Sense Organs

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  • Topic: Auditory system, Olfactory receptor neuron, Middle ear
  • Pages : 11 (2656 words )
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  • Published : January 6, 2011
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SENSE ORGANS
RECEPTORS (Sense organs)
* Transducers of specific forms of kinetic energy
* Change mechanical, electrical, thermal, chemical, or radiant energy into nerve impulses in sensory neurons Two major categories:
* GENERAL RECEPTORS
* Often exist as individual cells or receptor units
* Widely distributed throughout the body
* Most numerous such as:
* touch, temperature, and pain: and
* to initiate various reflexes necessary for maintaining homeostasis * SPECIAL RECEPTORS
* Large and complex organs
* Localized grouping of specialized receptors
* Have limited distribution and mostly paired
* Function to produce vision, hearing, balance, taste, and smell; and * to initiate reflexes important for homeostasis.

CLASSIFICATION OF RECEPTORS:
* Classified according to:
* Location;
* Stimulus detected; and
* Structure
Classification by Location:
* Somatic Receptors – provide information about the external environment * Exteroceptors: (cutaneous receptors)
* Located on or very near the body surface
* Respond mostly to external stimuli
* Detect pressure, touch, pain, and temperature
* Proprioceptors:
* Provide information about the skeletomuscular system * Less numerous and more specialized
* Limited to skeletal muscles, joint capsules, and tendons * Visceral Receptors – monitor the internal environment and provide information about the olfactory and gustatory information from the environment * Visceroceptors (enteroceptors):

* Located internally, often within the body organs (viscera) * Activated by pressure, stretching, and chemical changes * Involved in sensations of hunger and thirst
Classification by stimulus detected
* Five categories based on the types of stimuli that activate them: * Mechanoreceptors: (movement or deforming of capsule) * Activated by mechanical stimuli that some way “deform” or change the position of the receptor, resulting in the generation of a receptor potential * Examples: pressure applied to the skin or a blood vessel. Or by stretch or pressure in muscle, tendon, or lung tissue * Carotid sinuses are mechanoreceptors that monitor blood pressure. * Chemoreceptors: (chemicals)

* Activated by either the amount or the changing concentration of certain chemicals * Taste and smell depend on chemoreceptors
* Special chemoreceptors in the body also sense the concentration of chemicals such as pH, glucose, etc. * Carotid bodies and aortic bodies house chemoreceptors that monitor the oxygen content of blood

* Thermoreceptors: (temperature change)
* Activated by changes in temperature
* Nociceptors: (injury)
* Activated by intense stimuli of any type that results in tissue damage * Can by a toxic chemical, intense light, sound, pressure, or heat * Serve as the primary sensory receptors for pain as free nerve endings. * Photoreceptors: (light)

* Found only in the eye
* Respond to light stimuli if the intensity is great enough to generate a receptor potential.

CLASSIFICATION BY STRUCTURE
* General sensory receptors may be classified anatomically as either: * NAKED ENDING:
* Are the simplest, most common and most widely distributed sensory receptors * Ramify among epidermal cells and are stimulated by contact * Dendrites not wrapped in connective tissue

* ENCAPSULATED NERVE ENDINGS:
* Consist of tissue capsule and located within the dermal papillae at the dermal-epidermal interface * Dendrites wrapped by connective tissues
* Deal with touch and pressure and stretch receptors * Grandry’s corpuscles – found along the margins of the beaks of shore birds and freshwater fowls consist of a nerve ending and 2...
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