When you walk
up a flight of stairs, do you have to look at your feet to be sure each will
get to the next step? Most of us don’t (an occasional stumble doesn’t count),
and for this freedom we can thank our muscle sense. Muscle sense (proprioception)
is the brain’s ability to know where our muscles are and what they are doing,
without our having to consciously look at them.
are receptors called stretch recep-tors (proprioceptors
or muscle spindles). The general function
of all sensory receptors is to detect changes. The function of stretch
receptors is to detect changes in the length of a muscle as it is stretched.
The sen-sory impulses generated by these receptors are inter-preted by the
brain as a mental “picture” of where the muscle is.
We can be aware
of muscle sense if we choose to be, but usually we can safely take it for
granted. In fact, that is what we are meant to do. Imagine what life would be
like if we had to watch every move to be sure that a hand or foot performed its
intended action. Even simple activities such as walking or eating would require
our constant attention.
At times, we
may become aware of our muscle sense. Learning a skill such as typing or
playing the guitar involves very precise movements of the fingers, and
beginners will often watch their fingers to be sure they are moving properly.
With practice, however, the movements simply “feel” right, which means that the
brain has formed a very good mental picture of the task. Muscle sense again
becomes unconscious, and the experienced typist or guitarist need not watch
is a function of brain activity, and muscle sense is no exception. The impulses
for muscle sense are integrated in the parietal
lobes of the cere-brum (conscious muscle sense) and in the cerebellum
(unconscious muscle sense) to be used to promote coordination.