Anatomy L6

• types of muscle

  • skeletal: voluntary
  • cardiac: involuntary, heart
  • smooth: involuntary, pushes fluid and solid through internal sys
• excitability- response to stimulus
• contractility- shorten and exert tension to pull for movement
• extensibility- muscle tissue to contract over long period of time
• elasticity- ability to rebound back to original length
• functions of skeletal muscle

  • produce skeletal movement: pull on tendons to move
  • maintain posture and body position
  • support soft tissue
  • regulate entering and exiting of material: eating; digestive track; control urine and feces
  • maintain body temp: E from contractions generate heat
• skeletal muscle

  • bone; tendon; epimysium; fascicle; perimysium; muscle fiber (cell); endomysium; myofibril
• sarcomere: action takes place

  • myosin (thick filaments)
  • actin (thin filament)
  • both arranged in repeating units called sarcomeres
  • myofilaments are arranged parallel to long axis of cell
• I band: isotopic; stay same; only actin

  A band: actin and myosin

  H band: myosine only
• muscle contraction:

  • contracting muscle shortens in length by exerting a pull (tension)
  • caused by interactions btwn thick and thin filaments w/in the sarcomere
  • triggered by presence of calcium ions
  • requires ATP
  • muscle contracts: actin filaments slide toward e/o - sliding filament theory
• sliding filament theory

  • actin and myosin doesn't change lengths
  • z lines closer together
• Muscle contraction

  • nerve impulse ultimately causes release of neurotransmitter (ACh), which comes in contact w/ sarcoplasmic reticulum
  • causes a change in membrane potential (action potential spreads across surface along T tubules)
  • sarcoplasmic reticulum releases its stored calcium ions
  • Ca2+ bind to troponin
• bound Ca2+ causes tropomyosin molec. to roll so that it exposes active sites on actin

  myosin head now extend and bind to exposed active sites on actin

  cycle repeated: cross-bridge binding
• muscle Relaxation

  • acetylcholine is broken down by acetylcholinesterase: action potential stops
  • sarcoplasmic reticulum reabsorbs Ca2+
  • troponin/tropomyosin complex returns to its normal position
  • active sites are blocked
  • cross-bridges can't bind to active sites
  • muscle relaxes
• motor unit: motor neuron and all of muscle fibers it innervates; all or none: multiple units for lots of force
• muscle tone: tension of muscle when it is relaxed
• muscle spindles: specialized muscle cells that are monitored by sensory nerves to control muscle tone; detect changes in length; sensory nerves that control muscle tone
• muscle atrophy

  • discontinued use of muscle (reduce mass and tone)
  • illness, injury, age
  • physical therapy and exercise help reduce effect of atrophy
• fast fibers

  • white fibers, FG, Type 2b
  • less RBC, hemoglobin
• slow fibers

  • red fibers, SO, Type 1
  • more myoglobin
  • lower extremities
  • endurance muscles (spine, core- posture)
• intermediate fibers

  • pink fibers, FOG, type 2b
  • endurance trained muscles
• origins: point of muscle attachment to bone that is stationary
• insertions: point of muscle attachment to bone that will move
• actions: function of muscle upon contraction
• innervation: which motor nerve is controlling mvmt
• actions: muscles can be grouped according to their primary actions into 4 types
• prime movers (agonists)

  • responsible for producing a particular mvmt
  • biceps brachii- flex forearm at elbow
• antagonists: actions oppose the action of agonist; extends forearm at elbow
• synergist: assist the prime mover in performing an action; brachilias
• fixators: agonist and antagonist muscles contracting at the same time to stabilize a joint; flexors and extensors
• stabilizers:

  • muscles that are going to stabilize or restrict mvmt at an area/region while prime movers are active
  • stabilize hips to perform mvmt at leg
• brachialis: brachium of arm

  tibialis anterior: associated w/ anterior tibia

  trapezius: trapezoid shape

  deltoid: triangular shape
• rectus femoris: straight muscle of leg

  external oblique: muscle on outside that is oriented w/ fibers at an angle

  biceps brachii: two origins

  teres major: long, big, rounded muscle
• sternocleidomastoid: sternum, clavicle, mastoid process

  genioglossus: chin and tongue
• flexor carpi radialis: near radius, flexes, abducts the wrist

  adductor longus: long muscle that adducts leg at hip
• changes occur in muscles as we age:

  • skeletal muscle fibers become smaller in diameters
  • decrease in number of myofibrils
  • contain less glycogen reserves, less myoglobin
  • less elastic, develop fibrosis
  • all of above results in a decrease in strength and endurance
  • muscles fatigue rapidly
  • ability to recover from injury decreases
  • muscle can be built with resistance training
• aging and muscular sys.

  • skeletal muscle fibers become less elastic
  • develop fibrosis- brittle
  • tolerance for exercise decreases
  • ability to recover from injury decreases