Cynologist
Cynology: Puppies DogsArchive for the ‘Anatomy Of Dog’ Category
Do dogs possess a sixth sense? Many authors writing to a popular audience, among them trainers, veterinarians, and behavioral consultants, have suggested that dogs may use information derived from sources other than the normal senses. These beliefs have been reinforced in the publics mind by animal psychics claiming to communicate with dogs telepathically and to perform extraordinary feats, ranging from locating lost pets (both dead and alive) to diagnosing behavioral and medical problems by psychically "talking" with the distressed animals. Such extraordinary abilities have not been successfully demonstrated under controlled laboratory conditions; nonetheless, they are widely held to be real abilities and supported by the testimonies of many satisfied customers. Some dog trainers, most notably Woodhouse (1982), claim that a very active telepathic linkage exists between trainer and dog:
It is extraordinary how dogs pick up praise straight from your brain almost before you have time to put it into words. A dog's mind is so quick in picking up your thoughts that, as you think them, they enter the dog's mind simultaneously. I have great difficulty in this matter in giving the owners commands in class, for the dog obeys Read more [...]
Much of a dog's behavior is under the reflexive control of involuntary mechanisms. Neonatal puppies exhibit a great variety of reflexes that are predominately geared to maintaining contact with the mother to secure basic survival needs. These early neonatal reflexes gradually disappear and are replaced by more centrally controlled behaviors as puppies mature. Neonatal reflexive behavior has been carefully studied and cataloged. Understanding how the body's reflexes work was the primary emphasis of Sherrington's (1906) experimental work. He discovered that many of the dog's apparently voluntary behaviors were to some extent under the control of involuntary reflexive mechanisms. A dog's scratch reflex, for example, could be elicited by applying an electrical "itch" to its skin. Although mechanical and stereotypic, the scratch response was organized and well directed toward the source of the itch. What makes this noteworthy is that the dogs involved were decerebrate, having undergone previous surgeries to cut nervous pathways going to (afferent) or leaving (efferent) the brain. Other surprising abilities of decerebrate dogs included unsteady treadmill walking, withdrawal and crossed extensor reflexes to pain (the stimulated Read more [...]
The dog's body is equipped with a variety of receptors sensitive to stimuli impinging on the skin or arising from within the body itself. Specific receptors have evolved for the detection and measurement of pressure, vibration, heat and cold, chemicals, and various noxious stimuli. In addition, internal receptors sensitive to joint location, muscle stretch, and tendon tension provide kinesthetic information about the relative location, direction, and action of the body. In combination, these highly specific sensory organs provide a tremendous amount of information about the external and internal environment and a dog's moment-to-moment orientation within it.
Dogs exhibit significant differences with respect to their individual responses to somatosensory stimulation. Some dogs are much more sensitive to touch than are others. Thresholds for stimulation are profoundly affected by an individual dog's emotional state, general physical condition, and past experience (learning). For example, fearful or hypervigilant dogs will likely respond to nociceptive stimulation at a much lower level of intensity than dogs that are relaxed and confident. Fearful dogs are also more likely to exhibit emotionally reactive behavior when Read more [...]
The ability to taste depends on the activation of gustatory receptor cells concentrated in the taste buds. The taste buds are found in various papillae (foliate, fungiform, and circumvallate to name the most common) that are distributed over the surface of the dog's tongue. Taste buds contained in the fungi-form papillae are located on the anterior two-thirds of the tongue and transmit gustatory information via the chorda tympani, a branch of the facial nerve (seventh cranial nerve). The posterior third of the tongue is associated primarily with the circumvallate papillae, which are innervated by the lingual branch of the glossopharyngeal nerve (ninth cranial nerve). Both the seventh and ninth cranial nerves form central synapses in the nucleus of the solitary tract located in the medulla. Ascending pathways are relayed from the solitary tract via the pontine nucleus to the ventral posteromedial (VPM) nucleus of the thalamus and then to higher somatosensory cortical areas associated with the conscious experience of taste. Another pathway from the pontine nucleus carries taste information via the lateral hypothalamus, amygdala, and basal forebrain areas. These subcortical pathways may be involved in the production of Read more [...]
The vomeronasal organ (VNO) is a specialized sensory apparatus located in the anterior portion of the palate, with ducts opening into the mouth just behind the front teeth. The organ is an elongated pouchlike structure that is lined with olfactory receptor cells. These cells are similar to those found in the olfactory mucosa except that they use microvilli instead of cilia. Scent information received by these receptor cells is projected via the accessory olfactory bulb (AOB) directly into the limbic system (amygdala and medial hypothalamus). Although there is some overlap between the olfactory system and the vomeronasal organ, the latter is particularly well suited for the detection of pheromone molecules of a higher weight than reliably detected by olfaction. This difference makes the vomeronasal organ more sensitive for the detection of nonvolatile chemical messages deposited in the urine and other bodily secretions. An important function of the vomeronasal organ is the detection and subcortical analysis of these sexual pheromones. Destruction of the vomeronasal organ results in the loss of normal sexual activities and several other vital functions (e.g., maternal care, aggressiveness, and secretion of sex hormones) Read more [...]
