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The sense of touch
Somatosensory receptors located within the skin of the dog provide him with the ability to discriminate touch stimulation. There are five categories of these receptors. The nociceptors, associated with pain, proprioceptors, sensitive to body movement and position, thermoreceptors, sensitive to hot and cold, chemoreceptors, sensitive to chemical stimulation and mechanoreceptors, sensitive to pressure due to physical changes of the body.
Mechanoreceptors
These receptors are the most abundant and located at the base of each hair follicle. These special hair follicle receptors become activated whenever the “…hair is disturbed by external movements that cause the surrounding tissue to stretch or bend.” The dog’s whiskers, known as vibrissae are unique follicle receptors since they provide the dog protection of his muzzle in navigating around objects protecting him from injury to his eyes or collision with objects. The vibrissae are also capable of detecting vibration and simple changes in air currents (Lindsay, 2000).
If you have ever blown air in a dog’s face, you may have experienced a negative reaction. Lindsay suggests a “…possible cause of reflexive aggressive behavior” possibly linked to a “…species-typical defensive reaction mediated by vibrissae.” He suggests that vibrissae may provide information on location and movement during dog-dog combat and possibly “…mediating some measure of defense through the reflexive organization of combative behavior.” According to Lindsay, the dog’s vibrissae “…quickly flare and reorient in a forward direction when a dog is aggressively aroused” speculating vibrissae has some sort of purposeful role.
According to Coren, neuropsychologists tend to agree the amount dedicated to the sensory cortex of the brain used in processing information from particular body areas indicates the importance the area is in perceiving an animal’s world. In the dog, nearly 40 % is dedicated to the face, specifically to the area around the upper jaw including the vibrissae. Coren says, each individual vibrissa can be tracked to specific locations in the brain.
Studies on vibrissae have centered mostly from rats and cats, however the studies on dogs concluded “…the wiring and functions of the vibrissae are similar in all animals” who have them, says Coren. He says, animals use them much like a “blind person uses a cane.” They may even allow dogs to discriminate between textures, location and picking up objects. Coren suggests dogs move more tentatively when vibrissae are cut or removed, especially in dim light conditions. The vibrissa allows air to bend it enough to avoid contact with objects such as walls.
The trigeminal nerve responsible for sensory information received from the face and associated with vibrissae also provides chemoceptive information received from chemical stimulation near the nose and within the mouth.
In addition to the mechanoreceptors found in the skin of mammals, scientists have identified other receptors. Mammalian skin has two layers known as the dermis and epidermis. Within the epidermis scientist have discovered a “…pressure-sensitive and slowly adapting receptor” identified as Merkel’s receptor. These receptors respond to pressure near the skins surface. Also identified are Meissner’s corpuscles that are responsive to “…touch and low-frequency vibrations (50 Hz).” These corpuscles are very receptive, discriminative and rapidly adaptive.
Pacinian corpuscles are found much deeper within the dermis and respond depending on the amount of pressure. They have a large receptive field, stimulated at a higher vibration frequency, respond quickly, and rapidly adapt to this type of stimulation. The last mechanoreceptor known is Ruffini’s corpuscles also located in the dermis. They respond to a large receptive field, but are slower in adapting to continuous stimulation over long periods.
Nociceptors
These receptors are bare (unmyelinated) nerve endings responsive to harmful stimulation that threatens body tissue. These receptors are associated with pain and tend to stimulate escape mechanisms in animals. There are four types of nociceptors and identified according to the source and type of stimulation. They are mechanical, thermal, chemical and polymodal.
The result from nociceptive stimulation causes a debilitating effect on most of the bodies major organs. Additionally, localized tissue damage may result with a quick release of “pain-enhancing hormones” known as prostaglandin. The secretion sensitizes the “…nerve endings to histamine…an inflammatory by-product of cell damage (Carlson, 1994)” according to Lindsay. The use of anti-inflammatory products interrupts the production of prostaglandin through analgesic effects (Lindsay, 2000).
Lindsay cites Thompson (1993) saying, “[p]ain information is relayed along two pathways: a fast pain system and a slow pain system.” According to Lindsay, the fast pain system provides immediate information related to trauma and the slow pain system maintains the painful feelings after the stimulus is removed.
The fast pain system is associated with the cerebral cortex, which receives the stimulus via two thalamic nuclei. The slow pain system relays stimuli via “the reticular formation” to the “hypothalamus and the limbic system” where emotional responses are interpreted and motivate “flight-freeze” responses. According to Lindsay, “[t]he fast pain system is limited to surface nociception and…more recent evolutionary development than the slow pain system” associated with the limbic system considered to have “evolved out of primitive structures involved in…analysis and interpretation of olfactory information.” He points out, the limbic system in higher vertebrates, including dogs, has “diversified” in providing new and more complex emotional functions (Lindsay, 2000).
