6.2 - Lab - Muscle

Question 1

Smooth Muscle

Answer 1

• evolutionarily very old
• controls involuntary movements
• often referred to as “visceral smooth muscle”
• chiefly found in walls of organs

Question 2

Striated muscles

Answer 2

• much more well-developed intracellular organization
• specialized for efficient generation of lots of force
• two types:
  1) Skeletal Muscle (all of the body’s musculature that is under voluntary control)
  2) Cardiac Muscle ( comprises the wall of the heart)

Question 3

basic unit of Skeletal Muscle?

Answer 3

• Muscle fiber

because it is the functional unit that is bound by a cell membrane

Question 4

Describe the organization of skeletal muscle from Fascicles down

Answer 4

• each fascicle is composed of several muscle fibers
• each muscle fiber has several filaments
• each filament has a string of connected sarcomeres

Question 5

Describe the appearance of striated muscle in LM and what contributes to that appearance? Is there any organizational structure of the muscle you cannot resolve in LM?

Answer 5

• appearance is due to sarcomeres (and the ordering of thin and thick filaments within them)
• see striations across all myofibrils/myofibers because the sarcomeres are kept in orderly arrangements across filaments
• individual filaments are not resolvable in LM (fibers are though)

Question 6

What is the appearance of the A-band in LM and what does it represent

Answer 6

A-band is a dark line across the sarcomeres (perpendicular to the fiber) and it represents the myosin portion of the sarcomere

Question 7

What is the appearance of the I-band in the LM and what does it represent

Answer 7

I-band is the lighter portion across the sarcomere (perpendicular to the fiber) + it represents that portion of the sarcomere where myosin is absent

Question 8

What is one way to tell if the muscle is contract or stretched at the time of fixation in LM

Answer 8

• thickness of the I-band

- measuring the sarcomere?

Question 9

Perimysium

Answer 9

• Surrounds the muscle fascicles

- primarily composed of type I collagen

Question 10

Endomysium

Answer 10

• CT that outlines the myofibers
• primarily type III collage (think of external lamina and reticular fibers)
• the smallest capillaries are often found here (often will see a capillary when corners of three myofibers come together)

Question 11

Epimysium

Answer 11

• CT within the muscle layer but outside the perimysium

- will see the largest blood vessels of muscle in this layer

Question 12

What are the three layers of Connective Tissue with in muscle tissue (outside to inside)

Answer 12

1) Epimysium
2) Perimysium
3) Endomysium

Question 13

What are the three layers of the heart (inside to outside), and which composes the bulk of the heart

Answer 13

1) Endocardium
2) myocardium (composes the bulk of the heart)
3) Epicardium

Question 14

Epicardium (location and composition)

Answer 14

• Outside surface of the heart

- beneath it are large amounts of adipose tissue, some nerve fibers, and major vessel

Question 15

Endocardium (location + composition)

Answer 15

• Inner surface of the heart (towards the blood)

- beneath it is a small CT layer , perhaps a small amount of adipose tissue

Question 16

Myocardium

Answer 16

• composes the bulk of the heart
• almost completely composed of cardiac myocytes that form serial connections with each other
• the intercalated disc is similar to junctional complex - connects cardiac muscle fibers?

Question 17

What is Acytokinetic mitosis and how does it relate to muscle tissue

Answer 17

• mitosis with out cell division
• occasionally occurs in perinatal cardiac muscle
• results in the occassional multi-nucleated cardiac myocyte