Unit 2.2: Electrical Properties of Neurons Flashcards
How do neurons transmit electrical impulses?
Via energy stored as an electro-chemical gradient
Which molecules can cross the cell membrane?
Hydrophobic molecules can slip past the phospholipid bilayer (steroid hormones)
What is the equilibrium state?
If concentration gradient of ions balances, there’s no net movement (cell dies)
What does the Nernst equation calculate?
The electrical potential of the cell needed to generate an equilibrium state (but you have to know the concentration gradient)
What is the charge of a cell at rest?
-70 mV to -90 mV
What can we predict about ions knowing there equilibrium potential?
Ions with positive equilibrium potential will tend to move into a resting cell
Ions with a very negative equilibrium potential will tend to move out of a resting cell
What is the charge difference between the inside and the outside of a cell at rest called?
Resting membrane potential
What sets the resting membrane potential?
Concentration of each ions and their relative permeability
Which ions want to move in/out the cells?
- K+ wants to move out
- Na+, Ca2+, Cl- want to move in
What is the equilibrium potential for K+?
-90 mV
What is the equilibrium potential for Na+?
+60 mV
Which molecules contribute the most to the resting membrane potential?
Those that are most permeable, the more easily it can cross the membrane, the more important it is for resting membrane potential
How do we calculate membrane permeability?
Goldman-Hodgin-Katz (GHK) equation
Which ion is the most important to resting membrane potential?
K+ ions
Why doesn’t K+ keep leaking out of the cell (and Na+ into the cell) until they reach their equilibrium potentials?
They do leak out but Na+/K+ ATPase activity offsets the leak
How are gates channels controlled?
- mechanically gated
- chemically gated
- voltage-gated
What are the 4 major types of selective ion channels in the neuron?
Na+, K+, Cl-, Ca2+ channels
When do electrical signals in neurons occur?
When there are changes in membrane permeability to specific ions
What is depolarization?
A decrease in the membrane potential difference
Cell membrane potential becomes less negative
What is hyperpolarization?
A increase in the membrane potential difference
Cell membrane potential becomes more negative
What is it called when the cell membrane returns to its resting membrane potential?
Repolarization
How do cells change their membrane potential?
Change the membrane ion permeability
How can cells change their permeability?
- Change total number of protein channels
This is slow, requires transcription, translation - Open or close existing protein channels
This is fast, only needs a change in protein channel conformation
Does Na+ contribute a lot to the resting membrane potential?
not really, due to low permeability
How is Na+ critical to the cell?
It is critical in generating the changes in membrane potential that cause electrical signals
What are the 2 types of signals generated by neurons?
Graded potentials (short distance) Action potentials (long distance)
