In order to be able to perceive your environment, you need your senses. The five human senses are touch, taste, smell, hearing and sight. Each of these senses has a specialized sensory organ. From the incredible amount of information that is constantly pouring in at you from the environment, the sensory organ filters only that which it can also process. Your five sense organs are the skin, mouth, nose, ear and eye.
Sense organs – definition
Organs, due to specific location and arrangement of sensory cells Stimuli can absorb are considered sense organs designated. Each sensory organ is geared to a specific type of stimulus and can only process this.
The function of the sense organs
The sense organs trigger so-called stimulus-response chains out. This is the connection between sensory, nerve and reacting cells. A stimulus-response chain is triggered when one of the sensory organs absorbs stimuli from the environment. In this way, humans and other living beings can perceive the environment and react to it – sensory organs are therefore a basic requirement for the preservation of life.
Not only humans and animals have senses. Plants also have senses, but do not have direct sensory organs. They perceive their environment through the production of certain hormones. These hormones transmit sensory stimuli to their organs via a fine network of veins. As experiments have shown, plants can perceive their environment very sensitively and also communicate with each other.
Your sensory organs always consist of two basic units: the actual sensory cells and so-called auxiliary structures. while the sensory cells are responsible for stimulus processing and transmission, the auxiliary structures improve or filter the reception of the stimuli.
An example of this is your ear cup. As an auxiliary structure, it ensures that the sound waves get through a funnel directly into your inner ear and ultimately to the hearing cells.
Not every sense is equally valuable for every living being. Its importance can be roughly estimated based on the size and characteristics of a sensory organ. That’s how he decrees olm, a cave dweller, only has rudimentary, i.e. stunted eyes. It is so dark in its habitat that well-defined eyes would be «pointless» anyway. The situation is similar with moles, whose sense of touch and smell is particularly well developed. The human world of experience, on the other hand, is mainly based on the sense of sight.
The human sense organs
As you have already learned, humans have five senses, i.e. five sensory organs. You will learn more about these in the following section.
The sense organ eye
For humans, the sense of sight is the most best pronounced sense. We therefore take in most of the information through our eyes. Our eyes are able to perceive and pass on light stimuli.
Figure 1: Schematic structure of the eye Source: wikipedia.com
All vertebrates have a similar eye structure. Light enters the eye through the pupil through the lens. As it passes through the lens, the image is turned upside down (inverted) and scaled down. It hits a layer of vision cells located in the retina. The visual sensory cells are oriented in such a way that their light-sensitive side faces away from the light.
The amount of light entering the pupil can be iris be regulated. This acts as an aperture. The lens can go through zonular fibers and the ciliary muscle be stretched or compressed. This allows the eye to adapt to different distances by changing the refractive power of the lens (accommodation).
Most of the visual sensory cells, also called photoreceptors, are found in the yellow spot on the retina. This is where most of the light hits the retina. The vision cells have nerve endings that reach into the brain. They come out of the eye bundled to form the optic nerve. There are no visual cells where the optic nerve leaves the eye. Hence this point Blind spot.
You can find out more about the eye as a sensory organ in the article of the same name.
The sense organ skin
The skin covers your entire body. It is the largest organ in the human body. The skin is not only a protective barrier that protects the underlying tissues from danger, it is also a sensory organ.
Distributed over its entire surface you will find different receptors that can react to the stimuli of temperature, pain, pressure and touch. The distribution of these receptors is not even. So there is much more at your fingertips touch receptors, than on your back, for example. This concentration of sensory cells in the fingertips enables you to perceive touch stimuli separately, which are only two millimeters apart. On the back, the spatial resolution is only around 70 millimeters.
ability to resolve stimuli
Pressure points per cm² of skin
fingertip
2
200
lip
4
50
poor
40
40
the back
70
10
If you want to know more about this sensory organ, take a look at the explanation about the skin!
The sense organ nose
What you can do with your nose is, of course, smell. However, the nose is a very special organ. The olfactory cells are located in their mucous membrane. These are the so-called primary sensory cells. Therefore, the olfactory cells of the nose, so also neurons.
The olfactory cells are able to perceive dissolved gases and odorous substances in the air. This allows the air quality, but also the quality of food to be determined. However, your sense of smell has certain limits. With yours 10 million olfactory cells you are unfortunately quite inferior to a dog in a sniffing contest. Dogs usually feature about 200 million olfactory cells.
Your sense of smell also plays an important role in your sense of taste. You’ve probably already noticed that you can hardly taste anything with a stuffy nose.
You can read more about the function of the nose in the article on the nose!
The sense organ mouth
The mouth itself is not really the sensory organ we are talking about here. The organ responsible for taste is your tongue. The tongue is able to distinguish four basic tastes: sweet, sour, bitter and salty.
In addition to the four classic tastes, the Japanese chemist Kikunae Ikeda discovered a fifth quality of taste in 1909, which he umami baptized. The Japanese term is composed of the words umai for «tasty, spicy» and wed for «essence» together. Nowadays, the term is usually translated as «hearty» or «spicy». trigger of umamiIncidentally, the taste sensation is glutamic acid. Shortly after its discovery, Ikeda therefore also began the industrial production of monosodium glutamate – one of the most widespread and controversial flavor enhancers nowadays.
The tongue’s sensory cells are located in the mucous membrane and perceive the taste carriers dissolved in the saliva. Several sensory cells are organized into so-called taste buds.
You’ve probably heard that the taste buds for different tastes are clustered in certain areas of the tongue. A mistake that persists. The fact is that there are fewer receptors in the middle of the tongue than on the edge. However, it is not possible to differentiate between sweet and salty areas.
In the mouth article you can find out more about the function of the tongue as a sensory organ.
The sense organ ear
Perhaps when you hear the word «ear» you think primarily of the pinna. However, these two cartilage structures hanging on the left and right of your head are just a kind of funnel and carry the sound to the actual sensory organ: the inner ear.
The sound waves, or the air vibrations that trigger the sound waves, travel through the auditory canal to the eardrum. Here, the air vibrations are translated into mechanical vibrations, since the movements of the eardrum are transmitted to the cochlea via the auditory ossicles. The lumen of the cochlea is filled with a liquid and provided with so-called hair cells that can absorb and transmit the vibrations.
Figure 2: Anatomy of the ear
A noise or tone naturally has different properties, such as frequency, duration and localization. All these properties are transmitted to the brain via the auditory nerve and evaluated there.
In addition to the sense of hearing, the inner ear is also responsible for another «sense»: the sense of balance. This consists of the sense of rotation and position. Its sensory cells are located in the so-called vestibular organ (semicircular canals). Together they provide information about movements and the spatial position of the head.
There is also a article on the ear that explains the function and processes in more detail. Have a look there!
Sense organs – the most important
- Sensory organs are organs that can receive stimuli based on a specific position and arrangement of sensory cells
- They consist of two units: the sensory cells and the auxiliary structures
- When sensory organs perceive stimuli from the environment, a stimulus-reaction chain is triggered – this is how living beings perceive their environment and can react to it
- Which sense is most important for a living being varies and is related to the environmental factors of the habitat
- The relevance of a sensory organ for the living being can be roughly estimated by its size
- Humans have five sense organs: eyes, nose, ears, skin and mouth – the sense of sight is of the greatest importance for humans