M-7

• Muscles make up the bulk of the body and account for 1/3 of its weight
• Blood vessels and nerves run to every muscle, helping control and regulate each muscle's function
• Muscular System


  Composed mainly of muscle tissue, the most abundant tissue of the body & one of the most adaptable
• Major functions of the muscular system

  • Movement of the body
  • Maintenance of posture
  • Respiration
  • Production of body heat
  • Communication
  • Constriction of organs and vessels
  • Contraction of the heart
• The muscular system creates body heat and also moves the bones of the Skeletal system, food through Digestive system, blood through the Circulatory system, and fluids through the Excretory system
• Epimysium / Muscle Fascia


  Connective tissue sheath that surrounds entire skeletal muscle (outside)
• Muscle Fascicles

  Bundles of muscle fibers
• Perimysium


  Loose connective tissue that separates muscle fascicles from each other
• Muscle Fiber


  Separate muscle cells in each fascicle; a single cylindrical cell with several nuclei
• Endomysium


  Loose connective tissue that surround each muscle fiber
• Sarcolemma


  Muscle Fiber Structure
• T Tubules

  Tube-like inward folds associated with sarcoplasmic reticulum; connects the sarcolemma to terminal cisternae to form a triad
• Sarcoplasmic Reticulum


  A type of smooth ER that surrounds myosin; stores & releases Ca2+
• Terminal Cisternae


  Enlarged portion of the sarcoplasmic reticulum; part of triad
• Sarcoplasm


  Cytoplasm that contains many bundles of myofibrils
• Myofibrils


  Thread-like bundles of proteins that make up muscle fibers
• Myofilaments


  Protein fibers that make up the myofibrils (actin and myosin)
• Actin Myofilaments


  Thin myofilament that are made up of 3 components: Actin strands, Troponin molecules, Tropomyosin filaments
• Myosin Myofilaments

  Thick myofilaments; contain myosin heads that have 3 important properties: 1) Bind to attachment sites on actin myofilaments, 2) Bend & straighten during contraction, 3) Break down ATP, releasing energy
• Muscle Tissue

  • Skeletal
  • Cardiac
  • Smooth
• Skeletal Muscle

  • Attach to and move bones by contracting and relaxing in response to voluntary messages from the nervous system
  • Composed of long cells called muscle fibers that have a striated appearance
  • Organized into bundles supplied by blood vessels and innervated by motor neurons
• Skeletal muscles attach to bones by tendons (connective tissue) and enable movement
• The typical male body contains approximately 640 muscles, which compose around two-fifths of its weight. The same number in a female body make up a slightly smaller proportion
• Tendons


  Tough, fibrous cords of connective tissue that link skeletal muscles to bones
• Tendons in the hands and feet are enclosed in self-lubricating sheaths to protect them from rubbing against the bones
• Skeletal Muscles


  • Also known as voluntary muscles, since we control their actions at will, and as striated muscles, from their microscopic appearance
  • Connected to the skeleton, either to bone or to connective tissues such as ligaments
  • Always attached at two or more places
• Smooth Muscle

  • In the walls of body parts such as the airways, stomach, Alimentary canal, and blood vessels
  • Involuntary muscle, because it works automatically rather than under conscious control
• Cardiac Muscle


  • Makes up the walls of the heart
  • Part of both the Muscular System and the Circulatory System
  • Responsible for circulating blood throughout the body
  • Has its own pacemaker for rhythmic beating
• How skeletal muscles move

  1. Somatic signals are sent from the cerebral cortex to nerves associated with specific skeletal muscles

  2. Signal, an impulse called an action potential, travels through a motor neuron

  3. Neuromuscular junction is where the motor neuron reaches a muscle cell

  4. Chemical message, a neurotransmitter called acetylcholine, binds to receptors on the muscle fiber

  5. Multistep molecular process within the muscle fiber begins

  6. When stimulation of the motor neuron stops, the chemical reaction that causes muscle contraction is reversed and the muscle relaxes
• Muscle Pairs

  • Muscles are grouped together in pairs on the skeleton
  • Muscles can't push - they only contract and pull the bones to which they are anchored
• When one muscle of a pair contracts, the other relaxes
• Skeletal muscles only pull in one direction, so they always come in pairs
• Facial Muscles


  • Interact to steady and move the head and to move facial features such as the eyebrows, eyelids, and lips
  • Highly complex, allowing for a huge range of facial expressions
  • Some are anchored to bones, others are joined to tendons or to dense, sheet-like clusters of fibrous connective tissue called aponeuroses
  • Many have their other end inserted into deeper layers of the skin, so even slight muscle contraction produces movement of the face's skin, revealing expressions or emotions
• Laughter Lines


  Wrinkles that form as the skin's elastin degenerates with age and the skin can no longer stretch or shrink easily
• Facial Expressions


  • Among our most important methods of non-verbal communication
  • Convey an enormous variety of emotions
• The smile is a highly ambiguous and versatile expression, which can also convey relief or pity, or widen into a grin for sarcastic disapproval
• A frown can articulate various feelings, including disappointment and confusion
• Carpal Tunnel Syndrome


  • Occurs when the tendons in the carpal tunnel become inflamed, causing compression of the median nerve
  • Symptoms include pain, numbness, and eventual weakness in the hand
  • Can occur due to repetitive movements, hereditary predisposition, diabetes, or thyroid disorders
• Bursitis


  • Occurs when bursae (fluid-filled sacs that cushion bones, tendons, and muscles near joints) become red and inflamed, causing pain
  • Often occurs near joints that perform frequent repetitive motion, such as the shoulder, elbow, hip, and knee
• The strongest muscle in the body is the masseter (jaw)