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Brain Stem III

Brain Stem III. Basic Neuroscience James H. Baños, Ph.D. Yesterday CN I CN II CN III CN IV CN VI. Today CN V CN VII CN VIII CN IX CN X CN XI CN XII. CN V - Trigeminal. CN V - Trigeminal. CN V is the general sensory nerve for the head Touch Proprioception Pain/temperature

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Brain Stem III

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  1. Brain Stem III Basic Neuroscience James H. Baños, Ph.D.

  2. Yesterday CN I CN II CN III CN IV CN VI Today CN V CN VII CN VIII CN IX CN X CN XI CN XII

  3. CN V - Trigeminal

  4. CN V - Trigeminal • CN V is the general sensory nerve for the head • Touch • Proprioception • Pain/temperature • CN V and its connections are to the head what dorsal roots and the spinal cord are to the body • Also has a motor component

  5. CN V - Trigeminal • Trigeminal = “tri” + “geminus” • Tri = 3 • Geminus = at the same birth “Three at the same birth”

  6. CN V - Trigeminal • Peripheral afferent fibers distributed in three divisions • V1 - Ophthalmic - Sensory only • V2 - Maxillary - Sensory only • V3 - Mandibular - Sensory and motor

  7. CN V - Trigeminal • Peripheral sensory afferents converge at the trigeminal ganglion • This is a homologue of the dorsal root ganglion of spinal sensory nerves

  8. CN V - Trigeminal • Discriminative touch and conscious proprioception • The main sensory nucleus of V is a homologue of dorsal column nuclei (gracilis and cuneatus)

  9. CN V - Trigeminal • Spinal Cord: Medial Lemniscus Thalamus Dorsal Columns NG NC

  10. CN V - Trigeminal • Trigeminal System: Medial Lemniscus Thalamus Dorsal Columns NG NC CN V V Main sensory nucleus of V

  11. CN V - Trigeminal Main sensory nucleus of V V V NC NG NG NC

  12. CN V - Trigeminal • Mesencephalic nucleus of V • Actually not a true nucleus • Cell bodies of what would otherwise be the ganglionic portion of proprioceptive fibers from the muscles of the jaw

  13. CN V - Trigeminal Mesencephalic nucleus of V Main sensory nucleus of V V V

  14. CN V - Trigeminal • Pain and temperature • The spinal nucleus of V is a long upward extension of the posterior horn of the spinal cord • It contains a set of neurons resembling the substantia gelatinosa in the spinal cord • The tracts entering the spinal nucleus of V are like an upward extension of the tract of Lissauer

  15. CN V - Trigeminal • Pain and temperature • Trigeminal pain and temperature fibers descend caudally to enter the spinal nucleus of V • Fibers from the spinal nucleus of V decussate and join the ascending spinothalamic tract

  16. CN V - Trigeminal Mesencephalic nucleus of V Main sensory nucleus of V Spinal nucleus of V V V V V Spinothalamic tract

  17. CN V - Trigeminal • Motor - Muscles of mastication • The Motor nucleus of V is homologous to ventral horn in the spinal cord • Corticobulbar upper motor neurons synapse on lower motor neurons originating in this nucleus

  18. CN V - Trigeminal UMN Mesencephalic nucleus of V Main sensory nucleus of V LMN Motor nucleus of V V V V V V V Spinal nucleus of V

  19. Clinical Correlation • Afferent limb of corneal blink reflex • Direct and consensual response

  20. Clinical Correlation • Jaw muscle weakness • Jaw deviates toward the weak side

  21. Clinical Correlation • Disorders of sensation • Trigeminal neuropathy • Trigeminal neuralgia • Traumatic brain injury • Loss of smell does not include harsh or unpleasant smells • This can be a means of detecting “faking” • Smelling salts and the ARAS

  22. CN VII - Facial

  23. CN VII - Facial • Motor (branchial) • Muscles of facial expression via the motor nucleus of VII • Eye closure • Motor (autonomic) • To salivary and lacrimal glands from superior salivatory nucleus

  24. CN VII - Facial • Somatic sensory • Skin of the outer ear to spinal trigeminal nucleus • Visceral Sensory • Palate and taste buds on anterior 2/3 of the tongue to the Nucleus of the solitary tract

  25. CN VII - Facial Nucleus of the solitary tract Superior salivatory nucleus Motor nucleus of VII VII VII

  26. CN VII - Facial • Motor nucleus of VII • Corticobulbar fibers for upper face synapse on the motor nucleus of VII bilaterally (most fibers decussate) • Fibers bound for the lower face synapse on the contralateral nucleus only

