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What is a potential?
an energy state of an object that has the ability (potential) to do work (expend energy). TERM 2
For charged molecules and in electrical
circuits, the potential to do work is expressed
as what?
DEFINITION 2 voltage TERM 3
For membrane potentials, voltage is
measured where?
DEFINITION 3 between two compartments separated by a membrane (usually inside and outside of a cell). TERM 4
A difference in electrical potential can help to
do what?
DEFINITION 4 move ions and other charged molecules across the membrane in either direction depending upon the conditions TERM 5
Why have a membrane potential?
DEFINITION 5 useful for controlling intracellular environmenttransport of metabolic precursors into and out of the cellenergy link for metabolic processes
What important things in the NS are coded as
changes in membrane potential?
almost all rapid signals within the nervous system including external and internal stimuli and communication between cells TERM 7
The movement of ions across a membrane is
essentially the same as what?
DEFINITION 7 an electrical circuit TERM 8
. In a simple electrical circuit, the ability to
move (potential or voltage) charged particles
(electrons) is created how?
DEFINITION 8 through chemical reactions in a battery TERM 9
Ohm's Law
DEFINITION 9 The electrons move through a conductor (wire) and some resistance (load) according to Ohms Law: (I=V/R, also rearranged to V=IR) where:I = electrical current in amperesV= voltage in voltsR= resistance in ohms TERM 10
Ohm's law demonstrates what?
DEFINITION 10 that voltage current and resistance are all interdependent.also shows that if any component is 0, (e.g. no voltage, very high resistance) no current will flow.
Salts (sodium chloride, potassium chloride)
and other ionic solutes that make up the
cytoplasm of cells dissociate into what?
hydrated charged ions in solution. These ions move and will diffuse in solution relatively independently TERM 17
With a concentration gradient of a salt and a
permeable membrane what happens?
DEFINITION 17 both the positive and negative ion species will also diffuse through a permeable membrane independently.Under these circumstances, both positive and negative charged ions will move across the membrane and the compartments will be electrically neutral. TERM 18
What happens if a membrane is only
permeable to one type of ion?
DEFINITION 18 there will still be a diffusion potential, but only for that ion. This creates the possibility of establishing an electrical charge across the membrane TERM 19
Equilibrium potential for the ion
DEFINITION 19 The amount of electrical force needed to hold the diffusion forceAt the equilibrium potential there will be no net flow of the ion across the membrane. This is described by the Nernst Equation TERM 20
What are the charged elements that can
move (current) between the intracellular and
extracellular established by a cell membrane?
DEFINITION 20 For most cells, sodium, potassium, calcium and chloride
How do cells create and maintain
concentration gradients?
by actively transporting (pumping) ions from one side of the membrane to the other usually against a concentration gradient.sodium potassium pump TERM 22
What does the Na-K pump move?
DEFINITION 22 This pump (a protein complex in the membrane) moves 3 sodium ions out of the cell and 2 potassium ions into the cell at the cost of an ATP molecule (energy). in this process the exchange of 3 sodium ions out and 2 potassium ions in not only acts to establish a concentration gradient, but also an electrical gradient (net -1 each cycle). TERM 23
Transport mechanisms that create an
electrical potential/concentration difference
and are called what?
DEFINITION 23 electrogenic TERM 24
The Na+/K+ pump takes up what % of energy
used by the brain?
DEFINITION 24 20-40% of the energy used by the brain and is largely responsible for the generation of the concentration gradients necessary to maintain a resting membrane potential. TERM 25
What happens if the pump is inhibited
through poison or insufficient ATP stores?
DEFINITION 25 the membrane potential will gradually approach 0 as the ion concentration gradients across the membrane are lost
For the resting membrane potential, the
contribution a particular ion will have on the
net potential is determined how?
by how permeable the membrane is to that ion TERM 32
Ions that cannot cross the membrane
(permeability is near 0), can contribute to
what?
DEFINITION 32 a charge difference across the membrane, but not current flow of the particular ion TERM 33
The control of how permeable the cell
membrane is to a particular ion mediated
how?
DEFINITION 33 through ion channels TERM 34
The control permeability is a function of
what?
