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2012-05-21 13:45:00
Systems Lectures S3

Systems 3 Lectures 3-4
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  1. ´╗┐What are the features of Meissner corpsucles?
    • found beneath epidermis in glabrous skin
    • commin in lips and perioral
    • layered schwann cells interdigetating myelinated axons
    • low threshold (high sensitivity)
    • low-freq vibrations
    • RA (rapidly adapting)
    • single afferent innervates multiple corpuscles
    • small receptive field with "hot spots"
    • perceive: bump, texture, grip from slip
  2. What are the features of Pacinian corpsucles?
    • SubQ
    • variable size
    • single axon
    • low threshold (high-sensitivity)
    • high freq vibrations
    • RA (bec layered)
    • Large receptive field
    • perceive: fine textures, blowing on hand
  3. What are Merkel's disks?
    • mechanoreceptors just beneath epidermis
    • contain vesicles of peptides that modulate nerve terminal
    • low threshold (high-sensitivity)
    • SA
    • multiple per axon
    • overlapping receptive fields
    • perceive: Shape(firing) and force, coarse textures (braille)
  4. what are Ruffini's corpuscles?
    • deep
    • vary in length
    • slngle axon
    • collagen thru and binds CT on ends
    • low threshold (high sensitivity)
    • SA
    • large receptive field
    • sensitive to cutaneous stretching
  5. What is the difference between kinesthesia and proprioception?
    • kinesthesia: awareness of body position and movement
    • proprioception: sub-concious lnfO for feedback control of posture and precise movements
  6. what are the features of muscle spindles?
    • Stretch receptor: sensitive to length changes
    • Gamma fibers
    • la: all fibers, patellar reflex. dynamic (rate of change)
    • II: nuclear chain fibers, static (absolute change)
  7. Explain what happens in the knee-jerk reflex.
    • 1. Tap stretches muscle-activates Ia afferent
    • 2. tells alpha-motor neuron that muscle is too stretched
    • l. alpha-motor increases extensor muscle activity
    • 4. interneuron inhibits antagonist alpha to relax flexor
  8. what does the golgi-tendon organ do?
    • @ junction between muscle fibers and associated tendon
    • contraction causes collagen to produce response
    • Ib (large myel1nated) afferent
    • SA (slow adapt)
    • senses: change in tension
  9. what does a joint receptor do?
    • similar to Ruffini end organs in joints
    • respond to joint angle over small movement ranges usually near extremes
  10. What are the first order neurons in the DC-MlS?
    • cell bodies in DRG
    • pseudo-unipolar neurons
    • enter dorsal horn of spinal cord ipsilaterally
    • topographic representation: medial to lateral superiorly
    • below T6: Gracile tract
    • above T6: Cuneate tract
  11. Where do the 2nd order neurons in the DC-MLS synapSe?
    • caudal medulla,: Gracile and'cuneate Nucleus
    • Axons form Internal Arcuate Fibers that decussate to contralateral medial Lemniscus
  12. Where do the 2nd order axons terminate?
    • In the Ventral Posterior Lateral(VPL) nucleus of the Thalamus
    • VPL topograpy: legs = lateral, arms = medial
  13. What is the facial sensory pathway?
    • Pseudo-unipolar cell bodies in trigeminal ganglion
    • EXCEPT PROPRIOCEPTION: MESENCEPHALIC nucleus in CNS (has motor outputs too jaw-jerk)
    • 2nd order: principle sensory nucleus in PONS
    • some decussate and join TRIGEMINOTHALMIC TRACT (adjacent to medial lemniscus)
    • others(oral cavity insides) DONT decussate and join ipsilateral TRIGEMINOTHALMIC TRACT
    • 2nd axons: teminate in VPM(Ventral Posterior Medial) nucleus of Thalamus
    • project to PRIMARY SOMATIC-SENSORY CORTEX via Posterior Limb of Internal Capsule
  14. What are the divisions of the Somatic Sensory cortex?
    • Postcentral gyrus (sensory)
    • 1: tactile (several digits), texture
    • 2: tactile & proprioception (several digits),complex stimuli (specific shapes), coordiation, shape & size
    • 3a: proprioception
    • 3b: tactile (usually on single digit), texture & shape
  15. Explain the somatosensory cortex topography.
    • medial-sacral (1st in)
    • lateral-trigeminal (last in)
    • things highly used are more represented leading to better two-point discrimination (fingers, thumb, lip, cheek, nose, toe etc)
