Summary Skeletal muscle histology notes

Arrangement of skeletal muscle

 Skeletal muscles
o Moves and stabilises the skeleton
o Forms sphincters in digestive system and urinary tracts
o Involved in respiration
 Characteristics
o Long, cylindrical cells
o Striated (appear striped)
o Multiple peripherally located nuclei
o Innervated by somatic nervous system
 Arrangement
o Endomysium
 Connective tissue layer surrounding single muscle fibre
o Fascicle
 Bundle of muscle fibres
 Surrounded by perimysium (connective tissue layer)
o Muscle
 Group of fascicles
 Surrounded by epimysium (connective tissue)

Muscle fibres and muscle spindle

 Slow twitch (type 1)
o Involved in aerobic respiration
o Generate more ATP for continuous, extended contraction
o Fire more slowly
o Resist fatigue
o Rich in mitochondria and myoglobin
 Appear dark red in vivo of some species
o E.g. postural muscles
 Fast twitch (type 2)
o Use anaerobic respiration
o Good for short bursts of strength of speed
o Fatigue quickly
o Few mitochondria and little mitochondria
o Type 2a = intermediate fast twitch
 Use both aerobic and anaerobic respiration
o Type 2b
 Use only anaerobic resp
 Both fibre types in all muscles
o All the fibres of a single motor unit are of the same type
o Motor unit = LMN with all the fibres it innervates
o Darker stained fibres are usually aerobic
 Muscle spindle
o Sensory stretch receptor
 Detects fibre length
o Lies in parallel to muscle fibres