Skeletal Muscle Basics

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Questions and Answers

What is the primary function of the sarcoplasm in skeletal muscle fibers?

Provision of ATP for muscle contraction (correct)

Conduction of action potentials

Storage of Ca2+ ions

Maintenance of the transmembrane potential

Which of the following is NOT a characteristic of skeletal muscle?

Ability to initiate their own contraction (correct)

Support of soft tissue

Controlled by the somatic nervous system

Voluntary contraction

What is the primary function of the transverse tubules (T-tubules) in skeletal muscle fibers?

Storage of Ca2+ ions

Regulation of muscle contraction

Passage of nerve messages directly to the sarcoplasmic reticulum (correct)

Conduction of action potentials

What is the purpose of the extensive vascular system in skeletal muscle?

To supply oxygen and nutrients, and to carry away wastes Signup and view all the answers

What is the role of the sarcoplasmic reticulum (SR) in skeletal muscle fibers?

Storage of Ca2+ ions Signup and view all the answers

Which of the following is a characteristic of skeletal muscle fibers?

Development from myoblasts Signup and view all the answers

What is the purpose of the connective tissue (epimysium, perimysium, endomysium) in skeletal muscle?

To provide structural support to the muscle Signup and view all the answers

What is the role of the sarcolemma in skeletal muscle fibers?

Maintenance of the transmembrane potential Signup and view all the answers

In the T-tubule membrane, what is the function of DHPR?

Voltage-gated sensors Signup and view all the answers

What is the primary function of Troponin-C?

Binding to Ca2+ ions Signup and view all the answers

What is the main component of thick fibers in myofibrils?

Myosin Signup and view all the answers

What is the function of Nebulin in myofibrils?

Non-elastic anchor Signup and view all the answers

What is the structure formed by a transverse tubule flanked by two terminal cisternae?

Triad Signup and view all the answers

What is the function of Tropomyosin in resting muscle cells?

Prevents muscle contraction Signup and view all the answers

What is the binding site for actin in myofibrils?

Heavy chain of myosin Signup and view all the answers

What is the function of Titin in myofibrils?

Keeps the myosin and actin in place Signup and view all the answers

Study Notes

Muscle Structure and Function

A/I bands and H zones are fused together in skeletal muscle.
DHPR (Dihydropyridine receptor) is a voltage-gated sensor in the T-tubule membrane.
RYR (Ryanodine Receptor) is a Ca2+ release channel in the SR membrane.

Muscle Fiber Components

Myofibrils: site of contraction, consisting of thick and thin filaments.
Thick filaments: • Made up of myosin, composed of 2 heavy chains and 4 light chains. • Heavy chain is the motor domain for binding ATP and releasing to create movement.
Thin filaments: • Actin: a globular protein that polymerizes to form F-actin filaments. • Tropomyosin: a strand protein wrapped spirally around F-actin filaments. • Troponin: a complex of 3 subunits (T, I, and C) that regulate muscle contraction.

Troponin and Muscle Contraction

Troponin-C binds to 4 Ca2+ ions, initiating muscle contraction.
In the absence of Ca2+, tropomyosin inhibits myosin head attachment to actin, preventing contraction.
When Ca2+ binds to troponin, the complex shifts, allowing myosin heads to bind to actin and initiate contraction.

Skeletal Muscle Characteristics

Contract in response to signals from somatic motor neurons.
Cannot initiate their own contraction.
Functions: movement, maintaining posture, supporting soft tissue, and storing nutrient reserves.

Skeletal Muscle Structure

Consists of muscle fibers developed from myoblasts.
Surrounded by connective tissue (epimysium, perimysium, and endomysium).
Nerves: controlled by somatic nervous system, with each fiber supplied with nerve endings that control contraction.
Blood vessels: extensive vascular system supplies oxygen and nutrients and removes waste.

Muscle Fiber Components

Sarcolemma: maintains transmembrane potential.
Sarcoplasm: rich in glycogen and myoglobin, providing ATP for muscle contraction.
Myofibrils and sarcoplasmic reticulum (SR): site of muscle contraction and Ca2+ storage.

Transverse Tubules (T-Tubules) and Sarcoplasmic Reticulum (SR)

T-tubules: passageways from extracellular space to terminal cisternae of SR, allowing nerve message and nutrient passage.
SR: stores Ca2+ at rest, releasing it upon stimulation, and pumping it back in the absence of stimulation.