Neuroscience Test 2, Pons and Midbrain

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  1. Pontine tegmentum
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    • The dorsal part of the pons that contains:
    • Motor cranial nerve nuclei (VI, VII, and motor nuclei of V)
    • Sensory cranial nerve nuclei (VIII, main sensory nucleus of V, spinal nucleus of V)
    • Salivatory nuclei (GVE nuclei)
    • Solitary nucleus and tract
    • Spinal trigeminal nucleus and tract
    • Medial lemniscus & spinothalamic tracts
  2. Basis Pontis
    • Ventral part of the pons that contains:
    • Pontine nuclei
    • Corticofugal tracts (include corticobulbar, corticoreticulobulbar, corticospinal, and corticopontine fibers)
    • Pontocerebellar fibers
    • Reticular formation
  3. Abducens and facial nuclei location and function
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    • Location: Pontine tegmentum
    • Facial function: Innervates muscles of facial expression, stylohyoid, posterior digastric, and stapedius; this is a branchiomotor structure (SVE) and has migrated away from the floor of the IVth ventricle (see picture)
    • Abducens function: Innervates the lateral rectus muscle; remains close to the midline beneath the floor of the IVth ventricle
  4. Motor & spinal nuclei of CN V location and function
    • Location: Caudal pontine tegmentum
    • Motor function: Innervate muscles of mastication MATT (mylohyoid, anterior digastric, tensor tympani, and tensor veli palatini); these are branchiomotor neurons
    • Spinal function: Crude touch from face and cornea
  5. Main sensory nucleus of CN V location and function
    • Location: Mid pontine tegmentum; cross to form ventral trigeminothalamic tract (VTT) or do not cross to form dorsal trigeminothalamic tract (DTT); ascends in trigeminal lemniscus
    • Function: 2-point discriminatory touch and vibration from the face (NOT proprioception)
  6. Trigeminal lemniscus location and function
    • Location: Pontine tegmentum
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    • Function: Carries ventral and dorsal trigeminothalamic tracts to the ventral posterior medial nucleus of the thalamus; relays 2-point discriminative touch and vibration from the face
  7. Medial lemniscus location and function
    • Location: Pontine tegmentumImage Upload 4
    • Function: Carries conscious proprioception, vibration, and discriminative touch from the contralateral body
    • Becomes associated with spinothalamic tract by mid pons because the inferior portion of the medial lemniscus is pushed laterally
  8. Spinothalamic tract location and function
    • Location: Pontine tegmentum
    • Function: Carries pain, temp, and crude touch from contralateral body
    • Becomes associated with medial lemniscus by mid pons because the inferior portion of the medial lemniscus is pushed laterally
  9. CN VIII related structures
    • Auditory structures: Superior olive, lateral lemniscus, trapezoid body
    • Major connections with vestibular nerve, spinal cord, cerebellum, and nuclei of extraocular muscles: Lateral and superior vestibular nuclei
    • Variable function: Medial longitudinal fasciculus
  10. Medial longitudinal fasciculus function based upon location
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    • Medulla: Contains the medial vestibulospinal tract
    • Pons: Tracts that connect the vestibular nuclei with the abduscens, trochlear, and oculomotor nuclei to coordinate eye movements with the head; and connects the abducens and oculomotor nuclei to enable lateral conjugate gaze
    • Remember, this is associated with CN VIII and is found in the pontine tegmentum!
