Term
| What is Electricity? Negative/Positive Pole? Electrical Potential? |
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Definition
electricity - a flow of electrons from a high charge (more e-) to a lower charge (fewer e-)
Negative Pole- source of electrons, higher charge
Positive Pole- Locations where e- flow, lower charge
Electrical Potential
-diff in electrical charge (in volts) between pos and neg poles
-Term potential used because the e- on neg pole have the potential to flow to pos pole
-Neg charged electrons are attracted to the pos pole because opposite charges attract |
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Term
| What Was Galvani's Contribution to Electricity and Neural Activity? What is Electrical Stimulation? |
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Definition
-*Intracellular fluid of an axon is generally polarized in comparison to outside of cell membrane*
-Electrical current applied to a dissected nerve caused the connected muscle to twitch
-He concluded that electricity flows along the nerve (causing twitching in the muscle)
Electrical Stimulation
-Passing an electrical current from the tip of an electrode through brain tissue (or muscle) resulting in changes in the electrical activity of the tissue
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Term
| What did Fritsch/Hitzig (mid 1800's) and Barthlow (1874) contribute? |
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Definition
-Electrical Stimulation Studies (brain- not muscle)
Fritsch/Hitzig
-Electrical stimulation of the neocortex (rabbits and dogs) causes movement (arms and legs)
Bartholow
-Cincinnati Physician
-First report of human brain stimulation (neocortex) |
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Term
| What did Caton do? (Early 19th century)? What is an EEG? |
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Definition
-Electical Recording Study
-First attempt to measure electrical currents of the brain using a voltmeter and electrodes on the skull
Electroencephalogram - Electrical brain graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons
- As a person thought/did things there were changes in potential frequency
-Phenomena of sleep was divided into stages of diff waves of ptential change moving across the brain |
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Term
| What was the significane of Hermann von Helmholtz (19th century) ? What did Bernstein contribute? |
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Definition
-Electrical Recording Studies
-Realized flow of information in nervous system was too slow to be electricity
-Realized it was a wave not a charge that travels along an axon
•getting into neural tissue more specifically) found that passing the flow of electricity through a nerve is much slower than electric flow through a wire. Moved the electrode along the neuron for electric conduction and measured the speed. This led to an issue b/c it was too slow in comparison to electric flow
Bernstein
the movement of ions that perpetuates itself as it rolls down the axon like a wave, the ions have to be moving across the membrane that (not purely electrons that) create a difference in potential and thus are slower in speed
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Term
Hodgkin and Huxley Giant squid Axon? Oscilloscope? Microelectrode? Patch Clamping? |
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Definition
-Squid axon up to 1 millimeter (humans 1-20 micrometers)
-Easier to perform experiment
Squid have un-myelinated axons (thus speed is relative to size of axon)
-This large size aids in escape reflexes
-Ultimately recorded electrical voltage on an axon's membrane and explained the nerve impulses as changes in ion concentration across the membrane. The basis of this electrical activity is the movement of intr/extra cellular ions, which carry pos and neg charges
-Used oscilloscope - a device that serves as a sensitive voltmeter. An electron beam leaves a trace on a screen, deflections of the beam can be used to record voltage changes on an axon
-Microelectrodes- a set of electrodes small enough to place on or into an axon. Used to measure a neuron's electrical activity, deliver an electrical current to a single neuron (stimulation)
Patch Clamping- suck up a piece of membrane with ion channel, meant for a small area of tissue
•At rest, negative potential exist, applying stimulation creates a depolarization of the membrane (we go from having a negative internal membrane to positive and then back to negative)
•This is a Big DEAL! Detecting resting potential and recording it |
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Term
| What are Cations and Anions? |
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Definition
Cations- pos charged ions (Na+)
Anions- neg charged ions (Cl-), protein molecules (A-)
•Proteins are big complex structures, molecules are confined to interior cells, generally negatively charged (cell membrane is generally negative in part due to protein) |
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Term
| What are three factors that influence movement of ions in and out of cells? |
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Definition
Diffusion
