-electrochemical signal is needed for communication
an electrical signal based on depolarization of a neuron, which travels its full length (big difference b/w action and graded), based on the flow of ions into and out of the cell
Where does an action potential begin?
depends on location in NS
Where does AP begin for a sensory neuron?
at 1st node of ranvier on the distal process of the sensory neuron
Where does the lower motor neuron AP begin?
What is the axon hillock?
where the cell body tapers off
Where does AP begin for projection neurons?
What is a projection neuron?
projects from one point to another in brain
Where does AP for commissural neuron begin?
Where does AP for association neuron begin?
What does threshold of activation mean?
What does it take for a neuron to fire?
Threshold of activation:
critical level of depolarization of neuron's membrane at which the cell can actively generate an AP
What is the threshold of activation in humans?
What does the "all or none law" have to do with threshold of activation?
once an action potential starts, it will not stop
no matter how fast or slow it takes to reach the threshold, the AP will fire at the same velocity
you either activate it, or you don't
What is required to activate threshold?
What makes cell membrane permeable?
Energy that could be:
-mechanical-voltage gated channels
-chemical-ligand gated channels
after membrane potential is reached there is an influx of NA ions through voltage-gated channels causing depolarization of cell membrane. When Na comes in, there is a reversal of polarity. More positive ions inside, tendency to change polarity in inside to be positive and outside to be negative
Stimulation of various kinds will cause a change in cell membrane to make it 600x more:
permeable to Na
What is the key to action potentials?
based on the function of Na permeability--influx of Na due to stimulation (mechanical, chemical, heat, general sensation)
What is depolarizaiton due to?
influx of Na using voltage-gated channels
Does Na conduct to a high or low concentration when passing through a voltage-gated channel?
Na conducts to high concentration and passes through voltage gated channel changing the shape of the membrane and also changing:
W/in milliseconds (of depolarization), Na equilibrium is reached and Na channels:
During depolarization, K gated channels:
open and let K out of cell
When is K let out of the cell?
at the same time Na is coming in
occurs as a result of efflux of K, reestablishing RMP
An action potential only takes a few ___ ions to cause depolarization.
An action potential only takes a few ___ ions to cause repolarization.
Repeated AP over time results in:
excess of Na and K, causing an imbalance
How is excess Na and K taken up to maintain the concentration gradient?
How many AP would be needed to deplete the concentration gradient to where no more AP will take place?
occur during depolarization; flow from region of positive potential to negative potential
decrease in membrane potential ahead of depolarized region occurs, bringing it to threshold
-same currents responsible for repolarizing the membrane behind the impulse
-consequence of difference in potentials, doesn't create those differences
What are the types of conduction?
Saltatory conduction involves what kind of neurons?
Are saltatory conduction more rapid or less than non-myelinated?
How fast is saltatory conduction?
How does saltatory conduction work?
leaps from one node of raniver to another (entire axon does not have to be depolarized
What are examples of saltatory conduction?
lower motor neurons, proprioceptors (Type 1)
What type of neurons are involved in continuous conduction?
Is continuous conduction faster or slower than myelinated neurons?
How fast is a continuous conduction?
What are examples of continuous conduction?
Type III (A-delta) and Type IV (C-fibers) (pain receptors)
What determines AP velocity?
where or not the axon is myelinated
How does the diameter of the axon help to determine AP?
the greater the diameter the faster the AP
b/c there is less resistance w/ a large diameter than w/ a small diameter (fire hose v. water hose)