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الكلية كلية طب الاسنان     القسم  العلوم الاساسية     المرحلة 2
أستاذ المادة حيدر حميد عباس الحيدري       09/09/2020 23:37:46
Sensory functions of the CNS
Sensory receptors and their basic mechanisms of action:

Input to the NS is provided by the sensory receptors that detect sensory stimuli. Sensory receptors are specialized cells or neurons that trasduce environmental signals (mechanical forces, light, sound, chemicals, and temperature) into neural signals (action potential) in neuron attached to it. Each type of receptors has its own histological structure. The skin, for example, contains various types of sensory endings. These include naked nerve endings, expanded tips on sensory nerve terminals (which include Merkel’s disks and Ruffini endings), and encapsulated endings (which include pacinian corpuscles and Krause’s end-bulb). Although cutaneous sensory receptors are not stimulus-specific according to their histological appearance, they are physiologically specific.
• Merkel cells and Ruffini endings respond to steady pressure
• Pacinian corpuscles and Meissner s corpuscles give the sense of vibration
• There are separate warm and cold receptors
• Receptors associated with skin hairs allow you to feel the displacement of hairs
• Several types of pain receptors respond to mechanical trauma or very high or low temperatures.





According to the type of energy or stimulus that stimulate receptors, there are five different types of sensory receptors:
[1] Mechanoreceptors, which detect mechanical deformation of the receptor or of cells adjacent to the receptor which include tactile sensations (touch, pressure, vibration, tickles, itch), hearing, equilibrium, and the position sense. An example of such receptors is the Pacinian corpuscle (which detect vibration), Ruffini`s corpuscle (which detect pressure), Merkel`s (which detect the site), Meissner`s corpuscles (which detect the rate of stimulus application and present in non-hairy skin), joint receptors, stretch receptors in muscle, hair cells in auditory and vestibular systems.
[2] Thermoreceptors, which detect changes in temperature, some receptors detecting cold and others warmth.
[3] Pain receptors (nociceptors), which detect damage in the tissues, whether it be physical damage or chemical damage.
[4] Electromagnetic receptors (photoreceptors), such as rods and cones which detect light on the retina of the eye.
[5] Chemoreceptors, which detect taste in the mouth (taste receptors), smell in the nose (olfactory receptors), O2 and CO2 concentrations in the blood (carotid body receptors), osmolality of body fluids (osmoreceptors), and perhaps other factors that make up the chemistry of the body.



In general, senses can be classified into three types:
(a)- Somatic senses: Which process sensations that arise from the skin and include tactile sensations (touch, pressure, synthetic, tickling and itch sensations), pain sensation (including those arised from viscera) , thermal sensations.
(b)- Special senses: Which include vision, smell, taste, hearing, and equilibrium sensations (rotational and linear acceleration).
(c)- Visceral sensations: which are those concerned with perception of the internal environment such as those receptors which detect the changes in the osmolarity of the plasma, the pH, and other body fluids chemistry and pressure.


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .