Section 2

Question 1

Which type of muscle tissue is the only voluntary type in the human body?

Answer 1

Skeletal muscle

Question 2

What is voluntary muscle?

Answer 2

Muscle that is controlled consciously

Question 3

What are the functions of skeletal muscle?

Answer 3

Skeletal muscle contracts to move parts of the body. Most skeletal muscles are attached to two bones across a joint, such that when contracted the muscle brings parts of those two bones closer to each other.

• produce movement
• maintain posture and stabilize joints
• control excretion (elimination of urine and feces) and swallowing
• produce heat
• support and protect internal organs

Question 4

Describe the organization of skeletal muscle

Answer 4

• consists of muscle tissue and connective tissue
• connective tissue surrounds the muscle tissue and attaches the ends of each muscle to bone

Question 5

What are the three layers that connective tissue in skeletal muscle is categorized as?

Answer 5

1. Epimysium
2. Perimysium
3. Endomysium

Question 6

Describe epimysium

Answer 6

• the layer of connective tissue that surrounds an entire muscle and is continuous with the tissue that becomes the tendon

Question 7

Describe perimysium

Answer 7

• the layer of connective tissue surrounding a bundle of muscle fibers (fascicle) within a muscle

Question 8

Describe endomysium

Answer 8

• the layer of connective tissue that surrounds the individual muscle cells (muscle fibers) within a muscle bundle

Question 9

What is another word for myofiber/what is a myofiber?

Answer 9

A muscle cell

Question 10

What is a myofiber vs myofibril vs myofilament?

Answer 10

Muscle cells (myofiber) –>
has many myofibrils –>
that contain numerous myofilaments

Question 11

List the features of a muscle cell (there is 6 to list)

Answer 11

1. Sarcolemma
2. Nuclei
3. Myofibril
4. Myofilament
5. Sarcoplasmic reticulum
6. T-tubules

Question 12

What is the sarcolemma?

Answer 12

• found in a muscle cell
• the cell membrane surrounding the muscle cell
• beneath it are the nuclei, myofibrils, and the sarcoplasm (cellular fluid)

Question 13

Explain the nuclei of skeletal muscle cells

Answer 13

• multinucleated (they have more than one nucleus)
• these nuclei are located towards the outside of the myofiber

Question 14

What are myofibrils?

Answer 14

• the structural units of the muscle cell
• contain the contractile myofilaments

Question 15

What are myofilaments?

Answer 15

The contractile units of the muscle cell

Question 16

What is the sarcoplasmic reticulum?

Answer 16

• surrounds each myofibril
• this is where the muscle stores calcium, which is necessary for muscle function

Question 17

What are T-tubules?

Answer 17

• Transverse tubules (T-tubules)
• extensions of the sarcolemma that surround the myofibrils
• they transmit nerve stimulation to the sarcoplasmic reticulum within the cell

Question 18

How are myofilaments organized?

Answer 18

• they are organized into repeating structural units AKA sarcomeres
• one sarcomere spans from one Z line to the next

Question 19

How does contraction occur in sarcomeres?

Answer 19

When shortened, the sarcomeres cause contraction of the muscle. each unit consists of actin and myosin

Question 20

Describe the structure of a sarcomere

Answer 20

It consists of thick and thin myofilaments
- thick = myosin
- thin = actin
Skeletal muscle has a striated appearance due to the arrangement of action and myosin into organized sarcomeres that form distinct lines and bands.

(look at an image, in mod3, section2, page 5 or online)
Z-line in the middle of actin filaments
M-line in the middle of myosin filaments
A band of myosin
I band of actin

Question 21

What happens when muscles contract (actin & myosin)? + what would this look like on a micrograph

Answer 21

The actin and myosin filaments slide over each other, which shortens the sarcomere.
This increases muscle tension grossly resulting in the movement of structures.

**Basically in a micrograph, all the thick black bands in the middle look like they disappear (since the filaments are sliding over each other)

Question 22

Why does the sarcomere appear to have light and dark bands?

Answer 22

• Due to the overlap of thick and thin filaments
• The I-band is light because that area only consists of thin filaments (actin). The Z-line in the middle is dark because it contains an abundance of structural protein
• The A-band is dark because it consists of thick filaments (myosin) and is even darker towards the sides because it is overlapping with actin, thus that area has both thick and thin filaments. The M-line in the middle is an abundance of structural protein that creates a dark line.