Muscle

Question 1

Nuclei of skeletal muscle

Answer 1

Multinucleated, peripherally placed under sarcolemma

Question 2

Skeletal muscle cell structure

Answer 2

Long, cylindrical, multibucleated
Length varies up to few mm to 1m

Question 3

Satellite cells

Answer 3

Small population of reserve progenitor cells remain adjacent to many mature skeletal muscle cells

Question 4

Endomysium

Answer 4

Delicate layer of reticular fibers that immediately surrounds individual muscle fibers

Question 5

Perimysium

Answer 5

Thicker layer of CT that surrounds fascicles

Question 6

Fascicle

Answer 6

Bundle of muscle fibers

Question 7

Epimysium

Answer 7

Thick external sheath of dense CT that surrounds the entire collection of fascicles that make up the muscle
- Carries/supports larger nerves, blood vessels and lymphatics

Question 8

Myofibrils

Answer 8

Bundle of myofilaments (actin & myosin)

Question 9

Basic functional unit of muscle cell

Answer 9

Sarcomere

Question 10

Sarcomere

Answer 10

• basic functional repetitive contractile subunit of striated muscle
• segment of myofibril between two Z lines

Question 11

Z line

Answer 11

Bisects light (I) band, anchors adjacent thin filaments (actin)

Question 12

H band

Answer 12

Bisects dark (A) band
Only myosin, adjecent to actin

Question 13

M line

Answer 13

Bisects H band
Adjacent thick filaments (myosin) link

Question 14

I bands during contraction

Answer 14

• Actin filament slides past myosin filaments
• Shortens during contraction

Question 15

A bands during contraction

Answer 15

Individual myosin filaments do not move, width does not change

Question 16

H band during contraction

Answer 16

Narrows as actin overlaps myosin

Question 17

What are the contractile units of skeletal muscle

Answer 17

Myofilaments (actin & myosin)

Question 18

What are the striations shown in longitudinal sections of skeletal muscle?

Answer 18

Alternating dark & light bands due to organized parallel arrangement of myofibrils

Question 19

Dark bands

Answer 19

A bands - mark extent of myosin filaments, actin overlaps

Question 20

Light bands

Answer 20

I bands - contain only actin

Question 21

Primary proteins of thin myofilaments

Answer 21

F-actin, tropomyosin, Troponin

Question 22

F-actin

Answer 22

Forms double stranded helix

Question 23

Tropomyosin

Answer 23

Double helix of 2 polypeptides, forms filaments that run in the groove between F-actin molecules in the thin filament
- in resting muscle works with Troponin to mask myosin binding sites

Question 24

Troponin

Answer 24

Complex of 3 subunits:
- Troponin-C (TnC) - smallest subunit, binds Ca in initiating contraction
- Troponin-T (TnT) - binds to tropomyosin, anchoring Troponin complex
- Troponin-I (TnI) - Binds to actin inhibiting actin-myosin interaction

Question 25

Thick myofilament structure

Answer 25

- 2 heavy chains twisted together as myosin tails, and 4 light chains - globular projections containing he 4 light chains form head at 1 end of heavy chain

Question 26

Sarcoplasmic reticulum

Answer 26

- Smooth ER of muscle cell - forms highly organized tubular networks around myofibrils, extending between A-I junctions

Question 27

Terminal cisternae

Answer 27

At the A-I junction, SR forms ring-like channel

Question 28

Function of terminal cisternae

Answer 28

Reservoir for Ca

Question 29

Transverse (T) tubule system

Answer 29

Numerous tubular invaginations of the sarcolemma reach to the A-I junction

Question 30

The T-tubule and 2 terminal cisternae form ______

Answer 30

a triad

Question 31

Function of triad complex

Answer 31

Triggers Ca release when sarcolemma is depolarized to initiate contraction of Sarcomeres

Question 32

Repair & healing of skeletal muscle

Answer 32

- mature skeletal muscle cells are permanent (non-dividing) - limited ability to repair via satellite cells - more typically, fibroblasts repair injury site with scar tissue

Question 33

Epicardium

Answer 33

External CT covering around heart muscle (myocardium), lined by mesothelium

Question 34

Intercalated discs

Answer 34

Junctions between cardiac muscle cells forming strong intercellular adhesion and gap junctions

Question 35

Gap junction

Answer 35

Allow for communication allowing cardiac muscle to act as a syncytium allowing informational macromolecules to pass rapidly from cell to cell

Question 36

Cardiac vs skeletal muscle fibers

Answer 36

- Sarcomeres organized and function similarly to skeletal muscle - myofibrils sparser than skeletal muscle (moth eaten appearance) - Autonomic nerves regulate contraction

Question 37

Repair and healing of cardiac muscle

Answer 37

- permanent cells (non-dividing) - lack satellite cells - very little potential to regenerate after injury (most likely from nearby stem cells) - myocardial infarction - healing by fibroblasts laying down scar tissue

Question 38

Motor end plates / neuromuscular junctions

Answer 38

Contact made by terminal branches of motor axons with the skeletal muscle fiber

Question 39

Smooth muscle characteristics

Answer 39

- non-striated, random placement of actin & myosin (no Sarcomeres) - elongated cells with tapered ends, one central nucleus - cells linked by gap junctions - No T-tubule system (disorganized SR)

Question 40

Smooth muscle contractile proteins

Answer 40

myosin light-chain kinase (MLCK) and calmodulin

Question 41

Calmodulin

Answer 41

Ca binding protein

Question 42

Dense bodies

Answer 42

Attachment sites in cell membrane anchoring Actin myofilaments

Question 43

Location of smooth muscle

Answer 43

Major muscle component of blood vessels, digestive, respiratory, urinary, and reproductive tracts

Question 44

Repair and healing in smooth muscle

Answer 44

Capable of more active regenerative response - stabile (quiescent) cells

Question 45

What structure is located in the I-band and attaches to the thin filaments?

Answer 45

Z-line