B3.3 Muscle and motility

Question 1

What is the difference between mobility and motility in organisms?

Answer 1

Mobility refers to an organism’s ability to locomote and move from one location to another, while motility refers to any independent movement using metabolic energy, such as peristalsis in the digestive tract.

Question 2

What is sessility in organisms?

Answer 2

Sessility is the trait by which an organism is fixed in its location and unable to move, such as plants that are sessile but can still exhibit motility through tropisms.

Question 3

Are all organisms motile and mobile?

Answer 3

All organisms are motile, meaning they can independently move using energy, but not all organisms are mobile, meaning they can move from one location to another.

Question 4

Why do organisms locomote? Provide three examples for each reason.

Answer 4

1. Foraging for food: Bees fly to search for nectar.
2. Escaping danger: Prey, like rabbits, move to avoid predators.
3. Searching for a mate: Animals travel to find mates to avoid inbreeding.
4. Migration: Birds migrate during colder seasons.

Question 5

What is streamlining, and how does it help marine mammals swim?

Answer 5

Streamlining refers to the shape of marine animals, which minimizes water resistance by reducing drag and friction through smooth, hairless skin and a tapering body toward the rear.

Question 6

How are the limbs of marine mammals adapted for swimming?

Answer 6

he limbs of marine mammals are adapted to form flippers for steering, and their fluked tails, which move up and down, provide increased thrust for swimming.

Question 7

How have the airways of marine mammals adapted to allow for periodic breathing between dives?

Answer 7

Marine mammals have a blowhole for breathing that is not connected to the mouth, allowing them to close their airways during dives and breathe periodically when they surface.

Question 8

What are the main components of a motor unit in skeletal muscle?

Answer 8

A motor unit consists of a motor neuron, muscle fibers, and neuromuscular junctions that connect them.

Question 9

What are muscle fibers composed of?

Answer 9

Muscle fibers are made of myofibrils.

Question 10

What is a neuromuscular junction, and what role does it play in muscle contraction?

Answer 10

A neuromuscular junction is a synapse connecting the axon terminal of a motor neuron and the sarcolemma of a muscle fiber, using acetylcholine (ACh) as the neurotransmitter to pass the electrical signal to the muscle, causing contraction.

Question 11

What initiates muscle contraction at the cellular level?

Answer 11

The transmission of the action potential to the muscle causes Ca²⁺ ions to be released from the sarcoplasmic reticulum, initiating muscle contraction.

Question 12

What is a sarcomere, and why is it important?

Answer 12

A sarcomere is the functional unit of muscles, and it is essential for muscle contraction.

Question 13

Describe the process of muscle contraction according to the sliding filament model.

Answer 13

Muscle contraction involves the sliding of actin and myosin filaments within the sarcomere, leading to the shortening of muscle fibers through a series of steps, including:

1. Ca²⁺ ions bind to troponin, changing tropomyosin’s conformation to expose myosin binding sites on actin.
2. ATP hydrolysis occurs, powering up the myosin head into a “cocked” position.
3. Myosin attaches to actin, triggering the power stroke and sliding actin toward the H-zone.
4. Myosin remains attached until a new ATP molecule binds, breaking the cross-bridge.

5.ATP is hydrolyzed to return myosin to its “cocked” position, repeating the cycle.

Question 14

What role does ATP play in muscle contraction?

Answer 14

ATP provides the energy for myosin to “cock” its head, detach from actin after the power stroke, and return to its original position for another contraction cycle.

Question 15

What is the role of the protein titin in muscle function?

Answer 15

Titin helps sarcomeres recoil after stretching, prevents overstretching, and connects myosin filaments with the Z-line to ensure proper alignment.

Question 16

Why are antagonistic muscles important for muscle movement?

Answer 16

Antagonistic muscles are necessary because muscle tissue can only exert force when it contracts; they work in pairs where one muscle contracts while the other relaxes, allowing for controlled movement.

Question 17

How is the range of motion of a joint determined?

Answer 17

The range of motion of a joint is determined by its structure and can be measured using computer analysis of images or with a goniometer.

Question 18

What functions does titin serve in the muscle sarcomere?

Answer 18

Titin connects myosin filaments to the Z-line, ensuring their proper positioning, stores potential energy during stretching, and prevents overstretching of the sarcomere.

Question 19

How do the internal and external intercostal muscles facilitate ribcage movement?

Answer 19

The internal and external intercostal muscles have different fiber orientations, allowing them to move the ribcage in opposite directions; when one layer contracts, it stretches the other, storing potential energy in titin.

Question 20

What are the roles of skeletons in muscle movement?

Answer 20

Skeletons provide anchorage for muscles and act as levers; arthropods have exoskeletons, while vertebrates have endoskeletons, with joints acting as fulcrums to enable movement.

Question 21

What are the key components involved in movement at a synovial joint?

Answer 21

Key components include bones, cartilage, synovial fluid, ligaments, muscles, and tendons. For example, in the human hip joint, the femur and pelvis interact to facilitate movement.

