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MSK PHYSO Flashcards

1
Q

What is the role of ACh in muscle cell excitation?

A

ACh (acetylcholine) is released by motor neurons to stimulate the muscle cell, initiating a change in membrane potential.

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2
Q

How do changes in membrane potential relate to muscle contraction?

A

Changes in membrane potential lead to the development of action potentials, which ultimately force the muscle to shorten or contract.

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3
Q

What does it mean for a muscle to be “excitable”?

A

“Excitable” means that muscles can respond to nerve signals and initiate action potentials.

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4
Q

Explain the contractile nature of muscles.

A

Muscles are contractile because they can forcibly shorten in response to nerve stimulation.

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5
Q

Describe the concepts of muscle extensibility and elasticity.

A

Muscle extensibility refers to the ability of muscles to stretch beyond their normal resting length, and muscle elasticity enables them to return to their resting length after stretching.

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6
Q

How do muscles contribute to producing movement?

A

Muscles contribute to producing movement by contracting together to move the skeleton.

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7
Q

Why is muscle stabilization important for maintaining posture?

A

Muscle stabilization is crucial for maintaining posture against the force of gravity.

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8
Q

How do muscles wrap around joints to stabilize them?

A

Muscles stabilize joints by wrapping around them, providing support and preventing excessive joint movement.

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9
Q

What is the relationship between cellular respiration and heat generation in muscles?

A

Heat generation in muscles is a byproduct of cellular respiration, with energy released in the form of heat.

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10
Q

What is the purpose of shivering in relation to muscle function?

A

Shivering involves quivering contractions of muscles, generating heat as a response to cold temperatures.

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11
Q

Describe the characteristics of the epimysium.

A

The epimysium is a tough, dense, fibrous, irregular connective tissue that forms the outermost layer of muscle tissue covering.

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12
Q

What is the role of fascicles within a muscle?

A

Fascicles are bundles of muscle fibers found within the muscle belly.

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13
Q

Explain the function of the perimysium and its relationship to the epimysium.

A

The perimysium is a dense, fibrous, irregular connective tissue that covers groups of fascicles and is a direct continuation of the epimysium.

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14
Q

How are individual muscle cells organized within fascicle bundles?

A

Muscle fibers (cells) make up the fascicle bundles within a muscle.

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15
Q

What is the composition of the endomysium, and what does it cover?

A

The endomysium is made up of areolar connective tissue and covers the plasma membrane (sarcolemma) of individual muscle cells within a fascicle.

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16
Q

Describe the characteristics of tendons.

A

Tendons are rope-like connective tissues rich in collagen, connecting muscles to bones.

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17
Q

How does aponeurosis differ from tendons in connecting muscles to bones?

A

Aponeurosis is a sheet-like connective tissue that also connects muscles to bones.

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18
Q

During a muscle contraction, what is the “origin” of the bone, and what is the “insertion”?

A

. During a muscle contraction, the “origin” refers to the part of the bone that remains stationary, while the “insertion” is the part of the bone that moves. Tendons connect muscles to the bones at these respective points.

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19
Q

How is a tendon involved in connecting muscles to bones during movement?

A

Tendons play a critical role in connecting muscles to bones, allowing muscle contractions to move bones and perform various movements.

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20
Q

What do connective tissue sheaths contribute to?

A

Connective tissue sheaths contribute to elasticity.

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21
Q

How do connective tissue sheaths affect muscle elasticity?

A

Connective tissue sheaths enhance muscle elasticity.

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22
Q

What runs through the connective tissue sheaths in muscles?

A

Blood vessels and nerve fibers run through the connective tissue sheaths in muscles.

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23
Q

How do muscles connect to bones, and what are the two main types of connections described?

A

Muscles can connect to bones directly via the epimysium, periosteum, or perichondrium, or indirectly through tendons.

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24
Q
  1. What is the role of the sarcoplasmic reticulum in muscle fibers?
A

The sarcoplasmic reticulum serves as a calcium storage and release system within muscle fibers.

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25
Q

Describe the appearance and characteristics of skeletal muscle fibers.

A

Skeletal muscle fibers are cylindrical, multinucleated, and excitable, contractile , exnsible and elastic

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26
Q

Which of the following is NOT a characteristic of muscle: elasticity, contractility, excitable, or porous?

A
  1. d. Porous
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27
Q

True or False: Direct connections of muscle to bone are more common in the human body than indirect connections.

A

b. False

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28
Q

True or False: The origin of the muscle always moves toward the insertion of the same muscle during a muscle contraction.

A

b. False

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29
Q

What is the term for the outermost layer of connective tissue that covers a muscle?

A

c. Epimysium

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30
Q

What is the name of the rope-like connective tissue that helps connect muscles to bones?

A

b. Tendon

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31
Q

What is the outer covering of the muscle belly called, and what is it made of?

A

The outer covering of the muscle belly is called the epimysium, and it is made of dense fibrous irregular connective tissues.

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32
Q

What structures are found within the muscle belly?

A

Within the muscle belly, there are numerous fascicles.

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33
Q

Describe the composition and function of fascicles.

A

Fascicles are bundles of muscle fibers.

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34
Q

What covers the fascicles, and what is its composition?

A

Fascicles are covered by the perimysium, which is made of dense fibrous irregular connective tissues.

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35
Q

What makes up the structure of muscle fibers?

A

Muscle fibers are covered by the endomysium, which is made of areolar connective tissues.

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36
Q

What is the function of the endomysium, and what is its composition?

A

The endomysium’s function is to provide support and protection to individual muscle fibers.

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37
Q

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

A

The sarcoplasmic reticulum is the calcium storage factory within muscle fibers.

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38
Q

What is the striated appearance of muscle fibers due to?

A

The striated appearance of muscle fibers is due to the arrangement of myofibrils and sarcomeres.

