The SensesCh 36.2

The 5 Major Senses• Smell• Taste• Sight• Touch• Hearing

• How our brain/body takes in stimulus from the environment

• How we learn about the world

Smell• Breathing air through your

nose pulls in particulate matter (chemicals floating in the air)

• Olfactory:– collection of receptors in top

of the nose– Chemicals bind to receptors,

and signals are sent to the brain along a cranial nerve

– Brain interprets good and bad smells based on what chemicals are detected

• Why have a sense of smell?

Good Smells vs. Bad Smells• Things smell good because

they are good for the body or the mind:Meat- smell of fats and proteinsFlowers- smell triggers release of hormones that relax usFruits- smell of sugars and vitamins

• Things smell bad because they might kill us:Waste material- contain bacteria; no usefulmaterialRotten Food- contain bacteria; bad for digestion

Taste• Smell and taste are strongly

linked• Taste buds:

- receptors for each of the 5 tastes:

salty, sweet, sour, bitter, umami- Chemical reacts with receptor and signals are sent to the brain

Why do things taste good? Why do they taste bad?

Sight• Sight is detecting the photons

of light bouncing of objects• Pupil: opening into the eye• Lens: focuses the light to

clear the image; made of clear cells

• Retina: special part of the eye that reacts to photons

Images passing through the lens are flipped and our brain learns to flip them back

Rods and Cones• Rod cells:

detect low levels of light (black and white)• Cone cells:

detect high levels of light (color)

S- detect blue lightM- detect green lightL- detect red light

Overlapping signals from cones create the other colors

Hearing• Sound travels as waves

through media (air, water, etc…)

• Eardrum:– Vibrates to changing pressure

from sound waves– Vibrations travel through the

body’s smallest bones(Malleus, Incus, and Stapes)

• Cochlea:– Vibrations from travel into fluid– Fluid activates hire-like receptors

which send impulses to the brain– Ear as a hair for different

frequencies

Hearing (Balance)• Cochlea as 3 semicircular

canals filled with fluid and motion receptors (hair-like)

• Movement in the fluid triggers impulses that tell the brain direction and orientation

• Small Ca+ stones inside also push down on the hairs

Why?-Feel which way is up/down

Touch• A collection of different

receptors:– Temperature– Pressure– Pain

• Different parts of the body have higher concentration of touch sensors– Eyelids, fingers, feet, tongue,

etc…• Some receptors fire faster

than others:– You can feel the texture of an

object before its temperature

Extra Senses• Echolocation: use

sound waves to find objects

• Infrared vision: can see heat of an object

• UV vision: see UV signals

• Electroreception: can sense electric fields

• Magnetoreception: can sense magnetic fields