receptors, eye and chemo/baro receptors

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;

Question 3

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

Answer 3

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 4

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

Answer 4

1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid /f all in pH
2. Send impulses to cardiac centre/medulla;
3. more frequent impulses from accelerator centre in medulla so More impulses to SAN;
4. By sympathetic (nervous system for chemoreceptors / CO2)
5. so heart rate increases

Question 5

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 5

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

Question 6

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

Answer 6

• 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 7

Explain why increased cardiac output is an advantage during exercise.

Answer 7

• 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 8

Describe how the Pacinian corpuscle propagates an action potential.

Answer 8

• (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 9

Describe what is meant by the term threshold

Answer 9

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

Question 10

HR

Answer 10

wave of depolarisation from san spreads over avn and atria causing atria to contract
non conducting tissue stops wave of depolarisation passing down through walls of venticles
delay at avn which allows atria to finish contracting
electrical impulse passes thru bundle of his
ventricles contract from apex upwards