Section 3: Sensory systemsKinesthetic OrgansIf you had to live without one sensory system (vision, proprioception, vestibular), which one would it be? Why?Somatosensory systemSomatosensory system• Most diverse sensory system• Mediates a range of sensations: touch, pressure, vibration, limb position, heat/cold, pain• Functional subsystems: Skin mechanoreceptors: touch, pressure, vibration Muscle, tendon joint receptors: proprioception Pain receptors: pain, temperatureoverview① How do cutaneous receptors work?② What different types of cutaneousreceptors exist?③ What is a receptive field?④ How do somatic sensory (afferent) fibers reach the brain? ⑤ What happens in the brain in the somatic sensory cortex?Somatosensory afferents convey information from skin surface to central circuitsDermatomesDermatome: maps of body regions innervated by each spinal nerveTransduction in a mechanosensory afferent (a Pacinian corpuscle)Stimulus (deformation)Ion channels open in the afferent nerve endingReceptor potential (depolarization current)Afferent action potentialoverview① How do cutaneous receptors work?② What different types of cutaneousreceptors exist?③ What is a receptive field?④ How do somatic sensory (afferent) fibers reach the brain? ⑤ What happens in the brain in the somatic sensory cortex?Slowly and rapidly adapting mechanoreceptors respond differently to a stimulussize and shapetap on shoulderMechanoreceptor typesPain & temperatureLow-frequency vibration;grip control (slippage); rapidForm & texture; high spatial resolution; slowSkin stretch; slowHigh frequency vibration; rapidTextSimulated activity patterns in different mechanosensory afferents as Braille is readForm & texture Low frequency Grip ControlSkin stretchslow high frequency vibrationrapid270 mphoverview① How do cutaneous receptors work?② What different types of cutaneousreceptors exist?③ What is a receptive field?④ How do somatic sensory (afferent) fibers reach the brain? ⑤ What happens in the brain in the somatic sensory cortex?Receptive fields and two-point discrimination thresholdReceptive field: area of the skin surface over which stimulation results in a significant change in the rate of action potentials of afferent fibers.Loss of sensation: Neuropathic Arthropathy• Loss of sensation, numbness, blood flow to limbs  unstable and deformed joints• Occur with several diseases affecting the sensory nervous system (diabetes, syphilis, alcoholism, leprosy)Charcot joints in a patient with diabetic neuropathyoverview① How do cutaneous receptors work?② What different types of cutaneousreceptors exist?③ What is a receptive field?④ How do somatic sensory (afferent) fibers reach the brain? ⑤ What happens in the brain in the somatic sensory cortex?Mechanosensory pathwaysPain-temperatureSynapse in cordMechanoreceptorsSynapse above cordCuneate=upper bodyGracile=lower limbsDecussation= where fibers cross midlineWhat happens to lower limb sensation with spinal cord hemisection?= mechanoreceptor= pain/tempSpinal cord hemisection=> crosses at brainstem=> crosses in cord=> interruption of ascending fibers on one sideOverview① How do cutaneous receptors work?② What different types of cutaneousreceptors exist?③ What is a receptive field?④ How do somatic sensory (afferent) fibers reach the brain? ⑤ What happens in the brain in the somatic sensory cortex?S1= primary somatic sensory cortexWhat would it be like to lose proprioception but have a normal efferent system?Ian Waterman: Pride and a Daily Marathon (Cole, 1995)• At age 19, got flu, his immune system attacked nerves for touch and proprioception• Initially did not move - he says he could move but his lack of control made it dangerous and ineffective• Taught himself how to walk, to drive, to hold an office job• All his movements done “under conscious control and continuous visual inspection. Without thought, there was no