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39
Q

What is a sarcomere and how does it relate to muscle fibers?

A

A sarcomere is the structural and functional unit of a muscle fiber, and it represents the connection between thin and thick fibers.

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40
Q

How would you describe the shape of muscle fibers?

A

Muscle fibers have a cylindrical shape.

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41
Q

What surrounds each muscle fiber, and what is its name?

A

Each muscle fiber is surrounded by a plasma membrane called the sarcolemma.

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42
Q

What composes myofibrils, and where are they found?

A

Myofibrils are contained within each muscle fiber.

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43
Q

What is the sarcomere, and what is its function?

A

The sarcomere is the functional unit of a myofibril responsible for muscle contraction.

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44
Q

How is the sarcomere’s length defined, and what is the distance between Z-discs in a sarcomere?

A

The sarcomere’s length is defined by the distance from one Z-disc to another Z-disc.

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45
Q

What is the composition and function of the Z-disk in the sarcomere?

A

The Z-disk in the sarcomere is composed of a filamentous protein called ?-actinin, and it attaches myofibrils to one another.

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46
Q

Describe the structure of the thick filament and its composition.

A

The thick filament in the sarcomere is composed of myosin filaments.

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47
Q

What is the role of titin in the sarcomere, and how does it stabilize the thick filament?

A

Titin anchors the thick filament to the Z-disc, stabilizes it, and maintains the side-by-side relationship between myosin and actin filaments.

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48
Q

Why is titin described as “springy”?

A

Titin is described as “springy” because it provides elasticity to the sarcomere.

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49
Q

What is the M-line in the sarcomere, and what proteins make it up?

A

The M-line runs in the middle of the sarcomere and is responsible for connecting and stabilizing the thick filament. It is made up of three proteins: Myomesin, C-proteins, and Creatine kinase.

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50
Q

What does the A-band represent in a sarcomere, and what filaments are found in it?

A

The A-band represents the dark band in a sarcomere and contains myosin filaments and ends of actin filaments where they overlap the myosin.

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51
Q

How is the A-band defined in terms of filament arrangement?

A

The A-band is defined as the distance from one end of the thick filament to the other end in the same sarcomere.

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52
Q

What does the I-band represent in a sarcomere, and what filaments are found in it?

A

The I-band represents the light band in a sarcomere( disttance between twon thick filaments) and consists of actin filaments.

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53
Q

How is the I-band defined in terms of filament arrangement?

A

The I-band is defined as the distance from one end of a thick filament to the other end of the adjacent thick filament.

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54
Q

How are thin filaments anchored in the sarcomere, and what is the primary protein in the thin filament?

A

Thin filaments are anchored to the Z-disk through the nebulin protein, and the primary protein in the thin filament is actin.

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55
Q

What is the H-zone, and where is it located in the sarcomere?

A

The H-zone is the distance between thin filaments in the same sarcomere.

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56
Q

What is the composition and function of the actin filament in the sarcomere?

A

The actin filament in the sarcomere is composed of two helical strands of F-actin molecules and two strands of tropomyosin molecules.

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57
Q

What are G-actin and F-actin, and how do they differ?

A

G-actin is the monomer of actin filaments, while F-actin represents polymers of G-actin.

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58
Q

What is the role of tropomyosin in the sarcomere, and how does it relate to myosin binding?

A

Tropomyosin surrounds and blocks the active sites of actin in a resting position, preventing myosin heads from binding.

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59
Q

What is the function of troponin, and what are its three subunits?

A

Troponin contains three active sites binding to actin, tropomyosin, and Ca2+ and has three subunits: Troponin C, Troponin T, and Troponin I.

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60
Q

How does troponin interact with Ca2+ to initiate the contraction process in muscle fibers?

A

Troponin interacts with Ca2+ by binding to Troponin C, which changes the shape of Troponin T and pulls on tropomyosin, opening up the active sites for myosin heads to bind.

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61
Q

Why is troponin clinically significant, particularly in the context of heart damage?

A

Elevated troponin levels are a marker for heart damage, and it may leak into the bloodstream.

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62
Q

What happens when troponin levels rise, and why is it used as a marker for heart damage, such as myocardial infarction?

A

When troponin levels rise, it is often indicative of myocardial infarction (heart attack). It is used as a diagnostic tool to assess heart muscle damage.

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63
Q

What is the composition of a myosin filament, and how many polypeptide chains does it consist of?

A

A myosin filament is composed of six polypeptide chains, including two heavy chains and four light chains.

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64
Q

How is myosin’s tail structured, and what does it connect to in the sarcomere?

A

Myosin’s tail is structured as an ?-helix composed of two heavy chains, and it connects to the thick filament in the sarcomere.

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65
Q

What is the structure of myosin’s head, and what is its role in muscle contraction?

A

Myosin’s head is a globular polypeptide structure made from bilateral folding of the ends of the heavy chains, and it plays a crucial role in muscle contraction.

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66
Q

How does myosin’s head contribute to the sliding of myofilaments in muscle contraction?

A

Myosin’s head binds to the actin active sites, allowing the sliding of myofilaments during muscle contraction.

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67
Q

What important enzymatic activity is found in myosin’s head?

A

Myosin’s head contains myosin ATPase, an enzyme that can cleave ATP to ADP and Pi, which is essential for myofilament sliding.

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68
Q

What is the function of myosin ATPase, and how does it relate to myofilament sliding?

A

Myosin ATPase’s function is to provide energy for the sliding of myofilaments by breaking down ATP.

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69
Q

What are the two types of light chains in myosin, and what are their respective roles?

A

Myosin has two types of light chains: the regulatory light chain (RLC) and the essential light chain (ELC).

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70
Q

What is the function of the regulatory light chain (RLC) in myosin?

A

The regulatory light chain (RLC) can phosphorylate and change the activity of the myosin, regulating muscle contraction.

