Module 4 Lecture 1

Question 1

What are the two types of muscles? Either has lines or not…

Answer 1

Striated and Non-striated

Question 2

What muscle fall under striated muscle?

Answer 2

Skeletal muscle and cardiac because they have lines running through them

In the image (skeletal muscle) you can see the light and dark lines indicating the A band and I band

Even the diaphragm is skeletal muscle because it has a central tendon that it attaches to

Question 3

Skeletal muscles include being…?

Answer 3

Respiratory and locomotor muscle

Locomotor = movement of the body

Question 4

What falls under unstriated?

Answer 4

Smooth muscles (stomach, intestines, etc.)

Question 5

What is unique about cardiac muscle fibres?

Answer 5

fused together by intercalated discs unlike skeletal which are not fused

Question 6

What are myofibres and what are they formed by?

Answer 6

Myofibre refers to a muscle cell; they are formed by fusing undifferentiated & mononucleated cells = Myoblast

Myoblasts are precursor muscle cells only specfic to becoming muscle once fully matured, nothing else

Question 7

Purposes of having multiple nuclei on skeletal muscle?

Answer 7

1. Muscle fibres are very long
2. If there is a tear, a nearby nuclei can move down to express the gene for replication to occur

Question 8

What are satellite cells?

Answer 8

Like myoblasts; they are responsible for muscle regeneration (mononucleated & undifferentiated stem cells)

Especially important for post birth muscle growth

Question 9

Explain the process of how muscle fibres get repaired?

Answer 9

1. If you have muscle injury (myotrauma) satellite cells (myoblasts) are called to the site of the injury
2. Recruited to the site via chemotaxis - things inside the cell membrane leave the cell which chemically attract the satellite cells to that region of leakage
3. Jumps into the site of injury to fuse
4. After fusion, it differentiates to generate fibre

Muscle cells cannot undergo mitosis because they are too big
Chemotaxis - movement of cell due to chemical attraction

Question 10

If satellite cells are so important to generating muscle fibre how do we preserve them?

Answer 10

Although muscle fibres cannot undergo mitosis, the satellite cells which generate muscle fibres can. After injury some satellite cells are preserved and they undergo mitosis to proliferate.

Question 11

What surrounds a Muscle?

Answer 11

Connective tissue in the form of collagen; there are connective tissues that surround each fascicle, fibre and fibril

Question 12

What are fascicles?

Answer 12

Group of fibres in an entire muscle; surrounded by collagen

Question 13

What are muscle fibres with respect to the fascicle?

Answer 13

Within fascicle and smaller; a single cell

Question 14

What are the epimysium, perimysium and endomysium

Answer 14

Epimysium: Connective tissue on the outermost layer of muscle
Perimysium: Fascicles surrounded by collagen
Endomysium: Muscle fibre surrounded by collagen (not the myofibrils but the entire muscle fibre within the fascicle)

Question 15

Purpose of connective tissue?

Answer 15

Protection for the muscle

Epimysium and Endomysium has two membrane for more protection

Question 16

What gives muscle its striations?

Answer 16

Arrangment of thick and thin filaments along the myofibril of the muscle fibre; dark A band for thick and light I band for thin

Myofibrils is where the calcium binds to make the muscle fibre “shorten”

Question 17

What is the sarcomere and what makes one sarcomere?

Answer 17

The sarcomere is a repeating contracile unit which is from one Z-line to another.
* Z-lines are anchors for other sarcomeres to connect and they are found on the I band in a zig-zag line going down

Question 18

What are the thick and thin lines on the sarcomere?

Answer 18

Thick (A) band and Thin (I) band; A is because its darker and I because it is lighter

• Thick bands refer to myosin
• Thin bands refer to actin

Question 19

When you zoom into the sarcomere and look at the myosin and actin what is myosin doing?

Answer 19

Myosin has these nobs that are the heads of the myosin sticking out and trying to interact with actin but it is unable to due to certain reasons

Question 20

What does the sliding filament theory of contraction say about actin and myosin?

Answer 20

Myosin and actin do not shorten the muscle, rather they slide over each other to induce contraction of the muscle

Question 21

The A band (thick filament = Myosin) is anchored to the Z-line by what?

Answer 21

Titin

• Strongest protein in the body
• Spring that stabilizes myosin so it doesn’t move

Because myosin doesn’t move, when contraction occurs and the myosin and actin slide over each other, the actin is the one moving and it looks as though the actin disappears but in fact it blends in with myosin