Would you see more or less SDH - succinate dehydrogenase-- in slow-twitch muscles in an SDH stain of muscle fibres?
You would see more SDH in slow-twitch. SDH is used in the citric acid cycle as a substrate, so in slow oxidative Type I muscle fibres, you would see a lot of mitchondria.
When muscle fibres are stained for myosin-ATPase, muscle fibres with lots of myosin-ATPase are stained light and those with less are very dark. How would fast-twitch, Type II or Type IIb look? How would slow-twitch type I look?
Type II & IIb would be light because they are fast-twitch muscles that have a lot of myosin-ATPase for rapid contraction.
Type I slow-twitch muscles have less and are thus dark (remember this is reverse staining).
Are fast-twitch muscles located superficially or deep, in general?
Superficial, like thigh muscles and cutaneous muscles.
Mr Smith, a greyhound trainer has decided to switch his dog to 800m races from 400 m. What type of muscle adaptations will you see?
You will see hypertrophy of muscle fibres due to exercise. You would also see an increase in the proportion of slow-twitch muscle fibres with more SDH/mitochondria.
Cinnamon McCain’s racehorse Blue Brandy has been underperforming and so Cinnamon has increased the incline for his hill work during training. What muscle-fibre adaptations will you see?
Hypertrophy of muscle fibres, and transition to fast-twitch, Type IIB fast-glycolytic fibres.
Mrs Arnold has been prescribed a physiotherapy regime of gentle stretching and light walks for her spaniel Darcy after her leg was in a ￼￼￼cast for 6 weeks. What muscle adaptions will you see?
Decreased number of sarcomeres due to being casted. Light walking & stretching will add muscle fibres; maybe some selective hypertrophy. Slow fibre types will be re- established. Example of de-training.
What role does satellite cells play in muscle plasticity/adaptation?
Satellite cells play a role in adaptation as they have stem-cell-like properties & are stimulated by IGF and other growth factors to migrate & form myotubules, or bind to myofibres at times of injury to help repair muscle. They are important in hypertrophy.
In terms of muscle innervation, what is the difference between spatial summation & temporal summation?
Spatial summation - increasing levels of force brought about by increasing number of motor units; interesting way animals can change what their muscles are doing to suit different locomotor needs. Motor-unit “recruitment”.
Temporal summation - within a single motor unit; increasing the force of contraction within the muscle that neuron innervates by increasing frequency of firing