Brain stem. Pons (bridge)

(1)

Brain stem

(2)

(3)

(4)

Ventral brain stem

cerebral peduncle

middle

cerebellar

peduncle

(5)

Dorsal brain stem

(6)

Ventral

brain stem

Basilar Pons

Cranial Nerve VI

Cranial Nerve V

(7)

Brainstem

–

_–

macroscopic overview

_{macroscopic overview}

Dorsal view

Ventral view

(8)

Neural tube folding

(9)

Origin of CNS subdivisions

(10)

Primary/secondary brain vesicles & flexures

that separate them

(11)

Neural tube folding

–

pontine flexure

Neural tube folding (5

(12)

Alar vs. Basal plate derivatives

-

medulla

infeior olivary nucleus

Basal plate = efferent = motor

Alar plate = afferent = sensory

(13)

Alar vs. Basal plate

-

_-

pons

_pons

Spinal cord Medulla

(14)

Alar vs. Basal plate derivatives

-

pons

Basal plate = efferent = motor

Alar plate = afferent = sensory

somatic

visceral

somatic

The basal plate → primarily efferent nuclei (CN V, VI, VII, superior salivatory nuclei) The alar plate → somatic and visceral sensory nuclei (CN V, VIII, pontine nuclei)

(15)

Estimated time of development of various brain regions

(16)

Longitudinal zones in the brain stem

cranial

caudal

Structures in Pons:

Nuclei

→→

neuronal

bodies

Reticular formation

→

neuronal bodies

Tracts

= =

white matter

→

neuronal

axons

passing throughpassing through

ending in ponsending in pons

basis tegmentum

(17)

Level of CN V

-

Pons

(18)

Level of CN VI, VII

-

Pons

(19)

The brainstem is connected to the cerebellum

via the cerebellar peduncles

middle cerebellar peduncle (MCP)

Medulla oblongata

↔

Cerebellum

_Cerebellum

Pons

→

Cerebellum

Midbrain

↔

Cerebellum

_Cerebellum

superior cerebellar peduncle (SCP)

inferior cerebellar peduncle (MCP)

Brachium pontis

Brachium conjunctivum

(20)

Afferent cerebellar pathways in brainstem

(21)

Structures in basis pontis

Cortico

-

ponto

-

cerebellar fibers

Corticospinal fibers

Corticobulbar fibers

(

cortex

→

cranial nerve

nuclei

)

direct c

orticobulbar

indirect c

ortico

-

reticulo

-

bulbar (

cortex

→

RF

→

CN

nuclei

)

(22)

Corticopontocerebellar fibers constitute the

largest group of fibers in the basis pontis

W

ide areas of cortex

→

ipsilateral pontine nuclei

→

contralateral

cerebellum via

MCP (some 10%

-

ipsilat

.)

Number of fibers

-

19 million

on each side/number of

pontine nuclei neurons

–

23 million on each side (~1:1)

Principal

cortical input

–

primary sensorimotor areas

→

correction of movements

(23)

Corticopontocerebellar

pathway

(24)

Origin: Premotor, primary motor, and primary somatosensory cortex

Course: Internal Capsule (A/P), cerebral peduncles, Pons

Termination: Pontine nuclei

Laterality: Ipsilateral

(25)

Origin: Premotor, primary motor, and primary somatosensory cortex

Course: Internal Capsule (A/P), cerebral peduncles, Pons

Termination: Pontine nuclei

Laterality: Ipsilateral

Pontine Nuclei

Fibers will then synapse on pontine nuclei, which then decussate in the transverse fibers of the pons and enter the MCP…

(26)

Inputs, MCP

Pontocerebellar Tract

Origin: Pontine Nuclei

Course: Immediately decussates and enters MCP

Termination: granule cells of the cerebellar hemispheres

(27)

C

(28)

Origin: Primary motor cortex (BA 4)

Course: Post Limb IC, Pyramids

Termination: Spinal cord ventral horn

Laterality: CONTRA (lateral), IPSI (anterior)

Corticospinal tract

(29)

Origin: Primary motor cortex (BA 4)

Course: Post Limb IC, Pyramids

Termination: Spinal cord ventral horn

Laterality: CONTRA (lateral), IPSI (anterior)

Corticospinal tract

(30)

Corticobulbar tracts

Motor input to:

Reticular formations

–

pontine

Cranial Nerve motor nuclei

–

V, VI, VII, VIII

Note

–

No direct connections from the primary motor

cortex to CN VI; this nucleus gets input from frontal

(31)

