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Sensory Biol. 211 Anatomy & Physiology 1 Tony Serino, Ph.D. Biology Department Misericordia University Sensation –state of awareness of external and internal conditions of the body • Four conditions for sensation: – – – – 1. Adequate stimulus 2. Adequate receptor (transducer) 3. Conduction 4. Translation (interpretation) Brain’s Assumption in Translating Assumption: Source of light is from above Reversing X pattern; notice shading. How many triangles? Assumption: Straight lines should connect. Which dark line is larger? Assumption: perspective Characteristics of Sensation • Modality –ability to interpret nerve impulses differently • Projection –referral of sensation to point of origin • Adaptation –decrease in sensitivity of receptors to continued stimulation – Phasic (fast) – Tonic (slow) – Some receptors never adapt (pain, cold, etc.) • Afterimage –persistence of sensation after stimulus ceases Classification of Receptors • Type of Sensory Information Relayed – Exteroreceptors, Enteroreceptors, Proprioceptors • Type of Stimulus Transduced – Mechanoreceptors, Thermoreceptors, Chemoreceptors, and Nociceptors • Complexity of Receptor – Simple structure (usually single cell) –most general senses – Complex structure (many cells) –special senses Receptor Physiology • Stimulation of a receptor leads to the generation of a receptor (generator) potential in its membrane. • These are usually excitatory, and are similar to the EPSPs found in neurons • If the receptor potential reaches the threshold potential for the sensory neuron; it fires an AP into the CNS • Strength of the stimulus is therefore encoded by the number of AP generated • Sensations may be sharpened through Lateral Inhibition Lateral Inhibition - - General Senses • Cutaneous –skin receptors • Proprioception –sense of body position • Nociception –pain perception (chemoreceptors that perceive locally secreted warning hormones (prostaglandins)) Distribution of Cutaneous Receptors Sensitivity of Skin due to Receptive Fields Cutaneous Receptors Proprioceptors Muscle sensors Muscle spindles (Intrafusal fibers: -senses degree of length of muscle fibers and the rate of change in length Golgi Tendon organs –sense tension within tendon Relationship of Stretch to AP Referred Pain Illustrates projection. General Pathway of Perception Taste (Gustatory) Sense Taste Bud Olfaction (smell) Sense Olfactory Epithelium Olfaction Signal Transduction Vision Accessory Structures of the Eye Lacrimal Apparatus Extrinsic Ocular Muscles Action and Innervation of Ocular Muscles Which cranial nerve is injured? Eye Anatomy Aqueous Humor Flow (Canal of Schlemm) Glaucoma results from inadequate drainage of Aqueous Humor leading to increase pressure in the eye. Iris controls amount of light entering the eye. Distant Vision Near Vision (Accomodation) Near and Far-sightedness Astigmatism and Presbyopia • Astigmatism –results from imperfections in the resolving structures in the eye (lens and/or cornea) • Presbyopia is the loss of near vision with age; resulting from a decrease in elasticity of the lens. Retina Cellular Arrangement Special Areas of Retina Blind Spot Optic Disc (blind spot) Optic N. Photoreceptors: Cones and Rods Three Population of Cones Rod’s and Cone’s Photopigments Rhodopsin Light Signal Transduction Visual Processing Sound Frequency vs. Loudness Frequency measured in hertz (Hz) Loudness measured in decibels (dB) Anatomy of the Ear Middle and Inner Ear Ossicles Amplify Sound Loud Sound Protection Middle Ear Ossicles Cochlea and Cochlear Duct Organ of Corti Hair Cells in Cochlear Duct Frequency Perception • Different frequency (pitch) of sound stimulates different areas of cochlear duct • The overall area stimulated relates to the sound intensity Vestibular Apparatus Macula of Utricle and Saccule Macula Otoconia (otoliths) Hair Cell of Macula AP Generation in Macula Ampulla Anatomy