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Physiological Systems > Muscle > Flashcards

Muscle Flashcards

1
Q

How are skeletal muscles attached to bones?

A

Skeletal muscles are attached to bones via tendons. When the muscle contracts or relaxes, this leads to movement of the skeleton.

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2
Q

How do skeletal muscles work in pairs?

A

Skeletal muscles tend to act in pairs. For example, the biceps brachii and triceps brachii work together to flex or extend the elbow joint.

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3
Q

What is the smallest skeletal muscle in the body and where is it located?

A

The smallest skeletal muscle is the stapedius muscle, located in the inner ear. It stabilizes the stapes bone and is approximately 1 mm in size.

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4
Q

What is the longest skeletal muscle in the body and where is it located?

A

The longest skeletal muscle is the sartorius muscle, which is found in the thigh. It can be up to 30 cm long.

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5
Q

What are the main functions of skeletal muscle?

A

The main function of skeletal muscle is the movement of the skeleton. Additional functions include maintaining posture, supporting visceral organs, thermoregulation, and storing glycogen and triglycerides.

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6
Q

How is skeletal muscle contraction initiated?

A

Contraction of skeletal muscle occurs only following activation of the central nervous system.

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7
Q

What are the two levels at which the anatomy of skeletal muscle can be considered?

A

The anatomy of skeletal muscle can be considered at the organ level or cellular level.

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8
Q

What is the epimysium?

A

The epimysium is a layer of connective tissue that binds large numbers of skeletal muscle cells together at the organ level.

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9
Q

What type of supply do skeletal muscles have?

A

Skeletal muscles have a rich nerve and blood supply.

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10
Q

What are fascicles?

A

Fascicles are small bundles of skeletal muscle cells grouped together within a layer of connective tissue called the perimysium.

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11
Q

What is the endomysium?

A

The endomysium is a layer of connective tissue that encases each individual skeletal muscle cell within a fascicle.

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12
Q

What are skeletal muscle fibres?

A

Skeletal muscle fibres are skeletal muscle cells. They are different from other cells, and their diameter can be up to 100 μm.

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13
Q

What is the shape and nucleus position of a stereotypical skeletal muscle cell?

A

A stereotypical skeletal muscle cell is round and has a single nucleus situated in the middle of the cell.

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14
Q

What is the structure and size of skeletal muscle fibres?

A

Skeletal muscle fibres are cylindrical and can extend the entire length of the skeletal muscle, up to 30 cm.
They are multinucleated, with nuclei located on the periphery of the cell.

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15
Q

Why is the presence of mitochondria in skeletal muscle fibres significant?

A

Skeletal muscle fibres have an abundance of mitochondria, which is beneficial as it allows for a high degree of oxidative metabolism to occur within the cell.

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16
Q

What is the role of myosatellite cells in skeletal muscle fibres?

A

Myosatellite cells ensure that when the skeletal muscle is damaged, the cell can repair itself.
This repair process helps fix microscopic tears in the fibres caused by resistance exercise after the exercise is terminated.

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17
Q

What happens to skeletal muscle during hypertrophy?

A

During hypertrophy, the skeletal muscle fibre increases in size due to supercompensation of wear and tear.
This results in an increase in the cross-sectional area of the organ and a consequent increase in muscle strength.

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18
Q

What is observed when a biopsy of skeletal muscle is taken and examined?

A

A regular pattern of light and dark bands can be seen running along the length of each muscle fibre.
This striated appearance is due to the arrangement of thin and thick proteins in the cytoplasm of the muscle fibre.

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19
Q

What is a myofibril, and how large is it?

A

A myofibril is the structural component of the skeletal muscle fiber. It is approximately 1–2 µm in diameter.

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20
Q

What are the proteins found in a myofibril, and what are their functions?

A

The thin proteins in a myofibril are called actin filaments, and the thick proteins are called myosin filaments.
These proteins are responsible for muscle contraction.

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21
Q

What are the light and dark bands in skeletal muscle called?

