Generation and Propagation of Action Potentials Study Guide Flashcards
In terms of resting membrane potential, what is unique about neurons?
Neurons can rapidly change their membrane potential
Opposite charges _____; same charges _______.
- attract
- repel
It requires energy to keep opposite charges separated. So, when opposite charges are separated by a membrane, the system has ____________.
potential energy
voltage
the measure of potential energy generated by separated charges – the charge difference across a plasma membrane
current
flow of electrical charge (ions) from 1 points to another
What is used to measure voltage?
- Always measured between 2 points – called the potential or potential difference
- Measured in volts (V) or millivolts (mV)
- The greater charge difference between the 2 points, the higher the voltage
resistance
hindrance to charge flow
current equation
- current (I) = voltage (V) / resistance (R)
- Greater voltage = greater current, current is directly proportional to voltage
- Greater resistance = smaller current, current is inversely proportional to resistance
In terms of resistance, define conductor and insulator.
insulator: substance with high electrical resistance
Conductor: substance with low electrical resistance
In the human body, what TWO things generate the resting membrane potential?
The slight difference in the amount of positive and negative ions on either side of a cellular plasma membrane creates potential
Plasma membranes provides resistance to current flow
What are the two types of ion channels? Functionally, what is different about leakage vs gated channels?
Leakage (nongated) channels: always open
Gated channels: requires a change in protein shape to open/close the channel
What are the 3 types of gated channels? How does each open/close? Give examples of chemically gated and voltage gated channels from the muscle portion of this unit.
- Chemically gated: open only with binding of a specific chemical (ex - neurotransmitter_
- ACH, sodium potassium pump
- Voltage gated: open/close in response to changes in the membrane potential
- t-tubules
- Mechanically gated: open/close in response to physical deformation of receptors
- Sensory receptors for touch/pressure
What are the two components of an electrochemical gradient?
Chemical concentration gradient
Electrical gradient
Based on chemical concentration, ions will move from _______ to _______ concentration.
- higher
- lower
Based on electrical charge, ions will move towards _________________ .
the opposite electrical charge
What are the differences in ionic composition across a plasma membrane? Of these differences, which ion plays the most important role? T
- ECF has higher concentration of Na+ than ICF
- Balanced by chloride ions Cl-
- ICF has higher concentration of K+ than ECF
- Balanced by various negatively charged proteins
- K+ plays the most important role in membrane potential - tangerine story of high potassium
How permeable are plasma membranes to the following:
- Large anionic proteins
- Cl-
- Na+
- K+
- Large anionic proteins impermeable
- Cl- quite permeable
- Na+ slightly permeable (leakage channels)
- K+ 25x more permeable to K+ than Na+ (more leakage channels)
- K+ diffuses out of a cell – down its concentration gradient
Through the leakage channels, which direction does Na+ move? How about K+?
More K+ diffuses out than NA+ diffuses in
Based on movement of Na+ and K+, how is the negative resting membrane potential established?
- Membrane is highly permeable to K+, so K+ flows down its concentration gradient
- As positive K+ leaks out, a negative voltage (electrical gradient) develops on the membrane interior. The electrical gradient pulls K+ back in
Which direction are Na+ and K+ moved through Na+/K+ pumps? How does this help to maintain resting membrane potential? Recall why this process requires energy.
Sodium-potassium pumps stabilize resting membrane potentials by maintaining concentration gradients for Na+ and K+
- 3Na+ are pumped out of the cell while 2K+ are pumped into the cell
What are the TWO things that can change a resting membrane potential?
- Changes in the concentrations of ions across the membrane
- Changes in membrane permeability to ions
Changes in resting membrane potential can produce 2 different types of signals. Name and define the 2 types. Be sure to note what is different about the 2 types in terms of their strength.
- Graded potentials: incoming signals with variable strength operating over short distances
- Action potentials: long-distance signals of axons with consistent strength
Define depolarization
decrease in membrane potential (moves toward zero and above)
- inside of the membrane becomes less negative than resting membrane potential
Ex. -70mV → -55mV
- Probability of producing impulse increases
Define hyperpolarization.
Increase in membrane potential (away from zero)
- Inside of the membrane becomes more negative than resting membrane potential
Ex. -70mV → -75mV
Why are graded potentials “graded”?
Their magnitude varies directly with stimulus strength
- Stronger stimulus → more voltage change → farther current flow
The associated current flows __________________________ with distance.
decay or decrease in magnitude
When is a postsynaptic potential produced?
When the stimulus is a neurotransmitter released by another neuron
__________ are the principal way neurons send signals over long distances.
action potentials
_______ potentials are often initially activated by _______ potentials. where does this transition take place?
- action
- graded
the initial segment of the axon
What is the average change in membrane potential for an action potential?
~100mV
Do action potentials decay over distance?
they do not decay over distance
Define an activation gate and an inactivation gate.
- Activation gate: closed at rest, opens with depolarization to allow Na+ to enter
- Inactivation gates: opens at rest, blocks the channel when it is open to prevent more Na+ from entering the cell
What defines “threshold”? What kind of feedback loop is triggered by reaching a threshold?
- Membrane is depolarized to 15 to 20 mV from resting value
- Na+ permeability increases and Na+ influx far exceeds K+ efflux – positive feedback cycle
How does an action potential propagate - i.e. how are adjacent areas depolarized?
Influx of Na+ through the voltage gates in one area of the membrane causes local currents that will depolarize adjacent areas of the membrane in the forward direction (away from the point of origin)
Why are action potentials only propagated in one direction?
The refractory period of repolarization
What is meant by the all-or-none phenomenon?
Action potential either happens completely or does not happen at all - like igniting a fire
Why is propagation a better term to describe what is happening in an axon than conduction?
AP is regenerated anew at each membrane patch; every subsequent AP is identical to the one that generated initially
