Muscle Structure and Function Flashcards
How much skeletal muscle is present in normal young people?
- About 40% male bodyweight
- About 30% female bodyweight
What is the principle function of skeletal muscle and how does it do this?
- Principle function is contraction/ shortening distance between bones.
- Skeletal muscle moves bones attached to it by tendons.
- Muscle groups work together
- When a muscle contracts, its insertion is pulled towards its origin.
Where does more force come from in skeletal movement?
- More complete activation of one muscle
- More activation of agonist muscle
- More inactivation of antagonist muscles.
What are the levels of skeletal muscle structure from most superficial to deep?
- Whole muscle
- Fasicles
- Muscle fibre (cell)
- Myofibrils
- Sarcomeres
What are fasicles?
-Bundles of cells surrounded by connective tissue
What provides strength of muscle fibres?
-Strength of muscle fibres comes from bundling.
What are the histological layers of skeletal muscle?
- Thick epimyseium
- Perimyseium
- Endomyseium
What is a motor unit?
- A single motor neurone and all the muscle fibres it innervates.
- The functional units of motor control
- Final common pathway for info leaving the CNS.
How many motor units does a muscle contain and how many muscle fibres would a motor unit contain?
- A muscle may contain 100’s of motor units and each motor unit may contain 100’s of muscle fibres.
- These ammounts will relate to the function of the muscle in question and the size of the muscle.
What factors would impact no. of fibres, motor units and muscle fibres in a motor unit?
- No. of fibres = size of muscle
- No. of motor units = size and funtion
- No. of muscle fibres in a motor unit = function
What are some things to be careful about when talking about motor units?
- Muscle characteristics are different species by species.
- In any one species, different muscles have different properties.
- In any one muscle in any one species, the motor units have very different properties.
What are some classification properties of motor units?
-Mechanical: twitch responses; speed, force, rate of fatigue.
-Histological: metabolic profile; oxidative, glycolytic; aerobic or anaerobic, myosin ATPase activity
-Motor neurone properties: cell body size, axon diameter, synaptic inputs, axon branching
-Other: Colour; red/white
Use; phasic (tends to be pale, more glycolytic, faster contracting and fatiguing)/tonic (tends to be red, oxidative, slow contracting.
What is the most simple and common motor unit classification?
-By speed of contraction and fatigue rate
What are the 3 main types of motor units?
- Slow (S or type 1) (smaller twitch, slower fatigue)
- Fast fatigue resistant (FFR, 2a)
- Fast fatiguing (FF, 2b, 2x etc.) (larger twitch, faster fatigue)
What determines the properties of motor units?
- Genetics
- Probably pattern of use
- Probably not training
