Human Body

The skin (cutis) is the largest sense organ in the human body. It possesses numerous special receptors and nerve endings, enabling it to register touch, pressure, pain and temperature. Pressure is registered by means of what are called the Merkel's touch cells, located on the border between the outer skin (epidermis) and the true skin (corium).

Touch is registered by means of oval corpuscles located in small protrusions (papillae) within the true skin, as well as networks of nerves located around the hair roots.

For our orientation in the environment, hearing is of about the same importance as seeing. In our communication by means of language, the ear plays a significant role. The ear has a special sensitivity to audio frequencies in the range of speech.

By means of the ear, certain vibrations in the air can be detected. Vibrations emitted

from a body (sound sources)

are picked up by the air which, acting as a sound carrier, conducts them to the ear:

If these vibrations lie in a range from 16 to a maximum of 20.000 cycles per second, they can be detected by the human ear.

Some animals hear considerably better and are able to detect vibrations that exceed 20.000 vibrations per second. Deep sounds are caused by slow vibrations of about 50 vibrations per second. The highest audible sounds have a frequency of a maximum of 20.000 per second.

Faster vibrations are referred to as ultrasound. These are not detectable by the human ear. The audible number of vibrations and thus the pitch is called audio frequency and is measured in hertz.

One hertz is equal to one vibration per second.

The highest deviation of a sound wave from its resting position is called an amplitude. Its increase means a louder sound, its decrease means a quieter sound. The standard measure of loudness is the decibel (dB).

In the ear, the oscillations in the air are converted into electric nerve impulses which can be interpreted by the brain as noise.

In addition, the ear contains mechanisms imparting sensations of movement and position.

In its exterior structure, the ear can be divided into three sections. The first two sections, the external ear and the middle ear, conduct the sound.

The third section, the internal ear, houses the sensory cells.

The inner ear consists of:

the cochlea (Greek kokhleas = snail) with the sensory cells for the reception of sounds

the semicircular canals with the sensory cells for the sensations of movement

the two sacs containing the sensory cells for the sensations of position

The external ear, middle ear and cochlea form the organ of hearing, the semicircular canals and the two sacs form the organ of equilibrium.