Nerve impulses

The electron micrograph shows the junction between two neurones.

State the name given to the region labelled B.

Identify whether structure A or structure C is the first neurone in the pathway.

Use one piece of evidence visible in the electron micrograph to explain your choice.

Complete the sentences about the action potential.

The action potential involves rapid opening of voltage-gated sodium ion channels.

This is an example of........ feedback. During the action potential,

the inside of the neurone becomes more positive than the outside. This is known as

Mutations in genes coding for proteins in the cytoskeleton have been associated with several diseases of the nervous system, including neurodegenerative disorders.

Give three functions of the cytoskeleton.

Suggest how a mutation in cytoskeleton genes could cause a disease of the nervous system.

The graph represents the potential difference across the membrane of an axon during an action potential.

Use the graph to answer questions 7 and 8.

The graph represents the potential difference across the membrane of an axon during an action potential.

Use the graph to answer questions 7 and 8.

Which of the statements about the graph is correct?

A Depolarisation is occurring at 4 and hyperpolarisation is occurring at 6.

B Depolarisation is occurring at 2 and hyperpolarisation is occurring at 5.

C Hyperpolarisation is occurring at 5 and repolarisation is occurring at 6.

D Repolarisation is occurring at 4 and hyperpolarisation is occurring at 6.

Which of the following statements about nervous transmission is not correct?

A Breakdown of the myelin sheath can lead to uncoordinated movement.

B Saltatory conduction increases the rate of propagation of a nerve impulse.

C The myelin sheath is formed from Schwann cells.

D The nodes of Ranvier act as electrical insulators.

FURA-2 is a fluorescent dye that can be used to measure the concentration of Ca²⁺ ions inside 18 cells.

The structure of FURA-2 is shown below.

Use the information in the figure to explain why FURA-2 is unable to cross cell membranes.

Scientists have used FURA-2 to study the role of Ca²⁺ ions in the synapses of living nerve (b) tissue.

FURA-2 was injected into a single sensory neurone that was connected by a synapse to a relay neurone.

FURA-2 fluorescence inside the neurone was observed using a confocal microscope.

Explain one advantage of using a confocal microscope in this study.

The sensory neurone was stimulated electrically and the FURA-2 fluorescence in the synaptic bulb was measured. At the same time, an electrode recorded the membrane potential in a postsynaptic neurone.

The results of this study are shown in the table.

The intensity of FURA-2 fluorescence is proportional to the concentration of Ca²⁺ ions.

The scientists concluded that changes in the concentration of Ca²⁺ ions in the presynaptic neurone caused an action potential in the postsynaptic neurone.

Evaluate and explain the scientists’ conclusion.

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?

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.