  11. Pontine nuclei location and function
    • Location: Make the bulk of the grey matter of basis pontis
    • Function: Receive information from virtually every area of the ipsilateral cerebral cortex via corticopontine fibers and connect the cerebrum with the cerebellum
  12. Corticopontine tract location and function
    • The largest descending system in the brain (14 million axons) and forms much of white matter of rostral pons
    • Location: Basis pontis
    • Function: Carry information from the ipsilateral cerebral cortex to the pontine nuclei
  13. Pontocerebellar fibers location and function
    • Location: Basis pontis
    • Function: Carry information from the pontine nuclei (via axons of those cells) to the opposite cerebellum via the middle cerebellar peduncle
  14. Corticofugal fibers location and tracts included
    • Location: Basis pontis
    • Tracts: Corticobulbar, corticoreticulobulbar, corticospinal, and corticopontine fibers
  15. Corticonuclear fibers location and function
    • Location: Basis pontis
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    • Function: Carry information from the cerebral cortex to nuclei of CN V, VI, and VII in the tegmentum of the upper pons
  16. Corneal blink reflex
    • Mediated by fibers in the pons, this reflex uses A╬┤ (mechanoreceptor) and C (nociceptor) fibers to carry information to the facial nucleus (motor to orbicularis oculi) and rostral spinal trigeminal nuclei via long ciliary branches of V (opthalmic nerve)
    • Results in a consensual reflex to unilateral stimuli
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  17. Vestibulo-ocular reflex (VOR)
    Involves vestibular nuclei, medial longitudinal fasciculus, and CN VI nuclei in the pons
  18. Pontine micturition centers
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    • Barrington's Nucleus
    • Found in the dorsolateral upper pons, it is connected with pre-ganglionic parasympathetics (excitatory) and Onuf's nucleus (inhibitory) in the sacral cord
    • Activated to cause urination when the bladder is full
    • Pontine lesions result in urine retention
    • Pontine Storage Center
    • Inhibits detrusor but disinhibits Onuf's allowing for urinary retention
  19. Pneumotaxic center location and function
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    • Found in the upper pons near the cerebellar peduncle in the pontine tegmentum
    • Ends inspiration by inhibiting the dorsal respiratory group; also important in establishing respiration rate
  20. Apneustic center
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    • Located in lower pontine tegmentum
    • Drives inspiration; inhibited by the pneumotaxic center and by input from lung stretch receptors; possibly a second center of breathing
  21. Blood supply of pons
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    • All supply is from the basilar artery
    • Paramedian vessels: Supply medial parts of basis pontis and pontine tegmentum
    • Short circumferentials: Supply ventrolateral region of basis pontis
    • Long circumferentials: Supply lateral and dorsal pontine tegmentum; includes AICA and superior cerebellar arteries
  22. Differences between lesions to abducens nerve versus abducens nucleus versus MLF
    • Nerve: Loss of abduction of the eye on the lesioned side (lateral rectus palsy)
    • Nucleus: In addition to above, loss of conjugate gaze to the lesioned side (conjugate gaze palsy)
    • This loss of conjugate gaze occurs because the neurons of the abducens nucleus send their axons to the contralateral III nucleus, specifically to neurons exciting the contralateral medial rectus; this no longer can happen, resulting in conjugate gaze palsy
    • MLF: Internuclear opthalmoplegia (INO) because the axons running to the III nucleus are damaged; failure of adduction of eye on lesioned side on gaze to the opposite side and nystagmus of the eye on unaffected side on abduction
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  23. Differences between lesions to facial nerve versus facial nucleus
    • Nerve: Facial hemiplegia
    • Nucleus: In addition to facial hemiplegia, bilateral hyperacusis will be present because of loss of innervation of stapedius muscle (which receives bilateral input)
  24. Differences between lesions to UMN versus LMN of face
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    • Central VII lesion: UMNs (above facial nucleus) go to both nuclei for upper face and same side for lower face. If we lesioned these, we would only see a deficit on the opposite lower face since the upper face would still receive input from the opposite cortex
    • Peripheral VII lesion: Lesions of VII nucleus or LMNs will affect the same side of the face--both upper and lower
  25. Psedo bulbar palsy
    • Damage to corticonuclear fibers, resulting in UMN defects of CN V, VII, IX, XII
    • Speech problems (dysarthria) and dysphagia
    • Emotional facial reactions intact, resulting in inappropriate outbursts of laughter and crying
  26. Eight-and-a-half syndrome
    One and a half syndromes (conjugate gaze palsy and part of internuclear opthalmoplegia) plus CN VII hemiplegia
  27. Locked-in syndrome
    • Large lesions of the basal pons, damaging the corticospinal and corticobulbar pathways bilaterally, thus interfering with facial expression, speech, and movement
    • Some eye movements spared (inputs to CN III); medulla intact so breathing/cardiac is okay; somatosensory pathways and reticular formation (no coma) are usually spared
    • Results in patient being awake and aware of his surroundings
  28. Generalizations of pontine lesions
    • Tegmental: Same-side CN signs and contralateral sensory loss over body; rostral lesions affect MLF, medial lemniscus, superior cerebellar peduncle, and spinal lemniscus; caudal lesions cause VII palsy and conjugate gaze palsy
    • Basal: Corticospinal, corticobulbar, and VI and VII nerve fibers; caudal have same side facial LMN hemiplesia and contralateral UMN hemiplegia
  29. Regions of the midbrain
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    • Tectum: Superior and inferior colliculi
    • Tegmentum: CN nuclei, major ascending and descending tracts, periaqueductal grey, and reticular formation
    • Substantia nigra
    • Basis pedunculi: Corticofugal projections (corticopontine, corticoreticular/corticoreticulobulbar, corticobulbar, and corticospinal)
  30. General contents of midbrain
    • CN III and IV nuclei (GSE) and Edinger-Westphal nucleus (GVE)
    • Mesencephalic nucleus of CN V (GSA; carries proprioception of face)
    • Red nucleus and substantia nigra (large motor-related areas) and superior colliculus (small motor-related area)
    • Superior cerebellar peduncle tract (???)
