B3.3 Muscle and motility

Question 1

What are sessile organisms?

Answer 1

These are organisms that cannot move from place to place, but are still able to alter their body form in response to environmental stimuli.

Question 2

What are motile organisms?

Answer 2

These are organisms that have adaptations allowing movement within their habitat

Question 3

Sessile organism example

Answer 3

Venus flytrap: this is a carnivorous plant native to the subtropical wetlands found in north + south carolina. This plant species lives in soils that are deficient in minerals, especially nitrogen. The plant’s traps ia a pair of leaves with short but sturdy trigger hairs. It waits for and insect to fly insides it’s paired leaves and trigger the hairs, once triggered both sides close, to prevent prey from escaping. The internal portion of these leaves then secretes enzymes to digest the trapped insect

Question 4

Example of a motile organism

Answer 4

Brown-throated three-toed sloth: is motile but a very slow moving mammal. Sloths are arboreal (tree dwelling) and herbivorous. Their digestive process is slow, it takes them about a month for them to process an ingested leaf. Once a week the sloth will descend to the ground to use bathroom, leaving behind the equivalent of 1/3 of their body mass. They have 3 long toes, in combination with their bone structure and musculature are adapted to hanging from branches and moving using a pulling motions. These adaptations make movement on the ground almost impossible for a sloth

Question 5

What is the sliding filament model of muscle contraction?

Answer 5

explains how muscles contract by actin (thin filaments) sliding over a myosin (thick filament), shortening the sarcomere and the entire muscle fiber without changing the filament length

Question 6

What are muscle cells + why are they multinucleate?

Answer 6

Muscle fibers are elongated, multinucleated cells formed by the fusion of multiple embryonic cells. They contain myofibrils and many nuclei to efficiently control protein synthesis and muscle contraction

Question 7

What are Myofibrils, and how are they structured?

Answer 7

Myofibrils are long, cylindrical structures inside muscle fibers made up of repeating contractile units called sarcomeres. These are aligned in a striated pattern due to alternating actin and myosin filaments

Question 8

What are sarcomeres + what happens when they contract?

Answer 8

Sarcomeres are the basic contractile units of myofibril, located between the z-lines. During contraction;
- Z-lines move closer together
-I-band shortens
- A-band remains the same
- H-zone disappears

Question 9

What happens to actin and myosin filaments during muscle contraction?

Answer 9

During contraction, actin filaments slide over myosin filaments, pulling the z-lines closer together and shortening the sarcomere. Neither actin nor myosin changes in length; only their relative positions shift. This process is known as the sliding filament theory

Question 10

Why do sarcomeres appear as dark and light bands in muscle fibers?

Answer 10

The dark bands (A-bands) are regions where actin and myosin filaments overlap, while the light bands (I-bands) contain only actin filaments. When the muscle contracts, the I-band shortens, and the H-zone (only myosin) disappears, causing the entire sarcomere to shrink

Question 11

What are the 4 steps of the cross-bridge cycle in muscle contraction?

Answer 11

1. ATP hydrolysis; ATP is broken down into ADP +Pi, energizing the myosin head, which moves into a ready position
2. Cross-bridge formation; myosin heads bind to actin at exposed binding sites, forming cross-bridges.
3. Power stroke; myosin heads bend inward, pulling actin filaments toward the center of the sarcomere. ADP and Pi are released
4. Detachment; A new ATP molecule binds to myosin, breaking the cross-bridge, allowing myosin to detach from actin and reset for another cycle

Question 12

What is the role of ATP in muscle contraction?

Answer 12

ATP is essential for;
- detaching myosin heads from actin (breaking cross-bridges)
- Resetting myosin heads to their high energy state (ATP hydrolysis)
- Powering calcium ion pumps in the sarcoplasmic reticulum to restore calcium levels after contraction

Question 13

How does calcium regulate muscle contraction?

Answer 13

When a ner signal reaches the muscle;
- Calcium ions are released from the sarcoplasmic reticulum
- Calcium binds to troponin, causing tropomyosin to move, exposing actin’s binding sites
- myosin heads can not attach -> allowing contraction
- when calcium is pumped back into the sarcoplasmic reticulum, muscle relaxation occurs

Question 14

What are tendons + what is their function?

Answer 14

tendons are connective tissues that attach muscles to bones, allowing force transfer from muscle contraction to skeletal movement

Question 15

What is the difference between the origin and insertion of a muscle?

Answer 15

Origin; the fixed attachment point of a muscle that does not move during contraction
Insertion: the moveable attachment point that shifts when the muscle contracts

Question 16

Why do muscles work in antagonistic pairs?

