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Anatomy and Structure of Human Sense Organs

The human sense organs are classified into 5: the organ of sight, organ of smell, organ of taste, organ of touch and organ of hearing. Each of the 5 senses is made up of an organ that has specific cellular structures that have receptors for specific stimuli.

These cells have links to the nervous system and therefore to the brain. Sensing is done at primordial levels in the cells and incorporated into sensations in the nervous system.
Sight is in all probability the main developed sense organ in humans, followed narrowly by organ of hearing.

The Sense Organ of Sight

The eye is the organ of vision. It has a composite structure made up of a transparent lens that focuses light on the retina. The retina is enclosed with two essential types of light-sensitive cells-rods and cones.
The cone cells are sensitive to color and are situated in the part of the retina known as the fovea, where the light is focused by the lens. The rod cells on the other hand are not sensitive to color, but possess greater sensitivity to light than the cone cells.
These cells are found around the fovea and are in charge of peripheral vision and night vision. The eye is joined to the brain through the optic nerve. The point of this connection is known as the “blind spot” due to the fact that it is insensitive to light.
The brain joins the input of our two eyes into a distinct three-dimensional image. Again, even though the image on the retina is upturned due to the focusing action of the lens, the brain recompenses and provides the upright-side image perception.
Experiments have been conducted with subjects built-in with prisms that invert the images. The subjects pass through a preliminary period of immense confusion, but afterward they identify the images as upright.
The range of perception of the eye is extraordinary. In the dark, a substance formed by the rod cells increases the sensitivity of the eye so that it is possible to sense extremely dim light. In well-built light, the iris contracts minimizing the size of the aperture that admits light into the eye and a defensive ambiguous substance minimizes the exposure of the light-sensitive cells.
The range of light to which the eye is sensitive differs from the red to the violet. Lesser electromagnetic frequencies in the infrared are detected as heat, but cannot be seen. Elevated frequencies in the ultraviolet and beyond cannot be seen either, but can be detected as tingling of the skin or eyes depending on the frequency.
The human eye is not sensitive to the polarization of light- light that move back and forth on a definite plane.
Bees, on the contrary are sensitive to polarized light, and possess an image range that expands into the ultraviolet.
A few types of snakes possess specific infrared sensors that allow them to hunt in complete darkness merely with the help of the heat given out by their prey.
Birds possess an advanced concentration of light-sensing cells than humans have in their retinas, and as a result, have a more advanced visual acuity.
Color blindness or “Daltonism” is a widespread anomaly in human vision that makes it impractical to distinguish colors correctly. One type of color blindness results in the incapability of differentiating red from green.
This can be actual handicap for definite types of occupations. To a colorblind individual, a person with standard color vision would seem to possess an extrasensory perception.
Nevertheless, we want to put to one side the term “extrasensory perception” for perception that is ahead of the range of the normal.

The Organ of Hearing

The ear is the sense organ of hearing. The outer ear sticks out away from the head and is shaped like a cup to guide sounds in the direction of the tympanic membrane, which transmits vibrations to the inner ear via a series of small bones in the middle ear known as the malleus, incus and stapes.
The inner ear, or cochlea, is a spiral-shaped cavity enclosed within by nerve fibers that respond to the vibrations and transfer impulses to the brain through the auditory nerve.
The brain joins the input of our two ears to establish the direction and distance of sounds.
The inner ear possess a vestibular system produced by three semicircular canals that are roughly at right angles to each other and which are answerable for the sense of balance and spatial direction.
The inner ear possess chambers overflowing with a viscous fluid and small particles (otoliths) consisting calcium carbonate. The association of these particles over tiny hair cells in the inner ear transmits signals to the brain that are interpreted as movement and speeding up.
The human ear can pick out frequencies from 16 cycles per second, which is an extremely deep bass, to 28,000 cycles per second, which is a very high pitch. Bats and dolphins can detect frequencies above 100,000 cycles per second.
The human ear can sense pitch alterations as minute as 3 hundredths of one percent of the original frequency in a few frequency ranges. A few individuals possess “perfect pitch”, which is the capability to chart a tone accurately on the musical scale without indication to an exterior standard.
It is projected that less than one in ten thousand people possess perfect pitch, but speakers of tonal languages such as Vietnamese and Mandarin exhibits amazingly clear-cut absolute pitch in reading out collection of words due to the fact that pitch is a crucial aspect of passing on the meaning of words in tone languages.

