neuroanatomy brain stem

5/24/2018 Neuroanatomy Brain Stem

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MEDULLA OBLONGATA

Inferior olive

coronal

Human, 10% formalin, Pal-Weigert and carmine stains, 7 x.

Nucleus gracilis:Fully developed at this level. Only a small remnant of thefasciculus gracilis caps the nucleus.

Cuneate nucleus and tract:Note that a definite portion of the fasciculus cuneatus

caps the nucleus cuneatus as compared to that seen on the adjacent nucleus gracilis.The lightly stained island in the fasciculus cuneatus represents neurons of the

accessory cuneate nucleus.

Spinal tract and nucleus of nerve V: Continuation of similar structures seen at

more caudal levels (see Plates324and328 ).

Medial longitudinal fasciculus:Note the change of position of the fasciculus inthis figure as compared to a more caudal level (see Plate328 ). This is a result of

the formation of the medial lemniscus, which displaces the medial longitudinalfasciculus to a more dorsal location.

Principal and medial accessory inferior olive:This nuclear group distinguishessections of the medulla at this level. The principal olive is the larger component

with its hilum directed medially. The medial accessory olive is found along the

border of the medial lemniscus. Inferior olive neurons give rise to olivocerebellarfibers that project into the cerebellum.
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Pyramid:See the same structure at more caudal levels. Plates324,325,326,328,

and329.

Internal arcuate fibers:See also Plate328,Axons of gracile and cuneate neurons.

Spinocerebellar tract:See alsoPlates 317,324,327,and328.Continuation of the

same tract seen in the spinal cord.

Medial lemniscus: Formed by the decussating internal arcuate fibers. Constitutesthe second-order neurons of the posterior column pathways (fasciculi gracilis and

cuneatus and their nuclei), conveying kinesthetic sense and discriminative touch to

higher levels of the neuraxis.

Nerve XII rootlets:Hypoglossal cranial nerve. Note their characteristic location

medial to the inferior olive and lateral to the pyramid. This proximity to thepyramid is the anatomical basis for the inferior or hypoglossal alternatinghemiplegia resulting from lesions in this area. This syndrome (also known asmedial medullary syndrome) consists of lower motor neuron paralysis of the

ipsilateral half of the tongue and contralateral (upper motor neuron) hemiplegia.The hypoglossal nerve supplies all the intrinsic and extrinsic muscles of the tongueexcept the palatoglossus muscle.
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MEDULLA OBLONGATA

Inferior olive

coronal

Choroid plexus:Located in the caudal part of the roof of the fourth ventricle.

Inferior vestibular nucleus:One of four vestibular nuclei. Characteristicallylocated medial and dorsal to the restiform body, and traversed by myelinated

bundles.

Tractus solitarius: Contains general visceral as well as special visceral (taste)fibers from the vagus, glossopharyngeal, and facial nerves. Fibers project ontoneurons in the nucleus solitarius located in close proximity to the tract.

Nucleus solitarius:Located in close proximity to the tractus solitarius, from which

it receives fibers.

Hypoglossal (CN XII) nucleus:A group of large neurons located dorsal to themedial longitudinal fasciculus in the floor of the fourth ventricle in a paramedian

position. Rootlets of hypoglossal nerve course in tegmentum of medulla between

the medial lemniscus and inferior olive.

Hypoglossal (CN XII) rootlets:Coursing in the tegmentum of the medulla

oblongata between the medial lemniscus and the inferior olive. Exit from the

ventral surface of the medulla between the pyramid and inferior olive.


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Dorsal accessory olive: A component of the inferior olivary complex located

dorsal to the principal olive.

Medial longitudinal fasciculus: Descending portion of a fiber system with

ascending and descending components. Neurons of origin are from various brainstem nuclei, but with a major vestibular component. The fibers descending in thisfasciculus are destined to synapse on motor neurons in the cervical region of the

spinal cord, which supply neck musculature.

Accessory cuneate nucleus: Receives fibers of the dorsal spinocerebellar tractentering the spinal cord above the eighth cervical segment. Projects to the

cerebellum via the restiform body.

Restiform body:Also known as the inferior cerebellar peduncle. A compact

bundle of nerve fibers connecting the medulla with the cerebellum. Described firstin 1695 and named by Humphrey Ridley, an English anatomist. Tracts and fibers

forming this bundle originate in the medulla and the spinal cord.

Nucleus of spinal tract of trigeminal (CN V) nerve:Receives exteroceptivefibers from the ipsilateral side of the face via the spinal tract of the trigeminalnerve. Lesions result in loss of pain sensation in the ipsilateral face.

Medial lemniscus:Axons of gracile and cuneate nuclei. Forward continuation ofthe same structure seen in more caudal sections.

Principal inferior olive:Located dorsal and lateral to the pyramid. Note thecharacteristic convoluted appearance. The principal inferior olive is the largest

component of the inferior olivary complex, which includes, in addition, the dorsalaccessory inferior olive and the medial accessory inferior olive.

Pyramid: Heavily myelinated motor fiber system. Represents descending fibersfrom the cerebral cortex that pass through the internal capsule, cerebral peduncle,

and pons before reaching the medullary pyramids. Fibers in the pyramid undergopartial crossing in the motor decussation to give rise to the lateral corticospinal

tract. It is estimated that, in man, about one million fibers are present in eachpyramid.


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MEDULLA OBLONGATA

Cochleovestibular and

Glossopharyngeal nerves

coronal

Human, 10% formalin, Pal-Weigert, 3.8 x.

