3 - Force of muscular contraction

The sarcomere is:

The sarcomere is:

An element of the striated muscle fiber, located between two Z discs

Thin myofilaments in striated muscle cells are composed of:

3 types of proteins

The major protein component of the thin myofilaments in striated muscle cells is:

Actin

The major protein component of the thick myofilaments in striated muscle cells:

Myosin

In skeleton muscles the ratio between actin and myosin filaments is:

Always 6:1

The myosin molecule in striated muscles has:

Two active sites : for bonding with F - actin and ATP

The sarcoplasmic reticulum (SR) in striated muscles is:

Related to the muscle contraction through the release of Ca2+ ions

The thin myofilaments in striated muscles are build of the following proteins:

Troponin, actin, tropomyosin

The three types of Troponin found in striated muscles are?

T - C and I - type

Troponin molecules from the thin myofilaments of striated muscles are:

Attached to tropomyosin molecules on specific locations

During contraction , muscle cells convert :

The chemical energy of ATP into mechanical work

Contraction of skeletal muscles begins after (choose the best) :

Certain latent period

Troponin I in skeletal muscles:

In the absence of Ca2+ it blocks the site of actin than bonds to myosin , and thus it inhibits the formation of actin - myosin cross bridges

Which of the following processes occurs immediately before the formation of actin-myosin cross bridges in skeletal muscles?

The bonding of Ca2+ with the molecules of Troponin C

What is the role of Troponin C in the contraction process in skeletal muscles?

Bonds to 4 Ca2+ ions, changes the conformation of the Troponin- tropomyosin complex, and allows the formation of actin - myosin cross bridge

The direct energy donor for the contraction of skeletal muscles is:

The hydrolysis of adenosine triphosphate

Which of the following processes take place in the sarcomere during contraction?

The sliding between thin and thick filaments

Which of the following processes is involved in the bending of the myosin head at 50 degrees after the formation of cross bridges?

The hydrolysis of ATP after bonding to the myosin head

in striated muscles, myosin heads bond to actin filaments to form cross- bridges:

Spontaneously

When an over threshold stimulus reaches the striated muscle cell, the following events take place:

Release of calcium from the sarcoplasmic reticulum

Muscle contractions could be classified in the following three types:

Isometric, isotonic, auxotonic

Which of the following types of muscle contraction does not produce classical work even though there still is an ATP consumption?

isometric

The major source of Ca2+ for skeletal muscle contraction is:

intracellular depots located in the sarcoplasmic reticulum

Choose the correct statement regarding striated muscles:

Muscle contraction (mechanical event) comes second , and it is triggered by an action potential (electrical event) in the membrane of the contracting cell.

What is the role of Ca2+ in the contraction of striated muscles?

Ca2+ ions (at most 4) bond to Troponin C, cause a conformational change which allows myosin to bond to actin and form cross-bridges

Which set of characteristics describes best the contraction of striated muscles?

Voluntary, fast, large energy intake

Electro mechanical (excitation - contraction) coupling in the so called “triad” in striated muscle cells occurs when:

An action potential activates the voltage gated dihydropyridine receptors

Which of the following muscles do not have a sarcomere ?

Smooth muscles

The lighter shaded H zone in skeletal muscle fibres is made of:

Myosin

The Troponin molecule bonds to:

Tropomyosin

What facilitates the Ca2+ transport from the sarcoplasm into the sarcoplasmic reticulum?

Ca2+ pumps

During the contraction of striated muscles , the following section of the sarcomere remains without change:

The length of A - band (anisotropic)

The resting potential of the sarcolemma is:

More positive than the K+ equilibrium potential

During the process of electro-mechanical coupling in striated muscle cells, Ca++ ions are released into the sarcoplasm and bond to this protein:

Troponin

Which type of troponin bonds to calcium?

