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Neuroscience > Pons Anatomy, Pathology > Flashcards

Pons Anatomy, Pathology Flashcards

1
Q

What structure in the metencephalon is closely related to the pons?

A

The cerebellum

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2
Q

What cells cause the enlargement of the pons?

A

Pontine nuclei

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3
Q

What region of the pons is phylogenetically newer?

A

The basis

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4
Q

What 3 types of fibers are found in the basis?

A
  • Corticospinal fibers
  • Corticobulbar/ corticonuclear fibers (only in pons)
  • Corticopontine fibers (only in pons)
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5
Q

What tract is related to the corticospinal fibers found in the basis of the pons?

A

The pyramidal tract

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6
Q

What are the function of the corticobulbar/ corticonuclear fibers of the pons?

A
  • Fractionalize movement on cranial nerve nuclei
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7
Q

What cranial nerve nuclei are involved in the corticobulbar/ corticonuclear systems?

A 
CN V
CN VII
CN IX
CN X
CN XI
CN XII
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8
Q

What do the path do the axons of the pontine nuclei take after being synapsed on by corticopontine fibers?

A

The pontine nuclei project ventrally,and then move contralaterally and dorsally to the contralateral cerebellum

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9
Q

What tract/ structure is formed by the axons of the pontine nuclei?

A
  • The middle cerebellar peduncle

- Pontocerebellar tract

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10
Q

What is the name for the combination of the corticopontine and pontocerebellar tracts?

A

Corticopontocerebellar

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11
Q

What nuclei lie in the lower pons?

A
  • CN VI/ Abducens nucleus
  • Spinal nucleus of V/ trigmeninal nucleus with associated tract
  • CN VII/ Facial nerve proper nucleus
  • CN VIII/ Vestibulocochlear nucleus
  • Pontine nuclei
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12
Q

How does the facial nerve proper exit the lower pons?

A
  • Winds posteriorly between the MLF and CN VI nuclei and exits the pons laterally
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13
Q

How does the abducens nerve exit the lower pons?

A
  • Travels directly anteriorly
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14
Q

What is the SVE of the facial nerve proper?

A

Muscles of facial expression and stapedius

- Parotid gland (?)

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15
Q

What muscle is innervated by CN VI?

A

Lateral rectus of the eye

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16
Q

Where does the medial lemniscus become somatopically arranged?

A

From lower to mid pons.

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17
Q

What nuclei are found in the mid-pons?

A
  • Chief/ primary nucleus of CN V

- Motor nucleus of CN V

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18
Q

What tract arises in the mid pons?

A

The ventral trigemonothalamic tract

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19
Q

What sensory information travels along the VTTT?

A
  • Pain
  • Thermal
  • Touch

from face

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20
Q

What are the GSA and SVE components of CN V?

A

GSA: Sensory information from face and anterior 2/3rds of tongue
SVE: Muscles of mastication

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21
Q

What tracts are present in the mid pons?

A
  • VTTT
  • Medial lemniscus
  • Medial longitudinal fasciculus
  • Spinothalamic tract
  • Corticospinal tract
  • Cotricobulbar/ corticonuclear fibers
  • Corticopontocerebellar tract/ middle cerebellar peduncle
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22
Q

What nucleus arises in the upper pons?

A
  • Mesencephalic nucleus of CN V
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23
Q

What sensory information is processed by the mesencephalic nucleus of CN V?

A
  • Proprioception
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24
Q

What structure related to higher centers arises in the upper pons?

A
  • Central tegmental bundle
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25
Q

What system is the central tegmental bundle involved in?

A

The ascending reticular activating system

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26
Q

What structures does the central tegmental bundle terminate onto?

A
  • Thalamus, and then cortex
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27
Q

What is the function of the ascending reticular activating system?

A
  • Arousal
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28
Q

What is the shape of the medial lemniscus in the upper pons?

A

Curving from medioanterior to lateroposterior

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29
Q

Describe the path of the saccade reflex.

A
  • Superior colliculus sends axon to CN VI motor nuclei in low pons
  • CN VI sends an axon to the ipsilateral lateral rectus
  • CN VI sends a collateral off to an interneuron which crosses sides in the low-pons, and ascends up to CN III nuclei, which activates the contralateral medial rectus
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30
Q

What are the 5 types of eye movement?

A
  • Saccades
  • Smooth pursuit movements
  • Vergence
  • Vestibulo-ocular movements
  • Optokinetic movements
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31
Q

What is a saccade?

A

Rapid shift of fovea to target in periphery

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32
Q

How fast can a saccade move the eye?

A

900 degrees/second

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33
Q

What is a smooth pursuit movement?

