Basic muscle pathalogy
Skeletal muscle:
Multiple nuclei are beneath the cell membrane (Sarcolemma).
It is normal in 3-5 % to see the nucleus in the center and more than that is pathologic.
Most of the cytoplasm is filled with Myofilaments .
Myofilament is constitute of myofibril which itself include the thin actin and thick myosin filaments.
Dystrophin is a sub sarcolemmal protein which can bind to Actin.
Sarcoplasmic reticulum and Z bands and T tubules are parallel to each other.
Multiple nuclei are beneath the cell membrane (Sarcolemma).
It is normal in 3-5 % to see the nucleus in the center and more than that is pathologic.
Most of the cytoplasm is filled with Myofilaments .
Myofilament is constitute of myofibril which itself include the thin actin and thick myosin filaments.
Dystrophin is a sub sarcolemmal protein which can bind to Actin.
Sarcoplasmic reticulum and Z bands and T tubules are parallel to each other.
Smooth mus:
Notice the elongated, "cigar-shaped" nuclei of the smooth muscle cells, the intercellular spaces between the smooth muscle cells, Don't expect every fiber in a section to exhibit a nucleus
Skeletal muscle stains:
First stain is the H&E (as the first picture above)
second is :
ATPase alkaline
type 2 dark
Checker board pattern
Fiber typing in denervation
type 2 dark
Checker board pattern
Fiber typing in denervation
ATPase acidic type 2 light
Checker board pattern
Fiber typing in denervation
Checker board pattern
Fiber typing in denervation
Trichrome:
mitochondrial ‘Red ragged fiber”
Rime vacuoles (in I.B.M.)
Nemaline rods (nemaline myopathy)
Subsarcolemma aggregation in channelopathies
mitochondrial ‘Red ragged fiber”
Rime vacuoles (in I.B.M.)
Nemaline rods (nemaline myopathy)
Subsarcolemma aggregation in channelopathies
NADH:
congenital Structural abnormality,target
fiber(central core
disease) or vacules and ..
congenital Structural abnormality,target
fiber(central core
disease) or vacules and ..
Acid phosphatase:
Mnemonic (acid chews up so acid for degeneration )
and it will look red. in opposite Alk phosphate shows regenerating fibers.
Also a good stain to trace the inflammation
and it will look red. in opposite Alk phosphate shows regenerating fibers.
Also a good stain to trace the inflammation
Alk phosphatase, Regenerating fiber will look blue
,nicely highlight the vessels too.
,nicely highlight the vessels too.
PAS: glycogen storage disease , type 1 darker (more glycogen)
SDH: Succinate dehydrogenase
TYPES OF MUSCLE FIBERS
Humans have basically three different types of muscle fibers.
A:Slow- twitch (ST or Type I) fibers are identified by a slow contraction time and a high resistance to fatigue. Structurally, they have a small motor neuron and fiber diameter, a high mitochondrial and capillary density, and
high myoglobin content, Energetically, they have a
low supply of creatine phosphate (a high-energy substrate used for quick, explosive movements), a low glycogen content, and
a wealthy store of triglycerides (the stored form of fat). Functionally, ST fibers are used for aerobic activities requiring low-level force production, such as walking and maintaining posture. Most activities of daily living use ST fibers.
B:Fast-twitch (FT or Type II) fibers:
The differences in the speeds of contraction that gives the fibers their names can be explained, in part, by the rates of release of calcium by the sarcoplasmic reticulum (the muscle's storage site for calcium) and by the activity of the enzyme (myosin-ATPase) that breaks down ATP inside the myosin head of the contractile proteins.
Both of these characteristics are faster and greater in the FT fibers (Fitts & Widrick, 1996; Harigaya & Schwartz, 1969).
Fast-twitch fibers are further divided into fast-twitch A (FT -A or Type IIA) and fast- twitch B (FT -B or Type lIB) fibers. FT -A fibers have a moderate resistance to fatigue and represent a transition between the two extremes of the ST and FT -B fibers. Structurally, FT -A fibers have a large motor neuron and fiber diameter, a high mitochondrial density, a medium capillary density, and a medium myoglobin content. They are high in creatine phosphate and glycogen and medium in triglyceride stores. They have both a high glycolytic and oxidative enzyme activity. Functionally, they are used for prolonged anaerobic activities with a relatively high force output, such as racing 400 meters.
Fast-twitch B fibers, on the other hand, are very sensitive to fatigue and are used for short anaerobic, high force production activities, such as sprinting, hurdling, jumping, and putting the shot. These fibers are also capable of producing more power than ST fibers. Like the FT -A fibers, FT -B fibers have a large motor neuron and fiber diameter, but a low mitochondrial and capillary density and myoglobin content. They also are high in creatine phosphate and glycogen, but low in triglycerides. They contain many glycolytic enzymes but few oxidative enzymes. Table 1 summarizes some major characteristics of the three fiber types.
Fast-twitch fibers are further divided into fast-twitch A (FT -A or Type IIA) and fast- twitch B (FT -B or Type lIB) fibers. FT -A fibers have a moderate resistance to fatigue and represent a transition between the two extremes of the ST and FT -B fibers. Structurally, FT -A fibers have a large motor neuron and fiber diameter, a high mitochondrial density, a medium capillary density, and a medium myoglobin content. They are high in creatine phosphate and glycogen and medium in triglyceride stores. They have both a high glycolytic and oxidative enzyme activity. Functionally, they are used for prolonged anaerobic activities with a relatively high force output, such as racing 400 meters.
Fast-twitch B fibers, on the other hand, are very sensitive to fatigue and are used for short anaerobic, high force production activities, such as sprinting, hurdling, jumping, and putting the shot. These fibers are also capable of producing more power than ST fibers. Like the FT -A fibers, FT -B fibers have a large motor neuron and fiber diameter, but a low mitochondrial and capillary density and myoglobin content. They also are high in creatine phosphate and glycogen, but low in triglycerides. They contain many glycolytic enzymes but few oxidative enzymes. Table 1 summarizes some major characteristics of the three fiber types.
RECRUITMENT OF MUSCLE FIBERS
Muscles produce force by recruiting motor units (a group of muscle fibers innervated by a motor neuron) along a gradient. During voluntary isometric and concentric contractions, the orderly pattern of recruitment is controlled by the size of the motor unit, a condition known as the size principle (Henneman, et al., 1974). Small motor units, which contain slow-twitch muscle fibers, have the lowest firing threshold and are recruited first. Demands for larger forces are met by the recruitment of increasingly larger motor units. The largest motor units that contain the fast-twitch B fibers have the highest threshold and are recruited last.
