  We investigate the spin structure of the nucleon in an extended Jaffe-Lipkin
quark model. In addition to the conventional $3q$ structure, different
$(3q)(Q\bar{Q})$ admixtures in the nucleon wavefunction are also taken into
account. The contributions to the nucleon spin from various components of the
nucleon wavefunction are discussed. The effect due to the Melosh-Wigner
rotation is also studied.
