absolute refractory phase
A brief period of complete insensitivity to stimuli.
A neurotransmitter produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain.
The propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminals.
The positive or negative change in membrane potential that may follow an action potential.
A molecule, usually a drug, that binds a receptor molecule and initiates a response like that of another molecule, usually a neurotransmitter.
The fact that the amplitude of the action potential is independent of the magnitude of the stimulus.
A negatively charged ion, such as a protein or chloride ion.
A molecule, usually a drug, that interferes with or prevents the action of a transmitter.
In epilepsy, the unusual sensations or premonition that may precede the beginning of a seizure.
Referring to a synapse in which a presynaptic axon terminal synapses onto another axon's terminal.
Referring to a synapse in which a presynaptic axon terminal synapses onto a dendrite of the postsynaptic neuron, either via a dendritic spine or directly onto the dendrite itself.
A cone-shaped area from which the axon originates out of the cell body. Functionally, the integration zone of the neuron.
Referring to a synapse in which a presynaptic axon terminal synapses onto the cell body (soma) of the postsynaptic neuron.
A toxin, produced by poison arrow frogs, that selectively interferes with Na+ channels.
A neurotoxin, isolated from the venom of the banded krait, that selectively blocks acetylcholine receptors.
calcium ion (Ca2+)
A calcium atom that carries a double positive charge because it has lost two electrons.
A positively charged ion, such as a potassium or sodium ion.
The lipid bilayer that ensheathes a cell.
A genetic abnormality of ion channels, causing a variety of symptoms.
chloride ion (Cl-)
A chlorine atom that carries a negative charge because it has gained one electron.
Referring to cells that use acetylcholine as their synaptic transmitter.
complex partial seizure
In epilepsy, a type of seizure that doesn't involve the entire brain, and therefore can cause a wide variety of symptoms.
Variation of the concentration of a substance within a region.
The speed at which an action potential is propagated along the length of an axon (or section of peripheral nerve).
The phenomenon of neural connections in which many cells send signals to a single cell.
An alkaloid neurotoxin that causes paralysis by blocking acetylcholine receptors in muscle.
The chemical breakdown of a neurotransmitter into inactive metabolites.
Referring to a type of synapse in which a synaptic connection forms between the dendrites of two neurons.
A reduction in membrane potential (the interior of the neuron becomes less negative).
The spontaneous spread of molecules of one substance among molecules of another substance until a uniform concentration is achieved.
The phenomenon of neural connections in which one cell sends signals to many other cells.
A compensatory reduction in receptor availability at the synapses of a neuron.
Cell-cell communication based on release of neurotransmitter in regions outside traditional synapses.
Also called gap junction. The region between neurons where the presynaptic and postsynaptic membranes are so close that the action potential can jump to the postsynaptic membrane without first being translated into a chemical message.
A recording of gross electrical activity of the brain recorded from large electrodes placed on the scalp.
The propensity of charged molecules or ions to move, via diffusion, toward areas with the opposite charge.
Any substance, produced within the body, that selectively binds to the type of receptor that is under study.
A brain disorder marked by major sudden changes in the electrophysiological state of the brain that are referred to as seizures.
Here, the point at which the movement of ions across the cell membrane is balanced, as the electrostatic pressure pulling ions in one direction is offset by the diffusion force pushing them in the opposite direction.
event-related potential (ERP)
Also called evoked potential. Averaged EEG recordings measuring brain responses to repeated presentations of a stimulus. Components of the ERP tend to be reliable because the background noise of the cortex has been averaged out.
excitatory postsynaptic potential (EPSP)
A depolarizing potential in the postsynaptic neuron that is caused by excitatory presynaptic potentials. EPSPs increase the probability that the postsynaptic neuron will fire an action potential.
Any substance, originating from outside the body, that selectively binds to the type of receptor that is under study.
The fluid in the spaces between cells (interstitial fluid) and in the vascular system.
A class of proteins that reside next to the intracellular portion of a receptor and that are activated when the receptor binds an appropriate ligand on the extracellular surface.
Referring to the property by which an ion channel may be opened or closed by factors such as chemicals, voltage changes, or mechanical actions.
grand mal seizure
A type of generalized epileptic seizure in which nerve cells fire in high-frequency bursts.