The Organ of Taste

The receptors for taste, known as the taste buds, are located mainly in the tongue, but they are as well situated in the roof of the mouth and close to the pharynx. They are capable of detecting four basic tastes: salty, sweet, bitter, and sour.
The tongue as well can detect a sensation known as “umami” from taste receptors responsive to amino acids. By and large, the taste buds located near the tip of the tongue are sensitive to sweet tastes, while those in the backside of the tongue are sensitive to bitter tastes.
The taste buds on apex and on the side of the tongue are sensitive to salty and sour tastes. At the bottom of every taste bud there is a nerve that transmits the sensations to the brain.
The sense of taste works in coordination with the sense of smell. The number of taste buds differs considerably from person to person, but higher numbers add to sensitivity. Women, commonly possess a higher number of taste buds than men. As in the case of color blindness, a number of people are numb to a few tastes.

The Sense of Smell:

The nose is the organ in charge of the sense of smell. The cavity of the nose is covered with mucous membranes that possess smell receptors linked to the olfactory nerve. The smells themselves are composed of vapors of different substances.
The smell receptors interrelate with the molecules of these vapors and send out the sensations to the brain.
The nose as well has a structure known as the vomeronasal organ whose function has not been discovered, but which is suspected to be sensitive to pheromones that manipulate the reproductive cycle. The smell receptors are responsive to seven types of sensations that can be described as camphor, musk, flower, mint, ether, acrid, or putrid.
The sense of smell is sometimes momentarily lost when a person has caught a cold. Dogs possess a sense of smell that is a lot of times additionally sensitive than man’s.

The Sense of Touch

The sense of touch is dispersed all through the body. Nerve endings in the skin and other parts of the body send out sensations to the brain. A few parts of the body possess a larger number of nerve endings and, consequently, are more sensitive.
Four kinds of touch sensations can be recognized: 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.
Away from the five sense organs
Apart from the 5 generally accepted and recognized sense organs of sight, smell, taste, touch, and hearing, human beings as well possess sense of consciousness of balance known as equilibrioception, pressure, temperature also known as thermoception sense of pain as well known as nociception, and motion all of which might involve the coordinated use of several sensory organs.
The sense of balance is regulated by a complex communication of visual inputs, the proprioceptive sensors which are controlled by gravity and stretch sensors located in the muscles, skin, and joints, the inner ear vestibular system, and the central nervous system.
Disturbances occurring in any part of the balance system, or even within the brain’s integration of inputs, can cause the feeling of dizziness or unsteadiness.

Kinesthesia

Kinesthesia is the accurate responsiveness of muscle and joint action which permits us to coordinate our muscles when we walk, talk, and make use of our hands.
It is the sense of kinesthesia that allows us to touch the tip of our nose with our eyes shut or to become aware of which part of the body we need to scratch when we are experiencing itching.

Synesthesia

A few individual experiences a phenomenon known as synesthesia in which a single type of stimulus leads to the sensation of another. For instance, the hearing of a sound may lead to the sensation of the visualization of a color, or a shape may be sensed as a smell.
Synesthesia is hereditary and it is likely to take place or exist in 1 out of 1000 people with variations of form and intensity. The most widespread forms of synesthesia connect numbers or letters with colors.

Path of Sensory Impulses

The following is the part a sensory impulse takes before they are finally translated to the individual. The impulse from the receptors are transmitted through the nerve to the brain which translates it and send back the message through nerves to the effectors which would now react or respond accordingly.
Receptors > Nerves > Brain > Nerves > Effectors (such as muscles)> response
As illustrated above, our sensory organs first receives the stimuli transmits the nervous impulse to the brain which interprets it and take decision of what would be the best thing to do. The brain would then send the nerve impulses to the associated effectors or effectors muscle which would then respond accordingly.

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