the five human senses

The Five Senses: Eye, Ear, Nose, Mouth, and Skin Explained

The Five Senses

We, humans, have the five primary senses eye (visual), ear (auditory), nose (olfactory), mouth (gustatory), and skin (cutaneous) which helps us to sense the things around us. These senses are referred to as “gateways to knowledge”.

Human life would be very different without our ability to sense and perceive. We can see, hear, feel, taste, smell, or sense because of our sense organs and nervous system. Without these processes, life would be so unusual that we might not call it life at all. Without the ability to sense and perceive, we could not move. We would have no ability to balance and avoid dangerous objects or even eat unsafe food because there would be no work of sense organs. Everything we do is dependent upon information encoded in messages from our receptors.

The human body has the basic five senses, and also some additional senses. Here, we discuss the five primary senses and other additional senses, and what happens when we lost our senses one after another.

The Five Senses of Human

Eye – Sight, Seeing

Vision – Visual

Vision is the most important of all the five senses. To understand the visual sensation, it is necessary to know light energy. Light energy is the source of vision. When light strikes our eyes it is not the color of the object but a small part of electromagnetic energy or radiation is experienced in the form of color.

The electromagnetic spectrum ranges from very short gamma waves to long broadcasting radion waves and x-rays. The length of waves is measured through a nanometer (Nm). Nm is billionths of a meter. A human can detect only wavelengths between 380nm to 760nm from the visible spectrum. There are three characteristics of wavelength: hue, amplitude, and saturation.

Hue (color) is the different color we experience as blue or green or red. Amplitude (intensity or brightness) is the amount of energy in the light waves. Saturation is the purity or trueness of the color we perceive, like pure red or pure green, and so on.

Structure of The Eye

structure of the eye
Structure of the Eye

From the five senses, the eye is the one that lets us visualize things. The eye is the window to the soul and the world. It involves a different chain of actions to make us see the world. As light enters the eye it reaches the cornea. The cornea is a transparent, protective window. It helps to focus the light waves. The cornea becomes an opaque covering known as the sclera. The sclera is a whitish part of the eyeball.

The light waves then enter into an open area called the anterior chamber. Where it passes through a clear watery fluid called aqueous humor.

Aqueous humor continuously recycles and provides nourishment to the eye. The light then enters the pupil. A pupil has a round opening whose size varies with lighting conditions. The less light present, the wider the pupil opening. These adjustments are mediated by the iris. Iris is a colored membrane around the pupil that changes shape to arrange the size of the pupil to adjust the amount of light in the eye.

After the pupil light travels to the lens. Lens help to regulate the changing shape to focus on objects at varying distances. When we look at a distant object, the lens becomes thinner and flatter or big when we fixate on a nearby object, the lens becomes smaller. This focus of the lens is known as accommodation.

Light waves then reach their destination of the eye called the retina. The retina is a source of visual receptors of the eyes. It has two types of receptors: the rods and the cons. The retina contains 5 million cones and about 120 million rods. Retina transfers the electromagnetic energy of light into neural codes used by the brain with the help of these receptors. Most of the cones found in the area, known as the fovea, are the entrance of the retina. Rods are found outside of the fovea and function in lower levels of illumination or night. Retina receives an upside-down image. It is millions of receptors cells that convert light energy into neural impulses. These impulses are sent to the brain and construct into a perceived, upright seeing image.

In short, the visual sensation process in the eye is through, Cornea to the pupil, pupil to the lens, and lens to the retina, then we get a visualized image.

Ear – Hearing

Audition

Audition is the second important of the five senses after the vision. The link between how we hear and what we hear is possible through sound waves. Sound waves are the vibrations of the moving air. Audition is possible through the ear, which has a complex auditory system that transfers sound waves into neural messages and finally to the brain. Like light waves, sound waves have also three characteristics: wavelength (frequency), amplitude (intensity), and purity (timbre).

The amplitude or height refers to the loud and soft sounds. Intensity is produced by the difference between the peak and valley of air pressure. It is measured in decibel (DB) units. The normal conversation of the human being consists of about 60 DB sounds.