DEFINITION 34 how selective channels are for a particular ion, and the opening and closing of channels. TERM 35
passive channels or leakage channels
DEFINITION 35 act basically like selective holes in the membrane and allow some types of ions to pass freely into and out of the cell
Gating
refers to the ability of ion channels to be open (allow the passage of ions) or closed (not allow ion passage). TERM 37
In neurons at rest , there is a relatively high
permeability (conductance) for what?
DEFINITION 37 potassium (leakage current).The permeability for other ions is low. This makes potassium the primary ion determining the resting membrane potential. TERM 38
What voltage is the resting membrane
potential?
DEFINITION 38 -70 mVresting membrane potential lies close to the equilibrium potential for potassium at the concentrations present across the cell membrane (-80mV). TERM 39
gating allows for what?
DEFINITION 39 Gating allows membranes to rapidly change their permeability to particular ions or classes of ions TERM 40
For a single ion, the membrane potential will
be determined by what?
DEFINITION 40 the concentration gradient of that ion.
Graded responses can be of what type?
can be depolarizing (opening sodium or calcium channels) or hyperpolarizing (open potassium or chloride channels). TERM 47
Depolarizing postsynaptic potentials tend to
do what?
DEFINITION 47 excite the postsynaptic cell and are called excitatory postsynaptic potentials (EPSPs). TERM 48
Hyperpolarizing potentials do
what?
DEFINITION 48 are inhibitory and called inhibitory post synaptic potentials (IPSPs) TERM 49
If there are no other ion channels that are
opened as a result of the local depolarization
effect, what happens?
DEFINITION 49 the discharge of the membrane capacitance will continue to spread passively across the membrane (electrotonic conduction).The electrical potential (voltage) sustaining the depolarization declines in amplitude exponentially as a function of distance and time and is effective over very short distances, usually several hundred microns or less than a millimeter TERM 50
Adding graded potentials does
what?
DEFINITION 50 While graded potentials dont travel very far, they can interact to summate or subtract from each other on the postsynaptic membrane.The two primary mechanisms involved are temporal and spatial summation.
temporal summation
takes place at a single synapse and uses the frequency of incoming action potentials. TERM 52
temporal summation relies on
what?
DEFINITION 52 the fact the time needed for a postsynaptic potential to be generated and die away (synaptic delay) is substantially longer than the shortest interval between action potentials arriving at presynaptic terminals (1 ms). If multiple action potentials arrive at a synapse before the prior potential has completed, it will cause the release of more neurotransmitter, open more ion channels and add to the postsynaptic potential. TERM 53
An increased frequency of action potentials
and their temporal summation at the synapse
can produce what?
DEFINITION 53 a larger postsynaptic potential that has a greater chance of activating the postsynaptic neuron. TERM 54
spatial summation
DEFINITION 54 greater effects can be produced by the combined effects of multiple synapses spatially across the neuronal membraneLike waves, the peaks and troughs can combine either in an additive or subtractive fashion in space TERM 55
The decline in magnitude of graded potentials
as they spread across the membrane results
from what?
DEFINITION 55 membrane capacitance, potassium (leakage channels; e.g. Carrying a leaky bucket) and the cytoplasmic resistance to ionic movement.
what provides the primary source of
depolarization in an AP?
voltage gated sodium channels TERM 62
two mechanisms of gating in sodium
channels
DEFINITION 62 activation gateinactivation gate TERM 63
activation gate
DEFINITION 63 gate-responds to depolarization by opening (quickly) TERM 64
inactivation gate
DEFINITION 64 responds to gate opening by closing (a little delayed). This closing is not voltage sensitive and occurs essentially as an automatic process. TERM 65
In response to a local depolarization, the
effect voltage gated sodium channel opeining
is to produce what
DEFINITION 65 a brief period of increase in sodium conductance that drives the membrane potential toward that of sodium (depolarization). The rapid inactivation of the channels by the inactivation gate ensures that the sodium current from individual channels is brief.
importance of voltage gated potassium
channels
The membrane needs to recover from depolarization to conduct another signal, this is achieved through voltage gated potassium channels. TERM 67
when will voltage gated potassium channels
be opened?
