unit 8

Why is it that many intelligent scientists deny the intelligent design of the ear and eye?

In Psalm 94:9, because people are afraid of a God that can hear their thoughts and see their thoughts is scary. 

 How does sound travel through the air to get to our ears?

Air compresses as the sound is made and the compressed air travels in waves to the 

hearer. 

 What are the three basic parts of the ear and how is sound conducted in each?

Outer ear (air), middle ear (bone), inner ear (liquid).

Why is a liquid (mainly water) necessary in the inner ear?

The cells in the inner ear would dry out and die in air-so they need to be under a specific liquid with the right salt concentration and pH. 

How are wax and dead skin cells removed from the outer ear canal?

The cells lining the outer ear canal grow sideways, carrying wax and particles out. 

What is the function of the auricle of the ear?

The auricle collects sound and helps us tell where the sound is coming from. 

What are the three bones of the middle ear?

Hammer (malleus); anvil (incus); stirrup (stapes). 

What is the function of the small bones in the middle ear?

They restore the energy that would otherwise be lost in transmitting the sound waves from air in the outer ear to water in the inner ear. 

Why is it we often don't recognize our own voice when we are recorded?

We hear our voice through the air and through the bones of our skull when we speak. 

 How much does the eardrum have to move for us to hear a quiet sound?

Less than the diameter of a hydrogen atom

What is the vistibulocochlear system?

It is made of the cochlea (used for hearing) and semicircular canals (sense of position in space)

What is the function of the semicircular canals and how is it accomplished?

The semicircular canals are used to help us sense our movement in space. The liquid in the canals move as we move a sail-like structure in the ampulla that transmits a signal to our brain telling it which way we're moving. 

 What is the function of the saccule of the inner ear and how does it work?

Tiny stones sit on the floor of the saccule and the nerves in the floor sense the movement of the stones when the body moves thus the brain can tell whether a person is upright or upside down. 

 What does the word cochlea mean and why is it appropriate?

Cochlea means snail shell and this is appropriate because the cochlea is snail-shaped. 

What is the organ of Corti and how is it arranged in the cochlea?

The organ of Corti converts the mechanical movements of sound into electrical signals the brain perceives as sound. It spirals around inside the cochlea. 

What are the functions of the oval window and the round window of the cochlea?

The oval window receives the compression of the stirrup increasing the fluid pressure in cochlea; the round window relieves the pressure created by the stirrup pushing in at the oval window

How does the organ of Corti function to produce electrical signals from sound?

As the organ of Corti moves up and down, the tectorial membrane causes a shearing force on the hairs of the hair cells. This causes ion channels to open on the tips of the hairs which generate electrical signals the brain can interpret as sound.

What is the structure and function of the tectorial membrane?

The tectorial membrane is a flat membrane over the hair cells in the organ of Corti that causes the hairs to bend which creates electrical signals that the brain perceives as sound. 

 How does loud sound damage our hearing? 

The hair cells tear out of the tectorial membrane. 

How does wiggling the "hairs" of the hair cells produce electrical signals that our brain can interpret as sound?

The hairs have a hole that allows sodium ions in and out; a trapdoor covers the hole; a spring is attached to the trapdoor; the spring controls the opening and closing of the trapdoor; the spring is attached to a bracket on the next longer hair; the bracket moves up and down. The ions entering the hair send signals to the brain that interprets the signals as sound. 

How high pitched a sound can young people normally hear?

20,000 cycles/second. 

Why is it occasionally necessary to put tubes through the eardrum?

Tubes help to equalize the pressure on both sides of the ear drum if the Eustachian canal is blocked. 

Why is it important that the air pressure be the same on both sides of the eardrum?

If the air pressure isn't the same, the ear drum will be pulled one way or the other producing pain and interfering with the perception of sound.  

What structure of the ear serves to equalize the pressure on both sides of the eardrum?

Eustachian tube. 

25. How does yawning often clear the pressure in our ears?

Yawning kinks the Eustachian tube, causing whatever is clogging the tube to move out of the way. 

