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Touch - Coggle Diagram

- - - - Meissner’s corpuscles and Merkel’s disks
        
        small receptive fields
      - Pacinian corpuscles and Ruffini’s endings
        
        large receptive fields
      - frequencies
        
        Pacinian corpuscles most sensitive to vibrations of about 200–300 Hz
        
        while Meissner’s corpuscles respond best around 50 Hz
    - - rapidly adapting receptors
        
        Meissner’s and Pacinian corpuscles
        
        tend to respond quickly at first but then stop firing
      - slowly adapting receptors
        
        Merkel’s disks and Ruffini’s endings
        
        more sustained response
      - selectivity depends on the structure of its special ending
        
        e.g.
        
        Pacinian corpuscle capsule
  - - - Force can be applied to a channel by the membrane itself
      - or force may be applied through connections between the channels and extracellular proteins
      - or connections with intracellular cytoskeletal components (e.g., actin, microtubules)
      - Alternatively, mechanical stimuli may somehow trigger the release of second messengers (e.g., DAG, IP3) that secondarily regulate ion channels.
      - specific types of channels in most of the somatic sensory receptors are still unidentified.
- - - - enter the spinal cord through the dorsal roots; their cell bodies lie in the dorsal root ganglia
        
        neurons that receive sensory input from primary af- ferents are called second-order sensory neurons
        
        most lie within the dorsal horns
        
        path to the brain entirely distinct from that taken for pain and temperature
        
        called the dorsal column–medial lemniscal pathway
        
        ascending branch of the large sensory axons (Aβ) enters the ipsilateral dorsal column of the spinal cord
        
        axons of the dorsal column terminate in the dorsal column nuclei, which lie at the junction of the spinal cord and medulla
        
        axons from the dorsal column nuclei arch toward the ventral and medial medulla, and decussate :crossed_flags:
        
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      - have varying diameters and their size correlates with the type of sensory receptor to which they are attached
        
        axons from skin sensory receptors: A(α, β, δ)–C
        
        axons from muscles and tendons: groups I–IV
        
        similar size
        
        C/Group IV
        
        temperature/pain/itch
        
        unmyelinated & smallest diameter: slowest
        
        Aα/Group I
        
        skeletal muscle proprioceptors
        
        myelinated & largest diameter: fastest
        
        Aβ/Group II
        
        skin mechanoreceptors
        
        Aδ/Group III
        
        pain/temperature
  - - - divided into four groups
        
        cervical (C) 1–8, thoracic (T) 1–12, lumbar (L) 1–5, and sacral (S) 1–5.
        
        area of skin innervated by the right and left dorsal roots of a single spinal segment is called a dermatome
        
        the dermatomes are mapped as a set of bands on the body surface
        
        When a dorsal root is cut, the corresponding dermatome on that side of the body does not lose all sensation.
        
        explained by the fact that the adjacent dorsal roots innervate overlapping areas
  - - - enter the brain at the pons
        
        twin trigeminal nerves, one on each side, and each breaks up into three peripheral nerves
        
        innervate the face, mouth areas, the outer two-thirds of the tongue, and the dura mater covering the brain
        
        Additional sensation from the skin around the ears, nasal areas, and pharynx is provided by other cranial nerves
        
        the facial (VII), glossopharyngeal (IX), and vagus (X).
        
        connections analogous to those of the dorsal roots.
        
        large-diameter sensory axons of the trigeminal nerve carry tactile information from skin mechanoreceptors
        
        synapse onto second-order neurons in the ipsilateral trigeminal nucleus
        
        axons decussate and project into the medial part of the VP nucleus of the thalamus
        
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- - - - primary somatic sensory cortex
        
        because
        
        (2) its neurons are very responsive to somatosensory stimuli (but not to other sensory stimuli);
        
        (3) lesions here impair somatic sensation; and
        
        (4) when electrically stimulated, it evokes somatic sensory experiences.
        
        (1) it receives dense inputs from the VP nucleus of the thalamus;
    - - include areas 3a, 1, and 2 on the postcentral gyrus, and areas 5 and 7 on the adjacent posterior parietal cortex
        
        Areas 1 and 2 receive dense inputs from area 3b. The projection from
        
        3b to area 1 sends mainly texture information
        
        3b to area 2 emphasizes size and shape.
  - - - neurons of layer IV project, in turn, to cells in the other layers
    - - homunculus roughly resembles a body with its legs and feet at the top of the postcentral gyrus and its face at the opposite, lower end of the gyrus
        
        not scaled like the human body
        
        relative size of cortex devoted to each body part is correlated
        
        density of sensory input received from that part
        
        importance of the sensory input from that part
        
        also reflections of how often it is used
        
        can vary greatly in different species
        
        somatotopic map of rodent vibrissae is easily seen in thin sections of S1
        
        five rows of cortical barrels precisely match the five rows of facial vibrissae
      - not limited to a single map