Experiencing the World
The human body has an intricate system of sensors that provide information about the environment to the brain to elicit a response, which may be either conscious or subconscious, to provide better conditions for health and survival. The sensory system works 24/7 to keep your body functioning properly.
Reception and Perception
Obtaining information about the environment, whether interior or exterior, is a two-step process. The information must be obtained via specialized cells that can detect stimuli and it must be interpreted in context by the brain before a response can be made.
Receptors in your body provide a vast array of information to the brain such as internal and external temperature, blood pressure, light, sound, taste, and smell, as well as balance and body position. If any of these receptors fail, the information doesn’t reach the brain and isn’t detected. Therefore, no response, either reflex or conscious, is made.
The cause of “phantom limb”
While reception and perception generally require stimulus, the brain may have established patterns of dealing with sensory information that can continue even after loss of input. For example, amputees often experience sensation in the limb that is lost, something that is called phantom limb. Although the limb is gone, the brain still provides signals that make the person feel touch, pain, or temperature in that limb. This shows the power of the brain and its importance in the perception of a stimulus.
Information from receptors must be understood appropriately by the brain to be perceived. Tastes, smells, and images must be learned in the early years of life and assembled into a library of sensory information that can be sorted through when encountered again. If the brain never develops these early patterns because it was deprived of sensory input until later in life, the brain may never be able to accurately interpret the information and the individual may be unable to perceive certain stimuli. For example, individuals who have been blind from birth due to eye problems that are repaired later in life often have a difficult time with depth perception.
It takes both aspects of the sensory system working in unison for an individual to be able to adequately function and monitor the internal and external world in which we exist and survive.
Special Senses
The sensory receptors are categorized into groups based on how localized or widespread they occur in the body. Those that are localized in a single location are referred to as organs of special senses. This group includes the cells and tissues required for smell, taste, vision, hearing, and balance. In the past, touch was included among the “5” senses (instead of balance). However, much of the external surface of the body can detect touch as pressure. For that reason, touch was moved into the category of general senses.
General Senses
Unlike the special senses, receptors for the generalized senses are spread throughout the body. The detection of temperature, pressure, pain, and body position occur over much of the body surface and provide an abundance of sensory information to the brain.
Touch
You can find the receptors for touch between the upper layer of skin (epidermis) and the deeper layer (dermis). Some receptors are adept at detecting changes in pressure while others respond to vibrations or sustained pressure. Two of the more common receptors, Meissner’s and Pacinian corpuscles, respond to slow and fast vibrations, respectively. Additionally, the Pacinian corpuscle detects deep pressure. These cells are specialized and encapsulated in such a way that the mechanical pressure leads to a signal transduction cascade and neuronal signaling. This is how the brain perceives touch.
How is pain detected?
Pain receptors (nociceptors) are free nerve endings that respond to various stimuli, which leads to the perception of pain. Extreme temperatures, excessive mechanical forces, and chemical damage are a few of the more common stimuli that are detected by these free endings as pain.