Ch.4, MIDTERM 2 STARTS, Neurons/Electrical Signals Flashcards
What part of the neuron makes the decision whether it will fire an action potential or not?
axon intiial segment; sums all IPSPs and EPSPs then decides
Electricity
the flow of electrons from a body that contains a higher charge (MORE ELECTRONS) to lower charge (FEWER ELECTRONS), denoted by e-
Battery
source of potential energy (energy matter possesses bc of its spatial arrangement or location)
Voltage and current
difference in charge between two points (electrical potential energy) measured in volts
neruons are typically measured in millivolts
Current: movement of charged particles (ions in a biological system); magnitude of flow is measured in coloumbs/per second = amperage (Amps, A)
Resistance
controls current level: resistance goes up, current goes down, voltage goes up, current goes up
Selective Permeability
some substances are able to cross the membrane more easily than others
difference between concentration gradient and voltage gradient
CG: substyances diffuse from an area of higher to lower concentration
VG: ions move down a VG from an area of higher charger charge to lower charge
electrochemical equilibrium
when the chemical and electrical gradients are equal in magnitude, the ion is said to be in electrochemical equilibrium
Membrane potential
electrical
charge difference across the
neuron’s plasma membrane
(between inside and outside of
cell)Measured in units of mV
(1/1000th of a volt)
The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement.
why is the inside of the neuron negatively charged compared to the outside
BECAUSE OF
Unequal distribution of positively and negatively charged ions
* Creates an electrical potential difference (opposite charges attract)
what effect does the cell membrane have on charge
Membrane =
dam/charged battery
* Separation of charge
(ions) measured in mV
* flow of charged particles
= water
* Measured in pA
Vrest
Resting potential: The voltage across the plasma membrane of a
resting neuron (rest = not firing)
* About -70 mV
How is the resting potential generated? through concentration gradients
it has high Na+ outside, high cl- outside, high k+ inside, and high A- (negatively charged anion/all negatively charged proteins) = -70mV resting potential charge
How is the resting potential generated through proteins
K+ is freee to enter and leave the cell
Na+ channels are ordinarily closed to prevent the entry of Na+
sodium potassium pumps out three sodium for every two potassium
What does the sodium potassium pump do for negative resting potential?
contributes to more positive chartge outside the membrane
Three main factors that keep Vrest negative
sodium potassium pump
. High [A-] INSIDE of cell
3. K+ leaking OUT through leak channels
Voltmeter
device that measures the strength of electrical
voltage by recording the difference in electrical potential
between two points (between the reference and the one we’re actually trying to measure)
Hodgkin
and Huxley squid giant axon preperation and microelectrodes
- Squid giant axon preparation used by Hodgkin
and Huxley in the 1930s and 1940s, kept alive in
a saline solution (contains ions) - Were able to determine the neuron’s ionically-
based electrical activity Nobel Prize
used trhe north atlantic squid, loligo vulgaris
Osciliscope
sensitive voltmeter
voltage-gated ion
channels
Selective to a particular ion
* Open and close in response to
changes in membrane potential
(voltage)
* Highly concentrated at Nodes of
Ranvier: can only be generated at nodes, since they are sites of low membrane resistance UNLIKE myelin, and therefore can generate a lot of current due to channel s
Voltage gated potassium channels states
Voltage-gated channels
* K+ channels have 2 conformational
states:
* Closed at resting membrane
potential (-70 mV)
* Open at repolarization and hyperpolarizatiom
* K+ exits
Influx vs efflux
influx: coming into cell
Efflux: leaving the cell
Voltage gated sodium channel conformational states
Closed at resting membrane potential (-70 mV)
* Open at -50mV (depolarization)
* Na+ enters
* Inactivated at +30 mV (inactivation
gate closes) because sodium is entering
Drugs that enable us to isolate the study of V.G.P.C vs V.G.S.Cs y
TEA: tetramethylammonium : blocks voltage gated potassium channels, and it is a neurotoxin
TTX: tetrodotoxin, blocks the voltage gated sodium channels, neurotoxin, found in puffer fish
Differences in speed of closing and opening between voltage gated sodium channels and voltage gated potassium channels
voltage gated sodium: rises quicker, open quicker, close quicker
voltage gated potassium: slower to open,. slower to close
Graded potentials
small stimuilus, happening in dendrites, small voltage fluctuation across the cell membrane if stimulus is small
hyperpolarization vs depolarization
hyper: inside of the cell bnecomes MORE negative, usually bc of outward flow of K+, or inward flow of Cl-; inhibitory post-synpatic potentials, represses activity
de: inside of the cell becomes less negative = more positive, usually bc of inward flow of Na+, excitatory postsynpatic potentials
Action potential
elecvtrical signal neurons use for communication, a change in membrane voltage in response to a stimulus that is transmitted along the axon towards a synaptic terminal; brief reversal in membrane polarity
2-membrane potential reverses from negative to positive=depolarization
3-rapid repolarization=cell becomes negative again
Stimulus: factor that causes a nerve signal/action potential to bew generated, canb be ipsp or epsp
All or none response
you will always generate the same action potential with the threshold stimulus of -50MV, by increasing the stimulus, you only increase the amount of action potentials, not its strength
Difference between action potentials and graded potentials
action potentials: are always all opr none
graded potentials: amplitude of voltage deflection depends on stimulus strength
Extracellular vs intracellular sides of the sodium potassium pump
intracellular (inside): increases affinity for sodium to come in
Extracellular (outside): increases affinity for potassium to come in
Difference between concentration gradient, electrical gradient, and electrochemical gradient
Concentration gradient is the change in concentration of a substance over a given distance. An electrical gradient is a change in electric potential over a given distance. An electrochemical gradient is a change in the concentration of ions across a membrane or membrane potential.
