1. Peripheral Somatosensory Neurons
   1. Q: What determines info process speed? diameter of axons (larger), degree of axonal myelination and number of synapses
      1. Q: How info travels? Info proceeds from receptor through a series of neurons to the brain
         1. Q: Sensory info from skin aka superficial or cutaneous responds to? touch, pressure, vibration, stretch, noxious (pain) stimuli and temperature
   2. Somatosensory Receptors
      1. Are Classified as responding to: (subset of each is nociceptors (pain))
         1. Mechano: touch, pressure, stretch or vibration
         2. Chemo: substances released by cells including damaged cells following injury or infection
         3. Thermo: heating or cooling
   3. Somatosensory Peripheral Neurons
      1. Two Axons
         1. Distal Axons from receptor to cell body
         2. Proximal axons from cell body into spinal cord or brain stem
      2. Peripheral axons aka afferents
         1. classified by axon diameter declining order
            1. Ia, Ib, II or AB, Ad, C
   4. Cutaneous Innervation - Peripheral vs Dermatomal Intervention
      1. Body senses: Somatosensation
      2. What are the receptors? Mechanoreceptors:
      3. 1.Meissner corpuscles –located on surface of your skin; sensitive and respond to light touch
      4. 2.Merkel discs –respond to pressure, like sustained pressure
      5. 3.Ruffini endings –respond to the stretch of skin over joints
      6. 4.Pacinian corpuscles –deepest located and are very sensitive to vibration/pressure; turn off w/habituation
      7. 5.Hair follicle receptors –receptor at the root of the hair that senses whenever the hair on skin surface moves
      8. 6.Free nerve endings (nociceptors) –pain
   5. Musculoskeletal Innervation
      1. muscle spindle
         1. Respond to quick and prolonged stretch of muscle. Length: signaled by type Ia and II afferents, sensitivity to changes is adjusted by gamma static efferents, velocity of change via type Ia afferents with info from nuclear bag fibers sensitivity adjusted by gamma dynamic efferents
      2. Golgi Tendon Organ
         1. Tension, signal force generated by muscle contraction or by passive stretch of tendon
      3. Joint Receptors
         1. Respond to mechanical deformation of joint capsules and ligaments
         2. Afferents associated
            1. ligament receptors type Ib
            2. Ruffini's and paciniform endings type II
            3. Free nerve endings
2. Function of Different-Diameter Axons
3. Somatosensory Pathway
4. Pathways to the Brain
   1. Conscious relay pathways to cerebral cortex
      1. Discriminative touch and conscious proprioception
         1. Sensory information essential for identifying objects by palpation, between closely spaced stimuli, and controlling fine movements and smoothness of movement travels in dorsal columns, then in medial lemniscus to the primary sensory cortex. Tactile info from face travels in trigeminal nerve, then to the sensory cortex. (stregnosis) aility to use touch and proprioceptive info to identify object.
         2. Uses 3 neuron relay
            1. 1st order: info from receptor to medulla
            2. 2nd order: from medulla to thalamus
            3. 3rd order: from thalamus to cerebral cortex
         3. dorsal column/ medial lemniscus system
      2. Discriminitive Pain & Temp, Coarse Touch
         1. info localize noxious sensations and consciously distinguish between warmth and cold travels to cerebral cortex via SPINOTHALAMIC pathway (into dorsal horn to spinal cord to thalamus to cerebral cortex) @ anterolateral colums
         2. temp sensation: Adelta fibers carry impulses by cooling and C fibers carry heat info.
         3. pain: both protective sensation and emotional response
            1. fast or spinothalamic pain: dull throbbing ache not well localized
            2. slow or spinolimbic pain: acute pain
         4. comparison of dorsal column/ medial lemniscus and spino thalamic systems
            1. dorsal columns: contain axon of primary neurons and ascend ipsilaterally
         5. fast pain info from face
            1. travels in trigmental nerve, lesions interupting this produce analgesia (absence of pain)
         6. fast vs slow pain
            1. slow pain occurs later bc it travels on smaller unmyelinated axons
   2. Divergent pathways
      1. Medial Pain system: Slow Pain
      2. first neuron: small unmyelinated C fiber sensitive to heat, chemical or mech stimulation
      3. ascending projection neurons: 3 tracks in anterolateral spinal cord
         1. spinomesencephalic (midbrain)
            1. carries nociceptive info to superior colliculus and area surrounding cerebral aqueduct (periaqueductal gray)
            2. turning of eyes and head towards pain source and activating descending tracts to control pain
         2. spinoreticular
            1. in reticular formation (brainstem network) arousal, attention, sleep/ waking cycles are modulated. Severe pain interupt sleep
         3. spinolimbic
            1. transmit slow pain info to medial and intralaminar nuclei in thalamus. Spinoret + spinolim = arousal, withdrawal, autonomic & affective pain response
         4. slow pain pathways provide info that produces automatic movements and autonomic emotional response to pain stimuli
      4. Trigeminoreticulolimbic pathway for slow pain info
   3. Temparature Information
      1. transmitted in older pathways to reticular, nonspecific thalamus nuclei, subcortical nuclei and hypothalamus
      2. if conscious awareness not reached it contributes to arousal, gross localization and autonomic regulation
   4. Unconscious Relay Tracts to Cerebellum
      1. info from proprioceptors & about activity in spinal interneurons are transmitted to cerebellum via spinocerebellar tracts. Critical for adjusting movements
         1. Spinocerebellar tracts FUNCTION: for unconscious adjustments to movements and posture.
      2. High-fidelity pathways: arrange info to cerebellar cortex
         1. posterior spinocerebellar: transmit info from legs to lower half of body
         2. cuneocerebellar: begins with primary afferents from arm and upper half of body; central axons travel via the posterior columns to lower medulla
      3. Internal feedback tracts: monitor activity of spinal interneurons and of descending motor signals from cerebral cortex & brainstem
         1. Anterior spinocerebellar
            1. transmits info from thoracolumbar spinal cord
         2. Rostrospinocerebellar
            1. transmits info from cervical spinal cord to ipsilateral cerebellum and enters the cerebellum via inferior and superior cerebellar peduncles, neurons that control muscle activity, convey info about spinal reflex circuit activity
   5. Diff Spinocerebellar tract from cerebellar lesions
      1. compare coordination of movement with vision vs without vision. Spinocerebellar tract lesion: coordinated movements with vision, but not without vision
   6. info in spinocerebellar tracts is received from proprioceptors, spinal interneurons and descending motor pathways. Info reach unconscious, contributes to automatic movements and postural adjustments
5. Dermatome
   1. The signal is carried to the spinal cord on a spinal nerve
   2. •31 pairs of spinal nerves
   3. •Each pair innervates a specific area of the skin surface = a dermatome
6. dermatomes anterior view
7. dermatomes posterior view
8. Nociceptive info pathway