Neurones and the reflex arcEdexcel International A Level Biology: Subtopic test

1. 1
   A person touches a hot saucepan handle and pulls their hand away before they feel any pain. The withdrawal is a spinal reflex.

   (a)

   Which type of neurone carries the impulse from the receptor in the skin to the spinal cord?

   [1 mark]

   • ASensory neurone
   • BRelay neurone
   • CMotor neurone
   • DSchwann cell

   (b)

   Where are the cell bodies of the motor neurones that cause the hand to withdraw found?

   [1 mark]

   • AIn the white matter of the spinal cord
   • BIn the skin, next to the receptor
   • CIn the muscle fibres of the hand
   • DIn the grey matter of the spinal cord

   (c)

   Explain why the withdrawal reflex is faster than a conscious, voluntary response.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A neurobiologist examines a transverse section through a human spinal cord and a longitudinal section through a motor neurone with its myelin sheath.

   (a)

   Which statement describes the white matter of the spinal cord?

   [1 mark]

   • AIt contains the cell bodies and synapses of neurones
   • BIt consists mainly of myelinated axons running along the cord
   • CIt is the central H-shaped region of the spinal cord
   • DIt contains only the dendrites of sensory neurones

   (b)

   What is the function of the Schwann cells shown around the axon?

   [1 mark]

   • AThey release the neurotransmitter at synapses
   • BThey carry the impulse along the axon
   • CThey wrap around the axon to form the insulating myelin sheath
   • DThey contain the receptors that detect stimuli

   (c)

   Describe how Schwann cells form a myelin sheath and explain why the sheath insulates the axon.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A child steps on a sharp drawing pin and lifts her foot straight away. A student describes the pathway. A receptor in the skin detects the pin. A neurone carries the impulse into the spinal cord through the dorsal root, and the cell body of this neurone lies in a swelling outside the cord. In the spinal cord the impulse passes across a synapse to a short neurone, then across a second synapse to a neurone that leaves the cord through the ventral root and reaches a muscle in the leg.

   (a)

   Describe the pathway of the impulse in this reflex, from the receptor to the response, naming the types of neurone involved.

   [3 marks]

   (b)

   Describe two differences in structure between the sensory neurone and the motor neurone in this reflex, and explain how each is suited to its function.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Patient P has been infected with the poliovirus, which has destroyed the cell bodies of motor neurones in the grey matter of his lower spinal cord. He can feel a pinprick on his foot, but cannot lift it away and has no withdrawal reflex. Patient G has an autoimmune condition in which her immune system attacks the Schwann cells and myelin sheaths of her neurones. She has tingling sensations, weak muscles and slow reflexes.

   (a)

   Explain why Patient P can feel the pinprick but cannot lift his foot away.

   [6 marks]

   (b)

   Explain how the loss of myelin affects Patient G's neurones and gives her symptoms, and describe the role of the Schwann cells in the healthy nervous system.

   [6 marks]

   Total for question 4: 12 marks

End of questions