AP Bio Chapter 48

Neurons, Synapses, and Signaling

neuron

nerve cell; the fundamental unit of the nervous system, having structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its plasma membrane.

axon

A typically long extension, or process, of a neuron that carries nerve impulses away from the cell body toward target cells.

equilibrium potential (Eion)

the magnitude of a cell's membrane voltage at equilibrium; calculated using the Nernst equation.

Schwann cell

A type of glial cell that forms insulating myelin sheaths around the axons of neurons in the peripheral nervous system.

saltatory conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

acetylcholine

One of the most common neurotransmitters; functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.

threshold

The potential that an excitable cell membrane must reach for an action potential to be initiated.

cell body

The part of a neuron that houses the nucleus and most other organelles.

ganglion

A cluster (functional group) of nerve cell bodies.

myelin sheath

Wrapped around the axon of a neuron, an insulating coat of cell membranes from Schwann cells or oligodendrocytes. It is interrupted by nodes of Ranvier, where action potentials are generated.

summation

A phenomenon of neural integration in which the membrane potential of the postsynaptic cell is determined by the combined effect of EPSPs or IPSPs produced in rapid succession at one synapse or simultaneously at different synapses.

refractory period

The short time immediately after an action potential in which the neuron cannot respond to another stimulus, owing to the inactivation of voltage-gated sodium channels.

hyperpolarization

A change in a cell's membrane potential such that the inside of the membrane becomes more negative relative to the outside, reduces the chance that a neuron will transmit a nerve impulse.

resting potential

The membrane potential characteristic of a nonconducting excitable cell, with the inside of the cell more negative than the outside.

endorphin

Any of several hormones produced in the brain and anterior pituitary that inhibit pain perception.

interneuron

An association neuron; a nerve cell within the central nervous system that forms synapses with sensory and/or motor neurons and integrates sensory input and motor output.

ligand-gated ion channel

a transmembrane protein containing a pore that opens or closes as it changes shape in response to a signaling molecule (ligand), allowing or blocking the flow of specific ions; also called an ionotropic receptor.

excitatory postsynaptic potential (EPSP)

an electrical change (depolarization) in the membrane of a postsynaptic cell caused by the binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more likely for a postsynaptic cell to generate an action potential.

brain

Organ of the central nervous system where information is processed and integrated.

oligodendrocyte

a type of glial cell that forms insulating myelin sheaths around the axons of neurons in the central nervous system.

neurotransmitter

A molecule that is released from the synaptic terminal of a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds to the postsynaptic cell, triggering a response.

depolarization

A change in a cell's membrane potential such that the inside of the membrane is made less negative relative to the outside. For example, a neuron membrane is depolarized if a stimulus decreases its voltage from the resting potential of −70mV in the direction of zero voltage.

sodium-potassium pump

A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.

membrane potential

The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

neuropeptide

A relatively short chain of amino acids that serves as a neurotransmitter.

synapse

The junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling.

dendrite

One of usually numerous, short, highly branched extensions of a neuron that receive signals from other neurons.

glia (glial cells)

Cells of the nervous system that support, regulate, and augment the functions of neurons.

graded potential

In a neuron, a shift in the membrane potential that has an amplitude proportional to signal strength and that decays as it spreads.

voltage-gated ion channel

A specialized ion channel that opens or closes in response to changes in membrane potential.

motor neuron

A nerve cell that transmits signals from the brain or spinal cord to muscles or glands.

gated ion channel

A gated channel for a specific ion. The opening or closing of such channels may alter a cell's membrane potential.

ion channel

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.

action potential

An electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization.

inhibitory postsynaptic potential (IPSP)

an electrical change (usually hyperpolarization) in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more difficult for a postsynaptic neuron to generate an action potential.