Neurons and Glial Cells in the Nervous System

Neuron

A specialized cell that can transmit electrical signals to other nerve cells, muscles, or glands.

Cell body (soma)

Contains the neuron's nucleus and most of its cytoplasm, along with molecular machinery for building and transporting proteins.

Dendrites

Branched projections that extend from the cell body and collect incoming signals from other neurons.

Axon

Electrical signals travel down this extension from the cell body to the axon terminal.

Axon Terminal - Synapse

Where the signal is passed across a synapse to other cells.

Astrocytes

Regulates ion concentrations around neurons, provides them with nutrients.

Microglia

The main 'immune cells' of the brain are phagocytes.

Ependymal cells

Make the cerebrospinal fluid that cushions the brain inside the skull.

Oligodendrocytes

Increase signal speed by wrapping axons in a fatty sheath called myelin.

Chemically gated (ligand-gated) channels

Open only with binding of a specific chemical (example: neurotransmitter).

Voltage-gated channels

Open and close in response to changes in membrane potential.

Mechanically gated channels

Open and close in response to physical deformation of receptors, as in sensory receptors.

Electrochemical gradient

Electrical and chemical gradients combined.

Resting membrane potential (RMP)

A neuron at rest has a negative resting membrane potential of -70 mV.

Depolarization

Occurs when the membrane potential becomes more positive.

Hyperpolarization

Results when the membrane potential is more negative than -70 mV.

Action potential

An electrical signal that is propagated along the length of an axon.

Sodium (Na+)

An ion that is involved in the electrical signaling of neurons.

Chloride (Cl-)

An ion that is involved in the electrical signaling of neurons.

Potassium (K+)

An ion that is involved in the electrical signaling of neurons.

Neurotransmitter release

Changes in electrical potential are coupled to neurotransmitter release by a neuron.

Action Potential

A rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane.

Synapse

The junction between two neurons where neurotransmitter release occurs.

Neurotransmitter Release

The process initiated by the arrival of the action potential at the synaptic knob, leading to neurotransmitter release by exocytosis.

Excitatory Neurotransmitter

A neurotransmitter that, when released from presynaptic neurons, initiates an excitatory postsynaptic potential.

Inhibitory Neurotransmitter

A neurotransmitter that, when released from presynaptic neurons, initiates an inhibitory postsynaptic potential.

EPSP

Excitatory postsynaptic potential, which is a temporary depolarization of the postsynaptic membrane.

IPSP

Inhibitory postsynaptic potential, which is a temporary hyperpolarization of the postsynaptic membrane.

Threshold Membrane Potential

The critical level to which a membrane potential must be depolarized to initiate an action potential.

Summation

The process through which multiple excitatory or inhibitory signals combine to determine whether an action potential is generated.

Axon Diameter

A factor that affects the velocity of action potential transmission, with larger diameters allowing faster transmission.

Myelin Sheath

A fatty layer that surrounds axons and increases the speed of action potential transmission through saltatory conduction.

Nerve Fiber Type A

Large diameter fibers (4-20 μm) with a speed of approximately 150 m/s and high myelination.

Nerve Fiber Type B

Intermediate diameter fibers (2-4 μm) with a speed of approximately 15 m/s and low myelination.

Nerve Fiber Type C

Small diameter fibers (<2 μm) with a speed of approximately 1 m/s and no myelination.

Saltatory Conduction

The process by which action potentials are transmitted faster in myelinated axons.

Voltage

A measure of potential energy generated by separated charge, measured in volts (V) or millivolts (mV).

Potential Difference

The difference in voltage between two points, also known as potential.

Ion Channels

Large proteins that serve as selective membrane channels for ions.

Leakage Channels

Nongated ion channels that are always open.

Gated Channels

Ion channels that open or close in response to a stimulus, changing shape to allow ions to pass.

Chemically Gated Channels

Ion channels that open in response to the binding of a chemical messenger.

Voltage-Gated Channels

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

Calcium Channels

Voltage-gated channels that, when opened, allow calcium ions to enter the cell, initiating neurotransmitter release.

Acetylcholine (ACh)

A neurotransmitter that triggers an action potential at the neuromuscular junction.