Nervous Communcation Booklet

Question 1

The cardiac cycle is controlled by the SAN and the atrioventricular node (AVN).

Describe how (5).

Answer 1

1. SAN initiates heart beat (acts as a pacemaker).
2. SAN sends wave of electrical activity.
3. AVN delays electrical activity.
4. Allowing atria to snotty before centrioles contract.
5. AVN sends wave of electrical activity.
6. Causing ventricles to contract from the base upwards.

Question 2

When a neurone transmits a series of impulses, its rate of oxygen consumption increases.
Explain why.

Answer 2

More respiration is needed (which uses oxygen).
More ATP is supplied
For the transport of ions

Question 3

A myelinated axon conducts impulses faster than a non-myelinated axon.

Explain this difference.

Answer 3

In myelinated axons, depolarisation occurs only at the node of Ranvier.
So the impulse jumps from node to node.
So that the impulse doesn’t travel along the whole length.

Question 4

Explain how a lower temperature leads to slower nerve impulse conduction.

Answer 4

Diffusion occurs slower in colder conditions. Therefore there’s a slower diffusion of ions.

Question 5

Give three factors that affect the speed of nerve impulse conduction.

Answer 5

• temperature
• myelination
• the axon diameter

Question 6

Explain what causes vision using the fovea to be in colour.

Answer 6

Each cone cell (three different types) respond to different waves lengths of light.

Question 7

Explain what causes vision using the fovea to have high visual acuity.

Answer 7

Impulses along separate neurone from each receptor cell (receptor cell connects to separate neurones).

Question 8

Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina would be different in a nocturnal mammal from the number and distribution in a human. Explain your answer.

Answer 8

More rod cells and fewer cone cells present at the fovea in nocturnal animals.
Rods have a high sensitivity to light, whereas cone cells are not.
Because rhodopsin is bleached at low light intensities.

Question 9

When a person looks directly at an object, it’s focused on the fovea.

When the image is focused on the fovea, the person sees the object in colour. Explain why.

Answer 9

Colour is detected by cone cells.
The fovea contains many cone cells.
There are 3 different types of cone cells that detect different wavelengths.

Question 10

Vision at the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina.

Explain why vision using the fives has high visual acuity.

Answer 10

Each recover in the fovea is connected to a separate neurone.

Question 11

Vision using the fovea has high visual acuity but low sensitivity to light, compared with vision using other parts of the retina.

Explain why vision using other parts of the retina has high sensitivity to light.

Answer 11

Many rod cells in other parts of the retina.
Rod cells are sensitive to light.
Rods are connected in groups to the neurone.
This is summation (if enough light above threshold hits any cells in the group, then nerve impulses to the brain).

Question 12

Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the post synaptic membrane.

Answer 12

Binds to the receptor and opens Na+ channels.

Na+ enters and depolarises it.

Question 13

Explain what causes transmission at a synapse to occur in only one direction.

Answer 13

Because the vesicles containing neurotransmitters are only found in the pre-synaptic membrane.
Receptors for neurotransmitters are only found in post synoptic membrane.

Question 14

When sarcomeres contract, what happens to the length of the I-band?

Answer 14

They shorten.

Question 15

When sarcomeres contracts what happens to the length of the A band?

Answer 15

Remains the same.

Question 16

People who have McArdle’s disease produce less ATP than healthy people. As a result, they’re not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding film and theory to suggest why.

Answer 16

1. Cross bridges between actin and myosin
2. Movement of myosin heads
3. Detachment of myosin
4. Myosin heads move back to original position.

Question 17

What is the role of phosohocreatine (PC) in providing energy during muscle contraction?

Answer 17

PC is stored in muscles and acts as a reserve supply of phosphate, as ATP is made by phosphorylation for ADP in active muscles.

Question 18

There’s variation in the time taken for phosphocreatine (PC) to be reformed in muscles in people of a vey similar age.

Suggests reasons for this variation.

Answer 18

High muscle mass
Sex
Genetic differences 
Ethnicity
Metabolic rate
Number of fast / slow muscle fibres

Question 19

Describe the roles of calcium ions and ATP and the contraction of a myofibril.

Answer 19

1. Calcium ions diffuse unto myofibrils from the sarcoplasmic reticulum.
2. Calcium ions cause the movement of tropomysin in actin.
3. This movement causes exposure of the binding sites on the actin.
4. Myosin heads attach to binding sites on actin.
5. Hydrolysis of ATP on myosin head causes myosin heads to bend
6. Bending actin molecules.

Question 20

Both slow and fast muscle fibres contain ATPase.

Explain why.

Answer 20

Because ATPase breaks down (/hydrolyses) ATP into ADP.

Use of ATP by myosin.