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71
Q

What role does the essential light chain (ELC) play in the myosin molecule?

A

The essential light chain (ELC) structurally stabilizes the myosin head and neck, ensuring proper functioning.

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72
Q

How do individual myosin molecules combine to form a myosin filament?

A

Individual myosin molecules combine to form a myosin filament through their tails, which connect to the thick filament in the sarcomere.

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73
Q

What is the role of dystrophin in muscle structure, and how does it link actin in the sarcolemma?

A

Dystrophin links actin in the sarcolemma to the protein complex and subsequently connects to the extracellular matrix in muscle cells.

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74
Q

How does the protein complex connect to the extracellular matrix in muscle cells?

A

The protein complex connects to the extracellular matrix to provide structural integrity to muscle fibers.

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75
Q

What is the clinical significance of dystrophin, and how does a mutation in the dystrophin gene lead to muscular dystrophy?

A

Dystrophin has clinical significance because a mutation in the dystrophin gene can lead to muscular dystrophy, a group of genetic disorders causing muscle weakness and degeneration.

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76
Q

What type of genetic disorder is muscular dystrophy, and why is it more common in males?

A

Muscular dystrophy is an X-linked recessive genetic disorder, making it more common in males, who have one X chromosome.

77
Q

What is Duchenne Muscular Dystrophy, and why is it more severe compared to Becker Muscular Dystrophy?

A

Duchenne Muscular Dystrophy is a more severe form of muscular dystrophy that typically develops by the age of 5-6 years and is characterized by the absence of dystrophin due to a nonsense mutation.

78
Q

What causes Duchenne Muscular Dystrophy at the genetic level, and how does it affect the production of dystrophin?

A

Duchenne Muscular Dystrophy is caused by a nonsense mutation that introduces a premature STOP codon in the mRNA, resulting in incomplete protein production.

79
Q

How does Becker Muscular Dystrophy differ from Duchenne Muscular Dystrophy in terms of severity and the genetic basis of the condition?

A

Becker Muscular Dystrophy is a less severe form of the condition that typically develops by the age of 10-20 years and is characterized by misfolded protein due to a missense mutation.

80
Q

What causes Becker Muscular Dystrophy at the genetic level, and how does it result in a misfolded protein?

A

Becker Muscular Dystrophy results from a ‘‘missense mutation’’ that leads to a substitution of an amino acid, altering the protein’s shape and function.

81
Q

What is the concept of “complementarity” in the context of protein structure and function?

A

The concept of “complementarity” suggests that the structure of a protein complements its function, and any alteration in structure can affect its function.

82
Q

What is the overview of the pathophysiology of muscular dystrophy, and how does the absence of dystrophin affect muscle cells?

A

In muscular dystrophy, the absence of dystrophin results in a lack of anchoring to the cell membrane, leading to membrane sagging, breakdown, and muscle weakness over time.

83
Q

What are the clinical presentations and complications associated with muscular dystrophy, particularly in terms of muscle weakness?

A

Clinical presentations and complications of muscular dystrophy include respiratory failure, a waddling gait, dilated cardiomyopathy, and the Gower sign.

84
Q

How does muscular dystrophy lead to respiratory failure, and which muscle is primarily affected?

A

Muscular dystrophy leads to respiratory failure due to the impaired or weak diaphragm, a primary respiratory muscle.

85
Q

What is the “waddling gait,” and why does it occur in muscular dystrophy patients?

A

The “waddling gait” occurs in muscular dystrophy patients due to weak hip muscles, affecting their walking pattern.

86
Q

How does muscular dystrophy lead to dilated cardiomyopathy, affecting the heart muscles?

A

Muscular dystrophy can lead to dilated cardiomyopathy, causing the heart muscles to become enlarged and less effective at pumping blood.

87
Q

What is the Gower sign, and why is it commonly observed in patients with Becker or Duchenne muscular dystrophy?

A

The Gower sign is when patients use their upper extremities to help them stand, often seen in patients with Becker or Duchenne muscular dystrophy.

88
Q

What management approaches are used for muscular dystrophy patients, and why is there currently no cure for the condition?

A

Currently, there is no cure for muscular dystrophy, but management involves physical therapy to improve quality of life.

89
Q

How does physical therapy contribute to improving the quality of life for individuals with muscular dystrophy?

A

Glucocorticoid therapy may be used, but it can have adverse effects such as weight gain, a cushingoid appearance, and hirsutism.

90
Q

What is the role of glucocorticoid therapy in managing muscular dystrophy, and what are the potential adverse effects associated with it?

A

Glucocorticoid therapy helps improve muscle strength in muscular dystrophy but may cause side effects like weight gain, a cushingoid appearance, and bone problems. Treatment decisions are made carefully to balance benefits and risks.

91
Q

What is a muscle twitch, and how is it initiated?

A

A muscle twitch is a very brief muscle contraction in response to a single neural stimulus.

92
Q

Define the term “motor unit” and explain its components.

A

A motor unit consists of a motor neuron and all the muscle fibers that neuron innervates.

93
Q

What does “graded muscle response” refer to, and how can it be achieved?

A

Graded muscle response refers to how muscle cells respond to different types of stimuli, such as changes in the frequency and strength of neural stimuli.

94
Q

What are the two ways to achieve a graded response in a muscle cell?

A

A graded response in a muscle cell can be achieved by changing the strength of the neural stimulus or changing the frequency of the neural stimuli.

95
Q

In muscle physiology, what does “latent phase” refer to, and what happens during this phase?

A

The “latent phase” of a muscle twitch is a very brief period during which cross-bridges are formed, but the muscle fibers aren’t contracting yet. It ends when Ca2+ binds to troponin.

96
Q

Describe the “contraction phase” in a muscle twitch, including the role of myosin and actin.

A

During the “contraction phase” of a muscle twitch, myosin and actin are actively moving, myosin heads create power strokes, actin moves closer to the M line of the sarcomere, and the muscle fiber shortens.

