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Lecture Exam 2 (Set 3)


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Driving forces:
membrane potential-equilibrium potential
-channels close with stimulus gone
equilibrium potential:
membrane potential where the two driving forces acting on the ion (gradients) are equal in size but opposite in direction
What causes resting membrane potential?
1. unequal distribution of ions (concentration gradient)
2. relative membrane permeability to those ions.
Define primary active transport common name:
Na+-K+ pump
Polarized membrane:
one side positive, other side negative
more negative than rest
Membrane potential more positive, less negative
Define graded potentials:
-use in nervous system
-gathering information
-analyze input
-communicate between cells
Characteristics of graded potentials:
1. size is graded (bigger=bigger potential charge
2. decremental conductance--as potential travels across membrane of cell, it gets smaller
3. exhibit summation--they can add together
Decremental conductance:
As potential travels across membrane of cell, it gets smaller
They can add together
Types of graded potentials:
1. Receptor potentials-change in resting membrane potential due to sensory stimulation of sensory cell terminals--triggered by stimulation-signals
2. (Post) synaptic potentials--change in resting membrane potential due to communication received by another neuron
Stimulus gated channels:
gate is closed unless gets appropriate stimulus, open if correct signal is received
Kinds of summation:
1. Spatial summation--graded potentials that occur in different places on neuron, add together
2. Temporal summation--coming in at same place, occurring at same place and occur one right after the other
--occurring at same time, or both can be active
--allows neurons to analyze information, adding up input
Action potentials:
Used by neurons for rapid long distance signal
Characteristics of action potentials:
1. constant amplitude--size always same
2. not related to size of stimulus
3. all-or-none
4. propagation--does not get smaller as it travels--always same size
What part of cell gets action potential?
Axon hillock and axon
minimum depolarization necessary to produce action potential
Three phases of action potential:
Phase 1: depolarization
Phase 2: repolarization
Phase 3: after-hyperpolarization
Action potential caused by?
gated channels and voltage-gated channels (voltage needed to open at threshold)
Sodium channels:
1. Will open when membrane potential reaches threshold
2. Na+ voltage-gated channels cause more depolarization
3. "sodium channel activation" "depolarization"
4. Na+ channels automatically close
5. closing time is dependent
Potassium channels:
1. Potassium voltage-gated channels respond to threshold
2. will open in response to threshold
3. they open slower
4. as sodium channels are beginning to close
5. will help repolarize the cell
6. close voltage dependently--returning below threshold
after action potential
Steps for producing action potential:
1. Membrane potential is depolarized to threshold
2. Some Na+ voltage-gated channels open
3. Na+ ions flow into cell
4. Cell gets more polarized which causes more Na+ channels to open
5. K+ voltage-gated channels open slowly in response to threshold depolarization
6. Na+ channels close because time is up
7. K+ ions flow out of cell which causes membrane potential to repolarize
8. K+ voltage-gated channels start to close when membrane potential drops below threshold
9. K+ channels close slowly so the membrane potential gets more negative than rest (after-hyperpolarization)
10. K+ channels closed and membrane potential returns to rest
Two types of refractory period:
1. Absolute refractory period: that time immediately after action potential when you cannot make another--being caused by Na+ voltage-gated channels
2. Relative refractory period--time after absolute refractory period when you can get action potential, but threshold is higher
Inactivation gate:
closes, but channel remains open--won't respond to voltage
What is speed of action potential?

What affects that speed?
very fast

1. diameter of axon--bigger=faster
2. if they have myelin-insulating wire
Saltatory conductance:
movement-jumping in myelinated axon--only place is advantages: 1. speed, 2. metabolic savings, 3. size

Disadvantages: diseases can destroy myelin so can't make action potential

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