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INTS > INTS10 - Muscle Contraction, Bone Development and Disease/Injury > Flashcards

INTS10 - Muscle Contraction, Bone Development and Disease/Injury Flashcards

1
Q

What are the four main functions of the musculoskeletal system.

A

Movement. Posture. Stabilising joints. Heat.

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2
Q

Give structure of a muscle at each stage from macroscopic view to microscopic view.

A

Muscle - muscle fascicles - myofibres - myofibrils - myofilaments

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3
Q

Define myocytes.

A

Muscle cells.

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4
Q

Define multinucleate, with reference to muscle fibres.

A

Muscle fibres are multinucleate structures as they are composed of fused myocytes, therefore meaning there is no clear one nucleus per cell structure.

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5
Q

What makes up a muscle.

A

Muscle fibres, blood vessels, nerves and connective tissue.

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6
Q

If muscles are under voluntary control, which nervous system controls it.

A

Somatic nervous system.

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7
Q

How are bones and muscle attached.

A

By tendons,

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8
Q

Name the connective tissue surrounding muscles.

A

Epimysium.

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9
Q

Name the connective tissue surrounding muscle fascicles.

A

Perimysium.

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10
Q

Name the connective tissue surrounding muscle fibres.

A

Endomysium.

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11
Q

Define the sarcolemma.

A

Plasma membrane of the myofibres.

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12
Q

Define the sarcoplasm.

A

Cytoplasm of myocytes.

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13
Q

What are the two main structures present in myocytes, which aid its function of contraction.

A

Mitochondria - provide ATP for release of Ca2+ and cross bridge cycle of myosin-actin contraction.
Myoglobin - haemoglobin equivalent for myocytes with differing oxygen affinities ensuring oxygen supply is present for aerobic respiration and energy production.

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14
Q

Which structures are present around myofibres, and aid it’s functioning.

A

Blood capillaries surround the myofibres, ensuring that oxygen supply is constantly available.

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15
Q

What is the role of T tubules.

A

Transverse tubules go deep into the centre of myofibrils ensuring that action potentials can be propagated, along the entirety of the muscle fibre.

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16
Q

Define the sarcoplasmic reticulum.

A

A network of fluid filled tubules that are present in myocytes.

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17
Q

Link between sarcoplasmic reticulum and T-tubules.

A

T tubules are responsible for propagating an action potential along a myofibre and do so by communicating with the sarcoplasmic reticulum.

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18
Q

What are the five types of muscle contraction.

A

Eccentric. Concentric.

Isotonic. Isovelocity. Isometric.

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19
Q

What are the contractile units of muscles.

A

Myofibrils.

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20
Q

What are the two proteins that constitute myofibrils.

A

Actin and myosin.

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21
Q

Define and discuss striated appearance of muscle.

A

Striated means stripy - stripes can be observed in muscle. This is because the fibres are arranged into parallel overlapping arrays, giving the striated appearance.

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22
Q

Define a sarcomere.

A

Region between two protein Z discs.

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23
Q

Difference in appearance between actin and myosin.

A

Actin is the thin filament whereas myosin is the thick filament.

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24
Q

Define the I band.

A

Region on actin filaments only spread through the edges of two sarcomeres.

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25
Q

Define the A band.

A

Region constituting the myosin filaments (can include the actin crossover also) within one sarcomere.

26
Q

What is the name given to the middle of one sarcomere.

A

M-line.

27
Q

What is the H zone.

A

Area within a sarcomere that is just the myosin filaments (does not include region of overlap with actin filaments).

28
Q

Give the sequence of events /systems used for formation of a muscle contraction/ force power.

A

Information starts at brain and is relayed down the spinal cord through peripheral nerves. Signal reaches the neuromuscular junction and is propagated through muscle fibre membrane by the transverse tubule system. This results in the release of calcium ions which activate actin-myosin contractions, through the formation of cross bridges. This produces the force.

29
Q

Where does the term ‘sliding’ come from in the ‘sliding filament theory’.

A

Actin filaments within a sarcomere are thought to slide relative to the myosin filaments.

30
Q

Define the terms eccentric and concentric, relative to muscle contractions.

A

Concentric - shortens.

Eccentric - lengthens.

31
Q

Define the terms isotonic, isovelocity and isometric, relative to muscle contractions.

A

Isotonic - constant force with change in length.
Isometric - force produced with no change in muscle length.
Isovelocity - force with constant velocity, either lengthening or shortening

32
Q

Where are force signals for contractions, generated in the brain and what does this area constitute of.

A

Sensorimotor cortex. Consists of the pre and post central gyri, as well as the primary motor and sensory cortex.

33
Q

What is the pathway taken by information relayed by motor nerves, within the spinal cord.

A

Signals are related to the motor neurons in the ventral horn of the spinal cord, from the brain. Axons from the ventral horn exit the spinal cord near the ventral root, and join mixed spinal nerves and travel to all muscles around the body.

34
Q

How many axon terminals per myocyte.

A

Axons have many axon terminals each of which makes contact with a single myocyte, forming the neuromuscular junction.

35
Q

What is the neuromuscular junction.

A

Direct point of contact between the nervous system and the muscular system,

36
Q

Discuss full process of neurotransmitter release at the synaptic junction.

A

Action potential arrives at the pre-synaptic knob. At the unmyelinated axon tmerinal, this causes voltage gated calcium ion channels to open resulting in an influx of calcium ions into the pre-synaptic knob. This causes synaptic vesicles containing neurotransmitter to undergo exocytosis, releasing the neurotransmitter into the synaptic cleft. Neurotransmitter binds to receptor cation channels, which opens them. Local current flows between the non polarised end plate and adjacent membrane, propagating an action potential in the muscle fibre. When stimulus ceases, neurotransmitter gets broken down by respective enzyme, which ceases muscle contraction.