Waves which have 120 DB or more are very painful and irritating which are called noise.

Timbre is the purity of the tone which is very hard to experience. For example, we find sound waves are composed of many waves of different frequencies and intensities. The voice of a friend, noise of the traffic from the street, and singing birds may occur at once which may create complexity while hearing.

Ear – The Auditory System

Form the five senses, it is an ear through which we hear the sounds. The ear is composed of three components, the outer ear, the middle ear, and the inner ear.

structure of the year

The outer ear – when the air molecules from an object are vibrating sound is produced. These sounds waves travel to the ear through the medium of the ear. The external part of the ear called “pinna” collects these sound waves where the hearing process begins to take place.

The sound waves then travel down to the external auditory canal. The auditory canal connects the outer and middle ear. The sound waves in the auditory canal then strike the eardrum to vibrate. The eardrum is the first structure of the middle ear.

Middle Ear – Eardrum is a thin membrane stretched across the inner end of the canal. The pressure of the sound wave causes it to move which in turn vibrates three bones called: malleus, incus, and stapes that transmit the energy to the inner ear.

Inner Ear – The vibrating stirrup which is attached to the oval window transmits the energy to it. The oval window is a thin membrane that connects the middle ear with the inner ear. It strikes the liquid-filled snap-shaped cochlea of the inner ear. The vibration of the liquid in the cochlea causes sound energy to reach the basilar membrane. The basilar membrane then transmits the auditory information to the brain.

The Chemical Senses: Smell and Taste

The senses of smell (olfaction) and the senses of taste (gustation) both respond to the substances in solution in the form of gas (air) or fluid (water), which is the reason smell and taste are referred to as the chemical senses. They are sometimes called primitive sense because many animal species heavily rely on these chemical senses. These chemical senses are interlinked to our everyday life.

The Sense of Smell (Olfaction)

From the five senses, the nose is the sense of smell. Our life would be bland if we cannot smell. Sense of smell although not crucial for human beings’ survival, is very important for the survival of animals. The olfactory stimuli and olfactory system get reacted to the molecules of various substances contained in the air. When substance molecules mix the air, our olfactory receptors located at the top of the nasal cavity are active.

structure of the nose

The nose collects and filters the air we breathe. The air then reaches the nasal tissues which are in a moist form. The molecules then react to the receptors cells “cilia” contained in the olfactory epithelium. Cilia are hair-like substances, which are projected in the olfactory epithelium. Human beings have about 50 million of these receptors and can detect approximately 10,000 cents, while dogs can detect more because they have more than 200 million receptors.

Odor types that humans can smell: a widely used division of odors consist of seven primary qualities namely:

  • Flowery (e.g. rose)
  • Fruity (e.g. apple)
  • Musky (e.g. perfumes)
  • Resinous (e.g. camphor)
  • Putrid (e.g. ill smell)
  • Acid (e.g. Vinegar)
  • Minty (e.g. Peppermint)

The Sense of Taste (Gustation)

From the five senses, it is our tongue that gives us a sense of taste. Taste receptors are active when the substances are located in the tongue and throat known as taste buds. The taste buds are small bumps called papillae.

Most of the buds are located in the tip, sides, and back of the tongue. Some are found in the back of the throat, the roof of the mouth, and inside the cheeks. These taste buds contain approximately 20 test receptors. Human beings possess about 10,000 taste buds. These help to detect a large number of tastes in foods.

tongue anatomy taste buds

These taste buds stimulate when substances are in solutions and penetrate the taste buds. Psychologists have classified the taste bud of food into four primary types: sweet, sour, bitter, and salty. Every taste that we experience is made up of a combination of these four basic qualities. The receptors of tastes are not evenly distributed over the tongue but are grouped in different areas.

In the middle of the tongue, there are no receptors at all. This suggests that we have four different receptor sites. Different areas of the tongue are sensitive to different tastes. The sides of the tongue are sensitive to sour, the tip of sweet and side of the tip to salt and the back to bitter.

