LIFESCI 2C03 Lecture Notes - Myotonia, Channelopathy, Rate Equation

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10 Apr 2012
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Summary:
Resting Membrane
Potential:
Is at -70mV, and is observed
in a giant axon of a squid
4 things that keep the
resting membrane potential
are:
The capacitor charge of the
membrane (negative inside,
positive outside)
1.
(things want to go from a
[high] to a [low])
2.
Passive electrical forces (as
the k+ leaves the inside, it
becomes more negative in
turn attracting back the
positive k+ ions) and
polyanions (negatively
charged proteins inside the
cell which attract the k+ ions
and form a negative field at
the bottom of the
membrane)
3.
Active forces (ion channels
and protein pumps)
4.
There are passive and active
ion channels
Ouabain is a plant toxin that
inhibits the na/k pump
allowing more sodium->
more calcium in the body
which helps heart
contraction
Action potentials:
Action potential is initiated
when the sodium ion
channels are opened and
allow sodium to enter the
cell
There are two types of gated
ion channels:
Voltage-gated (the channel
opens when a specific
voltage of electrical stimulus
Note-Taking Area:
The resting potential is at -70 mV
Every cell has a membrane potential
Resting membrane potential
Large diameters axons are very important for quick propulsion to escape
danger
The axons of a squid are 400 times the diameter of mammalian axons
In squids the axoplasm can be easily squeezed out and replaced by fluid of
interest
Giant nerve cells of squid
Cell membrane capacitance: The cell membrane itself is charged. The cell
membrane is negatively charged on the inside and positively charged on the
outside. The resting membrane potential lies at -70mV.
1.
Passive Osmotic Forces: molecules like to move from a high concentration to
a low concentration. The extracellular compartment of the cell contains Na+
ions and the inside contains K+ions. Due to osmotic pressure Na+ ions want
to go inside the cell and K+ions want to go outside.
2.
Passive Electrostatic forces and Polyanions: As the ions enter and exit the
cell membrane they change the charge of the outside and inside of the cell.
Polyanions are large negatively charged ions located inside the cell, they
attract the K+ions inside the cell which in turn creates a negative field at the
bottom of the membrane.
3.
Active Forces: ion channels, hydroxylation of sodium and potassium ions
(when sodium is hydrolyzed it's diameter becomes larger, smaller when
potassium is hydrolyzed. This allows the sodium to stay outside the cell and
potassium to enter the cell)
4.
What keeps the resting membrane potential in a resting state
Allows ions to diffuse down the concentration gradient
Causes selective permeability to certain ions
Doesn't use any energy (ATP)
Passive Ion Channels:
Actively move ions against concentration gradient
Uses ATP
Active Ion Channels:
There are two types of Ion Channels:
Ion channels and Transporters cause unequal distribution of ions
across neuronal membranes
The Sodium/Potassium pump is an protein that requires ATP to function. It
throws out 3 sodium ions and throws in 2 K+ions. Since both are positively
charged, it throws out more positive charges then it throws in, making the
inside negative.
It is usually active after a burst of action potential (which causes lots of
sodium to go inside the cell)
This pump alone consumes 40-50% of energy
Is slower than Ion channels
It is important to restore the resting membrane potential after an action
potential
Ouabain can be used in case of heart failure, it forces the heart to
pump more forcefully. This is due to the inactivation of the Na/K
pump, which causes a high accumulation of sodium inside the cell,
which in turn increases the amount of calcium in the body which
helps with heart contractions.
Ouabain inactivates the Na/K pump. Ouabain is a plant toxin.
The Na+ / K+pump
Lecture 21
March-05-12
10:30 AM
LIFE SCI 2C03 Page 1
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