Neurons & the Action Potential

!2

» As you watch; » What is an action potential? » What is the difference in the action

potentials in strong sensation compared to weak sensations?

!3

!4

https://www.youtube.com/watch?v=pvBlSFVmoaw

https://www.youtube.com/watch?v=rSQNi5sAwuc

!5

» Why did moving the girl’s hand not move the boy’s hand?

» Why did he choose the particle nerve he did to manipulate the boys hand?

»

STRUCTURE

- dendrites on motor neurons receive impulses and conduct them toward the cell body, then down the axon

Resting Potential

In a resting neuron, there is a difference in electrical charges on the outside and inside of the plasma membrane.

The outside has a positive charge and the inside has a negative charge

ATP energy, actively transports 3 Na+ out & 2 K+ ions into the cell, by the sodium-potassium

pump.

• How can the membrane be charged (positive on the outside and negative on the inside) when both Na and K are positive ions?

• ANS: Note that for every 3 Na+ ions moved, only 2 K+ ions move. Because more Na+ ions are moved out the outside is positive.

!10

- a resting membrane is POLARISED - the resting potential of the cell is approx. -70mV

!13

!14

!15

!16

Action Potential-when the cell mb is stimulated, there is a change in the

permeability of the mb to Na+ ions - the mb becomes more permeable to Na+ and K+ --> Na+ ions

diffuse into the cell disturbing the resting potential - the inside of the cell becomes more positive relative to the

outside. (peak value = +30mV)

DEPOLARIZATIONAs the outside of the cell becomes more negative than the

inside of the cell, the mb is now DEPOLARIZED. When enough sodium ions enter the cell to depolarize the mb

to a critical level (threshold level) an action potential arises which generates an impulse.

= all or none principle

!19

REPOLARIZATION• K+ leaves the cell • charges switch • the outside of the cell becomes more positive than the

inside of the cell • the mb is now repolarized

Refractory Period - after firing, the mb cannot send another signal for a short time = refractory period

- until the mb stabilizes the action potential is higher than normal…

!22

How do signals pass between neurons?

» Synapse = space between neurons » chemical neurotransmitters are used to

transmit signal

!24

Classwork/ Homework» Read 11.2 » Complete #1, 2, 5

» Research or watch online videos that will help you list the steps that occur when signals travel from one neuron to another at a synapse.