Topic 11.2 - Movement Flashcards
Endoskeleton and exoskeleton
Exoskeletons - over muscle, protect body surface (usually crustaceans and insects)
Endoskeletons - protect organs, produce blood cells, facilitate movement, and support structure.
Both skeletons facilitate movement by providing anchorage for muscles and acting as levers
Bones - muscle - exoskeleton
Levers and forces
Levers have an effort force, a pivot point (fulcrum), and a load.
Class of lever depends on location of effort, fulcrum and load.
1: Effort - fulcrum - load (head movement)
2: Effort - load - fulcrum (Standing on the ball of the foot)
3: Fulcrum - effort - load (bicep curls, grasshopper legs)
Antagonistic muscle
Skeletal muscles work in pairs that are antagonistic.
Movement of the body requires antagonistic pairs.
Antagonistic - when one muscle contracts, the other relaxes.
Insect (grasshopper) leg
Femur - tibia - tarsus (at the bottom)
When extensor muscles on the femur relax, the flexor muscles contract, bringing the femur and tibia closer together. (flexing)
When the extensor muscles then contract and flexor muscles relax, the tibia is extended and a powerful propelling force is generated.
Synovial joints
scapula - glenohumeral joint - humerus - humero-raidial and humero-ulna joint - radius and ulna
Humerus and radius are connected to bicep
Humerus and Ulna are connected to the tricep
Points where bones meet are joints. Most articulated joints (joints that allow bones to move in relation to each other) have a similar structure of cartilage, synovial fluid, and joint capsule.
Cartilage -> tough, smooth tissue that covers the bones. These prevent contact where bones might rub together and help prevent friction. Cartilage also helps to absorb shocks that might cause bones to fracture.
Synovial fluid -> fills a cavity between cartilages, lubricates the joints, and helps reduce friction that would occur with dry cartilage.
Joint-capsule -> tough ligamentous covering to the joint. Seals the joint and holds synovial fluid and prevents dislocation.
Joints and movements
The structure of a joint (including joint capsule and ligaments) determine movements that are possible.
Hinge joint - knee joint - only two movements: flexion (bending) and extension (straightening)
Knee joint = tibia (at the front)/ fibula (behind) - Patella (kneecap) - Femur (thigh bone)
Knee has a greater range of movement when it is flexed.
Ball and socket joint - hip joint - can do a various range of movements: flex, extend, rotate, move sideways (abduction), and back (adduction).
Striated muscle fibres
Movement (skeletal) muscles contain stripes so they are also called striated muscles.
Striated muscle is composed of muscle fibres. Muscle fibres are longer than typical cells and this is because embryonic muscle cells fuse to form muscle fibres.
Striated muscle fibre structure
sarcolemma - (single plasma membrane) surrounds each muscle fibre
Sarcoplasmic reticulum - (modified version of the endoplasmic reticulum) extends throughout the muscle fibre, wrapped around every myofibril, conveying the signal to contract to all parts of the muscle fibre by releasing the calcium ions involved in contraction.
Myofibril - involved in contraction.
Myofibril structure
between myofibril are large numbers of mitochondria which provide the ATP (adenosine triphosphate) for contractions
Myofibril are inside each muscle fibres, they are parallel elongated structures.
Myofibril contain light and dark bands, giving striated muscle its stripes. In the centre of each light band, there is a disc-shaped structure, referred to as the z line.
The space between z lines is referred to as a sarcomere.
The band colours in sarcomeres is due to precise and regular arrangements of two types of protein filaments: Thin actin filaments and thick myosin filaments.
Actin filaments -> thin and cause light bands
Myosin filament -> thick, causes dark bands, and has myosin heads that can attach to the actin (in the actin gaps there are no heads)
Contraction of skeletal muscle (process)
Occurs by sliding of actin and myosin filaments. The heads on myosin filaments can bind to special sites on actin filaments and create cross bridges.
Contraction of skeletal muscle (results)
actin filaments pulled and shortened. Light band shortens and dark bands remain the same.
Cross bridges
Cross bridges can exert a force using energy from ATP and the myosin heads are regularly spaced along the myosin filaments so many cross-bridges can form at once.
Contraction of skeletal muscle (Control)
Calcium ions and the proteins tropomyosin and troponin control contraction.
In a relaxed muscle, a regulatory protein called tropomyosin blocks the actin binding sites.
When a motor neuron sends a signal to a muscle fibre to contract, the sarcoplasmic reticulum releases calcium ions. These ions bind to troponin which cause tropomyosin to move, exposing actin binding sites.
Myosin heads can then bind and swivel towards the centre of the sarcomere, moving the actin filament a small distance.
ATP in sliding filaments
For significant contraction, myosin heads must repeat a process a significant amount:
1 - ATP causes the breaking of cross bridges by attaching to myosin heads, detaching them from actin binding sites.
2 - Hydrolysis of ATP to ADP and phosphate provides energy for the myosin heads to swivel outwards away from the centre of the sarcomere - it is now ‘cocked’ as it has the energy stored from the ATP.
3 - New cross-bridges formed by myosin heads binding to actin. These bind to the site adjacent to the one previously occupied (one position further from the sarcomere centre)
4 - Energy stored in myosin heads from when they were cocked causes swivelling towards the sarcomere center, moving the actin filament a small distance (ungefähr 10nm). This is called the power stroke.
These stages are continued until the motor neurone stops sending signals to contract. Calcium ions are then pumped back into the sarcoplasmic reticulum, so tropomyosin moves and covers the bonding site, relaxing the muscle.
Studying contraction
By attaching fluorescent dye to myosin molecules, it can be shown that myosin will “walk along” actin filaments after being supplied with ATP and having stimulated contraction.
^^?^^
This demonstrates the ATP-dependence of myosin-actin interaction.
