FREE NERVE ENDINGS FUNCTION SKIN

The pain and temperature receptors in the dermis of the skin are examples of neurons that have free nerve endings. The cells that interpret information about the environment can be either (1) a neuron that has a free nerve ending (dendrites) embedded in tissue that would receive a sensation (2) a neuron that has an encapsulated ending in which the dendrites are encapsulated in connective tissue that enhances their sensitivity or (3) a specialized receptor cell, which has distinct structural components that interpret a specific type of stimulus ( Figure 13.1.1). They can also be classified functionally on the basis of the transduction of stimuli, or how the mechanical stimulus, light, or chemical changed the cell membrane potential. Receptors can be classified structurally on the basis of cell type and their position in relation to stimuli they sense. Receptor cells can be classified into types on the basis of three different criteria: cell type, position, and function. Different types of stimuli are sensed by different types of receptors. Stimuli in the environment activate specialized receptors or receptor cells in the peripheral nervous system. Physical changes in these proteins increase ion flow across the membrane, and can generate a graded potential in the sensory neurons. Other transmembrane proteins, which are not accurately called receptors, are sensitive to mechanical or thermal changes. For example, a molecule in food can serve as a ligand for taste receptors. Some transmembrane receptors are activated by chemicals called ligands.

A transmembrane protein receptor is a protein in the cell membrane that mediates a physiological change in a neuron, most often through the opening of ion channels or changes in the cell signaling processes. A receptor or receptor cell is changed directly by a stimulus. Receptors are the structures (and sometimes whole cells) that detect sensations. Perception is dependent on sensation, but not all sensations are perceived. Perception is the central processing of sensory stimuli into a meaningful pattern involving awareness. Sensation is the activation of sensory receptors at the level of the stimulus. The central integration may then lead to a motor response.ĭescribing sensory function with the term sensation or perception is a deliberate distinction. If strong enough, the graded potential causes the sensory neuron to produce an action potential that is relayed into the central nervous system (CNS), where it is integrated with other sensory information-and sometimes higher cognitive functions-to become a conscious perception of that stimulus. This occurs when a stimulus is detected by a receptor which generates a graded potential in a sensory neuron. This process is called sensory transduction. Different types of stimuli from varying sources are received and changed into the electrochemical signals of the nervous system. Describe different types of sensory receptorsĪ major role of sensory receptors is to help us learn about the environment around us, or about the state of our internal environment.By the end of this section, you will be able to:

Free nerve endings function