|action potential |
aka nerve impulse
|momentary change in electrical voltage potential (wave of depolarization) on the surface of a nerve or muscle cell or gland cell which takes place when the cell is stimulated at or above its threshold level;|
the all or none AP is capable of transmitting information (inhibition or excitation) to the next cell(s) in the communication pathway
|DEpolarization||the change in membrane voltage potential which triggers the AP;|
the change is due to the opening of Na+ channels which allow Na+ ions to enter the cytoplasm causing the resting potential of -70mV to change to +30mV in the cell interior;
similar events are observed when muscle cells are stimulated to contract and when glandular cells are stimulated to secrete.
|threshold||the point that must be exceeded to begin producing a given effect or result or to elicit a response;|
in the case of excitable cells, the amount of stim of whatever form (light, heat, mechanical activity, pH changem binding of ligand to receptor, voltage change etc) required to trigger the AP
|suprathreshold stimulus||an amount of stim in whatever form (light, heat, mechanical activity, pH change, binding of ligand to receptor, voltage change, etc) greater,usually markedlky greater, than the minimum stim required to trigger the AP|
|repolarization||the restoration of polarized (resting) state across a membrane, as in a muscle fiber following contraction, a gland cell following secretion, or a neuron following transmission of a nerve impulse (AP);|
the change is d/t closing of Na+ channels and opening of gated K+ channels which allow K+ ions to exit the cytoplasm causing the resting potential of -70mV to be restored from the +30mV in the cell interior during depolarization
|term de3scribing the fact that certain physiological process, including the generation of an AP and the triggering of a muscle fiber contraction utilizing the sliding filament mechanism, proceed in the same fashion, at the same rate, at the same strength, EVERY time they occur;|
once stimulated, the process completes itself without significant variation in performance.
|refractory period(neuron)||time interval, after a nerve fiber has been stimulated and an AP has been acheived, which has to pass before the neuron can be stimulated again;|
this interval can be subdivided into absolute and relative refractory periods.
|absolute refractory period (neuron)||the interval fro the beginning of the AP until the nerve fiber is abler to conduct another AP;|
during most of this interval the Na+ and K+ channels remain open
|relative refractory period (neuron)||the interbal which follows the absolute refractory period and is the time period in which, although the neuron has not fully recovered, a small weak AP can be generated as the result of strong input stimulus;|
the Na+ channels are closed and cannot easily reopen for a set period of time;
during this interval the K+ channels remain open
|means or process by which an impulse=wave of depolarization=AP is spread over the surface of an excitable cell's membrane;|
the specific trigger is the opening of voltage gated ion channels, usually Na+ channels
|continuous conduction||the step-by-step depolarization (the timed opening and then closing of Na+ and K+ channels) of each adjacent area of the plasma membrane of an excitable cell, such as a muscle or gland cell or over the regions of the dendrites and cell bodies of neurons, and including unmyelinated axons.|
|saltatory conduction||the rapid sequential depolarization (the timed opening and closing of Na+ and K+ channels) of distant segments of a myelinated axon as the impulse jumps from neurofibrillar node to node;|
only the segments of the axolemma exposed at each node are depolarized to generate a local AP, while myelin sheath covered portions of the axon do not depolarize
|axodendritic||term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic dendrite(s) of a receiving neuron in a nerve impulse pathway|
|axosomatic||term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic cell body/soma of a receiving neuron in a nerve impulse pathway|
|axoaxonic||term pertaining to an excitatory or inhibitory synaptic connection between the presynaptic axon of a transmitting neuron and the postsynaptic axon hillock or axon of a receiving neuron in a nerve impulse pathway|
|electrical synapse||specialized type of synapse between two excitable cells, e.g., cardiac muscle cells, some smooth muscle cells, and some neurons, in which the impulse is transmitted from one cell to the next by the depolarization of the sending cell creating a local ionic current flow which destabilizes the voltage gated Na+ channels in the adjacent cell so that it also depolarizes;|
such cells are usually connected by gap junctions;
no neurotransmitter is required.
|gap junction||a type of communicating intercellular junction; a bridging network of integral protein channels present in both cells' outer membrane which facilitates the cell-to-cell passage of ions, hormones, and neurotransmitters;|
these junctions are often found in autorhythmic cells such as cardiac and smooth muscle cells.
|connexon||functional unit of gap junctions;|
an assembly of six membrane spanning proteins, connexins, having a water-filled gap in the center;
two connexons in juxtapose3d membranes link to form a continuous pore through both membranes
|chemical synapse||general type of synapse between two excitable cells, e.g., a neuron connected to a muscle cell, glandular cell, or another neuron, in which the impulse is transmitted from one cell to the next by the release of neurotransmitter molecules from the sending neuron's axon end bulbs which bind to the receptors on gated Na+, K+, or Cl- channels in the synaptic cleft of the adjacent cell causing a local ionic current flow which destabilizes the receiving cell so that it either depolarizes or hyperpolarizes to some degree, creating a local graded potential.|
|synaptic cleft||the crevice or indentation in the cell membrane of an excitable cell (neuron, muscle cell, or gland cell) which is immediately adjacent to the axon end bulb of the neuron which can transmit a nerve impulse to the excitable cell;|
the two cell membranes are very close to each other but do not actually come into contact.
