![]() ![]() An interoceptor is one that detects stimuli from internal organs and tissues, such as the receptors that sense the increase in blood pressure in the aorta or carotid sinus. An exteroceptor is a receptor that is located near a stimulus in the external environment, such as the somatosensory receptors that are located in the skin. These cells release neurotransmitters onto a bipolar cell, which then synapses with the optic nerve neurons.Īnother way that receptors can be classified is based on their location relative to the stimuli. Photoreceptors in the eyes, such as rod cells, are examples of (c) specialized receptor cells. Sensory neurons can have either (a) free nerve endings or (b) encapsulated endings. Figure 13.1.1 – Receptor Classification by Cell Type: Receptor cell types can be classified on the basis of their structure. If this graded post-synaptic potential is strong enough to reach threshold it will trigger an action potential along the axon of the sensory neuron. These graded potentials cause neurotransmitter to be released onto a sensory neuron causing a graded post-synaptic potential. Graded potentials in receptor cells are called receptor potentials. Action potentials triggered by receptor cells, however, are indirect. When strong enough to reach threshold they can directly trigger an action potential along the axon of the sensory neuron. Graded potentials in free and encapsulated nerve endings are called generator potentials. The cells in the retina that respond to light stimuli are an example of a specialized receptor cell, a photoreceptor. Also located in the dermis of the skin are lamellated and tactile corpuscles, neurons with encapsulated nerve endings that respond to pressure and touch. 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: ![]()
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