What are sensory receptors?Structures that are specialized to respondto the changes in the environmentThese are called stimuliSensory receptors in periphery detects thestimuliSensation and interpretation takes place inthe brain
How sensory receptors are classified?Location - location of the stimulus to which they respondStimulus type - named by the stimulus that activates themStructure - the anatomy of the receptor
Classification according to location Exteroceptors - any receptor that responds to stimulioutside the body such vision, sound, touch, smell,temperature and smell
Interoceptors or visceroceptors - respond to stimuli arising within thebody such as chemical stimuli, deeppressure, and many others.
Proprioceptors - respond to muscle or tendon stretchand help the body monitor body position
Classification according to stimulus typeMechanoreceptors - respond to a mechanical stimulus:examples are touch, pressure, stretch,hearing, balance, position and movement,vibration, muscle contraction, as well aspress receptors and bar receptors.
Thermoreceptors -respond to temperature change:example heat and cold.
Photoreceptors -respond to light: example vision
Chemoreceptor -respond to various chemicals such asglucose, oxygen, carbon dioxide,hormones and many, many more
This pseudostratified columnar epitheliumis composed of olfactory cells,sustentacular cells and basal cells.Modified cilia on the surface serve asolfactory receptors.
Nocireceptors - pain receptors from any noxiousstimulus
Classification according to structureSimple ( large majority ) - similar to modified dendritic endings - found on skin, mucous membrane, muscles and connective tissues
Location of simple receptors
Complex (sense organs) - localized collection of cells that workstogether to perform a specific process - also known as special senses
Vertebrates Sensory ReceptorsChemoreception -Vertebrates usually accomplishchemoreception by moving chemically richair or water into a canal or sac thatcontains the chemical receptors.
Specialized receptors of vertebratesGustatory receptors - The receptors for the gustatory nerves are knownas taste buds located on the tongue and the roof of themouth. Sweet, sour, bitter, and salty are the four basictaste sensations resulting from stimulation of the tastebuds and the stimulation of the olfactory receptor. This iswhy it is harder to taste when one has a cold. These fourbasic tastes may evolutionarily developed to show somebasic food properties. Sweet taste signals foods high incalories, salty foods signal for food that helps maintainwater balance, sour tastes may help to signal foods thatcould be dangerous if eaten in excess, and bitter tastesensations signal toxic foods.
Olfactory receptors - The receptors for the olfactory nerves are located in the upper part of the nasal cavity. The olfactory sense organ consists of hair-like cells at the end of a neuron and is simple compared to the complex visual and auditory organs. The olfactory receptors are very sensitive to stimuli; however, they also become very fatigued. This explains why odors seem to go away after being easily noticeable. Canals lined with sheets of receptors with the nasal cavity are called turbinate. Protruding from the end of the nerve are thin cilia that are covered by mucus. Molecules are absorbed into the mucous layer and passed to the cilia where the chemical is detected. Notice the chemicals must be dissolved in the mucus and absorbed in order for the olfactory receptors to react. This is a lot like the gustatory mechanisms.