 How widespread in the animal kingdom are "camera" eyes similar to what we see in humans? 

All vertebrates have such an eye. 

How does the cornea differ from the sclera (whites) of the eye?  

The cornea is a clear window in the skin; the sclera is opaque and has blood vessels. 

The cornea and lens have the same embryonic origin as what other organ we have studied?

The cornea and lens are derived from embryonic skin. 

The eye and optic tract (excluding the lens and cornea) are actually part of what structure of the body?

Brain (diencephalon). 

What is the function of the iris diaphragm?

Changes the diameter of the pupil adjusting for the brightness of light.

Changes the diameter of the pupil adjusting for the brightness of light.

The apple of the eye. 

The expression "you are the apple of my eye" comes from the Bible, but what is the original expression and what does it mean?

"I will protect you like the apple of my eye." It means that God will protect His children in the same way people protect their eye-instantly and reflexively and to the death. 

Why is our blink reflex so much faster than the knee-jerk reflex?

Since the eye is part of the brain, the signal doesn't have to travel that far, so the blink reflex is the fastest in the body. 

What is the function of the blink reflex and what causes it to occur?

The blink reflex protects the eye. It happens when something comes near the eye. 

What simple test can be done in an emergency to see if an accident victim might be dead?  

Touch the cornea over the pupil to see if the blink reflex still functions. 

What is the difference between the orbits of the human eye and the orbits of all apes and monkeys?

Apes and monkeys have a flat forehead and the bone comes right up to the outer edge of the orbit, so you can't see into the orbit, as you can with human orbits. 

 What are the four rectus muscles of the eye and what is their function?

The medial and lateral recti move the eyeball left and right; the superior and inferior recti move the eye up and down. 

What is the function of each of the two oblique muscles of the eye?

The oblique muscles rotate the eyeball like a doorknob keeping our horizon level as we tilt our head. 

 How does the superior oblique muscle of the eye differ in structure from the inferior oblique?

 What are the two different axes of the eye and why are they different?

Optical axis is straight forward; anatomical axis is at an angle because of the way the orbits slope in on the outside. 

How is the control of our oblique muscles different from the control of our rectus muscles?

We have control over the rectus muscles but do not have control over the oblique muscles-they are controlled automatically. 

What purpose is served by the rotation of the eye with the oblique muscles?

They keep the horizon level when the head is tilted.

What happens to our vision if all twelve muscles in our two eyes do not work in perfect coordination?

You would see double. 

Why is the muscular action of looking up or down so much more complicated than looking left and right?

To move the eye up and down, three different muscles are involved, with three different nerves. 

The embryonic development of the eye is another example of the "pushed in balloon" principle. What is formed from the inner layer, and what is formed from the outer layer?

The inner layer forms the retina; the outer layer is the sclera/choroid. 

How does the lens of the eye develop?

The lens buds off a layer of embryonic skin. At first it is a hollow ball, but then the cells on the rear of the ball become greatly thickened filling in the empty space. 

What are the two lenses of the eye and which of the two bends light the most?  

The cornea bends the light four times more than the actual lens. 

How does the lens focus and how does this differ from the focusing mechanism of a camera?

The lens focuses by changing its shape. Camera lenses move in and out. 

 What is the natural shape of the lens and would this be focused up close or at a distance?

Spherical, focused close. 

How does the eye minimize spherical aberration when it is close-focused?

The eye closes the iris diaphragm to make it smaller, only using the center of the lens 

 Why does reading or other close work often require more light than when our eyes are focused on a 

distant object?

Because the iris is more closed with close work, it requires more light to see. 

How does the lens survive without blood vessels?

 It gets its oxygen from the air. 

What is the function of the pigment in the iris?

The black pigment (melanin) in the back of the iris helps to prevent too much light from entering the eye. 

What are lens fibers (prisms)?

Lens fibers are long cells that go from the front of the lens to the back. 

