Your Senses • A loud “boom!” is heard across the street. You turn quickly and duck slightly. Your senses are in action! The unexpected noise produces impulses in sensory receptors in your ears. These impulses travel to your brain, where they create a sense of awareness called a sensation. The sensory receptors in your eyes send impulses to your brain, which recognizes the sound as being a car crash.
The Four Senses • Sight • Touch • Hearing • Taste
The Human Eye Your Sense of Sight!
Cornea • The cornea is a thin, clear membrane that covers the front of the eye • It protects the eye while allowing light to enter
Pupil • Light from the front of the eye enters through an opening called a pupil
Iris • The pupil is surrounded by the iris, a ring of muscle • The iris controls the amount of light that enters the eye and gives the eye its color • In bright light, the iris contracts, which makes the pupil smaller in diameter • In dim light, the iris relaxes, which dilates the pupil to let in more light
Lens • The oval-shaped piece of clear, curved material behind the iris. • The lens refracts, or bends, the light rays and focuses the image, before sending it off to the retina in the back of the eye • Muscles in the eye change the shape of the lens in order to focus light onto the retina • When you look at objects that are close to the eye, the lens becomes more curved. It becomes flatter when you look at distant objects
Nearsightedness • If the lens focuses light in front of the retina, this results in nearsightedness • Cause: the cornea’s curvature is too steep for the shape of the eye, causing distant objects to appear blurry
Farsightedness • Here the person can see distant objects better than close up objects • It results from the lens focusing light behind the retina • Children with mild to moderate cases of farsightedness can see distances far and near without correction because the muscles and lens within the eye can overcome the farsightedness
To correct near or farsightedness you need to change the way the light is bent using contacts, eye glasses or surgery
Focusing the Light • Light travels in a straight line until it passes through the cornea and the lens.
Retina • A layer of light-sensitive cells, called photoreceptors, found in the back of the eye • They respond to light energy • These photoreceptors create electrical impulses • The brain perceives these impulses as light
Two Types of Photoreceptors ROD CELLS CONE CELLS Retinal cells that are very sensitive to bright light Impulses from cones allow you to see detail and color Impulse travels along an axon • Retinal cells that are sensitive to dim light • Important in night vision • Impulses from rod cells are interpreted as black and white images • Impulse travels along an axon
FOVEA • Located in the back of the eye • It is responsible for sharp, central vision necessary in reading, watching television, driving, or in any other activity that requires seeing detail
Optic Nerve The impulse leaves the back of each eye through an optic nerve. The optic nerve carries the impulses to your brain, where the impulses are interpreted
What does 20/20 vision mean? • 20/20 vision means that if you stand 20 feet away from an eye chart, you can see what the human eye is supposed to see at 20 feet away • 20/40 vision means that you standing 20 feet away from the chart, you see what a normal human can see when standing 40 feet away • 20/ 200 is the cut off for legal blindness
The Sense of Hearing (auditory processing) The human ear is the most complex sensory system in the human body. Vision and smell are extraordinary, too, but they do not match the complexity of turning waves of sound pressure from air molecules banging against the ear drum in to the neural signals that get sent to the brain and interpreted as sound.
What is a Sound wave? It is just a wave of sound. Music is just a bunch of sound waves, arranged in a nice pattern. A sound wave is comprised of the changes in tone of air pressure through compression and refraction.
The Outer Ear Sounds are pressure changes in the air that travel in waves. The outer ear collects these waves which travel down your ear canal to enter the middle ear • The ear canal channels sound waves to your ear drum, a thin, sensitive membrane stretched tightly over your middle ear • The waves cause your ear drum to vibrate
Middle Ear The middle ear lies between the tympanic membrane (ear drum) and the inner ear Like the outer ear, the middle ear space is filled with air and contains three small bones called the ossicles: the hammer (malleus), anvil (incus), and the stirrup (stapes) These bones amplify the pressure of waves from the vibrating tympanic membrane which provides an efficient transfer of sound energy to the fluid filled inner ear
The Inner Ear 1.The stirrup touches a liquid filled sac and the vibrations are passed on to the inner ear’s cochlea 2.The hollow channels of the inner ear are filled with fluid The cochlea, semi-circular canals, and the auditory nerve make up the inner ear
Cochlea A snail-shaped organ of the inner ear filled with fluid Inside the cochlea there are hundreds of special hair-like cells attached to nerve fibers, which can transmit information to the brain by changing sound waves to nerve impulses The brain processes the sounds we hear and lets us distinguish between different types of sound
Auditory Nerve The waves are turned into a nerve impulse in the cochlea and sent to the brain for interpretation via the auditory nerve.
Exposure to too much noise can damage ear cells and lead to hearing loss. Hair cells in the cochlea do not replace themselves naturally, so take care of the healthy ones you have ! Damaged ear cells in the cochlea Normal ear cells in the cochlea
The Inner Ear and Your Balance • The semi-circular canals in the inner ear help you maintain your balance (vestibular system) • Also fluid filled with nerve cells to send messages to the brain • The vestibular system works closely with the visual cortex and skeletal muscles to help maintain balance
The Eustachian Tube • Tube that connects your middle to your throat • The tube allows air to pass between the tympanic cavity and the outside of the ear by way of the throat and mouth • It is important to maintain equal pressure on both sides of the ear drum, which is important for normal hearing • For example, if a person goes from a high altitude to a low one pressure on the outside of the ear gets greater and greater, pushing the eardrum inward, out of its normal position, and hearing may be inpaired