chap 8

• Muscles


  Soft tissues found in most animals
• Muscle


  • Soft tissue found in both animals and humans
  • Cells comprise protein filaments of actin and myosin that slide past one another, producing contraction and changes in length and shape
• Term "muscle"


  Derived from the Latin word "musculus" which refers to a little mouse, due to the shape of certain muscles or the contraction of muscles that look like a moving mouse
• Functions of muscles in humans

  • Locomotion
  • Maintaining and changing body posture
  • Circulation of blood cells throughout the body
  • Movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis
• Human muscular system


  • Includes more than 600 muscles, which make up about 40 to 50 percent of the total body weight
  • Muscles are attached to bones, blood vessels, and other internal organs
  • Mainly composed of skeletal muscles, tissue, tendons, and nerves
  • Muscles are composed of a kind of elastic tissue
• Every movement in our body is the result of muscle contraction and is found in every organ, including the blood vessels, heart, digestive organs, etc.
• The energy required for the functioning of muscles is predominantly powered by the oxidation of fats and carbohydrates particularly from the stored energy molecules adenosine triphosphate (ATP)
• Types of muscles


  • Skeletal or striated muscles
  • Cardiac muscles
  • Smooth muscles
• Classification of muscles based on muscle action

  • Voluntary muscles
  • Involuntary muscles
• Skeletal muscles


  • Muscle tissue that is attached to the bones and is involved in the functioning of different parts of the body
  • Also called voluntary muscles as they come under the control of the central nervous system in the body
• Structure of skeletal muscle

  • Series of muscle fibers composed of muscle cells, which are long and multinucleated
  • Cylindrically shaped with branched cells attached to the bones by an elastic tissue or collagen fibers called tendons
  • Group of muscle fibers present below the epimysium, collectively called the fascicles
  • Muscle fibers surrounded by a protective shield formed from collagen called the perimysium
• Functions of skeletal muscle

  • Maintains body posture
  • Regulates body temperature
  • Connects to and controls the motions of the skeleton
  • Responsible for performing muscular involuntary movements
  • Responsible for body movements such as breathing, extending the arm, typing, writing, etc.
  • Responsible for the erect posture of the body
  • Protect the internal organs and tissues from any injury and also provide support to these delicate organs and tissues
  • Support the entry and exit points of the body
• Cardiac muscles


  • Found only in the heart and are self-stimulating, with an intermediate speed of contraction and energy requirement
  • Not part of the musculoskeletal system
  • Striated muscles responsible for keeping the heart functioning by pumping and circulating blood throughout the body and performing muscular involuntary movements
  • Involved in continuous rhythmic contraction and relaxation
• Structure of cardiac muscle

  • Exists only within the human heart
  • Specialized form of muscle that evolved to continuously and repeatedly contract, providing circulation of blood throughout the body
  • Has a regular pattern of fibers similar to that of smooth muscles
  • Comprise cylindrical, branched fibers and a centrally located nucleus
  • T-tubules or transverse tubules are rich in ion channels and are found in the atrial muscle cells
  • Striated muscles with cylindrical-shaped cells, which include intercalated discs and join neighboring fibers
• Functions of cardiac muscle

  • Regulate the functioning of the heart by the relaxation and contraction of the heart muscles
  • Function as the involuntary muscles
  • Involved in the movement or the locomotion
  • Work without stopping, day and night, automatically, to make the heart contract and fill up with blood again
  • Comprise "pacemaker" cells that contract and expand in response to electrical impulses from the nervous system
• Smooth muscles


  • Non-striated, involuntary muscles, controlled by the Autonomous Nervous System (ANS)
  • Found almost in all organs such as the stomach, bladder, blood vessels, bile ducts, the eye, the sphincters, the uterus, etc.
  • Function by stimulating the contractility of the digestive, urinary, and reproductive systems, blood vessels, and airways
  • Spindle-shaped with a single nucleus
  • Under involuntary control, cannot be moved with conscious thought
• Structure of smooth muscles

  • Spindle-shaped muscle fibers with a single nucleus
  • Thickness ranges between 3-10 µm and length ranges between 20 to 200 μm, shorter compared to skeletal muscle
  • Lack filaments, special proteins, actin, and myosin and produce their own connective tissue
• Functions of smooth muscles

  • Involved in the sealing of orifices
  • Produces connective tissue proteins such as collagen and elastin
  • Transports chyme (a pulpy acidic fluid) for the contractions of the intestinal tube
  • Plays a vital role in the circulatory system by maintaining and controlling the blood pressure and flow of oxygen throughout the body
  • Responsible for contracting the irises, raising the small hairs on your arm, contracting the sphincters in our body, and movement of fluids through organs
  • Much more useful for providing consistent and elastic tension
• Voluntary muscles


  • Long, multinucleated cells, containing sarcomeres arranged into bundles
  • Composed of cylindrical fibers and usually attached to bones and the skin
  • Play an important role in allowing the body to move by contracting and relaxing, and their actions are mainly under the control of the somatosensory nervous system
  • Include skeletal muscles
• Involuntary muscles


  • Striated and branched in the case of cardiac muscle
  • Actions mainly controlled by the autonomic nervous system in the body
  • Include smooth muscles and cardiac muscles