SENSES

SENSES

Senses are physiological capacities of organisms that provide data for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology, and philosophy of perception. The nervous system has a specific sensory system or organ, dedicated to each sense.

Human beings have a multitude of senses. Sight , hearing, taste , smell , and touch are the five traditionally recognized. Whilst the ability to detect other stimuli beyond those governed by the traditional senses exists, including temperature, kinesthetic sense , pain, balance, acceleration , and various internal stimuli , only a small number of these can safely be classified as separate senses in and of themselves. What constitutes a sense is a matter of some debate, leading to difficulties in defining what exactly a sense is.

Disorders

Sensory Processing Disorder (SPD) is a neurological disorder that causes difficulties with processing information from the five senses: vision, auditory, touch, olfaction, and taste, as well as from the sense of movement (vestibular system), and/or the positional sense (proprioception). For those with SPD, sensory information is sensed, but perceived abnormally. Unlike blindness or deafness, sensory information is received by people with SPD; the difference is that information is processed by the brain in an unusual way that causes distress, discomfort, and confusion.

Although a sensory processing disorder is not considered a qualifying characteristic for a diagnosis of autism, I have yet to meet a person on the autism spectrum who does not have a challenge in this area. 

Color blindness or "Daltonism" is a common abnormality in human vision that makes it impossible to differentiate colors accurately. One type of color blindness results in the inability to distinguish red from green. This can be a real handicap for certain types of occupations. To a colorblind person, a person with normal color vision would appear to have extrasensory perception. However, we want to reserve the term "extrasensory perception" for perception that is beyond the range of the normal.

·     It is estimated that one to three out of every 1,000 babies are born with congenital hearing loss. Congenital birth defects that cause hearing problems in children can also be caused by factors that occur during the pregnancy.

·    If your problems are not easily resolved, a family doctor can refer you to an audiologist. Age-related hearing problems are very common. The inner ear is home to many small hairs.

·    Abnormalities in the ear canal, tympanic membrane, and middle ear are common causes of this condition. The diagnosis of conductive hearing loss relies on a physical examination and audiometric tests. Treatment of this condition varies depending on the reason that the hearing loss developed.

·     Generally, conductive hearing loss is only temporary and can be fixed medically or with surgery. Common in children, conductive hearing loss can be diagnosed by an audiologist or ear, nose, and throat doctor.

Some people experience a phenomenon called synesthesia in which one type of stimulation evokes the sensation of another. For example, the hearing of a sound may result in the sensation of the visualization of a color, or a shape may be sensed as a smell. Synesthesia is hereditary and it is estimated that it occurs in 1 out of 1000 individuals with variations of type and intensity. The most common forms of synesthesia link numbers or letters with colors.

Human Sense Organs

Sight.

The eye is the organ of vision. It has a complex structure consisting of a transparent lens that focuses light on the retina. The retina is covered with two basic types of light-sensitive cells-rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. These cells are located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The point of this connection is called the "blind spot" because it is insensitive to light. Experiments have shown that the back of the brain maps the visual input from the eyes.

The brain combines the input of our two eyes into a single three-dimensional image. In addition, even though the image on the retina is upside-down because of the focusing action of the lens, the brain compensates and provides the right-side-up perception. Experiments have been done with subjects fitted with prisms that invert the images. The subjects go through an initial period of great confusion, but subsequently they perceive the images as right side up.

Hearing.

The ear is the organ of hearing. The outer ear protrudes away from the head and is shaped like a cup to direct sounds toward the tympanic membrane, which transmits vibrations to the inner ear through a series of small bones in the middle ear called the malleus, incusand stapes. The inner ear, or cochlea, is a spiral-shaped chamber covered internally by nerve fibers that react to the vibrations and transmit impulses to the brain via the auditory nerve. The brain combines the input of our two ears to determine the direction and distance of sounds.
The inner ear has a vestibular system formed by three semicircular canals that are approximately at right angles to each other and which are responsible for the sense of balance and spatial orientation. The inner ear has chambers filled with a viscous fluid and small particles (otoliths) containing calcium carbonate. The movement of these particles over small hair cells in the inner ear sends signals to the brain that are interpreted as motion and acceleration.

Taste.

