Essential questions: how is movement in the body produced at a cellular level? What are the roles of each tissue in enabling movement?
Lesson One Joints and movement
Lesson objective: Understand how synovial joints are designed to produce certain movements. Understand the role of bones, muscles, tendons, ligaments and synovial fluid.
- Ligament – a tissue that holds skeletal bones together in synovial joints
- Synovial joints- comprise most of the joints in the human skeleton. Include synovial fluid and connective tissues
- Cartilage – a connective tissue which reduces friction and absorbs physical shocks, found on the inner surfaces of bones in a synovial joint.
- Tendons – connect muscles to bones, allowing muscles to produce movement by contraction
- Synovial fluid – a viscous fluid which reduces friction and increases freedom of movement in synovial joints.
- Antagonistic muscles – muscles that work in opposition to each other for example bicep and tricep.
- Joint capsule – is a tough ligamentous covering to the joint. It holds everything together including the synovial fluid
Synovial joints allow a specific range of movements. There are different kinds of synovial joints, for example ball-and-socket joints, such as the shoulder; and hinge joints, such as the elbow. Movement is produced by the action of contracting muscles, which are attached to joints by tendons.
Bones anchor muscles and act as levers for muscles. Levers amplify an input force to produce a greater output force.
Discussion: Which is the best and worst tissue to damage in a sporting accident – justify your response. Arthritis means pain in the joints (permanent pain).
The elbow joint – a synovial joint.
ActivityA : Watch the tutorial and summarise the function of each part of the elbow joint in a table.
the level of detail is for medical students, and so you will have to extract only what is needed for this task.
Activity B: Study of an insect leg
How does the leg of a grasshopper compare with an elbow joint? Page 478 in the book.
- Does the grasshopper leg show antagonistic muscle action?
- What do we mean by antagonistic muscle action?
- What are the requirements for antagonistic muscle action?
- What happens to the both muscles (flexor and extensor) when the leg extends?
- What happens to the both muscles (flexor and extensor) when the leg contracts?
Lesson two: Structure of Muscles
Lesson objectives: Learn the different tissues that make up muscles. Understand how muscles contract at the cellular level.
- Sarcomere: the functional unit of muscle. Not called a cell because it is hard to divide striated muscle into cells.
- A muscle fibre: a bundle of muscle strands called myofibrils
- Myofibrils: an elongated structure with many nuclei and alternate light and dark bands.
- Myosin and Actin: protein fibres which slide past each other in order to produce a contraction
- Sarcolemma is a single plasma membrane that surrounds each muscle fibre.
Macrosctructure of Skeletal muscle (the big picture)
There are different kinds of muscle. Striated muscle is formed from highly organised bundles of contractile myofibrils. Striated muscle includes skeletal muscle and cardiac muscle. Non-striated muscle includes smooth muscle such as that is found in the lining of the intesines. Skeletal muscle will be considered in this lesson.
Skeletal muscle is formed from bundles of myofibrils, which are organised into muscle fibres. Muscle fibres have a membrane surrounding them called a sarcolemma.
Striated muscle is not clearly divided into cells. Myofibrils are multinucleate and are made from compartments called sarcomeres (which are not considered cells as they are not clearly divided by cell membranes).
Sacrcomeres have the ability to contract, because they contain specialised rods of protein that can slide past each other. These rods of protein are called actin and myosin.
- The Z-lines represent the boundaries between sarcomeres, and are connected to the sarcolemma (this aids in stimulation of the muscle).
- The dark bands (A bands) represent the thicker protein mysosin (actin is also present, but it is the thicker myosin that causes the darker colour)
- The light bands (I bands) represent the thinner protein actin.
The rods of protein slide past each other in a process powered by ATP. It is the contraction of all of the component sarcomeres, which causes the bulk structure of a muscle to contract.
Deduction exercise – Muscle contraction (work through in pairs)
1) What happens to the A bands and the I bands during both contraction and relaxation (you may want to draw a table).
2) What is the meaning of the H zone?
3) Which of the following statements are true:
- A Sarcomere contraction happens because the z lines pull together
- B Sarcomere contraction happens because the actin pulls against the myosin with cross bridges
- C Sarcomere contraction happens because the myosin has cross bridges which pull against the actin
- D Sacromere contraction happens because the sarcomere is expanding and contracting as the muscles pull it.
Why did you choose that answer?
4) What is the specific role that ATP (an energy source) plays in the mechanism of muscle contraction?
5) Choose a metaphor for the mechanism for muscle contraction, and explain your choice:
- A the mechanism for muscle contraction is like a catapault
- B. the mechanism for muscle contraction is like a rowing boat
- C. the mechanism for muscle contraction is like ‘angry birds’
- D. Other of your choice
Discussion: Using bioluminescence to study muscle contraction
Bioluminescence: the production of light by a living organism.
A jellyfish (cnidarian) called Aequorea produces a protein called Aequorin which bioluminesces when exposed to calcium. Remembering that calcium triggers muscle contractions, by injecting the muscles of the other organisms with this protein, the release of calcium can be observed because the tissue bioluminesces.
Discussion: Experiments that could be used to take advantage of this bioluminescent protein aequorin