Troponin C

In striated muscle, the regulation of contractions with Ca2+ ions can be classified as:

Actin-based regulation

During the contraction of striated muscles, the length of this feature will shorten:

The length of the sarcomere

What is meant by the term “electro-mechanical coupling”:

The connection between an electrical signal and muscle contraction

The thin myofilaments of the striated muscle cells contain:

Actin, tropomyosin, troponin

Transverse tubules (T tubules) are features in the membrane of:

Striated muscles

The cross sectional arrangement of actin and myosin filaments in the sarcomere of skeletal muscles is:

Hexagonal

Muscle contraction in striated muscles is induced by:

Ca2+ influx into the cytosol

Order the following processes, related to the striated muscle contraction, according to their sequence of occurrence:

A) activation of dyhidropyridine receptors at the sarcolemma and ryanodine receptors of the sarcoplasmic reticulum

(B) contraction

(C) excitation of action potential

D) release of the Ca2+ from the sarcoplasmic reticulum

E) calcium regulation of the contraction reticulum

1. (C) excitation of action potential

2. (E) calcium regulation of the contraction reticulum

3. (A) activation of dyhidropyridine receptors at the sarcolemma and ryanodine receptors of the sarcoplasmic reticulum

4. (D) release of the Ca2+ from the sarcoplasmic reticulum

5. (B) contraction

Thick myofilaments are composed of the protein:

Myosin

Myofilaments of the striated muscle cells are composed of the proteins:

Myosin, actin , Troponin, tropomyosin,

The resting potential for skeletal muscle cells is about:

-75 mV

The source of calcium for the contraction of striated muscles is:

Sarcoplasmic reticulum

Acetylcholine (ACh) is a neurotransmitter that takes a major part in the contraction of striated muscle. How can ACh be inhibited without blocking the ACh - receptors at the membrane?

Through the hydrolysis of ACh by acetylcholinesterase

Choose the correct order of events, related to the increase of Ca2+ concentrations in sarcoplasm to 10 -5 M:

Ca2+ bonds to Troponin C ➡️ change in confirmation of the Troponin - tropomyosin complex ➡️ myosin heads are allowed to bond to actin ➡️ formation of cross bridges

OPEN Q- describe the sequence of events starting with an action potential and leading to the contraction of striated muscles:

1. action potential in a motor neuron triggers the release of Ca2+ ions from the sarcoplasm reticulum

2. calcium ions bind to Troponin (on actin) and cause tropomyosin to move, exposing binding sites for the myosin heads

3. the actin filaments and myosin heads form a cross bridge that is broken by ATP

4. ATP hydrolysis causes the myosin heads to swivel and change orientation

5. Swiveled myosin heads bind to the actin filament before returning to their original confirmation

6. the repositioning of the myosin heads move the actin filaments towards the centre of the sarcomere

7. the sliding of actin along myosin therefore shortens the sarcomere, causing muscle contraction

OPEN q- Describe the difference between actin-regulated and myosin-regulated muscle contraction.

• In actin-linked regulation = Troponin and Tropomyosin regulates actin by sites on actin required for the actin-myosin complex

• In myosin-linked regulation =myosin are blocked in the absence of calcium

OPEN q- Describe the sequence of events in a striated muscle cell following the formation of actin-myosin cross-bridge.

● Cross bridge occurs when the myosin head attaches to the actin while adenosine diphosphate (ADP) and inorganic phosphate (Pi) are still bound to myosin

● Pi is then released, causing myosin to form a stronger attachment to the actin,

● after which the myosin head moves toward the M-line, pulling the actin along with it.

● As actin is pulled, the filaments move  toward the M-line.

● This movement is called the power stroke

● as movement of the thin filament occurs at this step.

● In the absence of ATP, the myosin head will not detach from actin.

OPEN Q- Which major neurotransmitter has excitatory effects on skeletal muscles? What are the cellular mechanisms that carry this excitation?

Google ans: neurotransmitter acetylcholine is excitatory at the neuromuscular junction in skeletal muscle, causing the muscle to contract

Acetylcholine

● Synaptic terminal receives AP and releases ACh , which binds to the receptor in muscle and triggers AP in the muscle fibre

● AP is then propagated along the plasma membrane and down t-tubules

OPEN q - Sketch a sarcomere and label its major components: