All about human eyes and ears Kemi and javarn

1. All about human eyes and ears Kemi and javarn

2. eyes • Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptor cells in conscious vision connect light. • Kemi and javarn

3. Ears • The word "ear" may be used correctly to describe the entire organ or just the visible portion. In most mammals, the visible ear is a flap of tissue that is also called the pinna and is the first of many steps in hearing. In humans, the pinna is often called the auricle. Vertebrates have a pair of ears placed somewhat symmetrically on opposite sides of the head. This arrangement aids in the ability to localize sound sources.

4. Sound • Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation).

5. listening • There are far fewer inner hair cells in the cochlea than afferent nerve fibres - many auditory nerve fibres are innervated by each hair cell. The neural dendrites belong to neurons of the auditory nerve, which in turn joins the vestibular nerve to form the vestibulocochlear nerve, or cranial nerve number VIII.1 The region of the basilar membrane supplying the inputs to a particular afferent nerve fibre can be considered to be its receptive field.

6. Hearing test • An audiometer hearing test is usually administered to a person sitting in a soundproof booth wearing a set of headphones which is connected to an audiometer. Small foam insert earphones placed in the ears may also be used. The audiometer produces tones at specific frequencies and set volume levels to each ear independently. The audiologist or licensed hearing aid specialist plots the loudness, in decibels, on an audiogram. People having their hearing tested will convey that they have heard the tone by either raising a hand or pressing a button. As the test progresses, the audiologist or hearing aid specialist, plots points on a graph where the frequency is on the x-axis and the loudness on the y-axis. Once each frequency of hearing ability is tested and plotted, the points are joined by a line so that one can see at a glance which frequencies are not being heard normally and what degree of hearing loss may be present. Normal hearing at any frequency is a sound pressure of 20 dBSPL or quieter; with worsening hearing as the number increases.1

7. Eye test • Our eyes are the windows not just to our souls but also to our health. • Eye tests are important health examinations that provide information about the eye and its function. • Eye tests fall in to two parts – testing the eyes for glasses (refraction) and examining the eyes for signs of eye or general disease. • Adults should have their eyes tested to keep their prescriptions up to date and also to detect early signs of eye disease. • Young children are routinely screened at nursery for visual problems before they go to school.

8. How your eyes work • When you look at an object, the light from it enters your eye through the pupil. The iris changes the size of the pupil, depending on how bright the light is. The lens focuses the light onto the back of the eye: the retina. The retina is a mass of light-sensitive neurons, called photoreceptors, which change light signals into electrical ones.

9. How your ear work • Your ears are very important. Think what it would be like if you could not hear people talking or music or the telephone ring or your pet dog bark. We all need to take care of our ears - the topic 'Ears - looking after your ears', will tell you how you can do this.