the midbrain 2

8/11/2019 The Midbrain 2

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The Midbrain

Josephine M. Lumitao MD, MHPED, FPOGS

Section of Neuroanatomy

Department of AnatomyUSTFMS


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Functions of the Midbrain

Conduit for ascending and descending fibertracts

Contains nuclei of cranial nerves III and IV and

midline nuclei with diverse functions

Center for pupillary light reflex


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Developmental Features of the

Midbrain

Dorsoventral orientation of alar-basal plates Neural cavity- Cerebral aqueduct

Alar plate derivatives : Inferior colliculus

Superior colliculus Substantia nigra

Red nucleus

Basal plate derivatives : Trochlear nucleus

Oculomotor nucleus

Edinger-Westphal nucleus

Marginal zone invaded by fibers that form cruscerebri/cerebral peduncles


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Boundaries of the midbrain

Ventral surface: Caudal boundary- Superior pontine sulcus where

crus cerebri enters the pons

Rostral boundaryexit of crura cerebri from

cerebral hemispheres and mammillary bodies

Dorsal surface:

- Caudal boundaryExit of trochlear nerves

- Rostral boundary- midbrain-diencephalicboundary formed by posterior commissure


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External FeaturesDorsal Surface

Caudal boundary: Exit oftrochlear nerves

Rostral boundary:Posterior commissure

Four elevations- Corpora

quadrigemina Inferiorcolliculus(caudal)

Superior colliculus(rostral)

Pineal gland extends

posteriorly above andbetween the superiorcolliculus
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External FeaturesVentral Surface

Caudal boundary: Superiorpontine sulcus

Rostral boundary:

Mammillary bodies

Crura cerebripair oflarge axon bundles from

cerebral hemisphere

caudal to the optic tract

Oculomotor nerves exit atinterpeduncular fossa
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Lateral View of Midbrain
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Internal Anatomy of Midbrain

Tectumarea posterior tocerebral aqueduct; containsthe superior and inferiorcolliculus

Tegmentumextends from

base of tectum; does notinclude substantia nigra;contains ascending anddescending fiber tracts andcranial nerve nuclei

Basis pedunculiAnterolateral portion ofmidbrain on each side madeup of Substantia nigra andCrus cerebri



Caudal MidbrainLevel of the Inferior Colliculus

-TECTUM:

Inferior colliculus made up of a

large central nucleus, dorsal

nucleus and lateral nucleus;

auditory relay nuclei receiving

fibers of the lateral lemniscus

Brachium of the inferior colliculus

projects to medial geniculate body
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Inferior Colliculus

Central nucleus-egg shaped core of the inferiorcolliculus at the base of afferent fibers of the laterallemniscus; consist of parallel shaped layers of cellswith disc shaped dendritic fields; receives andintegrates information from multiple hindbrainauditory sources and projects to medial geniculatenucleus; ascending projections converge in a point-to-plane order, low frequencies posterolaterally andhigh frequencies anteromedially

Paracentral nucleimade up of pericentral nucleus(posterior) and external (lateral) nucleus; receive input

from central nucleus, cerebral cortex and non-auditoryinput from spinal cord and superior colliculus;projects to MGN, superior colliculus and reticularformation; involved in functions related to attention,multisensory integration and auditory-motor reflex



Inferior Colliculus receives auditory input from

Lateral lemniscus; projects to medial geniculate body
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TEGMENTUM:

- Periaqueductal graycollection of

nerve cell bodies that surround the

cerebral aqueduct; opiate receptors;

receives spinomesencephalic tract and

projects to nucleus raphe magnus; for

modulation of pain transmission-Trochlear nucleussupplies superior

oblique muscle

-Medial longitudinal fasciculus

-Mesencephalic nucleusand tract

-Decussation of superior cerebellar

peduncle-crossed fibers from deep

cerebellar nuclei to red nucleus and/or

thalamus

-Anterolateral system and medial

lemniscus; Central tegmental tract



Trochlear Nerve

Only motor cranial nerve formed by axons thatcross the midline before their exit

Longest intracranial course

Trochlear nucleus provides GSE fibers tosuperior oblique which functions to direct the

eyeball down when turned inwards (intorsion,

depression)

