Lecture 10

Question 1

What is a Muscle

Answer 1

A bundle of muscle fibers, anchored to a bone by tendons

Question 2

What is a Muscle Fiber

Answer 2

A multinucleated muscle cell

Question 3

What is a Myofibril

Answer 3

Longitudinal component inside a striated muscle cell, composed of a series of sacromeres

Question 4

What is a Sarcomere

Answer 4

The contractile unit of striated muscle, composed of myofilaments

Question 5

What are the Two Types of Myofilaments bound by Z disks in each Sarcomere?

Answer 5

1. Actin thin filaments
2. Myosin thick filaments

Question 6

What is a Thin Filament (in a sarcomere)

Answer 6

A two-strand actin helix + the filamentous protein tropomyosin + the troponin complex

Question 7

What is a Thick Filament ( in a sarcomere)

Answer 7

Hundreds of identical myosin proteins

Question 8

The head Regions of Myosin (what it contains and what it forms)

Answer 8

• Contains actin- and ATP-binding sites
• Form cross-bridges with the thin filament during contraction

Question 9

The Sliding-Filament Theory:

Answer 9

Sarcomeres shorten during muscle contraction because the thin filaments actively slide along the thick filaments

Question 10

What do Cross-bridges Do?

Answer 10

Convert chemical energy into mechanical energy

Question 11

Without ATP myosin where does it Bind?

Answer 11

Binds irreversibly to actin (rigor mortis)

Question 12

Binding to Cross-bridges (ATP):

Answer 12

Hydrolysis of ATP causes myosin head to extend and attach to actin

Question 13

Power Stroke of Cross-Bridges:

Answer 13

Release of phosphate promotes myosin head rotation

Question 14

Release of Cross-Bridges

Answer 14

Binding of ATP causes myosin to detach from actin

Question 15

Regulation of Muscle Contraction (When Ca 2+ is Low):

Answer 15

Tropomyosin blocks the myosin binding sites on actin

Question 16

Regulation of Muscle Contraction (When Ca 2+ is High):

Answer 16

Ca 2+ binding to troponin removes an attachment inhibition between myosin cross-bridges and thin filaments

Question 17

How are APs Conducted to Skeletal Muscles:

Answer 17

Through large myelinated motor neurons

Question 18

What Does the Neuromuscular Junction Include:

Answer 18

Pre- and post-synaptic specialization

Question 19

Excitation-Contraction Coupling - Why do Muscle Fibers Contract:

Answer 19

When a postsynaptic end plate potential at the neuromuscular junction causes a propagated AP in the fiber sarcolemma

Question 20

An AP in the Muscle Fiber Changes What (in regards to Ca 2+):

Answer 20

The free [Ca 2+] in the cytosol

Question 21

What do Transverse (T) Tubules Do:

Answer 21

Conduct APs into the cell interior, causing Ca 2+ release from the sarcoplasmic reticulum that surround the myofibrils

Question 22

Control of Free [Ca 2+] in the Cytosol (DHPR and RyR):

Answer 22

Voltage-sensitive DHPR and RyR work together, linking depolarization of the T tubule to the opening of Ca 2+ channels in the SR membrane

Question 23

Control of Free [Ca 2+] in the Cytosol (Ca 2+ Pumps):

Answer 23

In the SR membrane re-sequester Ca 2+ from the cytosol

Question 24

Control of Free [Ca 2+] in the Cytosol (Calsequestrin):

Answer 24

Inside the SR binds Ca 2+ reducing the free [Ca 2+] inside the SR

Question 25

Excitation Contraction Coupling (Skeletal):

Answer 25

DHPR and RyR physically interact –> depolarization-induced Ca 2+ release

Question 26

Excitation Contraction Coupling (Cardiac):

Answer 26

Entrance of extracellular Ca 2+ through DHPR triggers opening of RyR –> Ca 2+ induced Ca 2+ release