Chapter 14 Working Muscles

Question 1

What are Skeletal muscles?

Answer 1

• The muscles that enable us to walk, run and carry out a wide range of voluntary physical activities.
• These muscles are under conscious control and are attached to the bones of the skeleton.

Question 2

What is the function of the skeletal muscles?

Answer 2

• Contractions of the skeletal muscles bring about movement at the joints.
• They also give the body it’s form and contours.

Question 3

What are Smooth muscles?

Answer 3

• They are not under conscious control, involuntary muscles.
• Many or the internal organs, such as the stomach and intestines, have muscles for movement.

Question 4

What is the Cardiac Muscle?

Answer 4

Heart muscle.

Question 5

What is the difference between the contraction in a skeletal muscle and the contraction in a cardiac muscle.

Answer 5

• Skeletal Muscle - contraction brings the attached points closer together, so that the bones move.
• Cardiac Muscle - reduces the space in the chambers of the heart and pushes the blood from the heart into the blood vessels.

Question 6

What is difference between Extensibility and Elasticity.

Answer 6

Extensibility is the ability to be stretched, while elasticity is the ability to return to the original length after being stretched.

Question 7

What are the 3 properties that allow muscles to work together to create movement.

Answer 7

1 Contractibility

2. Extensibility
3. Elasticity

Question 8

Muscles are able to shorten their length and can be stretched

Answer 8

They are unable to increase their own length.

Question 9

What are muscles attached to the bones of the skeleton by?

Answer 9

Fibrous, inelastic connective tissue called tendons.

They are attached to the bones in such a way that they bridge the joints, so when contraction occurs the bones move.

Question 10

Why are the muscles that move the parts of the skeleton are always grouped in pairs?

Answer 10

• Muscles can only contract.
• They can pull bones together but they cannot push them apart.
• If muscles contract pulling a bone in one direction, another set of muscles must contract to pull the bone in the opposite direction.

Question 11

What is an Antagonist?

Answer 11

When coordination of paired muscles provides body movement, with one of the pair producing movement of bones in one direction and the other producing movement in the opposite direction.

Question 12

Why are some pairs of muscles referred to as Antagonists?

Answer 12

This is because they have opposite actions.

Eg. The muscles of the upper arm

Question 13

Explain the structures of the muscles of the upper arm, the biceps and triceps which are antagonists.

Answer 13

The triceps and the biceps are antagonists muscles. They produce movements that are opposite - the triceps straightens the arm, and the biceps bends the arm.

The belly is the thick, fleshy part of the middle of the muscle.

Question 14

How does the movement of the forearm about the elbow joint occur?

Answer 14

These two muscles must cooperate.

When the biceps contracts to bend the arm, the triceps must relax; the opposite occurs when the arm is straightened.

Question 15

What is the Origin?

Answer 15

It is the end of the muscle fixed to the stationary bone.

Question 16

What is the insertion?

Answer 16

The attachment of the other end of the muscle, to the movable bone, is the insertion.

Question 17

What is the Belly?

Answer 17

It is the fleshy portion of the muscle between the tendons of the origin and the insertion is called the belly.

Question 18

What is an Agonist?

Answer 18

Aka prime mover. It is a muscle that causes a desired action to occur.

Question 19

Where is the origin of the triceps and biceps?

Answer 19

• Triceps - It is at the shoulder. It is attached to the scapula and the humerus.
• Biceps - It is at the shoulder. It he attached to the scapula.

Question 20

Why is the Triceps an Extensor and the Biceps a Flexor?

Answer 20

• Triceps - when It contracts it straightens the arm at the elbow.
• Biceps -

Question 21

Where is the insertion of the triceps and the biceps?

Answer 21

•Triceps - It is at the forearm. It is attached to the ulna, one of
the bones in the forearm.

•Biceps - it is at the forearm. It is attached to the radius, one if the bones in the forearm.

Question 22

Explain the process of the Biceps contracting and the Triceps relaxing.

Answer 22

• In this situation the biceps is the agonist, because it moves the forearm; the triceps is the antagonist, because it has an effect that it is opposite to that of the agonist - that is, it yields to the movement of the agonist.
• However, when the triceps is contracting to straighten the forearm, the biceps is relaxing and their roles are reversed. Now the triceps is the angin just and the biceps the antagonist.

Question 23

What are Synergists?

Answer 23

Synergists are muscles that help indirectly in steadying a joint during a particular movement; in this way they prevent unwanted movement and allow the agonist to function more efficiently.

Eg. The wrist would flex every time the fist was clenched if it were not for synergistic muscles because the muscles that curl the fingers also pass across the wrist.

-Synergistic muscles immobilize the wrist, stopping it from flexing.

Question 24

Give an example of a Synergistic muscle.

Answer 24

The wrist would flex every time the fist was clenched if it were not for synergistic muscles because the muscles that curl the fingers also pass across the wrist.

-Synergistic muscles immobilize the wrist, stopping it from flexing.

Question 25

What is a fixator?

Answer 25

It is when a synergist immobilizes a joint in this way it is called a fixator.

•Other examples of Fixators are the many muscles that attach the scapula to the axial skeleton.

Question 26

Why are the muscles that attach to the scapula to the axial skeleton important as Fixators?

Answer 26

• This is because the scapula is only attached to the axial skeleton at the ribs.
• To act as a firm origin for the muscles that move the arm, it must be held steady when those muscles contract.
• The Fixators hold the scapula firmly against the chest (or thorax), so when the arm muscles contract only their insertions are moved.

Question 27

What’s the difference between a conscious and unconscious movement?

Answer 27

• Conscious - nerve impulses are sent from the cerebrum, the part controlling conscious activities. The impulses are conducted along motor nerve fibres to the muscles that need to contract.
• Unconscious - they arise in the cerebellum and other parts of the brain to coordinate muscle activity. Such coordination is necessary for fine muscular movements, posture and balance.

Question 28

Explain the structure of the Skeletal Muscle.

Answer 28

• Muscle cells are held together in bundles.
• Red meat is muscle and it is these bundles of muscle cells that give meat its ‘stringy’ appearance when cut lengthwise.
• A sheath of connective tissue surrounds each bundle so that it can function as an individual unit.

Question 29

What does the connective tissue do?

Answer 29

• Allows adjacent bundles to slide easily over one another as they contract.
• The Sheaths of connective tissue around each bundle join each other, and towards the end of the muscle they taper and blend to form the tendon.
• It is the connective that gives any toughness to meat.

Question 30

Why is meat less tender when it comes from an older animal?

Answer 30

-This is because the amount of connective tissue increases with advancing age.

Question 31

What contributes to the decrease in muscular strength that gradually occurs as a person gets older?

Answer 31

The increased amounts of connective tissue.

Question 32

Explain the structure of a Muscle bundle.

Answer 32

• Each muscle cell is an elongated cylinder with many nuclei.
• Around the cell is a thin, transparent plasma membrane. the sarcolemma, containing cytoplasm, called the sarcoplasm.
• These cylindrical cells are the Muscle Fibres.

Question 33

Explain the structure of a Muscle Fibre.

Answer 33

• Dameter: Between 10 and 100 micrometres.
• Length: Varies from a few mm to several cm.

-Within the sarcoplasm of each fibre there are thread-like myofibrils, lying parallel to each other and running the length of the fibre. There may be from 100s to several 1000s of these myofibrils in each fibre.

Question 34

What does the Myofibrils composed of ?

Answer 34

Composed of many smaller myofilaments, made of protein, which are actual units involved in contraction of the muscle.

Question 35

Describe the 2 types of myofilaments.

Answer 35

1. Thick Myofilaments - Myosin; composed mainly of the protein.
2. Thin Myofilaments - Actin; composed mainly of the protein.

Question 36

What happens when a muscle fibre is supplied with sufficient energy and is activated by a nerve impulse?

Answer 36

These thick and thin protein filaments slide past each other in a manner that shortens the myofibril.

Question 37

What does the arrangement of the thick and thin filaments within a myofibril give?

Answer 37

A banded effect to the muscle.

Question 38

What is the function of these bands?

Answer 38

It is these bands that give skeletal and cardiac muscle fibres their striated appearance when viewed under a microscope.

Question 39

Where does the striated appearance of the skeletal muscle come from?

Answer 39

It is due to the variations in the actin and myosin content in different parts of the sarcomere.

Question 40

What are the only tissue that have the ability to contract?

Answer 40

Muscles.

Question 41

What is a the Sliding Filament Theory ?

Answer 41

It is an explanation of how muscle contraction occurs.

Question 42

Why does the sarcomeres shorten when the muscles contract?

Answer 42

The model suggests that this occurs because the actin myosin filaments slide over one another.

