Neurons

Neuron

A nerve cell that transmits information via electrical and chemical signals.

Sensory Neurons

Neurons that carry information from sensory organs to the CNS.

Motor Neurons

Neurons that carry signals from the CNS to muscles or glands.

Interneurons

Neurons that connect sensory and motor neurons within the CNS.

All-or-Nothing Principle

A neuron either fires completely or not at all.

Resting Potential

The electrical charge of a neuron when it is not firing (-70 mV).

Depolarization

The process during an action potential when a neuron’s membrane becomes less negative.

Refractory Period

The brief time after an action potential when a neuron cannot fire.

Threshold

The minimum level of stimulus needed to trigger an action potential.

Excitatory Neurotransmitter

Chemicals that increase the likelihood of a neuron firing (e.g., glutamate).

Inhibitory Neurotransmitter

Chemicals that decrease the likelihood of a neuron firing (e.g., GABA).

Dopamine

A neurotransmitter associated with reward, motivation, and motor control.

Norepinephrine

A neurotransmitter that increases alertness, arousal, and the stress response.

Glutamate

The main excitatory neurotransmitter in the brain.

Substance P

A neurotransmitter that transmits pain signals to the CNS.

Endorphins

Neurotransmitters that reduce pain and produce feelings of pleasure.

Serotonin

A neurotransmitter involved in mood, sleep, and appetite regulation.

GABA (Gamma-Aminobutyric Acid)

The main inhibitory neurotransmitter in the brain.

Acetylcholine (ACh)

A neurotransmitter involved in muscle movement, learning, and memory.

Myasthenia Gravis

An autoimmune disorder that blocks acetylcholine receptors, causing muscle weakness.

Multiple Sclerosis

A disease in which myelin sheaths of neurons are damaged, slowing nerve signals.

Glial Cells

Support cells in the nervous system that nourish and protect neurons.

Reflex Arc

The neural pathway that controls an automatic response to a stimulus.

Reuptake

The process by which neurotransmitters are reabsorbed by the neuron that released them.

Cell Body (Soma)

Contains the nucleus and organelles; integrates incoming signals.

Dendrites

Branch-like structures that receive messages from other neurons.

Axon

Long fiber that transmits electrical impulses away from the cell body.

Axon Terminals (Synaptic Terminals)

End points of the axon that release neurotransmitters to communicate with other neurons or muscles.

Myelin Sheath

Fatty layer that insulates the axon and speeds up signal transmission.

Nodes of Ranvier

Gaps in the myelin sheath where action potentials jump, speeding conduction.

Synapse

Junction between two neurons or a neuron and a target cell where neurotransmitters are released.