A

The light band is called the I band, and the dark band is called the A band.

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22
Q

What surrounds each myofibril in skeletal muscle, and what is its significance?

A

Each myofibril is surrounded by the sarcoplasmic reticulum, which is a rich source of calcium and plays a key role in muscle contraction.

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23
Q

What are transverse tubules (t-tubules) in skeletal muscle?

A

T-tubules are invaginations of the plasma membrane (sarcolemma) into the muscle fibre, filled with extracellular fluid, and help conduct action potentials.

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24
Q

What is a sarcomere, and how are proteins arranged within it?

A

A sarcomere is a structural unit of a myofibril, with thick and thin proteins arranged in a parallel manner.

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25
Q

How many sarcomeres can be present per myofibril, and what is their typical length?

A

Up to 10,000 sarcomeres per myofibril, each approximately 2μm in length.

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26
Q

What defines the length of a sarcomere?

A

The length is the distance between two Z lines.

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27
Q

What are the Z line and the M line in a sarcomere?

A

The Z line is at the midpoint of the I band, and the M line is at the midpoint of the A band.

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28
Q

What is the H zone in a sarcomere?

A

The H zone is the area containing only myosin filaments.

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29
Q

What distinguishes actin filaments from myosin filaments?

A

Actin filaments are smaller in molecular weight, while myosin filaments are larger.

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30
Q

What are the two sections of myosin proteins?

A

Myosin proteins consist of a tail and a head. The heads bind to actin during muscle contraction.

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31
Q

What happens during isotonic contraction?

A

The Z lines move closer together, reducing the lengths of the H zone and I band, while the A band remains unchanged.

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32
Q

What mechanism explains muscle contraction?

A

The sliding-filament mechanism explains muscle contraction, where actin and myosin interact.

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33
Q

What are cross-bridges in the sliding-filament mechanism?

A

Cross-bridges form when myosin heads attach to actin, facilitating contraction.

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34
Q

What enzyme is involved in the cross-bridge cycle?

A

The enzyme ATPase, which hydrolyses ATP to provide energy for muscle contraction.

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35
Q

Where is the actin-binding site located?

A

It is located on the myosin head.

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36
Q

What is the first step that occurs in skeletal muscle contraction following innervation?

A

The myosin head attaches to actin, initiating a process called cross-bridge cycling.

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37
Q

What are the four steps involved in cross-bridge cycling?

A
  • Attachment of myosin to actin.
  • Movement of the cross-bridge.
  • Detachment from actin.
  • Hydrolysis of ATP.
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38
Q

When does cross-bridge cycling stop?

A

The process continues until the muscle relaxes.

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39
Q

How does skeletal muscle relaxation differ from smooth muscle relaxation?

A

In skeletal muscles, myosin heads remain phosphorylated upon relaxation.

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40
Q

What regulates skeletal muscle contraction?

A

The availability of actin filaments rather than myosin filaments.

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41
Q

What two additional proteins are crucial in regulating skeletal muscle contraction?

A

Troponin
Tropomyosin

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42
Q

What is tropomyosin, and where is it located when the skeletal muscle is relaxed?

A

Tropomyosin is a long protein extending along the length of the actin filament. When the muscle is relaxed, it covers the binding sites where myosin heads attach.

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43
Q

What happens to tropomyosin during contraction?

A

Tropomyosin moves away from the actin binding sites, allowing cross-bridge cycling to occur.

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44
Q

What is troponin, and what is its role in muscle contraction?

A

Troponin is a small protein bound to both actin and tropomyosin. It undergoes a conformational change in response to calcium ions (Ca²⁺), which moves tropomyosin away from the binding sites.

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45
Q

What is the role of calcium ions (Ca²⁺) in muscle contraction?

A

Calcium ions bind to troponin, triggering a shape change that removes tropomyosin from actin binding sites, enabling myosin head attachment.

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46
Q

What role does calcium play in skeletal muscle regulation?

A

Calcium is key in skeletal muscle regulation. Following electrical stimulation, calcium moves into the cytosol, binds to troponin, causing conformational changes, and enables myosin attachment.

