muscle tissue

muscle tissue functions

1. enables movement to occur

2. participates in body’s thermoregulation by producing heat

constitutes 30-40% of total body mass

myofibril

specialized organelles or muscle tissue

sarcomere

contractile unit of myofibrils

• made up of myofilaments (stress fibers)

  • arranged within myofibriles

sacromere order of abundance

myosin ~55-70%

microfilaments/actin filaments ~20%

alignment of sarcomeres

across muscle fiber microscopically visible as striations of light and dark bands

what does endomysium wraps

single muscle fiber (1000-2000 myofibrils)

what does perimysium wraps

bundles of muscle fibers → fascicles

• 1° fascicle: group of 20-40 muscles fibers

• 2° fascicle: group of multiple 1° fascicles

what does the epimysium wrap

multiple 2° fasicles to contain entire muscle

what is included endomysium bundle

blood vessels + organelles + extracellular protein-fluid filled + nutrients

what is included in perimysium bundle

blood vessels + adipose tissue + motor nerve endings

what is included in epimysium bundle

at least 1 vein + at least 1 artery + bundles of motor nerves

myogenesis: muscle fiber formation

myotome cells delaminate as mesenchymal cells from somites = muscle progenitor cells

• muscle progenitor cells migrate to target locations in body

• differentiate into appropriate muscles at target locaiton

muscle progenitor cell

myotome cell that has undergone determination and differentiation

1. migrate to target region

2. engage in sym and asym division

myoblast

muscle cell precursor that ultimately differentiates into a myocyte

• transietntly/transit amplifying (TA)

myocyte

immature, fully differentiated muscle cell

• fuses with other myocytes to form a single muscle fiber

• one nucleus

2 waves of myotome

1st wave→ embryonic

2nd wave→ fetal

• mostly completed before birth