Skeletal Muscle Skeletal Muscle TissueTissue

HierarchyHierarchyMuscle (belly) Muscle (belly) → fasciculus → → fasciculus →

myofiber (cell) → myofibril → myofiber (cell) → myofibril → myofilamentsmyofilaments

Myoneural (neuromuscular) Myoneural (neuromuscular) JunctionJunction

Where nerves meet the muscle to Where nerves meet the muscle to give messagegive message

Color Code: Anatomy of MuscleColor Code: Anatomy of Muscle

a.a. TendonTendon-connects muscle to -connects muscle to periostiumperiostium

b/cb/c. . bellybelly is surrounded by is surrounded by epimysiumepimysium

d.d. fasciculusfasciculus-bundle of fibers -bundle of fibers surrounded by surrounded by perimysiumperimysium

e.e. MyofibersMyofibers-surrounded by -surrounded by endomysiumendomysium

f/g.f/g. myofibrilmyofibril- made up of - made up of myofilamentsmyofilaments

Muscle SizeMuscle SizeThe number of myofibers doesn’t The number of myofibers doesn’t

change change

aa. Atrophy: decrease in size due to . Atrophy: decrease in size due to lack of use in extended atrophy, the lack of use in extended atrophy, the fiber will actually die. fiber will actually die.

If you don’t use it, it will shut down! If you don’t use it, it will shut down!

Atrophy can be Atrophy can be reversed unless it is reversed unless it is

permanent permanent damage!!!!!damage!!!!!

HypertrophyHypertrophy Increase in number and size of Increase in number and size of

myofibrilsmyofibrils

TestosteroneTestosterone Stimulates hypertrophyStimulates hypertrophy

Steroid-synthetic testosterone Steroid-synthetic testosterone hormone to artificially build muscle. hormone to artificially build muscle.

Do boys and girls have it?Do boys and girls have it?

Yes-boys produce 20-30 more than Yes-boys produce 20-30 more than females!!females!!

Maintenance of muscle mass and strength Maintenance of muscle mass and strength Maintenance of bone density and strength Maintenance of bone density and strength Libido and clitoral engorgement/penile Libido and clitoral engorgement/penile

erection frequency. erection frequency. Mental and physical energy Mental and physical energy Excessive testosterone in males can lead Excessive testosterone in males can lead

to an increased risk of prostate cancer to an increased risk of prostate cancer

Anatomy of MyofiberAnatomy of Myofiber1.1. SarcolemmaSarcolemma: Cell membrane: Cell membrane

2.2. SarcoplasmSarcoplasm: muscle cytoplasm, contains : muscle cytoplasm, contains myoglobin & mitochondria, glycogen-myoglobin & mitochondria, glycogen-stored glucose. stored glucose.

3.3. Sarcoplasmic Reticulum (SR):Sarcoplasmic Reticulum (SR):surrounds myofibrils surrounds myofibrils stores calcium ions Ca ++stores calcium ions Ca ++(important for muscle contraction)(important for muscle contraction)

a.a. Cisternae:Cisternae: calcium storage area calcium storage area

b.b. T Tubules:T Tubules: transverse tubules, transverse tubules, connect sarcolemma to connect sarcolemma to

sarcoplasm. sarcoplasm.

Anatomy of MyofibrilAnatomy of Myofibril

Responsible for contractionResponsible for contraction 2 myofilaments: actin- the thin one2 myofilaments: actin- the thin one

myosin- the thick onemyosin- the thick one Sarcomeres: functional unit of contraction; Sarcomeres: functional unit of contraction;

area between 2 z-lines area between 2 z-lines 10,000 or more sarcomeres along each 10,000 or more sarcomeres along each

myofiber. myofiber.

g. I Band: Light region, actin onlyg. I Band: Light region, actin only

f. A Band: dark region, both actin f. A Band: dark region, both actin and myosinand myosin

h. H Zone: center of the A band, h. H Zone: center of the A band, myosin onlymyosin only

j. Z line: dark zig-zag line in center j. Z line: dark zig-zag line in center of I bandof I band

k. Actin: thin myofilamentk. Actin: thin myofilament

They have active sites They have active sites (handles) if calcium is present.(handles) if calcium is present.

l. Myosin: thick myofilamentl. Myosin: thick myofilament

m. Cross Bridges: part of myosin, m. Cross Bridges: part of myosin, attach to actin in the presence of attach to actin in the presence of calciumcalcium

Sliding Filament TheorySliding Filament Theory

1.1. Actin filaments slide past myosinActin filaments slide past myosin

2.2. Z lines get closer togetherZ lines get closer together

3.3. Sarcomere shortens-neither Sarcomere shortens-neither actin or myosin get shorter. actin or myosin get shorter.