Chapter 3 Flashcards

absolute refractory phase
See refractory phase (definition 1).
acetylcholine (ACh)
A neurotransmitter produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain.
action potential
Also called nerve impulse. The propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminals. See Figures 3.6, 3.7.
afterpotential
The positive or negative change in membrane potential that may follow an action potential.
agonist
1. A molecule, usually a drug, that binds a receptor molecule and initiates a response like that of another molecule, usually a neurotransmitter. Compare antagonist (definition 1). 2. A muscle that moves a body part in the same general way as the muscle of interest; a synergistic muscle. Compare antagonist (definition 2). See also synergist.
all-or-none property
The fact that the amplitude of the action potential is independent of the magnitude of the stimulus. See Table 3.1. Compare postsynaptic potential.
anion
A negatively charged ion, such as a protein or chloride ion. Compare cation.
antagonist
1. A molecule, usually a drug, that interferes with or prevents the action of a transmitter. Compare agonist (definition 1). 2. A muscle that counteracts the effect of another muscle. Compare agonist (definition 2) and synergist.
aura
In epilepsy, the unusual sensations or premonition that may precede the beginning of a seizure. See Figure 3.20.
autoreceptor
A receptor for a synaptic transmitter that is located in the presynaptic membrane telling the axon terminal how much transmitter has been released.
axo-axonic
Referring to a synapse in which a presynaptic axon terminal synapses onto another axon’s terminal. Compare axo-dendritic, axo-somatic, and dendro-dendritic.
axo-dendritic
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. Compare axo-axonic, axo-somatic, and dendro-dendritic.
axo-somatic
Referring to a synapse in which a presynaptic axon terminal synapses onto the cell body (soma) of the postsynaptic neuron. Compare axo-axonic, axo-dendritic, and dendro-dendritic.
axon hillock
A cone-shaped area from which the axon originates out of the cell body. Functionally, the integration zone of the neuron. See Figure 2.6.
batrachotoxin
A toxin, secreted by poison arrow frogs, that selectively interferes with Na+ channels.
bungarotoxin
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.
cation
A positively charged ion, such as a potassium or sodium ion. Compare anion.
cell membrane
The lipid bilayer that ensheathes a cell.
channelopathy
A genetic abnormality of ion channels, causing a variety of symptoms.
channelrhodopsin
A protein that, in response to light of the proper wavelength, opens a channel to admit sodium ions, which results in excitation of neurons.
chloride ion (Cl)
A chlorine atom that carries a negative charge because it has gained one electron.
cholinergic
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. See Figure 3.20.
concentration gradient
Variation of the concentration of a substance within a region. Molecules and ions tend to move down the concentration gradient from areas of high concentration to areas of low concentration. See Figure 3.2.
conduction velocity
The speed at which an action potential is propagated along the length of an axon (or section of peripheral nerve).
convergence
The phenomenon of neural connections in which many cells send signals to a single cell. Compare divergence.
curare
An alkaloid neurotoxin that causes paralysis by blocking acetylcholine receptors in muscle.
degradation
The chemical breakdown of a neurotransmitter into inactive metabolites.
dendro-dendritic
Referring to a type of synapse in which a synaptic connection forms between the dendrites of two neurons. Compare axo-axonic, axo-dendritic, and axo-somatic.
depolarization
A reduction in membrane potential (the interior of the neuron becomes less negative). See Figure 3.5. Compare hyperpolarization.
diffusion
The spontaneous spread of molecules of one substance among molecules of another substance until a uniform concentration is achieved. See Figure 3.2.
divergence
The phenomenon of neural connections in which one cell sends signals to many other cells. See Figure 3.18. Compare convergence.
down-regulation
A compensatory reduction in receptor availability at the synapses of a neuron. Compare up-regulation.
ectopic transmission
Cell–cell communication based on release of neurotransmitter in regions outside traditional synapses.
electrical synapse
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. See Box 3.2.
electroencephalography (EEG)
The recording and study of gross electrical activity of the brain recorded from large electrodes placed on the scalp. The abbreviation EEG may refer either to the process of encephalography or to its product, the encephalogram. See Figures 3.19, 14.10.
electrostatic pressure
The propensity of charged molecules or ions to move, via diffusion, toward areas with the opposite charge.
endogenous ligand
Any substance, produced within the body, that selectively binds to the type of receptor that is under study. Compare exogenous ligand.
epilepsy
A brain disorder marked by major sudden changes in the electrophysiological state of the brain that are referred to as seizures. See Box 3.3.
equilibrium
In chemistry, the point at which all ongoing reactions are canceled or balanced by others, resulting in a stable, offset, or unchanging system.
