PONS (BRIDGE)

PONS

(BRIDGE)

Prof.Dr. Selda Önderoğlu

1- Prosencephalon (Fore Brain)

Telencephalon Diencephalon

2- Mesencephalon Mid Brain

3- Rhombencephalon (Hind Brain)

-Metencephalon -Pons

-Cerebellum - Myelencephalon

- MO

4- Spinal cord

Pons-

L=about 2.5 cm Relations:

Posterior,

fourth ventricle, cerebellum

Anterior,

pontine cistern

clivus

Clivus

- Transvers pontine fibers

- Middle cerebellar peduncle (= brachium pontis)

- Basilar sulcus

(basilar artery)

Anterior Surface- features

- 5th cranial nerve

(

- Pyramidal eminence

7 6

8

Basilar artery

* *

*

*

Pyramidal eminence

Transverse pontin

fibres

*

Posterior Surface

- Hidden by cerebellum

-Superior cerebellar peduncle

(bw.mesenc.-cerebell.)

-Superior

medullary vellum, apex

(thin white membrane)

-Middle cerebellar peduncle

(bw pons-cerebel.)

-Inferior cerebellar peduncle

(bw.medulla- cerebel.)

- Median sulcus

- Medial eminence

- Sulcus limitans

- Facial colliculus

-Vestibular area -Lateral recess

-Foramen

Luschka (lateral foramen)

- Auditory tubercle (dorsal cochlear nucleus & a

part of cochlear nerve)

Posterior Surface continue

Sulcus limitans

Separates the medial motor

neurons from the lateral

sensory neurons.

Facial colliculus (

Fibers coursing around it)

* *

Vestibular area and nuclei

Foramen Luschka (lateral foramen)

Connects 4th ventricle to Subarachnoid space

Auditory tubercle and dorsal cochlear nucleus

* *

Internal Structure

1- Pons proper

(ventral pons, basilar portion)

2- Pontine tegmentum

(dorsal pons)

Two portions are separated by the

trapezoid body of the

auditory pathway

Ventral Pons = (Pons proper, basilar portion)

- Has Similar arrangement at all levels

- Acts as a relay (synaptic) station for motor fibers from the cerebrum to the cerebellum

- Consists:

Transverse fibers Longitudinal fibers Pontine nuclei

Pontine nuclei

Longitudinal fibers: ^{formed by}

- Corticospinal fibers

- Corticobulbar (Corticonuclear) fibers - Corticopontine fibers

Corticospinal tract

Corticobulbar fibers:

(corticonuclear fibers)

Fibers that Separated from the cortico-spinal tract

Descends from cortex to the

contralateral cranial nerve

nuclei

Corticopontine fibers

Arise from the frontal, temporal, parietal and occipital cortex, descend&

without crossing (ipsilateral) and terminate upon the pontine nuclei ( * ^).

Pontine nuclei give rise (axons) to transvers fibers of pons

which cross the Midline (pass to contralateral Side) and enter cerebellum as the:

middle cerebellar peduncle (=cortico-ponto-cerebellar fibers).

*

Dorsal Part

(= pontine tegmentum)

-Has differences in its lower and upper

portions

-- Continuous with the reticular formation of medulla

Tegmentum contains:

- Cranial nerve nuclei - Ascending,

descending tracts - Reticular formation

Pons Lower level Pons Upper

level

Upper section Lower section

Tracts of dorsal portion:

-Medial lemniscus ( Continuation of fasciculus gracilis and cuneatus) - Lateral lemniscus (upper pons)

- MLF (medial longitudinal fasciculus) - Tectospinal and spinotectal tracts

- Anterior and lateral spinothalamic tracts - Anterior spinocerebellar tract

- Spinoreticular and reticulospinal fibers - Vestibulospinal tract

- Rubrospinal and rubroreticular tracts -Descending autonomic pathways

- Central tegmental tract

Cranial nerve nuclei in PONS:

- 5 (trigeminal n.):

-Lower part of mesencephalic nucleus (upper pons) -Upper part of spinal nucleus (lower pons)

-Sensory principle nucleus - Motor nucleus (upper pons)

-6 (abducens n.):

- Motor nucleus (lower pons)

- 7 (facial n.):

-Superior salivatory nucleus (lower pons) -Motor nucleus (lower pons)

- Solitary nucleus (lower pons)

-8 (vestibulocochlear n.):

-Sup. and lat. vestibular nuclei (lower pons) -Ant.(^ventral) and post.^(dorsal) cochlear nuclei (lower pons)

