8.1 - The nervous system & nerve impulses

Question 1

What is the role of the motor neurone?

Answer 1

transmits action potential from the CNS to an effector

Question 2

What is the role of the sensory neuron?

Answer 2

carries impulses via an axons from sense organs to the CNS

Question 3

What is the relay neuron?

Answer 3

carry impulses from and to numerous other neurons

Question 4

What is the difference between a neurone and a nerve?

Answer 4

• neurone is a single cell
• whereas a nerve is a more complex structure made up of many neurones surrounded by a protective covering

Question 5

Where is the cell body and axon found in the motor neurone?

Answer 5

• cell body (and dendrites) is in the CNS
• axons comes out of the CNS

Question 6

Where are cell bodies found in a sensory neuron?

Answer 6

• cell bodies are just outside the spinal cord in the dorsal root ganglia

Question 7

What is the cell body found in a relay neuron?

Answer 7

have both their cell body & their axons inside the (CNS)

Question 8

What is the 3 components of motor neurone?

Answer 8

1. cells have cell body
2. short dendrites
3. long axon

Question 9

What are the 3 components of a relay neurone?

Answer 9

1. cell body
2. short dendrites
3. short or long axon

Question 10

What are the 3 components of a sensory neurone?

Answer 10

1. cell body
2. long dendrites
3. short axon

Question 11

What is the fatty layer that insulates the axon?

Answer 11

myelin sheath

Question 12

What type of cells make up the myelin sheath?

Answer 12

Schwann cells

Question 13

What occurs every 1-3mm along an axon?

Answer 13

nodes of ranvier

Question 14

What are 5 stages of a general reflex arc, in response to a stimulus?

Answer 14

1. receptors detect a stimulus & generate a nerve impulse to the sensory neurones
2. sensory neurones pass a nerve impulse to the CNS
3. sensory neurones pass on the electrical impulse to the relay neurones (in the CNS)
4. relay neurones pass the electrical impulse onto a motor neurone
5. motor neurone carries impulse to an effector which produces a response

Question 15

What controls the size of the pupil?

Answer 15

iris

Question 16

Which muscles in the iris, control the size of the pupil?

Answer 16

radial & circular muscles (antagonistic)

Question 17

Which nervous system are the radial and circular muscles controlled by?

Answer 17

autonomic nervous system

Question 18

What type of reflex controls the radial muscles?

Answer 18

sympathetic reflex

Question 19

What type of reflex controls the circular muscles?

Answer 19

parasympathetic reflex

Question 20

What do the radial and circular muscles do when the pupil constricts?

Answer 20

radial - relax
circular - contract

Question 21

What do the radial and circular muscles do when the pupil dilates?

Answer 21

radial - contracts
circular - relax

Question 22

What happens when high light levels strike the photoreceptors?

Answer 22

• photoreceptors in the retina cause nerve impulses to pass along the optic nerve to different sites within the CNS, including a group of coordinating cells
• impulses from these cells are sent along the parasympathetic motor neurones to the circular muscles of the iris which contract
• the radial muscles relax
• this constricts the pupil, reducing the amount of light entering the eye

Question 23

Which two organs are effectors?

Answer 23

muscles & glands

Question 24

Which is the potential difference of an axon? What is it measured in?

Answer 24

• difference in electrical charge across the plasma membrane
• millivolts (mV)

Question 25

What is the potential difference across the axon at the resting state of the axon?

Answer 25

-70 mV

Question 26

What does the resting potential of the axon tell us about which side of the axon is more negative? What does this tell us about the membrane?

Answer 26

the inside is more negative & the membrane is said to be polarised

Question 27

What causes the uneven distribution of ions across the cell surface membrane?

Answer 27

action of sodium potassium pumps in the cell surface membrane of the axon

Question 28

Which ions do sodium potassium pumps carry in & out of the cell?

Answer 28

Na+ out of the cell K+ into the cell

Question 29

What supplies energy for the sodium potassium pumps? Why is energy needed?

Answer 29

- hydrolysis of ATP - the ions move against the concentration gradient

Question 30

What is the first stage of the resting potential?

Answer 30

1. Na+/K+ pump creates concentration gradients across the membrane

Question 31

What is the second stage of the action potential?

Answer 31

2. K+ diffuse out of the cell down K+ concentraion gradient this means the outside = positive & inside = negative this creates a potential difference

Question 32

What is the third stage of the resting potential?

Answer 32

the potential difference will pull K+ back into the cell

Question 33

What is depolarisation?

Answer 33

a reversal of the charges across the membrane of an axon of a neuron. This makes the outside of the cell change positive to negative, and the side of the cell change from negative to positive

Question 34

What is repolarisation?

Answer 34

the charges across the axon returning to resting potential. So the outside of the axon becomes positive and the inside of the cell becomes negative again

Question 35

What is an action potential?

Answer 35

a large change in the voltage across the membrane of an axon of a neuron

Question 36

Explain how the IAA affects the growth of the coleoptile. (4 marks)

Answer 36

- IAA diffuses from the tip of the coleoptile - therefore can be taken up by cells in zone of elongation - which causes cells to elongate - therefore, the coleoptile grows increases in height

Question 37

What does auxin cause to happen to the cellulose cell wall, with regards to pH? What happens to the cell as a result? (3 points)

Answer 37

- lowers the pH of the cellulose cell wall - cell wall weakens - allowing the cell to expand & cells to elongate