Brainstem By Dr Manah Chandra Changmai IMS

Located between the cerebrum and the spinal cord Provides a pathway for tracts running between higher and lower neural centers.

Consists of the midbrain, pons, and medulla oblongata.

Each region is about an inch in length.Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts.

Produce automatic behaviors necessary for survival.

Brainstem

Midbrain

Pons

Medullaobongata

Midbrain

Pons

Medullaoblongata

Ventral surface of brain stem

MidbrainCerebral peduncles

PonsBasis pontis

Medulla

Ventral – Lateral View

Vertical Columns of

Cranial Nerves

Internal Columns of Nuclei

Motor nucleiSomatic motor

closest to midlineeyes, tongueCN III, IV, VI, XII

Branchial motorLateral positionBranchial arches: chewing, expression, middle ear, pharynx, larynx, sternomastoic, trapeziusCN V, VII, XIN. ambiguus (IX, X)

Visceral motorventral / ventrolateralParasympathetic: glands, smooth muscle, heart, lungs, GI above splenic flexureEdinger-Westfall (III)Sup. & Inf. salivatory

Sensory nucleiGeneral sensory

lateral to branchial motorFace, sinuses, meningesAll modalitiesCN V mainlyAlso CN VII, IX, X

Visceral sensorylateral to visceral motorTaste; cardiorespiratory, GI infoN. of the solitary tract (CN VII, IX, X)

Special sensoryfurthest lateralBalance; hearingCN VIII (vestibular)CN VIII (cochlear)

Subdivisions of Vertical Columns

Midbrain

Shortest brain stem,not more than2cm in length,lies in the posterior cranial Fossa.For descriptive purpose,divided intoDorsal tectum and right and left cerebralPeduncles.Each cerebral peduncles divide furtherinto ventral crus cerebri and a dorsalTegmentum by a pigmented lamina“ Substantia nigra”

Cerebral peduncles contains:-Descending fibers that go to the cerebellum via the pons-Descending pyramidal tracts

Running through the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.

Connects pons and cerebrum with forebrain

MidbrainCrus cerebri

Basis Tegmentum

Tectum

Ventral – Dorsal Organization

Patterning of the Midbrain

The roof of the aqueduct ( the tectum) contains the corpora quadrigemina

2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli

Corpora quadregemina

Superior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons inSuperior colliculi

Superior and inferior colliculi seperated by cruciform sulcus

Superior colliculi

Inferior colliculi

Internal Structure of Midbrain

Cross section at two levels

• Level of inferior colliculus

• Level of superior colliculus

Internal structure Transverse section of midbrainCommon to both at inferior and superior colliculus:Crus cerebri (or basis pedunculi): - Consists of fibres descending from cerebral cortex. - Its medial one-sixth is occupied by coticopontine fibres from frontal lobe,lateral one-sixth fibres from temporal,occipital and parietal lobes,the intermediate two third by corticospinal and cortico- nuclear fibres.

Substantia nigra : - Present immediately behind and medial to basis pedunculi. - It appears dark as neuron within it contain pigment. ( neuromelanin )

Crus cerebri

Substantia nigra

Basis pedunculiSubstantia nigra

Crus cerebri(cerebral peduncle)

Cerebral aqueduct

Cross section at inferior colliculus

Internal Structure of Midbrain

Section at the level of inferior colliculus

Inferior colliculus

- large mass of grey matter lying in the tectum - Forms cell station in auditory pathway.

Trochlear nucleus: - Lies in the ventral part of central grey matter

Mesencephalic nucleus of trigeminal nerve: - Lies in lateral part of the central grey matter

Medial leminiscus: - Fibres of ventral spinothalamic tract

Spinal leminiscus: - Fibres of lateral spinothalamic and spinotectal tract.

Trigeminal leminiscus

Inferior colliculus

Inferior colliculus

Mesencephalic nucleus of V cranial nerve

Trochlear nerve(N)

Medial longitudinal fasciculus

Cross section at

• Level of superior colliculus

Section at the level of superior colliculus

Two large masses of grey matter seen at this level

Superior colliculus in the tectum

– Receives visual input from retina and frontaland occipital eye fields– Receives auditor input from inferior colliculus– Mediates audiovisual refflexes

Commissure of superior colliculus– Connects two superior colliculus

Brachium of superior colliculus– Pathway for fibres from superior colliculus toCortex

Red nucleus in the tegmentum - Lies in the anterior part of the tegmentum, dorsomedial to the substantia nigra- It is called because of reddish colour which is due to the presence of iron pigment in its neurons.

