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Flashcards in chapter 3: neurophysiology Deck (73):
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Neurophysiology

The study of the life processes of neurons

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Polarized

Exhibiting a difference in electrical charge between the inside and outside of the cell

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Ion

An atom or molecule that has acquired an electrical charge by gaining or losing one or more electrons

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Anion

A negatively charged ion, such as a protein or a chloride ion

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Cation

A positively charged ion, such as a potassium or sodium ion

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Intracellular fluid

The watery solution found within cells

Also called cytoplasm

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Extracellular fluid

the fluid in the spaces between cells (interstitial fluid) and in the vascular system

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Cell membrane

The lipid bilayer that ensheathes a cell

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Microelectrode

An especially small electrode used to record electrical potentials in living cells

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Resting potential

A difference in electrical potential across the membrane of a nerve cell during an inactive period

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Ion channel

A pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open

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Millivolt (mV)

A thousandth of a volt

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Potassium ion (K+)

A potassium atom that carries a positive charge because it has lost one electron

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Selective permeability

The property of a membrane that allows some substances to pass through, but not others

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Diffusion

The spontaneous spread of molecules until a uniform concentration is achieved

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Electrostatic pressure

The propensity of charged molecules or ions to move, via diffusion, toward areas with the opposite charge

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Sodium-potassium pump

The energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in

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Sodium ion (NA+)

A sodium atom that carries a positive charge because it has lost one electron

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Equilibrium potential

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

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Axon hillock

The cone-shaped area on the cell body from which the axon originates

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Hyperpolarization

An increase in membrane potential (the interior of the neuron becomes even more negative)

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Depolarization

An increase in membrane potential (the interior of the neuron becomes less negative)

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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

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Threshold

The stimulus intensity that is just adequate to trigger an action potential at the axon hillock

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Action potential

A rapid reversal of the membrane potential that momentarily makes the inside of the membrane positive with respect to the outside

Also called spike

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All-or-none property

The fact that the size (amplitude) of the action potential is independent of the size of the stimulus

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Afterpotential

The positive or negative change in membrane potential that may follow an action potential

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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

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Refractory

Temporarily unresponsive or inactivated

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Absolute refractory phase

A brief period of complete insensitivity to stimuli

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Relative refractory phase

A period of reduced sensitivity during which only strong stimulation produces an action potential

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Conduction velocity

The speed at which an action potential is propagated along the length of an axon (or section of peripheral nerve)

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Myelin

The fatty insulation around an axon, formed by glial cells. This sheath boosts the speed at which nerve impulses are conducted

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Node of Ranvier

A gap between successive segments of the myelin sheath where the axon membrane is exposed

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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

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Neurotransmitter (transmitter)

The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons

Also called transmitter, synaptic transmitter, or chemical transmitter

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Presynaptic

Referring to the region of a synapse that releases neurotransmitter

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Postsynaptic

Referring to the region of a synapse that receives and responds to neurotransmitter

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Postsynaptic potential

A local potential that is initiated by stimulation at a synapse, which can vary in amplitude, and spreads passively across the cell membrane, decreasing in strength with time and distance

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Excitatory presynaptic 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

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Synaptic delay

The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential

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Inhibitory postsynaptic potential (IPSP)

A hyperpolarizing potential in the postsynaptic neuron that is caused by inhibitory connections. IPSPs decrease the probability that a postsynaptic neuron will fire an action potential.

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Chloride ion (Cl-)

A chlorine atom that carries a negative charge because it has gained one electron

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Spatial summation

The summation of postsynaptic potentials that reach the axon hillock from different locations across the cell body. If this summation reaches threshold, an action potential is triggered

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Temporal summation

The summation of postsynaptic potentials that reach the axon hillock at different times. The closer in time the potentials occur, the more complete the summation is

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Synaptic vesicle

A small, spherical structure that contains molecules of neurotransmitter

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Synaptic cleft

The space between the presynaptic and postsynaptic neurons at a synapse. This gap measures about 20-40 nm

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Calcium ion (Ca2+)

A calcium atom that carries a double positive charge because it has lost two electrons

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Ligand

A substance that binds to receptor molecules, such as a neurotransmitter or drug that binds postsynaptic receptors

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Acetylcholine (aCh)

A neurotransmitter that is produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain

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Neurotransmitter receptor

A protein that captures and reacts to molecules of a neurotransmitter or hormone

Also called receptor

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Curare

A neurotoxin that causes paralysis by blocking acetylcholine receptors in muscle

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Bungarotoxin

A neurotoxin, isolated from the venom of the banded krait, that selectively blocks acetylcholine receptors

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Agonist

A molecule, usually a drug, that binds a receptor molecule and initiates a response like that of another molecule, usually a neurotransmitter

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Antagonist

A molecule, usually a drug, that interferes with or prevents the action of a neurotransmitter

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Cholinergic

Referring to cells that use acetylcholine as their synaptic transmitter

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Degradation

The chemical breakdown of a neurotransmitter into inactive metabolites

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Acetylcholinesterase (AChE)

An enzyme that inactivates the transmitter acetylcholine

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Reuptake

The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity

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Transporter

A specialized receptor in the presynaptic membrane that recognizes transmitter molecules and returns them to the presynaptic neuron for reuse

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Axo-dendritic synapse

A synapse at which a presynaptic axon terminal synapses onto a dendrite of the postsynaptic neuron, either via a dendritic spine or directly onto the dendrite itself

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Axo-somatic synapse

A synapse at which a presynaptic axon terminal synapses onto the cell body (soma) of the postsynaptic neuron

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Axo-axonic synapse

A synapse at which the presynaptic axon terminal synapses onto the axon terminal of another neuron

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Dendro-dendritic synapse

A synapse at which a synaptic connection forms between the dendrites of two neurons

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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

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Electroencephalogram (EEG)

A recording of gross electrical activity of the brain via large electrodes placed on the scalp

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Event-related potential (ERP)

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

Also called evoked potential

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Epilepsy

A brain disorder marked by major, sudden changes in the electrophysiological state of the brain that are referred to as seizures

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Seizure

An epileptic episode

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Grand mal seizure

A type of generalized epileptic seizure in which nerve cells fire in high-frequency bursts, usually accompanied by involuntary rhythmic contractions of the body

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Petit mal seizure

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

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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

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Aura

In epilepsy, the unusual sensations or premonition that may precede the beginning of a seizure