Neuro: 10:00 - 11:00Scribe: Taylor Nelson

Thursday, January 15, 2009Proof: Chaz Capra

Dr. BanosBrainStem IIIPage1 of 5

  1. CN V - Trigeminal [S4]
  2. Cranial nerve V is generally speaking the sensory nerve for the head
  3. We’re talking touch, proprioception, pain, and temperature
  4. It’s the equivalent of the dorsal root and dorsal root ganlia of the spinal cord (though it does contain a little motor component)
  5. CN - Trigeminal [S5]
  6. Trigeminal = “tri” + “geminus”
  7. Tri = 3
  8. Geminus = at the same birth
  9. “Three at the same birth” or Triplets meaning there will be three of something
  10. The different afferent fibers(sensory systems) are distributed into three divisions[S6]
  11. V1 - Ophthalmic - Sensory only
  12. V2 - Maxillary - Sensory only
  13. V3 - Mandibular - Sensory and motor
  14. The distribution is a dermatome arrangement just like with the spinal cord
  15. When you look at the physiologic appearance of CN V you do have a big ganglion with three major branches coming into the ganglion
  16. CN V - Trigeminal [S7]
  17. Homologue of the dorsal root ganglion of the spinal sensory nerves
  18. Here we have dorsal root ganglion, this is the sensory nerve coming into the dorsal aspect of the spinal cord so the sensory information coming into the face this would be the equivalent ganglion (see red arrows on slide)
  19. CN V - Trigeminal [S8]
  20. Discriminative touch and conscious proprioception – again these are familiar modalities
  21. Mediated by themain sensory nucleus of V is a homologue of dorsal column nuclei (gracilis and cuneatus), same system
  22. Here’s what we have in the spinal cord: dorsal columns, medial lemniscus [S9]
  23. Fasiculus cuneatus and gracilis synapse on to our nucleus cuneatus and gracilis, they decussate and continue to rise as the medial lemnicus up to the thalamus
  24. All we’re really doing is adding CN V to accomplish the same thing for the face [S10]
  25. The information is coming in from the face and jaw, synapsing onto the main sensory nucleus of CN V which then joins those fibers of the medial lemniscus
  26. Just adding the head onto the sensory fibers, so by the time it gets to the thalamus you have the entire body represented
  27. [S11] Can see the dorsal columns, medial lemniscus, fasiculus gracilis and cuneatus on to their respective nuclei decussating up the thalamus (drawn bilaterally), can see CN V coming into the main sensory nucleus decussating and joining the other fibers – same as the previous slide but on an anatomic framework
  28. CN V - Trigeminal [S12]
  29. Mesencephalic nucleus of V
  30. Trigeminal has several nuclei
  31. Not really a true nucleus
  32. Cell bodies of what would otherwise be the ganglionic portion of proprioceptive fibers from the muscles of the jaw and it goes on to the motor nucleus of CN V
  33. It’s not a true nucleus because a true nucleus consists of anerve coming in, synapsing on another nerve and transmits to another location, in this case it comes in and the cell body is located there but it is the same neuron so it’s not synapsing and making a multi-segmented pathway
  34. These are proprioceptive fibers so location-wise we’re talking in approximations [S13]
  35. We haven’t added the motor nucleus that goes to the jaw yet but a jaw jerk reflex is mediated by this pathway
  36. CN V - Trigeminal [S14,25]
  37. Pain and Temperature – different modalities must be accounted for so it makes sense that we would have these different nuclei
  38. Pain and temperature are associated with the spinal nucleus of CN V
  39. The spinal nucleus of V is a long upward extension of the posterior horn of the spinal horn, contains a set of neurons resembling the substantia gelatinosa in the spinal cord, extends up into the medulla to be the portion of the system that takes the pain and temperature information from the face
  40. The tracts entering the spinal nucleus of V are analogous to an upward extension of the tract of Lissauer
