depends on clusters of sensory cells called taste buds

-humans have 10,000 embedded in the epithelium of the tongue

-many are raised in papillae, the small bumps on the surface of the tongue

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-sweet bitter and umami (now sometimes called savoury): detected by G protein coupled receptors

-umami is a savory meat taste that is triggered by amino acids and by MSG

-salty and sour work through ion channels

cells that are sensitive to mechanical forces

-involved in skin sensations and sensing blood pressure

-the physical distortion of a mechanoreceptor leads to the opening of ion channels which leads to the generation of action potentials

very sensitive mechanoreceptors found mostly in non hairy skin.

-they adapt rapidly and provide information regarding changes in things touching the skin

hair cells

-vertebrate organs of equilibrium use hair cells to detect the position of the body with respect to gravity

-light receptor molecule

-can absorb photons of light and is composed of opsin and a light absorbing group 11-cis-retinal

-in the presence of light, 11 cis retinal changes to all trans-retinal signaling the detection of light

cells at the front of the retina

-fire action potentials

-their axons form the optic nerve

more sensitive to light

-provide black and white vision at low levels

-human retina has 125 million rods

less sensitive to light

-respond to different wavelengths of light for color vision

-provide the sharpest vision

-human retina has 6 million cones

-the fovea has only cone cells

L-type cones (absorb long wavelenght [yellow-gree])

M-type cones (absorb medium wavelength [blue -green])

S-type cones (absorb short wavelenght [blue -violet])

at the center of the macula

-responsible for sharp central vision