Histology/muscle

Front 1

What's a T-tubule and what's it good for?

Back 1

An invagination of the sarcolemma; it allows depolarizations to reach all parts of the cell.

Front 2

What's a thin filament made of?

Back 2

F-actin + G-actin + tropomyosin + troponin. F-actin holds G-actin in a helix pattern; tropomyosin is entwined in the helix; and troponin attaches to tropomyosin and actin via subunits.

Front 3

What causes a striated appearance?

Back 3

Sarcomeres--the arrangement of thin and thick filaments. Within the sarcomere, the A and I bands are responsible for striations.

Front 4

What is the "A" band?

Back 4

Anisotropic band. It marks the length of the thick filament.

Front 5

What's the "I" band?

Back 5

Isotropic band. Marks the portion of thin filaments on either side of the sarcomere that are not overlapping with the thick filament.

Front 6

What's the smallest functional unit of contraction?

Back 6

The sarcomere.

Front 7

What bounds the sides of the sarcomere?

Back 7

The Z lines. "Zwischenscheibe."

Front 8

What's a triad?

Back 8

The meeting of a T-tubule and the sarcoplasmic reticulum. Located at the A-I junctions of the sarcomere in mammals.

Front 9

Break muscular contraction down into 5 basic steps.

Back 9

1) ACh is released and binds to receptors on sarcolemma.
2) AP propagates and reaches t-tubule.
3) SR releases Ca++.
4) Actin is unmasked and myosin binds to actin.
5) Contraction begins.

Front 10

Break relaxation down into 4 basic steps.

Back 10

1) ACh is removed by acetylcholinesterase.
2) SR recaptures Ca++.
3) Active sites on actin are masked and myosin releases.
4) Contraction ends, relaxation occurs.

Front 11

What kind of sections of muscle show striations?

Back 11

Longitudinal sections.

Front 12

In a cross section of muscle fibers, where would you see the nucleus?

Back 12

Peripherally.

Front 13

Myofibrils are combined to form a:

Back 13

Muscle fiber.

Front 14

Muscle fibers are grouped into:

Back 14

Fascicles.

Front 15

Fascicles are surrounded by:

Back 15

Perimysium.

Front 16

Where do you find smooth muscle?

Back 16

Walls of visceral organs, like the stomach, intestine, digestive tract, urinary bladder, uterus, and the walls of blood vessels.

Front 17

What do smooth muscle cells look like?

Back 17

They're elongated with attenuated tips.

Front 18

What embryonic layer does smooth muscle come from?

Back 18

Mesoderm. It comes directly from progenitor cells in the walls of visceral organs.

Front 19

How are smooth muscle cells organized?

Back 19

They are bundled and overlap. They're surrounded by, and separated by fine collagenous, reticular connective tissue.

Front 20

What smooth muscle characteristic allow peristalsis?

Back 20

Cells are arranged in bundles and have gap junctions. Layers of muscle run perpendicular to each other, allowing them to contract both laterally and longitudinally.

Front 21

What layer is muscle derived from?

Back 21

Mesoderm.

Front 22

Where does muscle provide involuntary movement?

Back 22

Visceral organs, heart.

Front 23

What does it mean to say that muscle cells are "irritable"?

Back 23

They contract when stimulated.

Front 24

Size-wise, how do the three types of muscle fibers compare?

Back 24

Skeletal is biggest, then cardiac, then smooth.

Front 25

What role does fascia play in muscle?

Back 25

Supports muscle fibers, supplies nerve endings, supplies nutrients.

Front 26

Describe muscle cell development.

Back 26

Skeletal muscle is derived from somites that give rise to myoblasts from the myotome portion. Myofibers are formed when myoblasts fuse, forming myotubules (these represent a syncytium, or multinucleate mass). Myotubules become mature myofibers with peripherally located nuclei and SR.

Front 27

List the "layers" of muscle from inside (molecular) to outside (gross level).

Back 27

Filament (actin/myosin), Fibril, Fiber, Fascicle, Gross.

Front 28

What are the 3 CT wrappings in muscle and where are they?

Back 28

Muscle fiber wrapped in endomysium; fascicle wrapped in perimysium; gross muscle wrapped in epimysium (superficial fascia).

Front 29

What innervates cardiac muscle?

Back 29

Autonomic nerves.

Front 30

Are cardiac muscle fibers branched?

Back 30

Yes.

Front 31

What is an intercalated disc?

Back 31

The junction between cardiac muscle fibers; contains gap junctions and adhering junctions (fascia adherens).

Front 32

What is the purpose of adhering junctions in intercalated discs?

Back 32

Holds cells together, enables efficient contraction.

Front 33

What is the purpose of gap junctions in intercalated discs?

Back 33

Allows communication--small molecules and ions pass from one cell to another; direct electrical connection is created. Lets APs pass rapidly and in a synchronized way.

Front 34

What's the origin of cardiac muscle?

Back 34

Cardiac mesoderm.

Front 35

Where's the primary pacemaker and what does it do?

Back 35

It's the SA node, located in wall of the right atrium near the entrance of superior vena cava. Cells of the SA node spontaneously depolarize resulting in regular contractions.

Front 36

If the SA node fails, how does the heart keep pumping?

Back 36

The AV node takes over. AKA the secondary pacemaker.

Front 37

How can the autonomic nervous system affect pacemaking?

Back 37

It can alter the pace established by the pacemaker cells.

Front 38

What are Purkinje fibers?

Back 38

Specialized myocardial fibers that conduct electrical impulses without synapses; enable heart to contract in a coordinated fashion.

Front 39

Where are Purkinje fibers located?

Back 39

In the inner ventricular walls of the heart, subjacent to the endocardium.

Front 40

How do Purkinje fibers look on slides?

Back 40

The stain distinct from other cardiac muscle cells. They look much bigger.