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Somatosensory System (Mechanoreceptor (Mechanosensitive Ion Channels…

- - - - specialized nerve endings
        
        merkel's disk
        
        meissner's corpuscle
        
        pacinian corpuscle
        
        ruffini ending
      - free nerve endings
    - - muscle spindles
      - golgi tendon organs
  - - - certain area of skin where mechanoreceptor can transduce pressure/vibration
  - - - receptor respond quickly to stimulus but response is not sustained
        
        meissner's corpuscle
        
        small RF
        
        pacinian corpuscle
        
        large RF
        
        capsule around axon makes corpuscle sensitive to vibrating, high frequency stimuli
    - - receptor responds slowly but when stimulus is removed stimulus also falls slowly
        
        merkel's disk
        
        small RF
        
        ruffini's ending
        
        large RF
- - - - vision
      - hearing
      - touch
      - taste
      - smell
  - - - signaled by firing rate
    - - signaled by time course of response
- - - - segmental organization of spinal cord = related to sensory innervation of skin
        
        each spinal segment provide sensory innervation to particular region of skin
        
        dermatome – area of skin & deeper tissues innervated by single dorsal root
  - - - touch, vibration, & conscious proprioception
        
        travels us dorsal column (spinal cord) –> dorsal column nuclei (medulla) –> medial lemniscus (brainstem) –> ventral posterior lateral nucleus (VPl, thalamus) –> primary somatosensory cortex (S1)
        
        touch, vibration = myelinated Aβ
        
        proprioceptors = myelinated I, II axons
        
        crosses @ medulla – lesions b4 cross lead to loss of sensation on ipsilateral side of body
    - - Pain & Temperature
        
        pain
        
        nociceptors
        
        mediate transduction of pain
        
        activated by stimuli that could cause tissue damage
        
        temperature
        
        thermal receptor
        
        mediate transduction of cold, cool, warm & hot
        
        free nerve endings
        
        activate transient receptor potentials (TRP)
      - unmyelinated C fibers & lightly myelinated Aẟ
        
        cross to contralateral side –> travel up spinal cord in spinothalamic tract to VPL –> then to S1
        
        Aẟ & C afferent synapse in substantia gelatinosa & dorsal horn
      - crosses at beginning of spinal cord
        
        legions lead to loss of sensation on contralateral side
    - - carries info about touch, vibrations, pain & temperature in face to brain
      - pain & temperature info from contralateral orofacial region
      - CN V, from face –> principal sensory nucleus of V
- - - - broadmann's areas 1,2,3a,3b
        
        areas 3b & 1 = cutaneous stimuli
        
        3a & 2 = proprioceptive stimuli from muscles & joints
    - - found w/in somatotopic map
        
        neurons w/ same modality from pia to white
        
        column of slow adapting vs. column of fast adapting neurons
    - - adjust depending on amount of sensory experience
      - allows for sensory learning
      - cortical map plasticity
  - - - agnosia = inability to recognize objects
      - astereognosia = loss of stereognosis – ability to form an object by using sense of touch
      - neglect syndrome = part of body/world = ignored (usually ameliorates w/ time)
- - - - allows for 2 pt discrimination
        
        best for body regions w/ highest innervation density & amount of cortical area devoted to them (i.e. fingers & lips)