7.8 Structure of Skeletal Muscles

Skeletal muscles or striated muscles show alternate light and dark regions under microscope. They are composed of muscle fibres or muscle cells. Bundles of muscle fibres are enclosed by collagen fibres and connective tissue. At the ends of the muscle, the collagen and connective tissue forms tendons which attach the muscle to skeletal elements.

Definition

Skeletal Muscles: Skeletal muscles or striated muscles show alternate light and dark regions under microscope. Skeletal muscles are composed of muscle fibres or muscle cells.

Main Idea

• Skeletal muscles show alternate light and dark regions under microscope.
• They are composed of muscle fibres or muscle cells.
• Bundles of muscle fibres are enclosed by collagen fibres and connective tissue.
• At the ends of the muscle, the collagen and connective tissue forms tendons.
• Tendons attach the muscle to skeletal elements.
• Each skeletal muscle fibre is a single cylindrical cell.
• It is enclosed by a plasma membrane like structure called sarcolemma.
• It has several nuclei.
• The sarcolemma penetrates deep into the cell to form a hollow elongated tube, the transverse tubule (T-tubule).
• The cytoplasm of the muscle fibre is called sarcoplasm.
• It contains sarcoplasmic reticulum.
• Within the muscle fibres are numerous thin myofibrils which possess characteristic cross striations.
• The myofibrils are 1-2 μm in diameter.
• They run in parallel fashion and extend the entire length of the cell.
• Each myofibril is composed of two types of myofilaments: thin myofilaments and thick myofilaments.

Core Concept

• Skeletal muscles = striated muscles
• Muscle fibres = muscle cells
• Tendons = attach muscle to skeletal elements
• Sarcolemma = plasma membrane of muscle fibre
• T-tubule = transverse tubule
• Sarcoplasm = cytoplasm of muscle fibre
• Sarcoplasmic reticulum = endoplasmic reticulum of muscle fibre
• Myofibrils = thin, thread-like structures
• Myofilaments = thin and thick
• Striations = alternate light and dark regions

Detailed Explanation

Structure of Skeletal Muscles

• Skeletal muscles or striated muscles show alternate light and dark regions under microscope.
• Skeletal muscles are composed of muscle fibres or muscle cells.
• Bundles of muscle fibres are enclosed by collagen fibres and connective tissue.
• At the ends of the muscle the collagen and connective tissue forms tendons which attach the muscle to skeletal elements.
• Each skeletal muscle fibre is a single cylindrical cell, enclosed by a plasma membrane like structure called sarcolemma and has several nuclei.
• The sarcolemma of muscle fibre cell penetrates deep into the cell to form a hollow elongated tube, the transverse tubule (T-tubule).
• The cytoplasm of the muscle fibre is called sarcoplasm.
• It contains sarcoplasmic reticulum.
• Within the muscle fibres are numerous thin myofibrils which possess characteristic cross striations.
• The myofibrils are 1-2 μm in diameter that run in parallel fashion and extend the entire length of the cell.
• Each myofibril is composed of two types of myofilaments: thin myofilaments and thick myofilaments.

Summary Table of Skeletal Muscle Structure

Intermediate Level

Structure of Skeletal Muscles

Detailed Description of Each Structure

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Skeletal muscles are striated.
• 2. They show alternate light and dark regions.
• 3. They are composed of muscle fibres.
• 4. Bundles of muscle fibres are enclosed by collagen and connective tissue.
• 5. Tendons attach muscle to skeletal elements.
• 6. Each muscle fibre is a single cylindrical cell.
• 7. Sarcolemma is the plasma membrane.
• 8. Sarcolemma penetrates to form T-tubules.
• 9. Sarcoplasm is the cytoplasm.
• 10. Sarcoplasmic reticulum is the endoplasmic reticulum.
• 11. Myofibrils are thin, thread-like structures.
• 12. Myofibrils are 1-2 μm in diameter.
• 13. Myofibrils run in parallel.
• 14. Myofibrils extend the entire length of the cell.
• 15. Myofibrils possess cross striations.
• 16. Myofibrils are composed of thin and thick myofilaments.
• 17. Muscle fibres have several nuclei.
• 18. Skeletal muscles are attached to bones.
• 19. Skeletal muscles are responsible for movement.
• 20. Skeletal muscles produce heat.

Remember

• - Skeletal muscles = striated muscles
• - Muscle fibres = muscle cells
• - Tendons = attach muscle to skeletal elements
• - Sarcolemma = plasma membrane of muscle fibre
• - T-tubule = transverse tubule
• - Sarcoplasm = cytoplasm of muscle fibre
• - Sarcoplasmic reticulum = endoplasmic reticulum of muscle fibre
• - Myofibrils = thin, thread-like structures
• - Myofilaments = thin and thick
• - Striations = alternate light and dark regions

Common Mistakes

• 1. Confusing skeletal muscles with smooth or cardiac muscles — Skeletal = striated; smooth = unstriated; cardiac = striated.
• 2. Mixing up the structures — Sarcolemma, T-tubule, sarcoplasm, sarcoplasmic reticulum.
• 3. Forgetting the role of tendons — Attach muscle to bone.
• 4. Confusing myofibrils and myofilaments — Myofibrils are composed of myofilaments.
• 5. Mixing up the diameter of myofibrils — 1-2 μm.
• 6. Forgetting the number of nuclei — Muscle fibres have several nuclei.
• 7. Believing skeletal muscles are involuntary — Skeletal muscles are voluntary.
• 8. Mixing up the locations — Skeletal muscles are attached to bones.
• 9. Forgetting the role of striations — Alternate light and dark regions.
• 10. Mixing up the functions — Skeletal muscles move the skeleton.

Quick Revision

Skeletal muscles or striated muscles show alternate light and dark regions under microscope. Skeletal muscles are composed of muscle fibres or muscle cells. Bundles of muscle fibres are enclosed by collagen fibres and connective tissue. At the ends of the muscle the collagen and connective tissue forms tendons which attach the muscle to skeletal elements. Each skeletal muscle fibre is a single cylindrical cell, enclosed by a plasma membrane like structure called sarcolemma and has several nuclei. The sarcolemma of muscle fibre cell penetrates deep into the cell to form a hollow elongated tube, the transverse tubule (T-tubule). The cytoplasm of the muscle fibre is called sarcoplasm. It contains sarcoplasmic reticulum. Within the muscle fibres are numerous thin myofibrils which possess characteristic cross striations. The myofibrils are 1-2 μm in diameter that run in parallel fashion and extend the entire length of the cell. Each myofibril is composed of two types of myofilaments thin myofilaments and thick myofilaments.

60-Second Revision

• Skeletal muscles = striated muscles
• Muscle fibres = muscle cells
• Tendons = attach muscle to skeletal elements
• Sarcolemma = plasma membrane of muscle fibre
• T-tubule = transverse tubule
• Sarcoplasm = cytoplasm of muscle fibre
• Sarcoplasmic reticulum = endoplasmic reticulum of muscle fibre
• Myofibrils = thin, thread-like structures
• Myofilaments = thin and thick
• Striations = alternate light and dark regions
• Warning: Myofibrils are composed of thin and thick myofilaments

NEXT TOPIC

• Chapter:
• 7. Support and Movement

• Topic:
• 7.8.1 ULTRA-STRUCTURE OF SKELETAL MUSCLES

Source: