Nervous System Cells and Communication

Glial Cells (Glia)

Cells that provide physical and metabolic support to neurons, outnumbering them 10:1.

Neurons

Interconnected information-processing cells essential for nervous system function, numbering approximately 100 billion at birth.

Semipermeable Membrane

A membrane that allows small or uncharged molecules to pass while blocking larger or highly charged molecules.

Soma (Cell Body)

The core of the neuron that contains the cell nucleus.

Dendrites

Branching structures extending from the soma that serve as input sites to receive incoming signals.

Axon

The major extension of a neuron that conducts signals away from the soma toward the terminal buttons.

Myelin Sheath

A fatty insulating layer formed by glial cells that increases signal transmission speed along the axon.

Multiple Sclerosis

An incurable autoimmune disorder involving large-scale degradation of the myelin sheath, causing symptoms like dizziness and loss of motor control.

Terminal Buttons

Structures at the axon’s end that contain synaptic vesicles filled with neurotransmitters.

Synapse

The microscopic gap between neurons where chemical communication takes place.

Receptors

Surface proteins on the receiving cell that bind with neurotransmitters in a specific 'lock-and-key' configuration.

Resting Potential

The baseline charge of a non-firing neuron, typically held at approximately -70 mV.

Sodium-Potassium Pump

An active transport mechanism that moves ions across the membrane to maintain the resting potential.

Action Potential

A rapid change in membrane potential that occurs in neurons, consisting of several stages.

Threshold of Excitation

The internal charge required to trigger an action potential, approximately -55 mV.

Depolarization

The rapid influx of sodium ions ($ ext{Na}^+$) that causes the electrical charge to spike to about +30 mV.

Repolarization

The process where positively charged potassium ions ($ ext{K}^+$) exit the cell, returning the internal charge toward a negative state.

Hyperpolarization

A brief drop in internal charge below the baseline resting potential, making it more negative than -70 mV.