Chapter 2 basilar artery
acetylcholine An artery, formed by the fusion of the vertebral arteries, that supplies
A neurotransmitter produced and released by parasympathetic blood to the brainstem and to the posterior cerebral arteries.
postganglionic neurons, by motoneurons, and by neurons throughout the
brain. A nerve cell that has a single dendrite at one end and a single axon at the
allocortex other end.
Brain tissue with three layers or unlayered organization. bloodbrain barrier
The mechanisms that make the movement of substances from blood
A group of nuclei in the medial anterior part of the temporal lobe. vessels into brain cells more difficult than exchanges in other body organs,
angiography thus affording the brain greater protection from exposure to some
A brainimaging technique in which a specialized Xray image of the head substances found in the blood.
is taken shortly after the cerebral blood vessels have been filled with a brainstem
radiopaque dye by means of a catheter. The region of the brain that consists of the midbrain, the pons, and the
anterior cerebral arteries medulla.
Two large arteries, arising from the carotids, that provide blood to the cfos
anterior poles and medial surfaces of the cerebral hemispheres. An immediate early gene commonly used to identify activated neurons.
apical dendrite carotid arteries
The dendrite that extends from a pyramidal cell to the outermost surface of The major arteries that ascend the left and right sides of the neck to the
the cortex. brain, supplying blood to the anterior and middle cerebral arteries.
The thin covering (one of the three meninges) of the brain that lies The caudalmost spinal nerves, which extend beyond the spinal cord
between the dura mater and pia mater. proper to exit the spinal column.
arborization caudate nucleus
The elaborate branching of the dendrites of some neurons.
One of the basal ganglia; it has a long extension or tail.
astrocyte cell body or soma
A starshaped glial cell with numerous processes (extensions) that run in The region of a neuron that is defined by the presence of the cell nucleus.
all directions. cell nucleus
The spherical central structure of a cell that contains the chromosomes.
Collections of nerve cell bodies, belonging to the autonomic division of the central nervous system (CNS)
peripheral nervous system, that are found in various locations and The portion of the nervous system that includes the brain and the spinal
innervate the major organs. cord.
autonomic nervous system
The part of the peripheral nervous system that supplies neural A fissure that divides the frontal lobe from the parietal lobe.
connections to glands and to smooth muscles of internal organs. cerebellum
autoradiography A structure located at the back of the brain, dorsal to the pons, that is
A histological technique that shows the distribution of radioactive
involved in the central regulation of movement.
chemicals in tissues. cerebral cortex
axon collateral Sometimes called simply cortex. The outer covering of the cerebral
A branch of an axon from a single neuron. hemispheres, which consists largely of nerve cell bodies and their
A coneshaped area from which the axon originates out of the cell body. cerebral hemispheres
Functionally, the integration zone of the neuron. The right and left halves of the forebrain.
axon terminal cerebrospinal fluid (CSF)
Also called synaptic bouton. The end of an axon or axon collateral, The fluid that fills the cerebral ventricles.
which forms a synapse on a neuron or other target cell. cervical
axon Referring to the topmost 8 segments of the spinal cord, in the neck region.
A single extension from the nerve cell that carries nerve impulses from the choroid plexus
cell body to other neurons. A highly vascular portion of the lining of the ventricles that secretes
axonal transport cerebrospinal fluid.
The transportation of materials from the neuronal cell body to distant cingulate gyrus
regions in the dendrites and axons, and from the axon terminals back to A cortical portion of the limbic system, found in the frontal and parietal
the cell body. midline.
basal dendrite circle of Willis
One of several dendrites on a pyramidal cell that extend horizontally from A structure at the base of the brain that is formed by the joining of the
the cell body. carotid and basilar arteries.
basal ganglia coccygeal
A group of forebrain nuclei, including caudate nucleus, globus pallidus, Referring to the lowest spinal vertebra (also known as the tailbone).
and putamen, found deep within the cerebral hemispheres. computerized axial tomography (CAT or CT) A noninvasive technique for examining brain structure in humans through myelin.
computer analysis of Xray absorption at several positions around the gross neuroanatomy
head. Anatomical features of the nervous system that are apparent to the naked
conduction zone eye.
