B3.3 Muscles and motility

Question 1

What are the adaptations for movement as a universal feature for living organisms?

Answer 1

i) Movement within the organism (all organisms)
ii) Locomotion (not all organisms)

• motile organisms can do locomotion
• sessile organisms remain in one location

Question 2

Explain the sliding filament theory.

Answer 2

• Muscle fibres contain many parallel myofibrils. Each myofibril consists of a series of sarcomeres linked end-to-end at Z-discs. A sarcomere consists of:

a. Myosin filament (thick)
b. Actin filament (thin)
c. H zone- only myosin filament
d. A band- entire myosin filament
e. I band- actin filament present of either sides of the Z-discs

• For it to contract, the Z-discs need to move closer. When this occurs, the length of the myosin filament doesn’t change, whereas the length of the actin filament does as it overlaps or slides over the myosin filament.

Question 3

What does myosin do, that causes this contraction to happen?

Answer 3

The myosin filaments have myosin heads that attach to the actin filaments. This occurs when ATP is converted to ADP, which activates the myosin head. This forms a cross-bridge (myosin head attaches to the binding sites present on the actin filament). The myosin head flexes towards the center creating that pull or the sliding effect. It eventually detaches with the help of ATP and the cross-bridge breaks. This process is repeated and continued.

Question 4

What is titin and what role does it play in the sarcomere?

Answer 4

• Elastic
• Biggest polypeptide
• Titin connects the Z-line to the myosin filament
• Makes muscle contraction stronger
• Prevents Z-lines from getting too far apart

Question 5

What are antagonistic pairs?

Answer 5

• They are muscles that accomplish opposite movements, since muscles can only pull.
• example: biceps and triceps
• Neuromuscular junction- where the muscle fibre and the motor neuron meet.
• Acetylcholine: A neurotransmitter that is responsible for muscle contraction.
• Motor unit: Motor neuron + all the muscle fibres it connects to.

Question 6

Explain the movement at a synovial joint.

Answer 6

1. Ligament connects bone to bone
2. Tendons connect bone to muscle
3. Cartilage is present between bones to prevent friction which can be very painful.
4. A synovial capsule is present in between the bones.
5. Synovial capsule contains synovial fluid which also prevents friction.

Question 7

Give two examples of ranges of motion of a joint.

Answer 7

1. Hinge joint:
   - Joints that can only flex and extend.
   - Ex: elbows and knees.
   - Limited range of motion.
2. Ball and socket joint:

• Joints are capable of rotation, adduction, abduction, retraction, protraction.
• Circumduction
• Ex: Shoulders and hips.
• Wider range of motion.

Question 8

What is the name of the device used to measure joint angles?

Answer 8

Goniometer.

Question 9

Briefly explain the reasons for locomotion.

Answer 9

1. Foraging for food
2. Escaping from danger
3. Searching for a mate
4. Migration

Question 10

Outline the adaptations for swimming in marine animals.

Answer 10

Mammals evolved on land, need special adaptations for life in water;

1. Streamlined body shape-
   a) Teardrop shape
   b) Smooth, hairless body to reduce friction
2. Airways-
   a) Blowhole
   b) Mouth does not connect to the lungs (prevent water from entering lungs)
3. Locomotion-
   a) Fins, flippers, tails
   b) Blubber to increase buoyancy (ability of an object to float)