B3.3 Muscle and mobility

Question 1

What is movement?

Answer 1

Movement is one of the 8 characteristics of life(MRHMGREN) but movement can either refer to movements that can take place within the bode (e.g. peristalsis) or by moving an organism from one place to another(locomotion)

Question 2

What is a sessile organism?

Answer 2

Sessile organism (e.g. barnacles or corals or planta-mimosa pudica) do not perform locomotion – they remain in a fixed position but move individual body parts.

Question 3

What is a motile organism?

Answer 3

Motile organism move around while feeding within their territory – some further distances than others.
E.g. mammals, bacteria, squid/octopus

Question 4

What do muscles fibres contain?

Answer 4

Muscle fibers contain many parallel myofibrils, which consist of a series of sarcomeres.

Question 5

What are sarcomeres?

Answer 5

A sarcomere is the repeating unit of a muscle cell.

Question 6

What cause the contraction of sarcomeres?

Answer 6

The contraction of sarcomeres, and therefore a muscle, is due to the sliding of actin and myosin filaments.

Question 7

What are sarcolemma and sarcoplasma, in respect to the sliding filament model of contraction?

Answer 7

The sarcolemma and sarcoplasma are specific adaptations of the cell membrane and cytoplasm, respectively.

Question 8

What is the sarcoplasmic reticulum?

Answer 8

A specialised (modified) endoplasmic reticulum, the sarcoplasmic reticulum, is a fluid filled system of membranous sacs surrounding the muscle myofibrils.

Question 9

What is the function of the sarcoplasmic reticulum?

Answer 9

Wrapped around myofibrils, its function is to store calcium ions, and comes to action when conveying a signal to contract all parts of the muscle fibres.

Question 10

What does the sarcolemma contain?

Answer 10

The sarcolemma has multiple tunnel-like extensions that penetrate the interior of the cell, called T-tubules.

Question 11

What are between the myofibrils?

Answer 11

Between the myofibrils are large number of mitochondria, which provide ATP needed for contraction.

Question 12

What causes the pattern of light and dark bands in sarcomeres?

Answer 12

The pattern of light and dark bands in sarcomeres is due to a precise and regular arrangement of actin and myosin filaments.

Question 13

What happens during a muscle contraction?

Answer 13

A muscle contraction shortens each sarcomere and therefore the overall length of the muscle fibre. The contraction occurs by sliding of actin and myosin filaments.

Question 14

Describe the changes that occur to the sarcomere during muscle contraction/relaxation.

Answer 14

When muscle fibers contract the sarcomere length shortens and the Z-discs move closer together. When the muscle is relaxed, the sarcomere length is longer.

Question 15

What are skeletal muscles composed of?

Answer 15

A bundle of striated muscle fibres, each of them stimulated by a motor neuron.

Question 16

What are muscle fibres?

Answer 16

Each muscle fibre is a multinucleated cell containing numerous myofibrils, which are highly ordered assemblages of thick myosin and thin actin filaments.

Question 17

What causes muscles to contract or relax?

Answer 17

The release of calcium from sarcoplasmic reticulum (motor neuron–>nerve impulse) triggers muscle contraction.

Question 18

What is the neuromuscular junction?

Answer 18

At the synapse (neuromuscular junction) the stimulus is converted into a chemical signal using acetylcholine as a neurotransmitter. One motor neuron with multiple branches connecting to a number of muscle fibre. This results in a coordinated contraction.

Question 19

What are muscle fibres composed of?

Answer 19

Myofibrils which contain sarcomeres, and it contains a specialised cytoplasm called sarcoplasm.

Question 20

What is a sarcomere?

Answer 20

The basic contractile unit of a muscle containing actin(thin filament) and myosin (thick filament).

Question 21

Inside a sarcomere there are protein filaments called actin and myosin. These two fibrous structures are largely responsible for facilitating a muscle contraction: Describe the features of the thick and thin protein filaments.

Answer 21

The thin filament is made up of two twisted chains of the globular protein actin.
The thick filament is made of many molecules of the protein myosin. Each myosin molecule has a fibrous tail and a globular head. It has an actin binding site and an ATPase binding site.

Question 22

Explain how the sliding filament mechanism and cross-bridges of muscle fibres result in a muscle contraction.

Answer 22

The sliding filament theory explains contraction of a sarcomere. According to this theory, when a muscle is stimulated to contract, actin filaments slide over the myosin filaments towards centre of the sarcomere. This results in:
- 2-discs being pulled closer together. shortening sarcomere + resulting in overall shortening of muscle fibres
- H bands + I bands decrease length as actin is pulled inwards, overlapping more myosin + reducing area where only myosin or actin is present

Question 23

How does a contraction begin and how does that result in sarcomere shortening?