The part of the neuron over which the nerve’s electrical signal may be gyrus
actively propagated. Usually corresponds to the cell’s axon. A ridged or raised portion of a convoluted brain surface.
corpus callosum hindbrain
The main band of axons that connects the two cerebral hemispheres.
Also called rhombencephalon. The rear division of the brain, which, in
cortical column the mature vertebrate, contains the cerebellum, pons, and medulla.
One of the vertical columns that constitute the basic organization of the hippocampus
neocortex. A medial temporal lobe structure that is important for learning and
A nerve that is connected directly to the brain. horseradish peroxidase (HRP)
dendrite An enzyme found in horseradish and other plants that is used to
One of the extensions of the cell body that are the receptive surfaces of determine the cells of origin of a particular set of axons.
the neuron. hypothalamus
diencephalon Part of the diencephalon, lying ventral to the thalamus.
The posterior part of the forebrain, including the thalamus and immediate early genes (IEGs)
hypothalamus. A class of genes that show rapid but transient increases in expression in
dorsal root cells that have become activated.
The branch of a spinal nerve, entering the dorsal horn of the spinal cord, immunocytochemistry (ICC)
that carries sensory information from the peripheral nervous system to the A method for detecting a particular protein in tissues in which an antibody
spinal cord. recognizes and binds to the protein and then chemical methods are used
dura mater to leave a visible reaction product around each antibody.
The outermost of the three meninges that surround the brain and spinal in situ hybridization
cord. A method for detecting particular RNA transcripts in tissue sections by
edema providing a nucleotide probe that is complementary to, and will therefore
The swelling of tissue, especially in the brain, in response to injury. hybridize with, the transcript of interest.
enteric nervous system inferior colliculi
An extensive meshlike system of neurons that governs the functioning of Paired gray matter structures of the dorsal midbrain that receive auditory
the gut. information.
Also called prosencephalon. The frontal division of the neural tube, To provide neural input.
containing the cerebral hemispheres, the thalamus, and the input zone
hypothalamus. The part of a neuron that receives information, from other neurons or from
fornix specialized sensory structures. Usually corresponds to the cell’s dendrites.
A fiber tract that extends from the hippocampus to the mammillary body. integration zone
fourth ventricle The part of the neuron that initiates nerve electrical activity, described in
The passageway within the pons that receives cerebrospinal fluid from the detail in Chapter 3. Usually corresponds to the neuron’s axon hillock.
third ventricle and releases it to surround the brain and spinal cord. interneuron
frontal lobe A neuron that is neither a sensory neuron nor a motoneuron; it receives
The most anterior portion of the cerebral cortex. input from and sends output to other neurons.
functional MRI (fMRI) lateral ventricle
Magnetic resonance imaging that detects changes in blood flow and A complexly shaped lateral portion of the ventricular system within each
therefore identifies regions of the brain that are particularly active during hemisphere of the brain.
given task. limbic system
glial cells A loosely defined, widespread group of brain nuclei that innervate each
Also called glia or neuroglia. Nonneuronal brain cells that provide other to form a network.
structural, nutritional, and other types of support to the brain. lumbar
globus pallidus Referring to the 5 spinal segments that make up the upper part of the
One of the basal ganglia. lower back.
Golgi stain magnetic resonance imaging (MRI)
A histological stain that fills a small proportion of neurons with a dark, A noninvasive technique that uses magnetic energy to generate images
silverbased precipitate. that reveal some structural details in the living brain.
granule cell magnetoencephalography (MEG)
A type of small nerve cell. A passive and noninvasive functional brainimaging technique that
gray matter measures the tiny magnetic fields produced by active neurons, in order to
Areas of the brain that are dominated by cell bodies and are devoid of identify regions of the brain that are particularly active during a given task. mammillary body attracted to RNA, which encircles the nucleus.
