A&P I — Chapter 11: Nervous Tissue and Signaling

Vocabulary flashcards covering graded and action potentials, refractory periods, impulse conduction mechanisms, and synaptic transmission from Chapter 11 of the BIO 217 Exam #2 Study Guide.

Graded potentials

Local, short-distance changes in membrane potential occurring mainly in dendrites and the cell body; their size varies with stimulus strength, they diminish with distance, and they can summate to determine whether a neuron reaches threshold.

Action potentials

All-or-none impulses initiated at the axon initial segment when threshold is reached; they regenerate along the axon without decreasing in amplitude and depend primarily on voltage-gated sodium and potassium channels.

Depolarization

A change in membrane voltage, often driven by $\text{Na}^+$ entry, that makes the membrane less negative and brings it closer to threshold, producing an excitatory effect.

Hyperpolarization (or shunting inhibition)

A change in membrane potential where $\text{K}^+$ exit or $\text{Cl}^-$ conductance reduces the likelihood of the neuron reaching threshold.

Resting membrane potential

The baseline electrical state of a neuron near $-70\,\text{mV}$, maintained by ion gradients and leak channels.

Threshold

The membrane potential level of about $-55\,\text{mV}$ at which voltage-gated $\text{Na}^+$ channels open, allowing $\text{Na}^+$ to enter and causing voltage to rise rapidly toward $+30\,\text{mV}$.

Repolarization

The phase of an action potential in which $\text{Na}^+$ channels inactivate and voltage-gated $\text{K}^+$ channels open, permitting $\text{K}^+$ to exit the cell.

After-hyperpolarization

The phase following repolarization where delayed closure of $\text{K}^+$ channels briefly makes the inside of the cell more negative than the resting voltage.

Axon initial segment

The specific region of a neuron where an action potential normally begins once threshold is reached.

Absolute refractory period

The period during which no second action potential is possible, regardless of stimulus strength, because voltage-gated $\text{Na}^+$ channels are open or inactivated and unavailable for reactivation.

Relative refractory period

The interval during which a stronger-than-normal stimulus can generate another action potential because some $\text{Na}^+$ channels have recovered, though elevated $\text{K}^+$ conductance makes excitation harder.

Continuous conduction

The slower mode of nerve impulse propagation in unmyelinated axons, where action potentials regenerate sequentially along adjacent portions of the membrane.

Saltatory conduction

A rapid, energy-efficient mode of propagation in myelinated axons, in which electrical current travels rapidly beneath insulating myelin and action potentials regenerate at the Nodes of Ranvier.

Nodes of Ranvier

Unmyelinated gaps along a myelinated axon where action potentials regenerate during saltatory conduction.

Multiple sclerosis

An immune-mediated demyelinating disease of the central nervous system (CNS) in which myelin damage can slow or block nerve conduction.

Synapse

A specialized junction where a neuron communicates with another neuron or an effector cell.

Electrical synapses

Specialized connections where cells connect through gap junctions, allowing ions to flow directly between cells to provide very fast, often bidirectional communication.

Chemical synapses

Junctions where the presynaptic terminal and postsynaptic membrane are separated by a synaptic cleft, utilizing neurotransmitters to transmit signals unidirectionally with a brief synaptic delay.