A

Keeps image of a moving target on the fovea

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34
Q

How fast does a smooth pursuit movement move?

A

100 degrees/second

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35
Q

What is vergence?

A

Moves the eyes in opposite directions to position eye on both fovae (crossing of the eyes)

36
Q

What are vestibulo-ocular movements?

A

Hold images still on the retina during brief head movements

37
Q

What are optokinetic movements?

A

Hold images on retina during sustained head rotation

38
Q

What drives optokinetic movements?

A

Visual stimuli

39
Q

What tendency of movement causes optokinetic nystagmus?

A

Eyes tend to follow or track the motion of one element at a time of a steadily moving display. As a tracked element leaves the field of vision, the eyes will “snap back” to a new object

40
Q

When is optokinetic nystagmus present after birth?

A

5 days after

41
Q

What system is thought to control optokinetic nystagmus?

A

Tectopulvinar system

42
Q

How can optokinetic nystagmus be used as an evaluative tool?

A

The display can be altered such as a fineness of grating and contrast to determine if a patient perceives the different grating as single or multiple objects. This determines visual acuity or ability to determine contrast

43
Q

What muscle is innervated by the abducens?

A

Lateral rectus of the eye

44
Q

What muscle is innervated by the trochlear nerve?

A

Superior oblique of the eye

45
Q

What 5 muscles are innervated by the oculomotor nerve?

A
  • Superior rectus
  • Inferior rectus
  • Medial rectus
  • Inferior oblique
  • Levator palpebrae superiorus (eyelid opening muscle)
46
Q

What cranial nerve closed the eye? What is the name of the muscle?

A
  • CN VII

- Obiqularis occuli

47
Q

What is the parasympathetic component of CN III?

A

Innervates iris and muscles that control lens

48
Q

Which extraoccular eye muscle is found in the lower pons?

A

The abducens

49
Q

What orientation of eye movements is the paramedian reticular formation responsible for?

A

Horizontal

50
Q

What orientation of eye movements is the mesencephalic reticular formation responsible for?

A

Vertical

51
Q

Describe the circuitry of a horizontal gaze.

A
  • At rest, the OMNIPAUSE center in the nucleus of the DORSAL MEDIAN RAPHE inhibits the activations centers in the PONTINE RETICULAR FORMATION
  • When something enters the visual field, the excitatory nuclei of the pontine formation become disinhibited, and superior colliculus also provides excitation
  • Cells project to ipsilateral CN VI nucleus and contralateral CN III nucleus
  • CN VI goes to the ipsilateral lateral rectus
  • CN III goest to the contralateral medial rectus
52
Q

What are the 2 signals that control the motor circuit for horizontal saccades?

A
  • Velocity signal

- Position signal

53
Q

Which signal controls the saccade?

A

Velocity

54
Q

What 2 nuclei are responsible for the position/ step signal?

A
  • Medial vestibular nuclei

- Nucleus prepositus hypoglossi

55
Q

What is the function of the positional signal?

A

Maintains position of the eye through control of extraocular eye muscles

56
Q

During which signal is the omnipause neuron not active?

A

Velocity signal

57
Q

During what eye position is the abducens motor neuron most active?

A

Maintenance of lateral position

58
Q

When is the abducens motor neuron least active?

A

When eye is near midline

59
Q

What results from a lesion to the rootlet of CN VI?

A
  • LMN paralysis of ipsilateral rectus muscle
  • Diploplia
  • Eye can’t move directly laterally or inferior laterally
  • As eye tracks towards ipsilateral side, ipsilateral side will stop at midline, while the other continues to track
60
Q

What results from a lesion to the nucleus of CN VI?

A
  • LMN paralysis of ipsilateral rectus muscle

- No reflex to contralateral eye (so it will not move with rectus)

61
Q

Can the eyes move to the contralateral side with a CN VI lesion?

A

Yes

62
Q

What results from a lesion to the medial longitudinal fasciculus?

A
  • Contralateral eye will not move because the interneuron is lost
  • Ipsilateral rectus will move normally
63
Q

What results from a lesion to CN III?

A

Eye can only move laterally

64
Q

What results from a lesioning of the corticobulbar tracts?

A
  • Perimedial reticular formation of contralateral side lesioned
  • Contralateral CN VI affected
  • Ipsilateral CN III affected
65
Q

What is an alternative name of the a medial longitudinal fasciculus lesion?

A

Internuclear opthalmoplegia

66
Q

What is one and a half syndrome? What are the symptoms?

A

Lesion to medial longitudinal fasciculus and paramedian pontine reticular formation on one side OR lesion to abducens nucleus and medial longitudinal fasciculus on one side.

