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 Processing Chapter 13 1 Sensory Processes Sensory Systems Ch13 in your text 3 1
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 into organs 7-1 Randall et al. 2002 5 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. 2002 6 2
7 7-5 Randall et al. 2002 etc. 8 3
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 9 To measure quality need many receptors grouped into organ; different tunage (e.g, wavelength of light or frequency of sound) 10 4
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 11 Properties of Receptor Cells 7-2 Randall et al. 2002 Receptor Cells -Specialized - Selective for energy type and modality -either is a neuron or -Synapses immediately on a neuron (1 afferent neuron to CNS) Stimulus modifies conformation of receptor 12 5
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 13 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 14 6
Stimulus Intensity and Dynamic Range From lowest threshold, to upper limit imposed by refractory period: Note log axis 7-7 Randall et al. 2002 15 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 recruit receptors with different tunage or sensitivity (e.g., rods and cones in eye) 16 7
Sensory Adaptation Possibilities: 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) 17 -Accommodation Randall et al. 2002 18 8
Enhancing Sensitivity - Spontaneous basal activity - Constant rate of APs 7-12 Randall et al. 2002 - Directionality if or AP frequency 19 Tonic vs. Phasic receptors fast-adapting Slow-adapting 5-19 Randall et al. 2002 20 9
Hill et al. 2004, Fig 13.5 21 Sensory Adaptation Pacinian Corpuscle - Touch Example Movement of Oil between layers is what triggers APs Signal changes in pressure, not steady pressure 7-10 Randall et al. 2002 22 10
Star-Nosed Mole ( # neurons, subtlety) (receptor field size?) 23 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 Activated by stretch or distortion of plasma membrane 24 11
Whiskering Are these the hair cells we are talking about? 25 Mechanoreception 7-24 Randall et al. 2002 - Hair Cells in cupula one Kinocilium (or none) many stereocilia e.g., -lateral line system in fish and amphibians (motion/electricity) -hearing and equilibrium 7-25 Randall et al. 2002 26 12
Hearing and Equilibrium 7-26 Randall et al. 2002 - 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 Sacculus and Utriculus also contain patches of hair cells that detect position relative to gravity via otoliths 27 7-27 Randall et al. 2002 28 13
10-24 Silverthorn 2001 29 Hearing (in a nutshell 1) - external ear funnels sound -sound is oscillating air pressure - 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 30 14
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 31 7-27 Randall et al. 2002 32 15
Basilar membrane Mammalian Cochlea Hill et al. 2004, Fig 13.29&30 33 34 16
Barn Owl 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 Type of sensation received depends on where in CNS (~brain) AP arrives (LABELED LINES). Rub eyes and see light! Synesthesia: e.g., smell colors 37 17
Mechanisms and Molecules Lots of Evolutionarily Conserved Elements e.g., 7 transmembrane helices and G-protein intermediate e.g., Vision, olfaction, sweet and bitter taste (also muscarinic ACh receptors and many hormone receptors) 7-3 Randall et al. 2002 38 7-5 Randall et al. 2002 etc. 39 18