One of a pair of nuclei at the base of the brain. node of Ranvier
meninges A gap between successive segments of the myelin sheath where the axon
membrane is exposed.
The three protective sheets of tissue—dura mater, pia mater, and
arachnoid—that surround the brain and spinal cord. norepinephrine
meningitis Also called noradrenaline. A neurotransmitter produced and released
An acute inflammation of the meninges, usually caused by a viral or by sympathetic postganglionic neurons to accelerate organ activity. Also
bacterial infection. produced in the brainstem and found in projections throughout the brain.
A subdivision of the hindbrain that includes the cerebellum and the pons. Here, a collection of neuronal cell bodies within the central nervous
microglial cells system (e.g., the caudate nucleus).
Also called microglia. Extremely small glial cells that remove cellular occipital lobes
debris from injured or dead cells. Large regions of cortex covering much of the posterior part of each
midbrain cerebral hemisphere.
Also called mesencephalon. The middle division of the brain. olfactory bulb
middle cerebral arteries An anterior projection of the brain that terminates in the upper nasal
Two large arteries, arising from the carotids, that provide blood to most of passages and, through small openings in the skull, provides receptors for
the lateral surfaces of the cerebral hemispheres. smell.
A cellular organelle that provides metabolic energy for the cell’s A type of glial cell that forms myelin in the central nervous system.
processes. optical imaging
motoneuron A method for visualizing brain activity in which nearinfrared light is passed
Also called motor neuron. A nerve cell that transmits motor messages, through the scalp and skull.
stimulating a muscle or gland. output zone
multiple sclerosis The part of a neuron, usually corresponding to the axon terminals, at
Literally “many scars”; a disorder characterized by widespread which the cell sends information to another cell.
degeneration of myelin. parallel fiber
multipolar neuron One of the axons of the granule cells that form the outermost layer of the
A nerve cell that has many dendrites and a single axon. cerebellar cortex.
myelencephalon or medulla parasympathetic nervous system
The posterior part of the hindbrain, continuous with the spinal cord. A component of the autonomic nervous system that arises from both the
myelin cranial nerves and the sacral spinal cord.
The fatty insulation around an axon, formed by glial cells, that improves parietal lobes
the speed of conduction of nerve impulses. Large regions of cortex lying between the frontal and occipital lobes of
myelination each cerebral hemisphere.
The process of myelin formation. peripheral nervous system
neocortex (isocortex) or cortex The portion of the nervous system that includes all the nerves and
Cerebral cortex that is made up of six distinct layers. neurons outside the brain and spinal cord.
A collection of axons bundled together outside the central nervous system. The innermost of the three meninges that surround the brain and spinal
neural plasticity cord.
Also called neuroplasticity. The ability of the nervous system to change pons
A portion of the metencephalon; part of the brainstem connecting midbrain
in response to experience or the environment.
neural tube to medulla.
An embryonic structure with subdivisions that correspond to the future positron emission tomography (PET)
forebrain, midbrain, and hindbrain. A technique for examining brain function by combining tomography with
injections of radioactive substances used by the brain.
The hypothesis that the brain is composed of separate cells that are postcentral gyrus
distinct structurally, metabolically, and functionally. The strip of parietal cortex, just behind the central sulcus, that receives
neuron or nerve cell somatosensory information from the entire body.
posterior cerebral arteries
The basic unit of the nervous system, each composed of a cell body,
receptive extension(s) (dendrites), and a transmitting extension (axon). Two large arteries, arising from the basilar artery, that provide blood to
neurotransmitter posterior aspects of the cerebral hemispheres, cerebellum, and brainstem.
Also called synaptic transmitter, chemical transmitter, or simply postganglionic
Literally, “after the ganglion.” Referring to neurons in the autonomic
transmitter. The chemical released from the presynaptic axon terminal
that serves as the basis of communication between neurons. nervous system that run from the autonomic ganglia to various targets in
Nissl stain the body.
