Sensory Processes Sensory Systems

Transcription

1 9 th Lecture (9b) Wed 04 Feb 2009 Vertebrate Physiology ECOL 437 (MCB/VetSci 437) Univ. of Arizona, spring 2009 Kevin Bonine & Kevin Oh Sensory Processes Sensory Systems Ch13 in your text Sensory Processing Chapter Sensing the Environment Sensory Reception -Environment -Within body Integrated and Processed by NS Sensory Receptors send signals to brain so perceive sensations Sensory Receptor cells often organized Properties of Receptor Cells Sensory Modality Modalities include: vision, hearing, touch, taste, smell, chemical, thermal, proprioceptors Qualities within each modality e.g., Red or yellow; High or low-pitched 7-1 Randall et al into organs 7-1 Randall et al Randall et al etc

2 Mechanisms and Molecules Enzymatic Cascade to amplify Threshold of Detection e.g., 1 photon or hair cell movement of H diam. Sour (ph; H+) and salt (Na+) move directly no amplification To measure quality need many receptors grouped into organ; different tunage (e.g, wavelength of light or frequency of sound) 9 10 Enhancing Sensitivity - Efferent Control e.g., stretch receptors in muscle control length so can perceive stretch -Feedback Inhibition Auto (helps keep in dynamic range) vs. Lateral Properties of Receptor Cells Receptor Cells -Specialized -Selective for energy type and modality -either is a neuron or -Synapses immediately on a neuron (1 afferent neuron to CNS) 7-2 Randall et al Stimulus modifies conformation of receptor 12 Properties of Receptor Cells Transduction= Stimulus energy converted to nerve impulse Example Mechanoreceptors (touch) 1- Proteins respond to membrane distortion 2- Ion channels opened directly or indirectly 3- Current flows across membrane (often Na + ) 4-Vm changes (aka receptor potential changes) 5- Signal often amplified 6- AP sent or NT released causing AP Mechanisms and Molecules Sensory Adaptation - orders of magnitude different stimulus strength - often controlled via Ca++ availability -local controlor feedback from CNS Type of stimulus received depends on where in CNS (~brain) AP arrives (LABELED LINES). Rub eyes and see light! Intensity signalled by frequency of APs, but

3 Stimulus Intensity and Dynamic Range From lowest threshold, to upper limit imposed by refractory period: Note log axis Dynamic Range Shifting range of appropriate AP frequency Detectable light intensity varies over 9 orders magnitude Detectable sound intensity varies over 12 orders magnitude Range Fractionation - Function of sensory adaptation -Also recruitreceptors with different tunage or sensitivity (e.g., rods and cones in eye) 7-7 Randall et al Sensory Adaptation Possibilities: -Accommodation 1. Receptor cell mechanical properties may filter 2. Receptor cells may be depleted (e.g., visual pigments; need to be regenerated) 3. Enzyme cascade (during amplification) may be inhibited by (intermediate) product 4. Electrical properties change b/c [Ca ++ ] 5. Accommodation of spike initiating zone 6. Sensory adaptation in downstream neurons (CNS) Randall et al Enhancing Sensitivity - Spontaneous basal activity 7-12 Randall et al Tonic vs. Phasic receptors fast-adapting - Constant rate of APs - Directionality if or AP frequency Slow-adapting 5-19 Randall et al

4 Sensory Adaptation Pacinian Corpuscle - Touch Example Hill et al. 2004, Fig Movement of Oil between layers is what triggers APs Signal changes in pressure, not steady pressure 7-10 Randall et al Mechanoreception - Several Types: 1 Undifferentiated nerve endings in connective tissue 2 More specialized e.g., Pacinian Corpuscle e.g., Muscle stretch receptors 3 hairlike sensory receptors Star-Nosed Mole ( # neurons, subtlety) (receptor field size?) 23 Activated by stretch or distortion of plasma membrane 24 Mechanoreception 7-24 Randall et al Whiskering - Hair Cells in cupula one Kinocilium (or none) many stereocilia e.g., -lateral line system in fish and amphibians (motion/electricity) -hearing and equilibrium Are these the hair cells we are talking about? Randall et al

5 Hearing and Equilibrium 7-26 Randall et al Both are functions of the ear Equilibrium: 2 chambers Sacculus Utriculus w/ 3 semicircular canals in three perpendicular planes These three planes can detect movement in any direction as endolymph moves and cilia are bent 7-27 Randall et al Sacculus and Utriculus also contain patches of hair cells that detect position relative to gravity via otoliths Hearing (in a nutshell 1) - external ear funnels sound -sound is oscillating air pressure Silverthorn funneled to tympanic membrane (eardrum) - auditory ossicles transfer sound across air-fluid boundary to oval window (another membrane) -[auditory ossicles are malleus, incus, stapes] - tympanum area 19x oval window area = amplification Hearing (in a nutshell 2) -cochlea is fluid filled chamber on other side of oval window and it contains hair cells - hair cells in cochlea bathed in endolymph (high in K + ) - when cilia bent, ion channels for K + open and cell depolarizes, causing transduction - different hair cells (and location in cochlea) for different frequencies of sound 7-27 Randall et al

6 Basilar membrane Mammalian Cochlea Hill et al. 2004, Fig 13.29& Barn Owl Type of sensation received depends on where in CNS (~brain) AP arrives (LABELED LINES). Rub eyes and see light! Konishi and Knudsen (1977) identified an area in the midbrain containing cells called space-specific neurons that fired only when sounds were presented in a particular location. Astonishingly, the cells were organized in a precise topographic array, similar to maps of cells in the visual cortex of the brain. Aggregates of space-specific neurons, corresponding to the precise vertical and horizontal coordinates of the speaker, fired when a tone was played at that location. 35 Synesthesia: e.g., smell colors 37 Mechanisms and Molecules Lots of Evolutionarily Conserved Elements e.g., 7 transmembrane helices and G-protein intermediate 7-5 Randall et al e.g., Vision, olfaction, sweet and bitter taste (also muscarinic ACh receptors and many hormone receptors) 7-3 Randall et al etc. 39 6