DP Biology 11.2 Movement
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11.2.1 State the roles of bones, ligaments, muscles, tendons and nerves in human movement.
Skeletons support for the body of the organism whilst also facilitating movement
Endoskeletons are inside the body with muscles attached on the outsides of bones
Exoskeletons are outside the body with muscles attached on the inside. (Ex: insects)
Ligaments: tough and elastic tissues that hold the bones together. (Bone to Bone around a joint)
Muscles are effectors, pulling on bones to move them.
Tendons: strong connective tissue connecting muscles to bones.
Antagonistic Pairs: Muscles work in pairs, one Contracting and pulling, the other relaxing.
The Agonist, contracts (think, In Agony doing work!)
The Antagonist, relaxes (Anti-agony, not doing work).
Muscles are stimulated by nerve impulses from motor neurons (specialised cells adapted to rapidly carry electrical charges called nerve impulses from sensory neurons to the muscles)
Synovial joints are the most common type of joint in the human body
Joint cavity filled with a lubricating synovial fluid which reduces friction
The fluid is produced by the synovial membrane, which surrounds the joint
Synovial joints are capable of a variety of movements which depends on joint type and ligaments
The movements possible at the joint are
Flexion - movement brings two bones together (think humerus & radius when "flexing"
Extension - moves two bones apart (extending the arm)
Abduction (the movement of a limb away from the body)
Adduction (the movement of a limb towards the body)
Rotation - Spinning or moving around in three planes.
11.2.2 Label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones and antagonistic muscles (biceps and triceps).
11.2.3 Outline the functions of the structures in the human elbow joint named in 11.2.2.
Cartilage: reduces friction between bones where they meet
Synovial fluid: lubricates joint to reduce friction, made by synovial membrane.
Joint capsule: seals the joint and holds in the synovial fluid
Humerus: upper arm bone: attachment of biceps and triceps
Ulna & radius: forearm bones: attachment of biceps and triceps
Biceps: attaches from humerus to ulna & radius
Triceps: attaches from humerus to ulna
Antagonistic Pairs: biceps and triceps attach across elbow joint; while triceps contracts to to extend arm, biceps relaxes; conversely, while triceps relax and the biceps contract, flexing the arm
The one Contracting is in Agony, (agonist). The one Relaxing is NOT in agony (antAgonist)
11.2.4 Compare the movements of the hip joint and the knee joint.
Knee: hinge joint
allows considerable movement in one plane
constrains movement from other two planes
flexion bends the leg
extension straightens the leg
Hip: ball and socket joint
allows movement in three planes
protraction /retraction: forward and backwards
abduction/adduction: sideways in and out
rotation: circular movement
11.2.5 Describe the structure of striated muscle fibres, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma.
Skeletal fibers are multinucleated and very long
Embryonic muscle cells fused together
Each striated muscle fiber is a bundle of myofibrils
Nuclei and mitochondria are between myofibrils
Sarcolemma: fiber membrane
Contain specialized endoplasmic reticulum, "Sarcoplasmic reticulum" stretched throughout the fiber, to release Ca2+ ions
Myofibrils contain contractile Units:
Alternating light and dark bands.
I Band: light band is a disc-shaped structure called "z-line"
(Edge of Sarcomere)
A Band: Dark band containing Sarcomere fibers
11.2.6 Draw and label a diagram to show the structure of a sarcomere, including Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands.
No other terms for parts of the sarcomere are expected.
11.2.7 Explain how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of actin and myosin filaments, and the use of ATP to break cross-bridges and re-set myosin heads.
Details of the roles of troponin and tropomyosin are not expected.
Sliding Filament Model in Just 6 Steps!
Ca2+ ions are released by sarcoplasmic reticulum.
Ca2+ ions cause cross-bridges to form between actin and myosin heads.
Energy (ADP+P) in the head of the myosin moves the head,
The movement slides actin past the myosin – which shortens the muscle.
ATP is used to disconnect myosin head from actin
ATP is hydrolyzed into ADP+P, resetting the myosin head in a high energy position
11.2.8 Analyse electron micrographs to find the state of contraction of muscle fibres.
Muscle fibres can be fully relaxed, slightly contracted, moderately contracted and fully contracted.
Guidance: Look for the light bands! If light and dark are equal: relaxed. If more dark than light, contracted!
Levers of the Body
Muscles are anchored to the skeleton around joints, and the presence of pivot points means that skeletons act as levers transferring the magnitude and direction of force. Levers have a point of effort, a point of load and a pivot point called the fulcrum.
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