Why does the human eye often fail to focus as we get older?

The lens gets harder, losing its ability to focus well, and often becomes more yellow and develops cataracts.

How does the anterior lens epithelium differ from the posterior lens epithelium?

The anterior lens cells are cuboidal in shape and can divide. The posterior cells of the lens become greatly elongated to form lens prisms. 

 What is the protein that fills the lens?

Crystalline. 

 What keeps the lens prisms in a precise arrangement?  

Thousands of peg-and-socket joints lock the lens prisms in place. 

What is the difference between fiber tracks and nerves?

Fiber tracks, in the central nervous system, don't heal when cut, unlike nerves. 

How are the muscles of the iris arranged?

Ring-like sphincter muscles close the iris opening. Radially oriented muscles open the iris. 

Where is the iris diaphragm located in relationship to the cornea and lens?

The iris diaphragm is located between the cornea and lens. 

What muscle focuses the eye and how is it attached to the lens?

Muscles of the ciliary body attach by means of tiny tubular fibers to the capsule of the lens. 

What is the large gelatinous ball that fills the eyeball behind the lens and how was it formed?

The vitreous body formed from very loose connective tissue when the hollow ball from the brain that formed the eye got pushed in.

What is the watery liquid in front of the lens, how is it produced, and what is its function?  

Aqueous humor is produced by the ciliary processes. It is continuously produced and maintains the specific shape of the eye. 

Why must the interior of the eyeball be kept under constant pressure?

So that it stays just the right physical dimensions for optical reasons. 

Why do evolutionists think the eye is poorly designed?

They claim that the retina is facing upside down. 

Give several reasons why the seemingly "upside down" nature of the retina is advantageous.

The pigment epithelium traps the photons so that they don't bounce off the rods and cones more than once. The photoreceptor cells need a rich blood supply which is near the back. 

How does the Müller cell seem to solve the problem of the "upside down" retina?

The Muller cell goes from top to bottom in the retina. It is a living fiber optic. 

We can only see things sharply with what small part of the retina, and why is this a good design for us?  

Fovea centralis; our minds are designed to concentrate on one thing at a time, so the fovea allows us to focus on one area or thing at a time. 

About 5% of the blood vessels supplying the retina are on top of the retina and right in our path of vision. How are we able to avoid seeing these blood vessels in our vision?

 The brain has a rule, "if it doesn't move, ignore it." Because the blood vessels don't move in relation to the retina, the brain ignores them. 

What experiment can you do to actually see your own retinal vessels and why does this work?

With one eye, look at a brightly lit blank white surface through a small hole in a card. Close the other eye. Move the card from side to side quickly in front of the open eye. This causes the shadow of the blood vessels on the front of our retina to move, thus making them visible. 

 Where are the tear glands (lachrymal glands) located?

They are located above the eye ball near the outer rim of the orbits. 

How is the tear fluid removed from the surface of the eye?

There are small holes (puncta) and pumps in the eyelids near the nose that remove the fluid. 

 Why must the tear fluid layer be maintained at a precise thickness?

Tear fluid is optically part of the lens. 

What are the most important functions of tear fluid?

It removes debris, provides antimicrobial help, and covers the rough surface of the cornea making it smooth so it doesn't scatter light. 

What keeps the tear fluid on the eye?

Oil glands on the edges of the lids provide a hydrophobic barrier that keeps the fluid in place. 

Why do we get bleary-eyed and the sniffles when we cry?

The eyelid pumps the water into the nose, causing the sniffles. When too much fluid is produced and the pumps can't keep up, and a thicker layer of tear fluid changes the focus of the eye causing bleary vision.

What makes people nearsighted or farsighted?

The shape of the eyeball-if it's longer front to back, it causes nearsightedness; if the eyeball is flatter front to back, it causes farsightedness. 

How does a detached retina relate to the embryological development of the eye?

The space created between the retina and the choroid can cause the retina to detach if there is a jarring or some type of disease. The space between the retina and choroid resembles the embryonic condition.