Muscle and Contractile Proteins

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What factor affects a muscle's ability to generate force and contract by influencing the number of motor units stimulated?

Frequency of muscle stimulation (correct)

Type of myosin isoforms present in the muscle

Degree of stretch (Frank-Starling relationship)

Whether the muscle is allowed to shorten (Force-velocity relationship)

What clinical feature is associated with MyHC IIa mutations?

Atrophy near shoulders, back, hand, and thigh muscles (correct)

Improved muscle contractility

Joint stiffness

Excessive muscle growth

Which protein makes up approximately 10-15% of the total protein in the body?

Troponin

Titin

Actin

Myosin (correct)

In the context of muscle physiology, what does the 'Force-Velocity relationship' primarily refer to?

Whether a muscle is allowed to shorten Signup and view all the answers

What disease is associated with mutations in embryonic MyHC (MYH3)?

Distal arthrogryposis Signup and view all the answers

What is the primary function of myosin V?

Involved in melanosome transport and certain neurological functions Signup and view all the answers

What is the structure of muscle myosin II?

A dimer with each heavy chain having a motor domain and a tail Signup and view all the answers

What is the role of the active site in the motor domain of myosin?

Hydrolyzing ATP to provide energy for muscle contraction Signup and view all the answers

Which myosin type is involved in maintaining the organization of actin-filled stereocilia in the inner ear?

Myosin VI and Myosin VII Signup and view all the answers

Which component of the myosin molecule is responsible for binding to actin filaments?

Motor domain Signup and view all the answers

What is the primary function of myosin VI in muscle physiology?

Maintains the organization of actin-filled stereocilia in the inner ear Signup and view all the answers

Which molecule blocks myosin binding sites on actin filaments?

Tropomyosin Signup and view all the answers

In muscle physiology, what is the main role of myosin VII?

Plays a role in smooth muscle regulation Signup and view all the answers

Which myosin type is responsible for binding to actin filaments in muscle contraction?

Myosin II Signup and view all the answers

What is the effect of calcium binding to Troponin C in muscle physiology?

Moves tropomyosin away from myosin binding sites Signup and view all the answers

What is the primary function of CapZ and tropomodulin in muscle sarcomeres?

Cap the ends of actin filaments to maintain constant length Signup and view all the answers

Which protein complex is responsible for regulating the interaction between myosin and actin in skeletal muscle?

Troponin-tropomyosin Signup and view all the answers

What is the primary role of troponin C in muscle contraction?

Bind to calcium ions, causing a conformational change in tropomyosin Signup and view all the answers

Which protein is responsible for maintaining the position of thick filaments within muscle sarcomeres?

Titin Signup and view all the answers

What is the primary function of tropomyosin in muscle contraction?

Block or expose myosin-binding sites on actin filaments Signup and view all the answers

What is the primary difference between myosin V and myosin II?

Myosin V has a high duty ratio, while myosin II has a low duty ratio. Signup and view all the answers

How do muscle sarcomeres contract in the context of myosin and actin filaments?

Myosin thick filaments and actin thin filaments slide past each other. Signup and view all the answers

What is the role of accessory proteins like CapZ and tropomodulin in muscle?

CapZ and tropomodulin cap ends of actin to maintain filament length. Signup and view all the answers

What is the primary function of titin in muscle sarcomeres?

Titin maintains the position of thick filaments within the sarcomere. Signup and view all the answers

How are myosin II molecules assembled in muscle?

By association of hydrophobic regions in the tail. Signup and view all the answers

What term describes the phenomenon where a single stimulus is not strong enough to cause a muscle fiber to contract, but multiple stimuli in rapid succession result in a sustained contraction?

Tetanus Signup and view all the answers

During the refractory period following a muscle twitch, what physiological phenomenon ensures that a second contraction cannot be elicited regardless of the stimulus strength?

Recovery of calcium ions into the sarcoplasmic reticulum Signup and view all the answers

What is the term for the phenomenon where multiple stimuli are applied to a muscle in rapid succession before it has completely relaxed, leading to a stronger muscle contraction?

Wave summation Signup and view all the answers

Which statement best describes the relationship between motor units and muscle twitch?

Multiple motor units are recruited to generate stronger muscle contractions. Signup and view all the answers

How does the time interval between two stimuli affect the force generated by a muscle in a second contraction?

A shorter interval leads to temporal summation and increased force in the second contraction. Signup and view all the answers

What factor influences a muscle's ability to generate force and contract by considering the number of motor units stimulated?

Frequency of stimulation Signup and view all the answers

In the context of muscle physiology, what aspect is primarily affected by the 'Frank-Starling relationship'?

Length-tension relationship Signup and view all the answers

Which factor can alter actin-myosin ATPase activity and lead to muscle disorders if mutations occur?

Myosin isoforms Signup and view all the answers

What phenomenon involves maintaining a nearly constant tension in the total muscle through asynchronous motor-unit activity?

Motor unit summation Signup and view all the answers

How does the 'Force-Velocity curve' concept illustrate the relationship between shortening velocity and load in muscle physiology?

By showing the trade-off between speed and force production Signup and view all the answers

Which of the following describes the relationship between muscle length and the force it can generate?

The shorter the muscle, the greater the force it can generate. Signup and view all the answers

The Frank-Starling mechanism refers to the relationship between:

End-diastolic volume and stroke volume Signup and view all the answers

Which type of muscle contraction occurs when the muscle generates force but does not change length?

Isometric contraction Signup and view all the answers

How does the isotonic twitch response of a muscle fiber change when a greater load is applied?

The twitch amplitude decreases and the contraction time increases. Signup and view all the answers

The Force-Velocity relationship in muscle physiology primarily describes the connection between:

Muscle shortening velocity and the load it is moving against Signup and view all the answers

Which muscle disease is associated with mutations in the myosin heavy chain (MYH) gene?

Distal arthrogryposis Signup and view all the answers

What is the primary function of myosin V in muscle physiology?

Transporting melanosomes for pigmentation Signup and view all the answers

Which type of muscle myopathy is associated with mutations in the embryonic myosin heavy chain (MYH3) gene?

Freeman-Sheldon Syndrome Signup and view all the answers

What is the primary effect of mutations in the MYH3 gene associated with Sheldon-Hall Syndrome?

Contractures of the distal limbs Signup and view all the answers

Which muscle disease is associated with a point mutation in the myosin Va gene?

Griscelli Syndrome Signup and view all the answers

What is the primary function of muscle myosin II in cell division?

Involved in cell division Signup and view all the answers

What is the function of myosin V?

Involved in melanosome transport Signup and view all the answers

Which disease is associated with mutations in myosin Va and leads to hypopigmentation and neurological defects?

Griscelli's Syndrome Signup and view all the answers

What is the primary role of non-muscle myosin VI and myosin VII?

Maintaining organization of actin-filled stereocilia Signup and view all the answers

In muscle physiology, what does the dimeric structure of muscle myosin II consist of?

Motor domain and tail Signup and view all the answers