University:
Felician University
Course:
BIO-102 | Human Biology
Academic year:

2022
Views:

326

Pages:

1
Author:

SpaceCadet101

mOvEmEnT Movement Systems Human Elbow Joint Skeletons are a rigid framework (internal or external) that provide a surface for muscle attachment (i.e. act as levers) • Bones are connected to other bones by ligaments • Bones are connected to muscles by tendons The human elbow joint is an example of a hinge joint • It is capable of angular movement (flexion / extension) Synovial joints are capsules surrounding articulating bone surfaces that allow for certain movements but not others Muscles provide the force required for movement of bones • Muscles work in antagonistic pairs (one contracts, one relaxes) • E.g. Flexor and extensor muscles in insect hind leg Motor neurons provide the stimulus for muscle movement and coordinate sets of antagonistic muscles Bicep Humerus Tricep Joint Capsule Radius Cartilage Ulna Muscle Fibres Muscle Contraction Skeletal muscles consist of bundles of fibres (formed from fused muscle cells) that have several specialised features: Calcium Ion Release • Motor neurons release acetylcholine (neurotransmitter) • This triggers sarcolemma depolarisation, causing calcium ions to be released from the sarcoplasmic reticulum • • • • • They are multinucleated (multiple nuclei per fibre) There is a large number of mitochondria (for ATP) Are surrounded by a continuous membrane (sarcolemma) Have a specialised ER network (sarcoplasmic reticulum) Contain many striated myofibrils (for contraction) Sarcomeres Myofibrils are made up of repeating contractile sarcomeres • Sarcomeres contain two myofilaments (actin + myosin) Myosin (thick) has protruding heads that bind to actin (thin) • Overlapping of filaments creates a dark central A band • Sarcomere peripheries form light I bands (actin only) actin (thin) myosin (thick) z disc Cross-Bridge Formation • Calcium ions bind to a complex (troponin/tropomyosin) that blocks actin from binding with the myosin heads • Calcium ions displace this complex, allowing the actin and myosin heads to form a cross-bridge Sliding Mechanism • ATP binds to myosin heads and breaks the cross-bridge • ATP hydrolysis causes myosin heads to swivel and slide along the actin fibre – this shortens the sarcomere length • Via repeated ATP hydrolysis, skeletal muscles contract Muscle Contraction Fully Relaxed: Wide I bands (blue) and wide H zone (red) Fully Contracted: Narrow I bands (blue) and H zone (red) I band A band I band