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16 Cards in this Set

  • Front
  • Back
Classes of Muscle
1. Skeletal muscle- nuclei are inside bundles; striated
2. Cardiac muscle- continuous involuntary contractions; also striated; intercalated disks; nuclei are more scattered
3. Smooth muscle- not striated; fusiform shaped; weak contraction; involuntary contractions
CT associated with skeletal muscles
1. Endomysium- the delicate layer of reticular fibers that immediately surrounds individual muscle fibers. Only small-diameter blood vessels and the finest neuronal branches are present within the endomysium, running parallel to the muscle fibers. (very thin)
2. Perimysium-a thicker CT layer that surrounds a group of fibers to form a bundle or fascicle (functional units of muscle fibers that work together in a specific function). Larger blood vessels and nerves travel in here.
3. Epimysium- the sheath of dense CT that surrounds a collection of fascicles that constitutes the muscle. The major vascular and nerve supply of the muscle penetrates the epimysium.
Skeletal Muscle Fiber Types
1. Red- aka slow twitch (good for long periods of movement; red has a higher % of mitochondria and myoglobin. ex: wings of birds)

2. White- fast twitch; provides quick strength and fine movement (like finger movement)

3. Intermediate (in between)

- Based on: Mitochondria and Myoglobin (another O2 binding protein like hemoglobin)
Skeletal Muscle Organization
myofibrils (units of sarcomeres) --> muscle fibers --> muscle fascicles --> bisep/tricep (?)
Muscle Banding
- A Band = dark band (myosin-containing thick filaments)
- I Band = bigger light area (thin filaments)
- Z line = separates the I band
- Sarcomere- the functional unit (from one Z line to the next)
Contraction of Sarcomere
- the sarcomere is the basic contractile unit of striated muscle; it is the portion of a myofibril between two adjacent Z lines.
- sarcomere itself shortens but the A band doesn't shorten (the I band shortens)
- the Z lines become closer
Muscle contraction components
- tropomyosin covers up myosin binding sites
- when calcium binds to troponin complexes, it shifts the tropomyosin and exposes the myosin binding sites
-each tropomyosin molecule contains one troponin complex

- Troponin on top of tropomyosin on top of actin
Order of muscle contraction
1. Attachment- the myosin head is tightly bound to the actin molecule of the thin filament
2. Release- myosin head is uncoupled from the thin filament by ATP binding to the myosin head
3. Bending- myosin head, as the result of hydrolysis of ATP, advances a short distance in relation to the thin filament
4. Force Generation- myosin head releases inorganic phosphate and the power stroke occurs (ADP is lost from the myosin head)
5. Reattachment- the myosin head binds tightly to a new actin molecule
Regulation of Contraction
- T tubule: a continuation of a plasma membrane; allows action potential to continue down the cell. T tubules penetrate to all levels of the muscle fiber and contain voltage-sensor proteins.
- Sarcoplasmic reticulum: releases calcium. This reticulum forms a highly organized tubular network around the contractile elements in striated muscle cells.
- the electric impulses travel from neuron to muscle (neuro-muscular junction)
ALS (Lou Gehrig's disease)
- nerve cells become degenerated causing muscle cells to break down
- Stephen Hawking- has lived for over 40 years with ALS
Cardiac muscle
- in heart
- also striated
- has intercalated discs that separate cells
- mononucleated in center of cell (the cardiac muscle nucleus lies in the center of the cell)
Intercalated disc
- connections between cells
- run perpendicular and laterally
- function is to hold cells together and help them communicate
- they are cross-bands that cross the fibers in a linear fashion in a way that resembles the risers of a stairway
Junctions in intercalated discs
1. Adhering junctions- the major constituent of the transverse component of the intercalated disk. It holds the cardiac muscle cells at their ends to form the functional cardiac muscle fiber. It always appears as a transverse boundary between the cardiac muscle cells.
2. Desmosomes- bind the individual muscle cells to one another; they help prevent the cells from pulling apart under the strain of regular repetitive contractions.
3. Gap junctions- constitute the major structural element of the lateral component of the intercalated disk. They provide ionic continuity btwn adjacent cardiac muscle cells.
Smooth muscle
- fusiform, found in bundles
- mononucleate
- can range in cell size- range in size in woman's uterus (pregnancy)
- dense body- run throughout cytoplasm of cell
Smooth muscle contraction
- thin and thick fibers (dense fibers) are relaxed in the relaxed position
- contracted: the muscle cell twists ( a 3-dimensional contraction)
- it takes only 10% ATP that skeletal muscle uses
-smooth muscle is specialized for slow, prolonged contraction
Muscular Dystrophies
- there are different types that affect different ages
- characterized by muscle weakening and breaking down
- protein called dystrophin- links actin filaments to sarcolemma