Week 2 - Brain cells And Action Potentials

Question 1

What are the widely branching structures of a neuron called?

Answer 1

Dendrites

Question 2

What is the long, thin structure that carries information to another cell called?

Answer 2

Axon

Question 3

Which animal species would have the longest axons?

Answer 3

The longest axons occur in the largest animals eg Giraffes and Elephants have axons that extend from their spinal cord to their feet, nearly 2 metres away

Question 4

Compared to other neurons, would an interneuron’s axon be relatively long, short, or about the same?

Answer 4

Short, because an interneuron is contained entirely in one part of the brain

Question 5

What are the four major structures that compose a neuron?

Answer 5

Dendrites, soma (cell body), axon and presynaptic terminal

Question 6

Which kind of glia cell wraps around the synaptic terminals of axons?

Answer 6

Astrocytes

Question 7

Identify one major advantage of having a blood brain barrier

Answer 7

The blood brain barrier keeps out viruses

Question 8

Identify one disadvantage of the blood brain barrier

Answer 8

It keeps out most nutrients

Question 9

Which chemicals cross the blood brain barrier passively?

Answer 9

Small uncharged molecules such as oxygen, carbon dioxide, and water. So do chemicals that dissolve in the fats of the membrane

Question 10

Which chemicals cross the blood brain barrier by active transport?

Answer 10

Glucose, amino acids, purines, choline, certain vitamins and iron

Question 11

Santiago Ramón y Cajal was responsible for which of these discoveries?
A) the human cerebral cortex has many specialisation to produce language.
B) the brain’s left and right hemispheres control different functions
C) the nervous system is composed of separate cells
D) neurons communicate at specialised junctions called synapses

Answer 11

C) the nervous system is composed of separate cells

Question 12

Which part of the neuron has its own genes, separate from those of the nucleus?
A) the ribosomes
B) the mitochondria
C) the axon
D) the dendrites

Answer 12

B) the mitochondria

Question 13

What is the most distinctive about neurons, compared to other cells?
A) their temperature
B) their shape
C) their internal components, such as ribosomes and mitochondria
D) their colour

Answer 13

B) their shape

Question 14

Which of these do dendritic spines do?
A) they synthesise proteins
B) they increase the surface area available for synapses
C) they hold the neuron in position
D) they metabolise fuels to provide energy for the rest of the neuron

Answer 14

B) they increase the surface area available for synapses

Question 15

What does an efferent axon do?
A) it controls involuntary behaviour 
B) it controls voluntary behaviour
C) it carries output from a structure
D) it brings information into a structure

Answer 15

C) it carries output from a structure

Question 16

Which of the following is a function of astrocytes?
A) astrocytes conduct impulses over long distances
B) astrocytes build myelin sheaths that surround and insulate axons
C) astrocytes create the blood-brain barrier
D) astrocytes synchronise activity for a group of neurons

Answer 16

D) astrocytes synchronise activity for a group of neurons

Question 17

Which of the following is a function of microglia?
A) microglia remove dead cells and weak synapses
B) microglia build myelin sheaths that surround and insulate axons
C) microglia dilate blood vessels to increase blood supply to active brain areas
D) microglia synchronise activity for a group of neurons

Answer 17

A) microglia remove dead cells and weak synapses

Question 18

Which of these can easily cross the blood-brain barrier?
A) fat-soluble molecules
B) chemotherapy drugs
C) proteins
D) viruses

Answer 18

A) fat-soluble molecules

Question 19

Which of these chemicals cross the blood-brain barrier by active transport?
A) oxygen, water, and fat-soluble molecules
B) glucose and amino acids
C) proteins
D) viruses

Answer 19

B) glucose and amino acids

Question 20

What is the brain’s main source of fuel?
A) glucose
B) glutamate
C) chocolate
D) proteins

Answer 20

A) glucose

Question 21

For the brain to use its main source of fuel, what does it also need?
A) steroid hormones
B) vitamin c
C) thiamine
D) acetylsalicylic acid

Answer 21

C) thiamine

Question 22

When the membrane is at rest, where are the sodium ions more concentrated?

Answer 22

The outside of the cell

Question 23

When the membrane is at rest, where are the potassium ions more concentrated?

Answer 23

The inside of the cell

Question 24

When the membrane is at rest, what tends to drive the potassium ions out of the cell? What tends to draw them into the cell?

Answer 24

When the membrane is at rest, the concentration gradient tends to drive potassium ions out of the cell, and the electrical gradient draws them into the cell. The sodium-potassium pump also draws them into the cell.

Question 25

What does hyperpolarisation mean?

Answer 25

A hyperpolarisation is an exaggeration of the usual negative charge within a call, to a more negative level than usual

Question 26

What does depolarisation mean?

Answer 26

A depolarisation is a decrease in the amount of negative charge within the cell.

Question 27

What happens if the depolarisation does or does not reach the threshold?

Answer 27

If the depolarisation reaches or passes the threshold, the cell produces an action potential. If it is less than the threshold, no action potential arises.

Question 28

What is the all or none law?

Answer 28

The size and shape of the action potential are independent of the intensity of the stimulus that initiated it. That is, every depolarisation beyond the threshold of excitation produces an action potential of about the same amplitude and velocity for a given axon.

Question 29

Does the all or none law apply to dendrites? Why?

Answer 29

It does not apply to dendrites as they do not have action potentials.

Question 30

During the rise of the action potential, do sodium ions move into the cell or out of it? Why?