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47
Q

What is the term for the process of increasing cytosolic calcium concentration?

A

The process is called excitation-contraction coupling.

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48
Q

What is the primary source of calcium in skeletal muscles

A

The sarcoplasmic reticulum

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49
Q

What is a motor neuron, and what is its function?

A

A motor neuron is a specialized nerve cell with a myelinated sheath that innervates a single skeletal muscle fiber. Myelination allows rapid propagation of electrical potentials.

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50
Q

What is a motor unit?

A

A motor unit includes a motor neuron and the skeletal muscle fibers it innervates. One motor neuron can innervate multiple fibers, but a single skeletal muscle fiber is innervated by only one motor neuron.

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51
Q

What is the motor endplate, and what is its function?

A

The motor endplate is the region of a muscle fiber directly under the axon terminal. It ensures the action potential is propagated along the muscle fiber membrane.

52
Q

How is an action potential generated and propagated in skeletal muscle?

A

The action potential starts in the axon of the motor neuron, travels to the axon terminal, and causes acetylcholine release, leading to depolarization of the motor endplate and propagation along the sarcolemma.

53
Q

What happens when an action potential reaches the axon terminal of a motor neuron?

A

Calcium influx at the terminal triggers acetylcholine release, which binds to receptors on the motor endplate, generating a new action potential in the muscle.

54
Q

What is the role of acetylcholinesterase in muscle contraction?

A

Acetylcholinesterase cleaves acetylcholine from nicotinic receptors, ensuring plasma membrane repolarization for subsequent muscle contractions.

55
Q

What are the two types of skeletal muscle contraction?

A

Skeletal muscle contraction can be described as:

1) Isometric contraction: Force is produced by the muscle, but there is no change in muscle length.
2) Isotonic contraction: Involves changes in muscle length and includes:
- Concentric contractions: Muscle fibers shorten.
- Eccentric contractions: Muscle fibers lengthen.

56
Q

When does isometric contraction occur?

A

Isometric contraction occurs when:

  • The maximum force capacity of a muscle is exceeded, producing high force but no change in muscle length.
  • A muscle is unable to move a weight it is applied to.
57
Q

Can isometric contractions occur during activities other than maximum voluntary contraction?

A

Yes, isometric contractions can occur in everyday activities, such as carrying a bag. Force is produced to hold the bag, but there is no change in muscle length.

58
Q

What are the factors affecting skeletal muscle force production?

A

The factors include:

1) Number of cross-bridges formed:
Force depends on the number of cross-bridges between actin and myosin.
2) Length-tension relationship:
There is an optimal overlap between actin and myosin for maximum force production.
If the sarcomere length increases or decreases excessively, fewer cross-bridges form, reducing force production.
3) Force-velocity curve:
Describes the relationship between the velocity of muscle contraction and force production.
Maximum force occurs during isometric contraction.

59
Q

What happens when the sarcomere length increases or decreases excessively?

A
  • If the sarcomere length increases: Fewer cross-bridges form, and force production decreases.
  • If the sarcomere length decreases: Excessive overlap between actin and myosin reduces the number of cross-bridges, lowering force production.
60
Q

How does the force-velocity curve relate to muscle contraction?

A

The force-velocity curve outlines how the velocity of muscle contraction affects force production:

Maximum force production occurs during isometric contraction, where the velocity of contraction is zero.

61
Q

What are the types of muscle contraction

A
  • Concentric Contraction: Biceps shorten during activation.
  • Isometric Contraction: Biceps length remains constant during activation.
  • Eccentric Contraction : Biceps lengthen during activation.
62
Q

What is the length–tension relationship in muscles

A
  • Excessive overlap of actin and myosin reduces force production.
  • Optimum overlap of actin and myosin produces maximum force.
  • Excessive stretching reduces force due to fewer cross-bridge interactions.
63
Q

What does the force–velocity relationship describe

A
  • At zero velocity (isometric contraction), maximum force is generated.
  • As velocity of shortening increases, force decreases because fewer cross-bridges can form.
  • Maximum power occurs at approximately one-third of the velocity of shortening.
64
Q

What is muscle power, and when is it maximized?