Receives projections from neurons in frontaleye field via the rostral interstitial nucleus of

the MLF (medial longitudinal fasciculus)




-BASIS PEDUNCULI:

-Substantia nigrapars compacta

(dopamine rich) and pars

reticulata (GABA)

-Crus cerebrimiddle 3/5

Corticospinal and corticobulbar;medial 1/5 frontopontine (Arnolds

bundle); lateral 1/5 temporo-

parieto-occipito pointine fibers

(Turcks bundle)



Substantia Nigra

Functionally associated with the basal nuclei Made up of pars compacta and pars reticulata

Pars compactalarge number of neuromelanin

containing cells rich in dopamine; project to

neostriatum(caudate nucleus and putamen) as part ofnigrostriatal pathway

Pars reticulata- loose aggregations of medium to large

sized neurons rich in GABA; project to superior

colliculus, thalamus and pontine reticular formation Parkinson disease- associated with loss of dopamine ;

resting tremors, akinesia, bradykinesia , blank stare,

paucity of movement


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Parkinsons Disease
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TECTUM:

Superior Colliculus-made up ofalternating gray matter and white matter;

layers I-III receive input from retina and

visual cortices and project to thalamus;

layers IV-VII subserve gaze changesincluding eye movement and project to

thalamus, brain stem and spinal cord

-Detection of movements in visual fields

for visual orientation, searching and

tracking

-For audiovisual reflexes as it receives

input from inferior colliculus

-Connects with the lateral geniculate

nucleus via brachium of superior

colliculus

Features of Rostral MidbrainLevel of

Superior Colliculus
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TEGMENTUM:

Red nucleusMagnocellular divisionsend axons which cross the midline at

ventral tegmental decussation of Forel to

form the rubrospinal tract that innervates

the proximal limb flexorsParvocellular division (rostral)

axons form the rubroolivary tract that

descends in the central tegmental tract

and terminates in the ipsilateral inferior

olives

Receives afferents from the

contralateral deep cerebellar nuclei and

ipsilateral cerebral cortex


Superior Colliculus


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TEGMENTUM:

Dorsal tegmental decussation of

Meynertcrossed projections of

superior colliculus to brain stem areas

(tectoreticular, tectoolivary and

tectospinalcervical spinal cord)Tectobulbospinal system of brain stem

MLF

Medial lemniscus

Anterolateral system

Central tegmental tract

Ventral tegmental decussation of

Forel-crossed axons from red nucleus

that form ruprospinal tract


Superior Colliculus


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Oculomotor Nucleus

Composed of:

- central nucleus of Perlia that supplies the

ciliary muscle for convergence and accommodation

- lateral dorsal somatic cell column that innervates all extraocular musclesexcept the lateral rectus and superior oblique

- Midline dorsal subnucleus(caudal central subdivision) supply the levatorpalpebrae superioris

- midline dorsal visceral cell column (Edinger-Westphal nucleus) , origin ofpreganglionic parasympathetic fibers to the ciliary ganglion, postganglionicfibers of which innervate sphincter pupillae and ciliary muscles

Does not receive direct cortical projections via corticobulbar pathway; cortex offrontal eye field exerts its control over oculomotor neurons via projections torostral interstitial nucleus of the MLF (riMLF, the vertical gaze center) and thesuperior colliculus

Accessory nuclei: interstitial nucleus of Cajal, nucleus of Darkschewtisch,

nucleus of posterior commissure and riMLF Oculomotor nerve emerge at interpeduncular fossa medial to crus cerebri

Ipsilateral lesion will result in an abducted and depressed eye, diplopia (doublevision), mydriasis (dilated pupil) non reactive to light and cannot accommodateand drooping of eyelids (ptosis)


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R ti l d R h N l i f


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Reticular and Raphe Nuclei of

Midbrain

Reticular Nuclei arecuneiform and

subcuneiform nuclei

which forms part of

ARAS for maintaining

alertness and

wakefulness

Dorsal raphe nucleus

serotonergic neurons

that modulate neuronalactivity involved in

sleep/dream cycles


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Midbrain-Diencephalic junction

