ANAT 261 Lecture Notes - Epimysium, Endomysium, Perimysium

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Lab 5 – Muscle
- in the lab, we will look at three types of muscle:
oskeletal muscle
ocardiac muscle
osmooth muscle
*Need to know how to distinguish each in longitudinal AND cross
section!
Skeletal Muscle
- Contraction: voluntary, strong & quick
- muscle appears striated (due to sarcomeres)
- multinucleated cell (muscle cell = muscle fiber)
onuclei lie at periphery
onuclei are elongated
- in cross section:
ocan see myofibrils packed within a fiber (made of actin and
myosin)
oeach muscle fiber surrounded by endomysium
a layer of loose connective tissue, reticular fibers and
basement membrane
oa bundle of muscle fibers form a fascicle – surrounded by
the perimysium
a thicker layer of loose connective tissue, that
contains blood vessels and nerves
othe entire muscle is surrounded by the epimysium
a layer of dense irregular connective tissue
onuclei appear circular and at the edge of fibers
oBEWARE of fibrocytes in the connective tissue layers…their
nuclei can be deceiving
- in longitudinal section:
ostriations visible due to sarcomeres (contractile unit of
skeletal muscle)
onuclei appear long and peripheral (helps distinguish
between fibers)
omyofibrils are visible running parallel through the fiber
-sarcomere (seen best in EM):
oI band “light” band; only thin actin filaments
oA band “dark” band; thin actin filaments and thick
myosin filaments (defined by length of myosin filaments)
oH band only myosin present; located in the middle of the
A band
oM line middle of H band; contains creatine kinase
oZ line in the middle of I band
- a sarcomere is defined from Z line to Z line
- in EM: mitochondria can be seen between rows of sacromeres
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