A major job of sensory receptors is to help us learn about the environment around us, or about the state of our internal environment. Different sorts of stimuli from varying sources are received and transformed into the electrochemical signals of the nervous system. This process is termed sensory transduction. This occurs when a stimulus is detected by a receptor which generates a graded potential in a sensory cell. If powerful enough, the graded potential induces the sensory neuron to create an action potential that is conveyed into the central nervous system (CNS), where it is integrated with other sensory information—and potentially higher cognitive functions—to establish a conscious representation of that stimulus. The central integration may then lead to a motor reaction.
Describing sensory function with the phrase sensation or perception is a purposeful distinction. Sensation is the activation of sensory receptors at the level of the stimuli. Perception is the brain processing of sensory stimuli into a meaningful pattern incorporating awareness. Perception is dependent on sensation, yet not all sensations are perceived. Receptors are the structures (and sometimes complete cells) that detect sensations. A receptor or receptor cell is modified directly by a stimulus. A transmembrane protein receptor is a protein in the cell membrane that mediates a physiological change in a neuron, most typically by the opening of ion channels or changes in the cell signalling pathways. Some transmembrane receptors are triggered by substances termed ligands. For example, a chemical in food can function as a ligand for taste receptors. Other transmembrane proteins, which are incorrectly referred to as receptors, are mechanically or thermally sensitive. Changes in the physical properties of these proteins increase ion flow across the membrane, resulting in a graded potential in sensory neurons.
Sensory receptors
A live organism’s ability to respond to stimuli is one of its properties. The human sensory system is highly advanced and is capable of simultaneously processing thousands of incoming data. This intricacy enables you to be aware of your environment and respond appropriately. Sensory receptors are sensory neurons’ dendrites that are specialised in receiving specific types of stimuli. Three classification systems are used to classify sensory receptors:
Classification by receptor complexity:
- Free nerve endings are dendrites with little or no physical specialisation at their terminal ends.
- Dendrites with encapsulated nerve terminals have their terminal ends enclosed in a connective tissue capsule.
- Sensory organs (such as the eyes and ears) are composed of sensory neurons that include receptors for the five special senses (vision, hearing, smell, taste, and balance), as well as connective, epithelial, and other tissues.
Classification by location:
Exteroceptors- Exteroceptors are located on or near the skin’s surface and are responsive to stimuli found outside or on the body’s surface. These receptors include those that sense touch, pain, and temperature, as well as those that sense vision, hearing, smell, and taste.
Interoceptors- Interoceptors (visceroceptors) are sensory receptors that respond to stimuli emitted by visceral organs and blood arteries. These receptors are involved with the autonomic nervous system’s sensory neurons.
Proprioceptors- Proprioceptors detect and respond to stimuli in skeletal muscles, tendons, ligaments, and joints. These receptors acquire data about the position of the body and the physical conditions of its various sites.
Classification by type of stimulus detected:
- Physical forces such as pressure (touch or blood pressure) and stretch activate mechanoreceptors.
- Photoreceptors are light-sensitive.
- Thermoreceptors detect variations in temperature.
- Chemoreceptors detect dissolved chemicals during taste and smell sensations, as well as changes in internal body chemistry such as changes in O 2, CO 2, or H + levels in the blood.
- Nociceptors are activated by a range of stimuli that cause tissue injury. The brain interprets the sensation of pain.
Organ Systems Involved:
Numerous sensations are produced and communicated by specialised sensory organs; others, like the viscera, have nociceptors that activate in response to inflammation and tissue injury.
The retina is the eye’s sensory organ. Together with the cornea and lens, light focuses on the vision board, where information can be converted from physical matter to electrical energy, which enables the brain to interpret and comprehend the external environment.
The epidermis, dermis, and hypodermis all contain numerous sensory receptors that enable the skin to discriminate between different types of touch, such as pressure differences (light vs. deep). Additionally, skin sensory receptors analyse the external world’s properties such as temperature, discomfort, and itch.
The inner ear consists of the cochlea, which contains hair cells that convert sounds, and the vestibule, which is responsible for our feeling of balance.
The smell is experienced by molecules binding to chemoreceptors located in the cilia of the olfactory epithelium of the nose.
Load and position perception are mediated by the specific structures of muscle spindles and joint capsules, which include mechanoreceptors that detect joint angle, muscle length, and force.
Taste perception occurs as a result of chemicals dissolving in the taste buds located in the mouth and oropharynx.
Conclusion
Through its sensory systems, the human body can comprehend the world. Sensory systems are found throughout the body. They include those that detect the external world directly (exteroreceptors), those that detect information from internal organs and processes (interoceptors), and those that detect position and load (proprioception). Sensory receptors are found in both external and internal organs. They are found in specialised organs such as the eyes, ears, nose, and mouth. Each receptor type transmits a separate sensory modality that must finally be integrated into a single perceptual frame.