receptors, eye and control of heart rate

Question 1

Explain how the fovea increases the detail of an image.

Answer 1

• High (visual) acuity;
• Each / single cone is connected to a single bipolar/neurone;
• 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

Answer 2

• (Spatial) Summation means cannot distinguish between stimuli from different rod cells linked to same bipolar cell;
• Decreases acuity;
• (Summation of) sub-threshold stimuli produces threshold stimulation;
• Increases sensitivity;

Question 3

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

Answer 3

• Green sensitive pigment/cones non-functional
  OR
• Cones that detect green light non-functional;
• Three different types of pigment/cone;
• Other/different colours (‘seen’) due to stimulation of more than one cone/pigment;

Question 4

Explain how pressure on the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode A.

Answer 4

• (Pressure) deforms / opens (sodium) channels;
• Sodium ions enter;
• Causing depolarisation;
• Increased pressure opens more channels / greater sodium entry;
• [Size of generator potential determines frequency of action potentials]

Question 5

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

Answer 5

1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid /f all in pH
   OR
   Baro / pressure receptors detect rise in blood pressure;
2. Send impulses to cardiac centre/medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for chemoreceptors / CO2)
   OR
   By parasympathetic (nervous system for baro / pressure receptors / blood pressure);

Question 6

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.

Answer 6

• Greater entry of sodium ions / greater exit of K+
• in de-myelinated neurone;
• Ref. to active transport / ref. to ion pumps;

Question 7

Explain how nervous control in a human can cause increased cardiac output during exercise.

Answer 7

• Coordination via medulla (of brain) / cardiac centre;
• (Increased) impulses along sympathetic nerve;
• To S.A. node;
• Release of noradrenalin;
• More impulses sent from S.A.N (across atria);
• Increased heart rate / increased stroke volume;

Question 8

Explain why increased cardiac output is an advantage during exercise.

Answer 8

• Higher cardiac output - Increases O2 supply (to muscles);
• Increases glucose supply (to muscles);
• More ATP produced by oxidative phosphorylation / more energy release / more aerobic respiration / actively respiring muscles
• Increases CO2 removal (from muscles) / lactate removal;
• Increases heat removal (from muscles) / for cooling;
• Delays the formation of lactate

Question 9

Describe how the Pacinian corpuscle propagates an action potential.

Answer 9

• (Pressure causes) membrane/lamellae to become deformed/stretched;
• Sodium ion channels in membrane open and sodium ions move in;
• Depolarisation leading to generator potential;
• Greater pressure more channels open/sodium ions enter;

Question 10

Describe what is meant by the term threshold.

Answer 10

• When threshold has been reached;
• (Threshold or above) causes maximal response / all or nothing principle;