Exam 2 Lecture - Membrane Potential Flashcards
What is the resting membrane potential (RMP)?
-65 mV
What does the RMP represent?
reflects the uneven distribution of ions across the plasma membrane by the electrochemical gradients
What are the electrochemical gradients created by?
- the sodium/potassium pump
- K and Cl: non-gated or leak channels
- Na: a few nongated or some other channels for Na
- intracellular anions that are too large to exit the cell
What is sensory receptor signal transduction?
conversion of the sensory stimulus
What does the sensory stimulus open?
- Mechano-gated Na channels
- Heat-gated Na channels
- Cold-gated Na channels
What does opening stimulus specific Na channels lead to?
depolarizing of the receptor membrane
What is a potential produced by sensory transduction?
a depolarizing event resulting from inward current flow
What is depolarizing potential of receptor membrane referred to as?
receptor potential
What does receptor potential lead to?
action potential
When is an action potential created?
When the receptor potential goes over the threshold potential
What is the threshold potential?
(-55mV)
What does the generation of action potential require?
- Voltage gated Na channels
- Voltage gated K channels
What is depolarization?
the decrease in the potential difference across the plasma membrane, going more positive, approaching 0mV
What is overshoot?
When the difference goes over 0mV
What is repolarization?
the return of membrane potential to its normal RMP
What is hyperpolarization?
the increase in the potential difference across the membrane, going more negative, away from the RMP
Explain the importance of the threshold membrane potential.
an action potential will only be generated if the receptor potential goes over -55 mV
When will Na cross the membrane?
only at the activated state (-55 mV), not during resting or inactivated
When do the voltage gated channels open?
Once the receptor potential reaches threshold
What direction does Na flow when its voltage gated channel is open?
in
What direction does K flow when its voltage gated channel is open?
out
What ion channel is involved with generating depolarization?
opening stimulus of specific Na channels lead to depolarization
What ion channels are involved with generating overshoot and repolarization?
Voltage gated Na and K channels
What ion channels are involved with generating hyperpolarization?
K tries to reach equilibrium potential of -80 mV but cannot because the channel closes before it can do so
What is the absolute refractory period?
period during which voltage-gated Na channels are in an inactivated state and action potential cannot be generated
What is the relative refractory period?
a stronger than normal stimulus is needed to elicit action potentials (need more stimulus to bring hyperpolarized region up to threshold)
How do local anesthetics and tetrodotoxin block sensory signals from reaching their destinations?
tetrodotoxin prevents the generation of action potentials by blocking voltage gated Na channels
How does hyperkalemia affect resting membrane potential?
makes it easier to generate an action potential
resting potential is more positive
How does hypokalemia affect resting membrane potential?
makes it more difficult to generate an action potential’
resting potential is more negative
How is the action potential spread in a nonmyelinated axon?
the action potential triggers a local depolarizing electrical current that spreads along the axon, activating adjacent voltage-gated Na and K channels and generates an AP
What is the propagation of a non-myelinated action potential considered?
nondecremental
How does the action potential spread in a myelinated axon?
The action potential generates local currents that are strong enough to generate a new action potential
the voltage gated channels are at the node of ranvier
the myelination increases the conduction speed between each node
What does the propagation of a myelinated axon involve?
the generation of a new AP at each node of Ranvier resulting in saltatory conduction (ap jumps from node to node)
What two factors influence the conduction velocity of action potentials?
Size of axons and myelination (the larger the axon, the longer the internode, the faster the conduction speed)
Why does demyelination affect the conduction of action potentials?
loss of myelin decreases the signal transmission efficiency and action potentials cannot reach the node of Ranvier which is where the Na and K channels are located at
