Download All about human eyes and ears - St Ignatius RC Primary School

All about human eyes
and ears Kemi and javarn
eyes
• Eyes are organs that detect light
and convert it into electrochemical impulses in neurons.
The simplest photoreceptor cells
in conscious vision connect light.
•
Kemi and javarn
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
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).
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.
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
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.
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 lightsensitive neurons, called
photoreceptors, which change light
signals into electrical ones.
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.