RUFF work
THE BRAIN AND SENSES
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THE DOG'S BRAIN SYNTHESIZES, interprets, and acts on all the information it receives from the senses. Although thebrain of an average dog accounts for less than half a per cent of its body weight,
it needs a great deal of nourishment to function properly and receives over 20 per cent of the blood pumped out by the heart. Brain activity is, in part, predetermined by the "fixed wiring" of the dog's genes.
Just as our brains are pre-wired to learn language, the dog's brain is pre-wired to learn to interpret scent, and a large part of the brain is devoted to this process.
It is also able to interpret information from the other senses - touch, taste, hearing, and sight.
COORDINATION OF THE SENSES
Hearing
Highly mobile ears "capture" sounds and funnel them down to the
ear drum. A dog might cock one ear to capture an initial sound, then use both
ears to catch the maximum number of sound waves.
Experiments show that a dog can can locate the source of a sound in six-hundredths of a second.
Vision
This dog's facial anatomy is similar to that of the wolf, with widely
spaced eyes for good lateral vision.
Focusing on an image directly in front is most efficient in breeds with frontally placed eyes.
Taste and scent
Scenting and associated taste are both chemical senses. The average dog has
over 200 million scent receptors in
its nasal folds compared to a human's 5 million.
It also has a vomeronasal organ above the roof of the mouth for capturing sex scent and transferring it to the brain.
The brain
All sensory information is converted in sensory nerves to chemical
inessages for transmission and analysis by the brain.
Some of these messages influence the pineal gland, in the base of the brain, which synchronizes all body rhythms.
Touch
Touch receptors exist all over the body, but especially on the feet.
HOW THE BRAIN WORKS
The dog's brain stores information in two ways - it can either be conditioned or it can store what it learns. Both responses rely upon the individual dog's information-storage systems and are,
in part, determined by genetics. The brain consists of billions of cells (neurons), each of which may have up to 10,000 connections with other cells. The cells chemically communicate with each other through neurotransmitters. The speed of these transmissions depends partly upon a fatty substance called myelin. In the dog's prime, messages are transmitted at great speed, but as the brain ages, messages move more slowly. Anatomically, the dog's brain is similar to the brains of most other mammals. The cerebrum controls learning, emotions, and behavior, the cerebellum controls the muscles, and the brain stem connects to the peripheral nervous system. Each sense feeds into the brain through its own special nerves. A network of cells throughout the brain (the limbic system) almost certainly integrates instinct and learning. The conflict between what a dog instinctively wants to do and what we teach it to do probably takes place in the brain's limbic system. Humans can override this system by giving rewards to the dog for obeying its owners rather than its "instincts".
HOW THE SENSES WORK
The dog's senses are similar in function to those of humans. Information from the senses feeds into the brain, where it triggers either a body response or hormonal activity. For example, if a dog steps on something and feels pain, it quickly steps back - a physical response. If it smells male or female dog scent, the pituitary gland in its brain activates and stimulates a hormonal response.
SIGHT
A dog’s eyes are flatter than a human's; although the dog can change the shape of its lenses, thereby adjusting focal length, it cannot do so as effectively as a human. A dog's eyes are more sensitive to light and movement than those of a human, but their resolving power is correspondingly less efficient. The consequence is that a human finds it easier to see a lost tennis ball lying in the grass than a dog does, whereas a dog finds it easier to see slight movement out of the corners of its eyes than a human does.
HEARING
The dog's mobile ears allow it to scan the environment for sound. It may use one ear to scan, then both ears to capture and funnel sound waves. A dog can locate a source of sound in six-hundredths of a second, and it can hear sounds four times further away than a human can.
TOUCH
Touch is the first sense the dog develops, and remains a powerfully important sense throughout its life. Touch- sensitive hairs called vibrissae, which are capable of sensing air flow, develop above the eyes, on the muzzle, and below the jaws. The entire body, including the paws, is covered with touch-sensitive nerve endings.
TASTE AND SMELL
Dogs have far fewer taste buds than do humans, approximately one for every six. Although their limited number of taste buds register sweet, sour bitter, and salty tastes, it is probably more realistic to think of the dog's response to taste as pleasant, indifferent, or unpleasant. Smell is the dog's most advanced sense - a large part of its brain is devoted to interpreting scent. In addition, it has a sex-scent-capturing vomeronasal organ in the roof of its mouth. This scenting apparatus transmits information directly to the limbic system, the part of the brain most intimately involved in emotional behavior.
THE ANATOMY OF THE SENSES
The eyes
The eye consists of the corned, then an anterior fluid-filled chamber,
followed by the three-part uvea - iris, ciliary body, and lens. Behind the lens
is a large, fluid-filled posterior chamber, then the light sensitive retina
which feeds information down the optic nerve to the brain. The third eyelid
(nictitating membrane), which is hidden by the lower lid, sweeps the eye clean.
The lacrimal gland produces tears to keep the cornea moist. Tears drain down
the lacrinmal duct into the nasal cavity. This can block, causing tears to
overflow.
The ears
The cartilaginous outer ear (pinna) captures sound, and funnels it down the
external ear canal to the ear drum (tympanic membrane). Ear -drum vibrations
stimulate the organs of balance in the middle ear - the hammer, anvil, and
stirrup (malleus, incus, and stapes), which amplify and transmit sound, while
at the same time protecting the inner ear from excessive vibration. The cochlea
(part of the inner ear) captures these sounds and converts them to chemical
signals to the brain. Adjacent to the cochlea are the semicircular canals - the
saccule and utricle - the organs of balance in the inner ear, which feed the
brain with information on the alignment of the head.
The taste buds
Most taste receptors are on the anterior portion of the tongue and are
sensitive to sweet, our, bitter, and salty tastes. Other nerve endings act as
touch or texture receptors. Although
there are probably fewer than 2,000 taste receptors on the typical dog's
tongue, as a "chemical" sense taste works in conjunction with the
dog's infinitely more sensitive sense of smell. Odour initially attracts a dog
to food, then taste and texture receptors take over.
The
scent receptors
Moisture on the nose helps to capture scent, which is transmitted onto the
nasal membranes, which cover the nose's wafer-thin turbinate bones.
These bones have convoluted folds, ensuring that the tiniest
amount of
scent is captured within them. Sensory cells are closely
packed along the nasal-membrane lining, and convert scent to chemical messages
transmitted to the olfactory bulb region of the brain. Other scents are captured by the vomeronasal organ above the roof of the mouth, and transmitted to other parts of the brain.