  16. What are the features of free nerve endings?
    • dermis
    • high threshold (low-sensitivity)
    • tapping, squeezing, rubbing, pinching, stretching
    • A-delta fibers
    • non-discriminative touch
  17. What are the features of thermal recptors?
    • free nerve endings in dermis (A-delta)
    • no mechanical stimulation
    • Heat (35-45 C) and cold 17-35 C increasing reponses for extreme temps
    • ADAPT
  18. What are the features of mechanical nociceptors?
    • free nerve endings in dermis (myelinated A-delta)
    • multiple "hot spots" single afferent
    • mechanical injury associated w tissue damage
    • also have thermo-nociceptors >45, <17 SAME RECEPTOR
  19. What are the features of C-polymodal nociceptors?
    • dermis, 1-2mm diameter 1 or 2 hot spots single afferent
    • mechanical, thermal and chemical
    • unmyelinated C fibers
    • note:chemonociceptors respond to bradykinin, H+ and foreign irritants (venom)
  20. Are A-delta and C fibers only in the dermis?
    • No, also in pulp of tooth
    • they are smaller and slower than A-beta and alpha
  21. What kind of dental pains are transmitted by A-delta and C fibers?
    • A-delta = sharp dental hypersensitivity, smaller receptor areas acute
    • C: dull, throbbing (tooth ache)
  22. Explain the features of the Vanilloid receptor (VR-1).
    • TRP (transient receptor potential family
    • respond to heat >45, H+ and capsacin
    • capsaicin desensitizes recptor
  23. What does substance P do?
    • released from pain fiber stimlation to vasodialate and activate immune response (mast cell or neutrophil release histamine -> + feedback on nociceptor)
    • positive feedback can lead to allergic reaction
  24. Exlain the central pain pathway: sensory discriminative component.
    • pseudo-unipolar neuron cell bodies in DRG
    • enter dorsal horn or spinal cord
    • branch into ascending and descending collaterals to form DORSOLATERAL TRACT of LISSAUER
    • then synapse in gray matter of dorsal horn (2nd order)
    • 2nd order: decussate through the anterior white comissure immediately and form SPINOTHALAMIC TRACT or anterolateral tract
    • neurons terminate in the VPL (ventral posterior lateral) nucleus of thalamus
    • VPL: lower = lateral
  25. What is the topography of the spinothalamic tract?
    • lateral is sacral
    • medial is neck (newest push oldest lateral)
  26. What is the consequence of multiple levels of decussation in the anterolateral?
    • a spinal hemi-lesion will create a particular pattern of sensory loss
    • one side will have reduced pain and temperature sensation
    • while other side witll have reduced two-point discrimination, vibration or proprioception
  27. What is the facial nociceptor pathway?
    • 1st: pseudo-unipolar bodies in Trigeminal ganglion and ganglia associated with VII, IX, and X
    • enter brain stem and DESCEND to SPINAL TRIGEMINAL TRACT to the medulla where they synapse onto neurons of SPINAL NUCLEUS of TRIGEMINAL COMPLEX primarily the pars caudalis
    • 2nd order decussation
    • pars caudalis topography (upside down compared to anatomy of face) mouth rostral, back head (caudal)
    • 2nd order axons dessucate immediately and join the ascending TRIGEMINOTHALAMIC TRACT to terminate int he VPM of thalamus
    • 3rd order carry pain info to Primary and Secondary somatic-sensory cortex
    • Cortex: localization
    • Sub-cortical: perception
    • Paleospinothalmic: suffering component so you avoid in future (reduced by benzodiazepines)
  28. Where do projections from the intralaminar nuclei go?
    • INSULA and CINGULATE CORTEX: higher cortical functions
    • help quantify, worth and behavior of pain
  29. Where do projections from the parabrachial nucleus go?
    • HYPOTHALAMUS and AMYGDALA (emotional part of pain)
    • involved with motivation and affect
    • PERI-AQUEDUCTAL GREY: involved in the descending control of pain, gray matter around 3rd and 4th ventricles
    • filters to RAPHE NUCLEI: inhibitory interneuron decrease transmission of pain from C-fiber via endogenous opiod (enkephalin)
  30. How is pain locally controlled?
    • through interactions with dorsal column and anterolateral system regulates pain perception
    • stimulation of dorsal column ANTIDROMICALLY induce analgesia (rub injury)
    • A-alpha and A-beta excite interneurons that reduce the transmission of pain information
    • Descending fibers excite interneurons that reduce the transmission of pain information.