Oculomotor nucleus - Related to the ventral part of central grey matter

Cerebral aqueduct and periaqueductalgray matter

Medial longitundinal fasciculus– Vestibular fibres that coordinate eyemovements– Interconnects ocular motor CN 3, 4, 6

Central tegmental tract

Section at the level of superior colliculus……contd.

Medial lemniscus– Spinal afferent tract

Spinal lemniscus– Spinal afferent tract

Substantia nigra– Receives GAGAergic input from caudate putamen– Projects dopaminergic fibres to caudate putamen– Projects nondopminergic fibres to thalamus

Crus cerebri

Section at the level of superior colliculus……contd.

Superior colliculus

Edinger westfalnucleus

Red nucleus

Occulomotor nucleus

Superior colliculus

– relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation, cerebellum

Controls arm movement

Corticobulbar Fibers– Arise from precentral and postcentralGyri

– May synapse directly on motor neuronsor indirectly via interneurons(corticoreticular fibers)

– Innervate sensory relay nuclei– Innervate cranial nerve motor nucleibilaterally, with the exception of upperface division of the facial nucleus

– Innervates the ipsilateral spinal nucleusof CN 11, which supplies thesternocleidomastoid muscle and thecontralateral spinal nucleus of CN 11,which innervates the trapezius muscle

Pons

Pons

The pons shows a convex anterior surface with prominent transversely running fibres. These fibres collect to form bundles,the middle cerebellar peduncles.

Trigeminal nerve emerges from the anterior surface,at the junction between pons and middle cerebellar peduncle.

The anterior surface of pons is marked in the midline by a shallow groove,the sulcus basilaris which lodges the basilar artery.

Pons

s

Sulcus basilaris

Subdivided into ventral and dorsal part

Ventral part of the pons contains

Pontine nuclei:•Recieves corticopontine fibres from frontal, temporal,parietal and occipital lobes of cerebrum•The efferent fibres form the transverse fibres of pons.•It has been estimated that there are about twenty million neurons in pontine nuclei.Most of them are glutaminergic.

Vertically running corticospinal and corticopontine fibres.

Transversely running fibres arising in pontine nuclei

Pontine nuclei

The dorsal part of the pons may be regarded as continuation of the part of the medulla behind the pyramids.

Superiorly continous with the tegmentum of the midbrain.

Occupied predominately by reticular formation

Posterior surface help to form floor of fourth ventricle

The dorsal part is bounded laterally by inferior cerebellar peduncle in the lower part of the pons and superior cerebellar peduncle in upper part.

Dorsal part of pons

DORSAL PART

Midpons

Upper pons

4 Lateral lemniscus » Auditory pathway that conducts most contralateral cochlear input 5 Medial lemniscus » Spinal afferent pathway 6 Spinal lemniscus » Spinal afferent pathway

1 Dorsal and ventral cochlear nuclei – Receives auditory input from the cochlea through CN 8 2 Trapezoid body – Formed by decussating fibres of the ventral cochlear nuclei 3 Superior olivary nucleus – Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus

Six ascending tract

Dorsal surface of pons

Medial lemniscus Ascending 2nd order sensory neurons

Descending upper motor neurons

Middle cerebellar peduncle

Restiform body (inf. cerebellar peduncle)

Connection of pons to cerebellum

4th Ventricle

Section through lower part of the pons

Abducent nucleus of CN 6• Lateral gazeDorsal and ventral cochlear nuclei of CN8Medial, lateral and superior vestibularnuclei of CN 8• Receive proprioceptive input from vestibularsystems and cerebellum• Projects to cerebellum and medial longitudinalfasciculusSpinal trigeminal tract of CN 5Facial nucleus of CN 7 • Gives rise to fibres that innervate the muscles offacial expressionSuperior olivary nucleus– Auditory relay nucleus that receives inputfrom the cochlear nuclei and contributesto lateral lemniscus

Vestibular Nuclei Pure sensory lateral location Balance

Cranial Nerves of Lower Pons

Abducens N. nucleus

Facial N. nucleus

Abduction of eye

Longest, most vulnerable CN

Muscles of face

At a slightly higher level

Cranial Nerves of Lower Pons

Mid Pons

Middle cerebellar peduncle

4th Ventricle

Corticospinal tract, corticobulbar tract,

corticopontine fibers

Descending fibers

Lateral lemniscus

Pontine nuclei

Trapezoid body

Mid Pons

Trapezoid body : transverse fibers in pontine tegmentum

Medial leminiscus

fibers from dorsal column (position and vibration)

fibers from dorsal column (position and vibration)

Medial lemniscus fibers from dorsal column (position and vibration)

