Skeletal muscle contraction

* The three photomicrographs, D, E and F, show three different types of muscle tissue.

State which photomicrograph shows cardiac muscle, which shows involuntary (smooth) muscle and which shows skeletal muscle.

Describe the evidence that supports your identification of each type of muscle tissue.

Extra answer space if required.

The table lists events that occur during muscle contraction. Each event is represented by a letter.

Give the sequence of letters that shows the correct order of events during muscle contraction.

The first letter has been done for you.

Myasthenia gravis (MG) is a disease that causes muscle weakness.

In MG, antibodies bind to acetylcholine receptors in neuromuscular junctions which prevents acetylcholine from binding to the receptors.

The diagram shows this process.

Acetylcholine

State the name given to diseases such as MG.

Explain how the binding of antibodies to acetylcholine receptors in the neuromuscular junction reduces the rate at which Ca²⁺ ions bind to troponin.

An electromyogram (EMG) records the electrical activity of a muscle.

The figure shows an EMG trace of a muscle undergoing fatigue.

Which of the statements about muscle fatigue is/are correct?

1 Increased acidity in the muscle during long periods of contraction is a cause of muscle fatigue. 2 There is a decrease in the frequency of the signal on an EMG trace as the muscle becomes fatigued. 3 There is an increase in amplitude of the signal on an EMG trace as the muscle becomes fatigued.

A 1, 2 and 3 are correct

B Only 1 and 2 are correct

C Only 2 and 3 are correct

D Only 1 is correct

Your answer

The table lists structural and functional differences between different types of muscle.

Place a tick (✓) in each box where the structure or function applies to that type of muscle.

The first row has been completed for you.

Fig. 19.1 and Fig. 19.2 are transmission electron micrographs (TEMs) of striated muscle.

Identify three proteins that make up the filaments labelled Z on Fig. 19.1.

Labels X and Y in Fig. 19.1 indicate two distinct bands.

Explain why the two bands look different.

Use your knowledge of the sliding filament model of muscle contraction to explain why Fig. 19.2 represents contracted muscle.

After death, the concentration of ATP in muscle cells decreases. During this time, the muscles become rigid in a process called rigor mortis.

Suggest why a lack of ATP leads to muscle rigidity.

* Muscle contraction requires energy in the form of ATP.

Describe the different sources of the ATP that is used in muscle contraction during strenuous exercise.

Additional answer space if required.

Gestational diabetes is a medical condition that affects pregnant women. It results in high levels of glucose in the blood, even though the woman produces normal levels of insulin.

Gestational diabetes is most similar to which other type of diabetes?

Explain your answer.

Suggest two ways a woman with gestational diabetes can manage her condition.

Skeletal muscle is one of the main tissues where glucose is removed from the blood in response to insulin.

Name the other tissue.

Explain why glucose is required for the contraction of skeletal muscle.

During late pregnancy, women find ventilation more difficult, as the developing foetus reduces the volume of the thorax. This can lead to tiredness and difficulty breathing.

A student used a spirometer to measure ventilation in a woman who was 36 weeks pregnant.

Fig. 16.1 shows the trace produced.

Mean oxygen uptake rate at rest in women is around 0.020 dm³ s^–1.

Using these data, the student made the following conclusion:

My data show that being pregnant reduces rate of oxygen uptake by up to 20%.

Evaluate this claim, using the data in Fig. 16.1.

Multiple sclerosis (MS) is an autoimmune disease that damages the nervous system.

Suggest how the immune system causes damage to the nervous system.

Fig. 5 on the insert shows three neurones of different sizes from a person with MS.

One of the neurones has been affected by MS.

MS causes changes to neurones, which reduce the speed at which nervous impulses are conducted.

Using information from Fig. 5, what can you conclude about how MS causes a reduction in the speed of nervous impulses?

Guillain–Barré syndrome is another autoimmune condition in which neurones are damaged and the rate of nervous impulses is reduced.

MS affects the central nervous system.

Guillain–Barré syndrome affects the peripheral nervous system.

Suggest two symptoms of MS that might not be present in people with Guillain–Barré syndrome.

Explain your answers.

Multiple sclerosis and Guillain–Barré syndrome both cause muscle weakness and loss of muscle function.

Suggest and describe how the function of neuromuscular junctions will be affected by multiple sclerosis and Guillain–Barré syndrome.