A histological stain that outlines all cell bodies because the dyes are postsynaptic membrane The specialized membrane on the surface of the cell that receives Also called lateral sulcus. A deep fissure that demarcates the temporal
information by responding to neurotransmitter from a presynaptic neuron. lobe.
postsynaptic sympathetic chain
Referring to the region of a synapse that receives and responds to
A chain of ganglia that runs along each side of the spinal column; part of
neurotransmitter. the sympathetic nervous system.
precentral gyrus sympathetic nervous system
The strip of frontal cortex, just in front of the central sulcus, that is crucA component of the autonomic nervous system that arises from the
for motor control.
thoracic and lumbar spinal cord.
Literally, “before the ganglion.” Referring to neurons in the autonomic The tiny gap between neurons where information is passed from one to
nervous system that run from the central nervous system to the autonomic the other.
presynaptic membrane The space between the presynaptic and postsynaptic elements.
The specialized membrane of the axon terminal of the neuron that synaptic vesicle
transmits information by releasing neurotransmitter. A small, spherical structure that contains molecules of neurotransmitter.
Referring to the region of the synapse that releases neurotransmitter. The dorsal portion of the midbrain, including the inferior and superior
Purkinje cell colliculi.
A type of large nerve cell in the cerebellar cortex. telencephalon
putamen The frontal subdivision of the forebrain that includes the cerebral
One of the basal ganglia. hemispheres when fully developed.
pyramidal cell temporal lobes
A type of large nerve cell that has a roughly pyramidshaped cell body; Large lateral cortical regions of each cerebral hemisphere, continuous with
found in the cerebral cortex. the parietal lobes posteriorly, and separated from the frontal lobe by the
receptor Sylvian fissure.
Also called receptor molecule. A protein that captures and reacts to thalamus
molecules of a neurotransmitter or hormone. The brain regions that surround the third ventricle.
red nucleus third ventricle
A brainstem structure related to motor control. The midline ventricle that conducts cerebrospinal fluid from the lateral
reticular formation ventricles to the fourth ventricle.
An extensive region of the brainstem (extending from the medulla through thoracic
the thalamus) that is involved in arousal (waking). Referring to the 12 spinal segments below the cervical (neck) portion of
ribosomes the spinal cord, corresponding to the chest.
Structures in the cell body where genetic information is translated to tract
produce proteins. A bundle of axons found within the central nervous system.
sacral transcranial magnetic stimulation (TMS)
Referring to the 5 spinal segments that make up the lower part of the Localized, noninvasive stimulation of cortical neurons through the
lower back. application of strong magnetic fields.
Schwann cell unipolar neuron
The glial cell that forms myelin in the peripheral nervous system. Also called monopolar neuron. A nerve cell with a single branch that
sensory neuron leaves the cell body and then extends in two directions; one end is the
A neuron that is directly affected by changes in the environment, such as receptive pole, the other end the output zone.
light, odor, or touch. ventral root
spinal nerve The branch of a spinal nerve, arising from the ventral horn of the spinal
Also called somatic nerve. A nerve that emerges from the spinal cord. cord, that carries motor messages from the spinal cord to the peripheral
stroke nervous system.
Damage to a region of brain tissue that results from blockage or rupture of ventricular system
vessels that supply blood to that region. A system of fluidfilled cavities inside the brain.
substantia nigra vertebral arteries
A brainstem structure in humans that is related to the basal ganglia and is Arteries that ascend the vertebrae, enter the base of the skull, and join
named for its dark pigmentation. together to form the basilar artery.
sulcus white matter
A furrow of a convoluted brain surface. A shiny layer underneath the cortex that consists largely of axons with
superior colliculi white myelin sheaths.
