Chapter 9, Problem 4CCS

Children with Muscular Disorders

You're doing a clinical rotation with Dr. Barr, a world-renowned specialist in children's muscle disorders. On your first day, you meet three patients with the same probable diagnosis—nemaline myopathy. Jodi, age 2, has a waddling walk and difficulty standing; Linda. 6 months, has pneumonia associated with problems swallowing; and Tom, 12, has progressive weakness with foot drop and difficulty walking.

“This kind of variation is not surprising.” says Dr. Barr. “A mutation in one of 11 different genes related to thin filaments can cause nemaline myopathy, so you’d expect to see it present in different ways.”

Dr. Barr has scheduled all three children for a muscle biopsy (surgical removal of a small piece of muscle tissue for examination). He explains to you. “We’re going to use these biopsies for two things. First, we're going to look for the characteristic histology of nemaline myopathy. Second, we're going to test for malignant hyperthermia. It's not associated with nemaline myopathy but is associated with a different myopathy that has a similar presentation.”

Malignant hyperthermia is caused by a mutation in a gene related to calcium storage and release in skeletal muscle cells. In individuals with malignant hyperthermia, certain anesthetics can trigger a massive release of calcium into the cytoplasm. This leads to the generation of enough heat to substantially raise body temperature—a life-threatening reaction.

4. + NCLEX-STYLE Which statement best describes the importance of calcium in skeletal muscle contraction?

a. Extracellular calcium entering through ion channels binds to troponin to initiate muscle contraction.

b. Extracellular calcium entering through ion channels binds to tropomyosin to initiate muscle contraction.

c. Calcium released from the sarcoplasmic reticulum binds to tropomyosin to initiate muscle contraction.

d. Calcium released from the sarcoplasmic reticulum binds to troponin to initiate muscle contraction.