Question | Answer |
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. |