1. How Hearing works
A brief overview

2. What is sound?
If a tree falls in the woods and there is nobody, or nothing to hear it, does it make a sound?
The answer is no - but that is only because sound is an interpretation of vibrations.
If there is nothing to interpret those vibrations, there cannot be sound.

3. What is sound? Sound is caused by vibrating particles.
If there are no particles to vibrate, like in space, there can be no sound.
What type of energy would vibrating or moving particles be?
Kinetic or Potential

4. What is hearing?
When a vibration is made, the brain can interpret that as being a sound.
It must have an amplitude (loudness) large enough to cause the mechanisms in the ear to react
It must also be within the frequencies (pitch) of sound that our ears and brains can react to and interpret

5. Hearing Physiology
There are several parts of the ear and the brain that are involved in hearing.
The outer ear (pinna)
Dish shaped to help gather sounds and funnel them into the ear canal
The curves and ridges in your ear allow you to determine the direction sound is coming from
The ear drum (tympanic membrane)
A thin membrane of tissue that vibrates, sending the vibrations further into the ear

7. Hearing Physiology The Middle Ear (ossicles)
Comprised of three separate bones (the smallest bones in the human body!) that receive the vibrations from the eardrum and amplify the signal
The eardrum vibrates and causes the malleus (hammer) to hit the incus (anvil). That causes the stapes (stirrup) to move in and out, transferring the vibrations further into the ear.

9. Hearing physiology The Cochlea
Vibrations from the stapes cause the vibrations to further amplify inside this pressurized, fluid-filled tube.
Thousands of specially tuned fibers are activated by resonant frequencies and pass the information on.

11. Hearing physiology Inner Ear
The organ of corti contains hair cells that are activated when the fibers in the cochlea are activated by resonant frequencies.
The hair cells send electrical impulses to the cochlear nerve, and into the brain.
In the brain, the electrical impulses are translated into sounds- pitch is determined by what hair cells are activated, and volume is determined by how many cells are activated.

13. Hearing Crash Course

14. Vision
A brief overview

15. Anatomy of the Eye The sclera
Rigid top layer of the eye (the white part)
Responsible for keeping the eye’s shape
The cornea is part of the sclera, and is the top lens responsible for focusing light

16. Anatomy of the Eye The extraocular muscles
A mucous membrane covers the inside of the eyelid and the top of the sclera. This membrane is called conjunctiva.
The eye is housed in the orbital cavity in the skull. The eye is held in the socket by the muscles that are also used for movement of the eye.
The extraocular muscles
Attached to the sclera and responsible for the eye’s movement

17. Anatomy of the eye

18. Anatomy of the eye The choroid
Second layer of the eye, containing the vessels that supply the eye with blood.
Also contains the iris, which is the diaphragm that gets larger or smaller to let more or less light in to the pupil.
Contains the ciliary body, which is the muscles that are attached to the lens.
The ciliary body will contact or relax to control the size of the lens.

19. Anatomy of the Eye

20. Physiology of the eye
When light enters the eye, it passes through the cornea, lens, two layers of viscous liquids and finally reaches the retina.
The cornea, lens and layers of liquid are incrementally focusing and fine-tuning the image entering our eye.

21. Anatomy of the eye
Rhodopsin, a chemical that converts light into an electrical signal, is contained in the retina.
The retina
The inner area of the eye responsible for sensing light.

22. Anatomy of the eye

23. Physiology of the eye Rods sense the light and dark
We have 2 types of rod cells
Shadows, gray scale, shading, perception of depth are all results of the rods
Cones sense the color
We have 3 different cone cells
Senses Red, Green and Blue light
Deficiencies in the cones or their function can result in differing degrees of colorblindness

25. Physiology of the eye
The central area of the retina is called the macula, which contains only cones. This area is responsible for sharp, contrasting details in color.
When light hits the rhodopsin, it causes a series of physical and chemical changes. We call this “bleaching.”
This is why sometimes your vision is dark when you go from a dark place to a light place quickly. It takes about a second for all of these reactions to take place.

26. Physiology of the eye
When the rods and cones are activated, they send an electrical signal to the sensory cortex in the brain
Inside the sensory cortex, the signal is translated into an image
We have gotten pretty good at reading brain waves and patterns, so good that we can read a brain wave and nearly reconstruct the image a person is looking at!

27. Physiology of the eye The cones of the eye sense color
When light hits the cones, they vibrate with the frequency of light
Different cones have different sensitivities to light, and will activate depending on the color of light entering the eye

28. Diseases of the eye Macular degeneration Glaucoma Conjunctivitis
The slow breaking down of the macula. Causes blindness
Glaucoma
The inability for your eye to drain fluid. Causes pressure to build in the eye balls.
Conjunctivitis
An bacterial infection of the conjunctiva (mucous membrane) of the eye
Colorblindness
A genetic deficiency, located on the X chromosome, that causes one or more cones to be either absent or not function

29. What number do you see?

30. What number do you see?

31. What number do you see?

32. Vision Crash Course