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Whole Muscle Force Generation
The total force/strength of a muscle is determined by two components:
1. Active component: action potential on membrane of muscle fiber initiates a series of biochemical changes; causes binding of the heads of myosin filaments to the actin filaments
2. Elastic component: energy storage. Important for muscles engaged in repetitive actions.
Rectus abdominis
A group of hypaxial muscle
- Extend longitudinally on either side of linea alba
Arch muscles (not hyoid or mandibular)
- In fish the remaining branchial arches function in raising and lowering pharyngeal region and manipulating gills
- Cucullaris: formed by a fusion of several levators arising from adjacent arches
- Trapezius and mastoid: in tetrapods extends from axial musculature to scapula
- In tetrapods the remaining musculature has reduced, associated with larynx, pharynx
Where do cranial muscles arise from?
Hypobranchial muscles (throat, tongue): trunk somites
Branchiomeric muscles: head somites
Eye muscles: head somites
Define tendons.
What are their main functions?
Tendons are collagenous bundles continuous with those found in muscle sheath (epimysium) and periosteum.
- Allow muscles to be located in one area while acting on bones located some distance away
- Can also store energy
Load
External force that opposes the force of the muscle
Myofibrils
Rod-like unit of a muscle cell/fiber
Thin filaments: actin
Thick filaments: myosin
a. Compare red vs. white skeletal muscle
b. How does skeletal muscle differ in birds vs. fish
a. Red skeletal muscle:
- Lots of myoglobin
- Resistant for fatigue
- Good for long distances
White skeletal muscle:
- Less myoglobin
- Contracts rapidly
- Good for short bursts of activity
b. Birds:
- White flight muscles used for short bursts of flight
- Red muscle located in legs for prolonged use
Fish:
- Most: red muscle forms thin wedge just under skin
- Tuna & lamnid sharks: red muscle central in body
Explain the 'sliding filament mechanism' of muscle contraction
- Myosin binds actin
- Uses ATP
It is the process of muscle contraction involving the sliding of actin & myosin myofilaments past each other to shorten the length of each sacromere. When sacromere shortens, whole fiber shortens.
Why is muscle shape important?
It affects:
- Length the muscle can contract
- Velocity of contraction
- Force of contraction
Compare isotonic vs. isometric muscle contraction
- Isotonic muscle contraction muscle shortens (load < force of muscle)
- Isometric muscle contraction produces muscle tension without a change in limb movement; muscle does not shorten (load > force of muscle)
What are the main functions of muscles?
- Movement
- Restrain motion
- Sphincters
- Heat production
- Electrical signalling
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