Answer 16

Muscles can only pull (contract), so movement in the opposite direction requires a second muscle with the opposite function. This opposing pair is called an antagonistic pair

Question 17

Example of an antagonistic pair in human body;

Answer 17

Biceps (flexor); contracts to bend the arm
Triceps (extensor); contracts to straighten the arm

Question 18

what are antagonistic pairs?

Answer 18

are muscles that work opposite to each other to create movement. When one muscle contracts, the other relaxes, allowing a controlled motion

Question 19

What is titin?

Answer 19

Titin is an immense protein that has multiple folds that allow it to act as a spring. Muscles also use a force to help with relaxation, as a result of the spring-like action of the protein, titin

Question 20

How is titin involved in contraction?

Answer 20

When sarcomeres shorten during contraction, the two sides of each sarcomere move towards the centre. This creates a spring-like tension in titin that is released when the muscle relaxes. This allows each sarcomere of the muscle to undergo a contraction once again. Titin also holds myosin fibres in place in the sarcomere and prevents muscle fibres overstretching

Question 21

Which contraction is under control of your nervous system?

Answer 21

Skeletal muscle contractions. Every movement made requires many electrical impulses originating in your brain and terminating at synapses called neuromuscular junctions. These junctions are a types of synapse where a chemical message is sent into the muscle tissue to stimulate a contractions. Neurons that carry these ‘messages’ are motor neurons

Question 22

Which neurotransmitter is always released at the neuromuscular junctions?

Answer 22

It is always acetylcholine. Neurotransmitter = chemical that is released

Question 23

What is a motor unit?

Answer 23

A motor unit consists of a single motor neuron and all the muscle fibres it controls. The number of fibres in a motor unit varies depending on the function of the muscle

Question 24

How does the number of motor units activated affect muscle contraction intensity?

Answer 24

Low-intensity contraction -> few motor units activated
High-intensity contraction -> more motor units activated.
This allows the body to control force production based on the task

Question 25

What is the typical ratio of motor neurons to muscle fibres?

Answer 25

The ratio varies from 1:10 to 1:200

Question 26

What is an endoskeleton, and which animals have it?

Answer 26

an endoskeleton is an internal skeleton make of bone or cartilage found in vertebrates (eg humans, birds, kangaroos). Muscles attach to bones to enable movement

Question 27

How do differences in bone length and muscle attachment affect movement?

Answer 27

Different bone structures and muscle connections allow specialized movements, such as hopping in kangaroos vs walking in humans

Question 28

What is and exoskeleton, and what is it made of?

Answer 28

An exoskeleton is a hard external skeleton made of chitin, found in arthropods like insects

Question 29

How do muscles attach in animals with exoskeletons?

Answer 29

Unlike endoskeletons, where muscles attach outside bones, in exoskeletons, muscles attach to the inside of the hollow skeleton

Question 30

What is a lever in the skeletal system, and what is its purpose?

Answer 30

A lever is a bone that rotates around a fixed point (fulcrum), reducing the force needed for movement. Levers help maximise efficiency in actions like lifting or walking

Question 31

What is a fulcrum and how does it function in movement?

Answer 31

A fulcrum is a joint were a lever (bone) rotates. For example, in a nodding movement, that cranium-vertebrae joint acts as a fulcrum while muscles move the head

Question 32

How do arthropods use their exoskeletons for movement?

Answer 32

Arthropods use their jointed exoskeletons for leverage. Muscles attach inside the chitin armor, working in antagonistic pairs, allowing powerful movements like a fleas 200x body-length jump

Question 33

What is a synovial joint, and what is its function?

Answer 33

A synovial joint is a moveable joint where two bones meet, allowing a wide range of motion. Examples include the elbow, knee, shoulder, and hip joints

Question 34

What structures are involved in a synovial joint?

Answer 34

Bones: provide structure Cartilage: cushions the joint -> reducing friction Synovial fluid: lubricates the joint for smooth movement Ligaments: connect bones, stabilizing the joint Tendons: attach muscles to bones, enabling movement

Question 35

(Hip) what type of joint is the hip joint and how does it function?

Answer 35

The hip joint is a synovial joint in the type of a ball-and-socket joint, where the head of the femur fits into the pelvis. this structure allows for a wide range of motion in multiple directions

Question 36

What roles does cartilage play in the hip joint?

Answer 36

Cartilage covers the ends of bones preventing bone on bone contact, reducing friction, and absorbing shock during movement

Question 37

How do ligaments and tendons contribute to hip joint stability?

Answer 37

Ligaments; hold bones in place, providing stability while allowing movement Tendons; attach muscles to bones, enabling movement of the hip joint

Question 38

What is synovial fluid, and why is it important?