A
  • Power is the product of force and velocity.
  • Maximum power production occurs at approximately one-third of the velocity of shortening.
65
Q

How many muscle fiber types are commonly debated, and what are the most agreed upon?

A

There is debate about the number of muscle fiber types, but the most agreed-upon are:

Type I (slow-twitch)
Type 2a (fast-twitch, oxidative)
Type 2b (fast-twitch, glycolytic)

66
Q

What are the characteristics of Type I (slow-twitch) muscle fibers?

A
  • Small diameter with high density of mitochondria.
  • Rich blood supply with many capillaries.
  • Low fatigue levels, suited for aerobic activities.
67
Q

What are the characteristics of type 2b (fast-twitch) muscle fibers?

A

Type 2b fibers have a relatively large diameter, few mitochondria, and relatively few capillaries.
They store large amounts of glycogen, are highly fatigable, and are best suited to anaerobic activity.

68
Q

How do type 2a (intermediate) muscle fibers differ from type 2b fibers?

A

Type 2a fibers combine properties of type 1 and type 2b fibers. They have a smaller number of type 2a fibers in skeletal muscles, and evidence suggests they can be trained to become more like type 1 fibers or more like type 2 fibers.

69
Q

What is the general composition of skeletal muscles in terms of fiber types?

A

Every skeletal muscle has a proportion of type 1 and type 2 fibers. Muscles used for endurance, like postural muscles, have predominantly type 1 fibers, while others vary significantly between individuals.

70
Q

Give an example of a muscle with a varied proportion of fiber types.

A

The vastus lateralis muscle may consist predominantly of either type 1 or type 2 fibers, depending on genetic and activity-related factors.

71
Q

How does the distribution of muscle fiber types affect exercise suitability?

A

The distribution of fiber types influences whether a person is better suited for endurance activities (type 1 fibers) or power-based activities (type 2 fibers), and this distribution appears to be genetically determined.

72
Q

How does smooth muscle contraction differ from skeletal muscle contraction?

A

Smooth muscle contraction is not under voluntary control, and its innervation involves three different ways that do not include voluntary mechanisms.

73
Q

What role does smooth muscle play in the body?

A

Smooth muscle plays a vital role in all body systems by enabling actions such as changes in blood flow, airflow, and gastrointestinal motility.

74
Q

Where are layers of smooth muscle found, and what is their function in blood vessels?

A

Layers of smooth muscle are found in the tunica media of blood vessels. Their contraction or relaxation changes the vessel’s diameter, affecting blood flow.

75
Q

How does smooth muscle function in the respiratory system?

A

Smooth muscle surrounds terminal bronchioles. Contraction decreases the diameter of the bronchioles, reducing airflow, while relaxation increases airflow.

76
Q

What causes asthma attacks related to smooth muscle?

A

Asthma attacks occur due to the contraction of bronchial smooth muscle, which reduces airway diameter and airflow.

77
Q

How is smooth muscle involved in the integumentary system?

A

Smooth muscle is present in the arrector pili muscle. When it contracts in response to cold, it causes hair to stand on end (goosebumps).

78
Q

What is the role of smooth muscle in the gastrointestinal system?

A

Smooth muscle surrounds the stomach and intestines, enabling the movement of food through relaxation (increasing stomach volume) and contraction (peristalsis).

79
Q

How does the shape of smooth muscle differ from skeletal muscle?

A

Unlike skeletal muscle, smooth muscle is not cylindrical and appears as sheets stacked on top of each other without a specific arrangement.

80
Q

What are the dimensions of smooth muscle fibers?

A

Smooth muscle fibers are relatively short, with lengths up to 200 µm and diameters of up to 10 µm.

81
Q

How does the nucleus of smooth muscle differ from skeletal muscle?