Pretectal Areaconsist of groups of cells related to visualsystem; brainstem center for pupillary light reflex; receives inputfrom superior colliculus and project bilaterally to Edinger-Westphal nucleus mediating direct and consensual pupillary lightreflex

Posterior commissurerostral boundary of midbrain;functionally, contains fibers from the pretectal nuclei that projectto contralateral Edinger Westphal nucleus and upgaze fibersfrom riMLF; important in consensual pupillary light reflex andupward vertical gaze

Ventral tegmental area of Tsai-diffuse cell group

ventromedial to red nucleus and continuous with lateralhypothalamic area; contains dopaminergic neurons that projectto cortical and subcortical structures of limbic system (emotionalbehavior); fibers directed to nucleus accumbens that constitutethe mesolimbic or reward pathway


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Pupillary Light Reflex

Four neuron reflex arc:

Ganglion cells of retina

forms the OPTIC

NERVE

Pretectal area

Edinger-Westphal

nucleus (bilateral) of

OCULOMOTOR

NERVE

Ciliary Ganglion to

sphincter pupillae to

produce pupillary

constriction


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BLOOD SUPPLY OF

MIDBRAIN:

Superior cerebellar

artery supply the

tectum

Quadrigeminal artery

supply the posteriormidbrain and

ventrolateral regions

Posteromedial group

of branches from circleof Willis (P1 and P2)

from posterior

cerebral artery supply

ventromedial region of

midbrain


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Vascular Syndromes of the Midbrain

Webers syndromeipsilateralparalysis of extraocularmuscles except superioroblique and lateral rectus,dilated pupil ipsilaterally,contralateral paralysis ofextremities

Claude syndromeIpsilateralparalysis of all extraocularmuscles except LR and SO;ipsilateral dilated pupil,contralateral ataxia, tremorand incoordination

Benedikt syndromeipsilateral paralysis ofextraocular muscles exceptSO and LR; ipsilateral dilatedpupil; contralateral paralysisof extremities andcontralateral tremor and ataxia


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1 Which of the ff serves as caudal


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1.Which of the ff. serves as caudal

boundary of dorsal midbrain?

A. Superior pontine sulcus B. Exit of trochlear nerve

C. Mammillary body

D. Posterior commissure

2 Which of the ff forms the tectum in


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2.Which of the ff. forms the tectum in

rostral midbrain?

A. Superior colliculus B. Inferior colliculus

C. Cerebral peduncles

D. Cerebral aqueduct

3 Which of the ff is center for


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3.Which of the ff. is center for

pupillary light reflex?

A. Dorsal raphe nucleus B. Pretectal area

C. Posterior commissure

D. Ventral tegmental area of Tsai

Which of the ff. nuclei of the inferior colliculus


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.Which of the ff. nuclei of the inferior colliculusshows plane-to-order convergence of

projections?

A. Central nucleus B. Pericentral nucleus

C. Lateral nucleus

D. Paracentral nuclei

5 The pars compacta of the


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5.The pars compacta of the

substantia nigra is rich in_____.

A. GABA B. Serotonin

C. Dopamine

D. Norepinephrine

6 What is the functional significance


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6. What is the functional significance

of posterior commissure?

A. Direct pupillary light reflex B. Consensual pupillary light reflex

C. Upward vertical gaze

D. Both B and C

7 Which of the ff is a manifestation of


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7. Which of the ff. is a manifestation of

a lesion of R oculomotor nerve?

A. Ptosis of L eye B. Medially deviated R eye

C. Dilated R pupil

D. Dilated L pupil

8 Where do the superior colliculus


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8. Where do the superior colliculus

fibers project?

A. Medial geniculate body B. Lateral geniculate body

C. Red nucleus

D. Both A and B

9 Which of the ff structures is found


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9. Which of the ff. structures is found

in caudal midbrain?

A. Superior colliculus B. Red nucleus

C. Oculomotor nucleus

D. Decussation of superior cerebellarpeduncle

10 Which of the ff occupies the


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10. Which of the. ff. occupies the

middle 3/5 of the crus cerebri?

A. Frontopontine fibers B. Corticospinal fibers

C. Occipitopontine fibers

D. Temporopontine fibers

the midbrain 2

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