Biol 224 Theme 12

• -carboxylate anions and salts of the non-essential AA glutamic acid
• -most abundant excitatory neurotransmitter in the vertebrate nervous system
• -key role in learning and memory
• -stored in chemical vesicles in the chemical synapses
• -nerve impulses stimulate release from pre-synaptic cell and bind to post synaptic glutamate receptors

• -sodium-calcium channel that makes the cell voltage dependent
• -activation results in voltage dependent flow of Na⁺ and Ca²⁺ ions into the cell and K⁺ out of the cell
• -Ca²⁺ flow through the receptor is thought to be critical to synaptic plasticity(cellular mechanism for learning and memory)

• -found in vertebrates, squid, octopus, some snails and annelids 
• -light is transmitted through the pupil to the retina located at the back of the eye
• -light is captured by photorecepetors

• -specialized cells located in the retina
• -have phototransduction capability (convert visible electromagnetic radiation into electrical signals)
• -differ from other sensory receptor cells because their cell membrane potential is slightly depolarized when at rest

-strong outer white sheath around eye

• -continuous with sclera but thin and clear 
• -has two cavities (anterior, posterior)

-holds aqueous humor

• -holds thick vitreous humor
• -maintains eye shape

-pigmented smooth muscle controlling size of pupil

-fundamental unit of electromagnetic radiation with the properties of both a particle and a wave

• Deepest-rods and cones-up against the sclera 
• Intermediate-Bipolar Cells-interneurons that synapse with photoreceptors and ganglion cells(transparent)
• Shallowest(closest to front of eye)-Ganglion Cells-send axons out of eye into optic nerve(transparent)

• -interneurons in the retina
• -responsible for 70% of input to retinal ganglion cells

• -both transparent cells
• -responsible for other 30% of input to retinal ganglia and are regulated by amacrine cells

• -sensitive to low intensity light
• -used mostly at night
• -do not discriminate color
• -vitamin A increases sensitivity to light at night

• -require more light for stimulation
• -fewer cones than rods
• -detect color(in humans)
• -outer segment contains pigment
• -inner segment contains nucleus and other organelles 
• -synaptic terminal filled with neurotransmitter vesicles(no axons)

• -retinal and opsin
• -compounds bound together 
• -in humans cone pigments composed of retinal, plus 1 of 3 opsins
• -each different type of opsin detects a different wavelength(red, green or blue)
• -birds have 5 different opsins

-chromophore vitamin A derivative that absorbs energy from light

• -G protein coupled receptors that convert light into metabolic energy
• -enable vision in low light 
• -rhodopsin in rods
• -photopsins in cones
• -convert a photon of light into an electrochemical signal, which changes membrane permeability to ions
• -plasma membrane protein

• -In the absence of light and under the influence of glutamate membrane potential is
• in a slightly depolarized state (closer to zero than we would expect[normal value of -70mV])
• -Na channel open, K closed
• -results in continuous release of glutamate
• -interpreted as absorbance of light
• -get 11-cis-retinal

• -In the presence of light and in the absence of glutamate membrane potential is in
• a hyperpolarized state (farther from zero than we would expect)
• -Na channel closed, K open
• -glutamate release is stopped
• -interpreted as visual image
• -get all trans-retinal

• -seven transmembrane receptor covalently bound to retinal
• -assosiated with three different G proteins known as transducins (G_tα, G_tβ, G_tγ)
• -extremely sensitive to low light
• -enable vision in low light
• -responsible for first events in perception of light

• -all 11-cis-retinal are converted to all-trans-retinal
• -activates G-transducin 
• -G-Transducin then activates phosphodiesterase 
• -phosphodiesterase convert cGMP into GMP which cause cGMP bound to Na channels(keeping them open) to dissociate 
• -closes Na channels and results in hyperpolarization

• -constant glutamate release stimulates the conversion of GTP to cGMP(with release of two P_i)
• -cGMP binds to Na receptors which open and activate them, resulting in the membranes constant slightly depolarized state in darkness

• -absorb 0 blue wavelengths
• -can absorb up to 31% of green wavelengths
• -up to 83% of yellow wavelengths

• -absorb 0% of blue wavelengths
• -67%of green wavelengths
• -83% of yellow wavelengths

• -100% of blue wavelengths
• -36% of green wavelengths
• -0% of yellow wavelengths