A

Smooth muscle fibers have a single nucleus located in the middle of each cell, unlike the multinucleated skeletal muscle fibers.

82
Q

Why is smooth muscle referred to as “smooth”?

A

It is called smooth because it lacks visible striations, which are present in skeletal muscle due to the arrangement of actin and myosin.

83
Q

Do smooth muscles have sarcomeres?

A

No, smooth muscles lack sarcomeres, which are present in skeletal muscles and contribute to their striated appearance.

84
Q

How are actin and myosin filaments arranged in smooth muscle?

A

Actin and myosin filaments in smooth muscle have no regular arrangement and are found at oblique angles, leading to contraction in multiple dimensions.

85
Q

What structural feature replaces Z lines in smooth muscle?

A

Smooth muscle has dense bodies instead of Z lines. Dense bodies anchor actin filaments and serve a similar function to Z lines in skeletal muscle.

86
Q

What special connections exist between smooth muscle cells?

A

Smooth muscle fibers have gap junctions, allowing ion movement between cells for coordinated contraction.

87
Q

What is the role of the sarcoplasmic reticulum in smooth muscle?

A

Smooth muscle contains sarcoplasmic reticulum, but it is less abundant than in skeletal muscle and not arranged in any specific manner.

88
Q

How does smooth muscle contract?

A

Smooth muscle contracts through the interaction of actin and myosin, forming cross-bridges and utilizing a sliding-filament mechanism similar to skeletal muscle.

89
Q

How does the strength of smooth muscle contraction compare to skeletal muscle?

A

Smooth muscle contractions can be just as powerful as skeletal muscle contractions but take longer to reach maximal force due to the slower activity of the enzyme that hydrolyzes ATP.

90
Q

How is the regulation of smooth muscle contraction different from skeletal muscle?

A

Smooth muscle does not have troponin; its regulation depends on the interaction between actin and myosin, but the process is controlled differently, involving calmodulin instead of troponin.

91
Q

What triggers excitation-contraction coupling in smooth muscle?

A

Excitation-contraction coupling begins with an increase in cytosolic calcium as a result of an action potential and the phosphorylation of myosin heads.

92
Q

What happens to calcium during smooth muscle contraction?

A

Calcium enters the cytosol, binds to calmodulin, and forms a calcium-calmodulin complex, which activates myosin light chain kinase.

93
Q

What is the purpose of excitation-contraction coupling in smooth muscle?

A

Its purpose is to phosphorylate the myosin head, allowing myosin to bind to actin and initiate contraction.

94
Q

What is calmodulin, and how does it function in smooth muscle?

A

Calmodulin is a protein similar to troponin found in skeletal muscle. It binds calcium to regulate contraction by forming a calcium-calmodulin complex.

95
Q

What activates myosin light chain kinase in smooth muscle?

A

The calcium–calmodulin complex activates myosin light chain kinase.

96
Q

What role does myosin light chain kinase play in smooth muscle contraction?

A

It assists in the hydrolysis of ATP, leading to phosphorylation of the myosin head, enabling cross-bridge cycling.

97
Q

What happens to the myosin head during smooth muscle relaxation?

A

The myosin head becomes dephosphorylated.

98
Q

What is the main source of calcium in smooth muscle for excitation-contraction coupling?

A

The extracellular fluid provides most of the calcium, as the sarcoplasmic reticulum in smooth muscle is poorly developed.

99
Q

How does the range of lengths in smooth muscle fibers compare to skeletal muscle fibers?

A

Smooth muscle fibers exhibit a greater range of lengths than skeletal muscle fibers.

100
Q

What is the purpose of smooth muscle innervation?

A

To increase cytosolic calcium concentration for contraction.

101
Q

What are the three main mechanisms of smooth muscle innervation?

A

The autonomic nervous system, pacemaker potentials, and local factors.

102
Q

What type of receptors are found on the sarcolemma of smooth muscle fibers?

A

Receptors for neurotransmitters secreted by varicosities of autonomic neurons.

103
Q

How does neurotransmitter activation in smooth muscle differ from skeletal muscle?

