B3.3 Muscles and motility

What are the two types of movement in living organisms?

The two types of movement are:

1)Movements within the body, such as peristalsis in the gut or lung ventilation. 2)Locomotion, which is the movement of an organism from one place to another

Do all living organisms exhibit locomotion?

No, locomotion occurs in some organisms but not all. However, movements within the body happen in all living organisms, even unicellular ones.

What does it mean for an organism to be motile?

A motile organism can move from one place to another, often for feeding or migration.

Give an example of motile organisms

bar-tailed godwits migrate 10,400 km from Siberia to New Zealand in 7–8 days.

What does it mean for an organism to be sessile?

A sessile organism remains in a fixed position.

Examples of sessile organisms

most plants with roots in soil and animals like corals, which are sessile polyps in aquatic habitats.

How do sessile corals adapt to their stationary lifestyle?

Sessile corals build rigid skeletons around themselves to extend their tentacles into the water for filter-feeding, although they cannot move to new locations.

What do muscle fibers contain, and how are they structured?

Muscle fibers contain parallel myofibrils, which are made up of sarcomeres linked end-to-end at Z-discs.

How do the Z-discs and bands change in a relaxed muscle?

In relaxed muscle, the Z-discs are further apart, the light bands are wider, and the sarcomere is longer overall.

What causes the pattern of light and dark bands in a sarcomere?

The pattern is due to the arrangement of thin actin filaments and thick myosin filaments in a precise, regular pattern.

How are actin and myosin filaments arranged in a sarcomere?

Actin filaments are attached to the Z-disc at one end, while myosin filaments occupy the center and interlock with actin filaments at both ends.

What role do myosin heads play in muscle contraction?

Myosin heads form cross-bridges with actin filaments and use ATP to push the actin filaments toward the center of the sarcomere.

How does the myosin-actin interaction cause sarcomere contraction?

Myosin heads bind to actin, swivel to exert force, detach, and reattach at the next binding site, causing the actin and myosin filaments to slide past each other.

What is the term used to describe the myosin head mechanism?

The movement of myosin heads is often referred to as a ratchet mechanism.

Why can muscle fibers exert powerful forces despite each myosin head producing small forces?

The large number of myosin heads in many filaments, sarcomeres, myofibrils, and muscle fibers collectively exert very strong forces.

What is the first step in the myosin-actin interaction cycle?

Myosin filaments have heads that form cross-bridges by attaching to binding sites on actin filaments.

What happens when ATP binds to myosin heads?

ATP binds to the myosin heads, causing them to detach from the actin filaments by breaking the cross-bridges.

What is the role of ATP hydrolysis in the cycle?

ATP is hydrolyzed into ADP and phosphate, which changes the angle of the myosin heads and “cocks” them, storing potential energy.

How do myosin heads reattach to actin filaments?

The myosin heads attach to new binding sites on actin that are further from the sarcomere center than the previous sites.

What is the power stroke, and how does it occur?

The power stroke occurs when ADP and phosphate are released, causing the myosin heads to push the actin filaments inward toward the center of the sarcomere.

How does the cycle of myosin and actin interaction repeat?

What is titin, and how large is it in humans and mice?

Titin is the largest polypeptide discovered, consisting of 34,350 amino acids in humans and 35,213 amino acids in mice.

What is the primary function of titin in muscle structure?

Titin connects myosin filaments to the Z-disc, holding myosin in the correct position among six parallel actin filaments.

How does titin contribute to muscle elasticity?

Titin acts like a molecular spring, storing energy when stretched and releasing it as it recoils, adding to the force of muscle contraction.

Why is energy needed to stretch titin, and how is this energy provided?

Energy is required to stretch titin during muscle lengthening, which happens when muscles relax. This energy is supplied by the contraction of an antagonistic muscle.

What is the role of antagonistic muscle pairs in relation to titin?

Antagonistic muscles work together, with one contracting to supply the energy needed for the other to relax and stretch its titin molecules.

How do skeletal muscles contract?

Skeletal muscles contract when stimulated by a motor neuron, which passes the stimulus to the muscle fiber at a neuromuscular junction using the neurotransmitter acetylcholine.

What is a motor unit?

A motor unit consists of a single motor neuron and all the muscle fibers it stimulates via neuromuscular junctions.

How are muscle fibers organized within a motor unit?

Muscle fibers in a motor unit are not clumped together but are mingled with fibers from other motor units within the muscle.

How does a motor unit help achieve coordinated muscle contraction?

When a nerve impulse passes along a motor neuron and its branches, all the muscle fibers in the motor unit contract simultaneously, aiding coordinated muscle contraction with fewer motor neurons.

What is the primary function of a skeleton?

A skeleton provides a hard framework that supports and protects an animal's body.

What is the difference between exoskeletons and endoskeletons?

Exoskeletons are external and found in arthropods like insects and crustaceans, while endoskeletons are internal and made of bones, as seen in vertebrates.

What material are exoskeletons in arthropods primarily made of?

Exoskeletons are made of tough plates of chitin that cover most of the body surface.

How do skeletons facilitate movement?

