If these segments are cut transversely, it is apparent that they are divided into multiple sections. These are called fascial compartments, and are formed by tough connective tissue septa.
These compartments usually have a separate nerve and blood supply to their neighbours. The muscles in each compartment will often all be supplied by the same nerve.
This problem is called compartment syndrome and have happen acutely in a bleed (possibly caused by a fracture), or gradually, as with an athelete's overuse of a muscle.
Increased pressure within the compartment compresses the nerves, and it also decreases blood perfusion. In an acute situation it can cut off blood supply completely, leading to necrosis of the tissues in that compartment.
Compartment syndrome can be treated by a fasciotomy, where the septum enclosing the compartment is cut to relieve the pressure.
The (lower) leg is divided into three compartments also:
The (upper) arm is divided into:
The forearm is divided into two compartments:
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