  31. Rostral versus caudal midbrain contents
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  32. Inferior colliculus location and function
    • Location: Dorsal caudal midbrain
    • Function: Transmits auditory information from lower relay nuclei via the lateral lemniscus to the medial geniculate body of the thalamus
  33. Trochlear nucleus location, function, and lesions
    • Location: Caudal dorsal midbrain
    • Function: Innervate superior oblique (GSE)
    • Superior oblique depresses the eye when adducted and intorts it when abducted
    • Lesion (of nucleus or nerve): Leads to torsional diplopia; eye is extorted, but patient can correct by tilting head; gives this lesion the name pathetic
  34. Superior cerebellar peduncle
    • Output bundle of the cerebellum
    • Fibers arise from deep cerebellar nuclei, decussate, follow the dentato-rubro-thalamic tract, and end in the VL thalamic nucleus or in the red nucleus of midbrain
  35. Mesencephalic nucleus and tract of CN V location and function
    • Location: Rostral midbrain
    • Function: Conscious & unconscious proprioception of jaw and relay of periodontal reflex; sends axons near the principal nucleus of V (proprioception) and to the motor nucleus of V (reflexes)
  36. Location of trigeminal ganglion, motor nuclei of CN V, pontine trigeminal nucleus (principal?), spinal trigeminal nucleus, and mesencephalic nucleus of CN V
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  37. Periaqueductal grey location and function
    • Location: Surrounding the cerebral aqueduct in the midbrain
    • Function: Mediates stereotypic adaptive behaviors and reproduction while integrating analgesic inputs from the spinothalamic tract
  38. Mesopontine cholinergic neurons location and function
    • Location: Caudal midbrain tegmentum
    • Function: The ascending reticular activating system (ARAS) (as part of the mesencephalic reticular formation) innervates the thalamus by these neurons; these neurons are important for forced attention and consciousness
  39. Midbrain dorsal raphe location and function
    • Location: Midline of upper medulla, pons, and midbrain in the raphe
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    • Function: Contains a large population of serotonin-containing neurons; part of mesencephalic reticular formation, which is important in sleep/wake, attention, etc.