97
Q

What happens during the “relaxation phase” of a muscle twitch, and what is its significance?

A

The “relaxation phase” of a muscle twitch corresponds to the refractory phase when the membrane voltage reaches its maximum. During this phase, potassium channels open, Ca2+ is reuptaken in the sarcoplasmic reticulum, and the cross-bridge becomes inactive, causing a decrease in tension.

98
Q

How does the refractory period relate to the relaxation phase in muscle twitch?

A

The refractory period begins with the opening of potassium channels during the relaxation phase, signifying repolarization and preventing further action potentials. This phase typically lasts 10-100 ms.

99
Q

What determines the length of the relaxation phase in a muscle twitch?

A

The length of the relaxation phase depends on the muscle type, with some muscles having longer relaxation phases than others.

100
Q

What is the significance of the refractory period in muscle contraction?

A

The refractory period is essential as it ensures that the muscle cell cannot generate another action potential during this time, preventing continuous contraction.

101
Q

How does changing the strength of the neural stimulus affect a graded response in muscle cells?

A

Changing the strength of the neural stimulus is covered in the next lecture.

102
Q

What are the two types of tetanus in muscle physiology, and how do they differ?

A

In muscle physiology, there are two types of tetanus: incomplete (unfused) tetanus, where the frequency of stimulation only allows incomplete relaxation, and complete (fused) tetanus, which occurs when the stimulation frequency prevents any relaxation.

103
Q

In the context of incomplete tetanus, which statement is correct? a) The stimuli arrive one after the other, with no breaks in between. b) Maximum tension isn’t reached. c) It creates a strong and prolonged contraction. d) There’s a brief moment in which relaxation begins, but then the next AP arrives before the K+ channels can open.

A

a) The stimuli arrive one after the other, with no breaks in between.

104
Q

Regarding complete tetanus, which statement is accurate? a) The muscle fatigues rapidly. b) It’s performed on a daily basis. c) It doesn’t reach the maximum tension. d) There’s a relaxation period between two stimuli.

A

a) The muscle fatigues rapidly.

105
Q

What does “temporal summation” stand for in muscle physiology? a) Summation of several stimuli that, over time, increase the strength of contraction. b) Recruitment of many neurons that fire at the same time to increase the strength of contraction. c) Many neurons releasing enough Ach at the same time to create an end-plate potential in the muscle cell.

A

a) Summation of several stimuli that, over time, increase the strength of contraction.

106
Q

Considering a muscle twitch, which statement is accurate? a) In the contraction phase , the cross-bridges are formed, and the myosin is pulling the actin towards the M line. b) In the refractory phase, another AP can be elicited. c) No ATP is used. d) The length of the refractory phase is longer than the contraction phase.

A

a) In the contraction phase , the cross-bridges are formed, and the myosin is pulling the actin towards the M line.

107
Q

What factors affect graded muscle response?

A

Graded muscle response is affected by the frequency of neural stimuli and the strength of neural stimuli.

108
Q

How is the frequency of neural stimuli related to muscle contraction?

A

The frequency of neural stimuli is a key determinant of muscle contraction. It can lead to incomplete (unfused) tetanus or complete (fused) tetanus, impacting the level of muscle tension and contractions.

109
Q

What are the three types of potential stimuli discussed in the notes, and what do they each produce in terms of muscle response?

A

The three types of potential stimuli discussed are subthreshold potential/stimulus (produces no response), threshold potential/stimulus (generates the first observable muscle contraction), and maximal potential/stimulus (produces prolonged and powerful muscle contraction that remains the same even with increased voltage).

110
Q

What is the relationship between the strength of the stimulus and tension in muscle contraction?

A

The strength of the stimulus correlates with tension in muscle contraction. Subthreshold stimuli do not produce tension, threshold stimuli generate tension, and maximal stimuli produce the most force the muscle can exert.

111
Q

What does the term “motor unit recruitment” refer to, and how does it relate to muscle tension and contractions?

A

Motor unit recruitment refers to the activation of motor units, which consist of a motor neuron and all the muscle fibers it innervates. Greater motor unit recruitment leads to more force and tension in muscle contractions, while lesser recruitment results in finer movements.

112
Q

What does the first order of recruitment in the size principle involve, and how does it affect muscle contraction?

A

The first order of recruitment involves recruiting the smallest muscle fibers. These fibers are highly excitable, have a low threshold potential, and produce a limited amount of force, resulting in a weak contraction.

113
Q

Describe the second order of recruitment and its impact on muscle contraction.

A

The second order of recruitment recruits medium-sized muscle fibers with a moderate threshold potential. This generates moderate tension and a moderate contractile force, contributing to a moderate contraction.

114
Q

Explain the third order of recruitment and its role in muscle contraction.

A

The third order of recruitment involves recruiting the largest muscle fibers with the highest threshold potential. This leads to the generation of maximal tension and the highest contractile force, resulting in a powerful contraction.

115
Q

What is the significance of the term “motor unit recruitment” in relation to muscle contractions?

A

“Motor unit” refers to a single motor neuron and all the muscle fibers it innervates.

116
Q

What is multiple motor unit summation, and how does it contribute to muscle contraction?

A

Multiple motor unit summation is the combined effect of multiple motor units acting within a muscle at any given time. It contributes to muscle contraction, with lower tension recruiting smaller muscle fibers and higher tension recruiting larger muscle fibers.

117
Q

How does the strength of neural stimuli affect multiple motor unit summation?

A

The strength of neural stimuli affects multiple motor unit summation by determining the amount of tension produced. A weak stimulus results in lower tension, while a strong stimulus leads to higher tension in muscle contractions.

118
Q

What characterizes the first order of recruitment in the size principle, and how does it impact muscle contraction?