Skeletons provide anchorage for muscles and act as levers to facilitate movement.

What are the two points of muscle attachment to a skeleton, and what are their roles?

The origin is fixed and does not move during muscle contraction, while the insertion moves to create movement when the muscle contracts.

Give an example of a muscle attachment and its function.

The masseter muscle's origin is on the cheekbone, and its insertion is on the jawbone (mandible). Contraction moves the jawbone for biting and speech.

How do bones act as levers in the body?

Bones change the size and direction of forces, with effort applied by muscles and a fulcrum acting as the pivot point.

What determines whether a lever increases force or distance moved?

If effort is applied further from the fulcrum than the resultant force, the lever increases force but decreases distance. If effort is closer, the lever decreases force but increases distance.

What is the fulcrum in a bone acting as a lever?

The fulcrum is the joint where the bone meets another bone.

How is effort applied to bones in the body?

Effort is applied to bones by one or more muscles via tendons.

What are the two main types of joints, and how do they differ?

Fixed joints, like skull sutures, do not allow movement, while articulated joints allow bones to move in relation to each other.

What is the primary function of bones in synovial joints?

Bones provide anchorage for muscles and ligaments and guide the types of movement that can occur at the joint.

What is the role of cartilage in synovial joints?

Cartilage covers the bone at joints, preventing friction, reducing contact between bones, and absorbing shocks to prevent fractures.

What is synovial fluid, and what is its function?

Synovial fluid fills the cavity between the cartilages at a joint, lubricating the joint and reducing friction.

What is the function of ligaments in synovial joints?

Ligaments, made of collagen, prevent aberrant movements, dislocation, and damage to the joint.

What is the joint capsule, and what are its functions?

The joint capsule is a tough ligamentous covering that seals the joint, holds in synovial fluid, and helps prevent dislocation.

What role do muscles play in joint movement?

Muscles provide the forces needed to create movement at the joint.

How do tendons function in relation to muscles and bones?

Tendons attach muscles to bones, transmitting forces from muscles to bones over distances with their strong, collagen-rich structure.

What determines the range of movements possible at a joint?

The structure of a joint, including the ligamentous joint capsule and ligaments, determines the range of movements possible.

How do the elbow, knee, and hip joints differ in their range of movement?

The elbow and knee are hinge joints that allow flexion and extension, while the hip is a ball-and-socket joint with a greater range of motion, including protraction, retraction, abduction, adduction, and rotation.

How can the range of movements at a joint be measured?

The range of movements can be measured using a goniometer, digital goniometer apps, or computer programs analyzing joint angles.

What are the effects of muscle stretching on joint movement?

Muscle stretching can increase the range of motion at a joint, and research questions can explore the effects of different types of stretching, persistence of the effect, and differences between joints or genders.

What are the intercostal muscles and what is their function?

The intercostal muscles are the muscles between the ribs, made up of external and internal layers. They help in moving the ribcage during breathing by alternating contractions.

How do the external and internal intercostal muscles differ in their function?

The external intercostal muscles expand the ribcage for inhalation, while the internal intercostal muscles contract during exhalation. Stretching of the internal muscles stores potential energy in the titin.

What role does titin play in the intercostal muscles during inhalation?

During inhalation, the stretching of the internal intercostal muscles stores potential energy in the titin protein, which is released during exhalation when the internal muscles contract.

Why does locomotion require energy expenditure?

Locomotion requires energy because animals move only when there are benefits, such as finding food, escaping danger, or mating.

Why do herbivores move from place to place?

Herbivores move to find plant foods, such as nectar, pollen, and fresh pastures, necessary for their survival.

How do frugivores and predators use movement?

Frugivores move to find ripe fruit, while predators move to catch and kill their prey.

What motivates prey animals to move?

Prey animals move to escape predators or hostile members of their own species, often requiring rapid movement or stamina.

How do some animals utilize roosting sites?

Some animals, like jackdaws, return to roosting sites during inactive times, gathering at dusk and dispersing at dawn.

Why must animals in dispersed populations travel to find a mate?

Animals in dispersed populations must travel to avoid inbreeding by finding unrelated individuals for mating.

What is an example of migration in birds?

Many bird species, like snow geese, migrate between the northern and southern hemispheres to avoid food scarcities in winter and to breed in different regions.

How does migration work for species like salmon?

Some species, such as salmon, perform a once-in-a-lifetime migration to their breeding grounds, with the young later migrating back to the adult region.

What adaptations do marine mammals have to minimize resistance in water?

Marine mammals are streamlined with a shape that tapers towards the rear, flippers, flukes, and a dorsal fin with a teardrop profile. Their smooth body surface, absence of hind limbs, and hairless skin also reduce drag.

How do marine mammals use their body parts for locomotion in water?

How does blubber help marine mammals?

Blubber provides buoyancy, allowing marine mammals to float just below the water's surface, even while resting or sleeping, without needing to move.

What adaptations allow marine mammals to breathe efficiently underwater?

Marine mammals have a blowhole for breathing, which leads from the larynx to the upper surface of the head. They also have no connection between their mouth and lungs to prevent water from entering the lungs.