An interesting point about the limbic system and its association to pain can be explained in survival terms. Stimulation of the slow pain system produces a side effect in the release of endorphins. These endorphins, when activated affect “opioid receptor sites” alleviating pain and allowing an animal the ability to escape or fight (Lindsay, 2000).
The use of Naloxone, resembling morphine, serves as an antagonist impeding opioid activity limiting the effects of the “pain-reducing and pleasure-enhancing effects of increased opioid activity.” This chemical is used in managing “some compulsive behavior disorders…partially, mediated by the endogenous opioid system” (Lindsay, 2000).
Proprioceptors
Proprioceptors are located in the muscles and joints and responsible for determining the body’s position and movements. They are controlled by various areas of the brain, including the sensory motor cortex and cerebellum. These receptors relay information about the “body’s movements and its orientation relative to the location of its different parts.” The two common receptors are “muscle spindles and Golgi tendon organs” (Lindsay, 2000).
The muscle spindles are responsive to the rate and stretching of a working muscle. The Golgi tendon organs measure force exerted by the muscle on the tendon. Additionally, these type receptors are responsible for providing information relative to physical changes in joints and sensory information received from manipulation of objects and balance.
Thermoreceptors
It seems dogs and humans are different when it comes to perceiving heat stimuli. According to Coren, dogs possess only “cold–sensing temperature receptors” with heat sensors located only around their noses. However, this does not mean dogs are unable to feel warmth, it serves to point out they perceive it differently from humans.
Coren suggests, this may “…be a flaw in the evolutionary design of dogs.” He says, researchers “note that pressing warm or even moderately hot items against a dog’s skin produces very little response” and if the “heat is intense enough…the skin will be damaged and the dog will respond to the signals from the pain receptors in the skin.” As a result, dogs are unable to adapt to hot environmental conditions that may affect their well-being (Coren, 2004).
Furry-ness
Many people think the dog’s fur creates problems in warm climates, contrary to this the dog’s fur acts like an insulator, preserving body heat in the winter and providing a barrier against outside heat in hot weather. However, “heat can build up in the body” in hot environments and since dogs lack the ability to dissipate heat like humans, the only way is “panting or sweating through the pads of their feet.” This can be a problem if not monitored causing heat stroke and death (Coren, 2004).
Somatosensory receptors located within the skin of the dog provide him with the ability to discriminate touch stimulation. There are five categories of these receptors. The nociceptors, associated with pain, proprioceptors, sensitive to body movement and position, thermoreceptors, sensitive to hot and cold, chemoreceptors, sensitive to chemical stimulation and mechanoreceptors, sensitive to pressure due to physical changes of the body.
Mechanoreceptors
These receptors are the most abundant and located at the base of each hair follicle. These special hair follicle receptors become activated whenever the “…hair is disturbed by external movements that cause the surrounding tissue to stretch or bend.” The dog’s whiskers, known as vibrissae are unique follicle receptors since they provide the dog protection of his muzzle in navigating around objects protecting him from injury to his eyes or collision with objects. The vibrissae are also capable of detecting vibration and simple changes in air currents (Lindsay, 2000).
If you have ever blown air in a dog’s face, you may have experienced a negative reaction. Lindsay suggests a “…possible cause of reflexive aggressive behavior” possibly linked to a “…species-typical defensive reaction mediated by vibrissae.” He suggests that vibrissae may provide information on location and movement during dog-dog combat and possibly “…mediating some measure of defense through the reflexive organization of combative behavior.” According to Lindsay, the dog’s vibrissae “…quickly flare and reorient in a forward direction when a dog is aggressively aroused” speculating vibrissae has some sort of purposeful role.
According to Coren, neuropsychologists tend to agree the amount dedicated to the sensory cortex of the brain used in processing information from particular body areas indicates the importance the area is in perceiving an animal’s world. In the dog, nearly 40 % is dedicated to the face, specifically to the area around the upper jaw including the vibrissae. Coren says, each individual vibrissa can be tracked to specific locations in the brain.
Studies on vibrissae have centered mostly from rats and cats, however the studies on dogs concluded “…the wiring and functions of the vibrissae are similar in all animals” who have them, says Coren. He says, animals use them much like a “blind person uses a cane.” They may even allow dogs to discriminate between textures, location and picking up objects. Coren suggests dogs move more tentatively when vibrissae are cut or removed, especially in dim light conditions. The vibrissa allows air to bend it enough to avoid contact with objects such as walls.
The trigeminal nerve responsible for sensory information received from the face and associated with vibrissae also provides chemoceptive information received from chemical stimulation near the nose and within the mouth.
