  In this work the dynamics of a freely jointed random chain with small masses
attached to the joints is studied from a microscopic point of view. The chain
is treated using a stringy approach, in which a statistical sum is performed
over all two dimensional trajectories spanned by the chain during its
fluctuations. In the limit in which the chain becomes a continuous curve, the
probability function for such a system coincides with the partition function of
a generalized nonlinear sigma model. The cases of open or closed chains in two
and three dimensions are discussed. In three dimensions it is possible also to
introduce some rigidity at the joints, allowing the segments of the chain to
take only particular angles with respect to a given direction.
