A BRIEF OVERVIEW HOW HEARING WORKS

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.

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

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

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.

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.

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.

A BRIEF OVERVIEW VISION

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 The extraocular muscles Attached to the sclera and responsible for the eye’s movement

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.

ANATOMY OF THE EYE

The retina The inner area of the eye responsible for sensing light. Rod cells Senses grayscale and low-light environments Cone cells Senses color Only have 3 different cones in the human eye. Senses red, blue and green light. Macula Only contains cone cells and is responsible for seeing fine detail.

ANATOMY OF THE EYE

Rhodopsin, a chemical that converts light into an electrical signal, is contained in the retina. 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.

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. The retina is the light sensing part of the eye, and contains 2 types of photosensitive (light sensing) cells- Rods and Cones.

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

PHYSIOLOGY OF THE EYE Rods contain rhodopsin at the tips, which allow them to sense the different intensities of light Rhodopsin is made largely of a form of vitamin A Rods are responsible for our ability to see in the dark Cones contain color pigments, which allow them to sense color The inside of the retina is lined with a black substance called melanin It is used to lessen reflections, much like how a camera is lined in black for the same purpose

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.

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

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!

DISEASES OF THE EYE Macular degeneration 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

WHAT NUMBER DO YOU SEE?