Reading: Neurons

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Neuron

Basic functional cell of the nervous system that processes and transmits information

Neuron doctrine

Theory proposed by Ramón y Cajal that neurons are discrete individual units

Santiago Ramón y Cajal

Scientist who concluded neurons are the structural and functional units of the nervous system

Golgi stain

Staining technique that fills the entire neuron including its processes

Nissl stain

Staining technique that labels only the cell body of neurons

Advantage of Golgi stain

Stains only about 1–2 percent of neurons allowing individual cells to be distinguished

Continuous nerve theory

Early theory proposing the nervous system was a continuous network

Joseph von Gerlach

Scientist who proposed the continuous nerve network theory

Neuron structure

Underlying anatomy of neurons that supports their function

Dendrites

Branching processes that receive input from other neurons

Soma

Cell body of a neuron that contains the nucleus

Nucleus

Structure in the soma that contains genetic material and directs protein synthesis

Axon

Long process that carries the action potential away from the soma

Myelin sheath

Insulating layer around axons that speeds up signal transmission

Synapse

Junction where one neuron communicates with another

Terminal button

End of the axon that releases neurotransmitters

Dendritic spine

Small protrusion on dendrites where synapses form

Presynaptic neuron

Neuron that sends the signal

Postsynaptic neuron

Neuron that receives the signal

Synaptic cleft

Small gap between presynaptic and postsynaptic neurons

Synaptic vesicles

Structures that store neurotransmitters in the presynaptic terminal

Neurotransmitters

Chemical messengers that transmit signals between neurons

Sensory neurons

Neurons that receive information from the environment

Motor neurons

Neurons that control movement and behavior

Interneurons

Neurons that process information and connect sensory and motor neurons

Unipolar neurons

Neurons with one neurite specialized for relaying sensory information

Bipolar neurons

Neurons with one axon and one dendrite involved in sensory perception

Multipolar neurons

Neurons with one axon and many dendrites used for sensory and motor processing

Pyramidal neuron

Multipolar neuron with a pyramid-shaped cell body

Glial cells

Support cells in the nervous system that do not transmit electrical signals

Oligodendroglia

Glial cells that form myelin sheaths in the central nervous system

Microglia

Glial cells that remove debris and dead neurons

Astrocytes

Glial cells that provide nutrients and regulate extracellular fluid

Resting membrane potential

Stable negative charge of a neuron at rest around minus seventy millivolts

Intracellular fluid

Fluid inside the neuron

Extracellular fluid

Fluid outside the neuron

Ion

Electrically charged molecule

Cation

Positively charged ion

Anion

Negatively charged ion

Diffusion

Movement of ions from high to low concentration

Electrostatic pressure

Force between charged particles based on their electrical charge

Equilibrium potential

Voltage where diffusion and electrostatic forces are balanced

Sodium potassium pump

Active transport system that moves sodium out and potassium into the neuron using ATP

Action potential

Rapid all-or-nothing electrical signal that travels down the axon

All or nothing principle

Action potential either occurs fully or not at all

Depolarization

Change in membrane potential toward a more positive value

Threshold of excitation

Membrane potential at which an action potential is triggered

Excitatory postsynaptic potential EPSP

Graded depolarization that brings membrane potential closer to threshold

Inhibitory postsynaptic potential IPSP

Graded hyperpolarization that moves membrane potential away from threshold

Summation

Process by which EPSPs and IPSPs add together over time and space

Voltage dependent ion channel

Channel that opens or closes based on membrane potential

Refractory period

Time when a neuron cannot fire another action potential

Hyperpolarization

Membrane potential becomes more negative than resting level

Nodes of Ranvier

Gaps in myelin sheath where action potentials are regenerated

Saltatory conduction

Action potential jumping from node to node along a myelinated axon

Ionotropic receptor

Receptor that directly opens an ion channel when bound by neurotransmitter

Glutamate

Primary excitatory neurotransmitter in the brain

GABA

Primary inhibitory neurotransmitter in the brain

Reuptake

Process of transporting neurotransmitters back into the presynaptic neuron