  41. Trigeminal pain and temperature fibers descend caudally to enter the spinal nucleus of V, this is odd in the nervous system because you don’t see many things that choose to go down when the ultimate destination is upward
  42. Think of how this differs from Clark’s column, the nerves coming in above Clark’s column did not go down Clark’s column and then back up, they just went up
  43. Fibers from the spinal nucleus of V decussate and join the ascending spinothalamic tract, like the dorsal columns it joins it’s appropriate tract
  44. [S16] We have the spinal nucleus of CN V(again an upward extension of the substantia gelatinosa) the fibers coming in descend to various levels synapse onto that nucleus and the output is decussating and joining the spinothalamic tract so we’re adding the head onto the pain and temperature tract
  45. CN V - Trigeminal [S17]
  46. Motor - Muscles of mastication
  47. The Motor nucleus of V is homologous to ventral horn in the spinal cord – again, everything that is represented in the spinal cord is re-represented in a specialized way in the Trigeminal system
  48. Corticobulbar upper motor neurons synapse on lower motor neurons originating in this nucleus
  49. [S18] Just adding on the motor nucleus of CN V
  50. Corticobulbar tract decussates at multiple points
  51. You do still have the upper motor neuron and lower motor neuron representation
  52. You can have upper and lower motor neuron signs with your jaw, you can have an exaggerated jaw jerk reflex
  53. If somebody has an exaggerated jaw reflex and everything in the rest of the body is normal than we know that we have an upper motor neuron lesion where the trigeminal system goes to that muscle
  54. The upper motor neuron is providing regulation and supervision that keeps that reflex arc in check

Student Questions

  1. SQ: Inaudible – concerning upper and lower motor neurons
  2. A: Know where the different sets of symptoms are occurring, with regards a spinal cord lesion you will not have all lower motor neuron lesions, or all upper motor neuron lesions there will be a pattern of upper and lower that will help you narrow down where the lesion is. Also, don’t get caught up with upper and lower extremities and get that tangled up with upper and lower motor neuron – will have lower motor neuron signs in arms and upper motor neuron signs in legs etc. so often times it will be the reverse of what you think.
  3. SQ: Inaudible – concerning decussation
  4. A: The decussation especially when talking about motor neurons since they decussate in the medulla it will not give you a whole lot about where you are in the spine. Decussation points come in handy for localization when you have pathways that decussate at different levels. For example: in the corticospinal tract to have a contralateral deficit you would have to be hitting above the decussation (medulla or above), usually you will know if you are hitting at the medulla or above from reading the case so you begin looking at other pathways that decussate at different places. The oddball tends to be pain and temperature, it decussates at every level so knowing the level of the pain and temperature lesion longitudinally in the neuraxis gives you a lot more localizing information. Weakness and somatosensory deficits are great for lateralizing each side.
  5. SQ: Inaudible
  6. A: Sensory level is going to be (sensory level is the spot at which you lose pain and temperature sensation) extended down a little bit, giving you the best hint for longitudinal location. Motor and somatosensory are going to be ipsilateral and the pain will be on the contralateral side. Motor weakness and loss of sensation on the left side of the body and loss of pain sensation for some portion of the right side of the body the lesion will probably be on the left side – can’t get the weakness and the somatosensory deficit if the lesion is on the same side. You are expected to use the pathways you are learning to verify where you think a lesion is, so think through the pathways individually and if a pathway doesn’t fit then reassess your hypothesis.
