Unit 3.2: Skeletal Muscles

Question 1

What are the characteristics of skeletal muscles? How are they attached to bones?

Answer 1

Responsible for positioning and movement of the skeleton

Attached to bones via tendons

Question 2

What are tendons composed of?

Answer 2

Dense regular connective tissue (collagen)

Question 3

What is the structure of skeletal muscles?

Answer 3

Outer connective tissue: epimysium
Contains bundles of: Fascicles
Which are covered by perimysium
Fascicles contain muscle fibres
Which are covered by endomysium
Muscle fibres contain myofibrils

Question 4

What does the cytosol of muscle fibres contain?

Answer 4

Many glycogen granules (energy storage) and mitochondria (ATP synthesis)

Question 5

What is the structure of a muscle fibre?

Answer 5

Long, cylindrical cell

Has several hundred nuclei

Question 6

What is the cell membrane of the muscle fibre called?

Answer 6

Sarcolemma

Question 7

What is the ER of muscle fibres called?

Answer 7

Sarcoplasmic reticulum

Question 8

What is associated with the SR?

Answer 8

Transverse tubules (T-tubules)

Question 9

What is characteristic of the t-tubule’s lumen?

Answer 9

It is continuous with the ECM

Question 10

What is closely associated with t-tubules?

Answer 10

Terminal cisternae

Question 11

What do terminal cisternae do?

Answer 11

They sequester (store) Ca2+

Question 12

What is a triad?

Answer 12

One t-tubule with flanking terminal cisternae

Question 13

What do t-tubules allow?

Answer 13

Rapid AP diffusion into the muscle fibre

Question 14

What are the muscle equivalents of:
Muscle cell
Cell Membrane
Cytoplasm
Modified ER

Answer 14

Muscle cell ———– Muscle fiber
Cell Membrane —– Sarcolemma
Cytoplasm ———— Sarcoplasm
Modified ER ———- Sarcoplasmic reticulum

Question 15

What protein occupies most space in a muscle fibre?

Answer 15

contractile structures

Question 16

What are the different proteins found in a muscle?

Answer 16

1. Contractile proteins: Actin and Myosin
2. Regulatory proteins: Tropomyosin and Troponin
3. Accessory proteins: Titin, Nebulin, others

Question 17

What do myofibrils have under light microscope?

Answer 17

Striations

Question 18

What is one repeated pattern of striations called?

Answer 18

Sarcomere

Question 19

What is a sarcomere made of?

Answer 19

• Z-line (disks)
• I band (isotropic): reflects light uniformly
• A band (anisotropic): scatters light unevenly
• H zone (part of the A band)
• M-line

Question 20

What causes striations?

Answer 20

The organization of the protein components of the myofibrils

Question 21

What is the structure of myosin?

Answer 21

Consists of 2 coiled protein molecles that have 2 important parts: head and tail region
Head and tail are stiff and are joined by a flexible hinge

Question 22

What makes up a thick filament?

Answer 22

250 myosin molecules join

Question 23

How are myosins arranged in the cell?

Answer 23

Heads are at the ends

Question 24

What are the subunits of actin?

Answer 24

G-actin (globular actin)

Question 25

What is the structure of actin?

Answer 25

G-actin subunits polymerize to form chain called f-actin | 2 f-actins twist together to form a thin filament

Question 26

What does the coiled f-actin associate with?

Answer 26

Regulatory proteins troponin and tropomyosin

Question 27

What do the regulatory proteins do?

Answer 27

Regulate muscle contraction | forms the completed thin filament

Question 28

What is it called when myosin heads interact with actin filaments?

Answer 28

Crossbridges

Question 29

What are Z-lines?

Answer 29

Disks Site of attachment for thin filament One sarcomere is made of 2 Z disks and the filaments between them

Question 30

What are I band?

Answer 30

This is a region containing only thin filaments | Z-disc runs through th emiddle of an I band, thus each half of the I band is part of a different sarcomere

Question 31

What is the A band?

Answer 31

Region containing both thick and thin filaments They overlap at the edge of the A band Center is only thick filaments

Question 32

What is the H zone?

Answer 32

Part of the A band, it contains ONLY thick filaments

Question 33

What is the M line?

Answer 33

Site of attachment for thick filaments | M line is the center of the sarcomere

Question 34

What would cross sections of the muscles will show you?

Answer 34

One thin filament surrounded by 3 thick | One thick filament surrounded by 6 thin

Question 35

What proteins allow for proper alignment within a sarcomere?

Answer 35

1. Titin - elastic protein, largest known protein, stretches from Z-disc to M-line and stabilizes position of contractile filaments 2. Nebulin - non-elastic, attaches to Z disc and helps to align actin filaments in the sarcomere