Skeletal Muscle Tissue

skeletal muscle tissue (myology) slideshow

types of muscle tissue

one of the 4 primary types

  • skeletal → striated → voluntary
    • 40% of weight
  • cardiac (involuntary)
  • smooth (involuntary, nonstriated)

musculus = little mouse

made up of many tissue types

more than 700 skeletal muscles

word roots: sarco and myo

function of skeletal muscles

  • skeletal movement
  • posture and body position
  • support of soft tissues
  • joint stabilization
  • guarding of entrances and exits
  • maintenance of body temperature
  • protection
  • facial expression

 

epi-, peri- and endomysium

  • are interwoven
    • continuous with tendon, and eventually the periosteum
  • function
    • protection
    • blood supply
    • innervation
  • epimysium
    • on top of the muscle
  • perimysium
    • around a bundle of myofibers
  • endomysium
    • surrounds each myofiber

nerve and blood supply

  • skeletal muscles are rich in nerves and blood vessels
  • chemical communication at neuromuscular junction
  • synaptic terminal of axon meets motor end plant of muscle cell
  • coiled capillaries are able to adapt to changes in length of muscle fiber

 

 

origin and insertion

  • origin
    • the part that stays still
    • usually proximal
  • insertion
    • the part that moves
    • usually distal

 

microanatomy of skeletal muscle fibers

  • vocab
    • skeletal muscle cell = fiber or myofiber
    • sarcolemma
    • sacroplasm
    • sacroplasmic reticulum
    • myofibril
    • myofilaments
    • t-tubules

 

sacromere = thin and thick filaments

  • thin and thick filaments are organized in repeating functional units
  • each myofibril has linear arrangement of up to 10,000 sarcimeres
  • banded appearance (striation) due to arrangement of thick and thin filaments
  • interaction of thick and thin filaments responsible for contraction

motor unit

  • all muscle fibers that are controlled bu a single motor neuron (axon)
    • the lower the ration of muscle fibers to neurons, the more precise the movement can be
  • ratio is from 1:1 to 1:2000
  • acetylcholine is the neurotransmitter at the motor plate end
  • contraction of a motor unit is “all or nothing”

 

muscle control

  • muscle tone
    • resting tension of skeletal muscles
  • recruitment or multiple motor unit summation for greater force
  • some directional control depending on which motor units are stimulated

muscle hypertrophy vs atrophy

  • hypertrophy due to anaerobic exercise
  • atrophy if supply of myofilaments exceeds demand. muscle fibers become smaller and weaker
  • eventual death of muscle fibers is irreversible!

three types of skeletal muscle fibers

  • slow (or red)
  • fast glycolitic fibers
  • fast oxidative fibers
  • most skeletal muscles contain a mixture of fiber types
    • one motor unit only contains one fiber type

slow fibers

  • slow but continuous contraction for extended periods
  • smaller diameter
    • contain myoglobin
    • more capillaries
    • more mitochondria
  • do not fatigue as fast due to aerobic production of ATP

fast glycolitic fibers

  • fast contraction after nervous stimulation
  • large diameter
    • larger glycogen reserve
    • fewer mitochondria
    • densely packed myofibrils
    • fatigue fast

fast oxidative fibers

have attributes between slow and fast

muscle terminology

  • flexor → extensor
  • origin → insertion
  • agonist → antagonist
    • agonist is the prime mover
  • syngerist

naming of the skeletal muscles

  • orientation of fibers
  • size and shape
  • location
  • action
  • origin and/or insertion
  • specific features

use muscle name to help identify its location, appearance and function

grouping of muscles according to primary action

  • agonist → prime mover
  • synergists → assistant mover