EXAM 2: BIO&252 (Chapter 15)

  1. Labeled Line
    Neuronal pathway from receptor to cortex is the "labeled line"
  2. Rapidly-Adapting (phasic) Receptors
    • Reduce firing rate during constant stimulus
    • Fire rapidly at the beginning and end of the stimulation
    • Conveys information about changes in stimulus intensity
    • Examples: Pacinian Corpuscle, Thermoreceptor, Meissner's Corpuscle
  3. Slowly-Adapting (tonic) Receptors
    • Fire at some level all the time
    • Continue firing during constant stimulation
    • Conveys information about the duration of the stimulus
    • Examples: Pain receptors, Muscle spindle, Merkel disc
  4. Nociceptors (pain receptors)
    • Slow-adapting
    • Free-nerve endings
    • LARGE receptive fields
    • Extreme temp, mechanical damage, chemicals
    • Neurotransmitters: Glutamate, Substance P
    • Type A: Myleinated, "fast pain", Primary Sensory Cortex
    • Type C: Unmylinated, "slow pain", Thalamus and Reticular Formation
  5. Thermoreceptors
    • Free-nerve endings
    • Phasic (fast-adapting)
    • There are 3 to 4 times more cold than warm receptors
    • Information ascends in Lateral Spinothalamic Tract (with pain information)
  6. Mechanorecpetors
    Mechanically-gated ion channels

    • Tactile Receptors: touch, pressure, vibration
    • Fine touch: precisely localized (posterior column pathway)
    • Crude touch: poorly localized (anterior spinothalamic pathway)
  7. Free-Nerve Endings
    Tactile (touch and pressure) receptor

    • Between epithelial cells (corneal epithelium)
    • Touch and pressure
    • Tonic (slow adapting)
    • Small receptive fields
  8. Root Hair Plexus
    Tactile (touch and pressure) receptor

    • Dendrites surround hair root
    • Movement of hair
    • Phasic (fast adapting)
  9. Merkel's (Tactile) Discs
    Tactile (touch and pressure) receptor

    • Dendrites contact Merkel (epidermal) cells
    • Fine touch and pressure - very sensitive
    • Tonic (slow adapting)
    • Small receptive field
  10. Meissner's (Tactile) Corpuscles
    Tactile (touch and pressure) receptor

    • Papillary layer of dermis
    • Capsule = modified Schwann Cells
    • Fine touch and pressure, low freq. vibration
    • Phasic (fast adapting)
  11. Pacinian (Lamellated) Corpuscles
    Tactile (touch and pressure) receptor

    • Dermis, joint capsules, fasciae, serous membranes, some viscera
    • CT capsule
    • Deep pressure, high freq. vibration
    • Phasic (fast adapting)
    • Large size = large receptive field
  12. Ruffini Corpuscles (End Organs)
    Tactile (touch and pressure) receptor

    • Retcular layer of skin
    • Capsule covers dendrites innervation collagen fibers of skin
    • Senses stretch, distortion of dermis
    • Tonic (very slow adapting)
  13. Baroreceptors (Mechanoreceptors)
    • Monitors pressure (stretch due to fluid)
    • Free nerve endings with elastic tissue
    • Phasic (fast adapting): responds to change
    • Locations: digestive tract, urinary bladder, carotid sinus, aortic sinus, lungs
  14. Proprioceptors
    Do not adapt to constant stimulation

    • Muscle Spindles
    • Golgi tendon organs: free nerve endings, sense tension in tendons
    • Joint capsule receptors: free nerve endings, pressure, tension, movement of joint
  15. Chemoreceptors
    • Respond to water and lipid-soluble substances
    • Adapt rapidly
    • Send info to brain stem (not sensory cortex)
  16. Organization of Sensory Pathways
    (1st, 2nd, 3rd order neurons)
    • First-Order Neuron
    • Connected to receptor
    • Cell body in dorsal root ganglion or cranial nerve ganglion
    • Synapses with 2nd-order (interneuron) in brain stem or cord

    • Second-Order Neuron
    • Crosses over to contralateral side
    • Usually synapses with 3rd-order neuron in Thalamus

    • Third-Order Neuron
    • Synapses in post-central gyrus (primary sensory cortex)
    • Does not cross over
  17. Posterior Column Pathway (Ascending)
    • Sensations: Fine (highly localized) touch, pressure, vibration, conscious proprioception
    • Tracts: Fasciculus gracilis (lower half of body), Fasciculus cuneatus (upper half of body)

    • 1st order neuron: Receptor = synpase in nucleus gracilis or cuneatus in medulla
    • 2nd order neuron: Crosses over to other side in medulla, enter medial lemniscus, synapse in thalamus
    • 3rd order neuron: Thalamus = somatosensory cortex, thalamus processes info according to stimulus type and location
  18. Anterior and Lateral Spinothalamic Pathways (Ascending)
    Anterior Spinothalamic Pathway: Crude touch and pressure (poorly localized)

    Lateral Spinothalamic Pathway: Pain and Temp.

    • BOTH
    • 1st order neurons: Synapse in dorsal horn
    • 2nd order neurons: Cross over in spinal cord, synapse in thalamus
    • 3rd order neurons: Synapse in primary sensory cortex
  19. Spinocerebellar Pathway (Ascending)
    • Sensation
    • Unconscious Proprioception (cerebellum)
    • Input from Golgi tendon organs, muscle spindles, joint capsules

    • Pathway
    • 1st order neurons: Synapse in dorsal horn
    • 2nd order neurons: Synapse with Purkinje cells in cerebellum
    • 3rd order neurons: NONE
  20. Motor Pathways (Descending Tracts)
    • Upper Motor Neuron
    • Cell body in CNS
    • Synapses with lower motor neurons (Excitatory or Inhibitory)
    • Stays in CNS

    • Lower Motor Neuron
    • Cell body in brain stem or cord
    • Innervates skeletal muscle fibers of a motor unit (always excitatory at a synapse)
    • Called "Final Common Pathway"
  21. Corticospinal Pathway (Descending)
    • AKA "Pyrimdal System" or "Direct Pathways"
    • Conscious control of skeletal muscle

    • 1. Corticobulbar Tract
    • 2. Lateral Corticospinal Tract
    • 3. Anterior Corticospinal Tract
  22. Corticobulbar Tract (Descending)
    • "bulbar" = brain stem
    • UMN cell bodies in primary motor cortex
    • Synapse in cranial nerve nuclei
    • Conscious control of skeletal muscle¬†
    • Examples: eye, jaw, facial muscle movements
  23. Lateral Corticospinal Tract (Descending)
    • 85% of motor corticospinal pathway neurons
    • UMN in primary motor cortex (cross over at decussation of pyramids in medulla)
    • Synapse on LMN in cord
    • Conscious control of skeletal muscles
  24. Anterior Corticospinal Tract (Descending)
    • 15% of corticospinal neurons
    • UMN in primary motor cortex
    • Synpases on LMN in cord
    • Cross over in spinal cord (not medulla)
    • Conscious control of skeletal muscle
Card Set
EXAM 2: BIO&252 (Chapter 15)
Somatic Nervous System