3 steps of the sodium potassium pump
(1) ATP associates with the OPEN intracellular side , to allow sodium to come in, 3 enter into the cell,
(2) ATP transfers one of its phosphate groups to the transporter, giving it the energy needed to close the pumps intracellular side and open its extracellular side = decreases the pump’s affinity for sodium and increases its affinity for potassium
(3)2 potassium ions enter; extracellular side closes, ATP detaches to allow new atp molecule to associate with intracellular side and begin the cycle again
why doesn’t potassium influx occur during depolarization?
bc its against its gradient
what happens first during depolarization (the cell becoming more positive, ie less negative?)
- voltage gated sodium channels open first and faster: sodium is influxing into the cell
- Voltage gated potassium channels open shortly after
- Charge gets to -50mv
What happens to the V.G.P.C and V.G.S.C at rest?
Both are closed at -70mv
What happens to the channels during repolarization (cell returning to negative charge?)
- Sodium channels become inactivated? BECAUSE they do’t want the backflow of sodium, so they become inactivated to make sure the flow of sodium is unidirectional = going AWAY from the cell body.
- Potassium channels are still open. Potassium is effluxing out of the cell through leaky channels.
what happens to the channels during hyper polarization? (relative refractory)
hyperpolarization =becoming more negative than -70mv
1. Potassium channels are still open: potassium is still effluxing out of the cell through leaky channels
2. Sodium channels are now fully cllosed.
absolutely refractory and the two times it occurs at
a new potential cannot possibly be elicited
This occurs during two stages
1. during the depolarization period, where sodium gated channels open first and faster and sodium influxes into the cell, then potassium channels open after. The charge gets to -50mv. Because the sodium channels are already open, you can’t make them “more’ open.
2. During the repolarization period, where sodium channels become inactivated, to make sure sodium flow is unidirectionaal and going away from the cell body:impossible because the sodium channels are inactivated, and you need them open to start another action potential
Relatively refractory and when this happens
during the hyperpolarization phase: hyperpolarization =becoming more negative than -70mv
1. Potassium channels are still open: potassium is still effluxing out of the cell through leaky channels
2. Sodium channels are now fully cllosed.
It is still possible to start an action potential, but you would need a very strong stimulus.
Saltatory conduction
soLTAIRE: TO DANCE
the signal jumps from node to node, where there is a huge concentration of voltaged gated channels: they can produce high levels of current with little resistance = saltatory conduction
Why is an action potential generated?
bc of influx of sodiuum, spreads enough to activate the next segment of cell through depolarization
What does potassium influence?
only influences repropagation, NOT an action potential itself
Why do sodium channels have to open first?
bc they start the action potential
What is the domino effect of action potentials?
the reversal of polarity spreads to the next segment, then the next and the next
Why is the spacing of the nodes of ranvier so important?
the spacing is just close enough together that sodium can spread just far enough to start the next action potential of the next segment
Multiple sclerosis, symptoms, causes, type of disease
Symptoms: loss of sensation/motor control, usually appears in the hands and feet first
Causes: hard scar (plaque) forms at the site of myelin loss (can see this on an MRI)
Loss of myelin = disrupted ability of neuirons to propagate action potentials efficiently
Loss of myelin ONLY IN THE CNS, ONLY IMPACTS OLIGODENDROCYTES
most common autoimmune disease
What part of the neuron contains the most voltage gated channels
axon initial segment
where do graded potentials occur
soma and dendrites, when summed the axon initial segment will decide whether to fire
Where is the one place that voltage gated channels are NOT located in?
none in the cell body or dendrites: only ligand gated channels are there
difference between EPSPS AND IPSPS
excitatory postsynaptic potential: occurs in the dendritic spines, depolarization (making to less negative) of postsynaptic membrane in response to stimulation
Inhibitory postsynaptic potential: brief hyperpolarization (making it more negative than -70) of the postsynaptic membrane in response to stimulation, also occurs in the dendritic spines
Difference between temporal and spatial summation of inputs
Temporal: inputs on the SAME SPINE, occuring rapidly in succession,; if it is close enough together it will be summated into one larger EPSP
If they dont occur close enough together, the first input will fade and they won’t be summated
Spatial: input on different spines occuring at the same time: summate into a compound EPSP (you can also summate two EPSPS opr two IPSPS, or if it is close enough together and its one of each, they can cancel each other out
^EPSPS produced at the same time, but on sperate parts of the membrane, don’t influence each other, its only when they are close enough together that they summate
