Control of heart rate

The table compares features of different types of blood vessel in mammals.

Use the letters E to H to complete the following table.

Each letter may be used once, more than once, or not at all.

Unlike most other veins, pulmonary veins do not have valves.

Suggest why valves are not needed in pulmonary veins.

This is a drawing of a dissected human heart.

Identify the structures labelled J to M.

* This is an electrocardiogram (ECG) trace of a single heartbeat.

Describe how contraction of the heart muscle at rest is initiated and relate this process to the electrical activity recorded by the ECG.

Extra answer space if required.

Fig. 20.1 shows a normal ECG trace.

Fig. 20.1

Fig. 20.2 shows an ECG trace from a patient with abnormal heart activity.

Fig. 20.2

Identify this abnormality.

Give a reason for your identification.

Fig. 20.3 shows an ECG trace from another patient with abnormal heart activity.

Fig. 20.3

Identify this abnormality.

Give a reason for your identification.

Fig. 16.1 shows a drawing of a dissected human heart.

Identify the structures labelled A to E on Fig. 16.1.

State which subdivision of the peripheral nervous system supplies structure A Fig. 16.1.

Fig. 16.2 is a diagram of a section through the human brain.

Identify the letter and name of the structure in Fig. 16.2 that is connected by nerves to structure A in Fig. 16.1.

Normal human resting heart rate is approximately 70 beats per minute (bpm). Cutting the parasympathetic nerve to the heart increases this to approximately 100 bpm.

Suggest two conclusions that could be made from this observation about the control of resting heart rate in normal humans.

Injury to the parts of the brain labelled G and H in Fig. 16.2 can lead to a range of symptoms including:

• fatigue

• weight gain

• menstrual irregularities

• low blood pressure or dizziness

• increased sensitivity to cold.

Outline how injury to G and H is able to cause such a wide range of symptoms.

Suggest why it can be difficult for a doctor to conclude that the symptoms described in part (iii) are definitely caused by damage to parts of the brain.

Complete the following passage using the most appropriate terms.

The knee-jerk reflex is an example of a spinal reflex as it only goes through the

........ whereas the blinking reflex is a cranial reflex as the pathway goes

through the brain.

Reflexes are very fast as they only involve one or two........, which

are the slowest parts of nerve transmission. This is one reason why reflexes give a survival

advantage.

The drug metoprolol prevents stimulation of post-synaptic receptors in the sympathetic nervous system.

Which of the following conditions could this drug be used to treat?

1 Muscle fatigue 2 Tachycardia 3 High blood pressure

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

The greater blue-ringed octopus, Hapalochlaena lunulata, is one of the most venomous of all animals.

Its bite contains tetrodotoxin (TTX), a neurotoxin that can cause paralysis and death within minutes.

The following information has been discovered about the effects of TTX on nerve cells:

• TTX binds to the external surface of the voltage-gated sodium ion channels in the axon membrane.

• Binding of TTX changes the tertiary structure of the channel.

• This means the channel cannot open.

Using the information provided, explain how TTX affects the activity of neurones.

A common cause of death from TTX poisoning is suffocation (not getting enough oxygen) as a result of paralysis of the diaphragm.

Explain how paralysis of the diaphragm could lead to suffocation.

TTX is also known to reduce the speed of conduction in the Purkyne fibres of the heart.

Suggest and explain what effect this would have on the heart rate.

Molluscs such as H. lunulata have unmyelinated neurones. Saltatory conduction cannot occur in these neurones.

Why is transmission of action potentials along the axon slower in the absence of saltatory conduction?

A student looked at slides of different tissues under a light microscope.

The four viewed images are labelled W, X, Y and Z in Fig. 23.1, on the insert.

Identify tissues W, X and Y.

The student wrote the following summary about the control of heart rate.

Identify and correct any biological errors in the student’s summary.

Reflex actions are rapid responses that protect the body from harm.

The Moro reflex is found in babies up to five months of age, and occurs when the baby feels its head is suddenly no longer supported. The Moro reflex is made up of the following responses:

• The baby spreads out its arms then brings them together rapidly.

• The baby cries.

Suggest how the Moro reflex helps to prevent harm to a newborn baby.

The Moro reflex gradually disappears and usually stops completely after babies reach nine months. Other reflexes develop as children grow older.

Describe a reflex response a 3-year-old child would make to an object moving towards their eyes and explain the advantage of this response.