  40. Mesencephalic locomotor center location and function
    • Location: Caudal midbrain
    • Function: Serves as output of basal ganglia;
    • part of mesencephalic reticular formation; important for hard-wired locomotion
  41. Summary of mesencephalic reticular formation
    • Ascending reticular activating system: Contains mesopontine cholinergic cells that innervate the thalamus; important for forced attention and consciousness
    • Midline midbrain: Serotonin-containing neurons of the midbrain dorsal raphe
    • Mesencephalic locomotor center: Output of basal ganglia; important for hard-wired locomotion
  42. Hydraencephaly
    • Most of the telencephalon and diencephalon is replaced by CSF, leaving only the hypothalamus, midbrain, pons, and medulla functional
    • Patients survive but lack cognitive abilities; they can survive, grow, and exhibit emotional responses
  43. Summary of cell groups in midbrain specified by specific neurotransmitters
    • Mesopontine cholinergic cells: Acetylcholine; forced attention and consciousness
    • Midbrain dorsal raphe cells: Serotonin; sleep/wake, attention, etc
    • Substantia nigra cells: Dopamine in the pars compacta; GABA in the pars reticulata
  44. Substantia nigra location and function
    • Location: Rostral midbrain (black stuff); pars compacta located next to the tegmentum (uses neuromelanin/polymer of DOPA and dopamine); pars reticulata located next to crus cerebri
    • Function: Closely associated with basal ganglia; degeneration┬á of pars compacta causes Parkinson's disease
  45. Basis pedunculi somatotopy
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  46. Oculomotor nucleus location and functional divisons
    • Location: Rostral midbrain
    • GSE component: Innervates levator palpebrae superioris; superior, inferior, and medial recti (receives directions for conjugate gaze from VI nucleus); and inferior oblique
    • GVE component: Aka Edinger-Westphal nucleus; provides preganglionic parasympathetic innervation to ciliary ganglion, which sends postganglionic fibers to constrictor pupillae and ciliary muscles (lens accomodators)
  47. Lesion of III nucleus or nerve
    • Both cause "down and out" syndrome aka third nerve palsy (but most lesions occur to nerve usually in the midbrain tegmentum)
    • Ipsilateral strabismus (squint) from loss of medial rectus and depression from loss of superior rectus and inferior oblique
    • Ipsilateral ptosis from loss of levator palpebrae superioris
    • Ipsilateral mydriasis (dilation) from loss of constrictor pupillae
    • Loss of direct and consensual pupillary light reflexes in ipsilateral eye (since CN III carries constriction info from Edinger-Westphal nucleus)
  48. Vertical gaze center location, function, and lesion
    • Location: Rostral dorsal midbrain
    • Function: Coordinates SR, IR, SO, and IO for vertical gaze
    • Lesion: Parinaud's syndrome result in paralysis of upward gaze
  49. Pupillary light reflex
    • Afferent arc goes through optic nerve
    • Neurons come off and go into midbrain tectum to synapse in pretectal area
    • Pretectal neurons send axons to both Edinger-Westphal nuclei (they go to contralateral via posterior commissure)
    • Efferent arc goes through CN III with a synapse in the ciliary ganglion
  50. Superior colliculus function, somatotopy, and output tract
    • Function: Mediates movements of the eyes and head in response to visual, auditory, and somatic stimuli
    • Somatotopy: Outer layers receive inputs from retina and cerebral cortex; deep layers receive input from inferior colliculus (auditory info), spinal nucleus of V, and the spinal cord
    • Output: Extend ventromedially around periaqueductal grey to cross dorsal tegmental decussation and descend to the spinal cord via tectospinal tract and oculomotor nuclei via tectobulbar fibers
  51. Red nucleus location and function
    • Location: Rostral midbrain
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    • Function: Rubrospinal tract is questioned in humans, but in other mammals, it is responsible for generating gait; the major output of the red nucleus in humans is to the inferior olive via the rubro-spinal tract
  52. Common causes of midbrain lesions
    • Vascular (blood supply to midbrain below)
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    • Necrotic (such as uncal herniation)
    • Multiple sclerosis
  53. Weber's syndrome
    • Lesions involving the basal midbrain (basis pedunculi)
    • Cranial nerve III: Although found in the tegmentum, damage to these fibers causes 'alternating oculomotor hemiplesia' on the ipsilateral side
    • Corticobulbar/corticospinal fibers: Contralateral UMN paralysis
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  54. Benedikt's syndrome
    • Lesions involving midbrain tegmentum results in alternating oculomotor hemianesthesia with hemitremor
    • Cranial nerve III: Ipsilateral III nerve palsy
    • Cerebellothalamic fibers/red nucleus: Coarse tremor upon movement
    • Substantia nigra: Resting tremor
    • Medial and spinal lemnisci and ventral trigeminothalamic tract: Contralateral hemianesthesia (all modalities)
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Card Set:
Neuroscience Test 2, Pons and Midbrain
2013-04-04 19:44:29
Neuroscience nMedical School nCarver College Medicine

Flashcards over the lecture portion of neuroscience
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