Neurophysiology Flashcards
Galvani
-electrical current applied to a dissected nerve causes the muscle connected to the nerve to twitch
-concluded that electricity flows along the nerve
-experiment was conducted on frogs
Fritsch and Hitzig
-electrical stimulation of the neocortex causes movement of arms and legs
-experiment was done on dogs
Bartholow
-First report of human brain stimulation
-1874
Caton
-first attempt to measure electrical currents of the brain using a voltmeter and electrodes on the skull
-performed on rabbits and monkeys
von Helmholtz
-flow of information in the nervous system is too slow to be a flow of electricity
Bernstein
-determined that the charge doesn’t travel along the axon, the wave does
Microelectrodes
-electrodes small enough to place on or in an axon
-can be used to measure a neuron’s electrical activity and deliver an electrical current to a single neuron
Oscilloscope
-serves as a sensitive voltmeter
-used to record voltage changes on an axon
Squid axon
-much larger than human axons
-easier to perform experiments on
-used to investigate the basis of action potentials
Resting membrane potential
-a store of negative energy on the intracellular side relative to the extracellular side
-approximately -50 to -80 mV
-found by a microelectrode inserted into a resting cell
Ion channels
-found in the lipid bilayer
-allow ions to pass through the membrane
-open in close in response to voltage changes, chemicals, or mechanical action
Passive channnels
-always open to a specific ion
-ungated channels allow potassium and chlorine to move in and out of the cell freely
Potassium channels
-lined with oxygen that mimic water molecules
-potassium can pass through the filter but sodium cannot
Gated channels
-normally closed, ions can’t freely pass
-gated sodium channels keep sodium ions out
-electrical, chemical, and physical
Active transporters
-ex: sodium potassium pump
-enzyme that breaks bond in ATP
-each ATP pushes 3 sodium ions out of cell and 2 potassium ions into the cell
Sodium and chloride ions are at a higher concentration ____ the cell
outside
Potassium and larger proteins are at a higher concentration _____ the cell
inside
Diffusion
-movement of ions down the concentration gradient
Voltage gradient
-difference in charge between 2 regions that allows a flow of current if the two regions are connected
Electrostatic pressure
-causes ions to flow to oppositely charged areas
What two opposing forces drive ion movement?
- diffusion
- electrostatic pressure
At rest, K+ ions move ______ the cell because of electrostatic pressure
inside
As K+ ions build up inside the cell, they also _____ out of the membrane along the _______ ________
diffuse, concentration gradient
Sodium-Potassium Pump
-used to maintain membrane potential
-creates concentration gradient by pumping 3 Na+ outside the cell for every 2 K+ pumped in
T/F the sodium-potassium pump requires ATP
yes because the pumping of ions is against the concentration gradient
Why is the extracellular space more positive?
-membrane is more permeable to potassium ions
Nernst equation
-predicts the voltage needed to counterbalance the diffusion force pushing an ion across a membrane
-predicts the equilibrium potential of an ion, usually K+
-predicts -80mV
Goldman equation
-predicts voltage potentials closer to observed resting potentials at -65 mV
Neural transmission
Communication between neurons results from changes in the resting membrane potential
Hyperpolarization
increase in membrane potential, the interior of the membrane becomes even more negative, relative to the outside
Usually due to the inward flow of chloride ions or outward flow of potassium ions
Depolarization
decrease in membrane potential, interior of the cell becomes less negative
reaches up to +40 mV
Usually due to the inward flow of sodium
Ungated channels allow ___ and ___ to move into and out of the cell more freely, but gated sodium channels keep out ____.
k+, Cl-
Na+ ions
Inhibitory signals
Make the neuron less likely to fire
Excitatory signals
Make the neuron more likely to fire
Passive signaling
sensory stimulation or synaptic activity opens ion channels
generates electrical current
Graded Potential
Small voltage fluctuations in the cell membrane, passively conducted throughout the neuron.
Part of passive signaling
Tetraethylammonium (TEA)
Selectively blocks K+ channels
prevents hyperpolarization
Tetrodotoxin
Selectively blocks Na+ receptors
prevents depolarization
Passive signaling is important in producing…
action potentials
Excitatory Postsynaptic Potential (EPSP)
brief depolarization of a neuron membrane in response to stimulation
Neuron is more likely to produce an action potential
Inhibitory Postsynaptic Potential (IPSP)
brief hyperpolarization of a neuron membrane in response to stimulation
Neuron is less likely to produce an action potential
Temporal Summation
summing of potentials that arrive at the axon hillock at different times
the closer together in time that they arrive, the greater the summation and possibility of an action potential
Voltage-sensitive ion channels
-gated protein channel that opens or closes only at specific membrane voltages
Hodgkin-Huxley Cycle
Synaptic or receptor potential -> Membrane depolarizes -> Voltage-gated Na+ channels open -> Na+ flows into neuron
Steps 2,3, and 4 repeat
Nodes of Ranvier
-The only place where sodium ion channels are found
-Unmyelinated parts of axon
Spatial summation
summing of potentials that occur at different parts of the cell
Axon hillock
-rich in voltage-sensitive channels
-EPSPs and IPSPs are integrated here
-action potentials are initiated here
Action potential regenerates along the _____
axon
Initial depolarization phase mediated by ____
Na+
Repolarization phase mediated by ____
K+
Absolute refractory period
-new action potential cannot be elicited
-gate 2 of sodium channels closed (not voltage-sensitive)
Relative refractory period
-increased electrical current required to produce another action potential
-potassium channels still open
Saltatory conduction
propagation of an action potential at successive nodes of Ranvier
Gap junctions
-ion channels in pre and postsynaptic membrane aligned
-rapid conduction of information
Chemical synapses
-how most neurons communicated
-can be inhibitory or excitatory
-large variety of chemicals
Transmission sequence
- transmitters cross the synaptic cleft and bind to postsynaptic receptors and cause an EPSP or an IPSP
- EPSP or IPSP spread toward postsynaptic axon hillock
- axon potential travels down the axon
- Voltage gated calcium channels open and let in Ca 2+
- Synaptic vesicles fuse with membrane and release transmitter into cleft
End plate
on a muscle, the receptor ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron
Acetylcholine
activated skeletal muscles
Transmitter-sensitive channel
receptor complex that has both a receptor site for a chemical and a pore through which ions can flow
Event related potential
large potential shifts caused by discrete stimuli
peaks and troughs are responses produced by the brain to specific stimuli
Polarity of EEGs
positive does not mean an increase in activity and negative does not mean a decrease in activity
What is used to determine the timing of a brain response?
EEG/neurophysiology
What is used to determine the area a brain response is coming from?
Functional imaging
MEG
Only sensitive to sources parallel to scalp surface (tangential)
EEGs are sensitive everywhere, but most sensitive to ____ surfaces (parallel to the scalp
radial
TMS
-electrical current running through tms coils produces magnetic field that can stimulate neurons
-can be used with neuroimaging methods to look at changes in brain activity
-can be used for treatment-resistant depression (after trying ketamine)
What does an EEG measure
Post-synaptic membrane potentials (Jessica green repeated many times, will be on exam).
