CIE A Level Biology (9700) 2019-2021

Revision Notes

11.1.6 Myasthenia Gravis

Myasthenia Gravis

  • The body is capable of generating immune responses against pathogens and harmful substances (that contain non-self antigens) from outside the body
  • Sometimes, however, the body accidentally generates an immune response against itself
  • This is caused by a group of diseases known as autoimmune diseases:
    • Autoimmune disease occur because the body’s immune system attacks one or more self antigens (antigens that are produced by human body cells)
    • During the maturation of T cells, many of the T cells are destroyed because they have incorrect T cell receptors that are complementary to self-antigens (these T cell surface receptors should only be complementary to non-self antigens)
    • However, some of these incorrect T cells evade destruction and become activated to stimulate an immune response against these self-antigens (ie. against the body itself)
    • This starts an attack (usually involving antibodies and killer T cells) against the body
    • In some autoimmune diseases, this attack is localised and directed against one organ (eg. Type 1 diabetes). In others, it is directed against the whole body (eg. lupus)
  • Myasthenia gravis (MG), meaning grave (serious) muscle weakness, is an autoimmune disease:
    • That targets the neuromuscular junctions between motor neurones (nerve cells) and skeletal muscle cells
    • That causes the immune system to block receptor proteins at the neuromuscular junction (antibodies are produced, which then bind to these receptor proteins, blocking the transmission of impulses from motor neurons)
    • Where muscles fibres absorb the receptor-antibody complexes and destroy them
    • That results in non-functioning receptors which results in muscle cells receiving no stimulation and can lead to muscle tissue starting to break down

Author:

Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.
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