smooth muscle is present in most hollow organs of the body (not the heart) and in the circulatory system, eyes, GI tract, Respiratory tract.
there are two main types of smooth muscle - Unitary and multiunit
unitary muscle is the most common type of smooth muscle it is when there are groups of cells that are connected by gap junctions and focal adhesions which are all connected to the same neuron and so when a stimulation from the neuron occurs it will affect all of the cells at the same time these cells are important for the GI tract and things such as peristalsis to occur
multiunit smooth muscle cells are separate and all have their respective neurons which stimulate each cell separately from one another leading to finer motor skills these cell types are found in places like the fingers and eyes.
the structure of a smooth muscle cell is as follows
non-striated
not a lot of cytoplasm space around each nucleus
Explain the processes of contraction and relaxation in smooth muscle
smooth muscle can contract to 80% of its original size due to the organised way that actin and myosin are arranged within the cells (skeletal muscle can only contract about 20% of its original size. This is due to the fact that on either side of the myosin filament the myosin heads face opposing directions allowing tighter contraction to occur.
there are no T-tubules present in smooth muscle
in smooth muscle contraction calcium is still released from the sarcoplasmic reticulum however it is not the main source for contraction. in smooth muscle contraction extracellular calcium concentration in the main trigger for contraction
what is the latch mechanism?
it maintains prolonged contraction dephosphorolation occurs when myosin head is bound to actin and surrounding calcium levels are high.