Chp 3.1: Action Potentials

Question 1

Neurons

Answer 1

The basic building blocks of the nervous system

Question 2

What are the 3 (+1) main parts of a neutron?

Answer 2

a cell body, dendrites, and an axon (and axon terminal)

Question 3

Soma (Cell Body) (3)

Answer 3

• Contains structures needed to keep the neuron alive
• its nucleus contains the genetic information that determines how the neuron develops and functions
• Processes and integrates information

Question 4

Dendrites

Answer 4

-Receives information

Question 5

Axon (use of it)

Answer 5

-Conducts electrical impulses away from the cell body to other neurons, muscles, or glands

Simplified: Carries the information along long distances from one part of the neuron to another

Question 6

What are the functions of neurons? (2) And what are the use? (1)

Answer 6

1. Generate electricity
2. Release chemicals

Allows neurons communicate with other neurons, as well as muscles and glands

Question 7

Blood-Brain Barrier

Answer 7

Prevents many substances, including a wide range of toxins, from entering the brain

Question 8

Resting Potential

Answer 8

-Internal difference of around -70 millivolts (inside is 70mv less than positive than outside)

• Outside the cell: high concentration of sodium ions (Na+)
• Inside in cell: more potassium ions (K+) /protein (A-)

=creates a chemical gradient (cell membrane)

-at rest there are more positively charged ions outside the cell relative to the inside

=results in difference in charge across the the membrane
=electrical gradient

=electrochemical gradient

-Neuron is at a state of polarisation

Question 9

What happens when neuron is stimulated? (2)

Answer 9

• A flow of ions in and out of the cell membrane reverses the electrical charge of the resting potential
• This produces an action potential (nerve impulse)

Question 10

Action potential

Answer 10

-A sudden reversal in the neuron’s membrane voltage

-based on the strength of the incoming stimulation (to dendrite) the neuron decides whether to pass the signal along

-if the stimulation is strong enough, the signal is transmitted along the entire length of the axon in a phenomenon called an action potential
= the neuron fires

Question 11

Depolarization

Answer 11

The shift from negative to positive charge of a neuron.

Question 12

Absolute Refractory Period (2)

Answer 12

• A recovery period that reestablishes the original distribution of ions immediately after an impulse
• can’t generate another action potential during this time

Question 13

All-or-None Law (2)

Answer 13

• Action potential is not proportional to stimulation (not affected by strength)
• neurons fire at maximum intensity, or do not occur at all

(Neuron may fire many more times per second: eg. Pain/ or less frequent: eg. Breeze of air)

Question 14

Graded potentials

Answer 14

Explained:
-when the change in membrane potential is small, and not big enough to be an action potential

-as ions move through each channel, they cause the membrane potential of the cell to move away from the resting potential

=graded potential

-can be positive or negative

Question 15

Action Potential Threshold

Answer 15

The negative potential inside the axon has to be changed from -70 millivolts to -50 millivolts before triggering the action potential

Question 16

Myelin Sheath

Answer 16

A fatty insulation layer derived from glial cells during development

Question 17

What is the use of the myelin sheath? (2)

Answer 17

• Insulates axon from electrical activity

- acts to increase rate of transmission of signals

Question 18

Nodes of Ranvier

Answer 18

Gaps that exist in myelin sheath along axon

Question 19

What is the use of nodes of Ranvier in myelin sheath?

Answer 19

Signals jump from one gap to the next

Question 20

What is an example of a result of damage of myelin sheath?

Answer 20

Multiple sclerosis

• caused by demyelination of axons
• immune system attacks myelin sheath

Question 21

Axon terminal

Answer 21

-transmits the information to the next cell in the chain

Question 22

What do you call a bundle of axons travelling together?

Answer 22

Nerve (very long)