zoo-lect

• Muscular System


  Muscles provide the force essential for movement in all animals
• Vertebrates


  • Use their endoskeleton in conjunction with muscles to move
  • Movement is usually elicited in response to the information provided by the central nervous system (CNS)
  • Skeletal muscles move the body
  • Smooth muscles move materials through tubular organs and change the size of tubular openings
  • Cardiac muscle produces the beating of the heart
• Three Principal Kinds of Animal Movement

  • Amoeboid Movement
  • Ciliary and Flagellar Movement
  • Muscular Movement
• Amoeboid Movement


  • Exhibited by amoebas, many wandering cells of higher animals (white blood cells and embryonic mesenchyme)
  • Amoeboid cells change their shape by sending out and withdrawing pseudopodia from any point on the cell surface
• Ciliary Movement


  • Exhibited by ciliated protozoans and all major groups of animals, except nematodes and arthropods
  • Cilia are responsible for moving small animals such as protozoa through their aquatic habitat or in propelling fluids and materials across the epithelial surface of larger animals
  • Cilia lining respiratory airways, usually, prevent contaminants trapped in the mucus from reaching the lungs by sweeping mucus toward the throat
  • The sweeping action of ciliated cells lining the female reproductive tract facilitates the conduction of egg cells toward the oviducts and eventually to the uterus
• Flagellar Movement


  • Exhibited by flagellated protozoa, animal spermatozoa, and sponges
  • Flagellum is a whip-like structure longer than a cilium and usually present singly or in small numbers at one end of a cell
  • Cilia and flagella are structurally the same and differ only in their beating pattern
  • A flagellum beats symmetrically with snake-like undulation; hence the water is propelled parallel to the long axis of the flagellum
  • A cilium beats asymmetrically with a fast power stroke in one direction followed by a slow recovery during which the cilium bends as it returns to its original position; the water is propelled parallel to the ciliated surface
  • Cilia and flagella are moved by microtubules
• Muscular Movement


  • Brought about by the contraction of muscle cells or fibers; the muscle fibers shorten as they contract
  • Exhibited by the rest of the members of the animal kingdom
• Types of Invertebrate Muscle

  • Bivalve molluscan muscles contain striated muscle and smooth muscle
  • Insect flight muscles are fibrillar muscle

  
• Bivalve molluscan striated muscle

  • Capable of rapid contraction due to the presence of sliding thick and thin filaments, which aid the invertebrate to snap shut its valves when under stressed or disturbed condition
• Bivalve molluscan smooth muscle

  • Capable of slow yet long-lasting contractions, due to the intermediate filaments, which aid the invertebrate to keep its valves tightly shut for hours or even days
• Insect flight muscles


  • Contract at frequencies greater than 1,000 beats per second
• Types of Vertebrate Muscle

  • Skeletal Muscle
  • Cardiac Muscle
  • Smooth Muscle

  
• Skeletal Muscle


  • Named skeletal muscle because it is attached to skeleton and makes possible the movements of the trunk, appendages and other body parts
  • Consists of skeletal muscle cells, called muscle fibers, which are large, striated, cylindrical, and multinucleated cells that develop through the fusion of many individual cells
  • The muscle fibers are bundled together by a connective tissue into a fascicle
  • Most skeletal muscles taper at their ends, where they connect to bones by tendons
  • Skeletal muscles contract powerfully and quickly but fatigue more quickly than does smooth muscle
  • Skeletal muscles are also called voluntary muscles because they are stimulated by motor fibers and are under conscious cerebral control

  
• Cardiac Muscle


  • Striated, uninucleated, and is composed of branching cell fibers that give cardiac muscle an ability to resist tearing, making the heart walls tolerant of high pressures
  • Strong mechanical adhesions between adjacent cardiac muscle cells are provided by intercalated discs containing gap junctions for rapid conduction of impulses
  • Combines certain characteristics of both skeletal and smooth muscles; it is fast acting and striated like skeletal muscle, but contraction is under involuntary autonomic control like smooth muscle
  • Muscle contraction is initiated by specialized cardiac muscle cells, called the pacemaker cells which initiate the rhythmic contractions of the heart
• Smooth Muscle


  • Non-striated with long, tapering single-nucleated cells that are found encircling the walls of hollow, internal organs
  • The contractile machinery is not obvious when cells are viewed under light microscope since filaments of actin and myosin are not as regularly arranged unlike in striated muscle type
  • Primary functions include movement of material in the internal organs, such as the stomach, by peristalsis or regulation of the opening of certain organs, such as arteries, by sustained contraction
  • Smooth muscle is usually slow acting and can maintain prolonged contractions with very little energy expenditure; it is under the control of the autonomic nervous system, thus its contractions are involuntary and unconscious
• Functions of Muscles


  • Movement
  • Stabilization of body positions
  • Organ volume regulation
  • Thermogenesis
• Movement


  Relies on the integrative functioning of bones, joints, and skeletal muscles
• Stabilization of body positions


  Maintenance of posture, e.g. the contraction of the sternocleidomastoid and other muscles of the neck maintains the upright position of the head
• Organ volume regulation


  Exemplified in the regulation of contents of urinary bladder, gall bladder, heart, etc.
• Thermogenesis


  Contraction generates 85% of body heat
• Muscle


  Covered by epimysium and consists of many fascicles/fasciculi