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Organic Brain Biopsychology Chapter 2


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Absolute refractory period
the time immediately after an action potential, when the sodium gates close and the membrane cannot produce an action potential in response to stimulation of any intensity.
Action potential
rapid depolarization and slight reversal of the usual polarization caused by stimulation beyond the threshold.
Active transport
protein-mediated process that expends energy to pump chemicals from the blood into the brain.
Afferent axon
neuron that brings information INTO the structure.
All-or-none law
principle stating that the size, amplitude, and velocity of the action potential are independent of the intensity of the stimulus that initiated it.
Amino acids
acids containing an amine group.
memory loss.
Astrocyte (astroglia)
relatively large, star-shaped glia cell.
Axon hillock
swlling of the soma, the point where the axon begins.
single thin fibers of constant diameter that extend from a neuron.
Bipolar cells
type of neuron in the retina that receives input directly from the receptors.
Blood-brain barrier
the mechanism that keeps many chemicals out of the brain.
Cell body (soma)
the structure of a cell that contains the nucleus.
branching fiber that emanates from a neuron, growing narrower as it extends from the cell body toward the periphery.
Dendritic spine
short outgrowth along the dendrites.
reduction in the level of polarization across a membrane.
Efferent axon
neuron that carries information AWAY from the structure.
Electrical gradient
difference in positive and negative charges across the membrane.
Endoplasmic reticulum
network of thin tubes within a cell that transport synthesized proteins to other locations.
General anesthetics
drugs that decrease brain activity by opening potassium channels wider than usual.
type of cell in the nervous system that do not conduct impulses to other cells (unlike neurons)
a simple sugar; main fuel of vertebrate neurons.
Graded potential
membrane potential that varies in magnitude and does not follow the all-or-none law.
chemicals secreted by glands and conveyed by the blood to other organs, which are influenced by their activity.
increased polarization across a membrane.
Intrinsic neuron
a neuron whos axons and dendrites are all confined within a given structure.
Korsakoff's syndrome
a type of brain damate caused by thiamine deficiency, characterized by apathy, confusion, and memory impairment.
Local anesthetic
drug that attatches to the sodium channels of the membrane, preventing sodium ions from entering and thereby block action potentials (in this case, pain)
Local neuron
small neuron with a very short, or no axon.
structure that separates the inside of a cell from the outside.
very small cells.
Mictochondrion (pl: mitochondria)
the structure where the cell performs the metabolic activities that provide energy.
Motor neuron
a neuron that receives excitation from other neurons and conducts impoulses from its soma in the spinal cord to muscle or gland cells.
Myelin sheath
insulating material that covers many vertebrate axons.
Myelinated axon
an axon covered with a myelin sheath
cells that receive information and transmit it to other cells by conduction electrochemical impulses.

(See: Synapses)
Node of Ranvier
small, unmyelinated gap along the axon between segments of myelin.
Def. 1: structure within a cell that contains the chromosomes.
Def 2: cluster of neuron cell bodies within the central nervous system.
glia cells that surround and insulate certain axons in the vertebrate brain and spinal cord.
the electrical gradient across a membrane.
Presynaptic terminal
the tip of an axon from where the axon releases chemicals into the synapse.
Propogation of the action potential
the transmission of an action potential down an axon.
Radial glia
typoe of glia cells that guide the migration of neurons and the growth of their axons and dendrites during embryological development.
Refractory period
the brief period following an action potential, when the cell resists the production of further action potentials.
Relative refractory period
the time after the absolute refractory period, when potassium gates remain open wider than usual, thus requiring a stronger than usual stimulus to initiate an action potential.
Resting potential
the elctrical potential across a membrane when a neuron is not being stimulated.
the site where the cell synthesizes new protein molecules.
Saltatory conduction
the jumping of action potentials from one node to another by the flow of positive ions.
Schwann cell
a glia cell that surrounds and insulates acertain axons in the periphery of the vertebrate body.
Selective permeability
certain chemicals ability to pass more freely than other chemicals through a membrane.
Sensory neuron
a neuron specialized to be highly sensitive to a specific type of stimulation.
Sodium-potassium pump
the mechanism that actively "pumps" three sodium ions out of the cell while simultaneously "pumps" in two potassium ions.
Soma (cell body)
the structure of a cell that contains the nucleus.
(Vitamin B1)
a chemical necessary for the metabolism of glucose.
Threshold of excitation
the level of depolarization when a brief stimulation triggers a rapid, massive electrical change by the membrane.
Voltage-activiated channel
a membrane channel whose permeability to sodium (or any other ion) depends on the voltage difference across the membrane.

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