Module 3 Lecture 2 - Graded Potentials Flashcards
The greater the permeability of a plasma membrane for a given ion, the greater is the tendency for that ion to drive the membrane potential towards the ions own equilibrium potential
Permeability of a plasma membrane given a ion
Na+ and K+ cannot exist separately; must work together to affect the potential of the membrane
What is the net resting membrane potential of a neuron? What allows for this number?
-70mV is the net resting membrane potential of a neuron
* Ek, Ena, relative permeability of both ions and A- ions allow for the number -70mv
Potassium when a cell is at rest has 50-75x more permeability as to Na+. What does that mean?
It has more influence on the resting membrane potential due to having more leak channels (K+) than Na+ which results in the resting membrane potential being -70mV
What is the principle of neural communication?
Neural and muscle cells are excitable cells meaning that they can create changes in their membrane potential upon being excited => such transient and rapid changes in the membrane create electrical signals
What purpose do electrical signals have when it comes to neural communication?
Nerve cells use this electrical signal to:
1. Receive messages
2. Initiate/Elborate a message
3. Transmit a message
What is polarization?
When there are charges separated across a membrane; Membrane potential is not 0
Hence when we say a membrane is polarized = there is a charge separation
What is depolarization?
Reducing magnitude of negative potential; less polarized compared to resting conditions
*Movement in a positive direction
Determined as positive direction or negative direction with respect to resting membrane potential (-70mV)
What is repolarization?
Membrane returning to resting membrane potential after depolarization
What is hyperpolarization?
Increase in magnitude of negative potential => more polarized than resting membrane conditions
More charges separated across the membrane; hence more polarized
What are graded potentials and how are they different than action potentials
When a resting membrane is excited it produces an electrical signal which is either a graded or action
* Graded is a short distance signal
* Action is a long distance signal
- Local changes in membrane potential
- Short distance signals
- Various magnitudes and direction
(All fall under graded potentials)
What are the triggering events for a graded potential?
Chemical (either neurotransmiter) or mechanically (touch)
What happens during a triggering event for a graded potential?
- Commonly Na+ channels open and Na+ move inwards down electrochemical gradient
- Whenever a graded potential occurs, Na+ moves in first between origin of potential to area that is still at rest in the membrane
Membrane potential moves towards Na+ equilibrium potential (+65mV)
What is true about strength & duration of the triggering event?
- Stronger triggering event => more gate channels open => more positive entering cell => larger depolarizing graded potential at the origin
- Longer the duration of triggering event => longer the duration of graded potential
Explain Active and Inactive areas in a triggering event for a graded potential
Graded potentials are generated at specific points on the plasma membrane
* Na+ channel sits at random place on the membrane and when the triggering event occurs that region with the Na+ channel becomes active (Temporary depolarized region)
* Inactive areas are the ones surrounding the active area but are still at resting membrane potential (-70mV)
Active and inactive areas have opposite charge differences across the membrane - Current
What is a current? Which way does the current flow by convention?
A current is a flow of electrical charge
* Current flow is designated by the direction in which positive charges go towards
Spread of depolarization is the sodium coming in and moving throughout the membrane to the inactive areas
Does the magnitude of current stay the same?
No; there is a decremental loss which causes the local current to diminish with increasing distance from the initial site
Local currents this way die out in a few mm of distance and function as signals for very short distances