Trigeminal tract pain, temperature, touch from contralateral face

Mid Pons

Cranial nerve nuclei and Lemniscal sensory system – in tegmentum of the pons

Principal trigeminal sensory nucleus

Motor trigeminal nucleus

Section through upper part of pons

Superior cerebellar peduncle

Principal sensory nucleus of CN 5– Receives discriminative tactile and pressuresensation from face, terminates in thalamus

Lateral lemniscus» Auditory pathway that conducts mostcontralateral cochlear input

Trapezoid body– Formed by decussating fibres of theventral cochlear nuclei

decussationSuperior cerebellar peduncle

Transverse ponto-cerebellar fibers

Periaqueductal gray matter Medial longitudinal fasciculus

Upper Pons

Locus ceruleus

Parabrachial Nucleus

Pediculopontine Nucleus

Upper Pons

Some neurons release acetylcholine

Other neurons release glutamate

They assist in learning and voluntary motor control, e.g. locomotion, saccadic e

MEDULLA OBLONGATA

Medulla is broad above ,joins with pons narrow below, continous with spinal cord

Length is about 3cm, width is about 2cm at its upper end

Surfaces shows series of fissuresAnterior median fissurePosterior median fissure

Spinal cord Medulla oblongata

Most inferior region of the brain stem.

Becomes the spinal cord at the level of the foramen magnum.

External structure of medulla

Ventral surface of medulla oblongata containsPyramid•elevation between anterior median and anterolateral sulcus•Formed due to decussation of corticospinal fibres.

Pyramid

Olive

Olive •Oval swelling between anterolateral posterolateral sulcus,half an inch long•Produced by large mass of gray matter called inferior olivary nucleus

External surface of medulla

Anterior median fissure

Pyramid

Anterolateral fissure

Olive

The posterior part of medulla containsFasciculus gracilis medially ending in rounded elevation ,called nucleus gracilis

Fasciculus cuneatus laterally ending in rounded elevation,called nucleus cuneatus

Posterior part of the medulla forms the floor of the fourth ventricle

Tuberculum cinereum, longitudinal elevation in the lower part of medulla lateral to fasciculus cuneatus.

Posterior part of medulla oblongata

Posterior median sulcusPosterior median fissure

Obex Gracile tubercle

Cuneate tubercle

Floor of fourth ventricle

DORSAL SURFACE OF MEDULLA OBLONGATA

Cross section at three levels

Level of pyramidal decussation

Internal Structure of Medulla

Pyramidal tract

Lateral corticospinal tract

75 – 90%

spinal nucleus of VFrom pons to C4

Gracile nucleus

Anterior corticospinal tract -- fibers to innervate muscles of trunk

Level of Pyramidal Decussation

Cross section at level of lemniscal decussation

Internal Structure of Medulla

Medial lemniscus

Carries 2nd order sensory neurons to VPL thalamus

Internal arcuate fibers

Cuneate nucleus

Gracile nucleus Medial longitudinal fasciculus

Level of Lemniscal Decussation

Cross section at level of Level of inferior olivary nuclei

Inferior olivary nucleiRelay between cortex, vestibular nuclei, cerebellum, basal ganglia, and dorsal column nuclei

Inferior cerebellar peduncle = Restiform body

Hypoglossal nucleus CN XII

Vestibular nuclei Medial Inferior

Level of Inferior Olives

Vestibular nucleiN. solitarious

Sensory nucleus for CN VII, IX, X

Spinal trigeminal tract

CN V, VII, IX, X

N. ambiguus

Motor nucleus for CN IX, X & XI

Dorsal motor nucleus of X

Sensation behind ear

Posterior 1/3 of the tongue

Stylopharyngeus (lifts pharynx)

Cranial Nerves of the Medulla

N. solitarious

Sensory nucleus for CN VII, IX, X

Posterior 1/3 of the tongue

N. ambiguus

Motor nucleus for CN IX, X & XI

Stylopharyngeus (lifts pharynx)

Inf. salivatory nucleus

Parotid gland, parasympathetic

Spinal trigeminal tract

CN V, VII, IX, X

Sensation behind ear

CN IX: Glossopharyngeal Nerve

Dorsal motor nucleus of X

Parasympathetic, preganglionic

N. solitarious

Sensory nucleus for CN VII, IX, X

Taste, epiglottis CardiorespiratoryN. ambiguus

Motor nucleus for CN IX, X & XI

Pharynx Larynx

Spinal trigeminal tract

CN V, VII, IX, X

Ear

CN X: Vagus Nerve

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Mnemonic

The End