COMPARISON BETWEEN SKELETAL AND SMOOTH MUSCLES !!

SIMMILARITIES
# In contraction;
* Actin and myosin interact by the sliding filament mechanism
* The final trigger for contraction is a rise in the intracellular calcium ion level
* ATP energizes the sliding process
DIFFERENCES
# In structure;
* Skeletal muscles are FOUND attached to and covering the bones, while the smooth muscles are  found covering the walls of the hollow organs
* Skeletal muscle are long cylindrical cells with many cells in their sarcolemma, while the smooth muscles are spindle shaped (fusiform) with one centrally located nucleus
* Skeletal muscles consists of three connective tissues ( perimysium, epimysium and endomysium), while the smooth muscle consists of only endomysium
* Skeletal muscle have highly developed neuromuscular junctions, while the smooth muscles have varicosities secreting into diffuse junctions
* Skeletal muscle have sarcoplasmic reticulum, while the smooth muscle lacke a well developed srcoplasmic reticulum ( i.e lacking a regular pattern relative to the myofilaments)
* Skeletal muscle have T-tubules, while smooth muscles lack T-tubules but make use of caveolae
* Skeletal muscles have striations and so have sarcomere, while smooth muscles lack striations and so no sarcomere
* The ratio of thick to thin filaments is much higher in skeletal muscle than in smooth muscles
# In contraction;
* Contraction in skeletal muscles are fast and might not necessarily follow a repeated pattern, while contraction in smooth muscle is slow and synchronized
* During E-C coupling in skeletal muscles calcium ion contribution comes from the sarcoplasmic reticulum, while in the smooth muscle it comes from the the poorly developed sarcoplasmic reticulum and majorly from the extracellular space through calcium ion release channels  found in the caveolae
* Myosin is activated by the binding of Ca ion with troponin ( as is the case with all striated muscles), while in smooth muscle myosin is activated by the interaction of calcium ion with calmodulin (a cytoplasmic Ca- binding protein)
* In skeletal muscles relaxation is initiated by the decrease in intracellular calcium level, while in smooth muscle relaxation is more complex and may include; the detachment of calcium from calmodulin, returning of calcium to the sarcoplasmic and extracellular space and the dephosphorylation of myosin by a phosphorylase enzyme which reduces the activities of the myosin ATPases
* Muscle contraction regulation is voluntary and innervated by somatic nerves, while it is involuntary and innervated by autonomic nerves, hormones, chemicals and stretch
#In energy utilization and consumption;
*Skeletal muscle makes use of both aerobic  (  not surprising because of its activities )and anaerobic sources of ATP, while the smooth musles make use of aerobic pathways and can sustain contractile tension for longer periods
* Fatigue occurs in skeletal muscles, while it is not common in smooth muscle
* Resting membrane potential is stable in skeletal muscles and so tetanus can occur, while its not stable in smooth muscle so tetanus can not occur