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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
• Continues with tendon to attach
muscle at the myotendinous


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


What does skeletal muscle look like histologically?

Multiple nuclei peripherally located
Long cylindrical cells


What does cardiac muscle look like histologically?

Intercalated discs
Centrally located nucleus
Branched cells


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?

1. attachment/ reattachment
myosin head is tightly bound to actin. No ATP

2. release
ATP binds to the myosin head

3. bending
ATP hydrolysis induces conformation change and movement of myosin head

4. 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

1. tropomyosin

2. tropomodulin

3. 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