37
Q

Which neurotransmitter is found at the neuromuscular junction. What enzyme breaks it down.

A

Acetylcholine.

Acetylcholinesterase

38
Q

Discuss full process of muscle activation, following stimulation.

A

Action potential is propagated through T tubule network deep into the muscle fibres. Calcium ions are released from the sarcoplasmic reticulum. This results in the binding of troponin to the actin filaments. This causes a conformational change where tropomyosin moves to unblock the myosin binding site on actin. This allows myosin heads to bind to actin forming cross bridges. Release of calcium ions is continuous provided there is a stimulus. Calcium is actively pumped back into the sarcoplasmic reticulum whilst this occurs, to be re used.

39
Q

What is the role of tropomyosin.

A

Blocks the myosin binding site when muscle is relaxed, preventing cross bridge formation and so muscle contraction without a stimulus,

40
Q

What is the role of troponin.

A

Binds to tropomyosin helping to position the actin molecules. Binds to calcium ions to aid binding to the tropomyosin.

41
Q

Discuss structure of myosin protein.

A

Consists of two globular heads and a single tail. Several molecules wrap to form one large thick filament of myosin. Hence why myosin is the thick filament,

42
Q

Discuss structure of actin protein.

A

Molecules are twisted into a helix and contain troponin and tropomyosin proteins on surface.

43
Q

What is the thick and thin filament of a sarcomere.

A

Actin - thin.

Myosin - thick.

44
Q

Discuss full process of sliding filament theory.

A

Myosin head binds ATP and detaches from actin. ATP hydrolysed to ADP + Pi. Crossbridge is formed. Myosin head binds to actin. ADP + Pi released. Power stroke occurs where the actin filament slides relative to the myosin filament. Sarcomere shortens. Cycle repeats.

45
Q

Discuss full process for muscle relaxation.

A

Without a stimulus, action potential is now longer propagated along the muscle fibre. This prevents the release of calcium ions from the sarcoplasmic reticulum, therefore it cannot bind to troponin. This means that tropomyosin moves to block the myosin binding site, preventing the formation of cross bridges. This prevents any muscle contractions. Any remaining calcium ions are pumped back into the sarcoplasmic reticulum using the ATP driven pump.

46
Q

What does the force of a muscle contraction depend on.

A

Velocity and direction of contraction. Depends on proportion of cross bridges attached and force released by each respective cross bridge.

47
Q

Discuss the chemical composition of bones.

A

65% - calcium, magnesium, phosphorus, sodium.

35% organic - bone cells, protein matrix including type I collagen

48
Q

What are the two methods of bone formation.

A

Intramembranous ossification. Endochondral ossification.

49
Q

What processes complete the development of bone.

A

Growth plate fusion and ossification.

50
Q

Discuss process of intramembranous ossification as one method of bone formation.

A

Also referred to as direct bone formation. Results in formation of flat bones e.g. skull and ribs. Precursor cells directly differentiate from connective tissue to become osteoblasts - bone forming cells.

51
Q

What are osteoblasts and osteoclasts.

A

Osteoblasts - bone forming cells.

Osteoclasts - bone degrading cells.

52
Q

Give general overview of endochrondral ossification as method of bone formation.

A

Commonly forms long bones using a cartilage model. Precursor cells become chondroblasts - cartilage producing cells. Cartilage model of bone is produced. Blood vessels invade cartilage model brining osteogenic cells which transform cartilage into bone. Cartilaginous growth plate is present throughout growth between the various ossification centres. Various stages of bone formation throughout life.

53
Q

Discuss structure of a long bone.

A

Medullary cavity located in middle of large bones - contains bone marrow. Spongy/trabecular/cancellous bone present at ends.
Ends - epiphysis.
Para-mid - metaphysis.
Central - diaphysis.

54
Q

What is a chondroblast.

A

Cartilage producing cells.

55
Q

Discuss foetal stage of endochondral ossification.

A

Formation of initial cartilage model of the bone.

56
Q

Discuss new born baby stage of endochondral ossification.

A

Diaphysis of bone (middle region) is referred to as the bone shaft and is mainly bone. Epiphysis(ends of bone) are cartilage that will eventually calcify. Diaphysis arises from the primary ossification centre towards the centre of the bone.

57
Q

Discuss child stage of endochondral ossification.

A

Epiphysis at ends of bone contain secondary ossification centres from which bone can form. Cartilaginous growth plates are present between primary and secondary ossification centres, ensuring bone growth until specific mature length. Cartilage is calcified.

58
Q

Discuss adult stage of endochondral ossification.

A

Bone growth is finished by approx age 20. Bone shaft, cartilaginous growth the and epiphysis have all undergone ossification to form a continuous calcified bone.

59
Q

What hormonal factors influence bone growth.

A

Osteo-inductive mediators such as varying growth factors and cytokines,

60
Q

Discuss bone remodelling.

A

Bones are replaced every 10 years. Small regions of old or damaged bones are removed and replaced through bone remodelling. Osteoclasts remove bone. Osteoblasts build bone. Osteocytes form a mechanosensory network which is embedded within mature bone,

61
Q

Discuss action of various cells in bone during bone loss and bone growth.

A

Bone loss - osteoclasts action is greater than osteoblasts action.
Bone growth - osteoclasts action is less than osteoblasts action.

62
Q

Give examples of various musculoskeletal diseases.

A

Bone cancer, osteoporosis, osteoarthritis, myasthenia gravis. Muscular dystrophies

INTS (11 decks)

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