Physiology Unit 2

SENSORY PHYSIOLOGY Sensory System

• Sensory informaon – Conscious sensaons – Unconscious sensaons • Sensory processing – Transferring smulus energy into a graded potenal (receptor potenal) – Then to an acon potenal in an afferent • Paern of acon potenals is the code that provides informaon on the smulus General Classes of Receptors

• Mechanoreceptors • Thermoreceptors • Photoreceptors • Chemoreceptors • Nociceptors Sensory Receptors

• Specialized endings of sensory • Separate cells that signal the afferent neurons by releasing chemical messengers • The energy or chemical that acvates a sensory receptor is a smulus • The process by which a smulus is transformed into an electrical response is sensory transducon Receptor Potenal

• Sensory transducon involves the opening/closing of ion channels Graded Potenal to Acon Potenal

• The inial ion movement generates local current that flows a short distance along the 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

• Modalies – Temperature, taste, sound, touch • Submodalies of sensaon – Submodality of temperature: hot/cold – Submodalies of taste: sweet, bier, salty, sour, umame – Submodality of sound: pitch, volume Smulus Intensity Smulus 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. (RAS) 2. 3. Final neurons in the pathway terminate in the specific sensory area of the cortex • Excepon: olfactory neurons branch to the limbic system rather than the thalamus c Sensaon

• Sensaons from – Skin – Muscles – Bones – Tendons – Joints • Sensaons of – Touch – Pressure – Body posion – Temperature – Pathways Spinothalamic Pathway • 1st neuron travels into the • 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 • Propriocepon Decusaon in the brainstem Distribuon of Peripheral Smuli

Special Sense: Vision

• Opcal component – Focuses visual image on the receptor cells • Neural component – Transforms the visual image to a paern of graded and acon potenals Light

• The receptors of the eye are only sensive to a small poron of the electromagnec spectrum • The visible spectrum is between 400-750 nm • Different wavelengths of light are perceived as different colors Color Vision The Opcs of Vision

• Refracng light is how our eyes focus on objects • The cornea and the lens refract light to focus it in the rena • 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 • Renol is a derivave of vitamin A Photoreceptor Cells

• There are 4 unique photopigments in the rena • Rods have the photopigment rhodopsin • The others are found in the 3 types cones Phototransducon Neural Pathway of Vision

• Pathway: – Opc Nerve (C.N. II) – Opc chiasm • SCN – Opc tract – Thalamus –

Suprachiasmac nucleus (SCN) controls circadian rhythms Special Sense - Sound Transmission Organ of Cor

Sensory Hair Cells Neural Pathway for Hearing

• Pathway: – Sensory hair cells – Cochlear branch of vesbulocochlear nerve (C.N. VII, Auditory Nerve) – Brainstem – Thalamus – Vesbular System

• Vesbular apparatus – Semicircular canals – Utricle – Semicircular Canals Rotaonal Movement Utricle and Sacule

• The macula provides info on changes in head posion relave to: – Force of gravity – Linear acceleraon • Vesbular informaon is used for: – Control eye movements – Reflexes to maintain posture – Conscious awareness of ourselves in “space” Gustaon Olfacon