All animals receive information about chemical stimuli through chemoreceptors: responsible for smell and taste and for monitoring internal environmental factors such as
CO2 in the blood.
Olfaction, the sense of smell, depends on chemoreceptors//odorant molecule binds to its receptor on an olfactory neuron, a G protein is activated;causes elevated levels of a second messenger, which binds to cation proteins that
transport sodium ions. This results in the sensory neuron firing action potentials.
Gustation, the sense of taste, depends on clusters of sensory cells called taste buds, which are not neurons. Taste buds have pores, pore helps to expose the microvilli of the sensory cells,Receptor proteins in the microvilli bind specific molecules.
• This binding causes the release of neurotransmitters to the dendrites of associated sensory neurons.
Mechanoreceptors are cells that respond to mechanical forces.Merkel’s discs-->Merkel’s discs/Meissner’s corpuscles are very sensitive mechanoreceptors found on the surface of (primarily nonhairy)
skin./
Other mechanoreceptors are found deeper in the skin : 1.Ruffini endings-low frequencies
2.• Pacinian corpuscles-Higher frequencies
Mechanoreceptors in skeletal muscle are called muscle spindles ; stretch receptors embedded in connective tissues of skeletal muscle. Golgi tendon organ is another type of mechanoreceptor cell found in tendons and ligaments- it prevents muscle damage
Auditory systems use mechanoreceptors to convert pressure waves into receptor potentials.
Pinnae collect sound waves direct them into the auditory canal, which leads to the middle ear and the
inner ear. - The tympanic membrane vibrates -ossicles transfer the vibrations of the
eardrum to the oval window. - Movements of the oval window result in pressure
changes in the inner ear. - pressure changes are transduced into action potentials
hair cell has a set of stereocilia, which are really microvilli.
Rhodopsin molecules can absorb photons of light and undergo shape changes--consist of a protein called opsin and an associated nonprotein group, 11-cis-retinal.
When retinal absorbs a photon, it changes into a different isomer called all-trans-retinal. This changes
strains the bonds between retinal and opsin, changing the conformation of opsin. This change signals the
-
When light is absorbed by rhodopsin, it becomes photoexcited and activates a G protein called transducin.// In the dark, cGMP keeps sodium channels open; in
light, GMP levels rise and channels close (i.e., the cell hyperpolarizes).
retina-process visual information from the photoreceptors and produce an
output signal that is transmitted via the optic nerve. & Light that is not absorbed by rhodopsin is absorbed by a black pigment layer behind the retina & photoreceptors: cones and rods (more rods)& he fovea of the retina is the area with the densest concentration of photoreceptors. &we depend mostly on rods for night vision. & blind spot-there are no photoreceptors where blood vessels and bundles of axons going to the brain pass
through the back of the eye. & cells at the front of the retina are called ganglion cells. & • They fire action potentials, and their axons form the optic nerve & Between the ganglion cells and photoreceptors are bipolar cells- they do not fire action potential just like rods ans cones & Release of neurotransmitter from bipolar cells causes ganglion cells to fire action potentials & Amacrine cells connect neighboring pairs of bipolar cells and ganglion cells.