12.8- Physiological Events in the Neuron Segments Flashcards
What are the three types of chemically gated channels in the receptive segment of the neuron?
Cation, K+, and Cl-
How long do graded potentials last?
While the Na+ channels are open and until the ion current ceases.
The degree of change is dependent on what?
The degree of magnitude.
Depolarization
The change of membrane potential in the positive direction.
Hyperpolarization
When chemical gated channels allow K+ to flow out of the cell or Cl- to enter the cell. Making the cell more negative than prior compared to the IF.
Postsynaptic potentials that result in the cell becoming move positive are called?
Excitatory Postsynaptic potentials- aka depolarization- Na+ rushing into cells and K+ out.
Postsynaptic potentials that result in the cell becoming less positive are called?
Inhibitory postsynaptic potentials- aka hyperpolarization- K+ out of the cell or Cl- into cell.
Spacial summation
two or more presynaptic neurons stimulating the postsynaptic neuron and creating summation.
Temporal summation
Summation cause by only one presynaptic neuron firing rapidly to stimulate the postsynaptic neuron.
How is summation triggered by the initial segment?
The voltage gated channels must be stimulated by a minimum level of membrane potential. This is how the axon hillock “decides” if it will allow an action potential to extend down the axon. This threshold is -55 mV, a change of 15 mV from it’s original -70mV.
Threshold membrane potential
Minimum voltage change needed to cause a potential.
Subthreshold value
Any voltage that is generated but not sufficeintly to cause a potential.
All-or-none law
Law that says the minimum voltage must be reached to cause any potential, and that if a potential is released it will be completely. There are no weak or strong potentials.
What two process make up an action potential?
Depolarization and repolarization
What is depolarization the result of?
The opening of voltage gated Na+ channels allowing a rapid influx of Na+ into the cell.
What is repolarization?
The opening of voltage gated K+ channels and the subsequent movement of K+ out of the cell.
Nerve impulse
The propagation of an action potential down the axolemma.
What happens during hyper polarization?
The K+ channels stay open longer than they need to to create the -70 mV resting potential creating a charge more negative than the RMP. Usually around -80 mV.
refractory period
The period of time after depolarization when an axon is not yet ready to generate another action potential, or greater than normal stimulation is required to cause another action potential.
Absolute refractory period
Period after depolarization when no amount of stimulation will cause another depolarization.
What does repolarization do to the voltage gated Na+ channels?
Causes them to go into a resting state instead of an inactive state. During the time while this is the case, the absolute refractory period is in effect.
Relative refractory period
Period of time after depolarization when larger the normal stimulus is required to cause another depolarization.
Where does continuous conduction happen?
Unmyelinated axons.- Voltage gated channels open and close along the entire length of the axon.
Where does saltatory conduction happen?
In myelinated axons.- Voltage gated channels only open and close in the neurofibril nodes between myelin sheaths.
