Animal Ear Match

The Human Ear

Sound travels through matter as a soundwave, which is a form of energy. It is our sense of hearing and the structures of the body involved in hearing that translate a soundwave into recognizable sounds. The outer ear consists of the part of the ear visible on the outside of the head, the ear canal, and the eardrum. The shape of the ear funnels sound into the ear canal and sound waves reach the eardrum. The eardrum consists of a membrane called the tympanic membrane, which is stretched tightly so that it responds with great sensitivity to the vibrations of sound waves. As the sound waves reach the eardrum, the membrane begins to vibrate.

These vibrations are passed to the middle ear, which consists of three small bones called the hammer, anvil, and stirrup. As the eardrum vibrates, it passes the vibrations to the hammer, which causes the anvil to vibrate, which in turn causes the stirrup to vibrate.

Sound continues to travel from the middle ear into the inner ear. Within the inner ear lies the cochlea, a spiral-shaped structure filled with fluid. The vibrations from the stirrup cause waves in the fluid of the cochlea. Inside the cochlea is the organ of Corti, an organ containing tiny hair cells which move in response to the waves in the fluid, transmitting sound in the form of electrical impulses to the auditory nerve.

The electrical impulses travel through the auditory nerve to the parts of the brain responsible for processing the information. In this way, sound travels from its origin through the outer, middle, and inner ear, through the auditory nerve to the brain, where the information is processed so that we may respond to it appropriately.

Earlier, we looked at examples of different animal ears. We saw that ears can look quite a bit different from one animal to another. If you are really observant, you will notice that not all human ears look exactly alike either. For example, look at the slight differences between different human ears in the pictures below.

However, even though ears may look a bit different from each other on the outside, just like most everything else about human beings, the insides parts are identical and work in exactly the same way! However, not everyone’s hearing is as good at hearing different sounds. Doctors and audiologists perform hearing tests on people to test their hearing. Perhaps you have had a hearing test in the past.

Normal humans can hear a range of soundwaves, from very low sounds to very high sounds. The soundwaves of different sounds are measured as frequencies in units called hertz (abbreviated Hz). Humans can usually hear sounds that range from a low of about 20 Hz to a high of about 22,000 Hz. Many other animals, dogs, for example, can hear frequencies much higher than humans can. The video below plays a range of soundwave frequencies from 20 Hz to 22,000 Hz. Test to see what frequencies you can hear when you play the video.

In Investigation One, students will develop a beginning understanding of sound travel. They will use their sense of hearing to identify sounds in their classroom, to listen to an activated tuning fork, and to identify the location of the sound of the tuning fork.