An increase in membrane potential (the interior of the neuron becomes even more negative).
inhibitory postsynaptic potential (IPSP)
A hyperpolarizing potential in the postsynaptic neuron that is caused by inhibitory connections. IPSPs decrease the probability that the postsynaptic neuron will fire an action potential.
Also called cytoplasm. The watery solution found within cells.
A pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open.
An atom or molecule that has acquired an electrical charge by gaining or losing one or more electrons.
A receptor protein that includes an ion channel that is opened when the receptor is bound by an appropriate ligand.
A method of experimentally inducing an epileptic seizure by repeatedly stimulating a brain region.
knee jerk reflex
A variant of the stretch reflex in which stretching of the tendon beneath the knee leads to an upward kick of the leg.
A substance that binds to receptor molecules, such as those at the surface of the cell.
ligand-gated ion channel
Also known as chemically gated ion channel. An ion channel that opens or closes in response to the presence of a particular chemical.
The structure of the neuronal cell membrane, which consists of two layers of lipid molecules, within which float various specialized proteins, such as receptors.
An electrical potential that is initiated by stimulation at a specific site, which is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance.
A receptor protein that does not contain an ion channel but may, when activated, use a G protein system to alter the functioning of the postsynaptic cell.
An especially small electrode used to record electrical potentials from living cells.
A thousandth of a volt.
A negative electrical-potential difference relative to a reference electrode.
An equation predicting the voltage needed to just counterbalance the diffusion force pushing an ion across a semipermeable membrane from the side with a high concentration to the side with a low concentration.
A simple kind of neural circuit in which neurons are attached linearly, end-to-end.
The study of the life processes of neurons.
Also called synaptic transmitter, chemical transmitter, or simply transmitter. The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons.
node of Ranvier
A gap between successive segments of the myelin sheath where the axon membrane is exposed.
A type of synapse in which the presynaptic and postsynaptic cells are not in close apposition; instead, neurotransmitter is released by axonal varicosities and diffuses away to affect wide regions of tissue.
petit mal seizure
Also called an absence attack. A seizure that is characterized by a spike-and-wave EEG and often involves a loss of awareness and inability to recall events surrounding the seizure.
The process by which synaptic neurotransmitter is repackaged into synaptic vesicles.
A local potential that is initiated by stimulation at a synapse, can vary in amplitude, and spreads passively across the cell membrane, decreasing in strength with time and distance.
potassium ion (K+)
A potassium atom that carries a positive charge because it has lost one electron.
Also called receptor. A protein that captures and reacts to molecules of a neurotransmitter or hormone.
Transiently inactivated or exhausted.
relative refractory phase
A period of reduced sensitivity during which only strong stimulation produces an action potential.
resting membrane potential
A difference in electrical potential across the membrane of a nerve cell during an inactive period.
A synapse in which a signal (usually a gas neurotransmitter) flows from the postsynaptic neuron to the presynaptic neuron, thus counter to the usual direction of synaptic communication.
The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity.
The form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next.
An animal toxin that blocks sodium channels when applied to the outer surface of the cell membrane.
A slow-acting substance in the postsynaptic cell that amplifies the effects of synaptic activity and signals synaptic activity within the postsynaptic cell.
An epileptic episode.
The property of a membrane that allows some substances to pass through, but not others.
sodium ion (Na+)
A sodium atom that carries a positive charge because it has lost one electron.
The energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in.
The summation at the axon hillock of postsynaptic potentials from across the cell body. If this summation reaches threshold, an action potential is triggered.
The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential.
The summation of postsynaptic potentials that reach the axon hillock at different times. The closer in time that the potentials occur, the more complete the summation.
A toxin from puffer fish ovaries that blocks the voltage-gated sodium channel, preventing action potential conduction.
The stimulus intensity that is just adequate to trigger an action potential at the axon hillock.
Specialized receptors in the presynaptic membrane that recognize transmitter molecules and return them to the presynaptic neuron for reuse.
A compensatory increase in receptor availability at the synapses of a neuron.
The axonal swelling from which neurotransmitter diffuses in a nondirected synapse.
voltage-gated Na+ channel
A Na+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential; it mediates the action potential.