Paired gray matter structures of the dorsal midbrain that receive visual
information and are involved in direction of visual gaze and visual attention
to intended stimuli. Chapter 1
Sylvian fissure behavioral intervention An approach to finding relations between body variables and behavioral chromosome
variables that involves intervening in the behavior of an organism and A complex of condensed strands of DNA and associated protein
looking for resultant changes in body structure or function. molecules; found in the nucleus of cells.
Also called behavioral neuroscience. The study of the biological bases of The evolutionary process by which responses to similar ecological
psychological processes and behavior. features bring about similarities in behavior or structure among animals
consciousness that are only distantly related (i.e., that differ in genetic heritage).
The state of awareness of one’s own existence and experience.
conserved A measure of brain size relative to body size.
In the context of evolution, referring to a trait that is passed on from a endocast
common ancestor to two or more descendant species. A cast of the cranial cavity of a skull, especially useful for studying fossils
of extinct species.
The covariation of two measures. evolution by natural selection
dependent variable The Darwinian theory that evolution proceeds by differential success in
The factor that an experimenter measures to monitor a change in reproduction.
response to changes in an independent variable. evolution
dualism The process by which a population of interbreeding individuals changes
The notion, promoted by René Descartes, that the mind is subject only to over long periods of time.
spiritual interactions, while the body is subject only to material interactioevolutionary psychology
independent variable A field devoted to asking how natural selection has shaped behavior in
The factor that is manipulated by an experimenter. humans.
evels of analysis genetics
The scope of experimental approaches. A scientist may try to understand The study of inheritance, including the genes encoded in DNA.
behavior by genus
monitoring molecules, nerve cells, brain regions, or social environments, A group of species that resemble each other because of shared
or some combination of these levels of analysis. inheritance.
Also called nerve cell. The basic unit of the nervous system. A physical resemblance that is based on common ancestry, such as the
neuroplasticity or neural plasticity similarity in forelimb structures of different mammals.
The ability of the nervous system to change in response to experience or homoplasy
the environment. A physical resemblance that is due to convergent evolution, such as the
neuroscience similar body form of tuna and dolphins.
The study of the nervous system. mutation
ontogeny A change in the nucleotide sequence of a gene as a result of unfaithful
The process by which an individual changes in the course of its lifetime— replication.
that is, grows up and grows old. naturalist
phrenology A student of animal life and structure.
The belief that bumps on the skull reflect enlargements of brain regions neocortex or isocortex
responsible for certain behavioral faculties. Cerebral cortex that is made up of six distinct layers.
The scientific strategy of breaking a system down into increasingly smaller The evolutionary history of a particular group of organisms.
parts in order to understand it. sexual selection
somatic intervention Darwin’s theoretical mechanism for the evolution of anatomical and
An approach to finding relations between body variables and behavioral behavioral differences between males and females.
variables that involves manipulating body structure or function and looking species
for resultant changes in behavior. A group of individuals that can readily interbreed to produce fertile
Chapter 6 The classification of organisms.
Here, a trait that increases the probability that an individual will leave
offspring in subsequent generations.
analogy absolute refractory phase
Similarity of function, although the structures of interest may look differenA brief period of complete insensitivity to stimuli.
The human hand and an elephant’s trunk are analogous features. acetylcholine (ACh)
A neurotransmitter produced and released by parasympathetic
Of or related to Australopithecus, a primate genus, known only from the postganglionic neurons, by motoneurons, and by neurons throughout the
fossil record, thought to be an ancestor to humans. brain. action potential conduction velocity
The propagated electrical message of a neuron that travels along the axon The speed at which an action potential is propagated along the length of
to the presynaptic axon terminals. an axon (or section of peripheral nerve).
The positive or negative change in membrane potential that may follow an The phenomenon of neural connections in which many cells send signals
action potential. to a single cell.