Lesions:

  • Ipsilateral abducens lesioned
  • Contralteral oculomotor effectively lesioned
  • Ipsilateral oculomotor effectively lesioned

Symptoms:

  • When gazing to contralateral side
  • Contralateral abducens activates, but interneuron connection is lost, so ipsilateral eye does not move
  • When gazing to ipsilateral side
  • Drive to abducens, and interneuron is lost so neither eye moves
67
Q

Which direction will an individual with a CVA look with a cortical lesion? With a brainstem lesion?

A

Cortical: Away from lesion

Brain stem: Towards lesion

68
Q

What provides the blood supply to the pons?

A

Basilar artery, and its following 3 branches:

  • Paramedian
  • Short circumferential
  • Long circumferential
69
Q

What condition may result from a lesion to the basis of the pons?

A
  • Alternating Abducens Hemiplegia
  • Contraltaeral UMN of body
  • Ipsilateral LMN of lateral rectus
    (If medial lemniscus is involved–> contralateral loss of disciminitive sensation to body
70
Q

What is strabismus?

A

Eyes are not properly aligned (cross-eyed)

71
Q

What structures are potentially affected by a unilateral lesion to the tegmentum of the pons?

A

LSTT: Contralteral P&T to body
CN V: Ipsilateral P&T to body
Med Lem: UE & LE discriminitive touch loss to body
CN VII rootlet: Ipsilateral LMN of facial expression

72
Q

What is the term for a lesion to the rootlet of CN VII? What are the symptoms?

A

Bell’s Palsy

- LMN to facial expression muscles

73
Q

What is Millard-Gubler syndrome?

A

Lesion to ipsilateral:
CN VI
CN VII
Corticospinal tracts

74
Q

What syndrome involving the medial longitudinal fasciculus and median pontine reticular formation occurs in the tegmentum of the pons?

A

One and a half syndrome

75
Q

What results from a lesion to the pontine reticular formation?

A

Same effect as a lesion to CN VI and MLF ipsilaterally/ one and a half syndrome

76
Q

Which portion of the CN VII nuclei SVE is bilateral, which is contralateral?

A

Upper: Bilateral
Lower: Contralateral

77
Q

How is CN VII tested?

A
  • Pt smiles, moves face

- Corneal reflex

78
Q

What nerves does the corneal reflex assess?

A

CN V and VII

79
Q

How is the corneal reflex assessed?

A

Lightly cotton swab the eye

80
Q

Describe the pathway of the corneal reflex.

A
  • Discriminitive touch of CN V via grade II fibers and interneurons projects to CN VII ipsilaterally
  • CN VII goes to face and closes the eyelid
  • CN V also crosses over
81
Q

What is the CN V portion of the corneal reflex termed?

A

Consensual corneal reflex

82
Q

What structures may be lesioned in the mid-pons? What are the resultant symptoms of each?

A
  • CN V: Discriminitive sensation loss to ipsilateral face. (motor nucleus) LMNL to ipsilateral muscles of mastication (Motor nucleus)
  • STT: Contralateral P&T of body
  • VTTT: Contralateral P&T of face
  • MLF: Internuclear opthalmoplegia (above medulla)
83
Q

What syndrome will result from a bilateral lesion to the basil portion of the upper pons or midbrain?

A

Locked-in syndrome

  • Bilateral loss of all volitional movement except the eyes
  • No sensation or cognition loss
  • All CN nuclei except 3,4, and 6 are lesioned
84
Q

What syndrome results from a lesion to the superior cerebellar peduncle?

A

Neocerebellar syndrome:

  • Dysnergia
  • Ataxia
  • Dysmetria (inability to measure distance)
  • Dysdiadochokinesia (inability to execute alternate movements rapidly)
  • Dysarthria
  • Etc…
85
Q

What will result from a lesion to the basil portion of the midbrain?

A

Lesioning of corticospinal/ corticobulbar tracts?

UMNL to body and CN

86
Q

What structures may be affected by a lesion to the tegmentum of the midbrain?

A
  • Medial lemniscus: (contralateral disciminitive touch, proprioception, P&T to body)
  • VTTT: Contralateral discriminitive sensaiton, proprioception, P&T to contralateral face (possibly body? Look this up.)
  • Bilateral CTB: Coma
  • Bilateral Inferior colliculus: Hearing loss
  • CN IV: Contralateral superior oblique lesions (can’t look down and out)
87
Q

What is the nervus intermedius?

A

Portion of the facial nerve (from the pons) that provides:
SVA (taste from anterior 2/3rds of tongue)
GVE (parasympathetic motor to submandibular, sublingual and lacrimal glands)

Neuroscience (33 decks)

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