U5 lecture 35

Question 1

What are the 2 parts of neuronal action potentials

Answer 1

• neurons are ‘excitable cells’ (nerve and muscle)

- prinicple mechanism- voltage gated Na+ channel

Question 2

what are excited cells

Answer 2

they can change membrane potential to generate an electrical signal

Question 3

what is the first step in the generation of action potential

Answer 3

1. local change in membrane potential- such local changes can be hyper polarizing or depolarizing (graded potentials)

Question 4

what does an action potential begin with?

Answer 4

a local depolarization

Question 5

what charge is ‘hyper polarizing’ carry

Answer 5

more negative

Question 6

what charge is ‘depolarizing’ carry?

Answer 6

less negative

Question 7

where do graded potentials occur

Answer 7

in dendrites and cell body of neuron

Question 8

what makes the size of graded potentials vary?

Answer 8

strength of stimulus

Question 9

what are graded potentials generated by?

Answer 9

chemically and mechanically gated channels

Question 10

what are the two types of graded potentials

Answer 10

• inhibitory post synaptic potentials

- excitatory post synaptic potentials

Question 11

what is the second step in the generation of the action potential

Answer 11

2. depolarization to a threshold value induces a population of voltage gated Na-channels within the local region of membrane to open Na+ permeability

Question 12

what is the Na+ permeability cycle

Answer 12

• Na+ enters cell, carrying positive charge
• inside of cell gets more positive (increasing depolarization)
• more Na+ channels open

POSITIVE FEEDBACK CYCLE

Question 13

what is the third step in the generation of an action potential

Answer 13

critical point: shortly after Na channels open they spontaneously close
‘inactivation’

Question 14

what is the fourth step in the generation of the action potential

Answer 14

4. depolarization also opens (more slowly) a second population of channels: voltage gated K channels

Question 15

how does depolarization occur

Answer 15

inactivation of the voltage gated Na channels combined with activity of the voltage gated K channels

Question 16

what is a refractory period

Answer 16

periods during which it is difficult or impossible to generate a second AP

Question 17

what are the two types of refractory periods

Answer 17

absolute refractory period and relative refractory period

Question 18

what is an absolute refractory period

Answer 18

immediately follows inactivation of Na channels membrane cannot be restimulated to produce AP
-involved ‘resetting’ of Na channels

Question 19

what is a relative refractory period

Answer 19

a period during which a new AP can be produced but it takes a larger than normal stimulation
-involved resetting of K channels

Question 20

what is the importance of a refractory period

Answer 20

1. establish maximum rate of action potentials

2. influence the characteristics of AP propagation- forward propagation from axon hillock to axon terminal

Question 21

*** memorize chart on last slide

Answer 21

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