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Senses and receptors

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While there is debate among neurologists as to the specific number of senses due to differing definitions of what constitutes a sense, Gautama Buddha and Aristotle classified five ‘traditional’ human senses which have become universally accepted: touch, taste, smell, sight, and hearing.

Other senses that have been well-accepted in most mammals, including humans, include nociception, equilibrioception, kinaesthesia, and thermoception. Furthermore, some non-human animals have been shown to possess alternate senses, including magnetoception and electroreception. Receptors. Chemoreceptor. Classes[edit] There are two main classes of the chemosensor: direct and distance.


[citation needed] Examples of distance chemoreceptors are: olfactory receptor neurons in the olfactory system: Olfaction involves the ability to detect chemicals in the gaseous state. In vertebrates, the olfactory system detects odorants and pheromones in the nasal cavity. Within the olfactory system there are two anatomically distinct organs: the main olfactory epithelium (MOE) and the vomeronasal organ(VNO). Sensory Organs[edit] When inputs from the environment are significant to the survival of the organism, the input must be detected. Chemoreception is important for the detection of food, habitat, conspecifics including mates, and predators. In Physiology[edit] Carotid bodies and aortic bodies detect changes primarily in oxygen. Control of Breathing[edit] Chemoreceptors detect the levels of carbon dioxide in the blood.

Heart rate[edit] See also[edit] References[edit] Jump up ^ P. External links[edit] Photoreceptor cell. A photoreceptor cell is a specialized type of neuron found in the retina that is capable of phototransduction.

Photoreceptor cell

The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. The two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form a representation of the visual world, sight. The rods are narrower than the cones and distributed differently across the retina, but the chemical process in each that supports phototransduction is similar.[1] A third class of photoreceptor cells was discovered during the 1990s:[2] the photosensitive ganglion cells.

These cells do not contribute to sight directly, but are thought to support circadian rhythms and pupillary reflex. Mechanoreceptor. A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion.


Normally there are four main types in glabrous skin: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini endings. There are also mechanoreceptors in hairy skin, and the hair cells in the cochlea are the most sensitive mechanoreceptors, transducing air pressure waves into nerve signals sent to the brain. In the periodontal ligament, there are some mechanoreceptors, which allow the jaw to relax when biting down on hard objects; the mesencephalic nucleus is responsible for this reflex.

Research into the mechanoreceptors of the human body began in the late 1970s, when Vallbo and Johansson took percutaneous recordings of human volunteers.[1] The mechanoreceptors of rhesus monkeys are virtually identical to those of humans. Mechanism of sensation[edit] Feedback[edit] Types[edit] Receptors in hair follicles sense when a hair changes position. Thermoreceptor. A thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range.


In the mammalian peripheral nervous system, warmth receptors are thought to be unmyelinated C-fibres (low conduction velocity), while those responding to cold have both C-fibers and thinly myelinated A delta fibers (faster conduction velocity).[1] The adequate stimulus for a warm receptor is warming, which results in an increase in their action potential discharge rate. Cooling results in a decrease in warm receptor discharge rate. For cold receptors their firing rate increases during cooling and decreases during warming. Some cold receptors also respond with a brief action potential discharge to high temperatures, i.e. typically above 45°C, and this is known as a paradoxical response to heat.

The mechanism responsible for this behavior has not been determined. Nociceptor. A nociceptor is a receptor of a sensory neuron (nerve cell) that responds to potentially damaging stimuli by sending signals to the spinal cord and brain.


This process, called nociception, usually causes the perception of pain. History[edit] Nociceptors were discovered by Charles Scott Sherrington in 1906. In earlier centuries, scientists believed that animals were like mechanical devices that transformed the energy of sensory stimuli into motor responses. Sherrington used many different styles of experiments to demonstrate that different types of stimulation to a nerve's receptive field led to different responses.