Chapter 10

Question 1

The cytoplasm of muscle cells which contains cytosol and all organelles of a muscle cell is called the _______.

Answer 1

Sarcoplasm

Question 2

The plasma membrane of a muscle cell is called the ________.

Answer 2

Sarcolemma

Question 3

Cylindrical organelles that make up 50-80% of muscle cell volume and are bundles of specialized proteins used for muscle contraction are called _______.

Answer 3

Myofibrils

Question 4

The modified endoplasmic reticulum in muscle cells which surround each myofibril and store calcium is called the _______.

Answer 4

Sarcoplasmic Reticulum

Question 5

The structure that extends inward from the Sarcolemma, surrounds each myofibril, and forms a tunnel-like network within the muscle fiber is called the ________.

Answer 5

Transverse Tubules

Question 6

The combination of a Transverse Tubule and two terminal cisternae is called a ______.

Answer 6

Triad

Question 7

The hundreds of thousands of protein bundles that compose a myofibril are called ______.

Answer 7

Myofilaments

Question 8

The three types of myofilaments are ______.

Answer 8

Thick Filaments, Thin Filaments, and Elastic Filaments

Question 9

Each thick filament contains many contractile proteins called _________.

Answer 9

Myosin

Question 10

The contractile and regulatory proteins contained within thin filaments are called _______.

Answer 10

Actin (contractile), Tropomyosin (regulatory), and Troponin (regulatory)

Question 11

The two regulatory proteins found in thin filaments that help control muscle contraction are _______.

Answer 11

Tropomyosin and Troponin

Question 12

Elastic filaments are composed of a coiled structural protein, which stretches and recoils to provide elasticity to muscle fibers, called ______.

Answer 12

Titin

Question 13

The light region of muscle striation, which contains only thin filaments, is called the _____.

Answer 13

I-Band

Question 14

The dark region of muscle striation, which contains thick filaments, is called the ______.

Answer 14

A-Band

Question 15

The functional unit of contraction, where muscle tension is produced, from Z-Disk to Z-Disk in a myofibril is called a _______.

Answer 15

Sarcomere

Question 16

The interaction of thin and thick filaments during muscles contraction and relaxation is known as the _______.

Answer 16

Sliding-Filament Theory

Question 17

The only band that remains unchanged in size during muscle contraction is the ______.

Answer 17

A-Band

Question 18

The synapse of a motor neuron with a muscle fiber is called the ________.

Answer 18

Neuromuscular Junction

Question 19

The neurotransmitter in the axon terminals of motor neurons that connect to skeletal muscle fibers is ______.

Answer 19

Acetylcholine

Question 20

Describe the process of muscle contraction.

Answer 20

(1) Excitation Phase: First, the Sarcolemma must be stimulated by Acetylcholine released from a motor neuron. This causes an action potential.
(2) Excitation-Contraction Coupling: Once the muscle fiber is excited, this is conveyed to myofilaments.
(3) Contraction Phase: Then the sliding-filament mechanism occurs and the sarcomere contracts. Contraction in many sarcomeres produce contraction of the whole muscle.

Question 21

What are the steps of Excitation Phase?

Answer 21

1. Action potential arrives at motor neuron axon terminal via ACh contained in synaptic vesicles. Ca+ channels in the axon terminal are triggered to open.
2. Ca+ is released into the axon terminal, which triggers exocytosis of the synaptic vesicles containing ACh.
3. Synaptic vesicles release ACh into the synaptic cleft (between neuron and motor end plate of sarcolemma).
4. ACh binds to ligand-gated ion channels of motor end plate to trigger release of Na+.
5. The ion channels open and release Na+ into muscle fiber.
6. Entry of Na+ into the muscle fiber depolarizes the sarcolemma and causes end-plate potential.

Question 22

What are the steps of Excitation-Contraction Coupling?

Answer 22

1. End-plate potential left behind from Excitation Phase spreads down the sarcolemma and this stimulates an action potential within the muscle fiber.
2. The action potential continues like a wave into the Transverse Tubules and triggers more Na+ release into the muscle fiber.
3. The depolarization within the Transverse Tubules causes Ca+ channels to open in the sarcoplasmic reticulum, releasing Ca+ from the SR into the cytosol of the muscle fiber.

Question 23

What are the steps of Contraction Phase?

Answer 23

1. Ca+ that was left in the cytosol of the muscle fiber after Excitation-Contraction Coupling now binds to Troponin, the regulatory protein of the thin filament Actin.
2. Once Ca+ is bound to Troponin, the Tropomyosin shifts position and exposes the active sites of Actin.
3. When the active sites are exposed, the heads on the thick filament Myosin are able to bind to Actin using ATP.
4. ATP catalyzes into ADP and a Phosphate group when activating Myosin to bind to Actin. When the extra Phosphate group is released, Myosin pulls Actin toward the Sarcomere center.