Question

Why do you think that our bodies have different densities of receptors in different areas? How does this help humans survive/interact with their environment?

Answer 1

Different parts of the body do have different degrees of two-point discrimination. This is due to differences in both the number and type of "touch receptors" found in different parts of the body. Touch receptors are specialized structures or nerve endi ngs that relay information to the brain about the size, pressure, and texture of things touching our skin.

Parts of the body with the highest densities of touch receptors will have the greatest degree of two-point discrimination.

Human skin is innervated with different tactile afferents, which are found at varying densities over the body.The experience of touch gives rise to sensations concerning both sensory (e.g., tactile sensitivity and discrimination) and emotional (e.g., pleasant, painful) aspects.

It is well known that tactile sensitivity varies across the skin, where the finger tips and facial skin are particularly receptive to touch. Differences in tactile sensitivity can be related to the underlying neurophysiology of the skin. Here, both the sensory afferent type and density affect the level of sensitivity. Skin can be divided into three main categories: glabrous skin (e.g., the thicker, non-hairy skin on the palms), hairy skin (e.g., the vast majority of the skin on the body, which contains different types of hairs), and mucocutaneous skin (e.g., the lips).Various brain imaging studies have implicated other regions in assessing the emotional value of touch over the body, including the orbitofrontal cortex (OFC) and primary somatosensory cortex.

Different kinds of receptors respond to different kinds of stimulation, such as vibration, pressure, or tapping, and convert these into electrical signals. Table 1 below shows a few types of skin receptors, the kinds of input they detect, and their adaptation rate when stimulated. Slowly adapting receptors continue sending impulses to the brain for a relatively long time when a constant stimulus is applied. Rapidly adapting receptors fire at the time a stimulus begins and sometimes again when it is removed, but they do not continue firing to a constant stimulus. Having receptors with different preferences and different "reporting" capabilities allows us to tune in more acutely to our environment and to distinguish a wide variety of sensations.