Structures in the tegmentum pontis

Cranial nerve nuclei

–

CN V, VI, VII, VIII

Reticular formation

-

nucleus locus ceruleus

& other

Crossing pathways

ascending (sensory)

–

basal part of tegmentum

lemniscal

spinothalamic

anterior spinocerebellar tract

descending (motor)

central tegmental tract

(

basal ganglia

/

midbrain

→

inferior olive

)

rubrospinal tract

tectospinal tract

other

–

sympathetic fibers from hypothalamus;

medial

longitudinal fasciculus

(32)

Position of ascending to descending fibers in

tegmentum

(33)

Descending brain stem pathways

(to spinal cord)

(34)

Cranial nerve nuclei in brain stem

Hypoglossal XII

Hypoglossal

Spinal accessory (C1–5), ambiguus** XI

Accessory

Dorsal motor, ambiguus**, solitary* X

Vagus

Ambiguus*, inferior salivatory, solitary** IX

Glossopharyngeus

Cochlear (2 nuclei), vestibular (4 nuclei) VIII

Vestibulocochlear

Facial, superior salivatory, gustatory (solitary)** VII

Facial

Abducens VI

Abducens

Main sensory, spinal (descending), mesencephalic, motor (masticatory) V Trigeminal Trochlear IV Trochlear Oculomotor, Edinger–Westphal III Oculomotor

Nuclei

Nerve

Name

** The solitary nucleus is common for CN VII, IX, and X * The ambiguus nucleus is common for CN IX, X, and XI

midbrain

pons

(35)

(36)

(37)

CN V: Trigeminal

(38)

(39)

A

fferent and efferent roots of

_{fferent and efferent roots of}

CN V

_{CN V}

Trigeminal

Mesencephalic nucleus is

(40)

Jaw jerk reflex

–

_–

CN V

_{CN V}

Proprioceptive fibers to the mesencephalic nucleus convey pressure and

(41)

CN V: Trigeminal

-

_-

mesencephalic

_{mesencephalic}

The mesencephalic

nucleus and tract run

above the level of CN V

Origin:

Mesencephalic

Nucleus of V

Course:

Mesencephalic

tract of V

Termination:

Motor Nucleus

of V

(42)

CN V: Trigeminal

motor and chief sensory (level of CN V)

(43)

Corneal reflex

Touching the cornea elicits reflex closure of the eye → might be

disrupted in pontine lesions

(44)

CN V: Trigeminal

Spinal nucleus and tract at level of VI/VII

Neuron #1

Origin:

Trigeminal

(Gasserian)

Ganglion

(45)

(46)

(47)

CN VI: Abducens

-

_-

paralysis

_paralysis

(48)

CN VII: Facial

Origin:

Geniculate Ganglion

(sensory), Motor

Nucleus of VII (motor),

Salivatory Nucleus

(autonomic)

Course:

CNVII, through IAC,

temporal bone, exit

stylomastoid foramen

Termination:

Nucleus Solitarius

(taste), Muscles of facial

expression, stapedius,

post belly digastric,

Parasympathetic

ganglia (sublingual,

(49)

(50)

The

unusual course

_{unusual course}

of facial motor

_{of facial motor}

nucleus

(51)

CN VII: Facial

(52)

CN VIII: Vestibulocochlear

Cochlear Portion

Origin:

Spiral Ganglion

Course:

CNVIII, through internal

auditory meatus

Termination:

Cochlear Nucleus

Laterality:

Ipsilateral

Vestibular Portion

Origin:

Scarpa’s Ganglion

Course:

CNVIII, through internal

auditory meatus

Termination:

Vestibular Nucleus

(53)

cochlear nuclei

_{vestibular nuclei}

CN VIII: Vestibulocochlear

(54)

CN VIII

-

_-

nuclei

_nuclei

Cochlear nuclei

ventral cochlear nucleus

dorsal cochlear nucleus

Vestibular nuclei

superior vestibular nucleus (Bechterew)

inferior vestibular nucleus (Roller)

(55)

Vestibular System

Superior Vestibular Nucleus

(56)

Vestibular System

(57)

Upper pons

(

level of

locus ceruleus)

(58)

Upper pons

(59)

Mid

-

Pons

(

level of CN V)

(60)

Lower Pons

(61)

B

lood supply of the pons

–

basilar artery

Anterior inferior cerebellar artery (AICA)

lateral tegmentum dorsal

tegmentum