The receptors for taste, called taste buds, are situated chiefly in the tongue, but they are also located in the roof of the mouth and near the pharynx. They are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue also can detect a sensation called "umami" from taste receptors sensitive to amino acids. Generally, the taste buds close to the tip of the tongue are sensitive to sweet tastes, whereas those in the back of the tongue are sensitive to bitter tastes. The taste buds on top and on the side of the tongue are sensitive to salty and sour tastes. At the base of each taste bud there is a nerve that sends the sensations to the brain. The sense of taste functions in coordination with the sense of smell. The number of taste buds varies substantially from individual to individual, but greater numbers increase sensitivity. Women, in general, have a greater number of taste buds than men. As in the case of color blindness, some people are insensitive to some tastes.

Smell.

The nose is the organ responsible for the sense of smell. The cavity of the nose is lined with mucous membranes that have smell receptors connected to the olfactory nerve. The smells themselves consist of vapors of various substances. The smell receptors interact with the molecules of these vapors and transmit the sensations to the brain. The nose also has a structure called the vomeronasal organ whose function has not been determined, but which is suspected of being sensitive to pheromones that influence the reproductive cycle. The smell receptors are sensitive to seven types of sensations that can be characterized as camphor, musk, flower, mint, ether, acrid, or putrid. The sense of smell is sometimes temporarily lost when a person has a cold. Dogs have a sense of smell that is many times more sensitive than man's.

Touch.

The sense of touch is distributed throughout the body. Nerve endings in the skin and other parts of the body transmit sensations to the brain. Some parts of the body have a larger number of nerve endings and, therefore, are more sensitive. Four kinds of touch sensations can be identified: cold, heat, contact, and pain. Hairs on the skin magnify the sensitivity and act as an early warning system for the body. The fingertips and the sexual organs have the greatest concentration of nerve endings. The sexual organs have "erogenous zones" that when stimulated start a series of endocrine reactions and motor responses resulting in orgasm.

Hearing sense

Hearing begins with the ears, which receive sounds and send them to the auditory cortex, near the back of the brain, for processing. The primary instrument for sound gathering in the ear is the eardrum, or tympanic membrane, which separates the outer ear from the middle ear.

The eardrum passes along sound vibrations to the ossicles, the three smallest bones in the human body, when then divert it to the fluid-filled, labyrinth-like structure in the inner earcalled the cochlea, where the true hearing organs reside. Collectively, the assemblage of sound-processing organs is called the auditory system.

The sensory organ for hearing is the Organ of Corti, named after the Italian anatomist Alfonso Corti, who discovered it using a microscope in 1851. The Organ of Corti is internal to the cochlea, and contains about 15,000 - 20,000 specialized sensory cells, each with a little hair capable of picking up minute vibrations in the cochlear fluid. If destroyed by loud sounds, these hairs never grow back. Different hairs are specialized to detecting sounds at various frequencies, and turn them into nerve signals to be sent to the brain. Also in the cochlea is a triad of fluid-filled loops oriented in the vertical, diagonal, and horizontal directions, which help give us a sense of balance.

Vision sense 

Everything you look at is then sent to your brain for processing and storage much like a video cassette. This is a very simplified explanation, but as you read on, you will discover why the sense of sight is actually considered the most complex of the five senses.

The light rays enter the eye through the cornea, which is a thick, transparent protective layer on the surface of your eye. Then the light rays pass through the pupil  and into the lens.

When light rays pass through your pupil, the muscle called the iris makes the size of the pupil change depending on the amount of light that's available. You may have noticed this with your own eye if you have looked at it closely in a mirror. If there is too much light, your pupil will shrink to limit the number of light rays that enter. Likewise, if there is very little light available, the pupil will enlarge to let in as many light rays as it can. 

Just behind the pupil is the lens and it focuses the image through a jelly-like substance called the vitreous humor onto the back surface of the eyeball, called the retina.

The retina, which is the size of your thumbnail, is filled with approximately 150 million light-sensitive cells called rods and cones. Rods identify shapes and work best in dim light. Cones on the other hand, identify color and work best in bright light. Both of these types of cells then send the information to the brain by way of the optic nerve. The amazing thing is, when they send the image to the brain, the image is upside down! It is the brain's job to turn the image rightside up and then tell you what you are looking at. The brain does this in a specific place called the visual cortex.