The nervous system

Adrenaline is a hormone that increases heart rate when it binds to receptors on heart cells.

Beta blockers are drugs that bind to adrenaline receptors on heart cells.

Beta blockers are used to treat tachycardia (fast heart rate) and high blood pressure. They reduce the risk of a heart attack or stroke, which are two examples of cardiovascular diseases.

The conversion of ATP to cyclic AMP (cAMP) in a heart cell is prevented when beta blockers bind to adrenaline receptors on the cell surface membrane.

Describe one difference between the structure of ATP and the structure of ADP.

Suggest how the binding of beta blockers to adrenaline receptors prevents the conversion of ATP to cAMP.

Heart rate is lowered when the heart receives stimulation from the vagus nerve.

Explain why the vagus nerve is considered part of the peripheral nervous system and part of the autonomic nervous system.

Which of the following statements is/are correct?

1 The autonomic nervous system contains sensory and motor neurones. 2 Somatic and parasympathetic motor neurones use different neurotransmitters. 3 Somatic motor neurones stimulate skeletal muscles whereas autonomic motor neurons stimulate only glands.

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

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.

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.

Many organisms have evolved specialised gas exchange surfaces. One feature of these structures is their large surface area to volume ratio.

Describe how the structures of the insect tracheal system and fish gills provide a large surface area for gas exchange.

insect tracheal system........

The lugworm, Arenicola marina, is a species of segmented worm that lives in burrows in damp sand. They have hair-like external gills that increase the surface area available for gas exchange.

Many other species of segmented worm do not have external gills.

Suggest why lugworms have evolved external gills