A

The first order of recruitment involves recruiting the smallest muscle fibers, which are highly excitable, have a low threshold potential, and produce a limited amount of force, resulting in a weak contraction.

119
Q

Describe the second order of recruitment and its effect on muscle contraction.

A

The second order of recruitment recruits medium-sized muscle fibers with a moderate threshold potential, leading to moderate tension and a moderate contractile force, contributing to a moderate contraction.

120
Q

Explain the third order of recruitment and its role in muscle contraction.

A

The third order of recruitment involves recruiting the largest muscle fibers with the highest threshold potential, resulting in maximal tension and the highest contractile force, leading to a powerful contraction.

121
Q

How is a “motor unit” defined in the context of muscle physiology?

A

In muscle physiology, “motor unit” refers to a single motor neuron and all the muscle fibers it innervates.

122
Q

What is multiple motor unit summation, and how does it influence muscle contraction?

A

Multiple motor unit summation is the combined effect of multiple motor units acting within a muscle at any given time. It contributes to muscle contraction by recruiting smaller muscle fibers for lower tension and larger muscle fibers for higher tension.

123
Q

How does the strength of neural stimuli influence multiple motor unit summation and tension in muscle contractions?

A

The strength of neural stimuli influences multiple motor unit summation and tension in muscle contractions. A weak stimulus results in lower tension, while a strong stimulus leads to higher tension during muscle contractions.

124
Q

What is the role of torque in the context of levers, and how does torque affect the movement of a lever?

A

Torque is the rotational force that influences the movement of a lever. The direction of torque determines whether the lever moves in a clockwise or counter-clockwise direction.

125
Q

Explain the concept of mechanical advantage (MA) and mechanical disadvantage (MD) in lever systems, and provide examples of their applications.

A

Mechanical advantage (MA) occurs when the force arm (effort arm) is longer than the resistance arm. It is utilized for power movements. Mechanical disadvantage (MD) occurs when the force arm is shorter than the resistance arm. It is used for speed and directional changes.

126
Q

What is a Class 1 lever, and what is the arrangement of its fulcrum, load, and effort force?

A

In a Class 1 lever, the fulcrum is located between the load and the effort force. This arrangement allows for a variety of mechanical advantages and disadvantages.

127
Q

Can you provide physiological examples of Class 1 levers in the human body, including their fulcrum and direction of torque?

A

Class 1 lever examples in the human body include the posterior neck muscles (e.g., trapezius and splenius capitis) involved in neck extension. The fulcrum is at the atlanto-occipital joint, with the head acting as the load force and gravity generating a counter-clockwise torque.

128
Q

Describe Class 2 levers in terms of the location of the fulcrum, load, and effort force, and provide an example.

A

Class 2 levers have the fulcrum at one end, the load (resistance) at the other end, and the effort force in between. A common example is the body’s toe pressing against the ground, generating a clockwise torque, with the gastrocnemius and soleus muscles providing a counter-clockwise torque to lift the body’s weight.

129
Q

What is a Class 3 lever, and where are the fulcrum, load, and effort force typically located in this type of lever?

A

Class 3 levers have the fulcrum at one end, the load (resistance) at the other end, and the effort force in between. They are typically meant for speed.

130
Q

Share physiological examples of Class 3 levers in the human body and explain how they work.

A

A common example of a Class 3 lever in the human body is the action of the biceps in flexing the elbow. The fulcrum is at the elbow joint, with the load force at the hand, generating a clockwise torque due to gravity. The effort force from the biceps generates a counter-clockwise torque, enabling elbow flexion.

131
Q

In a Class 3 lever, if the Load force is 7N, the Load arm is 10m, and the Effort arm is 5m, what is the required Effort force to balance the Load? a) 14N b) 21N c) 9N d) 10N

A

a) 14N

132
Q

Where in the body can we find a Class 1 lever? a) Biceps brachii and brachialis at the elbow b) Ankle joint c) Triceps d) Knee joint

A

a) Biceps brachii and brachialis at the elbow

133
Q

What is the primary difference between isometric and isotonic contractions? a) In isometric contraction, there is lengthening of the muscle, while in isotonic contraction, there isn’t. b)isotonic contractions, can be of two types: concentric and eccentric. c) Isometric contractions generate less tension than isotonic contractions. d) In isometric contraction, the Load force is greater than the muscle force.

A

b) isotonic contractions, can be of two types: concentric and eccentric.

134
Q

What are the two primary types of muscle contractions mentioned in the notes?

A

The two primary types of muscle contractions mentioned in the notes are isometric contractions and isotonic contractions.

135
Q

How does the tension in an isometric contraction change over time, as described in the graph? a) It starts at a high tension and decreases over time. b) It remains low throughout the contraction. c) It increases quickly and reaches a plateau. d) It varies randomly with no specific pattern.

A

c) It increases quickly and reaches a plateau.

136
Q

Isotonic contractions can be classified into two types: concentric and eccentric. What distinguishes these two types? a) Concentric contractions involve load force greater than muscle force, while eccentric contractions involve load force less than muscle force. b) Concentric contractions cause muscle lengthening, while eccentric contractions cause muscle shortening. c) Concentric contractions generate less force than eccentric contractions. d) Concentric contractions happen when the muscle is at rest, while eccentric contractions occur during active muscle contraction.

A

a) Concentric contractions involve load force greater than muscle force, while eccentric contractions involve load force less than muscle force.

137
Q

What is the primary purpose of levers in the context of movement and biomechanics? a) To provide structural support to the body. b) To create energy for muscle contractions. c) To allow movement around a fixed point or fulcrum. d) To store excess tension in muscles.

A

c) To allow movement around a fixed point or fulcrum.

138
Q

How many classes of levers are discussed in the notes, and what are they?

A

Three classes of levers are discussed in the notes: Class 1, Class 2, and Class 3.

139
Q

What are the three main types of muscle fibers mentioned in the notes?

