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Skeletal Muscle Functions (4) Movement, Posture, Heat production, Joint stability.
Movement Locomotion: walking and running.
Posture Constantly adjusting: sitting and standing.
Heat Production Contraction produces heat, shivering.
Joint Stability Muscle tone keeps joints stable.
Characteristics of Muscles (4) Exitability, Contractibility, Extensibility, Elasticity.
Exitability Ability to receive and respond to stimuli.
Contractibility Ability to shorten forcibly as result of action potential.
Extensibility Ability to stretch.
Elasticity Ability to return to original shape after contraction.
Connective Tissues That Surround Muscle (3) Endomysium, Perimysium, Epimysium.
Endomysium Encloses a single muscle fibre.
Perimysium Surrounds fascicle (Muscle cells bundled together).
Epimysium Covers entire skeletal muscle.
Tendons Mostly collagen fibres, Attach muscle to bone, Often cross joint due to toughness and small size.
Aponeuroses Attach muscles indirectly to bones, cartilages, or connective tissue coverings.
Sarcolemma Specialised plasma membrane.
Myofibrils Long organelles inside muscle cell.
Sarcoplasmic Reticulum Specialised smooth endoplasmic reticulum - stores calcium and releases on demand.
Sarcomeres Chains of contractile units.
I Band Light band. Contains only actin filaments.
A Band Dark band. Contains thick myosin filaments.
H Zone Bare zone that lacks actin filaments.
How Muscles Contract: #1 Nerves activate the release of calcium.
How Muscles Contract: #2 Calcium changes the shape and position of the proteins blocking the binding sites allowing the myosin heads to grip the actin filament.
How Muscles Contract: #3 Myosin heads "cocked" and pull the actin filaments toward the centre of sarcomere. ATP provides the energy needed to release and recock the myosin heads.
How Muscles Contract: #4 The result is that the muscle is shortened (contracted).
How Muscles Contract: #5 Once all the extra calcium is absorbed, the proteins that were moved for the contraction return to their original spot and the muscle releases.
Rules of Contraction: #1 Muscle fibre contraction is "all or nothing".
Rules of Contraction: #2 Within a skeletal muscle, not all fibres may be stimulated during the same interval.
Rules of Contraction: #3 Different combinations of muscle fibre contractions may give differing responses.
Twitch Single, brief contraction.
Tetanus One contraction immediately followed by another. The muscle does not completely return to a resting state.
Muscle Fatigue When a muscle is fatigued, it is unable to contract even with a stimulus.
Oxygen Deficit Common cause for muscle fatigue is oxygen debt. Oxygen must be "repaid" to tissue to remove oxygen deficit. Oxygen is required to get rid of accumulated lactic acid.
Muscle Tone State of continuous partial contractions.
Isotonic Contractions The muscle shortens and movement occurs.
Isometric Contractions Tension in the muscles increases - no movement.
Flaccid Soft or flabby muscle; old age.
Atrophy Loses muscle tone and wastes away; cast.
Origin Attached to the immovable or less movable.
Insertion Attached to the movable.
Prime Movers Major muscle responsible for movement.
Antagonists Muscles that oppose each other (bicep/tricep).
Synergists Help the prime mover.
Fixators Stabilise origin so all tension can be used to move the insertion bone - postural muscles.
Golden Rules: #1 All skeletal muscles cross at least one joint.
Golden Rules: #2 The bulk of skeletal muscles lies proximal to the joint crossed. (Bulk of muscles is near the joint)
Golden Rules: #3 All skeletal muscles have at least two attachments, the origin and insertion.
Golden Rules: #4 Skeletal muscles can only pull, never push.
Golden Rules: #5 During contraction, a skeletal muscle insertion moves towards the origin.
Created by: UtauxIkuto