Answer 38

Synovial fluid is a lubricant found in synovial joints, including the hip, that reduces friction between bones and allows smooth movement

Question 39

Pelvis structure; Pelvis + femur, function (hip)

Answer 39

Bones forming the ball-and-socket joint of the hip

Question 40

Pelvis structure; cartilage, function (hip)

Answer 40

A smooth protective connective tissue that lines both the pelvis and femur within the hip joint

Question 41

Pelvis structure; synovial fluid, function (hip)

Answer 41

Lubricating fluid within the hip joint that reduces friction

Question 42

Pelvis structure; ligaments, function (hip)

Answer 42

Tough connective tissues that holds the bones of the hip joint in place

Question 43

Pelvis structure; Tendons, function (hip)

Answer 43

Connective tissue that connects each of the muscles of the hip joint to its appropriate bones

Question 44

Pelvis structure; muscles, function (hip)

Answer 44

Muscle tissues that contract and relax to enable movement of the femur within the socket of the pelvis

Question 45

What is the device used to measure range of motion?

Answer 45

A goniometer is used to measure the range of motion of a joint. Range of motion is the distance and direction that a joint can move, and is usually measured in degrees. The measurements can be used to document improvements in joint movement (After injury, etc). Some joints are capable of movement in a number of dimensions

Question 46

What are intercostal muscles, and where are they located?

Answer 46

they are paired muscles between each rib that control ribcage movement during breathing. They consist of external intercostal muscles (outer layer) and internal intercostal muscles (inner layers)

Question 47

What is the function of the external intercostal muscles?

Answer 47

The external intercostal muscles contract during inspiration, pulling the ribs upward and outwards, expanding the thoracic cavity to allow air intake

Question 48

What is the role of the internal intercostal muscles?

Answer 48

these contract during expiration, pulling the ribs downward and inward, reducing thoracic cavity volume and helping push air out

Question 49

How do intercostal muscles work as antagonistic pairs?

Answer 49

During inspiration, external muscles contract, and internal muscles relax to lift the ribcage During expiration, internal muscles contract, and external muscles relax to lower the ribcage

Question 50

How do intercostal muscles contribute to the mechanics of breathing?

Answer 50

By changing the volume of thoracic cavity, intercostal muscles help regulate air pressure in the lungs, allowing inhalation and exhalation to occur efficiently

Question 51

How does muscle stretching occur during breathing?

Answer 51

When the external intercostal muscles contract, the ribcages expands, stretching the internal intercostal muscles. When internal intercostal muscles contract, the external intercostal muscles stretch

Question 52

What role do titin fibres play in intercostal muscle function?

Answer 52

Titin fibres in the sarcomeres store potential energy when the opposite intercostal muscle stretches. This stored energy helps facilitate the next contraction

Question 53

How does potential energy storage aid respiration?

Answer 53

The stretching of the relaxed intercostal muscle stores potential energy, which is later used to make contraction more efficient and reduce energy expenditure

Question 54

What is locomotion?

Answer 54

the ability to move from place to place

Question 55

Why do animals move?

Answer 55

- to find food - to find mate - to escape predators - to migrate

Question 56

Moving reason; food + example + description

Answer 56

Honey bees. They are flying from flower to flower to collect nectar and pollen

Question 57

Moving reason; escaping danger + example + description

Answer 57

Flying fish. They are escaping predators by swimming fast and extending their very long pectoral fins to glide over the water

Question 58

Moving reasons; mate + example + description

Answer 58

Loggerhead sea turtle. Both males and females swim back to the beach where they were hatched to mate and lay eggs

Question 59

Moving reason; migration + example + description

Answer 59

Arctic tern. Migrating from their arctic breeding grounds to the antarctic region and back each year, to take advantage of available foot

Question 60

Marine mammals (dolphins, whales, seals, etc)

Answer 60

They are all descended from ancestral species that once lived on land. Their internal anatomy is adapted to a marine environment but still has many similarities with their land ancestors

Question 61

Adaptation of dolphins in order for them to be successful inhabitants of ocean waters

Answer 61

- have a streamlined body -> allowing the animal to move through water with ease and speed - no body hair -> reduce drag through the water - tail adapted to form a fluke -> allows up/down motion for propulsion - front limbs adapted to flippers -> used for steering - Have an airway -> to exchange air at periodic intervals with a minimum of the body leaving the water - Can seal blowhole tightly -> water does not enter airway - can stay underwater for several minutes -> they can make deep dives - they still have retained some mammalian characteristics (being endothermic, producing milk for their young, having an advanced two-sides circulatory system, and long-term parental care of their young