  1. Clinical Correlation [S19, 20, 21]
  2. The trigeminal nerve is the afferent limb of corneal blink reflex
  3. Direct and consensual response arrangement
  4. Photo of a test of the corneal blink reflex
  5. Cornea has pain receptors, not a fine touch sensation, anything touching your cornea for the most part will be perceived as a pain stimulus
  6. Jaw muscle weakness can be a symptom of a disfunctioning CN V
  7. Jaw deviates toward the weak side upon opening the mouth, so whichever side is disfunctioning the jaw opens that way
  8. Disorders of sensation
  9. Trigeminal neuropathy – loss of sensation in the trigeminal system
  10. Trigeminal neuralgia – extreme pain constantly in the trigeminal system to the point that you may have surgery to eliminate some of the pain
  11. Traumatic brain injury
  12. Loss of smell does not include harsh or unpleasant smells, the reason smelling salts work is because they are essentially a pain stimulus going into the ARAS, sensors in your nose that are part of the trigeminal system for pain (do not run through the cribiform plate)
  13. This can be a means of detecting “faking” – if they deny smelling things that trigger a different pathway they are most likely faking
  14. CN VII – Facial [S23]
  15. Motor (branchial)
  16. Muscles of facial expression via the motor nucleus of VII
  17. Eye closure
  18. Motor (autonomic)
  19. To salivary and lacrimal glands from superior salivary nucleus
  20. CN VII – Facial [S24]
  21. Somatic sensory
  22. Skin of the outer ear go to spinal trigeminal tract
  23. Visceral Sensory
  24. Palate and taste buds on anterior 2/3 of the tongue to the nucleus of the solitary tract
  25. As we get to CN VII and below we will start to see a lot of these extra neuclei that work with a couple of different cranial nerves and solitary tracts is one of them
  26. Visceral Motor (Autonomic)
  27. Superior Salivary Nucleus to salivary glands
  28. CN VII – Facial [S25]
  29. Photo:
  30. Motor nucleus of VII
  31. Superior salivary nucleus
  32. Nucleus of the solitary tract
  33. CN VII – Facial [S26]
  34. Motor nucleus of VII
  35. The fibers that go from the motor nucleus of VII to the face are arranged somatotopically in that the fibers going to the upper muscles of the face are the top part of the nucleus and the fibers going to the muscles of the lower part of the face are in the lower part of the nucleus
  36. The corticobulbar fibers for upper face synapse on the motor nucleus of VII bilaterally (most decussate)
  37. The fibers bound for the lower face synapse on the contralateral nucleus only, this leads to a clinically useful phenomena
  38. [S27, 28] Corticobulbar fibers synapse bilaterally to the upper face and contralateral to the lower face
  39. [S29] If a lesion occurs at the lightning bolt:
  40. Contralateral lower face weakness
  41. The muscles of the upper face are still intact
  42. Clinical Correlation [S30]
  43. Classic cortical stroke – ability to move forehead is retained and muscle weakness will occur in the contralateral lower face
  44. If the lesion is the motor nucleus itself or the peripheral nerve then the entire side of the face is affected, so usually if the entire side of the face is weak Bell’s palsy is the term you hear if the pathology just involves the nerve itself
  45. The less serious lesion has more prominent symptoms with an entire side of the face being weak and the more serious lesion (cortical stroke) will generate a less prominent symptom with only a quarter of the face being weak
  46. Clinical Correlation[S31]
  47. CN VII is the efferent limb of the corneal blink reflex with the afferent limb being the CN V
  48. So you should have a direct response and a consensual response
  49. CN VIII Vestibulochochlear [S35]
  50. Two divisions - both special sensory
  51. Cochlear (auditory)
  52. Vestibular
  53. Each function is related to the ear, inner ear is the balance (vestibular part), cochlea (hearing part)
  54. Tomorrow in lab the nerve will look like a pair of wires running together
  1. CN VIII Vestibulochochlear [S36]
  2. Cochlear division – Will build this later in more detail, slide is more for flavor now
  3. Cochlear ganglion to CN VIII
  4. CN VIII synapses in the cochlear nuclei
  5. Cochlear nuclei project to the superior olivary nucleus and inferior colliculus
  6. Superior olivary nucleus is also receiving input from contralateral cochlear nuclei
  7. Superior olivary nucleus projects to inferior colliculus
  8. Inferior colliculus projects to thalamus
  9. CN VIII Vestibulochochlear [S38]
  10. The important thing to know right now is that auditory information is bilaterally represented very early in the pathway, unlike a lot of things that may travel for a while before they decussate you have immediate bilateral representation
  11. This means that it is very hard to have unilateral hearing loss following a central nervous system lesion
  12. If you have a lesion to CN VIII itself or a lesion to the cochlear nuclei on one side you could have unilateral hearing loss
  13. Cortical lesions (i.e., Heschel’s Gyrus, primary auditory cortex) will not result in unilateral hearing loss
  14. This can be very critical localizing information
  15. CN VIII Vestibulochochlear [S39, 41]
  16. Vestibular division – inputs
  17. Vestibular afferents project to:
  18. The cerebellum
  19. Vestibular Nuclear Complex
  20. Inferior, lateral, medial, superior
  21. Vestibular Nuclear Complex also receives afferents from:
  22. Cerebellum
  23. Contralateral Vestibular Nuclear Complex
  24. This is a very complex system
  25. Vestibular division - Outputs
  26. Thalamus
  27. Nuclei of III, IV, and VI
  28. Spinal Cord
  29. Lateral Vestibulospinal Tract
  30. Medial Vestibulospinal Tract
  31. [S43] Medial and Lateral Vestibulocerebellar Tracts
  32. Part of a system that supports the voluntary motor system by providing corrective signals to muscles depending on vestibular feedback
  33. Part of what the vestibular system is doing (along with the cerebellar system, and others) is giving feedback to the muscles to correct balance