Upper Tegmentum: Section at the level of the trigeminal nerve

1- The sensory principle

nucleus of trigeminal nerve

2- The motor nucleus of trigeminal nerve

3- Nucleus of lateral lemniscus

4-

Reticulotegmental 6- The mesencephalic nucleus nucleus (pontine reticular

formation) of trigeminal nerve

5- nucleus of trapezoid body

Sensory Principle Nucleus of Trigeminal Nerve

- Takes the tactile and pressure sense impulses from head

and neck

*

The Mesencephalic Nucleus of Trigeminal Nerve

Begins to appear at uppermost levels of the pons Takes the proprioception sense of head and neck

*

Nucleus of Lateral Lemniscus

Nucl related to auditory pathway

Becomes apparent in the uppermost pons Located on the medial aspect of the lateral lemniscus

* *

Reticular nuclei (pontin reticular formation)

1- Nucleus reticularis pontis caudalis

2- Nucleus reticularis pontis oralis

3- Reticulo-tegmental nucleus

4- Superior central nucleus

5- Raphe nuclei: Scattered through the median parts of medulla and pons

6- Nucleus pigmentosus (locus ceruleus)

Reticular nuclei (pontin reticular formation)

N. Retic. pontis caudalis

Raphe nuclei

Reticulo

tegmental n.

N. Centralis superior N. Retic. pontis

oralis

LOCUS CAERULEUS

-Collection of pigmented cells near the periventricular gray of upper part of fourth ventricule.

- Secretes norepinephrine (NA)

-Important noradrenergic cell groups of the brain stem.

- It contains about 10 000 neurons.

Lower part of the pontine tegmentum:

Level of the facial colliculus

1- The spinal nucleus of the trigeminal nerve

2- Motor nucleus of abducens nerve 3- The motor nucleus of facial nerve 4- Superior salivatory nucleus of facial nerve

5- Solitary tract and nucleus of facial nerve

6- Vestibular nuclei or vestibular nuclear complex

7- Cochlear nucleus

Vestibular nuclei (vestibular nuclear complex)

- Located deep to the vestibular area

- Vestibular nuclear complex:

Medial, lateral, superior, inferior vestibular nuclei

Superior

Lateral

- Aff fibers of these nuclei come by vestibular nerve from inner ear

- Eff fibers from vestibular nuclei project ipsilaterally ( on the same side) to the:

cerebellum, MLF,

spinal cord

lateral lemniscus

Cochlear Nuclei: - Dorsal cochlear nucleus (deep the auditory tubercle) -Ventral cochlear nucleus

Nuclei of auditory pathway - Nucleus of trapezoid body (

trapezoid body)

- Superior olivary nucleus:

(lower pons)

Motor nucleus of facial nerve:

Facial colliculus

Superior salivatory nucleus:

Parasympathetic nucleus of facial nerve

Sends efferent fibers to the salivary and lacrimal glands

Solitary tract and nucleus of facial nerve:taste

7

9

10

Motor nucleus of abducens nerve:

Lies dorsal to the tegmentum

Fibers pass ventral and downwards

Leaves the brain stem from the pontabulbar sulcus

The spinal nucleus of the trigeminal tract:

Continues upwards through the lower part of the pons

At higher levels continuous with the principle sensory nucleus of

trigeminal nerve

Medial longitudinal fasciculus:

Retains its place near the midline at all levels of the pontine

tegmentum

MLF

Central tegmental tract:

- Not present at the medullary levels

- Located in the reticular formation

- Includes descending and ascending fibers

- Connecting the

reticular nuclei in the other parts

of the brainstem to each other.

MEDIAL INFERIOR PONTINE SYNDROME (MIDDLE ALTERNATING HEMIPLEGIA)

Paramedian br. of basilar a. and occlusion of its br. in lower pons - contralateral spastic paralysis--- corticospinal tract

- ipsilateral internal strabismus --- (6 th CN)---lateral rectus m.

- contralateral positional deficits --- medial lemniscus - ataxic gait --- cerebellar component --- pontin nuclei

Normal pain temperature perception

Normal 5th cranial

components

LATERAL INFERIOR PONTINE SYNDROME

Area supplied by ant. inf. cerebellar artery

- Dizziness (vertigo)/nausea/nystagmus--- vestibular n. and nucleus - Ipsilateral tinnitus/loss of hearing --- cochlear n. and nucleus

-Ipsilateral paralysis of upper and lower face mm --- facial nerve - Ipsilateral loss of sensation on face --- trigeminal nucleus

- contralateral loss of pain and temperature --- spinothalamic tract

- difficulty of walking --- middle cerebellar peduncle