FISIOLOGI SENSORIKOleh:Dr. Hedison Polii, Mkes, AIFM, AIFOSensory Systems Vision Hearing Taste Smell Equilibrium Somatic SensesSensory Systems Somatic sensory General transmit impulses from skin, skeletal muscles, and joints Special senses- hearing, balance, vision Visceral sensory Transmit impulses from visceral organs Special senses - olfaction (smell), gustation(taste) Stimulus - energy source Internal External Receptors Sense organs - structures specialized to respond to stimuli Transducers - stimulus energy converted into action potentials Conduction Afferent pathway Nerve impulses to the CNS Translation CNS integration and information processing Sensation and perception your realityProperties of Sensory SystemsSensory Pathways Stimulus as physical energy sensory receptor acts as a transducer Stimulus > threshold action potential to CNS Integration in CNS cerebral cortex or acted on subconsciouslyClassification by Function (Stimuli) Mechanoreceptors respond to touch, pressure, vibration, stretch, and itch Thermoreceptors sensitive to changes in temperature Photoreceptors respond to light energy (e.g., retina) Chemoreceptors respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors sensitive to pain-causing stimuli Osmoreceptors detect changes in concentration of solutes, osmotic activity Baroreceptors detect changes in fluid pressureClassification by Location Exteroceptors sensitive to stimuli arising from outside the bodyLocated at or near body surfacesInclude receptors for touch, pressure, pain, and temperature Interoceptors (visceroceptors) receive stimuli from internal visceraMonitor a variety of stimuli Proprioceptors monitor degree of stretchLocated in musculoskeletal organsClassification by Structure General somatic include touch, pain, vibration, pressure, temperature Proprioceptive detect stretch in tendons and muscle provide information on body position, orientation and movement of body in spaceSomatic SensesSomatic Receptors Divided into two groups Free or Unencapsulated nerve endings Encapsulated nerve endings - consist of one or more neural end fibers enclosed in connective tissueFree Nerve Endings Abundant in epithelia and underlying connective tissue Nociceptors - respond to pain Thermoreceptors - respond to temperature Two specialized types of free nerve endings Merkel discs lie in the epidermis, slowly adapting receptors for light touch Hair follicle receptors Rapidly adapting receptors that wrap around hair folliclesEncapsulated Nerve EndingsMeissners corpuscles Spiraling nerve ending surrounded by Schwann cells Occur in the dermal papillae of hairless areas of the skin Rapidly adapting receptors for discriminative touch Pacinian corpuscles Single nerve ending surrounded by layers of flattened Schwann cells Occur in the hypodermis Sensitive to deep pressure rapidly adapting receptorsRuffinis corpuscles Located in the dermis and respond to pressure Monitor continuous pressure on the skin adapt slowlyEncapsulated Nerve Endings - Proprioceptors Monitor stretch in locomotory organs Three types of proprioceptors Muscle spindles monitors the changing length of a muscle, imbedded in the perimysium between muscle fascicles Golgi tendon organs located near the muscle-tendon junction, monitor tension within tendons Joint kinesthetic receptors - sensory nerve endings within the joint capsules, sense pressure and positionMuscle Spindle & Golgi Tendon OrganSpecial SensesFigure 10-4: Sensory pathways Taste, smell, sight, hearing, and balance Localized confined to the head region Receptors are not free endings of sensory neurons but specialized receptor cells1- General Principles of Sensory Physiology Receptor physiology Sensory pathways Sensory codingSensory receptors Somatic-- Chemoreceptors (taste, smell, smell)-- Thermoreceptors (temperature)-- Photoreceptors (vision)-- Baroreceptors (sound, balance)-- Proprioreceptors (muscle stretch) Visceral-- Chemoreceptors (chemicals in blood, osmoreceptors)-- Baroreceptors (blood pressure)Sensory transduction Receptors transform an external signal into a membrane potential Two types of receptor cells:- a nerve cell- a specialized epithelial cellFigure 10.2Two types