Muscle structure and function Flashcards
What are the properties of muscle?
- Excitability
- Contractility
- Extensibility
- Elasticity
What is excitability?
Muscles can be activated by stimulation (artificially through electrical stimulation or biologically through nerves).
What is contractility?
When the muscle is stimulated cross-brides between actin and myosin in the sarcomeres produce force in the direction of shortening the muscle – although the muscle can still lengthen in an eccentric contraction if the external forces are greater than the contraction force.
What is extensibility?
Muscle cells can stretch. We have sensory fibres within our muscles called muscle spindles, which detect this stretch and elicit the stretch reflex if lengthening is too rapid and risks injury.
What is elasticity?
When you extend/stretch a muscle it stores elastic energy that is recovered when the muscle and tendon is released, and it returns to original length. In computer simulations of human movement, we build passive spring properties into muscles to make them work realistically. The effect of stored elastic energy is far greater from the tendons that the muscle connects to, but nonetheless, there is some effect in the muscle.
What is elasticity?
When you extend/stretch a muscle it stores elastic energy that is recovered when the muscle and tendon is released, and it returns to original length. In computer simulations of human movement, we build passive spring properties into muscles to make them work realistically. The effect of stored elastic energy is far greater from the tendons that the muscle connects to, but nonetheless, there is some effect in the muscle.
What is the key factor in the force a muscle can produce?
The maximum force a muscle can produce during contraction depends on its length, and this can change throughout the movement. At long and short lengths muscles are weak, the optimum length is in the middle.
As the muscle becomes stretched to very long lengths, there becomes elastic passive tension resisting further stretch. This contributes to the overall force produced, which will be the sum of active force and passive force.
During which type of contraction is the greatest force produced?
Eccentric contraction.
What units within the muscle determine the force produced?
Sarcomeres.
What is produced when sarcomeres are arranged in series?
Long fibres and a small cross-sectional area that can achieve high speeds, but relatively little force.
What is produced when sarcomeres are arranged in parallel?
Short fibres and a large cross-sectional area that can produce large forces but are relatively slow.
Why are forces greater when the sarcomeres are arranged in parallel?
When in parallel, the total force is equal to the sum of all individual forces. When in series, the total force cannot be any larger than the maximum force any one sarcomere can tolerate.
What are 3 ways muscle structure can be measured?
- Dissection
- Ultrasound
- MRI
What is a way to precisely measure strength?
Isokinetic dynamometry allows very controlled position and speed.
