Lecture 3: The Action Potential Flashcards
Golgi stain
a mixture of silver nitrate and potassium chromate that causes 2% of brain cells to darken in colour as silver chromate crystallizes inside of them, in every nook and cranny.
The structure of the nervous system was discovered by
Camillo Golgi & Santiago Ramón y Cajal. they won the Nobel Prize in 1906 for their work on the structure of the nervous system
Soma/ Cell body
Where the nucleus is located
Processes
protrusions of the neuron that extend out of the soma
Dendrites
branched, treelike extensions from the soma that are responsible for sensing the external environment (for collecting information relevant to the cell).
Axon
responsible for transmitting information (via an action potential) to downstream cells
Myelin sheaths
insulate the axon to improve the speed and fidelity of the action potential
Axon collaterals
the branches of an axon
Axon terminal/ Terminal Bouton
responsible for releasing neurotransmitters to downstream cells when there is an action potential
Synapse
The junction between an axon terminal and the membrane of a downstream neuron
Electrical Potential
The potential for electricity to flow (doesn’t mean there is actual current flowing)
Measuring electric potential
measured with glass micropipettes filled with solutions which conduct charge. The micropipette is inserted through the membrane into the cell. The voltmeter measures the difference in electrical charge between two points (the potential difference)
Electrical potential is measured in
millivolts (mV)
The resting membrane potential is
-40 and -90 mV
Ions
charged atom or molecule
Cation
positively charged ion
Monovalent Cation examples
Na+, K+
Divalent Cations examples
Ca 2+, Mg 2+
Anion
negatively charged ion
Monovalent anion example
Cl-
Electrostatic pressure
attractive force between molecules that are oppositely charged (i.e., positive and negative) or repulsive force between molecules that are similar charged (e.g., positive and positive)
Ion channels
Specialized protein molecules that sit in the cell membrane. They have a pore (hole) in them through which specific ions can enter or leave cells.
Leak channel
An ion channel protein that is in the membrane and has a pore that is always open (e.g., potassium leak channel).
Intracellular fluid
fluid contained within cells
extracellular fluid
fluid located outside of cells
neurons sit in and are full of ___
salt water
the lipid bilayer is ___ to ions
impermeable
If there is an equal charge of positively and negatively charged ions on either side of the membrane, then
inside of cell = 0 mV
Sodium-Potassium Pump goal
pumps sodium ions out of the cell and potassium ions in the cell
Sodium-Potassium Pump steps
- the sodium-potassium pump binds 3 sodium ions and a molecule of ATP
- the splitting of ATP provides energy to change the shape of the channel and drive sodium ions through the channel
- the sodium ions are released to the outside of the membrane and the new shape of the channel allows two potassium ions to bind
- release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane
the sodium-potassium pump causes K+ ions to be ___ times more concentration ____ the cell than ____
30; inside; outside
the sodium-potassium pump causes Na+ ions to be ___ times more concentration ____ the cell than ____
15; outside; inside
Diffusion
Molecules move from areas of high concentration to low concentration
Leak Potassium Channels
the cell membrane of neurons contains K+ leak channels that are selectively permeable to K+. allows K+ to move out of the cell & along the concentration gradient. sets up the negative resting membrane potential
If K+ was the only ion that could cross the membrane, the electrical potential of the membrane would settle at
-90mV
the more K+ leak channels a neuron has, the closer the membrane potential will be to
-90 mV
Membrane potential
the difference in electrical potential inside and outside the cell
Why is the resting potential of most neurons less than -90mV
because other ions can sneak through other types of leak channels
Resting potential
The membrane potential of a neuron when it is not being altered by signalling molecules that cause excitatory or inhibitory postsynaptic potentials
Receptors
proteins found in the cell membrane that act as sensors
T or F: Many receptors on the neuronal membrane are ion channels that allow ions to flow through
T
Depolarization
When the membrane potential of a cell becomes less negative than it normally is at rest
T or F: Potassium can always flow through the potassium leak channels in either direction
T (but will usually flow out due to the concentration gradient)
Sodium Channel
Opens in response to a nerve impulse (when the membrane potential reaches -40 mV). the influx of Na+ depolarizes the membrane and opens more Na+ channels, causing the membrane potential to shoot up to +40 mV
T or F: The sodium channel is inactivated for a brief period following activation
T
The Action Potential
A brief electrical impulse that provides the basis for the conduction of information along the axon
Threshold of excitation
value of the membrane potential that must be reached
The Action Potential Steps
- Sodium channels open
- Potassium channels open
- Depolarization
- Sodium channels close
- Repolarization
- Potassium channels begin to close
Potassium Channel
Start to open on the upswing of the action potential (when the membrane potential reaches above 0 mV). The outflux of K+ through these channels, driven now by diffusion and electrostatic forces, drives the membrane potential back down within a millisecond
Refractory period
post action potential hyperpolarization
Repolarization
When the membrane potential of a cell becomes more negative than it normally is at rest
Wire electrode
placed in the extracellular fluid; it is an electrical conductor that provides a path for the electricity to enter or leave the medium
Fine glass microelectrode
inserted into the axon to record the activity of a neuron
Oscilloscope
a sensitive voltmeter that turns electrical fluctuations into visible signals
Calcium Channels
When the action potential arrives at the axon terminal, Ca 2+ channels open, causing it to enter the axon terminal. The influx of calcium causes several synaptic vesicles to simultaneously fuse with the presynaptic membrane.
Calcium is ___ times ___ concentration outside the cell than in
1000; more
Synaptic transmission
transmission of messages from one neuron to another via the presynaptic release of a neurotransmitter that crosses the synapse and binds to receptors located on the postsynaptic membrane.
conduction of the action potential
the movement of information along the axon
T or F: Conduction of an action potential can happen in either direction
false
T or F: the size of the action potential remains constant
true
all-or-none law
action potentials occur or don’t occur and once triggered, they will propagate down the axon without growing or diminishing in size to the end of the axon
rate law
the strength of the stimulus is represented by the rate of the firing axon
the sodium-potassium pump requires
ATP
t or f: potassium leak channels are always open
t
neuron function
orchestrate and control the movement of the multicellular organism
ways neurons transmit information
electrically and chemically
electrical signalling
relies on changes in the membrane potential (Vm), the difference in charges inside and outside the cell
chemical signalling
relies on the release of neurotransmitters at the axon terminals onto other neurons
cytosol
the salty solution that fills the cell
In what direction do potassium leak channels go?
both
what is the threshold of excitation?
-55 mv
at the peak of the action potential, the membrane potential is
40 mv
when do potassium channels open?
on the upswing of the action potential (around 0 mv)
how would you widen an action potential?
by infusing a voltage-gated channel antagonist
