Mascular

• Muscular System


  Functions: Producing movement, Maintaining posture, Stabilizing joint, Generating heat, Communication, Constriction of organs, Contraction of heart
• Types of Muscle Tissue

  • Skeletal: voluntary, striated, and multinucleated
  • Smooth: involuntary, nonstriated, and uninucleated
  • Cardiac: involuntary, striated, and uninucleated
• Epimysium


  • External sheath of dense connective tissue surrounding the entire muscle
• Perimysium


  • Thin septa of connective tissue immediately surrounding the bundles of muscle fibers (fascicles)
• Endomysium


  • Very thin, delicate layer of reticular fibers & scattered fibroblasts
• Muscle Fiber


  A single cylindrical fiber, with several nuclei located at its periphery
• Sarcolemma

  • Cell membrane of the muscle fiber
• Transverse tubules (T tubules)

  • Opening to sarcoplasmic reticulum
• Sarcoplasmic reticulum


  • High Ca+2
• Myofibrils


  • Threadlike structures that extend from one end of the muscle fiber to the other (actin and myosin)
• Sarcomere


  Smallest repetitive subunit of the contractile apparatus. Extends from Z line to Z line.
• A Bands, I Bands, Z Line, H Zone, M line


  • Parts of the muscle fiber histology
• Motor unit


  All muscle cells innervated by one motor neuron
• Muscle cell properties


  Excitability - capabilitity to response

  Conductivity - extensability, strechable

  Contractility - shorthen forcefully

  Elasticity - to recoil
• Resting Membrane Potential (REP)

  Uneven distribution of ions across the cell membrane, develops due to higher K+ inside, higher Na+ outside, and cell membrane more permeable to K+

  (1) The concentration of K+ inside the cell membrane is higher than that outside the cell membrane;

  (2) the concentration of Na+ outside the cell membrane is higher than that inside the cell membrane;

  (3) the cell membrane is more permeable to K+ than it is to Na+.
• Action Potential


  Rapid depolarization and repolarization of the cell membrane resulting in muscle contraction
• Motor neurons


  Specialized nerve cells that stimulate muscles to contract, generate action potentials that travel to skeletal muscle fibers
• Muscle Contraction


  • Actin and myosin myofilaments slide past one another, causing the sarcomeres to shorten, shortening the entire muscle
  • occurs as actin and myosin myofilaments slide past to one another, causing sacromeres to shorten.

  1. Relaxed sarcomere. Fully contracted sarcomere
• Rigor Mortis


  Stiffening of the body after death
• Muscle Twitch


  Contraction of a muscle fiber in response to a stimulus, with latent period, contraction, and relaxation

  • Stimulus > latent (lag) period > contraction > relaxation
  • Contraction strength depends on

  1. Strength, speed, and duration of stimulus
  2. Weight of load
  3. Temperature

  • All-or-none law
• Factors affecting muscle twitch

  • Strength, speed, and duration of stimulus
  • Weight of load
  • Temperature
  • All-or-none law
• Summation


  Increase in force of contraction of individual muscle fibers by rapidly stimulating them, with less time for complete relaxation

  -LOW = MORE TIME FOR COMPLETE RELAXATION

  -HIGH = MUSCLES HAVE NO TIME TO RELAX
• Types of Muscle Contraction

  • Isometric (equal distance) - length of muscle does not change, tension increases
  • Isotonic (equal tension) - tension is constant, length of muscle decreases
• Smooth Muscle


  • Found in hollow structures, involuntary, uninucleated, nonstriated, arranged in longitudinal and circular layers
  • Autorhythmicity - periodic spontaneous contraction of smooth muscle. (sometimes controlled by hormones)
• Cardiac Muscle


  • Involuntary, uninucleated, striated, with intercalated disks to coordinate contraction, autorhythmic
• Ways to Name Skeletal Muscles


  Action (Flexor digitorum, which felexes the digits)

  Shape ( Deltoid, triagular)

  Origin and insertion (Brachioradialis, (brachio, arm) (biceps, bi - 2 + ceps, head)

  location (pectoralis (chest) muscle)

  Direction of fibers (rectus, straight) (oblique, diagonal)
• Origin


  More fixed attachment of muscle
• Insertion


  Movable attachment of muscle
• Tendons


  Attach muscle to bone
• Aponeurosis


  Wide flat tendon
• Actions of Skeletal Muscles

  • Flexors: bend limb
  • Extensors: straighten limb
  • Abductors: move limb away from midline
  • Adductors: bring limb toward midline
  • Rotators: revolve limb around axis
• Additional Actions of Skeletal Muscles

  • Dorsiflexors: raise the foot
  • Plantar flexors: lower the foot
  • Supinators: turn palm upward
  • Pronators: turn palm downward
  • Levators: raise a part of the body
  • Depressors: lower a part of the body
• Roles of Skeletal Muscles

  • Prime movers or agonists: bring about an action
  • Antagonists: oppose agonists
  • Synergists: assist prime movers
• Muscles of Facial Expression

  • Occipitalis, Frontalis, Zygomaticus, Levator labii superioris, Orbicularis oris and buccinator
• Muscles of the Eye

  • Superior rectus, Inferior rectus, Medial rectus, Lateral rectus, Superior and inferior oblique
• Muscles Moving the Head

  • Sternocleidomastoid
• Muscles Moving the Shoulder Girdle

  • Levator scapulae, Rhomboids, Pectoralis minor, Trapezius, Serratus anterior
• Muscles Moving the Humerus

  • Pectoralis major, Latissimus dorsi, Teres minor, Deltoid, Supraspinatus, Infraspinatus
• Muscles Moving the Elbow

  • Brachialis, Biceps brachii, Brachioradialis, Triceps brachii, Anconeus
• Muscles Moving the Wrist

  • Flexor carpi, Extensor carpi