  27. CN VII - Facial VII VII To upper face To upper face To lower face To lower face

  28. CN VII - Facial VII VII To upper face To upper face To lower face To lower face

  29. CN VII - Facial VII VII To upper face To upper face To lower face To lower face

  30. Clinical Correlation • Lesions of the cortex or corticobulbar tract • Contralateral lower face weakness • Ex: Stroke • Lesions of the motor nucleus of VII or peripheral nerve • Ipsilateral lower and upper face weakness • Ex: Bell’s Palsy

  31. Clinical Correlation • CN VII is the efferent limb of the corneal blink reflex ? - left VII left ? - right VII - right

  32. Clinical Correlation • Corneal blink reflex • Afferent fibers originate in the ophthalmic division of CN V • Synapse on Spinal Nucleus of V • Internerons project bilaterally (via the reticular formation) to neurons in the motor nucleus of VII

  33. Clinical Correlation • CN VII is the efferent limb of the corneal blink reflex V - left VII left V - right VII - right

  34. CN VIII Vestibulocochlear

  35. CN VIII - Vestibulocochlear • Two divisions - both special sensory • Cochlear (auditory) • Vestibular

  36. CN VIII - Vestibulocochlear • Cochlear division • Cochlear ganglion to CN VIII • CN VIII synapses in the cochlear nuclei • Cochlear nuclei project to the superior olivary nucleus and inferior colliculus • Superior olivary nucleus is also receiving input from contralateral cochlear nuclei • Superior olivary nucleus projects to inferior colliculus • Inferior colliculus projects to thalamus

  37. CN VIII - Vestibulocochlear • Cochlear division Sup. Olivary Nuc. Cochlear Nuclei VIII

  38. Clinical Correlation • Note that auditory information is bilaterally represented very early in the pathway • This means that you only have unilateral hearing loss following • Lesion to CN VIII itself • Lesion to the cochlear nuclei on one side • Cortical lesions (i.e., Heschel’s Gyrus) will not result in unilateral hearing loss

  39. CN VIII - Vestibulocochlear • Vestibular division - inputs • Vestibular afferents project to • The cerebellum • Vestibular Nuclear Complex • Inferior • Lateral • Medial • Superior • Vestibular Nuclear Complex also receives afferents from • Cerebellum • Contralateral Vestibular Nuclear Complex

  40. CN VIII - Vestibulocochlear • Vestibular division - inputs

  41. CN VIII - Vestibulocochlear • Vestibular division - Outputs • Thalamus • Nuclei of III, IV, and VI • Spinal Cord • Lateral Vestibulospinal Tract • Medial Vestibulospinal Tract

  42. CN VIII - Vestibulocochlear • Vestibular division - Outputs • Thalamus • Nuclei of III, IV, and VI • Spinal Cord • Lateral Vestibulospinal Tract • Medial Vestibulospinal Tract • Cerebellum

  43. CN VIII - Vestibulocochlear • Medial and Lateral Vestibulocerebellar Tracts • Part of a system that supports the voluntary motor system by providing corrective signals to muscles depending on vestibular feedback • Why are there projections to oculomotor nuclei?

  44. Clinical Correlation • Vestibuloocular Reflex (VOR) • Fixation of gaze despite head movement • Stabilizes image on the retina • Reflexive, not a pursuit movement • Works in the dark • Works if unconscious

  45. Clinical Correlation • Doll’s eye maneuver • Can be used to test the integrity of the brain stem in an unconscious patient

  46. CN IX - Glossopharyngeal

  47. CN IX - Glossopharyngeal • Glossopharyngeal means “tongue and throat” • Numerous afferents from • Carotid sinus • Walls of the pharynx • Mucous membranes • Taste bud from posterior 1/3 of the tongue

  48. CN IX - Glossopharyngeal • Sensory • Taste bud afferents travel to the nucleus of the solitary tract • Pain from the pharynx and posterior 1/3 of the tongue likely go to spinal trigeminal nucleus • Some sensory fibers likely reach the main sensory nucleus of V

  49. CN IX - Glossopharyngeal • Motor • Stylopharyngeus • Swallowing (with X anf XII) • Elevates the pharynx while swallowing and speaking • These fibers arise from the nucleus ambiguus, a poorly differentiated nucleus in the medullary tegmentum

  50. Clinical Correlation • Afferent of the Gag Reflex

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