  34. Why are there projections to the occulomotor nuclei?
  35. The eyes must be able to compensate and adjust when the body or head is moving, this forms part of the vestibulooccular reflex
  36. [S44] Vestibuloocular Reflex (VOR)
  37. Fixation of gaze despite head movement
  38. Stabilizes image on the retina
  39. Reflexive, not a pursuit movement
  40. Works in the dark
  41. Works if unconscious
  42. Clinical Correlation
  43. Doll’s eye maneuver can be used to test the integrity of the brain stem in an unconscious patient, if a lesion is present in the brainstem the odds are this system would be affected so if the VOR is intact and the eyes remain forward most of the brain stem is most likely reasonably intact
  44. CN IX - Glossopharyngeal[S47]
  45. Glossopharyngeal means “throat and tongue”
  46. Numerous afferents from:
  47. Carotid sinus
  48. Walls of the pharynx
  49. Mucous membranes
  50. Taste bud from posterior 1/3 of the tongue
  51. [S48] Sensory
  52. Taste bud afferents travel to the nucleus of the solitary tract
  53. Pain from the pharynx and posterior 1/3 of the tongue likely go to spinal trigeminal nucleus (this is not entirely clear)
  54. Some sensory fibers likely reach the main sensory nucleus of V
  55. Big picture: think throat, posterior
  56. [S40] Motor
  57. Stylopharyngeus
  58. Swallowing (with X and XII)
  59. Elevates the pharynx while swallowing and speaking
  60. These fibers arise from the nucleus ambiguus, a poorly differentiated nucleus in the medullary tegmentum
  61. [S50] Clinical Correlation
  62. Afferent of the Gag Reflex
  63. Glossopharyngeal, Gag – pneumonic
  64. CN X - Vagus [S51]
  65. Does a lot of different stuff
  66. Principal parasympathetic nerve
  67. Widely distributed (vagus = “wandering”)
  68. Some overlap in function with CN IX, when talking about throat and tongue functions start to overlap a bit
  69. Preganglionic parasympathetic fibers to the thoracic and abdominal viscera
  70. Arise in the dorsal motor nucleus of the vagus
  71. Fibers to the heart originate in the nucleus ambiguus
  72. [S52] Visceral sensory information from:
  73. Thoracic and abdominal viscera
  74. Taste buds of the epiglottis
  75. Most project to nucleus of the solitary tract
  76. Some may project to spinal nucleus of V
  77. Don’t get totally lost in all the different nuclei, take a look at different nuclei and have an idea of what they do
  78. [S53] Clinical Correlation
  79. Hoarseness (larynx)
  80. Dysarthria – broad term for speaking difficulty that is not related to neural damage in the brain (cortical damage), so this is weakness on one side of your face making you mumble etc.
  81. Paralysis of the soft palate
  82. Dysphagia – problems with swallowing
  83. Uvula deviates away from weakness
  84. Loss of cough reflex (anesthesia of pharynx and larynx)
  85. [S54] Efferent of the gag reflex
  86. IX  X
  87. Vagal nerve stimulator – if you stimulate the vagal nerve you can head off a seizure before it happens, not clear exactly how it works
  88. Now it is showing up for use in treating depression, but the problem remains nobody really knows how it does what it does
  89. CN XI - Spinal Accessory [S57]
  90. Motor only - neck and shoulder muscles
  91. Sternocleidomastoid
  92. Part of the trapezius
  93. Accessory Nucleus (similar to the grey matter in the spinal cord)
  94. [S58] Runs as a long row of rootlets
  95. CN XII - Hypoglossal [S58]
  96. Between the pyramid and the olive
  97. [S59] Motor - Muscles of the tongue
  98. Takes a lot of innervations because the tongue is really complicated
  99. The tongue deviates to the weak side when protruded

[End 40:23]