Muscle III

Question 1

What makes up the motor unit of a skeletal muscle?

Answer 1

Nerve, neuromuscular junction, and muscle itself

Question 2

What controls which and how many of our motor units contract?

Answer 2

CNS

Question 3

What determines the fiber type of a muscle?

Answer 3

The innervating nerve

Question 4

What are the two types of skeletal fiber types?

Answer 4

Type I (red) and Type 2 (white)

Question 5

Describe Type I skeletal fiber.

Answer 5

• Oxidative metabolism
• Lots of myoglobin and mitochondria
• Sustained, protracted force generation
• Slow

Question 6

Describe Type 2A skeletal fiber.

Answer 6

• Moderately oxidative
• Mixed aerobic and anaerobic
• Intermediate speed

Question 7

Describe type 2B skeletal fiber.

Answer 7

• Very glycolytic (anaerobic)

- Fast, but unsustained force generation

Question 8

Describe muscle bioenergetics of skeletal muscle.

Answer 8

• Bursts of activity separated by periods of rest (glycolysis THEN aerobic metabolism)

Question 9

What does skeletal muscle release after an immediate burst of activity?

Answer 9

Creatine phosphate

Question 10

Describe bioenergetics of cardiac muscle.

Answer 10

Continuous work demand w/ periods of increased demand (aerobic metabolism), no rest and relentless contraction

Question 11

What is preferred fuel of cardiac muscle?

Answer 11

Fatty acids

Question 12

Which type of muscle has the most mitochondria?

Answer 12

Cardiac muscle

Question 13

Describe bioenergetics of smooth muscle.

Answer 13

Slow, sustained activity and low energy consumption, mitochondria very scattered

Question 14

Which muscle type exhibits latching?

Answer 14

Smooth muscle

Question 15

What is a maternally inherited defect of the mitochondria and which muscles does it usually involve?

Answer 15

Mitochondrionapathies - skeletal and cardiac

Question 16

What is the plateau in cardiac skeletal muscle AP due to?

Answer 16

Voltage gated Ca2+ channels

Question 17

What causes the force of the cardiac myofiber contraction to increase?

Answer 17

Increase of cytoplasmic Ca concentration

Question 18

What is isometric contraction?

Answer 18

No change in muscle length

Question 19

What is preload?

Answer 19

Isometric tension generation at a preset length

Question 20

What is passive tension?

Answer 20

Tension developed by simply stretching a muscle to different lengths

Question 21

What is active tension?

Answer 21

The active force developed during cross-bridge cycling

Question 22

What is total tension?

Answer 22

Sum of active and passive tension

Question 23

When does maximal active tension occur?

Answer 23

When the overlap of actin and myosin is maximal

Question 24

Is maximal tension achieved with the shortest or longest sarcomere?

Answer 24

Shortest

Question 25

Why is isometric tension not really ever = 0, even when there is no actin/myosin overlap?

Answer 25

Titin elasticity and the reticular collagen and basal lamina in endomysium create some tension (the passive tension)

Question 26

Why does isometric tension plateau at the H zone?

Answer 26

There are no cross bridges

Question 27

Why does isometric tension drop as actin myofilaments cross M line?

Answer 27

Steric hindrance of cross bridges by double overlap of actin and polarity dichotomy

Question 28

Why does sarcomere have a minimum length it can shorten to?

Answer 28

The rigid platform of the myosin hits the Z lines.

Question 29

What is the afterload?

Answer 29

Force against which the muscle contracts

Question 30

What kind of relationship do the velocity of shortening and the afterload have?

Answer 30

Inverse - as afterload increases, velocity of shortening decreases

Question 31

When does Vmax occur?

Answer 31

Zero loading

Question 32

What happens when afterload exceeds force generation?

Answer 32

Velocity of shortening = 0

Question 33

Describe preload and afterload in cardiac contraction.

Answer 33

If preload is optimized, it can improve cardiac contraction. If afterload is high (pressure against which heart pumps is high), can have reduced velocity of contraction.

Question 34

What is unitary smooth muscle? Give examples.

Answer 34

Smooth muscle cells connected by gap junctions that act as one due to electrical coupling. Involves spontaneous, slow waves of depolarization. Ex: GI tract, uterus, ureter, bladder

Question 35

What is multiunit smooth muscle? Give examples.

Answer 35

No gap junction coupling, myofibers function individually so that each myofiber is innervated by autonomic nerve fibers. There is strong neural control involved. Ex: Iris, ciliary muscle of lens, vas deferns

Question 36

Describe regeneration in skeletal muscle.

Answer 36

Lmtd due to few stem cells (satellite cells). | Hypertrophy occurs in response to exercise.

Question 37

What is hypertrophy?

Answer 37

Enlargement of existing cells

Question 38

What is hyperplasia?

Answer 38

Generation of new cells

Question 39

Describe regeneration in cardiac muscle.

Answer 39

No regeneration b/c no stem cells. | Hypertrophy can occur in response to exercise and afterload (hi BP)

Question 40

Describe regeneration in smooth muscle.

Answer 40

Unlimited regeneration. Hypertrophy can occur in uterus during pregnancy. Hyperplasia can occur in breast glandular epithelium during pregnancy.