lab lesson 7

Introduction to Muscle Tissue

• Focus on muscle tissue as a complex topic across several lectures.

• Importance of recognizing the parts and functions rather than mastering muscular contraction initially.

• Emphasis on basic terms and structures related to muscle.

Types of Muscle Tissue

• Skeletal Muscle:

  • Long, striated cells with multiple nuclei; primarily voluntary control.

  • Provides movement by pulling bones.

  • Example of a muscle: Biceps, with muscle cells organized into bundles called fascicles.

• Cardiac Muscle:

  • Found in the heart; involuntary, striated, branched cells with one or two nuclei.

  • Contains intercalated discs for cell communication and stability.

• Smooth Muscle:

  • Non-striated, involuntary; smaller than skeletal muscle.

  • Found in walls of hollow organs (e.g., blood vessels, digestive tract).

  • Functions to constrict lumens rather than pulling in one direction.

Muscle Structure and Organization

• Muscle Fascicles: Bundles of muscle cells; the organization aids in contraction.

  • Epimysium: Connective tissue surrounding the entire muscle.

  • Perimysium: Connective tissue around each fascicle.

  • Endomysium: Connective tissue surrounding individual muscle cells.

• Muscle Cells (Fibers): Long cells filled with myofibrils, organized to facilitate contraction.

• Myofibrils:

  • Composed of actin and myosin proteins crucial for contraction.

  • Non-membrane bound organelles unique to skeletal and cardiac muscle.

Sarcomere Structure

• The basic unit of contraction in myofibrils.

• Composed of:

  • Z Disc: Ends of sarcomeres where actin filaments are anchored.

  • M Line: Middle line where myosin filaments attach.

  • A Band: Area containing myosin; darker in histological images.

  • I Band: Area of only actin; lighter in histological images.

  • H Zone: Region within the A band where only myosin is present.

Mechanism of Muscle Contraction

• Contraction Process:

  • Actin and myosin slide past each other (sliding filament theory) when calcium ions interact via troponin and tropomyosin.

  • Tropomyosin prevents interaction until troponin changes shape in presence of calcium, allowing contraction to occur.

• Calcium Storage: Exclusively in the sarcoplasmic reticulum, released into the cytosol during muscular contraction.

Role of the Nervous System

• Nervous system triggers calcium release from the sarcoplasmic reticulum, initiating contraction.

• T Tubules: Extensions of the cell membrane allowing rapid communication of the contraction signal to all myofibrils.

Differences between Muscle Types

• Cardiac vs. Skeletal Muscle:

  • Cardiac muscle relies heavily on aerobic metabolism due to higher mitochondrial content.

  • Structural differences include the presence of intercalated discs in cardiac muscle.

• Smooth Muscle:

  • No myofibrils; different arrangement of sarcomeres; contractions are more scrunching and multidirectional.

Muscle Nomenclature and Function

• Muscles are generally named based on:

  • Location (e.g., pectoralis major on the chest).

  • Size (e.g., maximus, minimus).

  • Shape (e.g., deltoid for triangular).

  • Action (e.g., levator for lifting).

  • Attachment points (e.g., biceps means two attachments).

Muscle Actions

• Key actions include:

  • Flexion/Extension: Decreasing/increasing angle of joints.

  • Adduction/Abduction: Moving limbs towards or away from the midline.

  • Medial/Lateral Rotation: Rotating towards or away from the body.

  • Elevation/Depression: Raising or lowering body parts (e.g., shoulders).

  • Protraction/Retracting: Moving forward/backward (e.g., jaw).

Conclusion

• Understanding the parts, structures, and basic functions of muscular tissue is crucial for further study and application in anatomy and physiology.

• Regular repetition of related content will aid in mastering complex topics in muscle physiology.