Topic 11.2: Muscles and Movement

Principles of locomotion:

•Most Animals are able to move from one place to another in what is generally known as locomotion.

•To change position animals have a variety of strategies including swimming (fish), walking (Arthropods) and flying (birds).

•The force for movement is created by muscle contraction when the muscle cell shortens its length

•Animals require a 'skeleton' to provide leverage for movement. Some examples of skeletons include.

Producing movement

•The force for movement (effort) is generated by the contraction of muscle cells.

•This shortening forces is applied to the skeleton that provides the leverage to either magnify the movement or the force.

•To achieve this effect muscles work in antagonistic pairs.

•As one muscle contracts providing the pulling power the other relaxes and is compliant.

•When the limb bends this is called flexion and when the limb is straightened is known as extension

Muscles:

Producing movement

•Bones are the levers of the skeletal system

•Magnify movement or the force of muscle contraction

•Also provide support and protection for other organs and tissues

Bones:

Producing movement

•Muscles attach to bones by tendons (non elastic) at the point of origin and then again to another bone at the insertion point.

•Between the origin and insertion points there are joints.

•The joints are the fulcrum (pivot) of the skeletal lever system.

•Some joints provide a wide range of movement for locomotion e.g. human arm. Others are more restricted and provide stability for the skeletal system e.g. Spine/ trapezius

Joints

Structure of the Human Elbow JointA Humerus (upper arm) bone

B Synovial membrane that encloses the joint capsule and produces synovial fluid

C Synovial fluid (reduces friction and absorbs pressure)

D Ulna (radius) the levers in the flexion and extension of the arm

E. Cartilage (red) living tissue that reduces the friction at joints

F. Ligaments that connect bone to bone and produce stability at the joint

Antagonistic Pairs: • To produce movement at a joint

muscles work in pairs.• Muscles can only actively contract

and shorten. They cannot actively lengthen.

• One muscles bends the limb at the joint (flexor) which in the elbow is the biceps.

• One muscles straightens the limb at the joint (extensor) which in the elbow is the triceps.

Functions of the parts of the elbow

1.Humerus forms the shoulder joint also the origin for each of the two biceps tendons

2. Biceps (flexor) muscle provides force for an arm flexion (bending). As the main muscle it is known as the agonist.

3. Biceps insertion on the radius of the forearm

4. Elbow joint which is the fulcrum or pivot for arm movement

5. Ulna one of two levers of the Forearm Technically in a flexion like this the Biceps performs a concentric contraction

6. Triceps muscle is the extensor whose contraction straightens the arm.

7. Elbow join which also the fulcrum for this movement.

Movement at the hip and knee joint

Knee Joint: • The knee joint is an

example of a hinge joint.

• A knee extension is powered by the quadriceps muscles.

• A knee flexion is powered by the hamstring muscles.

• Movement is one plane only.

The Knee Joint

The Hip Joint • Greatest range

of motion• Rotation is in all

planes and axis of movement.

• The effort is provided by the muscles of quadriceps, hamstring and gluteus.

Example of a ball and socket

• The shoulder is a ball and socket joint.

• The humerus is the lever.

• The shoulder (scapula and clavicle) form the pivot joint.

• Force is provided by the deltoids, trapezius and pectorals.

• Movement is in all planes.

Pick up a heavy object in concentric Biceps flexion. Now lower and straighten your arm. You should feel your Biceps contracted but Triceps relaxed. That an eccentric contraction of the Biceps This just shows how complex movement can be!

Structure of Skeletal Muscle

1. Tendon connecting muscle to bone. These are non-elastic structures which transmit the contractile force to the bond.

2. The muscle is surrounded by a membrane which forms the tendons at its ends.

Structure of Skeletal Muscle

3. Muscle bundle which contains a number of muscle cells

4. (Fibres) bound together. These are the strands we see in cooked meat

Structure of Skeletal MuscleMuscle fiber cell shown here is

multinucleated•There are many parallel protein structures inside called myofibrils.•Myofibrils are combinations of two filaments of protein called actin and myosin.

The filaments of actin and myosin overlap to give a distinct banding pattern when seen with an electron microscope.

This model show the arrangement of the actin and myosin filaments in a myofibril

Note how the thick myosin filaments overlap with the thinner actin filaments.Myofibril cross section:

a) Actin onlyb) Myosin onlyc) Myosin attachment

region adds stabilityd) Actin and myosin

overlap in cross sections

Electron Microscope images

Electron Microscope images

Note:•large number of mitochondria•Diagonal myofibrils•Sarcoplasmic reticulum

Sliding Filament theory (theory muscle contraction)

1. An action potential arrives at the end of a motor neuron, at the neuromuscular junction.

2. This causes the release of the neurotransmitter acetylcholine.

3 This initiates an action potential in the muscle cell membrane.

4. This action potential is carried quickly throughout the large muscle cell by invaginations in the cell membrane called T-tubules.

5. The action potential causes the sarcoplasmic reticulum (large membrane vesicles) to release its store of calcium into the myofibrils.

Sliding Filament theory (theory muscle contraction)

6. Myosin filaments have cross bridge lateral extensions

7. Cross bridges include an ATPase which can oxidize ATP and release energy

8.The cross bridges can link across to the parallel actin filaments

Sliding Filament theory (theory muscle contraction)

9. Actin polymer is associated with tropomyosin that occupies the binding sites to which myosin binds in a contraction

10. When relaxed the tropomyosin sits on the outside of the actin blocking the binding sites.

11. Myosin cannot cross bridges with actin until the tropomyosin moves into the groove.

Sliding Filament theory (theory muscle contraction)

12. The calcium binds to troponin on the thin filament, which changes shape, moving tropomyosin into the groove in the process.

13. Myosin cross bridges can now attach and the cross bridge cycle can take place.

Cross Bridge CycleIf electron micrographs of a relaxed and contracted myofibril are compared it can be seen that:

•These show that each sarcomere gets shorter when the muscle contracts, so the whole muscle gets shorter.•But the dark band, which represents the thick filament, does not change in length.

•This shows that the filaments don’t contract themselves, but instead they slide past each other.

Sliding Filament theory

The energy for the cycle is produced by the ATPasesection of the crossbridge structure. This energytemporarily changes the shape of the crossbridge which isnow attached to the actin polymer. The two slide relativeto each other giving an overall shortening

Sliding Filament theory

1. The cross bridge swings out from the thick filament and attaches to the thin filament.

2. The cross bridge changes shape and rotates through 45°, causing the filaments to slide. The energy from ATP splitting is used for this “power stroke” step, and the products (ADP + Pi) are released.

3. A new ATP molecule binds to myosin and the cross bridge detaches from the thin filament.

4. The cross bridge changes back to its original shape, while detached (so as not to push the filaments back again). It is now ready to start a new cycle, but further along the thin filament.

This model is for one myosin molecule cross bridging to one actin. Looking at some of the diagrams above we can see that there must

be many cross bridges formed but not quite together.