A molecule, usually a drug, that binds a receptor molecule and initiates a An alkaloid neurotoxin that causes paralysis by blocking acetylcholine
response like that of another molecule, usually a neurotransmitter. receptors in muscle.
allornone property degradation
The fact that the amplitude of the action potential is independent of the The chemical breakdown of a neurotransmitter into inactive metabolites.
magnitude of the stimulus. dendrodendritic
anion Referring to a type of synapse in which a synaptic connection forms
A negatively charged ion, such as a protein or chloride ion. between the dendrites of two neurons.
A molecule, usually a drug, that interferes with or prevents the action of a A reduction in membrane potential (the interior of the neuron becomes
transmitter. less negative).
In epilepsy, the unusual sensations or premonition that may precede the The spontaneous spread of molecules of one substance among molecules
beginning of a seizure. of another substance until a uniform concentration is achieved.
Referring to a synapse in which a presynaptic axon terminal synapses The phenomenon of neural connections in which one cell sends signals to
onto another axon’s terminal. many other cells.
Referring to a synapse in which a presynaptic axon terminal synapses A compensatory reduction in receptor availability at the synapses of a
onto a dendrite of the postsynaptic neuron, either via a dendritic spine or neuron.
directly onto the dendrite itself. ectopic transmission
axon hillock Cellcell communication based on release of neurotransmitter in regions
A coneshaped area from which the axon originates out of the cell body. outside traditional synapses.
Functionally, the integration zone of the neuron. electrical synapse
axosomatic Also called gap junction. The region between neurons where the
Referring to a synapse in which a presynaptic axon terminal synapses presynaptic and postsynaptic membranes are so close that the action
onto the cell body (soma) of the postsynaptic neuron. potential can jump to the postsynaptic membrane without first being
batrachotoxin translated into a chemical message.
A toxin, produced by poison arrow frogs, that selectively interferes with electroencephalogram (EEG)
Na+ channels. A recording of gross electrical activity of the brain recorded from large
bungarotoxin electrodes placed on the scalp.
A neurotoxin, isolated from the venom of the banded krait, that selectively electrostatic pressure
blocks acetylcholine receptors. The propensity of charged molecules or ions to move, via diffusion, toward
calcium ion (Ca2+) areas with the opposite charge.
A calcium atom that carries a double positive charge because it has lost endogenous ligand
two electrons. Any substance, produced within the body, that selectively binds to the type
cation of receptor that is under study.
A positively charged ion, such as a potassium or sodium ion. epilepsy
cell membrane A brain disorder marked by major sudden changes in the
The lipid bilayer that ensheathes a cell. electrophysiological state of the brain that are referred to as seizures.
A genetic abnormality of ion channels, causing a variety of symptoms. Here, the point at which the movement of ions across the cell membrane
chloride ion (Cl–) is balanced, as the electrostatic pressure pulling ions in one direction is
A chlorine atom that carries a negative charge because it has gained one offset by the diffusion force pushing them in the opposite direction.
electron. eventrelated potential (ERP)
cholinergic Also called evoked potential. Averaged EEG recordings measuring brain
Referring to cells that use acetylcholine as their synaptic transmitter. responses to repeated presentations of a stimulus. Components of the
complex partial seizure ERP tend to be reliable because the background noise of the cortex has
In epilepsy, a type of seizure that doesn’t involve the entire brain, and been averaged out.
therefore can cause a wide variety of symptoms. excitatory postsynaptic potential (EPSP)
concentration gradient A depolarizing potential in the postsynaptic neuron that is caused by
Variation of the concentration of a substance within a region. excitatory presynaptic potentials. EPSPs increase the probability that the postsynaptic neuron will fire an action potential. activated, use a G protein system to alter the functioning of the
exogenous ligand postsynaptic cell.
Any substance, originating from outside the body, that selectively binds to microelectrode
the type of receptor that is under study. An especially small electrode used to record electrical potentials from
extracellular fluid living cells.
The fluid in the spaces between cells (interstitial fluid) and in the vascular millivolt (mV)
system. A thousandth of a volt.
