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SENSORY PHYSIOLOGY Sensory System

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SENSORY PHYSIOLOGY Sensory System Physiology Unit 2 SENSORY PHYSIOLOGY Sensory System • Sensory informaon – Conscious sensaons – Unconscious sensaons • Sensory processing – Transferring s4mulus energy into a graded poten4al (receptor poten4al) – Then to an ac4on poten4al in an afferent neuron • Paern of ac4on poten4als is the code that provides informaon on the s4mulus General Classes of Receptors • Mechanoreceptors • Thermoreceptors • Photoreceptors • Chemoreceptors • Nociceptors Sensory Receptors • Specialized endings of sensory neurons • Separate cells that signal the afferent neurons by releasing chemical messengers • The energy or chemical that ac4vates a sensory receptor is a smulus • The process by which a s4mulus is transformed into an electrical response is sensory transduc"on Receptor Poten4al • Sensory transduc4on involves the opening/closing of ion channels Graded Poten4al to Ac4on Poten4al • The ini4al ion movement generates local current that flows a short distance along the axon to a region where the membrane has voltage-gated ion channels an an AP can be generated • Usually the first Node of Ranvier Primary Sensory Coding • Converng smulus energy that conveys relevant sensory informaon to the CNS is coding – Type of energy it represents (modality) – Intensity – Locaon of the body affected Sensory Unit Sensory Modality • Modali4es – Temperature, taste, sound, touch • Submodali4es of sensaon – Submodality of temperature: hot/cold – Submodali4es of taste: sweet, bi>er, salty, sour, umame – Submodality of sound: pitch, volume S4mulus Intensity S4mulus Duraon • Rapid adaptaon – Phasic receptors – Signal change – Rapid fading of sensaon – “on” and “off” response • Slow adaptaon – Tonic receptors – Signal slow changes or prolonged events – Joint, muscle receptors for maintaining posture Sensory Pathways • A Sensory Pathway – A bundle of parallel, 3 neuron chains that run together – Also called ascending pathways – Non-specific – Specific – Most sensory pathways convey informaon from a single type of sensaon (mechanoreceptors, thermoreceptors, etc.) Specific Ascending Pathways • Sensory pathways ascend to 1. Brainstem (RAS) 2. Thalamus 3. Final neurons in the pathway terminate in the specific sensory area of the cortex • Excep1on: olfactory neurons branch to the limbic system rather than the thalamus Somac Sensaon • Sensaons from – Skin – Muscles – Bones – Tendons – Joints • Sensaons of – Touch – Pressure – Body posion – Temperature – Pain Somatosensory System Pathways Spinothalamic Pathway • 1st neuron travels into the spinal cord • 2nd neuron decusates in the spinal cord and up to the thalamus • 3rd neuron travels to the somatosensory cortex • Processes • Pain • Temperature Decusaon in the spinal cord Somatosensory System Pathways Dorsal Column Pathway • 1st neuron passes into the spinal cord and up to the brainstem where it decusates • 2nd neuron travels to the thalamus • 3rd neuron travels to the somatosensory cortex • Processes • Fine touch • Vibraon • Propriocep4on Decusaon in the brainstem Distribu4on of Peripheral S4muli Special Sense: Vision • Op4cal component – Focuses visual image on the receptor cells • Neural component – Transforms the visual image to a paern of graded and ac4on poten4als Light • The receptors of the eye are only sensi4ve to a small por4on of the electromagne4c spectrum • The visible spectrum is between 400-750 nm • Different wavelengths of light are perceived as different colors Color Vision The Opcs of Vision • Refrac4ng light is how our eyes focus on objects • The cornea and the lens refract light to focus it in the re4na • Adjustments for distance is made by changes the shape of the lens. This is accommodaon Accommodaon Photoreceptor Cells • Outer segment made of stacked layers of membrane (discs). • The discs hold the photopigments which absorb light • Photopigments are membrane bound proteins called opsins which surround and bind a molecule called renol • Re4nol is a derivave of vitamin A Photoreceptor Cells • There are 4 unique photopigments in the re4na • Rods have the photopigment rhodopsin • The others are found in the 3 types cones Phototransduc4on Neural Pathway of Vision • Pathway: – Opc Nerve (C.N. II) – Op4c chiasm • SCN – Op4c tract – Thalamus – Visual cortex Suprachiasmac nucleus (SCN) controls circadian rhythms Special Sense - Hearing Sound Transmission Organ of Cor4 Sensory Hair Cells Neural Pathway for Hearing • Pathway: – Sensory hair cells – Cochlear branch of ves4bulocochlear nerve (C.N. VII, Auditory Nerve) – Brainstem – Thalamus – Auditory cortex Ves4bular System • Ves4bular apparatus – Semicircular canals – Utricle – Saccule Semicircular Canals Rotaonal Movement Utricle and Sacule • The macula provides info on changes in head posi4on relave to: – Force of gravity – Linear acceleraon • Ves4bular informaon is used for: – Control eye movements – Reflexes to maintain posture – Conscious awareness of ourselves in “space” Gustaon Olfac4on .
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