(3) A motor unit is the single motor neuron and the number of striated muscle
fibers activated by it (innervation). The importance of the motor unit is that its fibers
work in unison. Either all fibers within a unit contract or none contract. When a certain
amount of force is needed, one unit after another is recruited until just enough units are
available to produce the desired action.
5-3. NAMING SKELETAL MUSCLES
The name of a muscle may appear with the abbreviation M., meaning Musculus
or muscle. We abbreviate muscles (plural) with the symbol Mm. Skeletal muscles are
named according to their physical attributes (shape, size, length, etc.), their location, or
their function. For example:
DELTA = ∆ , Greek letter D
BICEPS = two-head
BI = two CEPS = head
adductor magnus M.
MAGNUS = great, large
adductor longus M.
LONGUS = long
biceps brachii M.
BRACHII = of the arm
biceps femoris M.
FEMORIS = of the thigh
ROTATORES = rotators
(They turn/rotate the vertebral column.)
5-4. ARRANGEMENT OF HUMAN SKELETAL MUSCLES
See figures 5-1 and 5-2 for some of the skeletal muscles.