Human Phys 2.3 Flashcards
Depolarization
mV moves up into positives
Hyperpolarization
mV moves down into negatives
Undershoot
Goes below resting potential before going back up to resting potential (K+ channels closing)
Repolarization
When the action potential is moving back to resting after depolarization (due to K+ leaving cell)
Excitability
Ability of membrane to change mV (repolarize and depolarize)
Threshold
Certain mV that if it’s crossed there will be an action potential generated
Action potential steps
- If the threshold is reached voltage gated Na+ channels are opened and Na+ pours into the cell the membrane depolarizations and then the inactivation gate closes stopping Na+
- K+ channels then open which repolarizes the cell bringing it back to the resting membrane potential
Action potential
Regenerating depolarization of membrane potential that propagates along an excitable membrane
Propagates
Conducted without decrement
Excitable
Capable of generating action potentials
What are the properties of action potentials?
All or none event
Initiated by depolarization
Have constant amplitude
Have constant conduction velocity
All or none event
Action potential either happens or it doesn’t
Initiated by depolarization
Action potentials can be induced in nerve and muscle by extrinsic stimulation
Have constant amplitude
Information is coded by frequency not amplitude (do not summate)
Have constant conduction velocity
True for given fiber
What type of fiber conducts faster?
Fiber with a large diameter
Action potential summary
During upstroke of action potential Na+ permeability increases due to opening of Na+ channels
During downstroke of action potential Na+ permeability decreases due to inactivation of Na+ channels and K+ permeability increases due to opening of K+ channels
After hyperpolarization the mV may drop below where it was due to delayed closure of K+ channels
Is there a specific direction of propagation?
No
What happens due to the presence of inactivation gates and refractory periods?
Backward propagation is prevented
How does lidocaine work?
Binds to voltage gates Na+ channels and inactivates them
What are axons surrounded by?
Myelin sheath
What is responsible for myelination?
Schwann cells
Node of ranvier
Break in myelin sheath every 1-3mm
Where are most of the Na+ channels located?
At the node of ranvier
Saltatory conduction
Current travels along axon under myelin sheath due to insulation and is amplified at the nodes of ranvier by the voltage gated Na+ channels
Why is myelinated faster than unmyelinated?
You need less action potentials
Multiple sclerosis
Auto immune disorder that causes demylination in 1 per 1000 people (causes decreased coordination)
Overshoot
Peak of action potential
