Skeletal Muscle 1 cont.

Question 1

What does tropomyosin do in a low calcium environment?

Answer 1

Blocks actin from binding to myosin

Question 2

What does tropomyosin do in a high calcium environment?

Answer 2

Binds to Tn-C; induces conformational changes that reveal binding site on actin for myosin.

Question 3

Describe the A-band.

Answer 3

The region of a myofibril all the thick filaments and some of the thin filaments. Does not change length during contraction.

Question 4

Describe the I-band.

Answer 4

Region with thin filaments; No overlap with thick filaments. Decreases in length during contraction.

Question 5

Discuss the Z-line.

Answer 5

Anchors thin filaments and actin binding proteins. Defines the boundaries of the sarcomere. Composed of alpha-actinin

Question 6

Discuss the M-line.

Answer 6

Anchors thick filaments including myomesin and C protein.

Question 7

Describe Titin

Answer 7

Extends from Z line to M line. Produces passive tension in muscle. Regulates the assembly of myosin into thick filaments.

Question 8

What is Desmin?

Answer 8

Intermediate filament that forms a lattice around a myofibril. Links z-lines of adjacent myofibrils together.

Question 9

What is Dystrophin?

Answer 9

Anchors structural actin filaments to glycoproteins of CM, which are linked to the basal lamina.

Question 10

Discuss the role of motor neurons.

Answer 10

1. Alpha-neurons arise from ventral horn of spinal cord and innervate muscle fibers.
2. Efferent innervation is necessary for survival of muscle fiber.

Question 11

What is a motor unit?

Answer 11

Motor neuron+muscle fibers. Muscle fibers in a given unit are identical in activation, metabolism, and size. Muscle fibers can’t produce their own coordinated contraction without a motor neuron.

Question 12

Describe muscle fiber unit distribution.

Answer 12

Muscle fibers of different motor units are intermixed within a fascicle.

Question 13

Discuss the NMJ

Answer 13

Each muscle fiber has one region for the NMJ, usually in the middle of the fiber. ACh receptors are concentrated here.

Question 14

What is the purpose of Muscle spindles?

Answer 14

1. Responsible for myotatic or muscle stretch reflex.

2. Provide info needed for fine adjustments to muscle position.

Question 15

What are golgi tendon organs?

Answer 15

A mechanoreceptor that responds to muscle tension. Excites antagonist muscles