G proteins negative polarity
A class of proteins that reside next to the intracellular portion of a receptor A negative electricalpotential difference relative to a reference electrode.
and that are activated when the receptor binds an appropriate ligand on Nernst equation
the extracellular surface. An equation predicting the voltage needed to just counterbalance the
diffusion force pushing an ion across a semipermeable membrane from
Referring to the property by which an ion channel may be opened or the side with a high concentration to the side with a low concentration.
closed by factors such as chemicals, voltage changes, or mechanical neural chain
actions. A simple kind of neural circuit in which neurons are attached linearly, end
grand mal seizure
A type of generalized epileptic seizure in which nerve cells fire in high neurophysiology
frequency bursts. The study of the life processes of neurons.
An increase in membrane potential (the interior of the neuron becomes Also called synaptic transmitter, chemical transmitter, or simply transmitter.
even more negative). The chemical released from the presynaptic axon terminal that serves as
inhibitory postsynaptic potential (IPSP) the basis of communication between neurons.
A hyperpolarizing potential in the postsynaptic neuron that is caused by node of Ranvier
inhibitory connections. IPSPs decrease the probability that the A gap between successive segments of the myelin sheath where the axon
postsynaptic neuron will fire an action potential. membrane is exposed.
intracellular fluid nondirected synapse
Also called cytoplasm. The watery solution found within cells. A type of synapse in which the presynaptic and postsynaptic cells are not
ion channel in close apposition; instead, neurotransmitter is released by axonal
A pore in the cell membrane that permits the passage of certain ions varicosities and diffuses away to affect wide regions of tissue.
through the membrane when the channels are open. petit mal seizure
ion Also called an absence attack. A seizure that is characterized by a spike
An atom or molecule that has acquired an electrical charge by gaining or andwave EEG and often involves a loss of awareness and inability to
losing one or more electrons. recall events surrounding the seizure.
ionotropic receptor pinocytosis
A receptor protein that includes an ion channel that is opened when the The process by which synaptic neurotransmitter is repackaged into
receptor is bound by an appropriate ligand. synaptic vesicles.
kindling postsynaptic potential
A method of experimentally inducing an epileptic seizure by repeatedly A local potential that is initiated by stimulation at a synapse, can vary in
stimulating a brain region. amplitude, and spreads passively across the cell membrane, decreasing in
knee jerk reflex strength with time and distance.
A variant of the stretch reflex in which stretching of the tendon beneath the potassium ion (K+)
knee leads to an upward kick of the leg. A potassium atom that carries a positive charge because it has lost one
A substance that binds to receptor molecules, such as those at the receptor molecule
surface of the cell. Also called receptor. A protein that captures and reacts to molecules of a
ligandgated ion channel neurotransmitter or hormone.
Also known as chemically gated ion channel. An ion channel that opens or refractory
closes in response to the presence of a particular chemical. Transiently inactivated or exhausted.
lipid bilayer relative refractory phase
The structure of the neuronal cell membrane, which consists of two layers A period of reduced sensitivity during which only strong stimulation
of lipid molecules, within which float various specialized proteins, such as produces an action potential.
receptors. resting membrane potential
local potential A difference in electrical potential across the membrane of a nerve cell
An electrical potential that is initiated by stimulation at a specific site, during an inactive period.
which is a graded response that spreads passively across the cell retrograde synapse
membrane, decreasing in strength with time and distance. A synapse in which a signal (usually a gas neurotransmitter) flows from
metabotropic receptor the postsynaptic neuron to the presynaptic neuron, thus counter to the
A receptor protein that does not contain an ion channel but may, when usual direction of synaptic communication. reuptake postganglionic neurons by motoneurons, and by neurons throughout the
The process by which released synaptic transmitter molecules are taken brain.
up and reused by the presynaptic neuron, thus stopping synaptic activity. adenosine
In the context of neural transmission, a neuromodulator that alters
The form of conduction that is characteristic of myelinated axons, in which synaptic activity.
the action potential jumps