A

Neurotransmitter activation in smooth muscle can cause either contraction or relaxation, unlike skeletal muscle, which contracts only.

104
Q

What neurotransmitters are most commonly associated with smooth muscle activity?

A

Acetylcholine (parasympathetic) and noradrenaline (sympathetic).

105
Q

What determines whether smooth muscle contracts or relaxes in response to neurotransmitters?

A

The type of receptor, not the neurotransmitter itself.

106
Q

How does noradrenaline affect smooth muscle when it binds to alpha-adrenergic receptors?

A

It increases cytosolic calcium concentration, causing contraction.

107
Q

How does noradrenaline affect smooth muscle when it binds to beta-adrenergic receptors?

A

It reduces cytosolic calcium concentration, causing relaxation.

108
Q

What are pacemaker potentials in smooth muscle fibers?

A

Gradual increases in resting membrane potential caused by ion movement, which can lead to an action potential once the threshold is reached.

109
Q

How do gap junctions contribute to smooth muscle activity?

A

They allow for the spread of action potentials between smooth muscle fibers, enabling coordinated contractions.

110
Q

Where is cardiac muscle found?

A

Cardiac muscle is found exclusively in the myocardial layer of the heart.

111
Q

What is the primary function of cardiac muscle contraction?

A

Cardiac muscle contraction increases pressure within the heart, leading to the movement of blood through the chambers of the heart and into the pulmonary or systemic circulations.

112
Q

What are the characteristics of cardiac muscle fibers in terms of size?

A

Cardiac muscle fibers are relatively short, with a length up to 100 μm and a diameter up to 20 μm.

113
Q

Are cardiac muscle fibers mono- or multi-nucleated?

A

Cardiac muscle fibers are mononucleated, with the nucleus located in the middle of the cell.

114
Q

How are cardiac muscle fibers connected for action potential transfer?

A

Cardiac muscle fibers branch and contain gap junctions for the transfer of action potentials.

115
Q

Why is cardiac muscle classified as striated?

A

Cardiac muscle is classified as striated due to the existence of myofibrils and sarcomeres.

116
Q

What structural feature do cardiac muscle fibers share with skeletal muscle?

A

Cardiac muscle fibers have T-tubules for the propagation of action potentials, similar to skeletal muscle.

117
Q

Describe the sarcoplasmic reticulum in cardiac muscle.

A

Cardiac muscle has a reasonably well-developed sarcoplasmic reticulum. It is more developed than in smooth muscle but less so than in skeletal muscle.

118
Q

What mechanism underlies cardiac muscle contraction?

A

Cardiac muscle contraction occurs via a sliding-filament mechanism, similar to skeletal and smooth muscle, due to the presence of actin and myosin in sarcomeres.

119
Q

How is the regulation of cardiac muscle contraction similar to skeletal muscle?

A

It involves the interaction between troponin, tropomyosin, and actin

120
Q

What is the purpose of excitation-contraction coupling in cardiac muscle?

A

It increases cytosolic calcium concentration, similar to other muscle types.

121
Q

How is the sarcoplasmic reticulum in cardiac muscle fibers different from skeletal muscle?

A

It is less developed in cardiac muscle fibers, so calcium is also derived from extracellular fluid.

122
Q

What happens to calcium during the excitation of cardiac muscle?

A

Following an action potential, calcium is moved from extracellular fluid into the muscle fiber and binds to troponin, enabling cross-bridge cycling.

123
Q

How does calcium contribute to cardiac muscle contraction after entering the sarcoplasmic reticulum?

A

It causes more calcium to be released into the cytosol, enhancing excitation-contraction coupling.

124
Q

Where does the innervation of cardiac muscle fibers originate?

A

From the conduction system of the heart.

125
Q

What role does the sinoatrial node play in cardiac muscle contraction?

A

Pacemaker potentials are generated there and propagated through the conduction system to cardiac muscle fibers, increasing cytosolic calcium and contraction.

Physiological Systems (8 decks)

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