DEFINITION 67 Voltage gated potassium channels will also opened by a depolarizing event. These channels only have two states, open and closed and generally have no automatic closing mechanism, but close as the depolarizing event decreases. TERM 68
describe the process of depolarization and
repolarizaton
DEFINITION 68 a depolarizing event opens voltage gated potassium channels will show the initial depolarization event followed by a rapid repolarization of the membrane by potassium efflux TERM 69
what is resting membrane potential?
DEFINITION 69 -70 mV near equilibrium potential for potassium TERM 70
how is an AP initiated?
DEFINITION 70 a depolarizing (usually a sodium current) stimulus must overcome this polarizing influence and create enough membrane depolarization to activate voltage gated sodium channels. This activation results in an explosive increase in sodium conductance and an associated rapid and dramatic membrane depolarization.
absolute refractory period
Refractoriness is the fundamental property of any object of autowave nature not to respond on stimuli, if the object stays in the specific refractory state. TERM 77
During the rest recovery phase of the
membrane, a new depolarization cycle can be
produced how?
DEFINITION 77 if the stimulus is large enough (usually much above the resting membrane threshold). TERM 78
relative refractory period
DEFINITION 78 continues until the membrane resting potential returns TERM 79
Refractory periods in also membranes help to
insure what?
DEFINITION 79 that action potentials travel primarily in one direction in cell processes. TERM 80
If an axon, essentially a tube, is stimulated in
the middle, the action potential can spread
how?
DEFINITION 80 in both directions, both orthodromic (normal direction of conduction toward the effector zone) and antidromic (abnormal direction, usually toward the receptor zone.
if the AP is generated in a trigger zone or at
one end of an axon, what happens?
the wave of depolarization progresses down the axon, followed by a wave of repolarization in which the membrane is in an absolute or relative refractory period. This essentially blocks the depolarization from reversing. TERM 82
The excitable regions of a cell are
characterized by what?
DEFINITION 82 high concentrations of voltage gated ion channels (usually for sodium). TERM 83
The non-excitable cell or region of the cell can
still have functions associated with what?
DEFINITION 83 graded potentials TERM 84
Action potentials can be induced in any area
of an excitable cell that contains what?
DEFINITION 84 enough voltage sensitive channels to initiate and sustain the depolarization cascade (Hodgkin Cycle). TERM 85
In neuronal cell bodies, the axon arises from
where?
DEFINITION 85 a specialized region of the cell body, that includes the axon hillock, at the junction of the cell body and axon and axon initial segment
where do trigger zones
exist?
exist in receptor structures in peripheral tissues. TERM 92
Any process that can interfere with the
operation of voltage gated channels can
interfere with what?
DEFINITION 92 the conduction of action potentials in axons and the generation local responses in other areas of the cell. This can include pharmaceuticals (toxins, local anesthetics) or physical interventions such as the application of current or anoxia.Agents which block voltage gated sodium channels (e. g. lidocaine) are particularly effective. TERM 93
In the peripheral nervous system, axons
classified how?
DEFINITION 93 into groups designated based on their relative contribution to the compound action potential (the wave produced by the stimulation of a whole spinal nerve). The compound action potential is produced by stimulating a nerve at one point and recording at another TERM 94
functional groupings by conduction
velocity
DEFINITION 94 groups A, B, C TERM 95
group A
DEFINITION 95 A the fastest (myelinated) conducting axons. The A group is divided into subgroups- A into a ,b and g.
how are sensory axons
divided?
into groups Ia,Ib,II,III, and V. TERM 97
function of sensory axons 1a,
1b
DEFINITION 97 motor afferent: golgi tendon organ TERM 98
function of sensory axons
II
DEFINITION 98 sensory afferent: touch, pressure, hair, joint TERM 99
function of sensory axons
III
DEFINITION 99 sensory afferent: hairfree nerve endings: fast pain, temperature TERM 100
function of afferent sensory axons
IV
DEFINITION 100 sympathetic, sensory afferent: slow pain, temp, mechanoreceptors
