transmit autonomic and sensory impulses at slow speeds of about $1\,\text{m/s}$.