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Tissues > Tissues 7- Muscles > Flashcards

Tissues 7- Muscles Flashcards

1
Q

What are muscles

A

Specialised cells that are responsible for movement through the generation of force.

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2
Q

What is skeletal muscle

A

Attached to bone and produces movement of the body relative to the external environment. Connect to bones in the arms, legs and spine. Used in complex coordinated activities.

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3
Q

What is the role of cardiac muscle

A

To pump blood around the body through the blood vessels.

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4
Q

Where is smooth muscle found and what is its function

A

Exists within the lining of hollow organs (blood vessels, gastrointestinal tract)- provided propulsion to move substances within the body.

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5
Q

Is the mechanism through which force is generated similar or different in each of the three different types of muscle

A

Similar

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6
Q

What do antagonistic muscle pairs consist of

A

A flexor and extensor

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7
Q

What are the two types of muscle contraction

A

Isotonic contraction: muscle changes length  tension remains the same
Concentric: shortening
Eccentric: lengthening
Isometric contraction: tension develops  muscle does NOT change length

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8
Q

What is an example of isometric contraction

A

Holding shopping bags- arm stays straight- but the muscle cells are still contracting.

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9
Q

What does skeletal muscle consist of

A

Skeletal muscle  bundle of muscle cells known as myofibres

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10
Q

Describe the characteristics of myofibres

A

Large & Cylindrical
Multinucleate
Packed with myofibrils

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11
Q

Describe the myofibrils

A

Extend across the length of the cell, they can be further divided into light and dark bands giving them a striated appearance. Sarcomeres are also present within the myofibril.

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12
Q

What is the sarcomere

A

The functional unit of the muscle, lies between two Z lines. It has a particular arrangement of myosin and actin. During contraction, it can become 30% shorter than its original length.

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13
Q

What is the Z-line

A

Defines the lateral boundaries of the sarcomere

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14
Q

Describe the arrangement of actin within the sarcomere

A

Polymeric thin filament composed of two twisted -helices - displays polarity
Along with another rope-like protein called tropomyosin, forms a chain around the actin filament, also associated with troponin. Actin is not found in middle

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15
Q

What is nebulin

A

Large filaments associated with actin

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16
Q

Describe the arrangement of myosin in the sarcomere

A

Found in the centre of the sarcomere

Thick filaments  ‘motor proteins’. Contain numerous ‘globular heads’ that interact with actin

17
Q

What is the role of titin within the sarcomere

A

Very large ‘spring-like’ filaments anchoring myosin to the Z-line.

18
Q

What is the role of CapZ and tropomodulin

A

Cap actin at certain points
CapZ at the Z-line
Tropomodulin- at centre

19
Q

Describe two properties of myofibres that play a major role in excitation-contraction coupling in skeletal cells

A 
T-tubules: Membrane invaginations that contact the extracellular fluid
Sarcoplasmic reticulum (SR): extensive network of Ca2+-stores surrounding each myofibril
20
Q

Ultimately, what is muscle contraction caused by

A

An increase in cytosolic Ca2+ concentration. Skeletal muscle cells maintain a low cytosolic Ca2+ concentration due to the actions of Ca2+ ATPase, that continually pumps Ca2+ from the cytosol into the sarcoplasmic reticulum.

21
Q

Describe the excitation of a myofibril

A 
Action potential (AP) propagates along myofibre membrane (sarcolemma) & T-tubules
Depolarisation activates dihydropyridine  receptors (DHPR)  conformational change in DHPR- contacts RyR.
This change is transmitted to ryanodine receptors (RyR) on SR  opening of RyR & Ca2+ release from intracellular stores 
Thus depolarisation  Increase in intracellular Ca2+
22
Q

Describe the sliding-filament model of muscle contraction

A

In the presence of Ca2+ movement of troponin from tropomyosin chain
Movement exposes myosin binding site on surface of actin chain
‘Charged’ myosin heads bind to exposed site on actin filament
This binding & discharge of ADP causes myosin head to pivot (the ‘power stroke’)  pulling actin filament towards centre of sarcomere- inward movement
ATP binding  releases myosin head from actin chain
ATP hydrolysis  provides energy to ‘recharge’ the myosin head- allows myosin head to bind to a different point on the actin filament.

23
Q

What information lead to the development of the sliding-filament model of contraction

A

The fact that thick and thin filaments do not change in length when the sarcomere shortens.

24
Q

Describe the tension-load relationship in isotonic contraction

A 
Muscle tension  force exerted by load
Muscle contracts  fibres shortens
Energy expenditure (ATP)  ‘recharging’ of myosin heads
25
Q

Describe the tension-load relationship in isometric contraction

A 
Muscle tension = force exerted by the load
Muscle DOES NOT contract  myosin heads reattach to the same point on actin chain
Energy expenditure (ATP)  ‘recharging’ of myosin heads
26
Q

What does the contraction of the whole muscle result from

A

The activity of hundreds of myosin heads on a thick filament interacting with the actin filament. This is amplified by the hundreds of thick filaments in a sarcomere and thousands of sarcomeres in a muscle fibre.

27
Q

What does the myocardium consist of

A

The wall of the heart is primarily made up of cardiac muscle cells, but also contains pacemaker cells and conducting fibres.

28
Q

Describe the pacemaker cells

A

The pacemaker cells are stored within the SA and AVN and they are excitable cells that depolarise and generate action potentials in a regular rhythmic pattern. Their discharge rate determines the heart rate- the action potential spreads from the pacemaker cells to the cardiomyocytes,

29
Q

Describe the differences between the SAN and the AVN

A

Sinoatrial (SA) node: small, ‘empty’, spindle shaped cells, spontaneously active- found at the top of the right atrium.
Atrioventricular (AV) node: spindle-shaped network of cells located at base of right atrium

30
Q

Describe the conducting fibres

A

Bundle of His: fast conducting cells adjoining the AV node & Purkinje fibres
Purkinje fibres: large cells that rapidly conduct electrical impulses- travel to the apex to stimulate contraction of the heart.

31
Q

What is the appearance of cardiomyocytes

A

They are striated muscle cells. They are also unicellular

32
Q

How are individual cardiomyocytes connected to each other, and what is the importance of this

A

Individual cardiomyocytes are connected to each other at specialised regions called intercalated disk- where many gap junctions allow action potentials to spread rapidly from cell to cell- essential for synchronous contraction of the heart.

33
Q

What is meant by striated muscle

A

The muscle contains a regular arrangement of actin and myosin.

34
Q

Describe the excitation of cardiomyocytes

A

Action potential propagates along the cardiomyocyte membrane and the T-tubules.
Depolarisation opens VGCCs- Ca2+ influx
Ca2+ induced Ca2+ release by binding of Ca2+ ions to RyR receptors on the SR
Further release of Ca2+ ions
Binds to troponin
Further depolarisation

35
Q

Why does smooth muscle appear smooth

A

No regular arrangement of actin and myosin.

36
Q

What is the consequence of smooth muscle not containing VGSCs on the speed of muscle contraction

A

Hence smooth muscle action potential is entirely dependent on depolarisation resulting from Ca2+ entering through VGCCs- hence the process of muscle contraction is a slower affair.

37
Q

Describe the process of excitation in smooth muscle

A

Depolarisation activates VGCCs- influx of calcium ions into cells
Calcium ions bind to intracellular protein CaM- calmodulin- forming a complex.
Ca2+-CaM complex activates the myosin light chain kinase
MLCK phosphorylates the myosin light chain allowing them to form cross-bridges with actin filaments, resulting in contraction.

Tissues (12 decks)

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