Short answers, pulled from the story.
The somatosensory system is a subset of the sensory nervous system responsible for perceiving external stimuli, internal stimuli, and regulating body position and balance through proprioception. It covers touch, vibration, pressure, pain, and temperature, and is thought to act as a pathway connecting different sensory modalities within the body.
The four low-threshold mechanoreceptors in glabrous skin are Merkel cell nerve endings (5-15 Hz vibrations, fine shapes and edges), tactile corpuscles (10-50 Hz, light touch and Braille reading), Pacinian corpuscles (around 250 Hz, gross touch and vibrations from a distance), and bulbous corpuscles (sustained skin stretch and object slippage).
Touch and vibration signals ascend via the dorsal column-medial lemniscus pathway, carried by gracilis (T7 and below) or cuneatus (T6 and above). A typical somatosensory pathway involves three neurons: a first-order neuron in the dorsal root ganglion, a second-order neuron in the spinal cord or brainstem, and a third-order neuron in the ventral posterior nucleus of the thalamus that terminates in the primary somatosensory cortex. All fibers cross to the opposite side at the medulla.
The sensory homunculus is the spatial map of the body preserved in the primary somatosensory cortex (S1), located in the postcentral gyrus of the parietal lobe. Neighboring neurons in S1 represent nearby locations on the skin or body, so stimulating one body region activates a predictable cluster of cortical neurons.
Affective touch intensity is encoded in the primary somatosensory cortex (S1), similar to how emotions from sight and sound are processed. The pleasantness of affective touch, however, activates the anterior cingulate cortex and prefrontal cortex more than S1; fMRI data shows that increased BOLD signal in those regions correlates strongly with pleasantness scores. Inhibitory TMS of S1 suppresses perceived touch intensity without affecting perceived pleasantness.
Tactile corpuscle density is greater in smaller fingers, and the same may hold for Merkel cells, which are responsible for detecting fine spatial details. This higher receptor density in smaller fingertips produces finer passive tactile spatial acuity, and appears to be the underlying reason why women, on average, outperform men on this measure.