Sensory Mechanisms

Energy Senses--Vision

• Visual Sense—turns light energy into a neural message (transduction)– Light is reflected off objects and gathered by

the eye• Your red shirt simply reflects red wavelengths

– The color we perceive depends on intensity and light wavelength.

Energy Senses--Vision

• Light is reflected first through the CORNEA—a protective covering

• Next, light goes through the PUPIL—open space.

• This is controlled by the IRIS—colored part of the eye and the hardest working muscle in the body. The IRIS either expands or contracts letting less or more light in. This is called accommodation.

Energy Senses--Vision

• Light is focused by the LENS

Try this—work those LENS muscles!

• Light is inverted and projected onto the RETINA--a screen on the back of your eye with specialized neurons activated by different wavelengths.

• RETINA contains RODS and CONES

Energy Senses--Vision

• Rods—black and white• Cones—color and bright• Fovea—concentration of cones in the

retina• TEST IT OUT—marker test!• If enough rods or cones are activated,

then a bipolar cell fires, then a ganglion cell fires next which connects to the optic nerve.

Energy Senses--Vision

• The axons of the ganglion cells make up the optic nerve which sends messages to the LGN (lateral geniculate nucleus) of the Thalamus.

• The spot where the optic nerve leaves the eyeball is called the blind spot--do the blind spot test in the book!

• The optic nerve is divided into two parts and the spot where the nerves cross is called the optic chiasm.

Thalamus--LGNThalamus--LGN

Energy Senses--Vision

• Feature Detectors—Hubel and Weisel

• Nobel Prize for their work

• Groups of neurons in the visual cortex that respond to vertical lines, curves, motion, etc..

Energy Senses--Vision

• 2 Theories of Color Vision– Trichromatic Theory—blue, red, and green

• Combine to form spectrum• People who are color blind are missing one

or more color receptors• Some animals may be dichromatic or

monochromatic—dogs are dichromatic and are missing green!

Energy Senses--Vision

• Opponent Process Theory—– Sensory receptors come in pairs, which

explains the after image effect• Red/green• Yellow/blue• Black/White

If you tire one receptor, the other while fire!

Energy Senses—Hearing/Audition

• Sound waves are vibrations in the air and are collected by the ear.

• These waves have amplitude and frequency

• Amplitude determines loudness

• Frequency determines pitch

Energy Senses--Audition

• Sound waves are collected by the pinna or the outer ear.

• The waves travel down the ear canal or the auditory canal.

• They reach the tympanic membrane or the eardrum.

• This is where swimmer’s ear occurs.

Auditory Canal

Energy Senses--Audition

• The sound vibrations move onto the 3 little bones or ossicles—first the Hammer (malleus), next the Anvil (Incus), and last the Stirrup (Stapes).

• This is where ear infections—Otis media occur— Eustachian tube.

• The vibrations are next transmitted to the oval window which is like the tympanic membrane or eardrum.

Energy Senses--Audition

• The oval window transfers to the sound waves to the cochlea—fluid filled snail looking structure.

• The sound waves cause the fluid to move.• The floor of the cochlea is called the basilar

membrane— it is lined with hair cells which are connected to the Organ of Corti which are neurons activated by the movement of the hair cells. These impulses are sent to the brain via the auditory nerve.

Energy Senses--Audition

• Pitch Theories—– Place Theory—where it is– Frequency Theory—the rate of it

Energy Senses--Audition

• Deafness– Conduction Deafness— outer ear or middle

ear, for example-- Patient with stirrup degeneration will eventually not be able to hear

– Nerve Deafness— hair cells in the cochlea are damaged usually by loud noise

Energy Senses--Audition

• Sound localization— how do we detect where a sound is coming from? Experiment and figure it out!

• If a sound gets to one ear faster, then you know which direction it is coming from—your ears and your brain can do physics even if you can’t!

Energy Senses--Touch

• Touch is very important to our human existence—it helps you live longer!– Harry Harlow– Kangaroo Care– Free Hug Movement

Energy Senses--Touch

• Pain, pressure, warm, cold

• Brain can interpret intensity from a light touch to a hard blow

• Nerve endings are more concentrated in different parts of our body with fingertips being the most sensitive.– Sensitivity TEST

Energy Senses--Touch

• Gate-control theory— some pain messages have a higher priority

Example--itching and scratching

• Endorphins (nature’s pain killers) can swing the gate shut.

Chemical Senses

• We are not strong in this sensory area. Why?

• What animals would be better than us? Why?

• What would their brains look like?

Chemical Senses—Taste/Gustation

• Chemicals in food like salt are absorbed using saliva by taste buds which are housed in papillae.

• The more densely packed your tastebuds the more sensitive you are to that taste.

• For example, I hate bitter things like coffee and alcohol which means that I might have more bitter buds in my tongue. I love really sweet things, so maybe I don’t have that many sweet buds.

• You have sweet, salty, bitter, sour, and umami on your tongue and in your mouth.

• Make a taste map of your tongue.

Chemical Senses—Smell/Olfaction

• Flavor is caused by an sensory interaction of taste and smell

• Molecules settle into a mucous membrane in our nose called the olfactory epithelium

• There we have about 100 different olfactory receptors which are linked to our olfactory bulb.

Chemical Senses--Pheromones

• Vomeronasal Organ senses somewhat undetectable chemicals called pheromones that may influence human behavior– Babies can identify their mother’s smell right after

birth– Women who are close, tend to menstruate together– Women can smell if a man is sick and will not want to

mate– Women tend to be most attracted to the

indiscriminate smells of a man’s sweat and men tend to be most attracted to things surrounding food like pumpkin and vanilla

Chemical Senses--Olfaction

• Nerve fibers from the olfactory bulb connect to the brain at the amygdala and then to the hippocampus, part of the limbic system.

• The other senses are all processed through the thalamus before being sent on.

• This may explain why smell can be such a powerful trigger for memories.

Body Position Senses—Vestibular/Balance

• Vestibular sense tells us how our body is oriented in space.

• Three semi-circular canals in the inner ear give the brain feedback about body orientation.

• Fluid in the canals move when you move.• When the brain receives confusing messages it

causes you to get sick.• Motion sickness, sea legs, rollercoasters,

spinning on a tire swing, etc.—what else?

Body Position Senses—Kinesthetic/Movement Sense

• Receptors in our joints and muscles send messages to our brain about our limbs which helps us keep track of our body.

• You can close your eyes and touch your toes and Peyton Manning can throw to his receiver blindfolded.