Example 1: Light Sensitive Visual Receptors The typical neuron is designed to receive neurotransmitter messages from other neurons. Sensory receptors, on the other hand, are specialized to receive sensory input from the outside world. Specialized to response to light waves, a form of electromagnetic energy (Book Fig. 6.7) Book Fig. 6.5 & 6.8 (Billionths of a meter) Light waves are a small range of wavelengths (~350-750 nanometers) of electromagnetic energy. Turning Light Waves Into Electrical Messages (Transduction) Rods vs Cones Rods & cones have molecules of light sensitive photopigments (11-cis-retinal+an opsin) embedded in cell membrane. Rods rhodopsin Cones 1 of 3 iodopsins Like the G-proteins of some neurotransmitter receptors, except they receive light! Absorption of light triggers change in protein releasing second messenger inside the cell. ~120 million/eye more in periphery very sensitive (low threshold) ~100 rods share same optic nerve fiber to brain night vision (scotopic vision) ~6 million/eye most in center, especially in the fovea Need bright light to reach threshold (photopic vision) have 1-to-1 lines to brain-good for detail vision or acuity 1
Example 2 Olfactory receptors are metabotropic receptors activated by molecules of odorants. Olfactory Nerves Book Fig. 7-21 Olfactory Receptors Book Fig. 7-19 G-protein type receptors on cilia. 100 s of different types of olfactory receptors. In the rat 1% of its genome is devoted to making these receptors. In humans at least 350-400 such genes. Examples 3 and 4 Hair cells in the auditory and vestibular systems open ion channels Cilia are dendrites dangling down from your nasal membranes 2
Cross section of Cochlea Organ of Corti http://www.youtube.com/watch?v=8wgfowbbtz0 Tectorial Membrane Auditory Nerve fibers Basilar Membrane http://www.youtube.com/watch?v=8wgfowbbtz0 Basilar Membrane Friction on tips of hair cells opens mechanically-gated K+ ion channels Fluid Waves Traveling Thru Cochlea Cause Basilar Membrane Movement K+ enters hair cells causing depolarization & transmitter release! (fluid in cochlea has a different ion balance disruption of that balance can lead to hearing abnormal sounds (tinnitus)) Georg von Bekesy 1961 Nobel Prize for his research on the traveling waves in the cochlea. Where the wave peaks varies with pitch. http://www.youtube.com/watch?v=dyenmlufauw&feature=related http://www.youtube.com/watch?v=wo84kjyh5k8&feature=related The Outer, Middle & Inner Ear Semicircular Canals Sense rotation Book Fig. 7.10 (forward/back) Sense linear movement (up& down) http://www.youtube.com/watch?v=bbku0abbarg 3
Vestibular System Senses movement/position of head (and body) Uses that input to : Connect to cerebellum -help maintain balance Control eye movements when head moves http://www.youtube.com/watch?v= BbKU0AbbARg&feature=related Rocks in Your Head (in your otolith organs) Saccule Utricle Fluid imbalances in vestibular system can cause Meniere s Disease-extreme dizziness, nausea, dysequilibrium, difficulty moving and impaired hearing. Example 5 Taste Our taste system has both ionotropic and metabotropic receptors. 4
Fungiform Papillae on the front of tongue) these don t have taste buds so center of your tongue can t taste Tste Buds Along Sides of Papilla Tastes Buds on Sides of Papillae (Other papillae may have a taste bud on the top) Taste Bud Taste Bud Many receptors in a bud Specialized skin cells replaced every 10-14 days With cilia But have excitable membranes and release transmitter like neurons Receptors sensitive to salty, sour, sweet, bitter & umami Salty opens Na+ channels, The hydrogen in acid (sour) closes normally open K+ channels & opens Na+ channels in sour receptors. The others activate G proteins (like metabotropic receptors) Certain chemicals can alter one type of receptor changing your experience of that taste 5