A

The three main types of muscle fibers mentioned in the notes are Type I, Type IIa, and Type IIx.

140
Q

What is another name for Type I muscle fibers, and what distinguishes them structurally?

A

Type I muscle fibers are also known as “red slow oxidative” muscle fibers. They have a small fiber diameter.

141
Q

What is the significance of a high capillary density in Type I muscle fibers?

A

High capillary density in Type I muscle fibers is significant because it means they are highly vascularized and have a large amount of blood vessel supply, allowing for efficient oxygen and nutrient delivery.

142
Q

Why do Type I muscle fibers appear reddish in hue?

A

Type I muscle fibers appear reddish in hue because of the high capillary density and the presence of hemoglobin in the blood, which gives the blood its red color.

143
Q

What is the primary role of mitochondria in Type I muscle fibers, and how do they contribute to ATP production?

A

high amount of Mitochondria in Type I muscle fibers are important for ATP production. They serve as the powerhouse of the cell, capable of utilizing various energy sources (glucose, amino acids, fats) in the presence of oxygen (aerobic pathway) to create ATP via aerobic cellular respiration.

144
Q

What is the primary metabolic pathway for ATP production in Type I muscle fibers, and what are the key processes involved in this pathway?

A

The primary metabolic pathway for ATP production in Type I muscle fibers is aerobic cellular respiration, involving the Krebs cycle, electron transport chain, and oxidative phosphorylation.

145
Q

How does the contractile speed of Type I muscle fibers compare to other muscle fiber types, and what contributes to their slower contractile speed?

A

Type I muscle fibers have a slower contractile speed compared to other muscle fiber types. Their slower speed is due to decreased myosin-ATPase activity, which affects the detachment of myosin from actin and the generation of power strokes.

146
Q

Why are Type I muscle fibers highly fatigue-resistant, and what factors contribute to their ability to maintain activity for extended periods?

A

Type I muscle fibers are highly fatigue-resistant due to their slow contractile speed and the large amount of ATP they produce. This allows them to carry out activities for extended periods, although they do not generate a lot of power.

147
Q

What is the main source of energy storage and fuel in Type I muscle fibers?

A

The main source of energy storage and fuel in Type I muscle fibers is triglycerides, specifically the fatty acids, which undergo ?-oxidation in the mitochondria to produce ATP.

148
Q

How does myoglobin in Type I muscle fibers function, and what role does it play in muscle contraction and ATP production?

A

Myoglobin in Type I muscle fibers temporarily holds onto oxygen. It stores and releases oxygen as needed during muscle contractions. Oxygen is essential for ATP production.

149
Q

What are some physiological functions and activities that rely on Type I muscle fibers, and why are they well-suited for these roles?

A

Type I muscle fibers are well-suited for activities such as marathon running because they require high ATP production, have high fatigue resistance, and contain lots of triglycerides. They also play a crucial role in anti-gravity and posture muscles, helping to maintain body position and posture.

150
Q

What are the characteristics of Type IIA muscle fibers in terms of structure, metabolic processes, and function?

A

Type IIA muscle fibers are large in diameter, have increased capillary density, appear reddish-pink in color, contain more mitochondria, and have glycogen stores. They primarily rely on aerobic cellular respiration but can also undergo anaerobic respiration. They have fast contractility and moderate fatigue resistance and are typically recruited second. These fibers are involved in activities like walking and sprinting.

151
Q

How does the capillary density of Type IIA muscle fibers compare to other fiber types, and why is this important for their function?

A

Type IIA muscle fibers have increased capillary density, which ensures better oxygen supply to the muscle and contributes to their reddish-pink hue. Capillary density is crucial for their function as it supports aerobic respiration.

152
Q

What is the primary metabolic pathway for ATP production in Type IIA muscle fibers, and do they have the capability to undergo anaerobic respiration?

A

The primary metabolic pathway for ATP production in Type IIA muscle fibers is aerobic cellular respiration. While they primarily rely on aerobic respiration, they can also undergo anaerobic respiration when necessary.

153
Q

What is the role of creatine phosphate in ATP production in Type IIA muscle fibers, and how does it relate to glycolysis?

A

Creatine phosphate in Type IIA muscle fibers plays a role in rapidly regenerating ATP from ADP. It is part of the creatine phosphate pathway, where creatine phosphate, together with ADP, helps regenerate ATP, which is essential for muscle contraction. It is related to glycolysis in the sense that both pathways contribute to ATP production.

154
Q

What is the order of recruitment for Type IIA muscle fibers, and what is their level of fatigue resistance?

A

Type IIA muscle fibers are typically recruited second in the order of recruitment. They have moderate fatigue resistance, allowing them to function for a limited duration. Their contraction speed is faster than Type I fibers but not as fast as Type IIX fibers.

155
Q

In which physiological activities or exercises are Type IIA muscle fibers typically involved?

A

Type IIA muscle fibers are typically involved in activities like walking and sprinting, which require moderate amounts of power and endurance.

156
Q

What are the structural characteristics of Type IIX muscle fibers, and how do they differ from Type IIA fibers?

A

Type IIX muscle fibers have an intermediate fiber diameter, low capillary density, very few mitochondria, significant glycosomes, and very little myoglobin. They primarily rely on anaerobic respiration for ATP production.

157
Q

What is the primary metabolic pathway for ATP production in Type IIX muscle fibers, and what is their level of fatigue resistance?

A

The primary metabolic pathway for ATP production in Type IIX muscle fibers is anaerobic glycolysis. They have very fast contractility and very low fatigue resistance, allowing them to produce significant power. They are typically recruited third in the order of recruitment.

158
Q

How do factors such as genetics and environmental stress influence the distribution of muscle fiber types in an individual?

A

Factors such as genetics and environmental stress can influence the distribution of muscle fiber types in an individual. Genetics determine the initial distribution, and environmental stress or exercise can lead to adaptations in muscle fiber composition.

