How Our Senses Work

Human beings have five basic senses. These are touch, sight, hearing, smell and taste. The sensing organs associated with each sense send information to the brain to help humans understand and perceive the world around them. The senses also enable humans to learn, to protect themselves, and to enjoy the world.  If one sense is not working due to an accident or illness, then other senses will take over or become stronger to make up for the missing sense.

Sense of Touch

Touch is thought to be the first sense that humans develop. Touch consists of several distinct sensations communicated to the brain through specialized neurons in the skin. Pressure, temperature, light touch, vibration, pain and other sensations are all part of the touch sense and are all attributed to different receptors in the skin. Touch isn't just a sense used to interact with the world; it is also very important to a human's well-being. For example, touch has been found to convey compassion from one human to another.

Sense of Sight

Sight, or perceiving things through the eyes, is a complex process.

First, light reflects off an object to the eye. The transparent outer layer of the eye called the cornea bends the light that passes through the hole of the pupil. The iris, (the coloured part of the eye) works like the shutter of a camera, retracting to shut out light or opening wider to let in more light.

The lens of the eye then bends the light and focuses it on the retina, which is full of nerve cells. These cells are shaped like rods and cones and are named for their shapes.

Cones translate light into colours, central vision and details. The rods translate light into peripheral vision and motion. Rods also give humans vision when there is limited light available, such as at night. The information translated from the light is sent as electrical impulses to the brain through the optic nerve.

Human beings who have no sense of sight compensate with enhanced hearing, taste, touch and smell and their memory and language skills may be better than those born with sight also.

Hearing

Hearing works via the complex labyrinth that is the human ear. Sound is funnelled through the external ear and piped into the external auditory canal. Then, sound waves reach the tympanic membrane, or eardrum. This is a thin sheet of connective tissue that vibrates when sound waves strike it.

The vibrations travel to the middle ear. There, the auditory ossicles — three tiny bones called the malleus (hammer), incus (anvil) and stapes (stirrup) — vibrate. The stapes bone, in turn, pushes a structure called the oval window in and out, sending vibrations to the organ of Corti. This spiral organ is the receptor organ for hearing. Tiny hair cells in the organ of Corti translate the vibrations into electrical impulses. The impulses then travel to the brain via sensory nerves.

Human beings are able to retain their sense of balance because the eustachian tube, or pharyngotympanic tube, in the middle ear equalizes the air pressure in the middle ear with the air pressure in the atmosphere. The vestibular complex, in the inner ear, is also important for balance, because it contains receptors that regulate a sense of equilibrium. The inner ear is connected to the vestibulocochlear nerve, which carries sound and equilibrium information to the brain. 

Sense of Smell

Humans may be able to smell over one trillion scents, according to researchers. This is done via the olfactory cleft, which is found on the roof of the nasal cavity, next to the "smelling" part of the brain, the olfactory bulb and fossa. Nerve endings in the olfactory cleft transmit smells to the brain. Research now suggests that the sense of smell is just as good in humans as in other mammals, like rodents and dogs. After all, humans have four hundred smelling receptors which isn't as many as animals have, but the much more complicated human brain makes up for the difference. 

Old age can also lessen the ability to smell properly.  More than seventy five percent of people over the age of eighty years may have major olfactory impairment. 

A poor sense of smell in people may be a symptom of a medical condition. For example, the distorted or decreased ability to smell is a symptom of schizophrenia and depression.

Sense of Taste

The sense of taste, otherwise known as the gustatory sense is usually broken down into the perception of four different tastes. These are salty, sweet, sour and bitter. There is also a fifth taste, defined as umami or savoury.  The sense of taste aided in human evolution because taste helped people test the food they ate. A bitter or sour taste indicated that a plant might be poisonous or rotten. Something salty or sweet, however, often meant the food was rich in nutrients.

Taste is sensed in the taste buds and adults have two thousand to four thousand taste buds.

Most of them are on the tongue, but they also line the back of the throat, the epiglottis, the nasal cavity and the oesophagus. Sensory cells on the buds form capsules shaped like flower buds or oranges. The tips of these capsules have pores that work like funnels with tiny taste hairs. Proteins on the hairs bind chemicals to the cells for tasting.

It is a myth that the tongue has specific zones for each flavour. The five tastes can be sensed on all parts of the tongue, although the sides are more sensitive than the middle. About half of the sensory cells in taste buds react to several of the five basic tastes. The cells differ in their level of sensitivity and each has a specific palette of tastes with a fixed ranking, so some cells may be more sensitive to sweet, followed by bitter, sour and salty, while others have their own rankings. The full experience of a flavour is produced only after all of the information from the different parts of the tongue is combined. The other half of the sensory cells are specialized to react to only one taste. It's their job to transmit information about the intensity, for example, how salty or sweet something tastes.

Other factors help build the perception of taste in the brain. For example, the smell of the food greatly affects how the brain perceives the taste. Smells are sent to the mouth in a process called olfactory referral. This is why someone with a stuffy nose may have trouble tasting food properly. Texture, translated by the sense of touch, also contributes to taste.

Sensory Processing Disorder

Sensory processing disorder is a condition in which one or more of the five human senses can be distorted or not functioning optimally or correctly. The brain has trouble receiving and responding to information that comes in through the senses.  It was formerly referred to as sensory integration dysfunction and not currently recognized as a distinct medical diagnosis.

Some people with sensory processing disorder are oversensitive to things in their environment. Common sounds may be painful or overwhelming. The light touch of a shirt may chafe the skin. They may be uncoordinated, bump into things easily and often, be unable to tell where their limbs are in space and can sometimes even find it hard to engage in conversation or play.

Supporting senses

Vision

• Eyebright. One of the most effective herbs to help maintain optimal eye health. It can also reduce dry eye and irritation. 
• Bilberry leaf. Bilberry can benefit the eyes. It aids in quickening the regeneration of the rhodopsin, the purple pigment that is used by the eyes' rods. Taking bilberry can also help improve vision, especially at night.
• Gingko Biloba. Ginkgo increases blood flow to the eye as well as circulation back to the eye. It has recently become popular in addressing eye health.

Hearing

In addition to relieving eye problems, gingko biloba can also help to improve hearing as it can aid in circulation to the head, including the ears. It also helps to quickly remove toxins that may have built up in the ears. Other herbs that can benefit the hearing include rosemary leaf, passion flower, plantain leaf, and yarrow flower. These herbs can sharpen the hearing as well as improve circulation so that the ears receive optimal blood flow.

Smell

If the sense of smell has been affected due to allergies or on-going chronic sinus issues then herbs such as horseradish root, bitter orange, golden seal, lobelia, nettle, echinacea and peppermint essential oil can all be useful to help with sinus congestion and draining of mucous.

Taste

Zinc deficiency is known to be a major cause of loss of taste and smell. Zinc supplements are the ideal option. Whole grains, nuts, beans and oysters can also be added to the diet.

Garlic. Sense of smell and taste can be restored with garlic. It effectively helps in clearing nasal congestion and opens up nasal passages that are blocked.  Either cut two to three cloves and boil them in a cup of water, simmer for ten minutes and then drink the mixture or alternatively taking garlic supplements three times daily.

References

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115993/
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