  This thesis describes the use of Dyson-Schwinger equations (DSEs) to study
baryon bound states in QCD. In this work, octet baryon axial form factors are
calculated using a symmetry-preserving treatment of a vector $\times$ vector
contact interaction (SCI). The baryons are considered as
quark-plus-interacting-diquark bound states, whose structure (wave function) is
obtained by solving a Poincar\'e-covariant Faddeev equation. Since it preserves
symmetries, all consequences of partial conservation of the axial current are
manifest. For instance, one finds that octet baryon axial properties are
consistent with only minor violations of SU(3)-flavour symmetry, being
interpreted as a dynamical consequence of emergent hadron mass (EHM).
Considering neutral axial currents, the SCI delivers predictions for the
flavour separation of octet baryon axial charges and, consequently, produces
values for the associated SU(3) singlet, triplet, and octet axial charges. The
results indicate that, at the hadron scale $\zeta_{\mathcal{H}}$, valence
degrees of freedom carry approximately $50\%$ of an octet baryon's total spin.
Proton structure is one of the principal topics in hadron physics. Its study is
expected to reveal key features of both the origin of mass and strong
interaction dynamics. This work therefore extended the above analyses to an
examination of in-proton parton helicity (spin) distribution functions (DFs).
Using Ans\"atze for hadron-scale proton polarised valence quark DFs,
predictions are delivered for all proton polarised DFs at the measurement scale
$\zeta_{\rm C}^2 = 3\,$GeV$^2$. The pointwise behaviour of the predicted DFs
and, consequently, their moments, shows good agreement with results inferred
from data. Based on these results, one finds that experimental measurements of
the proton flavour-singlet axial charge should return a value $a_0^{\rm
E}(\zeta_{\rm C}) = 0.35(2)$.