159
Q

How do endurance activities and resistance exercises impact muscle fiber composition and size?

A

Endurance activities lead to an increase in capillary density, mitochondria size and number, and myoglobin content in muscle fibers. There may also be a shift from Type IIA to Type I muscle fibers. Resistance exercises result in muscle hypertrophy, an increase in myofibrils, mitochondria, and glycosomes. There may be a shift from Type IIx to Type IIA fibers. Disuse atrophy occurs when muscles are not used, leading to decreased muscle size and a shift from Type IIx to Type IIA fibers, making the muscles weaker.

160
Q

What are the three major types of muscle in the human body, and what are their characteristics in terms of striation and control?

A

The three major types of muscle in the human body are skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle is striated and under voluntary control, cardiac muscle is striated and involuntary, and smooth muscle is non-striated and involuntary.

161
Q

What is the main difference between skeletal and cardiac muscles in terms of voluntary or involuntary control?

A

The main difference between skeletal and cardiac muscles is in their control. Skeletal muscles are under voluntary control through the somatic nervous system, while cardiac muscles are involuntary and regulated by the autonomic nervous system.

162
Q

List the functions of skeletal muscles in the human body.

A

Skeletal muscles serve various functions in the human body, including the maintenance of posture, purposeful movement in relation to the external environment, respiratory movement, heat production, and contribution to whole-body metabolism.

163
Q

What is a motor unit in skeletal muscle, and how does the number of muscle fibers per motor unit vary based on muscle function?

A

A motor unit in skeletal muscle consists of a single alpha motor neuron and all the skeletal muscle fibers it innervates. The number of muscle fibers per motor unit varies depending on the function of the muscle. Muscles that serve fine movements have fewer fibers per motor unit, while muscles where power is more important than precision have hundreds to thousands of fibers per motor unit.

164
Q

What is the structural organization of skeletal muscle fibers, and how are they bundled together?

A

Skeletal muscle consists of parallel muscle fibers (skeletal muscle cells) that are bundled together by connective tissue. These muscle fibers usually extend the entire length of the muscle and are attached to bones via tendons. The interaction between bones, muscles, and joints forms lever systems that allow a range of body movements.

165
Q

What are myofibrils, and what is their role within muscle fibers?

A

Myofibrils are specialized intracellular structures found within each muscle fiber. They contain alternating segments of thick (myosin - darker) and thin (actin - lighter) protein filaments.

166
Q

What are sarcomeres, and why are they considered the functional units of muscle?

A

Sarcomeres are the functional units of muscle. They are the smallest components of muscle tissue that perform all the functions of muscle contraction. Sarcomeres are found between two Z-lines, which connect the thin filaments of two adjoining sarcomeres.

167
Q

Describe the structure of a sarcomere, including its key components like the A-band, H-zone, M-line, and I-band.

A

Each sarcomere consists of four key zones: the A-band, H-zone, M-line, and I-band. The A-band is made up of thick filaments along with portions of thin filaments that overlap at both ends of thick filaments. The H-zone is a lighter area in the middle of the A-band where thin filaments do not reach. The M-line extends vertically down the middle of the A-band within the center of the H-zone. The I-band consists of the remaining portion of thin filaments that do not project into the A-band.

168
Q

What is the sliding filaments theory, and how does it explain the production of muscle tension?

A

The sliding filaments theory explains that muscle tension is produced by the sliding of actin filaments over myosin filaments. This process requires ATP for contraction (to power cross-bridges) and relaxation (for the release of cross-bridges and to pump Ca2+ back into the sarcoplasmic reticulum). Ca2+ is also required for cross-bridge formation.

169
Q

What role does ATP play in muscle contraction and relaxation according to the sliding filaments theory?

A

ATP plays a crucial role in muscle contraction and relaxation. It provides the energy required for cross-bridge formation and bending, allowing myosin to pull actin filaments towards the center of the sarcomere.

In relaxation, ATP is needed to release cross-bridges and transport Ca2+ back into the sarcoplasmic reticulum.

170
Q

Describe the excitation-contraction coupling process in muscle fibers. What role does Ca2+ play in this process?

A

Excitation-contraction coupling is the process by which a surface action potential leads to the activation of the contractile structures of the muscle fiber. In skeletal muscle fibers, Ca2+ is the link between excitation and contraction. Ca2+ is released from the lateral sacs of the sarcoplasmic reticulum when the surface action potential spreads down the T-tubules, which are extensions of the surface membrane that dip into the muscle fiber.

171
Q

How is the release of Ca2+ triggered in skeletal muscle fibers, and what are the consequences of this release in terms of muscle contraction?

A

The release of Ca2+ is triggered by the action potential in T-tubules, and these Ca2+ ions bind to troponin on actin filaments. This binding leads to the physical movement of tropomyosin, uncovering the cross-bridge binding sites on actin.

172
Q

Explain the steps involved in the binding of myosin cross-bridges to actin filaments and how it leads to muscle contraction.

A

When Ca2+ is bound to troponin, tropomyosin is moved aside, allowing myosin cross-bridges to attach to actin. The cross-bridges then bend and pull actin filaments toward the center of the sarcomere. This action is powered by ATP. After the contraction, Ca2+ is actively taken up by the sarcoplasmic reticulum. When Ca2+ is no longer bound to troponin, tropomyosin slips back into its blocking position over the binding sites on actin, and the contraction ends as actin passively slides back to the resting position.

173
Q

How does the number of muscle fibers contracting within a muscle influence the graduation of muscle tension? What is motor unit recruitment?

A

The number of muscle fibers contracting within a muscle influences muscle tension graduation. More muscle fibers contract with stronger contractions, a process known as motor unit recruitment. Asynchronous motor unit recruitment during submaximal contractions helps prevent muscle fatigue.