Answer 30

Sodium ions move into the cell. The voltage-dependent sodium gates have opened so the sodium can move freely. Sodium is attracted to the inside of the cell by both an electrical and a concentration gradient.

Question 31

As the membrane reaches the peak of the action potential, what brings the membrane down to the original resting potential?

Answer 31

The potassium ions exit the cell driving the membrane back to the resting potential. Important to note, the sodium-potassium pump is not responsible for returning the membrane back to its resting potential. The sodium-potassium pump is too slow for this purpose.

Question 32

In a myelinated axon, how would the action potential be affected if the nodes were much closer together? How might it be affected if the nodes were much farther apart?

Answer 32

If the nodes were closer, the action potential would travel more slowly. If they were much further apart, the action potential would travel faster if it could successfully jump from one node to the next. When the distance becomes too great, the current cannot diffuse from one node to the next and still remain above the threshold, so the action potentials would stop.

Question 33

Suppose researchers find that axon A can produce up to 1000 action potentials per second (at least briefly, with maximum stimulation), but axon B can never produce more than 100 per second (regardless of the strength of the stimulus). What could we conclude about the refractory periods of the two axons?

Answer 33

Axon A must have a shorter absolute refractory period, about 1ms, whereas B has a longer absolute refractory period, about 10ms.

Question 34

When the neutrons membrane is at rest, where are the sodium ions and potassium ions most concentrated?
A) Sodium is mostly outside and the potassium is mostly inside
B) Sodium is mostly inside and potassium is mostly outside
C) Both ions are mostly inside the cell
D) Both ions are mostly outside the cell

Answer 34

A) Sodium is mostly outside and the potassium is mostly inside

Question 35

When the membrane is at rest, what are the forces acting on sodium ions?
A) Both the concentration gradient and the electrical gradient tend to move the sodium ions into the cell
B) Both the concentration gradient and the electrical gradient tend to move sodium ions out of the cell
C) The concentration gradient tends to move the sodium ions into the cell, and the electrical gradient tends to move them out of the cell
D) The concentration gradient tends to move sodium ions out of the cell, and the electrical gradient tends to move them into the cell

Answer 35

A) Both the concentration gradient and the electrical gradient tend to move the sodium ions into the cell

Question 36

When the membrane is at rest, what are the forces acting on potassium ions?
A) Both the concentration gradient and the electrical gradient tend to move potassium ions into the cell
B) Both the concentration gradient and the electrical gradient tend to move potassium ions out of the cell
C) The concentration gradient tends to move potassium ions into the cell, and the electrical gradients tends to move them out of the cell
D) The concentration gradient tends to move potassium ions out of the cell, and the electrical gradient tends to move them into the cell

Answer 36

D) The concentration gradient tends to move potassium ions out of the cell, and the electrical gradient tends to move them into the cell

Question 37

Which direction dos the sodium-potassium pump move ions?
A) It moves both sodium and potassium ions into the cell
B) It moves both sodium and potassium ions out of the cell
C) It moves sodium ions into the cell and potassium ions out of the cell
D) It moves sodium ions out of the cell and potassium ions into the cell

Answer 37

D) It moves sodium ions out of the cell and potassium ions into the cell

Question 38

Under which conditions does an axon produce an action potential?
A) Whenever the membrane is hyperpolarised
B) Whenever the membrane’s potential reaches the threshold
C) Whenever the membrane is depolarised
D) Whenever the membrane’s potential reaches zero

Answer 38

B) Whenever the membrane’s potential reaches the threshold

Question 39

If a membrane is depolarised to twice its threshold, what happens?
A) The neuron produces an action potential at twice as much strength as usual
B) The neuron produces an action potential that travels twice as fast as usual
C) The neuron produces an action potential slightly stronger and slightly faster than usual
D) The neuron produces the same action potential it would at the threshold

Answer 39

D) The neuron produces the same action potential it would at the threshold

Question 40

To which part to parts of a neuron does the all or none law apply 
A) Axons
B) Dendrites
C) Both Axons and Dendrites
D) Neither Axons or Dendrites

Answer 40

A) Axons

Question 41

During the rising portion of the action potential, which ions are moving across the membrane and in which direction?
A) Sodium ions move out
B) Sodium ions move in
C) Both sodium and potassium ions move in
D) Potassium ions move in

Answer 41

B) Sodium ions move in

Question 42

After the action potential reaches its peak, the potential across the membrane falls toward its resting level. What accounts for this recovery?
A) The sodium-potassium pump removes the extra sodium
B) Sodium ions move out because their channels are open and the concentration gradient pushes them out
C) Potassium ions move out because their channels are open and the concentration gradient pushes them out
D) Potassium ions move in

Answer 42

C) Potassium ions move out because their channels are open and the concentration gradient pushes them out

Question 43

What does the myelin sheath of an axon accomplish?
A) It enables an axon to communicate with with other axons
B) It enables action potentials to travel both directions along an axon
C) It enables nutrients to enter the axon
D) It enables action potentials to travel more rapidly

Answer 43

D) It enables action potentials to travel more rapidly

Question 44

What causes the refractory period of an axon?
A) The sodium-potassium pump becomes inactive
B) The sodium-potassium pump increases its activity
C) The potassium channels are closed
D) The sodium channels are closed

Answer 44

D) The sodium channels are closed

Question 45

About what percentage of the brain does an average person use?
A) 10 percent
B) 30 percent
C) 50 percent
D) 100 percent

Answer 45

D) 100 percent