Histology Test Two

Front 1

Classes of Muscle

Back 1

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

Front 2

CT associated with skeletal muscles

Back 2

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.

Front 3

Skeletal Muscle Fiber Types

Back 3

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)

Front 4

Skeletal Muscle Organization

Back 4

myofibrils (units of sarcomeres) --> muscle fibers --> muscle fascicles --> bisep/tricep (?)

Front 5

Muscle Banding

Back 5

- 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)

Front 6

Contraction of Sarcomere

Back 6

- 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

Front 7

Muscle contraction components

Back 7

- 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

Front 8

Order of muscle contraction

Back 8

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

Front 9

Regulation of Contraction

Back 9

- 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)

Front 10

ALS (Lou Gehrig's disease)

Back 10

- nerve cells become degenerated causing muscle cells to break down
- Stephen Hawking- has lived for over 40 years with ALS

Front 11

Cardiac muscle

Back 11

- 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)

Front 12

Intercalated disc

Back 12

- 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

Front 13

Junctions in intercalated discs

Back 13

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.

Front 14

Smooth muscle

Back 14

- 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

Front 15

Smooth muscle contraction

Back 15

- 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

Front 16

Muscular Dystrophies

Back 16

- there are different types that affect different ages
- characterized by muscle weakening and breaking down
- protein called dystrophin- links actin filaments to sarcolemma