University of South Carolina BIOL 460L Skeletal Muscle Function Worksheet (2).BIOL 460L
Skeletal Muscle Function Worksheet
1. Skeletal muscle review:
a. What neurotransmitter is released at the neuromuscular junctions?
○ Acetylcholine (ACh)
b. What receptors are found on the motor end plate?
○ Nicotinic acetylcholine receptors
c. What do we call a somatic motor neuron together with all of the individual muscle fibers that it
innervates?
○ Motor unit
d. Where does most of the calcium come from in skeletal muscle contraction?
○ Sarcoplasmic reticulum
2. Explain how Duchenne’s muscular dystrophy is inherited.
Duchenne muscular dystrophy is a recessive X-linked disorder that often manifests itself in
young boys under the age of five. In addition to the effects on skeletal muscle, cardiac muscle
can be impacted. A mutation in the dystrophin gene on the X chromosome causes the
condition. With 2.6 million base pairs of DNA, this is the biggest gene in the human genome.
Dystrophin, a protein that binds the cell cytoskeleton to the extracellular matrix, is encoded by
the gene. Dystrophin defects cause excessive Ca2+ to enter muscle cells, resulting in cell death.
As cells die, muscular weakness intensifies, eventually affecting the respiratory muscles.
3. What is the difference between an isometric contraction and an isotonic contraction? Give an
example of each.
● An isotonic contraction causes the muscle to shorten. The muscle does not shorten
during isometric contractions. The muscles contract in both of these, the main difference
being that the muscle shortens in one but not the other.
● A person performing bicep curls is an example of an isotonic contraction. They raise the
dumbbell, causing the muscle to shorten.
● When a person pushes against a building's wall, this is an example of an isometric
contraction. The muscular tension rises, but the wall does not shift, implying that the
muscles stay the same length.