13.12 Receptors and Control of Heart Rate

Question 1

Receptor

Answer 1

• Specialised cells which detect a specific stimulus
• Convert one form of energy into a generator protein

Question 2

What is the Pacinian corpuscle?

Answer 2

• Pressure receptor
• Found mainly deep in the skin
• Also located in joints, tendons and ligaments
• Made up of many layers called lamellae which surround the ending of a single sensory neuron

Question 3

How does the Pacinian corpuscle work?

Answer 3

1. Increased pressure deforms sodium channels
2. Changes the stretched mediated Na+ channels
3. Na+ channel proteins open and Na+ diffuse in
4. Depolarisation leads to a generator potential

Question 4

Greater pressure in Pacinian corpuscle?

Answer 4

More stretch mediated Na+ ion channel proteins open, LARGER generator potential

Question 5

Types of eye receptors

Answer 5

Cones
Rods

Question 6

Rods

Answer 6

• Evenly distributed throughout the macula
• Sensitive to all wavelengths of light
• High visual sensitivity to low levels of light intensity
• Low visual acuity so image is unclear
• Retinal convergence due to several rods sharing a single Bipolar neuron

Question 7

Cones

Answer 7

• Densely packed in the fovea
• Each cone detects a specific wavelength of light
• Iodopsin is less sensitive than rhodopsin so requires higher light intensity of photons
• High visual acuity giving sharp image
• This is because each cone cell connected with a single bipolar neuron
• Cones send separate impulses to brain

Question 8

How many rods link to one neurone

Answer 8

3

Question 9

How many cones link to one neurone

Answer 9

1

Question 10

Pigment in rod

Answer 10

Rhodopsin

Question 11

Pigment in cone

Answer 11

Iodopsin

Question 12

How is generator potential created in eyes?

Answer 12

Photons cause pigment to break down
Altering the chemical structure
Leads to a production of generator potential

Question 13

How many types of rod cells

Answer 13

1

Question 14

How many types of cone cells

Answer 14

3 responding to diff wavelengths of light

Question 15

What type of summation do rods use

Answer 15

Retinal convergence (leads to spatial summation)

Question 16

What type of summation do cones use

Answer 16

Temporal summation

Question 17

Myogenic

Answer 17

Heart muscle is myogenic
Initiates its own contraction

Question 18

Sinoatrial node

Answer 18

Responsible for initial stimulus for the contraction in heart

Question 19

The heart controls and coordinates the regular contraction of the atria and ventricles.
Describe how.

Answer 19

• Sino atrial node sends wave or electrical activity across both atria
• Both atria contract
• Layer of nonconductive tissue prevents wave reaching ventricles
• Wave of electrical activity reaches the atrio ventricular node
• 0.1 second delay allowing atria to empty fully of blood
• Wave of electrical activity sent from the atrioventricular node
• Down the bundle of His to the base of the ventricles
• Up the Purkinje fibres
• Causing the ventricles to contract from the apex of the heart upwards

Question 20

Heart rate is under the control of

Answer 20

Autonomic nervous system
Medulla oblongata

Question 21

Two branches of the autonomic nervous system

Answer 21

Sympathetic
Parasympathetic

Question 22

Sympathetic

Answer 22

Stimulates effectors
Speeds up heart rate
Fight or flight
Noradrenaline

Question 23

Parasympathetic

Answer 23

Inhibits effectors
Controls activity at rest
Acetylcholine

Question 24

Two parts of cardio regulatory center

Answer 24

Acceleratory center
Inhibitory center

Question 25

Acceleratory centre linked to SA node by

Answer 25

Sympathetic nervous system

Question 26

Inhibitory centre linked to SA node by

Answer 26

Parasympathetic nervous system

Question 27

Two receptors for controlling heart rate

Answer 27

Baroreceptors
Chemoreceptors

Question 28

What change does baroreceptor detect?

Answer 28

Changes in blood pressure

Question 29

What happens to heart rate if blood pressure increases above normal?

Answer 29

• Detected by baroreceptors in walls of aorta & carotid arteries.
• More frequent impulses sent to medulla oblongata.
• More frequent impulses from inhibitory center in medulla to SA node via parasympathetic nerve.
• Decreases frequency of impulses from SA node across atria. (Acetylcholine)
• Heart rate decreases

Question 30

What happens to heart rate if blood pressure decreases below normal?

Answer 30

• Detected by baroreceptors in walls of aorta & carotid arteries.
• Less frequent impulses sent to medulla oblongata.
• More frequent impulses from acceleratory center in medulla to SA node via sympathetic nerve.
• Increases frequency of impulses from SA node across atria. (Noradrenaline)
• Heart rate decreases

Question 31

What change does chemoreceptor detect?

Answer 31

Changes in CO2 levels affecting blood pH

Question 32

What happens if CO2 levels rise, causing blood pH to decrease below normal after exercise?

Answer 32

• Detected by chemoreceptors in walls of aorta & carotid arteries.
• More frequent impulses sent to medulla oblongata.
• More frequent impuises from acceleratory center in medulla to SA node via sympathetic nerve
• more frequent impulses from SA node across atria (Noradrenaline)
• Heart rate increases
  There is no opposite effect for low CO2 levels of the blood.

Question 33

More CO2 present

Answer 33

Lower pH- more acidic

Question 34

Explain how the fovea increases the detail of an image

Answer 34

• High (visual) acuity
• Each / single cone is connected to a single bipolar/neurone
• Each cone sends separate impulse to the brain

Question 35

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

Answer 35

• (Spatial) Summation means cannot distinguish between stimuli from different rod cells linked to same bipolar cell;
• Decreases acuity;

Question 36

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

Answer 36

• (Summation of) sub-threshold stimuli produces threshold stimulation;
• Increases sensitivity;

Question 37

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

Explain why.

Answer 37

• 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 38

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

Answer 38

• (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 39

Explain why increased cardiac output is an advantage during exercise.

Answer 39

• 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 40

Describe what is meant by the term threshold

Answer 40

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