anat13.txt

Plasma membrance of a muscle fiber

cytoplasm of a striated muscle fiber

Muscle fiber (muscle cell)

Smooth ER in striated and smooth muscle fibers.

A motor neuron and all the muscle fibers it innervates.

• A specialized region of the sarcolemma
• Highly excitable
• Responsible for initiating the action potential that propagates across the myofiber causing the muscle contraction.

• neuromuscular junction
• the junction of the axon terminal of a motor neuron with the motor end plate 

Ventral horn.

• Found on the muscle fiber side of the NMJ
• There are different protein complexes at the crest and the bottom of the junctional folds.

• 1)  Action potential generated by the NMJ is propagated along the sarcolemma and down the T-tubules
• 2)  AP triggers Ca2+ release from terminal cisternae of SR
• 3) Ca2+ ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed
• 4)  Contraction; myosin cross bridges alternately attach to actin and detach, pulling the actin filaments toward the centre of the sarcomere; release of energy by ATP hydrolysis powers the cycling process
• 5) Removal of Ca2+ by active transport into the SR after the action potential ends
• 6)  Tropomyosin blockage restored blocking actin active sites; contraction ends and muscle fiber releases

• A toxin produced by the bacterium Clostridium botulinum.
• Inhibits Acetylcholine release by axon terminals
• Leads to botulism that causes muscular paralysis, respiratory failure, and eventual death.

• In DMD, the link between the actin cytoskeleton and the basal lamina is lost.  
• Muscle tissue is completely disrupted.
• There is an infiltration of macrophages, adipose tissue, and connective tissue.

• Found only in the heart where it forms a thick layer called the myocardium
• Pumps blood through the body
• Short and branched striated fibers
• One central nucleus per fiber
• Involuntary muscle
• Inherent rhythmicity
• T-tubules are much larger and deeper than in skeletal muscle

• Junctional complex found between two adjacent cardiac fibers
• Step-like pattern
• Has a transverse part and a lateral part

Zonula adherens and desmosomes

Gap junctions

ECM 

Gastrointestinal tract, respiratory tract, and around blood vessels

• Involuntary
• Non-striated, spindle-shaped, and tapered
• One central nucleus per fiber
• No T-tubules
• Fibers communicate via Gap junctions

• Thin filaments are arranged obliquely in the cell.  Some attach to the dense bodies in the cytoplasm while others attach to dense plaques in the plasma membrane.
• Contractile units consist of myosin filaments connecting actin filaments to a dense body or dense plaque.  They stretch across the cell between plaques.  

• Tunica media is made up of smooth muscle cells and elastic tissue - thicker in arteries compared to veins.
• Smooth muscle controls vessel diameter.

• Longitudinal layer:  muscle fibers run parallel to the long axis of the organ
• Circular layer:  muscle fibers run around circumference of the organ
• Longitudinal and circular layers participate in peristalsis.

Makes use of a longitudinal layer, a circular layer, and an oblique layer to acheive peristalsis