Lecture 6: Membrane Potential and Electrical Impulses Flashcards
What are the two main types of channels and their description?
Leakage channels: Always open
Gated Channels: Only open when stimulated these include ligand, voltage and mechanical gated channels.
What is active transport?
Ions are actively pumped to the side of the membrane where it’s more concentrated. This requires ATP to do work.
Which molecule is predominant in the intracellular and extracellular environments?
Na+ (sodium) and Cl- (chlorine) are found in the extracellular space.
K+ (potassium) is found in the intracellular space.
How does a neuron establish membrane potential?
- Difference in sodium and potassium concentrations inside and outside of the cell.
- Difference in permeability of the plasma membrane to these ions through leakage channels. (More leakage channel for potassium than sodium)
What is membrane potential?
The difference in sum of electrical charges from inside of plasma membrane to outside.
What is the resting membrane potential of a neuron?
-70mV (millivolts)
What is the difference between depolarization and hyperpolarization?
Depolarization: Inside of the membrane becomes less negative than resting m.p.
Hyperpolarization: inside of the membrane becomes more negative than resting m.p.
What is the difference between graded and action potentials?
Graded potential: Occurs over small distance in the receiving portion where stimulus opens ligand or mechanically gated channels.
Action Potential: Long distance signals which start at axon hillock of neuron. Stimulus opens voltage gated ion channels.
Describe the process of excitation of the neuron?
Exposure to a stimulus opens a few ligand gated/mechanical gated channels (graded potential) which may come from sensory organs. As a result, sodium flows down it’s concentration gradient into cytoplasm of neuron.
How can a neuron reach it’s threshold for membrane potential?
If influx of sodium ions is enough to reach the threshold potential at axon hillock, action potential can occur. The minimum threshold potential is -55mV.
If action potential is always the same strength, how can we distinguish between strong and weak stimulus?
Action potentials will be transmitted at a faster rate. (More impulses per second).
What do action potentials do in general?
Action potential’s do not decay over distance and travel along the axon. After it will stimulate/inhibit another neuron or effector organ through release of neurotransmitters.
How does depolarization of the axon occur?
Once threshold potential has reached, voltage gated channels open allowing for sodium to rush into axon.
How does repolarization of the axon occur?
When membrane potential reaches +30mV voltage gated sodium channels close and potassium channels open. This results in potassium to go out of cell and allow for m.p. to become negative again.
What is the difference between absolute and relative refractory period?
Absolute: Occurs from the opening voltage gated sodium channels until it is reset. A new stimulus cannot trigger the action potential at this time.
Relative: Occurs during the hyperpolarization period where stronger stimulus is required to generate an action potential.
What are the factors which determine speed of an action potential?
Speed of action potential is determined by the diameter of the axon and the presence of myelin sheath.
What is the continuous conduction of AP?
It is when the axon of the neuron is nonmyelinated. Requires sequential opening of sodium channels down the length of axon.
What is saltatory conduction?
Voltage gated sodium channels only have to open at the nodes of Ranvier. In this way, there is minimal loss of ions through leakage channels.
What is multiple sclerosis?
Myelin sheath of the axons in brain and spinal cord are progressively destroyed by immune cells (microglia).
What does local anesthesia do?
It prevents voltage gated sodium channels to open in local neurons. (Novocain and lidocaine)
What does neurotoxins do?
Blocks voltage gated sodium channels to open which results in paralysis of muscles and asphyxiation.