Question 43

Explain the process of the Sliding Filament theory.

Answer 43

• As the thin actin filaments slide over the thick myosin filaments, the Z lines are drawn closer together and the sarcomere is shortened.
• This results in a shortening of the muscle fibres and hence a shortening of the whole muscle.
• When the muscles relaxes, the actin and myosin filaments can be pulled past one another in the opposite direction and the muscle fibre returns to its original uncontracted state.
• At any given time some muscle fibres can be contracted, while others are relaxed.

Question 44

Where does the energy for shortening the muscle fibres come from?

Answer 44

The energy comes from the breakdown of adenosine triphosphate (ATP) in the muscle cells.

• Energy is released when ATP breaks down to adenosine diphosphate (ADP) and a phosphate group.
• When energy is again available from cellular respiration, ATP is re-formed.
• ATP is the molecule that transfers energy from cellular respiration to processes such as muscle contraction.

Question 45

Explain the process of the sliding filament model of muscle contraction.

Answer 45

1. Two sarcomeres of a myofibril in a muscle in the relaxed position.
2. As the muscle contracts, the actin and myosin filaments slide apart one another. Notice how the Z lines are moving closer together.
3. When the myofibril is at maximum contraction the Z lines are much closer together, but the actin and myosin filaments have not changed their length.

Question 46

How does the contraction of a skeletal muscle begin?

Answer 46

• Messages are sent along motor neurons that are part of the somatic division of the efferent part of the part of the peripheral nervous system.
• The cell bodies of these motor neurons are in the brain or spinal cord and their axons extend out to the muscles.
• At the muscle end the axon divides into branches. Each branch goes to a different muscle fibre so that each of the fibres in a muscle receive impulses from only one motor neuron.

Question 47

What happens when a nerve impulse comes to the end of an axon?

Answer 47

It is conducted along all of the branches so that all of the muscle fibres connected to that motor neuron contract together.

Question 48

What is a motor unit?

Answer 48

It is a motor neuron and all the muscle fibres stimulated by it.

-The muscle fibres that make up a motor unit are not all grouped together but spread through the muscle.

Question 49

What is the number of muscle fibres that make up a motor unit?

Answer 49

It varies. Where precise movement is required motor units are small.

• For example, the muscles that

Question 50

What is the number of muscle fibres that make up a motor unit?

Answer 50

It varies. Where precise movement is required motor units are small. Where strength of contraction is important, motor units are large.

• Eg. the muscles that control movements of the eye have only 3 to 6 muscle fibres in each motor unit.
• Eg. The large muscles of the legs may have 1000 fibres in each motor unit.

Question 51

When does motor unit ‘shifts’?

Answer 51

• When muscles are required to contract for long periods of time, such as when maintaining posture, the motor units can work in ‘shifts’.
• As the contracted fibres of one motor unit become fatigued, those of another motor unit can take over while the fatigued ones recover.
• In this way, a muscle can maintain contraction for lengthy periods.

Question 52

What is a neuromuscular junction?

Answer 52

The point where the message is passed from the motor neuron to the muscle fibre.

Question 53

What is a Synaptic knob?

Answer 53

• Each branch of the motor neuron ends in an enlarged area called the Synaptic Knob.
• The Synaptic knob fits into a depression in the surface of the muscle fibre called the Motor End Plate.

Question 54

Why can’t nerve impulses be transmitted across a synaptic knob to the motor end plate?

Answer 54

This is because they do no actually touch. There is a small gap between them.

• Nerve impulses are unable to cross to cross this small gap so the neuron releases a chemical called a neurotransmitter that diffuses across the gap and stimulates the muscle fibre.
• Many substances can act as neurotransmitters but the one released at neuromuscular junctions is acetylcholine (ACH).

Question 55

What controls the skeletal muscles?

Answer 55

They are controlled by nerves that are part of the peripheral nervous system.

• They contract when they receive messages transmitted along motor neurons originating in the motor areas of the cerebral cortex.
• The axons of these motor neurons extend out to the muscles where each divides into branches that go to different muscle fibres. When a nerve impulse intiates the contraction of a skeleta muscle, it results in movement about a joint.

Question 56

The motor pathways that carry nerve impulses from the brain to the muscles are composed of 2 neurons:

Answer 56

1. Upper Motor Neuron, which has a cell body in the brain (or sometimes the spinal cord).
2. Lower Motor Neuron, which has a cell body in the grey matter of the spinal cord.

