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The Muscular System (Structure & Organizational Levels (Muscle fibber…

- - - - occurs only in heart, where it constitutes bulk of heart walls
        
        are striated & involuntary
        
        contracts at fairly steady rate set by heart’s pacemaker, but neural controls allow heart to speed up for brief periods
    - - found in the walls of hollow visceral organs, such as the stomach, urinary bladder, & respiratory passages
        
        role is to force fluids & other substances thru internal body channels
        
        consists of elongated cells, non striated, & involuntary---- Its contractions are slow & sustained.
    - - composed of cylindrical multinucleate cells w/ obvious striations; muscle(s) attached to body’s skeleton; voluntary muscle.
        
        responsible for overall body mobility
        
        can contract rapidly, but it tires easily & must rest after short periods of activity
- - - - cross bridge attachments form & break several times during contraction to generate tension & propel thin filaments toward center of sarcomere.
      - occurs simultaneously in sarcomeres throughout the cell & muscle cell shortens.
      - nervous system stimulates muscle fibers-- myosin heads on thick filaments latch on2 myosin-binding sites on actin in thin filaments, & sliding begins.
    - - contraction ends when cross bridges become inactive, tension declines, & muscle fiber relaxes.
    - - distance between Z discs shortens--- as thin filaments slide centrally, Z discs to which they attach are pulled toward M line
      - H zones disappear.
      - I bands shorten.
      - contiguous A bands move closer together, but their length does not change.
- - - - function: flexion of trunk
      - location: inside abdominal region
    - - function: tilt & turn neck & head
      - location: back of neck, shoulders, & upper back
    - - function: twisting of trunk
      - location: outer surface of abdominal region
    - - function: flexion of humerus, adducts humerus, rotates humerus medially, & keep arm attached to trunk
      - location: upper chest
    - - function: responsible for various movements of shoulder joint
      - location: middle of back
    - - function: straighten back & provide side to side rotation
      - location: on each side of vertebral column
  - - - function: flex & radial abduct of arm
      - location: anterior part of forearm
    - - function: flexion of middle phalanges
      - location: forearm
    - - function: flex shoulder joint & rotate it, and abduction of arm
      - location: upper most part of arm & top of shoulder
    - - function: adduct & flex wrist
      - location: ulnar side of forearm
    - - function: extension of elbow joint
      - location: back of humerus
    - - function: helps in movements of wrist & elbow
      - location: backside of forearm
    - - function: control motion of shoulder & elbow joints
      - location: near scapula
    - - function: control movements of wrist
      - location: lateral side of humerus to base of 2nd metacarpal bone
  - - - function: control facial expressions & draw mouth's angle upward & outward
      - location: cheekbone area
    - - function: help bite down or chew, pull lower jaw upward
      - location: cheek area
    - - function: close eye & help pass/drain tears
      - location: around eyes
    - - function: compress cheeks against teeth & assist in chewing
      - location:anterior part of cheek & lateral wall of oral cavity
    - - function: control movement of mouth & lips
      - location: around mouth
    - - function: flex neck & help w/ movement of head
      - location: manubrium of sternum & clavicle
    - - function: move mandible, retract & move side to side
      - location: side of head, near temples
    - - function: pull down mandible
      - location: portion of neck, chest, & face
    - - function: to raise eyebrows
      - location: forehead
  - - - function: flexion of thigh & stabilize patella
      - location: front of thigh
    - - function: movement of hip & thigh
      - location: buttlocks
    - - function: adduct femur at hip joint
      - location: medial side of thigh
    - - function: bend knees & rotate lower leg
      - location: posterior thigh
    - - function: flexor & rotator of thigh at hip joint
      - location: front thigh
    - - function: dorsiflex & invert foot
      - location: near shin
    - - function: flexion of hip
      - location: hip area
    - - function: plantar flexing of foot at ankle joint & flexing leg at knee joint
      - location: back of lower leg
    - - function: extend foot at ankle
      - location: front of leg
    - - function: plantar flexion of foot, helping/ walking, running, & keeping balance
      - location: back part of lower leg
- - - - surrounded by endomysium
  - - - surrounded by perimysium
  - - - covered externally by epimysium
  - - - sliding of thin filaments past thick filaments produces muscle shortening. elastic filaments provide elastic recoil when tension is released & help maintain myofilament organization
      - thin filaments have actin molecules (plus other proteins)
      - thick filaments have bundled myosin molecules
- - - - may act as prime movers themselves
      - help regulate action of prime mover by providing some resistance, which prevents movement from going too far, or slows or stops movement.
      - may stretch or relax when prime mover is active
      - prime move & its antagonist are located on opposite sides of joint across which they act
    - - called fixture when they immobilize bone, or muscle’s origin so that prime mover has stable base on which to act