10 - Skeletal Muscle Physiology Flashcards
What are the three types of muscles? Which type is voluntary?
Muscle comprises largest group of tissues in body
– Cardiac muscle – found only in the heart
– Smooth muscle – appears throughout the body systems as components of hollow organs and tubes
– Skeletal muscle – makes up muscular system
What are skeletal muscles made of and how are they organized?
Made of groups of muscle fibres bundled together and attached to bones.
Connective tissue covering muscle divides muscle internally into bundles.
(Connective tissue extends beyond ends of muscle to form tendons - tendons attach muscle to bone)
What is a single skeletal muscle cell known as
A muscle fibre
– Multinucleated
– Large, elongated, and cylindrically shaped
– Fibres usually extend entire length of muscle
Actin (thin) and Myosin (thick) are interleaved and this shape allows for shortening
Describe the relaxed and excited muscle states?
How actin, troponin & myosin explain how the muscle shortens
- Ca2+ is released and binds with troponin that exposes the cross-bridge binding site
- Actin binds to Myosin cross-bridge and triggers power stroke that pulls thin filament inward during contraction
Describe what regions change in muscle excitement.
Sacromere, H-zone and I band shorten
A band is same width
Why is Calcium Concentration important?
The presence of Ca2+ in the myofibrils is crucial to forming cross-bridges between actin and myosin and generating muscle contractions.
What mechanism brings about muscle contraction?
Sliding filament mechanism
- Increase in Ca2+ starts filament sliding
- Decrease in Ca2+ turns off sliding process
- Thin filaments on each side of sarcomere slide inward over stationary thick filaments during contraction (Sarcomere shortens)
What is a motor unit? What is the point of motor unit recruitment?
Motor unit: One motor neuron and the muscle fibres it innervates
of muscle fibres varies among different motor units
- muscles for precise, delicate movements contain fewer fibres per motor unit
- muscles for powerful, coarsely controlled movement have a greater # of fibres per motor unit
Asynchronous recruitment of motor units helps delay or prevent fatigue.
What is fatigue? How does asynchronous recruitment of motor units work?
Fatigue: inability to maintain muscle tension at a given level during sustained contraction
Some muscle motor units rest while others are in use and they switch up
When is it impossible to to use motor unit recruitment?
- During maximal muscle contraction, all muscle fibres must participate, to motor units cannot be alternated
- Only possible during submaximal contractions
What are twitch muscle contractions?
Twitch
- Brief, weak contraction
- Produced from single action potential
- Too short and too weak to be useful
- Normally does not take place in body
What is twitch summation?
Happens when muscle fibre is re-stimulated before it has relaxed, so second twitch is added to first.
Results from sustained elevation of calcium in the intracellular environment.
What is tetanus?
It is a maximal sustained contraction
– Occurs if muscle fiber is stimulated so rapidly that it does not have a chance to relax between stimuli.
– Contraction is usually three to four times stronger than a single twitch.
– 2 types: unfused and fused.
What is unfused tetanus?
Type of tetanus where the stimulation rate of the muscle fibre is not at a maximum value and the fibre relaxes slightly between the stimuli
What is fused tetanus?
Type of tetanus where the stimulation rate is so fast that the muscle fiber does not have time to relax between stimulations.
Maximum tension in the muscle fiber is achieved with no period of relaxation.
The maximum number of cross-bridge binding sites remain uncovered so that cross-bride cycling and tension develop