In addition to the mechanoreceptors found in the skin of mammals, scientists have identified other receptors. Mammalian skin has two layers known as the dermis and epidermis. Within the epidermis scientist have discovered a “…pressure-sensitive and slowly adapting receptor” identified as Merkel’s receptor. These receptors respond to pressure near the skins surface. Also identified are Meissner’s corpuscles that are responsive to “…touch and low-frequency vibrations (50 Hz).” These corpuscles are very receptive, discriminative and rapidly adaptive.
Pacinian corpuscles are found much deeper within the dermis and respond depending on the amount of pressure. They have a large receptive field, stimulated at a higher vibration frequency, respond quickly, and rapidly adapt to this type of stimulation. The last mechanoreceptor known is Ruffini’s corpuscles also located in the dermis. They respond to a large receptive field, but are slower in adapting to continuous stimulation over long periods.
Nociceptors
These receptors are bare (unmyelinated) nerve endings responsive to harmful stimulation that threatens body tissue. These receptors are associated with pain and tend to stimulate escape mechanisms in animals. There are four types of nociceptors and identified according to the source and type of stimulation. They are mechanical, thermal, chemical and polymodal.
The result from nociceptive stimulation causes a debilitating effect on most of the bodies major organs. Additionally, localized tissue damage may result with a quick release of “pain-enhancing hormones” known as prostaglandin. The secretion sensitizes the “…nerve endings to histamine…an inflammatory by-product of cell damage (Carlson, 1994)” according to Lindsay. The use of anti-inflammatory products interrupts the production of prostaglandin through analgesic effects (Lindsay, 2000).
Lindsay cites Thompson (1993) saying, “[p]ain information is relayed along two pathways: a fast pain system and a slow pain system.” According to Lindsay, the fast pain system provides immediate information related to trauma and the slow pain system maintains the painful feelings after the stimulus is removed.
The fast pain system is associated with the cerebral cortex, which receives the stimulus via two thalamic nuclei. The slow pain system relays stimuli via “the reticular formation” to the “hypothalamus and the limbic system” where emotional responses are interpreted and motivate “flight-freeze” responses. According to Lindsay, “[t]he fast pain system is limited to surface nociception and…more recent evolutionary development than the slow pain system” associated with the limbic system considered to have “evolved out of primitive structures involved in…analysis and interpretation of olfactory information.” He points out, the limbic system in higher vertebrates, including dogs, has “diversified” in providing new and more complex emotional functions (Lindsay, 2000).
An interesting point about the limbic system and its association to pain can be explained in survival terms. Stimulation of the slow pain system produces a side effect in the release of endorphins. These endorphins, when activated affect “opioid receptor sites” alleviating pain and allowing an animal the ability to escape or fight (Lindsay, 2000).
The use of Naloxone, resembling morphine, serves as an antagonist impeding opioid activity limiting the effects of the “pain-reducing and pleasure-enhancing effects of increased opioid activity.” This chemical is used in managing “some compulsive behavior disorders…partially, mediated by the endogenous opioid system” (Lindsay, 2000).
Proprioceptors
Proprioceptors are located in the muscles and joints and responsible for determining the body’s position and movements. They are controlled by various areas of the brain, including the sensory motor cortex and cerebellum. These receptors relay information about the “body’s movements and its orientation relative to the location of its different parts.” The two common receptors are “muscle spindles and Golgi tendon organs” (Lindsay, 2000).
The muscle spindles are responsive to the rate and stretching of a working muscle. The Golgi tendon organs measure force exerted by the muscle on the tendon. Additionally, these type receptors are responsible for providing information relative to physical changes in joints and sensory information received from manipulation of objects and balance.
Thermoreceptors
It seems dogs and humans are different when it comes to perceiving heat stimuli. According to Coren, dogs possess only “cold–sensing temperature receptors” with heat sensors located only around their noses. However, this does not mean dogs are unable to feel warmth, it serves to point out they perceive it differently from humans.
Coren suggests, this may “…be a flaw in the evolutionary design of dogs.” He says, researchers “note that pressing warm or even moderately hot items against a dog’s skin produces very little response” and if the “heat is intense enough…the skin will be damaged and the dog will respond to the signals from the pain receptors in the skin.” As a result, dogs are unable to adapt to hot environmental conditions that may affect their well-being (Coren, 2004).
Furry-ness
Many people think the dog’s fur creates problems in warm climates, contrary to this the dog’s fur acts like an insulator, preserving body heat in the winter and providing a barrier against outside heat in hot weather. However, “heat can build up in the body” in hot environments and since dogs lack the ability to dissipate heat like humans, the only way is “panting or sweating through the pads of their feet.” This can be a problem if not monitored causing heat stroke and death (Coren, 2004).
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