-movement of ions from an area of higher concentration to a lower area through random motion
Concentration Gradient
-Differences in concentration of a substance among regions of a container that allows the substance to diffuse from an area of higher concentration to an area of lower
Voltage Gradient
-Diff in charge between two regions that allows a flow of current if the two regions are connected by a conductive medium
-Opposite charges attract, similar repel |
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Term
| What is Resting Potential? What particles take part in producing the resting potential? |
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Definition
Def- Electrical charge across the cell membrane in the absence of stimulation
-Store of negative energy on the intracellular side relative to the extracellular side
-Approximately -70 mV
-This is true for almost every cell in your body, at rest we have potential to do work/movement
1) Sodium Na+ and Chloride (Cl-)
Higher concentration outside cell
2) Potassium K+ and large proteins (A-)
Higher concentration inside cell
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Term
| How do we maintain Resting Potential? |
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Definition
-K+ is free to enter and leave the cell
-Na+ channels are ordinarily closed to prevent entry of Na+
-Na+-K+ pumps out three Na+ for two K+
•When potassium flow balances out, you are essentially at the resting potential
•Potassium can go in and out at resting state (leak through)
•This would not work if sodium were allowed to enter the cell.
• Cell membrane is permeable to potassium at rest but sodium cannot.
•There is a pump (special protein) that with the aid from energy (ATP) pumps forcefully move specific ions across membrane ratio of 3:2
•Resting potential is difference in voltage across membrane
•Gradient is forced by this process
•Key: At rest, neurons are in position to be active. This process will lead to redistribution of ions |
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Term
| What are Graded Potentials? |
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Definition
Def-
-Small voltage fluctuation in the cell membrane
-Restricted to the vicinity on the neuron where ions concentrations change
Stimulation changes proportionally
•The potential is limited to the small area on the membrane
•There is always leakage in the cell membrane, eventually helps return cell voltage to equilibrium
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Graded potentials are small |
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Term
| Hyperpolarization and Depolarization? What does TEA and Tetrodotoxin do? |
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Definition
Hyperpolarization
-due to an efflux of fluid, making the the extracellular side of the membrane more positive
•small grading potentials that make the interior of the cell more negative at rest
Depolarization
Due to an influx of Na+ through Na+ channels
•small grading potentials that make the interior of the cell more positive at rest
TEA- K+ channel blocker drug
Tetrodotoxin- Na+ channel blocker found in puffer fish, blocking this channel reduces depolarization in response to stimulation
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Term
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Definition
-Large, brief reversal in polarity in axon
-Lasts approximately 1 ms
-All-or-none signal
-Voltage-Sensitive Ion channels are crucial to the action potential
-gated protein channels that open or close only at specific membrane voltages
-Na+ and K+ have voltage gated channels
-Both are closed at membrane's resting potential
-Na+ channels are more sensitive to depolarization than K+ channels and therefore open sooner
•don’t occur in cell bodies or dendrites, occur generally in axons. Always same shape, size and don’t degrade as they travel down axon. # of action potentials is based on stimulation. Interior of the cell becomes briefly positive for about a millisecond. All-or-none in the sense that they occur or they don’t. Occur when threshold potential is reached. Depends on opening of Na and K channels. |
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Term
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Definition
-Voltage across a neural membrane at which an action potential is triggered
-Opening of voltage-sensitive Na+ and K+ channels
-Approximately -55 to -50 mV relative to extracellular surround
•occurs when the threshold is reached, triggering an action potential. Na+ and K+ channels are voltage gated sensitive (Na+ more sensitive to opening than K+ and close faster) |
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Term
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Definition
What happens first, reaching threshold activates gates and Na+ rushes into the cell (influx) making the interior of the cell more positive (Action Potential), this ion is time sensitive and the Na+ channel gate closes on its own automatically
•At the top of action potential, K+ channels open and come flowing out of the interior of the cell. At the end of the action potential, a lot of K+ flows out and makes the cell interior more negative overall and a refractory period is necessary to return to equilibrium
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•Only shows voltage gated channel
•Once the threshold is passed, another action potential cannot be generated (even if “bigger”), Na+ gates are closed during absolute refractory and thus stimulation has no effect
•Hyperpolarization period (relative refractory period) requires stimulation to return to resting state where more stimulation will be need to cross threshold
•If Ka+ voltage channels are blocked, Ka+ would still leak through but it would take longer for cell to repolarize
[image]
•Sodium Potassium pump is always running (kicking sodium out)
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Term
| What is the Absolute and Relative Refractory Period? |
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Definition
[image]Absolute Refractory Period
nThe state of an axon in the depolarizing and repolarizing phases of an action potential during which a new action potential cannot be elicited
n
[image]Relative Refractory Period
nThe state of an axon in the later phase of an action potential (hyperpolarization) during which increased electrical current is required to produce another action potential
n
nVoltage-gated potassium channels are still open keeping membrane slightly hyper
•You can only have a limited amount of action potentials in a given amount of time, we refer to that limitation as refractory periods (absolute and relative)
polarized. |
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Term
| What is the Nerve Impulse |
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Definition
[image]Nerve Impulse
nPropagation of an action potential on the membrane of an axon
nRefractory periods create a single, discrete impulse that travels only in one direction
nSize and shape of action potential remain constant along the axon
All-or-none law
The action potential stays the same size and shape while rolling down axon like a wave, only goes away from point of stimulation b/c it regenerates itself in adjacent sections of tissues |
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Term
| Saltatory Conduction: Myelin Increases Conduction Velocity |
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Definition
-Myelin is an insulator and there are few ion channels beneath it
•Squid axons need to be giant because they don’t have myelin sheaths
•If you don’t have myelin, electric conduction degrades very quickly. Myelin increases the velocity of a small axon making it very fast. More common on longer axons. Myelin allows for a more tightly packed
•Nodes, or gaps between myelin, have a lot of voltage gates |
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Term
| What is the Node of Ranvier |
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Definition
-part of an axon that is not covered by myelin, . As the nerve impulse travels by saltatory conduction, it jumps one node of ranvier to the next greatly incereasing the speed at which a nerve travels |
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Term
| What are Excitatory and Inhibitory Postsynaptic Potentials? |
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Definition
[image]Excitatory Postsynaptic Potential (EPSP)
nBrief depolarization of a neuron membrane in response to stimulation
n
nNeuron is more likely to produce an action potential n
[image]Inhibitory Postsynaptic Potential (IPSP)
nBrief hyperpolarization of a neuron membrane in response to stimulation
•Separated fibers of motor neurons and stimulate different pathways
•Depending on excitatory and inhibitory stimulation, the threshold will or will not be reached
n
nNeuron is less likely to produce an action potentiall |
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Term
| What is temporal summation? Spatial Summation? |
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Definition
Temporal - The relation between two excitatory pulses that are summed (added together to produce a larger depolarization of the mebrane than either would unduce alone)
Spatial - indicates two separate inputs occurring very close to one another on the cell membrane and in time sum. IPSPs produced at the same time if they occur at approximately the same tplace on the cell body membrane but not if they are widely separated |
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Term
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Definition
• Why does the action potential only go down the axon- B/c the voltage gated channels begin for the most part on the axon and thus action potentials have a fixed start point that go one way and the tissue behind them is in refractory period
•Will all EPSPs and IPSPs have an equal influence on axon Hillock? – EPSPSs that occur close to axon Hillock have more power over cell than distant connections (individually) |
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Term
| How Does Sensory stimuli Produce Action Responses |
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Definition
[image]Several different sensory modalities
nVisual, auditory, tactile, chemical (taste and olfaction)
n
[image]Many different types of sensory receptors
nIon channels on their cell membranes
[image]
[image]All types transduce one non-electrical form of energy into an electrochemical signalgnal. |
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