Muscle tissue

• • Muscle tissue is a specialized tissue found in animals which functions by contracting and thereby causing movement.
  • This contraction is achieved through the interaction of actin and myosin filaments within muscle cells, known as muscle fibers.
  • Muscle tissue is categorized into three types: skeletal muscle, cardiac muscle, and smooth muscle, each with distinct structures and functions.

  Types of Muscle Tissue

  1. Skeletal Muscle

     • Structure: Long, cylindrical, multinucleated fibers with striations from actin and myosin filaments arranged in sarcomeres.
     • Location: Attached to bones by tendons.
     • Function: Responsible for voluntary movements, posture maintenance, and heat generation.
     • Control: Voluntary, via the somatic nervous system.

  2. Cardiac Muscle

     • Structure: Branched cells (cardiomyocytes) connected by intercalated discs with gap junctions and desmosomes; striated like skeletal muscle.
     • Location: Walls of the heart.
     • Function: Pumps blood rhythmically and continuously.
     • Control: Involuntary, regulated by the autonomic nervous system and intrinsic conduction systems.

  3. Smooth Muscle

     • Structure: Spindle-shaped cells with a single central nucleus; lacks striations due to less organized actin and myosin.
     • Location: Walls of hollow organs (e.g., intestines, blood vessels, bladder, uterus).
     • Function: Involuntary movements such as peristalsis, vasoconstriction, and contractions during childbirth.
     • Control: Involuntary, via the autonomic nervous system.

  Structure of Muscle tissue:

  • Skeletal muscle: Multinucleated, long, cylindrical cells with a striated appearance.
  • Smooth muscle: Spindle-shaped, uninucleated cells without striations.
  • Cardiac muscle: Uninucleated, branched cells with striations and intercalated discs.

  Microscopic Structure

  

  1. Myofibrils:
  • Each muscle fiber contains numerous myofibrils, which are the contractile elements made up of repeating units called sarcomeres.
  2. Sarcomeres:
  • The basic functional unit of a myofibril, consisting of actin (thin) and myosin (thick) filaments. The arrangement of these filaments gives skeletal and cardiac muscle their striated appearance.
  3. Sarcoplasmic Reticulum:
  • A specialized form of the endoplasmic reticulum that stores and releases calcium ions, which are essential for muscle contraction.
  4. Mitochondria:
  • Muscle cells contain numerous mitochondria to meet the high energy demands required for contraction.

  Location:

  • Skeletal muscle: Attached to bones by tendons.
  • Smooth muscle: Walls of internal organs like the stomach, intestines, and blood vessels.
  • Cardiac muscle:

  Functions:

  • Movement: Muscle contractions enable body movement, facial expressions, and posture.
  • Regulation: Smooth muscle contractions regulate blood flow and control the passage of food through the digestive system.

  Pumping: Cardiac muscle contractions pump blood throughout the body.

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