03/12 Lecture (Muscles)

Types of Muscle Tissue

• Skeletal Muscle

  • Found throughout the skeletal framework.

  • Responsible for voluntary movement (e.g., running, dancing, swimming).

• Cardiac Muscle

  • Exclusive to the heart; not found in other organs or tissues.

• Smooth Muscle

  • Present in various organs such as blood vessels (regulating blood pressure), gastrointestinal tract (moving food), reproductive tract (uterus), and urinary bladder (expelling urine).

Functions of Muscles

• Movement

  • Allows actions like walking, running.

• Stability

  • Helps maintain upright posture. Improper muscle function can lead to issues like palsy or tremors.

• Communication

  • Involves skeletal muscles like the tongue for speech and facial expressions, demonstrating conscious control.

• Control of Body Openings and Passages

  • Includes sphincters that regulate the flow of materials (food into stomach, waste out of the GI tract).

• Heat Production

  • Muscles generate heat, contributing to body temperature regulation.

Connective Tissue and Muscle Structure

• Connective Tissue Layers:

  • Endomysium: Surrounds individual muscle fibers.

  • Perimysium: Surrounds bundles of muscle fibers (fascicles).

  • Epimysium: Surrounds the entire muscle.

• Fascia:

  • Deep Fascia: Encases muscles.

  • Superficial Fascia: Sits beneath the skin.

Muscle Physiology

• Muscle Cells (Myofibrils):

  • Bundled into fascicles.

• Muscle Activity:

  • Upon reaching maturity, no new muscle cells are produced. Growth occurs through Hypertrophy (increase in cell size) rather than Hyperplasia (increase in cell number).

  • Atrophy: Decrease in muscle size occurs due to lack of use or disuse.

Muscle Contraction Mechanism

• Sarcoplasmic Structure:

  • Sarcoplasmic Reticulum: Stores calcium essential for muscle contraction.

  • Contains unique components like T-tubules, terminal cisternae, and caveolae for calcium uptake.

• ATP Requirement:

  • ATP is essential for muscle contraction and relaxation.

Sarcomere Structure

• Sarcomere: Defined from one Z-disc to another.

• Components:

  • Thick Filaments: Primarily made of Myosin.

  • Thin Filaments: Primarily made of Actin, plus Tropomyosin and Troponin.

• Band Structures:

  • A Band: Length of myosin regardless of contraction.

  • I Band: Region containing actin only, decreases in size during contraction.

  • H Zone: Space between thin filaments, diminishes during contraction.

  • M Line: Center of the A Band.

Muscle Injuries

• Muscle Tears:

  • Result from overstretching or excessive load.

  • Leads to scar tissue formation and compromised muscle function.

Muscle Fiber Types

• Slow Oxidative (Type I):

  • Endurance fibers, resistant to fatigue.

• Fast Glycolytic (Type II):

  • Power-oriented, fatigue more easily.

  • World-class athletes often exhibit a higher proportion of type II fibers.

Neuromuscular Junction

• Components:

  • Motor Neurons: Release neurotransmitter Acetylcholine (ACh) that initiates muscle contraction.

  • AChE (Acetylcholinesterase): Breaks down acetylcholine, terminating the signal.

• Paralysis Causes:

  • Blocking ACh receptors leads to muscle paralysis.

  • Use of Curare in anesthesia leads to temporary muscle paralysis.

Conclusion

• Muscular fitness involves consistent practice, patience, and understanding of anatomy. Muscle anatomy knowledge is critical for medical practices and assessing physical performance.