HOW YOUR BODY WORKS

1. Tay-Sachs disease is a rare genetic disorder that destroys nerve cells in the brain and spinal
cord. There is currently no cure for the disease. Answer the following questions in relation to the
disease.
a) What are lysosomes? (2 marks)
b) Tay-Sachs disease results from mutations in the HEXA gene. What are the effects of the
gene mutation in the cell? (2 marks)
c) What are gangliosides, where in the body are they most abundant and what happens when
their cellular concentration increases? (2 marks)
d) Symptoms usually begin in children before six months of age. What are the clinical
ramifications of the disease? Mention at least two for full marks. (2 marks)

After visiting a country picnic, where Jack had eaten a slice of watermelon from a local
producer, he fell ill and was taken to the local clinic. According to the clinical signs, of which
there were many, he was diagnosed with organophosphate poisoning. It turns out that the
watermelon had been sprayed with an insecticide containing the chemical organophosphate.
a) Using a labelled diagram, outline the sequence of events that occurs at the neuromuscular
junction after an action potential is propagated to the axon terminal of a neuron. Use
Acetylcholine as the example and include a description of each step up to
neurotransmitter binding. (3 marks)
b) Provide a general description of each of the mechanisms for neurotransmitter removal
after it is used. (1.5 marks)
Specifically, how is Acetylcholine removed? (0.5 mark)
c) Explain what organophosphates are and how they interfere with neurotransmission.
(1 mark)
d) Name at least two of the clinical signs manifested by organophosphate poisoning in the
autonomic nervous system. Include the receptor type for full marks. (2 marks)
(Voula Gaganis) (8 marks total)
4. Following an illness due to campylobacter infection, a young University student presents to his
GP with weakness in his limbs and absent reflexes including the knee-jerk reflex. Sensory
testing in his feet to light touch, pressure, vibration, and temperature were conducted. In
addition, a sample of cerebrospinal fluid was taken. The patient was provisionally diagnosed
with a disease of the peripheral nervous system affecting production of myelin.
a) What is myelin? Provide a brief description of its composition and function. How is myelin
produced in the central and peripheral nervous systems? Include the specific cells
responsible. (2 marks)
b) Provide the rationale for the sensory testing. What would you expect the findings to be?
(1.5 mark)
c) Using a diagram, provide a detailed description of how the knee-jerk reflex works. Why
was the knee-jerk reflex absent in the patient? (3 marks)
d) What is cerebrospinal fluid (CSF)? Where is CSF usually sampled from and why? How
does CSF sampling help support the diagnosis of a demyelinating disease?

 

 

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