Muscles and Movement Flashcards
Skeletal system
Consists of bones or exoskeleton which act as levers and provide a structure for the muscles to pull
Muscular system
Muscles contract and deliver the force needed to move one bone in relation to another
When do muscles exert a force?
When they contract
Antagonistic muscles
Muscles that work in pairs and cause opposite movements. When one contracts, the other relaxes
What do bones provide?
The anchorage and insertion for muscles and act as levers
How are muscles attached to bones?
By tendons at both ends of the muscle
Anchorage
A firm point of attachment that does not move when the muscle contracts
Insertion
Muscle contraction causes the bone or section of exoskeleton forming the insertion to move
How are bones connected to other bones?
Ligaments
Joint
Junctions between bones
Synovial joints
Allow certain movements but not others
What are the three parts of a synovial joint?
Cartilage
Synovial fluid
Joint capsule
Annotate the diagram of the human elbow joint
Biceps
Flexor muscle- used to bend the arm at teh elbow
Triceps
Extensor muscle- used to straighten the arm
Radius
Bone that is the insertion for the biceps and acts as forearm lever for the biceps
Ulna
Bone that is the insertion for the triceps and acts as forearm lever for the triceps
Humerus
Bone that provides a firm anchorage for the biceps and triceps
Tendon
Attaches muscle to bone
Cartilage
Layer of smooth, tough tissue that covers the surface of the bones at the joint. It helps to prevent friction where the bones could rub against each other. It also absorbs shocks
Synovial fluid
Fills the cavity between the cartilage-covered surfaces of the bones. It lubricates the joint and helps to prevent friction
Joint capsule
Tough ligamentous covering to the joint. It seals the joint, holds the synovial fluid and helps to prevent dislocation
Ligaments
Tough tissue connecting the humerus with the ulna and radius. Holds the bones in proper alignment, restrict movement and help to prevent dislocation
Describe antagonistic muscles in an insect leg
Insects leg are divided in three parts: femur, tibia and tarsus. There is a pair of antagonistic muscles inside the femur which causes the tibia to flex and extend. The tendons at the distal ends of these muscles are attached to opposite sides of the exoskeleton of the tibia, so one of them is the flexor of the joint and the other the extensor
What happens when a grasshopper prepares to jump?
The flexor muscle contracts bringing the femur and the tibia closer. This causes the tibia to bend. The extensor muscle then contracts extending the tibia and producing a propelling force.
Describe the composition of skeletal muscle
It caused of muscle fibres which are multinucleated
The plasma membrane is called sarcolemma
Each muscle fibre has many myofibrils. Around each myofibrils there is sarcoplasmic reticulum.
Each myofibrils ahs many repeating units of sarcomeres.
Between the myofibrils are large numbers of mitochondria
Describe the structure of a sarcomere
- Sarcomeres have light and dark bands giving it a striated appearance
- Consists of thin actin filaments and thick myosin filaments
- Through the centre of each light band is a Z-line
- One sarcomere is the part of a myofibril between one Z-line and the next
-The part of the sarcomere containing myosin is the dark band and the part containing only actin filament is the light band.
Draw a repeating unit of sarcomere
Briefly describe muscle contraction
Skeletal muscle contracts when stimulated by a motor neuron. Contraction is achieved by the sliding of actin and myosin filaments over each other. The myosin filaments pull the actin filaments inwards towards the centre of the sarcomere. The sliding of the filaments requires energy from ATP.
Describe the mechanism of muscle contraction
- Myosin filaments have heads which form cross-bridges when bound to binding sites on actin filaments
- ATP binds to the myosin heads causing them to detach from the actin binding sites, thus breaking the cross-bridges
- ATP is hydrolysed to ADP and phosphate, causing the myosin heads to change their angle. The heads are said to be ‘cocked’ as they are storing potential energy from ATP
- The myosin heads attach to adjacent binding sites on actin that are further from the centre of the sarcomere than the previous sites.
- The ADP is released and the heads push the actin filament inwards towards the centre of the sarcomere. This is called the power stroke.
- The Z lines are pulled closer together, shortening the sarcomere
Describe the CONTROL of mechanism contraction
- In the relaxed muscle, the regulatory tropomyosin blocks the binding sites on actin
- Muscle fibres are stimulated to contract by motor neurons. When a nerve impulse arrives at motor end plates, the neurotransmitter acetylcholine is released into the synaptic cleft
- Acetylcholine diffuses across the synaptic cleft and binds to receptors in the membranes of muscle fibres causing their depolarisation which is spread through the muscle fibres via T tubules
- This causes the sarcoplasmic reticulum to release Ca2+
- The calcium ions binds to troponin a protein associated with actin filaments causing the shape of troponin to change
- This in turn causes tropomyosin to move, exposing the binding sites on actin
- This allows myosin heads to form cross-bridges by binding to actin and cause the power stroke, as myosin filaments pull actin towards the centre of the sarcomere.
When the motor neuron stops sending signals, calcium ions are pumped back into the sarcoplasmic reticulum.
How has radioactive calcium been used?
To investigate the control of muscle contraction and it was shown that radioactive calcium is concentrated in the region of overlap.
How do you measure the length of one sarcomere?
Measure the distance in mm from the start of one dark band to the start of a dark bands away.
Divide by ten to find the length of one sarcomere in the micrograph.
Concert the length to micrometre by multiplying by 1000
Divide this length by the magnification of the micrograph
How can you tell a contracted muscle fibre from a micrograph?
The light band decreases, but the dark band stays the same. Z lines are closer and sarcomere is shorter.