Introduction to Neurophysiology and Action Potentials

Vocabulary flashcards generated from the chapter lecture notes covering neuronal anatomy, action potentials, resting potentials, summations, myelination, and synaptic transmission.

Nervous System Metabolic Demand

The brain consumes approximately $20\%$ of the body's total energy, using ATP extensively to power sodium-potassium pumps and balance action potentials.

Dendrites

Rooting, finger-like projections extending from the neuronal cell body that function as signal integration sites by capturing incoming signals.

Axon Hillock

The specialized region of a neuron that integrates incoming dendritic signals and serves as the initiation site for action potentials.

Myelin Sheath

An insulating layer added to axons by Schwann cells that prevents signal leakage and increases the speed and efficiency of action potential transmission.

Axon Terminal

The specialized end structure of an axon where neurotransmitters are stored and released to communicate with adjacent cells.

Continuous Conduction

The propagation of an action potential channel-by-channel along an unmyelinated axon, which is relatively slow and energetically expensive.

Resting Membrane Potential

The steady-state electrical potential across a neuron's membrane, typically maintained at approximately $-70\,\text{mV}$.

Depolarization

A shift in membrane potential toward zero (making the interior less negative) caused by the influx of positive ions such as sodium.

Hyperpolarization

A change in membrane potential moving further away from zero (making the interior more negative), such as reaching $-90\,\text{mV}$.

Repolarization

The restoration of the membrane potential back toward its resting negative charge after a depolarization event.

Leak Channels

Ion channels that remain open continuously, allowing specific ions to passively diffuse down their concentration gradients across the membrane.

Voltage-Gated Channels

Ion channels that open or close in response to changes in membrane potential, specifically activating when reaching a threshold around $-55\,\text{mV}$.

Sodium-Potassium Pump

An active transport protein that uses ATP to push sodium and potassium ions against their concentration gradients to maintain the resting potential at $-70\,\text{mV}$.

Graded Potentials

Short-distance electrical signals localized to the dendrites and cell body that diminish in strength as they travel from their initiation site.

Action Potentials

Long-distance, all-or-nothing electrical signals that travel down axons without decreasing in strength regardless of distance.

Temporal Summation

The addition of multiple graded potentials triggered in rapid succession over time by a single presynaptic neuron to reach threshold.

Spatial Summation

The additive effect of multiple graded potentials arriving at roughly the same time from several different presynaptic neurons.

Absolute Refractory Period

The phase during an active action potential when no second action potential can be initiated regardless of stimulus strength.

Relative Refractory Period

The hyperpolarized period following an action potential during which a much stronger stimulus is required to reach threshold and trigger another fire event.

Gray Matter

Unmyelinated brain tissue responsible for higher-order cognitive functions and short-distance processing between neighboring cells.

White Matter

Myelinated axon components of the brain involved in rapid, long-distance communication and signal integration.

Nodes of Ranvier

Unmyelinated gaps situated between adjacent myelin sheaths along an axon where sodium influx and potassium efflux occur.

Multiple Sclerosis (MS)

An autoimmune disorder characterized by immune-mediated breakdown of myelin sheaths, leading to impaired action potential conduction and progressive neurological deficits.

Synaptic Knob

A swollen terminal structure at the end of a presynaptic axon that houses neurotransmitters stored inside secretory vesicles.

Synaptic Cleft

The small physical space separating the presynaptic neuron from the postsynaptic cell across which neurotransmitters diffuse.

Acetylcholinesterase

An enzyme located in the synaptic cleft that terminates chemical signaling by breaking down acetylcholine.