How do humans experience sound? Sound waves are collected in the pinna. The pinna is located on the outside of your head. It is the outer visible part of the ear made up of skin and cartilage. Sound waves are collected in the pinna and transported through the outer ear canal. Sound waves entering the ear at a certain frequency cause the ear drum to vibrate at the same frequency which in turn causes three tiny bones; malleus, incus and stapes in the middle ear to vibrate. The vibrations are transferred to the cochlea in the inner ear. The cochlea is filled with fluid and lined with 18,000 sensitive hairs. They are called hairs because each cell is topped with hair like structures called stereocilia. Excited hairs trigger the generation of nerve signals that are sent to the brain via the auditory nerve.
The cochlea is a spiral canal that starts out wide and gets narrower. The nerves near the wider part of the channel respond to long wavelength, lower frequency sounds. The inner channel responds to shorter wavelength, higher frequency sounds. On average, people can hear sounds in the frequencies between 20 to 20,000 Hertz.
As people age our hearing ability tends to change. Often older people will loss their ability to hear high frequencies of sound. Many adults cannot hear sounds higher than 15,000 Hz. while children can often hear as high as 20,000 Hz. (Katsuk Y, 1982).
Natural sources and modern technology are able to make sounds higher than the human ear can hear. Ultra Sound is a sound that has a frequency of 100,000 Hz or more. The human ear is unable to detect this frequency however the sound waves can easily pass through our bodies. Medical ultrasound instruments use the refraction and reflection of sound waves to produce images of structures inside the body. This is common procedure for doctors to produce images of beating hearts and developing babies in the womb. An echocardiogram is a moving image of the heart's action. A video is produced with false colors to indicate the speed and direction of blood flow and heart valve movements (Hsu Tom, 2003).
Activity 5 Analysis of different Specialized Cells
This will be a good time to review the parts of the eukaryotic cell. It is important to highlight the fact that we are made up of billions of cells. Of these billions of cells many are not at all the same. There are dozens of specialized groups of cells with different functions. I will obtain electron micrographs of different specialized cells and have student make predictions about what the function of each cell is. Students will be required to describe the similarities and differences of each cell. Most will be able to determine that each cell has a nucleus and cell membrane; however the shape and size of each cell will be different. One of the cells that will be used will be the hair cell of the inner ear. Students will notice the stereocillia of the cell and they will be asked to predict the importance of the appendage before the true function is reveled.