Body Senses – Skin, Touch, Feel

From the five senses, it is our body senses that give us feel when we touch something. It includes vestibular sense, kinesthetic sense, and cutaneous sense.

Vestibular Sense (The Sense of Balance)

The vestibular sense is also called somatosensory senses. It is located in the inner ear. It provides information about the body’s orientation and movement. It is concerned with balance and equilibrium and movement of the body. It is composed of two small sensory structures: the three semicircular canals and the utricle and saccule.

Each semicircular canal is filled with a jelly-like fluid. These fluids move as the head moves. These fluids contain sensory receptors, as the fluid moves in the canal, it causes hair cells in the canal to react. The activation of these hair cells sends information about the movement of the body to the brain.

The utricle and the saccule are also fluid-filled sacs in the inner ear. It works on the same principles as the semicircular canals. It helps to coordinate as a gravity detector providing information of the head and body.

The vestibular sense is very active during games.

Kinesthetic Sense (The Sensations of the Body Movement and Positions)

Kinesthetic sense is also known as “proprioception” refers to belonging to the body. It is concerned with the sensation of body movement and positions. Sometimes it is also called “Sixth Sense”.

Kinesthetic receptors are located all over the skin, muscles, joints, and tendons. They help us to walk, bend, talk, write, run, etc. The pressure and release of the parts of the body result in nerve impulses traveling to the brain. The activation of these impulses is sent back to the muscles, tendons, and joints again informing these systems for further action. When we talk without the knowledge of our muscles, tendons, and joints of our mouth and walk or swim without caring about this kinesthetic sense.

What happens if our jaws fall when we walk? When the kinesthetic system is active, the brain combines the information obtained from a variety of sensory systems such as vision, audition, etc. to determine the location of limbs. Kinesthetic information is vital during skilled activities such as swimming, dancing, driving, and so on.

Cutaneous Sense (Touch, Temperature, Pressure, and Pain)

The sense of skin works together to provide the information of objects we encounter. They warn us against potential danger to our bodies. Touch, pressure, temperature, and pain are the basic senses we obtain from the skin. When the skin is stimulated,, sensory information is conveyed to the somatosensory cortex located in the parietal lobe for higher-level processing.

Touch and Pressure

We experience touch or pressure when objects pass on the skin and hairs of the body are moved or touched. A gradient of pressure is not uniformly distributed. The most sensitive regions are the fingers, the lips, and the genitals, the sensitivity in the other areas is considerably less. Blind people use touch, pressure, and smell sensations much more than normal people. They read Braille up to 300 words per minute using their fingertips.

Temperature (Cold and Hot)

The sensation of temperature depends upon the temperature of the skin surface and the temperature of the blood circulating beneath it. For example, the temperature of the forearm is about 30 to 32 degrees celsius and the blood beneath it is 37 degrees celsius.

The sense of cold and warmth is experienced through different “spots” scattered in different skin placesspots detects warmth and the other detects coldness.

Pain

Pain sensation is much talked about among the cutaneous sensations. It is caused by different unwanted information, hot or cold, toxic chemicals, and cutting or problems with the skin. People want to reduce pain through different means as eating medicines, going to a safer place, etc. It helps us to warn against the problem and adapt to the environment.

The Other Senses, After The Five Senses

In addition to the five primary senses, there are three other senses which provide information about our bodies and position in space.

One of these, the kinesthetic sense, though we already discussed, in short, it provides informational feedback during the learning and performance of motor skills. It provides the knowledge of our muscles, tendons, and joints in movements or actions.

Another, the static sense, is concerned with equilibrium. Both the kinesthetic and static sense plays an important part, in telling us about the position of our limbs and facilitating general bodily coordination.

The third is, the organic sense, which works with the visceral components of emotional experience underlies such experiences as nausea, stomach, cramps, and bladder tensions.

What if We Lose Our Five Senses One After Another?

Here is, what happens when we lost our senses one after another. (Source: What. If Episode)

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