Muscle Histology Flashcards
Sarcolemma
muscle cell membrane
sarcoplasm
cytoplasm
sarcoplasmic reticulum
similar to smooth muscle ER. Stores calcium
sarcosomes
mitochondria
Contractile proteins
actin and myosin. In all 3 muscle types
sarcomere
repetitive contractile subunit
Epimysium
surrounds entire muscle, dense irregular CT
Perimysium
surrounds muscle fasicle; dense irregular CT. Neurovascular structures course through perimysium
Endomysium
surrounds single muscle cell/fiber. Reticular fibers. Capillaries and nerve terminals course though endomysium
Skeletal muscle charactoristics
multinucleated, nuclei are peripherally located (adjacent to sarcolemma).
Long (several cm) in length
Each fiber contains many myofibrils, each myofibril contains many sarcomeres
M line
middle of sarcomere. Includes myosin binding protein that holds myosin in place
H zone
location of only myosin
A band
entire length of myosin
I band
location of only actin
Z disk/z line
each sarcomere extends from z line to z line
tropomyosin
wrapped around actin, covers binding sites for myosin (except when moved by tropinin)
troponin
“tacks down’ tropomyosin to actin. Binds to calcium to cause conformational change revealing myosin binding sites
titin
stabilizes myosin at z disk.
alpha actin
stabilizes actin at z disk
Steps of skeletal muscle contraction
- 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)
T tubules
Transverse tubules. Invaginations of sarcoplasm that allow the AP to reach deep into the muscle fiber
Contractile mechanism (skeletal muscle)
- AP travels down T tubules
- sarcoplasmic reticulum cistern is on either side of each t tubule
- AP triggers release of calcium from adjacent SR
Triad
2 sarcoplasmic reticulum on each side of 1 t tubule.
termination of motor signal
- no ACh released from axon terminal
- calcium transported back into SR
- tropomyosin covers active site on actin
Cardiac muscle characteristics
branches, 1 or 2 (rare) centrally located nuclei with surrounded clear area.
Mitochondria are 40% of cytoplasmic volume
Short, 50-100 micrometers
Cytoplasmic cone
LM: glycogen and mitochondria.
Intercalated disc
dark lines (recipricol elevations and depressions) at ends (interface) of cardiac muscle cells
Components of intercalated disc
fascia aderens, desmosomes, gap junctions
Fascia adherens
on end to end contacts of cells (on intercalated discs)
desmosomes
on transverse (end) portions intercalated discs.
Function: prevent cardiac muscle cells from pulling apart under strain of repetitive contractions
Gap junctions (cardiac muscle)
Location: lateral aspect of intercalated discs
Function: provide ionic continuity between adjacent cardiac muscle cells so cells can behave as syncytium.
Dyads
term for single t-tubule adjacent to single SR
Smooth muscle characteristics
spindle shaped cells, taper along axis (longer than wide). Single central nucleus. Non striated. Oblique arrangement of contractile units
Dense bodies
- 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)
Dense plaques
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
Gap junction (smooth muscle)
electrically and chemically couple smooth muscle cells
Caveolae
slight invaginations of sarcolemma
- role in calcium signalling
- close proximity to SR
Smooth muscle signal transduction
- 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