Answer 23

Muscle contraction initiated by the brain via an action potential which causes an influx calcium ions that bind to troponin. Without electrical stimulation, myosin binding sites on the actin filaments are blocked by a thin + fibrous protein subunit called tropomyosin. Tropomyosin runs alongside the action filament preventing binding of myosin to actin + hence preventing contraction of muscle. Tropomyosin is associated with another protein subunit called troponin. When a muscle is stimulated by a motor neuron, calcium ions are released from sarcoplasmic reticulum, a specialized endoplasmic reticulum that is found in sarcoplasm (cytoplasm) of muscle cells. These calcium ions bind to the troponin causing it to undergo a conformational change –> troponin moves tropomyosin away from myosin binding site, allowing myosin to bind to actin.

Question 24

Why do the sarcomere shorten?

Answer 24

The shortening of the sarcomere comes about by the cocking of the myosin heads, when ADP and Pi is released. The breaking of the cross-bridges can only occur when a fresh molecule of ATP re-charges the myosin head.

Question 25

What is the function of tropomyosin?

Answer 25

In addition to the contractile filaments myosin and actin, the myofibril also contains troponin protein complexes and tropomyosin fibers.
Tropomyosin covers the myosin binding sites, effectively preventing attachment of the myosin head. During a contraction, Ca2+ ions bind to troponin, which moves away the tropomyosin fibres.

Question 26

What is titin?

Answer 26

Titin is the largest polypeptide being composed of 34350 amino acids. It is elastic and acts as a molecular spring.
Titin connects myosin filamints to the Z-discs.

Question 27

What are the functions and contributions of titin to muscle contraction?

Answer 27

Titin connects myosin filaments to the Z-discs. It stores potential energy when it is stretched and releases it when it recoils - thereby adding to the force of contraction. It also prevents overstretching of the sarcomere and it holds the myosin filaments in place surrounded by 6 actin filaments.

Question 28

What is the role of antagonistic muscle?

Answer 28

Energy is needed to stretch titin and therefore lengthen the muscle when relaxing. Energy cannot be supplied by the muscle itself because muscles can only exert force when contracting. The energy is therefore provided by another muscle called the antagonist.
E.g. In the elbow joint, the triceps and biceps muscles are an antagonistic pair. The biceps flexes the forearm, the triceps extends the forearm.

Question 29

Compare exoskeleton and endoskeleton.

Answer 29

An exoskeleton takes over the function of bones for muscle attachment in arthropods.
An endoskeleton- internal skeleton.

Question 30

What is the purpose of a skeleton?

Answer 30

-support
-shape
-protection

Question 31

What is the function of skeleton, muscle, joints in an animal?

Answer 31

The skeleton of an animal, together with the muscles attached across the joints, functions as a system of levers. Each joint acts as a pivot point (fulcrum). A muscle is normally attached to two parts of the skeleton – one is the origin one is the insertion. By acting as levers, bones can change the size and direction of a force.

Question 32

What is effort?

Answer 32

The force applied (when the muscle contracts) is called the effort.

Question 33

What is a lever?

Answer 33

A lever is a beam or rigid rod pivoted at a fixed hinge.

Question 34

How does the effort (the force) applied to a lever change with the distance away from the function (the joint)?

Answer 34

The further away from the fulcrum the effort is applied, the greater the leverage; that is, the smaller the force that is required to raise the load.

Question 35

What is an example of a first class lever in the human body?

Answer 35

Question 36

What is an example of a second class lever in the human body?

Answer 36

Question 37

What is an example of a third class lever in the human body?

Answer 37

Question 38

What determines the range of movements of joints?

Answer 38

The specific anatomical construction of a joint determines the range of movement.

Question 39

What are the six main types of joints?

Answer 39

-Planar joint
- Hinge joint
- Pivot joint
- Condyloid joint
- Saddle joint
- Ball and socket joint

Question 40

What is a synovial joint?

Answer 40

This is where two bones with cartilage and synovial fluid in between join.

Question 41

What cartilaginous joints?

Answer 41

Cartilaginous jointsare joints in which the bones are connected by cartilage.

Question 42

What is the range of motion?

Answer 42

The range of motion refers to the different movements that can be carried out at a joint e.g. rotation, abduction, adduction

Question 43

What is the type, range of directional movement, types of movements of the elbow joint?

Answer 43

1. Elbow joint
2. Hinge joint
3. Angular movement in only one direction
4. Flexion + Extension

Question 44

What is the type, range of directional movement, types of movements of the radio-ulnar joint(elbow)?

Answer 44

1. Radio-ulnar joint (elbow)
2. Pivot joint
3. Movement in all rotational direction (360°)
4. Rotations (pronation-supination)

Question 45

What is the type, range of directional movement, types of movements of the hip joint?

Answer 45

1. Hip-joint
2. Ball and socket
3. Angular movement in many directions
4. flexion, extension, abduction, adduction, circumduction, rotation

Question 46

What is the type, range of directional movement, types of movements of the knee joint?

Answer 46

1. Knee joint
2. Hinge joint
3. Angular movement in only one direction
4. Flexion and Extension

Question 47

Annotate this diagram.

Answer 47