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
What type of channels are found in the presynaptic terminals?
Voltage gated Ca2+ channels, that open to allow Ca to flow in where action potential runs through. Quantity of neurotransmitter release is directly proportional to the numbers of voltage gated calcium channels.
Ionotropic postsynaptic receptors
Directly open ion channels via ligand binding.
Open and close quickly.
Cation channels= excite neuron.
Anion Channels= inhibit neuron.
Metabotropic Postsynaptic Receptors
second messenger system
Prolonged response (memory).
Example: G-protein activates cAMP or cGMP.
Excitatory* Post Synaptic* Potentials (EPSP)
Na channels open, depressed conduction through Cl &/or K channels, and either excites cell activity, increases** excit. receptors, or decrerases inhibitory receptors.**
Inhibitory Post Synaptic Potential (IPSP)
Opening of chloride Cl- ion channels,increase in K ions out of cell, and change recetors that motivate its intent of inhibition
Summation of graded potentials-Spatial
Single terminal isnt enough power to release enough neurots, they need to add to one another to trigger an actional potential.
(When the EPSP becomes great enough, the threshold for firing will be reached)
A change in potential in any part of the intrasomal fluid causes what due to a very high electrical conductivity?
In Spatial Summation
Almost exactly equal change in potential at all other points inside the soma.
Summation of graded potentials-Temporal
Each time a presynaptic terminal fires= released neuroT opens membrane channels for ~1millisecond, but changed postsynaptic potential lasts up to 15 miliseconds.
A second opening= increases the post synpatic potential to a greater level and the more rapid the rate of stim.
Successive discharges from a single presynpatic terminal, occur rapidly enough, can add to one another or “Summate”.
Presynaptic Facilitation/Excitation
Presynaptic release of the transmitter closes** K+ channels= prologation of action potential–>increases calcium Ca2+ influx **into the postsynaptic axon termin and enhances excitatory transmitter release by neuron B at its synpase with the postsynpatic neuron C.
Presynaptic Inhibition
Occurs at the terminal before the singal ever reaches the synapse/before their own endings terminate on postsynaptic neuron. Inhibitory transmitter: GABA usually
Generally leads to opening of anion channel.
Glycine Amino Acid Neurotransmitter
Spinal Cord, Inhibitory
Glutamate Amino Acid Neurotransmitters
Secreted by the presynaptc terminals in many of the sensory pathways entering the CNS + cerebral cortex.
Excitation
GABA (Gamma aminobutyric Acid)
Spinal cord, Cerebellum, basal ganglia, cortex.
Inhibition
What does acetylcholine split up into and by what enzyme?
Acetate and Choline by cholinesterase (present in the proteoglycan reticulum)
