DLA 24 + lecture 34 Flashcards
What are the two general classifications of muscle tissue?
striated and smooth
What muscle tissues are striated?
skeletal, visceral, and cardiac
What classification of muscle are voluntary?
skeletal and visceral
what classification of muscle are involuntary?
cardiac and smooth
Where is skeletal muscle found?
somatic/ body wall
Where is visceral muscle found?
Soft tissue origin. Tongue, pharynx,
larynx, diaphragm and upper esophagus
Where is cardiac tissue found?
heart and roots of great veins
Where is smooth muscle found?
Walls of visceral organs. Stomach, gut tube etc
describe the epimysium?
Dense connective tissue encasing multiple fascicles. • Contains major blood vessels and nerves • Continues with tendon to attach muscle at the myotendinous junction
Describe the perimysium?
Groups of skeletal myocytes/fibers form a
fascicle (F)
• Each fascicle is surrounded by a layer of
connective tissue or perimysium
• Contains larger blood vessels & nerves
Describe the endomysium?
Delicate layer of reticular fibers that surrounds individual muscle fiber (myocyte) • Contains small blood vessels and very fine neuronal branches
What does skeletal muscle look like histologically?
Multiple nuclei peripherally located
Long cylindrical cells
Striations
What does cardiac muscle look like histologically?
Intercalated discs
Centrally located nucleus
Branched cells
Striations
What does smooth muscle look like histologically?
Spindle-shaped cells
Centrally located nucleus
What is the sliding filament hypothesis of huxley?
Sarcomere shortens and becomes thicker, but the
myofilaments remain the same length.
Sliding action results from repeated “make
and break” attachments between the heads
of the myosin molecules and neighboring
actin filaments
A band = constant
I and H band = both decrease in size
Z band = are drawn closer to the ends of the A bands
What are the stages of contraction?
- attachment/ reattachment
myosin head is tightly bound to actin. No ATP - release
ATP binds to the myosin head - bending
ATP hydrolysis induces conformation change and movement of myosin head - Force generation
I. myosin head weakly binds to actin, this leads to the release of Pi
II. powerstroke: the myosin head produces force as it returns to its normal position
III. As the myosin head straightens, it forces movement of the thin filament
How is a sacromere defined?
The segment of the myofibril between two adjacent Z lines
the functional unit of the myofibril and the basic unit of contraction
What are the contractile element of skeletal muscle?
Myosin II (thick filaments)
Actin (thin filaments)
What are the associated proteins of the thin filaments
- tropomyosin
- tropomodulin
- troponin complex
What does tropomodulin do?
capping protein which maintains & regulates length of the actin filaments
What makes up the troponin complex?
troponin C (TnC) = binds calcium
troponin T (TnT) = binds to tropomyosin and anchors troponin complex
Troponin I (TnI) = inhibits the interaction between myosin and actin
what does myomesin and C-protein do?
accessory protein to myofilaments
Myosin binding protein that aligns thick filaments at M line
What does myosin binding protein C do?
accessory protein to myofilaments
Associated with the M line and important for the assembly andstabilization of the thick filament
What does titin do?
Spring like protein→ keeps thick filament centered between two the Z lines of the sarcomere and prevents excessive stretching
What does nebulin do?
helps anchor thin filaments at Z line and regulates length of thin filaments during development
What does A-actinin do?
Actin binding protein that bundles and helps stabilize thin filaments at Z line
What does desmin do?
Surrounds the sarcomere at Z lines attaching them to one another and to the sarcolemma
What does the protein dystrophin do? what happens if this protein does not work properly?
is a rod-shaped cytoskeletal protein which links to ECM proteins laminin & agrin found in the external lamina of the myocyte
if not working muscular dystrophy is the result
What is myasthenia gravis?
an autoimmune disease which impacts the neuromuscular junction
Acetylcholine (Ach) receptor antibodies, which block and attack ACh receptors in the postsynaptic membrane
What do fewer Ach receptors result in?
fluctuating weakness and fatigue of the skeletal muscles
Ocular, bulbar, limb and respiratory muscles
are affected
What are intercalated discs in cardiac tissue?
they are attachment sites between adjacent cardiac myocytes
What are the transverse components of cardiac tissue
- fascia adherens- binds cardial myocytes at their ends
2. maculae adherentes (desmosomes) = bind muscle cells to each other
What is the lateral component of cardial tissue?
gap junctions
what type of fibers are found in cardial tissue?
purkinje fibers
Specialized to conduct impulses of the A-V bundle and allow synchronization of ventricular contraction
(few myofibrils, lots of glycogen and mito)
What characteristics does smooth muscle have?
Elongated, fusiform cells with tapered ends generally organized into bundles or sheets No cross-striations thus even staining with H&E staining
A central nucleus
How are smooth muscle cells interconnected?
gap junctions
explain smooth muscle contraction?
Contraction is regulated by the Ca2+-calmodulin-MLCK system
- Increase in Ca2+ concentration
- Ca2+ binds to calmodulin forming the Ca2+ -calmodulin complex
- Ca2+ -calmodulin complex binds MLCK
- MLCK phosphorylates regulatory light chain of myosin
- Actin-binding site of myosin head is activated & attaches to actin
How is smooth muscle contraction regulated?
- mechanical - Passive stretching of vascular
smooth muscle activates myogenic reflex - Electrical - neural stimulation
- chemical - use of second messenger pathways
what muscle types can go through hypertrophy?
skeletal - yes
cardiac- Hypertrophy as in hypertensive
cardiomyopathy
smooth - yes
what muscle types can go through hyperplasia?
skeletal- no
cardiac- no
smooth- yes in certain conditions
how does skeletal muscle respond to injury?
Satellite cells are responsible for skeletal muscle
regeneration
Regenerative capacity is limited
How does cardiac muscle respond to injury?
No regenerative capacity
After the death of cardiac muscle cells, the tissue is replaced with fibrous connective tissue (A)
Cardiac function is lost at site of injury
How does smooth muscle respond to injury?
vascular injuries can be repaired
