Definitions Flashcards
One coulomb is defined as
6.25 x 1018 electrons
The charge of one electron (or univalent ion) is
1.6 x 10-19C
Faraday’s constant
F = NAe0
= 6.022 x 1023 x 1.602 x 10-19
= 96,500 coulombs per mole
Current
the net movement of positive charge per unit time. Unit = Ampere (A). One ampere of current represents the movement of 1 coulomb of charge per second.
1 Ampere is defined as
the flow of 1 Coulomb of charge in 1 second
Resistance is a measure of
The ease with which a charge moves through the conductor
The reciprocal of resistance is
the conductance
The unit of conductance is
siemen
Capacitance indicates
how much charge can be stored for a given charging voltage
Capacitance is measured in
farad (F): when 1 F is the capacitance of an element that can store 1 C of charge given a 1 V potential difference
Factors affecting capacitance
Plate area, plate spacing and dielectric material
How does capacitance relate to area?
C = (absolute permittivity of dielectric x area of plate overlap in square meters ) / distance between plates in meters
P=
fraction of time the channel spends in the open state - can and normally dependent on voltage
g=
single channel conductance
i=
current that flows through a single channel when it opens
Total current =
NiP
3 factors of frequency coding
The strength-latency relationship and the
refractory period, together with the threshold
Selective permeability arises from
selectivity of ion channels
The equilibrium potential for an ion is the
potential difference that must be present across the
membrane of a cell in order to balance the concentration gradient for that ion.
The Nernst equation states that the equilibrium potential of an ion is equal to
a constant (RT/Fz) times the natural logarithm of the ratio of the external to internal concentrations of the ion
Why is the Nernst equation important?
equilibrium potential relative to the membrane potential determines the direction in which a given ion will flow through open ion channels.
Potential Difference (V or E):
The potential difference between two points is the work needed to move a unit of positive charge (1 coulomb) frictionless from one point to the other (= potential energy of the charge). Unit = Volt (V).
To move a coulomb of charge across a 1-volt potential difference requires
a joule of work.
Ra =
the internal longitudinal resistance of a 1 cm
length of a cylindrical process 1 cm2 in cross-sectional area. It is independent of geometry and it gives us a measure of how freely ions migrate through the
intracellular space.
λ =
membrane length constant - sqrt ( rm/ra)
Rm =
resistance of one square cm of membrane. Rm is independent of geometry, enabling us to compare the membrane of cells of different sizes and shapes
Electrotonic conduction =
The passive spread of voltage changes along the neuron
Electrotonic potential =
A non-actively propagated, local potential, resulting
from a local change in ionic conductance (e.g. synaptic or
sensory that engenders a local current). When it spreads along a stretch of membrane, it becomes exponentially smaller (decrement). Its spread and time course are largely determined by passive properties of the membrane.
The threshold, VT, is the
specific value of Vm at which the net ionic current (INa + IK + Il) just changes from outward to inward, depositing positive charge on the inside of the membrane.
