Brain mechanisms III Flashcards
Why is intracellular fluid negatively charged?
Because organic anions cannot leave the cell (A-)
Why is extracellular fluid positively charged?
The sodium-potassium pumps in the cell’s membrane continuously pump sodium ions out of the cell.
How many sodium ions are pumped out and how many potassium ions are pumped in by the sodium-potassium transporter?
3 sodium ions pumped out and 2 potassium ions pumped in.
What is a resting potential?
The resting potential of a cell is defined as the difference in electrical potential across the plasma membrane when the cell is not stimulated or when the cell is in a state of relaxation.
Describe the process of activating a neurone
Each stimuli briefly depolarises the membrane potential a little more, finally after a certain stimuli, the membrane potential suddenly reverses itself (reached threshold of excitation), it overshoots first becoming hyperpolarized.
Why does the intracellular level of Na+ remain low even after both diffusion and electrostatic pressure tends to push the Na+ into the cell?
Because the membrane is not permeable to Na+ and the sodium potassium pump pumps Na+ out of the cell.
What would happen if the membrane suddenly became permeable to Na+ ?
The forces of diffusion and electrostatic pressure would cause Na+ to rush into the cell. The sudden influx of positively charged ions would drastically change the membrane potential.
What follows an increase in permeability of the membrane to Na+?
An increase in membrane permeability of the membrane to K+
Describe the movement of sodium ions during the action potential.
Sodium channels open, sodium begins to enter the cell, sodium ion channels become refractory, no more sodium enters the cell. Sodium ion channels reset. (Page 18)
Describe the movement of potassium ions during the action potential.
Potassium ion channels open, potassium begins to leave the cell, potassium continues to leave the cell which causes the membrane potential to return to resting level, potassium ion channels close, extra potassium ions outside diffuses away. (Page 19)
What is the “all or nothing” principle?
An action potential either occurs or it does not occur. It always remains the same size, without growing or diminishing.
Where does salutatory conduction occur?
At the Nodes of Ranvier
What are the 2 advantages of saltatory conduction?
Economic in terms of energy and speed
