Sensory System

Introduction

The sensory system receives and processes information that generates an individual’s awareness of their environment. Various sensory perceptions then influence voluntary and involuntary motor activity to facilitate interaction with the world.

Broadly, sensations fall into two categories: General and special senses. General senses include touch, pain, temperature, proprioception, vibration, and pressure. Special senses include vision, hearing, taste, and smell. Special senses are processed via cranial nerves and differ from the pathway utilized in processing general senses. This article is focused on the discussion of the general senses.

Both innocuous and harmful mechanical and thermal stimuli are processed by different receptors and nerve fiber types in the skin, follow specific ascending pathways through the spinal cord (dorsal column or spinothalamic tract), and eventually relay to the somatosensory cortex. Based on these different pathways, the clinical picture of patients presenting with sensory abnormalities can help elucidate the suspected location of a spinal cord or central lesion based on the anatomical region and the type of sensation affected.

Cellular Level

Different receptor types and free nerve endings, each with their own specific function, generate the overall sense of touch, position in space, and pain. For the purposes of this article, “mechanoreceptor” refers to the mechanosensory end-organ structure and its associated low-threshold mechanoreceptor (LTMR).