Question 22

Why can muscles only pull and not push?

Answer 22

muscles can only pull because of their contractile nature; thus, they work in pairs as antagonistic muscles to produce controlled movement—when one contracts, the other relaxes.

Question 23

What is the function of acetylcholine in muscle contraction?

Answer 23

Acetylcholine acts as a neurotransmitter at the neuromuscular junction, transmitting the electrical signal from the motor neuron to the muscle fiber, which initiates muscle contraction.

Question 24

Outline the sliding filament theory.

Answer 24

The sliding filament theory states that during muscle contraction, actin filaments slide over myosin filaments, causing the sarcomere to shorten. This process involves the binding of myosin heads to actin, forming cross-bridges, and the subsequent power stroke that pulls the actin filaments towards the center of the sarcomere.

Question 25

Outline the antagonistic action of the intercostal muscles.

Answer 25

The external intercostal muscles contract to elevate the ribcage during inhalation, while the internal intercostal muscles contract to depress the ribcage during exhalation. This coordinated action allows for efficient breathing by expanding and contracting the thoracic cavity.

Question 26

Distinguish between motility and sessility, giving an example for each.

Answer 26

Motility refers to the ability of an organism to move independently from one location to another, such as a fish swimming. Sessility refers to organisms that are fixed in one place and cannot move, such as a barnacle attached to a rock.

Question 27

Outline the reasons for locomotion in living organisms.

Answer 27

Locomotion allows organisms to forage for food, escape from predators, search for mates, and migrate to suitable environments for survival and reproduction.

Question 28

Outline the roles of the different structures in the hip joint.

Answer 28

In the hip joint, the femur and pelvis provide the bony structure, cartilage cushions and reduces friction between bones, synovial fluid lubricates the joint, ligaments stabilize the joint, and tendons connect muscles to bones, enabling movement.

Question 29

Explain how marine animals are adapted for swimming.

Answer 29

Marine animals are adapted for swimming through streamlined bodies to reduce drag, modified limbs forming flippers for steering, and tails with flukes that provide powerful thrust. They also have specialized airways for efficient breathing while diving.

Question 30

Outline the evolutionary advantages of locomotion for species.

Answer 30

Locomotion enables species to access resources, escape from predators, migrate for better climates or food availability, and increase genetic diversity by finding new mates, all of which contribute to survival and reproductive success.

Question 31

Muscle fibers are adapted through:

Answer 31

• A high density of mitochondria for ATP production.
• Specialized contractile proteins (actin and myosin) for efficient contraction.
• Sarcoplasmic reticulum for rapid Ca²⁺ release and reuptake.

-The presence of titin for elasticity and recoil during muscle relaxation.

Question 32

Explain why an action potential in a single motor neuron can cause multiple muscle fibers to contract.

Answer 32

A single motor neuron can branch out to innervate multiple muscle fibers, forming a motor unit. When an action potential travels down the motor neuron, it causes the simultaneous release of acetylcholine at all neuromuscular junctions connected to that neuron, resulting in the contraction of all associated muscle fibers.

Question 33

Explain the structure and function of motor units in skeletal muscle.

Answer 33

A motor unit consists of a motor neuron and all the muscle fibers it innervates. The motor neuron sends signals that trigger contraction in all connected fibers simultaneously. This arrangement allows for coordinated movements and fine control, as smaller motor units enable precise control of smaller muscle groups, while larger units generate more force.

Question 34

Discuss the role of ATP in muscle contraction.

Answer 34

1. Provides energy for the myosin head to enter a “cocked” position.
2. Fuels the power stroke when myosin binds to actin and releases energy.
3. Allows myosin to detach from actin after the power stroke when ATP binds.
4. Powers the active transport of Ca²⁺ ions back into the sarcoplasmic reticulum for muscle relaxation.
5. Supports the overall metabolism of muscle cells to maintain energy levels during sustained contraction.

Question 35

Explain how the sliding filament theory describes the process of muscle contraction at the molecular level.

Answer 35

1. Ca²⁺ ions bind to troponin, moving tropomyosin away from the myosin binding sites on actin.

2.Myosin heads attach to exposed binding sites on actin, forming cross-bridges.

3. The power stroke occurs as myosin heads pivot, pulling actin filaments inward.
4. Myosin heads detach when a new ATP molecule binds, and the cycle repeats with ATP hydrolysis. This process results in the shortening of the sarcomere and overall muscle contraction.

Question 36

Explain how the musculoskeletal system moves, supports, and protects the human body.

Answer 36

Moves: Muscles contract to pull on bones, facilitating movement at joints; this allows for locomotion and manipulation of the environment.

Supports: The skeletal structure provides a framework that supports body weight and maintains posture.

Protects: Bones encase and protect vital organs (e.g., the skull protects the brain, and the ribcage protects the heart and lungs), while muscles provide additional protection through movement.