of sensory receptorsReceptor adaptation Tonic receptors-- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there(ex: proprioreceptors) Phasic receptors-- quick acting, adapt: stop firing when stimuli are constant (ex: smell) Sensory pathways The sensory pathways convey the type and location of the sensory stimulus The type: because of the type of receptor activated The location: because the brain has a map of the location of each receptorFigure 10.6The Somatosensory System Types of receptors- Mechanoreceptors: -- Proprioreceptors in tendons, ligaments and muscles body position-- Touch receptors in the skin: free nerve endings, Merkels disks and Meissners corpuscles (superficial touch), hair follicles, Pacinian corpuscles and Ruffinis ending- Thermoreceptors: Warm receptors (30-45oC) and cold receptors (20-35oC)- Nociceptors: respond to noxious stimuliFigure 10.13Skin touch receptorsFigure 10.15Pain perception Fast pain: sharp and well localized, transmitted by myelinated axons Slow pain: dull aching sensation, not well localized, transmitted by unmyelinated axons Visceral pain: not as well localized as pain originating from the skin pain impulses travel on secondary axons dedicated to the somatic afferents referred pain Figure 10.16aReferred painClassification of Sensory System by Structural ComplexitySomatic (= general) senses1. Touch2. Temperature3. Nociception4. Itch 5. ProprioceptionSpecial senses1. Vision2. Hearing3. Taste4. Smell5. EquilibriumConscious vs. UnconsciousSensory Receptors - Overview are transducers convert stimuli into graded potential (receptor potential) are of various complexity react to particular forms of stimuli Chemoreceptors mechanoreceptors thermoreceptors photoreceptorsSensory Transduction Converts Stimulus into graded potential= receptor potential. Threshold If receptor potential above threshold AP Adequate Stimulus Receptor potential in non-neural receptors change in membrane potential influences NT releaseSensory PathwayStimulus Sensory receptor (= transducer)Afferent sensory neuronsCNSIntegration, perceptionIntensity & Duration of Stimulus Intensity is coded by # of receptors activated and frequency of AP coming from receptor Duration is coded by duration of APsin sensory neurons Sustained stimulation leads to adaptation Tonic receptors Phasic receptorsTonic Receptors Slow or no adaptation Continuous signal transmission for duration of stimulus Monitoring of parameters that must be continually evaluated, e.g.: baroreceptors Rapid adaptation Cease firing if strength of a continuous stimulus remains constant Allow body to ignore constant unimportantinformation, e.g.: SmellPhasicReceptorsSomatic Senses Primary sensory neurons from receptor to spinal cord or medulla Secondary sensory neurons always cross over (in spinal cord or medulla) thalamus Tertiary sensory neurons somatosensory cortex (post central gyrus)Touch ReceptorsFree or encapsulated dendritic endingsIn skin and deep organs, e.g.: Paciniancorpuscles concentric layers of c.t. large receptive field detect vibrationopens mechanicallygated ion channelrapid adaptation receptor type?Temperature Receptors AKA thermoceptors or thermorecetors Free dendritic endings in hypodermis Function in thermoregulation Cold receptors (< body temp.) Warm receptors (> body temp.) Test if more cold or warm receptors in lab Adaptation only between 20 and 40C Nociceptors activated if T > 45CNociceptors Free dendritic endings Activation by strong, noxious stimuli - Function? 3 categories: Mechanical Thermal (menthol and cold / capsaicin and hot) Chemical (includes chemicals from injured tissues) Inflammatory Pain May activate 2 different pathways: Reflexive protective integrated in spinal cord Ascending to cortex (pain or pruritis)Pain A, and A fibers mediate pain C fibers mediate pruritis Fast (A fibers) pain is sharp Slow pain (C) is throbbing Ascend to limbic system and hypothalamusEmotional Distress Modulation Gate Control Theory:We can inhibit the pain response Pain control NSAIDs (inhibit COX) Opiates (inhibit NT release)Referred PainPain in organs is poorly localizedMay be displaced ifMultiple 1 sensory neurons converge on single ascending tract