|postsynaptic potential||the short-distance local membrane surface signaling events, induced by the arrival of neurotransmnitters, which alter membrane permeability and affect the threshold for firing, producing graded responses in proportion to the amount and kinds of neurotransmitters, excitatory and inhibitory, that are arriving at the dendrites and axon-hillock at any specific point in time.|
|synaptic delay||the time lag in impulse transmission which occurs when an impulse must cross a chemical synapse, d/t the relatively slow rate of neurotransmitter release and diffusion and interaction with postsynaptic receptors, compared to the more rapid time of transmission of an impulse along the length of a neuron membrane;|
the actual time of delay, approximately .3-.5 msec, is the RATE LIMITING STEP in neural transmission.
|excitatory postsynaptic potential (EPSP)||the local graded depolarization events which occur at excitatory postsynaptic membranes in response to the arrival of excitatory neurotransmitter molecules which bind with and open membrane gated Na+ channels;|
ESPSs help to trigger an AP at the axon hillock of the postsynaptic neuron.
|inhibitory postsynaptic potential (IPSP)||the local graded hyperpolarization events which occur at excitatory postsynaptic membranes in response to the arrival of inhibitory neurotransmitter molecules which bind with and open membrane gated K+ channels or Cl- channels;|
IPSPs help to raise the threshold for firing and thus inhibit an AP at the axon hillock of the postsynaptic neuron.
|diffusion||the spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to they system.|
|uptake (into cells)||the process of transferring molecules from the external environment across the cell membrane and into cells, usually referring to a process that is controlled by some form of specialized regulated transport by some form of specialized regulated transport protein in the cell membrane; e.g., the ability of neurons to reabsorb the breakdown products of their neurotransmitter from the synapse for resynthesis and storage in axon end bulbs./|
|enzymatic degradation||the enzyme catalyzed decomposition of a compound/molecule by stages, exhibiting well-defined intermediate products.|
|presynaptic facilitation||the response which occurs when the release of excitatory neurotransmitter by one neuron is assisted by the activity of another neuron via an axoaxonic synapse;|
the end result is that more neurotransmitter is released and bound, and larger excitatory postsynaptic potentials (EPSPs) are formed.
|presynaptic inhibition||the response which occurs when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axoaxonic synapse;|
the end result is that less neurotransmitter is released and bound, and smaller excitatory postsynaptic potentials (EPSPs) are formed.
|spatial summation (of PSPs)||the response which occurs when the postsynaptic neuron is stimulated at the same time by a large number of axon terminals from the same, or more commonly, different neurons;|
huge numbers of its receptors bind neurotransmitter and simultaneously initiate excitatory postsynaptic (EPSPs), which summate and dramatically enhance depolarization.
|temporal summation (of PSP)||the response which occurs when one or more presynaptic neurons transmit impulses in rapid-fire order and bursts of neurotransmitter are released in quick succession;|
the first impulse produces a slight excitatory postsynaptic potential (EPSP), and before it dissipates, successive impulses trigger more excitatory postsynaptic potentials(EPSPs);
these summate, producing a much greater depolarization of the postsynaptic membrane that would result form a single excitatory postsynaptic potential(EPSP).
|acetylcholine (ACH)||excitatory neurotransmitter that is a derivative of the amine, choline;|
released by motor neurons at the neuromuscular junction, by all preganglionic autonomic visceral motor neuronsm by al parasympathetic postganglionic visceral motore neurons, by sympathetic postganglionic visceral motor neurons for sweat glands, and by a variety of neurons in the CNS
|glutamate||salt or ester of amino acid glutamic acid, |
it often functions as an excitatory neurotransmitter in the CNS
|aspartate||salt or ester of the amino acid aspartic acid, |
it sometimes functions as an excitatory neurotransmitter in the CNS
|gamma aminobutyric acid (GABA)||an amino acid that is found in the CNS;|
acts as an inhibitory neurotransmitter
|glycine||the simplest amino acid|
acts as an inhibitory neurotransmitter in the spinal cord and brain stem.
|a catecholamine, both a hormone and neurotransmitter;|
may be excitatory or inhibitiry, depending on its target cell's response;
it is secreted by the adrenal medulla and by the postganglionic nerve endings of the sympathetic nervous system to cause vasoconstriction and increases in heart rate, blood pressure, and the glucose level of the blood.
|dopamine||A monoamine excfitatory neurotransmitter formed in the brain by the decarboxylation of L-Dopa and essential to the normal functioning of the CNS;|
It is a precursor to norepi and epi.
It may be used as a drug to treat hypotension and bradycardia. A reduction in its concentration within the brain is associated with Parkinson's.
|agonist||(1) The muscle which provides the major force for a particular movement.|
(2) A drug, neurotransmitter, hormone or other chemical which can combine with a receptor on a cell to produce or enhance a physiologic reaction in the target cell.
|antagonist||(1) The muscle(s) which oppose or reverse a particular movement. |
(2) A drug, neurotransmitter, hormone or other chemical substance which interferes with the physiological action of another chemical, especially by combining with and blocking a nerve or effector receptor.
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