Skeletal Muscle: Force, Work, And Energetics Flashcards
What is the integrator between the electrical stimulation (sensor) and the contraction of the muscle (effector)
Release of calcium into the sarcoplasmic reticulum
What are the two ways that peak tension production can be enhanced?
Hyperplasia: adding more myofibres
Hypertrophy: adding more myofibrils (larger fibres)
What are the two ways of organizing muscle fascicles?
- Parallel: tendons are parallel to longest axis
- Pennate muscle: longer tendon with fascicles attached along it at an angle — MORE FORCE (uni, bi, multi)
- Convergent:
What are pennate muscles stronger than convergent muscles?
The internal structure of the tendon is different
Convergent muscles: each muscle fibre pulls in a slightly different direction
Pennate muscles: each muscle fibre pulls in the same direction
How does a muscle “know” how to create the exact amount of force needed to balance its load and make an isometric contraction?
Sensory neurons monitor muscle length and create negative feedback signal if the length changes
What are the three types of muscle contractions?
- Isometric
- Eccentric: muscle lengthens, even when sarcomeres are going through the contraction cycle
- Concentric: force produced is greater than the weight it needs to pull
What is the purpose of the eccentric contraction?
Limits the speed at which the muscle is lengthening/slows down the movement at the joint
What are the three types of levers?
- Force in one direction, load moves in the other
- Small force can move a large load
- The load moves farther and faster than the muscle (short fast, inefficient movements)
What is the trade off between max tension and energy efficiency?
Need it quickly: anaerobic, less efficient and can work when oxygen is limited (glycolysis)
Have time: aerobic metabolism, very efficient but needs time and oxygen (citric acid cycle)
Last effort: muscle fibres can use phosphocreatine to recycle ATP, but this runs out very fast
What are the methods that muscles use depending on their activity levels?
Resting: aerobic +stores extra
Moderate activity: aerobic, and maintain O2 supply
Peak: anaerobic/CP— creates waste
What muscle fatigue factors affect excitation? What factors affect contraction?
Excitation: accumulation of K+ in T-tubules, depletion of ACh reserves
Contraction: build up of lactate and H+, leakage of Ca2+ back into sarcoplasm
What happens to lactate once the muscle stops contracting?
released into blood, taken up by liver and It is used for aerobic metabolism
What are the characteristics of Type I fibres?
- more capillaries per fibre (more oxygen)
- more mitochondria per fibre and fewer myofibrils (lower max tension, more ATP)
- slow maximal twitch tension
- not powerful
- fatigue resistant
What are the characteristics of type II fibres?
- fewer capillaries per fibre (lower O2 supply)
- more myofibrils per fibre and fewer mitochondria (higher max tension, less efficient ATP)
- maximal twitch happens quickly, and is short
- high forces, fatigue easily
What are the characteristics of Type IIB muscle fibres?
- fast contraction speeds
- intermediate twitch durations
- intermediate size and power
- some resistance to fatigue (higher mitochondrial layers and capillary levels than Type IIA)
