Motor mechanisms Flashcards
What are the three main functions of animal skeletons?
Support – maintain the shape or form of the animal’s body Protection – protect soft tissues from damage e.g. skull protects brain Movement – provide resistance for muscles to work/pull against
How does a hydrostatic skeleton provide support and allow movement?
The animal controls its shape and moves using muscles to change the shape of the fluid-filled compartments.
How do insects and molluscs grow inside an exoskeleton?
In molluscs, the exoskeleton is a calcareous shell secreted by the mantle. As the animal grows, the shell is enlarged by adding to outer edge. Some molluscs have a hinged shell which is opened/closed using muscles attached to the inside of the shell.
What is the difference between endoskeletons and exoskeletons? Which animals
have endoskeletons?
Endoskeletons - consist of hard elements buried inside soft tissues. The body of sponges are reinforced with spicules of inorganic material or protein fibres
Exoskeleton - consist of hard material deposited on the outer surface of the animal’s body. Muscles attach to knobs and plates of cuticle that extend into the body cavity to move body parts.
Contrast the properties of a lobster’s exoskeleton on the gripping surface of its
claws and on the hinge joint of the claw
hinged shell which is opened/closed using muscles attached to the inside of the shell
Describe the hierarchy of units making up a skeletal muscle, from myofilaments to
the whole muscle
A sarcomere is the basic contractile unit of muscle (one unit of myofilaments). The striated appearance of skeletal muscle is due to the regular arrangement of the thick and thin filaments into sarcomeres inside the muscle fibre.
How does a sarcomere shorten without the thin or thick filaments changing length?
When the muscle is at rest, the thick and thin filaments don’t overlap completely. The I band is the area at the edge of sarcomere near the Z line which is only thin filament (light band). The A band reflects the length of thick filaments in centre of sarcomere (dark band).
Outline the five steps involved in the myosin-actin interactions underlying muscle
contraction
- The head of the myosin molecule on the thick filament can bind ATP. When ATP is bound,
the head is in its low energy configuration. - The myosin head breaks ATP down into ADP + phosphate. This changes the shape of the myosin head to its high energy configuration.
- This shape change allows formation of a cross bridge with actin on the thin filament.
- When myosin releases ADP and P it reverts back to its low energy configuration. This shape change pulls the thin filament towards the centre of the sarcomere (towards the M line).
- The cross-bridge between myosin and actin is broken when a new molecule of ATP binds to the myosin head.
Outline the seven steps involved in muscle contraction beginning with the AP in the
motor neuron and ending with relaxation of the muscle.
- Acetylcholine from motor neuron triggers an AP in muscle fibre
- AP travels along plasma membrane and down T tubules
- AP triggers release of calcium from sarcoplasmic reticulum
- Calcium ions bind to troponin complex, moving tropomyosin and uncovering the myosin-
binding site on the thin filament - Myosin alternately forms and breaks cross-bridges with actin pulling the thin filament
towards the centre of the sarcomere. ATP powers sliding of the filaments. - Calcium is removed from the cytosol back into SR
- Tropomyosin covers myosin-binding sites on thin filament. Contraction ends and the
muscle fibre relaxes.
Describe two ways the nervous system controls how strongly a muscle contracts
The nervous system produces graded contraction of whole muscles by varying the number of muscle fibres that contract and the rate at which the muscle fibres are stimulated.
What is one major difference between skeletal and cardiac muscle?
Skeletal muscle is under voluntary control and will not produce an action potential unless stimulated by a motor neuron.
Cardiac muscle is striated like skeletal muscle but is found only in the heart. Cardiac muscle has unique electrical and membrane properties allowing it to spontaneously generate action
potentials without input from the nervous system.
Why does smooth muscle not have a striated/striped appearance?
Smooth muscle lacks striations because actin and myosin are not regularly arranged.
