Electrophysiology Flashcards
A cation will leave a … potential within the cell as it leaves.
An anion will leave a … potential within the cell as it leaves.
A cation+= - Diffusion potential
An anion- = +diffusion potential
Nernst Potential Definition and Equation
The greater the imbalance of the concentrations on the two sides of the cell membrane= the greater the potential has to be to prevent additional net diffusion.
The ions are Na,K, Cl.
Sign of the potential is positive (+) if the ion diffusing from inside to outside is a negative ion and negative (−) if the ion is positive
Goldman Equation
This is used to calculate the diffusion potential when the membrane is permeable to several different ions!
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```What is the normal membrane potential difference in a nerve fiber?
94 millivolts
What does the Na/K pump do to the membrane potential?
-86 +-4(continous acting)= **-90millivolts
Electrogenic Na/K pump, what are the values for three Nas out and 2 Ks in?
What’s special about Ks ions and membranes?
K+ leaks! Even in a resting cell. 100x more permeable to K than to Na.
Three Stages of Neuron Potential
1.Resting at -90 millivolts
2.Depolarization (Na comes in the cell)
3.Repolarization (Na channels begin to close and K channels open to a greater degree).
Nerve/Muscle Impulse
Transmission of the depolarization process along a nerve/muscle fiber
What is the threshold for stimulation?
-55 milivolts
*All or nothing process! The ratio of action potential to threshold for excitation but be >1. Called a safety factor.
What’s different in the heart in regard to action potentials?
The heart muscle has L-type (slow) sodium channels that **prolong **depolarization.
Average nerve trunk contains about twice as many …fibers to …fibers.
Average nerve trunk contains about twice as many unmyelinated fibers to myelinated fibers.
What do schwann cells deposit?
Sphingomyelin- electrical insulator that decreases ion flow through membrane
Saltatory Conduction
Action potentials only occur at Nodes of Ranvier. Increases speed, conserves energy.
Velocity of Conduction in Nerve Fibers
0.25 m/sec (small,unmyel fibers)
**100 m/sec **(large myelinated fibers)
Negative vs Positive electric stimuli
decreases/ increases potential across membrane and depolarizes/repolarizes
What three ways can excitation of an action potential occur?
1.Mechanical
2.Chemical
3.Electrical Stimuli
Absolute refractory
Period during which a second action potential cannot be elicited, even with a strong stimulus
Relative Refractory
Period during which the muscle is more difficult to excite than normal but nevertheless can be excited by a very strong excitatory signal
Example of chemical/neurotransmitter
Ach, Glutamata, Epinephrine,etc
Gap Junctions
Allow free movement of ions from the interior of one cell to the interior of the next cell.
Smooth muscle fibers and cardiac muscle fibers.
Bidirectional transmission: helps coordinate activities of large groups of interconnected neurons.
What does the presynaptic terminal have?
Transmitter vesicles and the mitochondria.
What do vesicles contain?
Excitatory or inhibitory neurotransmitters
Mitochondria do what in the presynaptic term?
Provide ATP for synthesizing new transmitters