The dog's sense of smell has attracted a great deal of enthusiastic attention from both applied and scientific quarters but has only slowly received appropriate experimental study. Historically, almost supernatural capabilities were attributed to a dog's nose, often resulting in the promulgation of some rather fantastic and insupportable claims about canine olfactory abilities. In addition, many equally incredible theories have been posited regarding the way in which a dog's olfactory apparatus works. These theories have ranged from the absurd to the occult. For example, one fanciful account hypothesized that irradiated energy emanating from living cells was absorbed by various materials stepped upon, and then re-emitted and detected by the dog's nose. Other discarded theories posited the notion that electrical waves or vibrations were responsible for the extraordinary feats of canine olfaction. One speculative adherent of the wave theory actually proposed that a pendulum be employed as an instrument for measuring the dog's olfactory acuity. Over the years, many important advances have been made in the study of olfaction, largely supplanting theories like the foregoing with more scientifically grounded alternatives. Read more [...]
The dog's ear is composed of an outer ear (pinna), auditory canal, and various structures designed to convert sound waves into auditory information. The pinna gathers and directs sound into the auditory canal, where it is carried to the tympanic membrane or eardrum. The eardrum is an extremely sensitive and elastic membrane reacting to the slightest vibrations on its surface: movement of less than one-tenth the diameter of a hydrogen atom can produce an audible sensation. The vibrations caused by the pressure of sound waves on the eardrum are mechanically conducted to the cochlea through the mediation of three tiny bones or ossicles: the malleus, the incus, and the stapes. The cochlea is a snail-like tubular structure that is innervated by the auditory nerve. Sound vibrations are passed into the cochlea at the oval window. These vibrations cause a fluid wave in the cochlear fluid, which causes a rippling effect against the surrounding basilar membrane. The vibratory displacement of the basilar membrane stimulates auditory receptors (called hair cells) to bend rhythmically, thereby evoking a nerve potential that is carried by individual fibers into the auditory nerve. Different sounds are distinguished by the specific Read more [...]
Dogs are equipped with a number of specialized sensory organs evolved to obtain biologically significant information from the environment. These various sensory systems gather and process chemical, mechanical, and physical inputs, transduce them into coded electrical impulses, and then conduct the raw sensory data to the brain. Once in the brain, the sensory data are further processed and encoded into meaningful representations about the surrounding environment. The animal is totally dependent on the reliability of this information processing for the procurement of vital biological needs and all forms of adaptive learning.
The sensory capacity of dogs can be divided into three broad categories:
1. Exteroception: Exteroceptors are sensitive to all stimulation acting on dogs from the external environment. These stimuli (including light, sound, chemical agents [taste and smell], heat, cold, and pressure) correspond to the special senses of sight, hearing, taste, smell, and touch.
2. Interoception: Interoceptors are responsive to stimulation arising from within the bodily organs, such as emotional reactions and some muscular sensations.
3. Proprioception: Proprioceptors coordinate kinesthetic sensations and reflexes Read more [...]
There are a number of tools available to the veterinarian to assess fetal well-being in the dog. These include knowledge of gestation length and maternal rectal temperature at term. This knowledge enables one to recognize primary uterine inertia. Radiographic and ultrasonic appearance of the fetus and knowledge of the duration of stages 1 and 2 of labor enable the veterinary and the breeder to monitor the health of the pre-natal puppy.
Gestation Length: One of the most useful tools for monitoring fetal growth and vialibility is an understanding the variation in gestation length in the dog. This variation not only influences determination of the estimated due date and dignosis of possible primary uterine inertia at term, but it also explains variable results of pregnancy diagnosis and the differences in appearance on radiographs and ultrasonic reading when gestational age is calculated from the first breeding. Although the average gestation length is 63 days in the dog, ranges of 58 to 71 days have observed. This is a remarkable 13 day-span out of a total gestation of only 9 weeks.
Variables of Gestation Length: Gestation length varies because the dog's sperm can survive in the estrous uterus for many days before ovalation Read more [...]
The heart can feel pain when deprived of oxygen, and the smooth membrane or pleura covering the lungs can also give rise to pain sensation when diseased, but the lungs themselves are insensitive to pain and may be diseased for a long time without any symptoms. The larger air passages such as the trachea and the main bronchi are sensitive and irritation causes reflex coughing.
Organs within the chest, abdomen and pelvis are called viscera; sensation arising from the abdominal organs is spoken of as visceral, but much of this does not reach conscious levels. Receptors on the lining of the stomach register acidity or alkalinity (the pH factor) of the contents. This may not reach conscious levels, but is concerned with the control of stomach movements. In common with the rest of the alimentary, urinary and genital systems, receptors in the muscle layer of the stomach are excited by distension and by muscle contraction. Over-distension or strong contraction may cause pain, but this is due to stretching of the outer covering, the peritoneum, as pain receptors are not present in the organs themselves. The gut can also distinguish between gas and solid matter, and in the urethra, receptors can recognize fluid flow.
Receptors Read more [...]