Receptors and Control of Heart Rate

Question 1

Explain how the fovea increases the detail of an image (3)

Answer 1

1. High visual acuity
2. Single cone connected to single bipolar neurone
3. Each cone sends separate impulse to the brain

Question 2

Explain how the connection of several rods to a single bipolar cell (retinal convergence) influences visual acuity (2)

Answer 2

1. Spatial summation means cannot distinguish between stimuli from different rod cells linked to same bipolar neurone
2. Decreases visual acuity

Question 3

Explain how the connection of several rods to a single bipolar cell (retinal convergence) influences sensitivity (2)

Answer 3

1. Sub-threshold stimuli produces threshold stimulation
2. Increases sensitivity

Question 4

People with red-green colour blindness are unable to distinguish between red and green, and also between other colours. Explain why (3)

Answer 4

1. Green sensitive pigment is non-functional
2. Three different types of pigment
3. Other colours due to stimulation of more than one pigment

Question 5

Explain what happens when pressure is applied to the Pacinian corpuscle (4)

Answer 5

1. Increased pressure deforms stretch-mediated Na+ channel proteins
2. Na+ channel proteins open and Na+ enter
3. Depolarisation leading to generator potential
4. Increased pressure opens more stretch-mediated Na+ channel proteins so larger generator potential

Question 6

Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process (4)

Answer 6

1. Chemo receptors detect rise in CO2
2. Send impulses to medulla
3. More impulses to sinoatrial node
4. By parasympathetic nervous system

Question 7

The rate of ATP consumption of a de-myelinated neurone is greater than that of a myelinated neurone when conducting Impulses at the same frequency. Explain why. (3)

Answer 7

1. Greater entry of Na+ and greater exit of K+
2. In de-myelinated neurone
3. Via active transport

Question 8

Explain how the nervous control in a human can cause increased cardiac output during exercise (6)

Answer 8

1. Coordination via medulla
2. Increased impulse along sympathetic nerve
3. To sinoatrial node
4. Release of noradrenaline
5. More impulses sent from sinoatrial node
6. Increased heart rate

Question 9

Explain why an increased cardiac output is an advantage during exercise (6)

Answer 9

1. Higher cardiac output so increases O2 supply
2. Increases glucose supply
3. More ATP produced by oxidative phosphorylation
4. Increased CO2 removal
5. Increases heat removal
6. Delays formation of lactate

Question 10

Describe what is meant by the term threshold (2)

Answer 10

1. When threshold has been reached
2. Causes maximal response / all or nothing principle

Question 11

Where are the rods found? (1)

Answer 11

Macula

Question 12

Where are the cones found? (1)

Answer 12

Fovea

Question 13

Describe how a heartbeat is initiated and coordinated (5)

Answer 13

1. Sinoatrial node sends wave of electrical impulses causing atrial contraction
2. Non-conducting tissue prevents immediate contraction of ventricles
3. Atrioventricular node delays impulse whilst blood leaves atria
4. AVN sends wave of electrical impulses down Bundle of His
5. Causing ventricles to contract from apex upwards

Question 14

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta (5)

Answer 14

1. Atrium has higher pressure than ventricle causing atrioventricular valves to open
2. Ventricle has higher pressure than atrium causing atrioventricular valves to close
3. Ventricle has higher pressure than aorta causing semilunar valve to open
4. Higher pressure in aorta than ventricle causing semilunar valve to close
5. Contraction causes increase in pressure

Question 15

What do Baro-receptors respond to? (1)

Answer 15

1. Changes in blood pressure

Question 16

What do Chemo-receptors respond to? (1)

Answer 16

1. Changes in pH

Question 17

Explain what happens when blood pressure increases above normal (5)

Answer 17

1. Detected by Baroreceptors in walls of aorta and carotid arteries
2. More frequent impulses sent to medulla oblongata
3. More frequent impulses from inhibitory centre in medulla to sinoatrial node via parasympathetic nerve
4. Decreases frequency of impulses from sinoatrial node across atria
5. Heart rate decreases

Question 18

Explain what happens when blood pressure decreases below normal (5)

Answer 18

1. Detected by Baroreceptors in walls of aorta and carotid arteries
2. Less frequent impulses sent to medulla oblongata
3. More frequent impulses from acceleratory centre in medulla to sinoatrial node via sympathetic nerve
4. Increases frequency of impulses from sinoatrial node across atria
5. Heart rate increases

Question 19

Explain what happens when blood pH decreases below normal due to increase in CO2 (5)

Answer 19

1. Detected by chemoreceptors in walls of aorta and carotid arteries
2. More frequent impulses sent to medulla oblongata
3. More frequent impulses from acceleratory centre in medulla to sinoatrial node via sympathetic nerve
4. More frequent impulses from sinoatrial node across atria
5. Heart rate increases

Question 20

Which neurotransmitter is associated with the sympathetic nervous system? (1)

Answer 20

Noradrenaline

Question 21

Which neurotransmitter is associated with the parasympathetic nervous system? (1)

Answer 21

Acetylcholine

Question 22

Which cardo regulatory centre is linked to the sinoatrial node by the sympathetic nervous system? (1)

Answer 22

Acceleratory centre

Question 23

Which cardo regulatory centre is linked to the sinoatrial node by the parasympathetic nervous system? (1)

Answer 23

Inhibitory centre