Muscle Histology

Question 1

Sarcolemma

Answer 1

muscle cell membrane

Question 2

sarcoplasm

Answer 2

cytoplasm

Question 3

sarcoplasmic reticulum

Answer 3

similar to smooth muscle ER. Stores calcium

Question 4

sarcosomes

Answer 4

mitochondria

Question 5

Contractile proteins

Answer 5

actin and myosin. In all 3 muscle types

Question 6

sarcomere

Answer 6

repetitive contractile subunit

Question 7

Epimysium

Answer 7

surrounds entire muscle, dense irregular CT

Question 8

Perimysium

Answer 8

surrounds muscle fasicle; dense irregular CT. Neurovascular structures course through perimysium

Question 9

Endomysium

Answer 9

surrounds single muscle cell/fiber. Reticular fibers. Capillaries and nerve terminals course though endomysium

Question 10

Skeletal muscle charactoristics

Answer 10

multinucleated, nuclei are peripherally located (adjacent to sarcolemma).

Long (several cm) in length

Each fiber contains many myofibrils, each myofibril contains many sarcomeres

Question 11

M line

Answer 11

middle of sarcomere. Includes myosin binding protein that holds myosin in place

Question 12

H zone

Answer 12

location of only myosin

Question 13

A band

Answer 13

entire length of myosin

Question 14

I band

Answer 14

location of only actin

Question 15

Z disk/z line

Answer 15

each sarcomere extends from z line to z line

Question 16

tropomyosin

Answer 16

wrapped around actin, covers binding sites for myosin (except when moved by tropinin)

Question 17

troponin

Answer 17

“tacks down’ tropomyosin to actin. Binds to calcium to cause conformational change revealing myosin binding sites

Question 18

titin

Answer 18

stabilizes myosin at z disk.

Question 19

alpha actin

Answer 19

stabilizes actin at z disk

Question 20

Steps of skeletal muscle contraction

Answer 20

• Calcium binds to troponin, causing troponin to change conformation
• tropomyosin is moved away from active site on actin
• myosin binds to actin
• ATP provides energy for power stroke
• sarcomere shortens (actin moves towards M line)

Question 21

T tubules

Answer 21

Transverse tubules. Invaginations of sarcoplasm that allow the AP to reach deep into the muscle fiber

Question 22

Contractile mechanism (skeletal muscle)

Answer 22

• AP travels down T tubules
• sarcoplasmic reticulum cistern is on either side of each t tubule
• AP triggers release of calcium from adjacent SR

Question 23

Triad

Answer 23

2 sarcoplasmic reticulum on each side of 1 t tubule.

Question 24

termination of motor signal

Answer 24

• no ACh released from axon terminal
• calcium transported back into SR
• tropomyosin covers active site on actin

Question 25

Cardiac muscle characteristics

Answer 25

branches, 1 or 2 (rare) centrally located nuclei with surrounded clear area. Mitochondria are 40% of cytoplasmic volume Short, 50-100 micrometers

Question 26

Cytoplasmic cone

Answer 26

LM: glycogen and mitochondria.

Question 27

Intercalated disc

Answer 27

dark lines (recipricol elevations and depressions) at ends (interface) of cardiac muscle cells

Question 28

Components of intercalated disc

Answer 28

fascia aderens, desmosomes, gap junctions

Question 29

Fascia adherens

Answer 29

on end to end contacts of cells (on intercalated discs)

Question 30

desmosomes

Answer 30

on transverse (end) portions intercalated discs. Function: prevent cardiac muscle cells from pulling apart under strain of repetitive contractions

Question 31

Gap junctions (cardiac muscle)

Answer 31

Location: lateral aspect of intercalated discs Function: provide ionic continuity between adjacent cardiac muscle cells so cells can behave as syncytium.

Question 32

Dyads

Answer 32

term for single t-tubule adjacent to single SR

Question 33

Smooth muscle characteristics

Answer 33

spindle shaped cells, taper along axis (longer than wide). Single central nucleus. Non striated. Oblique arrangement of contractile units

Question 34

Dense bodies

Answer 34

- along sarcolemma and within sarcoplasm. - contains alpha actin and serves as attachment site for actin - when actin and myosin interact, dense bodies move closer together (corkscrew shape)

Question 35

Dense plaques

Answer 35

AKA focal adhesions - dense bodies serve to mechanically attach adjacent cells, these adhesion sites include other proteins and are called dense plaques - allows for more efficient and forceful contraction

Question 36

Gap junction (smooth muscle)

Answer 36

electrically and chemically couple smooth muscle cells

Question 37

Caveolae

Answer 37

slight invaginations of sarcolemma - role in calcium signalling - close proximity to SR

Question 38

Smooth muscle signal transduction

Answer 38

- Calcium channels present in region of the caveolae - AP passes along caveolae causing influx of calcium from ECF and release of calcium from SR - intracellular contractions ride, actin and myosin bind, shortening contraction occurs in the presence of ATP