Question 57

Explain the relation of Involuntary Movement and the motor pathways.

Answer 57

• In the cases of voluntary muscle movement, the cell bodies of the upper motor neurons invovled are in the cerebrum.
• This is the region of the brain that controls concious actions.
• Involuntary muscle movement results from stimulation of upper motor neurons that have their cell bodies below the level of the cerebrum - in the cerebellum some other part of the brain or the spinal cord.

Question 58

Explain the relation of Voluntary Muscle Movement and the motor pathways.

Answer 58

• In the cases of voluntary muscle movement, the cell bodies of the upper motor neurons invovled are in the cerebrum.
• This is the region of the brain that controls concious actions.

Question 59

Explain the relation of Involuntary Muscle Movement and the motor pathways.

Answer 59

• Involuntary muscle movement results from stimulation of upper motor neurons that have their cell bodies below the level of the cerebrum - in the cerebellum some other part of the brain or the spinal cord.
• Such stimulation results in the coordination of muscle activity and is necessary for fine muscular movements and for posture and balance.

Question 60

What is the additional sensory input necessary for where Posture and Balance is concerned?

Answer 60

The balance receptors in the inner ear provide the cerebellum with information on the position of the head and body.

Question 61

What does the nerve fibres wrapped around a skeletal muscle fibres do?

Answer 61

They detect the extent of stretch that has occurred.

-This important sensory information is relayed via the spinal cord to the brain so that movement about the joint can be coordinated.

Question 62

Explain the process of walking across a room to pick up an object.

Answer 62

1. There would be the conscious thought necessary to begin walking.CEREBRUM.
2. Nerve impulses would then travel to the skeletal muscles of the legs and stimulate the neuromuscular junctions. Such stimulation would release Acetylcholine, which in turn would travel across the gap to bind to the receptors on the motor end plate.
3. This would result in further impulses that would causes the muscles to contract.
   - At the same time, antagonistic muscles would need to relax to allow movement about the joints of the lower limb.
   - While this was occurring, the inner ear would be providing the cerebellum with information about balance and movement; the cerebellum would be coordinating which muscles were to contract and the strength of the contraction for the necessary movement.
4. Impulses from the cerebellum transmitted along motor neurons result in the muscles achieving smooth, coordinated contractions as they pull on the bones to which they are attached.
5. Feedback to the brain from the stretch receptors provides information about the amount of muscle contraction taking place and the extent of movement at the joints.

Question 63

Give an example of when the Cerebellum appears to play an important role in enabling the body to stop at its intended spot.

Answer 63

This would be at the object we wished to pick up.

• The cerebellum has the ability to predict the position of a particular part of the body a few hundredths of a second in advance.
• Just before a moving body part reaches its planned point, impulses are sent from the cerebellum to slow that moving part and cause it to stop at the intended point.
• To allow this to happen, messages need to be sent to restrain the muscles causing the movement at the same time as impulses are being sent to stimulate the antagonistic muscles .

Question 64

List the steps of some of the sensory and motor nerve pathways involved in movement about a joint.

Answer 64

1. Initiation of Voluntary Muscle contraction by Cerebrum.
   - Upper motor neuron and Lower motor neuron. carry impulses to skeletal muscle.
2. Coordination by cerebellum.
   - Cerebellum sends impulses to Cerebellum, indicating which muscles are to contract and how strongly.
3. Input from balance receptors.
   - Inner ear detects movement and position of head (and body). Messages are

Question 65

List the steps of some of the sensory and motor nerve pathways involved in movement about a joint.

Answer 65

1. Initiation of Voluntary Muscle contraction by Cerebrum.
   - Upper motor neuron and Lower motor neuron. carry impulses to skeletal muscle.
2. Coordination by cerebellum.
   - Cerebellum sends impulses to Cerebellum, indicating which muscles are to contract and how strongly.
3. Input from balance receptors.
   - Inner ear detects movement and position of head (and body). Messages from inner ear give cerebellum information about balance and equilibrium.
4. Muscle Contraction.
   - Muscles from cerebellum achieve smooth, coordinated contraction. Upper and Lower motor neuron.
5. Feedback from Movement.
   - Stretch receptors in joint are stimulated.
   - Sensory neurons relay information to the Cerebrum, giving conscious awareness of the amount of joint movement and muscle contraction.