Ions cannot flow freely across the _____ ________. They must pass through ______ channels or be escorted by protein carriers.
cell membrane, protein
True or False
If a large number of positive charges accumulate outside a nerve cell, and the inside of the cell is negatively charged, the positive charges have a potential energy because the negative ions inside the cell attract them.
True.
Membrane Channels
ion channels
the non-polar tails of lipid molecules prevent charged molecules like ions, from crossing the cell membrane
Ion channels allow ions to pass down their concentration gradient (from high concentration to low)
Some are open all the time -leakage channels
Some are gated - open and close on demand
Voltage
interchangeably with potential
voltage describes the potential energy of particles
it is energy that is available but not released yet
the higher the voltage the more potential energy a particle has
Conductor
holds electrons loosely
Charges shift together from one end of the wire to the other
True or false
In metal wires, the electromagnetic wave that carries current moves at nearly the speed of light.
True.
See objective 12
it was hard to put this on a card.
Ohm's Law
Electric current flow is analogous to water flowing from a tank on the mountainside through a pipe.
Voltage = potential energy
-Water: height of the tank above your house
Current = kinetic energy, flow of ions or electrons
-Water: how many gallons per minute delivered by pipe.
Resistance = resistance to current flow
-Water : how narrow is the pipe?
True or false
Ohm's Law says that voltage (V) is equal to the current (I) times the resistance (R)
True.
V= I x R
See obj. 13
Selectively permeable
There are no channels for proteins, so protein is effectively trapped in the neuron
the channels for sodium, chloride, and potassium have special properties and there are no channels for phosphate or proteins
see obj 14
What are the two forces that act on Ions?
concentration forces
Electrical forces
Concentration forces
all atoms including sodium, potassium, chloride and calcium ions, want to move from where they are at high concentration to where they are at low concentraion
Electrical forces
Positive ions want to be where there are excess negative charges
Negative ions want to be where there are excess negative charges
"Like repels Like" for electricity and magnetism
particles with opposite charges attract each other .
Ions cannot move unless...
they pass through a channel
true or false
Channels must be open for forces to operate
true
At rest, the neuron is always negative inside relative to outside, so based on just electrical forces, ________ charged ions always want to flow in , and ________ charged ions always want to flow out
positively, negatively
See objective 15
concentration and electrical forces: Potassium
concentration and electrical forces: sodium
Equalibrium
the point at which the two forces (concentration and electrical) are equal and opposite.
Equilibrium potential (Nernst potential)
The voltage at which the concentration and electrical forces are exactly equal and opposite
For K+, the equilibrium potential is about ...
-80mV
Sodium Equilibrium potential
it cant be negative
+20 mV for a typical neuron
see objective 16
Resting Potential
the resting potential (resting voltage) of a neuron is maintained by leak channels
At rest, there are about 9K+ leak channels open for every 1 Na+ leak channel
