General considerations of sensation Basic features of sensory structures One way to classify sensory structures is by the stimuli to which they normally respond; thus, there are photoreceptors for lightmechanoreceptors for distortion or bendingthermoreceptors for heatchemoreceptors e. This classification is useful because it makes clear that various sense organs can share common features in the way they convert transduce stimulus energy into nerve impulses.
See Article History Mechanoreception, ability of an animal to detect and respond to certain kinds of stimuli—notably touch, soundand changes in pressure or posture—in its environment.
Sensitivity to mechanical stimuli is a common endowment among animals. In addition to mediating the sense of touch, mechanoreception is the function of a number of specialized sense organs, some found only in particular groups of animals.
Thus, some mechanoreceptors act to inform the animal of changes in bodily posture, others help detect painful stimuli, and still others serve the sense of hearing. Various laboratory devices are used to record and observe these electrical events in the study of mechanoreceptors.
In addition to electrophysiological studies, mechanoreceptive functions are also investigated more indirectly—i. These responses include bodily movements e. The behavioral method sometimes is combined with partial or total surgical elimination of the sense organs involved.
Not all the electrophysiologically effective mechanical stimuli evoke a behavioral response; the central nervous system brain and spinal cord acts to screen or to select nerve impulses from receptor neurons. Humans experience pain as a result of stimulation of pain receptors nociceptorswhich are located in the skin and other tissues.
Pain receptors respond to three different types of harmful noxious, or nociceptive stimuli: The pain sensation may be acuteinvolving a short-lived intense feeling of pain that subsides to dull throbbing, or chronic, involving long-lasting pain that often is associated with disease. The stimulation of pain receptors is characterized by a range of physiological and psychological responses, including an effort to withdraw from the stimulus.
The reflex withdrawal of the hand from a flame, for example, may begin even before the person becomes conscious of the pain sensation.
Responses to painful stimuli also occur in nonhuman animals, and the question of how animals experience pain is of considerable interest to researchers. Whether that is the case is inherently uncertain. The following observations illustrate some of the difficulties in making judgments of the inner experiences of creatures other than humans.
After the spinal cord of a fish has been cut, the front part of the animal may respond to gentle touch with lively movements, whereas the trunk, the part behind the incision, remains motionless.
A light touch to the back part elicits slight movements of the body or fins behind the cut. The head does not respond. To attribute pain sensation to the writhing but neurally isolated rear end of a fish would contradict evidence that persons with similarly severed spinal cords report absolutely no feeling e.
Aversive responses to noxious stimuli nevertheless have a major adaptive role in avoiding bodily injury. Without them, the animal may even become a predator against itself; bats and rats, for instance, chew on their own feet when their limbs are made insensitive by nerve cutting. Some insects normally show no signs of painful experience.
A dragonflyfor example, may eat much of its own abdomen if its tail end is brought into the mouthparts. If the head of a blow fly Phormia is cut off, it nevertheless stretches its tubular feeding organ proboscis and begins to suck if its chemoreceptors labellae are brought in touch with a sugar solution; the ingested solution simply flows out at the severed neck.
At any rate, responsiveness to mechanical deformation is a basic property of living matter; even a one-celled organism such as an amoeba shows withdrawal responses to touch.
The evolutionary course of mechanoreception in the development of such complex functions as gravity detection and sound-wave reception leaves much room for speculation and scholarly disagreement. Reception of external mechanical stimuli The sense of touch Sensitivity to direct tactual stimulation—i.
Usually the whole body surface is tangoreceptive, except for parts covered by thick, rigid shells as in mollusks. Mechanical contact locally deforms the body surface; receptors typically are touch spots or free nerve endings within the skin, often associated with such specialized structures as tactile hairs.
The skin area served by one nerve fibre or sensory unit is called a receptive fieldalthough such fields overlap considerably.In physical culture, especially the new art of modern dance, kinesthesia was theorized as a modern modality of perception; influential dance theorist Rudolph Laban defined it as "the sense by which we perceive muscular effort, movement, and position in space" ().
The position sense of a stationary arm was investigated subsequent to an horizontally adductive movement with axis the shoulder joint.
The right arm was the treated arm: it reached a test position. Jul 31, · An Online Tagalog - English Dictionary Learn Tagalog or Filipino Language for free.
The word kinesthesia or kinæsthesia (kinesthetic sense) strictly means movement sense, Phantom sensations can occur as passive proprioceptive sensations of the limb's presence, or more active sensations such as perceived . kinesthetic sense (1) The recognition of the body and its parts in space as the parts relate to each other.
(2) Kinesthesia, see there. (3) Myesthesia, see there. To control movement, the brain has to integrate proprioceptive information from a variety of mechanoreceptors.
The role of proprioception in daily activities, exercise, and sports has been extensively investigated, using different techniques, yet the proprioceptive mechanisms underlying human movement control are still unclear.