U5 lecture 35 Flashcards
What are the 2 parts of neuronal action potentials
- neurons are ‘excitable cells’ (nerve and muscle)
- prinicple mechanism- voltage gated Na+ channel
what are excited cells
they can change membrane potential to generate an electrical signal
what is the first step in the generation of action potential
- local change in membrane potential- such local changes can be hyper polarizing or depolarizing (graded potentials)
what does an action potential begin with?
a local depolarization
what charge is ‘hyper polarizing’ carry
more negative
what charge is ‘depolarizing’ carry?
less negative
where do graded potentials occur
in dendrites and cell body of neuron
what makes the size of graded potentials vary?
strength of stimulus
what are graded potentials generated by?
chemically and mechanically gated channels
what are the two types of graded potentials
- inhibitory post synaptic potentials
- excitatory post synaptic potentials
what is the second step in the generation of the action potential
- depolarization to a threshold value induces a population of voltage gated Na-channels within the local region of membrane to open Na+ permeability
what is the Na+ permeability cycle
- Na+ enters cell, carrying positive charge
- inside of cell gets more positive (increasing depolarization)
- more Na+ channels open
POSITIVE FEEDBACK CYCLE
what is the third step in the generation of an action potential
critical point: shortly after Na channels open they spontaneously close
‘inactivation’
what is the fourth step in the generation of the action potential
- depolarization also opens (more slowly) a second population of channels: voltage gated K channels
how does depolarization occur
inactivation of the voltage gated Na channels combined with activity of the voltage gated K channels
what is a refractory period
periods during which it is difficult or impossible to generate a second AP
what are the two types of refractory periods
absolute refractory period and relative refractory period
what is an absolute refractory period
immediately follows inactivation of Na channels membrane cannot be restimulated to produce AP
-involved ‘resetting’ of Na channels
what is a relative refractory period
a period during which a new AP can be produced but it takes a larger than normal stimulation
-involved resetting of K channels
what is the importance of a refractory period
- establish maximum rate of action potentials
2. influence the characteristics of AP propagation- forward propagation from axon hillock to axon terminal
*** memorize chart on last slide
s