174
Q

What factors determine the tension developed by each contracting muscle fiber?

A

The tension developed by each contracting muscle fiber depends on factors such as the frequency of stimulation and summation of contractions, the length of the muscle fiber at the onset of contraction, and the thickness of the muscle fiber.

175
Q

What is a twitch in the context of muscle contraction? Why is a single twitch insufficient for meaningful skeletal muscle activity?

A

In muscle contraction, a twitch refers to a single contraction produced when a skeletal muscle is stimulated once. However, a single twitch produces little tension and is not sufficient for meaningful skeletal muscle activity.

176
Q

How does muscle tension change with increasing frequency of stimulation, and what is the outcome of rapid stimulation without relaxation in muscle fibers?

A

The tension developed by skeletal muscle increases with an increasing frequency of stimulation. If muscle fibers are stimulated rapidly without relaxation between stimuli, a maximal sustained contraction known as tetanus occurs. Cardiac muscle cannot be tetanized due to its long refractory period.

177
Q

Why is the optimum length of a muscle important for achieving maximal tetanic tension?

A

The optimum length of a muscle allows for maximum overlap between thick filament cross-bridges and thin filament cross-bridge binding sites. This optimal overlap enables maximal tetanic tension. The resting length of a skeletal muscle is approximately its optimum length.

178
Q

Differentiate between isotonic and isometric contractions. What are their primary uses in the body?

A

Isotonic contraction occurs when muscle tension remains constant while the muscle length changes, and it is used for body movements and moving objects. Isometric contraction occurs when muscle tension develops at a constant muscle length and is used for supporting objects in fixed positions and maintaining body posture. In both isotonic and isometric contractions, muscle tension is transmitted to the bone via the elastic components of muscle.

179
Q

What are the main differences between different types of skeletal muscle fibers, and how do these differences affect their resistance to fatigue and speed of contraction?

A

The main differences between different types of skeletal muscle fibers include enzymatic pathways for ATP synthesis, resistance to fatigue, and the activity of myosin ATPase. Muscle fibers with greater ATP synthesis capacity are more resistant to fatigue, and the activity of myosin ATPase determines the speed of contraction.

180
Q

What are the metabolic pathways that supply ATP in muscle fibers, and under what conditions are they primarily utilized?

A

Muscle fibers use various metabolic pathways for ATP supply, including the transfer of a high-energy phosphate from creatine phosphate to ADP (immediate ATP source), oxidative phosphorylation (main source when oxygen is present), and glycolysis (main source when oxygen is not present).

181
Q

What are the characteristics and main uses of slow oxidative (Type I) muscle fibers, fast oxidative (Type IIa) muscle fibers, and fast glycolytic (Type IIx) muscle fibers?

A

There are three main types of skeletal muscle fibers: slow oxidative (Type I) fibers, which are used for prolonged low-intensity aerobic activities; fast oxidative (Type IIa) fibers, which use both aerobic and anaerobic metabolism and are useful for prolonged moderate-intensity activities; and fast glycolytic (Type IIx) fibers, which primarily use anaerobic metabolism and are used for short-term high-intensity activities.

182
Q

How does the nervous system control purposeful skeletal muscle activity, and what types of inputs can motor nerves receive?

A

The nervous system controls purposeful skeletal muscle activity, and motor nerves receive inputs from the brain and various receptors. These inputs can be either inhibitory or excitatory.

183
Q

What is a reflex action, and how are reflex pathways used in a clinical context to identify lesions in the motor system?

A

A reflex action is a stereotyped response to a specific stimulus. Reflex pathways are used in a clinical context to identify lesions in the motor system. For example, the knee jerk (stretch reflex) is commonly used to assess reflex responses.

184
Q

Explain the stretch reflex, its role in maintaining muscle length, and how it contributes to posture and coordinated movement. How is it typically elicited in a clinical setting?

A

The stretch reflex is the simplest monosynaptic spinal reflex and serves as a negative feedback mechanism to resist passive changes in muscle length. It helps maintain optimal resting muscle length and is involved in maintaining posture, such as during walking. The reflex involves muscle spindles, afferent neurons, and alpha motor neurons, leading to muscle contraction. It is elicited by tapping the muscle tendon, rapidly stretching the muscle, and triggering the reflex contraction.

185
Q

What are muscle spindles, and what is their role in the stretch reflex?

A

Muscle spindles are specialized muscle fibers that serve as sensory receptors for the stretch reflex. They detect changes in muscle length and play a key role in maintaining optimal resting muscle length and posture.

186
Q

How do muscle spindles differ from ordinary muscle fibers (extrafusal fibers)?

A

Muscle spindles are known as intrafusal fibers, while ordinary muscle fibers are called extrafusal fibers. Intrafusal fibers are found within the muscle belly and run parallel to ordinary muscle fibers, which are responsible for generating muscle force.

187
Q

What type of sensory nerve endings are present in muscle spindles, and how do they respond to muscle stretch?

A

Muscle spindles have sensory nerve endings known as annulospiral fibers. These sensory endings increase their discharge when the muscle is stretched, providing information about muscle length changes.

188
Q

Explain the function of ??-motor neurons in muscle spindles. How do they help maintain sensitivity in muscle spindles during muscle contraction?

A

??-motor neurons are efferent neurons that supply muscle spindles. They adjust the tension in muscle spindles to maintain their sensitivity when the muscle shortens during contraction. This ensures that the muscle spindles remain responsive to changes in muscle length.

189
Q

Do the contractions of intrafusal fibers within muscle spindles contribute to the overall strength of muscle contraction? Why or why not?

A

The contractions of intrafusal fibers within muscle spindles do not contribute to the overall strength of muscle contraction. Instead, their role is to provide sensory feedback regarding muscle length changes. The primary force generation for muscle contractions occurs in extrafusal fibers.

MSK (21 decks)

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