FRIDAY!
Todays sense:
Vision! Possibly hearing!
Please finish your vision lab
& turn in!
Dissection survey
Make sure you bring the frog
dissection letter home, get it
Signed, and bring it back!
Sound
Have you ever noticed what you do when you hear a new sound in your
surroundings? Most people turn toward the source of the sound. This is our
bodys way of using senses to find out about things in the environment. One
of our senses picks up the first signal that something is happening, and we
then use other senses to further investigate the area we have been alerted to.
Turning toward the source of a sound lets us direct our eyes to that area. In
the dark, however, we rely completely on our hearing. How do our ears detect
sound? How do our brains interpret it?
External Ear
The folds and ridges of the pinna are not
just decorations (or for holding earrings)
- they serve to channel sound efficiently
into the ear canal and to the eardrum, or
tympanic membrane, at its end. The
pattern of folds captures sounds in a way
that helps us localize the origin of sound
in space. The ear canal carries sound to
the eardrum, and its lining produces ear
wax to keep the eardrum and canal from
drying out and to trap dirt before it gets
to the eardrum. When sound waves
vibrate the eardrum, sound energy is
transferred to the middle ear.
Middle Ear
The middle ear is a small, air-filled pocket
bounded by the eardrum on one side and
the oval window of the inner ear on the
other. This pocket is connected to the mouth
and nasal cavity by the Eustachian tube. The
Eustachian tube allows air pressure to
equalize between the outside of the eardrum
and the inside of the eardrum. The middle
ear houses the three smallest bones in the
body, the malleus, incus, and stapes
(hammer, anvil, and stirrup), which form a
chain of levers connected by joints. This
series of membranes and bones forms a
pathway that carries vibrations from the
eardrum to the inner ear.
The stapes pulls or pushes on the
membranous oval window when the
eardrum and the three bones are
vibrated by sound waves; the oval
window is a closed membrane, but ac
as the entrance to the inner ear for
sound energy.
Inner Ear
The inner ear is composed of the
cochlea and the semicircular canals. The
cochlea is a tube covered by a very thin
layer of bone and wound around a tiny
central bone into a shape that
resembles a snail. The cochlea is filled
with a special fluid, and the pushing and
pulling of the stapes on the oval window
moves the fluid in this coiled tube.
Vibrations travel into the fluid of the
upper tube of the cochlea and around
the tip of the organ into the fluid of the
lower tube.
Forming the lengthwise boundary
between the lower large tube and the
small tube is the basilar membrane. On
this membrane sit the auditory receptor
cells, or hair cells. When the membrane
moves, it stimulates the hair cells, which
send signals about sounds to the brain.
All together now
Sound waves cause the tympanic membrane
(eardrum) to vibrate. The three bones in the
ear (malleus, incus, stapes) pass these
vibrations on to the cochlea. The cochlea is a
snail-shaped, fluid-filled structure in the inner
ear. Hair cells are located on the membrane of
the cochlea. The cilia of the hair cells make
contact with another membrane called the
tectorial membrane. When the hair cells are
excited by vibration, an electrical nerve
impulse is generated in the auditory nerve.
These impulses are then sent to the brain,
which makes sense of the vibrations, resulting
in us sensing sound.
Today - 2 mini-labs about sound!
In small groups, please complete the 2 mini-labs!
One is about where we best hear, the other about how we can tell differences
between things that look very similar and serve the same function (pennies).
The first five groups will start with the first activity and get a stopwatch; the
rest will start with the penny exercise.
When youre done with your activity, please trade out the materials at the
front! Turn in when complete.