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. See Figures 3.21, 18.8.
excitatory postsynaptic potential (EPSP)
A depolarizing potential in the postsynaptic neuron that is caused by excitatory connections. EPSPs increase the probability that the postsynaptic neuron will fire an action potential. See Figure 3.9. Compare inhibitory postsynaptic potential.
exocytosis
The process by which a synaptic vesicle fuses with the presynaptic terminal membrane to release neurotransmitter into the synaptic cleft. See Figure 3.12.
exogenous ligand
Any substance, originating from outside the body, that selectively binds to the type of receptor that is under study. Compare endogenous ligand.
extracellular fluid
The fluid in the spaces between cells (interstitial fluid) and in the vascular system. Compare intracellular fluid.
G proteins
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.
grand mal seizure
A type of generalized epileptic seizure in which nerve cells fire in high-frequency bursts. Grand mal seizures cause loss of consciousness and sudden muscle contraction. See Box 3.3. Compare petit mal seizure.
halorhodopsin
A protein that, in response to light of the proper wave length, opens a channel to admit chloride ions, which results in inhibition of neurons.
hyperpolarization
An increase in membrane potential (the interior of the neuron becomes even more negative). See Figure 3.5. Compare depolarization.
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. See Figure 3.9. Compare excitatory postsynaptic potential.
intracellular fluid
Also called cytoplasm. The watery solution found within cells. Compare extracellullar fluid.
ion
An atom or molecule that has acquired an electrical charge by gaining or losing one or more electrons.
ion channel
A pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open. See Figure 3.4.
ionotropic receptor
A receptor protein that includes an ion channel that is opened when the receptor is bound by an agonist. See Figures 3.15, 4.1. See also ligand-gated ion channel. Compare metabotropic receptor.
kindling
A method of experimentally inducing an epileptic seizure by repeatedly stimulating a brain region. See Box 3.3.
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. See Figure 3.17.
ligand
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; an example is the ionotropic neurotransmitter receptor. Compare voltage-gated Na+ channel.
lipid bilayer
The structure of the neuronal cell membrane, which consists of two layers of lipid molecules, within which float various specialized proteins, such as receptors. See Figure 3.4.
local potential
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.
metabotropic receptor
A receptor protein that does not contain an ion channel but may, when activated, use a G protein system to open a nearby ion channel. See Figures 3.13, 4.1. Compare ionotropic receptor.
microelectrode
An especially small electrode used to record electrical potentials from living cells.
millivolt (mV)
A thousandth of a volt.
negative polarity
A negative electrical-potential difference relative to a reference electrode. A neuron at rest exhibits a greater concentration of negatively charged ions in its interior than in its immediate surrounds; thus it is said to be negatively polarized. See Figure 3.1.
Nernst equation
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.
neural chain
A simple kind of neural circuit in which neurons are attached linearly, end-to-end.
neurophysiology
The study of the life processes of neurons.
neurotransmitter
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. See Figure 3.12; Table 4.1.
node of Ranvier
A gap between successive segments of the myelin sheath where the axon membrane is exposed. See Figures 2.7, 3.8.
nondirected synapse
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.
opsin
One of the two components of photopigments in the retina. The other component is retinal.
optogenetics
The use of genetic tools to induce neurons to become sensitive to light, such that experimenters can excite or inhibit the cell by stimulating it with light.
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. See Figure 3.20. Compare grand mal seizure.
postsynaptic potential
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. Compare all-or-none property.
potassium ion (K+)
A potassium atom that carries a positive charge because it has lost one electron.
receptor molecule
See receptor
refractory
Transiently inactivated or exhausted.
relative refractory phase
See refractory phase (definition 1).
resting membrane potential
A difference in electrical potential across the membrane of a nerve cell during an inactive period. See Figures 3.1, 3.5.
retrograde synapse
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.
reuptake
The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity.
saltatory conduction
The form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next.
saxitoxin (STX)
An animal toxin that blocks sodium channels when applied to the outer surface of the cell membrane.
second messenger
A slow-acting substance in the postsynaptic cell that amplifies the effects of synaptic activity and signals synaptic activity within the postsynaptic cell.
seizure
An epileptic episode. See Figure 3.20.
selective permeability
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.
sodium-potassium pump
The energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in.
spatial summation
The summation at the axon hillock of postsynaptic potentials from across the cell body. If this summation reaches threshold, an action potential is triggered. See Figure 3.11. Compare temporal summation.
synaptic delay
The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential. The delay is caused by the translation of an electrical event into a secretory event, and back to an electrical event on the postsynaptic side.
temporal summation
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. Compare spatial summation.
tetrodotoxin (TTX)
A toxin from puffer fish ovaries that blocks the voltage-gated sodium channel, preventing action potential conduction.
threshold
The stimulus intensity that is just adequate to trigger an action potential at the axon hillock.
transporters
Specialized receptors in the presynaptic membrane that recognize transmitter molecules and return them to the presynaptic neuron for reuse.
up-regulation
A compensatory increase in receptor availability at the synapses of a neuron. Compare down-regulation.
varicosity
The axonal swelling from which neurotransmitter diffuses in a nondirected synapse.
voltage-gated Na+ channel An Na+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential. Voltage-gated Na+ channels mediate the action potential. Compare ligand-gated ion channel.
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