Medial longitudinal fasciculus: Descending portion of a fiber system with

ascending and descending components. Neurons of origin are from various brain

stem nuclei, but with a major vestibular component. This system is concerned witheye and neck movements. The fibers in the descending component are destined to

synapse on motor neurons in the cervical spinal cord that supply neck musculature.

Medial lemniscus:Continuation of the same system noted in caudal sections.

Glossopharyngeal (CN IX) nerve:A mixed nerve. Characteristically enters themedulla, inferior and medial to the restiform body.

Amiculurn olivae:A bundle of fibers surrounding the inferior olivary complex.

Contains fibers that terminate on neurons of the olivary complex.

Inferior olive:Convoluted laminae of gray matter dorsal to the pyramid. Receives

fibers from cortical and subcortical sites and projects fibers primarily to thecontralateral but also to the ipsilateral cerebellum via the restiform body.Concerned with motor control.


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Pyramid:Heavily myelinated motor fiber system. Contains descending fibers

from the cerebral cortex that pass through the internal capsule, cerebral peduncle,

and pons before reaching the pyramids. Fibers in the pyramid undergo partialcrossing in the motor decussation caudal to this level.

Arcuate nucleus: Motor neurons ventral to the pyramid. Receives cortical inputand projects to the cerebellum via the stria medullaris and restiform body.

Homologous to pontine nuclei.

Olivocerebellar tract:Axons of neurons in the inferior olivary complex. Fibersarise from both olivary complexes but primarily from the contralateral complex.

Destined for the cerebellum via inferior cerebellar peduncle (restiform body).

Olivocerebellar fibers constitute the major component of the restiform body.

Cochlear (CN VIII) nerve:Central processes of bipolar neurons in the spiralganglion. Enters the lateral surface of the pons lateral and dorsal to the restiform

body. Projects upon the dorsal and ventral cochlear nuclei. Lesions in the cochlearnerve result in ipsilateral loss of hearing.

Ventral cochlear nucleus:Located ventral and lateral to the restiform body.Receives axons of the cochlear nerve originating in the upper turns of the cochlea.

Restiform body:Also known as inferior cerebellar peduncle. A compact bundle ofnerve fibers connecting the medulla with the cerebellum. Tracts and fibers forming

this bundle originate in the medulla and the spinal cord.

Dorsal cochlear nucleus:Characteristically located dorsal and lateral to the

restiform body. Receives axons of the cochlear nerve originating in the lower turnsof the cochlea.

Inferior vestibular nucleus: One of four vestibular nuclei. Characteristicallylocated medial to the restiform body and traversed by myelinated bundles.

Stria medullaris:Axons of arcuate neurons. Courses in the floor of the fourth

ventricle. Joins the restiform body to reach the cerebellum.

Medial vestibular nucleus:One of four vestibular nuclei. Characteristicallylocated medial to the inferior vestibular nucleus in the floor of the fourth ventricle.

Axons of neurons in this nucleus form the medial vestibulospinal tract.


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PONS

Trapezoid body coronal


Vermis of the cerebellum: Overlying the fourth ventricle. Midline portion ofcerebellum.

Medial longitudinal fasciculus:Continuation of the same structure seen at morecaudal levels. Concerned with ocular movement in response to vestibular

stimulation.

Central tegmental tract:Compact fiber bundle located dorsal to the mediallemniscus. Carries fibers from midbrain tegmenturn, red nucleus, and

periaqueductal gray matter to the inferior olivary complex.

Superior olivary nucleus: One of the tegmental nuclei that belong to the cochlear

system. Receives fibers from the trapezoid body and contributes to the formationof the lateral lemniscus.

Trapezoid body: Also known as the inferior acoustic stria. Axons of neurons in

the inferior cochlear nucleus form the trapezoid body.

Pontocerebellar tract:Axons of pontine nuclei on their way to the cerebellum viathe brachiurn pontis.


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Pontine nuclei:Scattered between the descending corticospinal, corticopontine,

and corticobulbar fibers and the horizontally oriented pontocerebellar fibers.

Receive input from the cerebral cortex via the corticopontine tract and project tocerebellum via the pontocerebellar tract.

Brachium conjunctivum: Also known as the superior cerebellar peduncle. Mostimportant efferent fiber system of the deep cerebellar nuclei. Located dorsolateral

to the fourth ventricle. Later in its course, it dips into the tegmenturn of the pons

and midbrain (seePlates 337,338and339). Nerve fibers in this bundle are

destined to reach the contralateral red nucleus and ventrolateral nucleus of thethalamus.

Restiform body: Also known as the inferior cerebellar peduncle. Continuation ofthe same fiber system seen at more caudal levels. The restiform body is shown here

entering the cerebellum.

Brachium pontis:A massive bundle of fibers connecting the basal portion of thepons with the cerebellum. Also known as the middle cerebellar peduncle. Contains

pontocerebellar tract.

Spinal tract and nucleus of trigerninal nerve: Continuation of the same

structures described at caudal levels.

Medial lemniscus:Continuation of the same fiber system described at more

caudal levels (seePlates 329,330and331). Note change in orientation of fibersfrom (previously) vertical in medulla oblongata to horizontal here in the pons.

Corticospinal, corticopontine, corticobulbar tracts:Descending fiber systemsectioned transversely. Destined for the pontine nuclei, cranial nerve nuclei, and

the spinal cord motoneurons.
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PONS

Facial and abducens

nerves coronal


Genu of facial (CN VII) nerve: A bundle of facial nerve fibers in the floor of thefourth ventricle.

Brachium conjunctivum: Also known as the superior cerebellar peduncle. Most

important efferent fiber system of the deep cerebellar nuclei. Located clorsolateralto the fourth ventricle.

Superior vestibular nucleus:Located dorsal and medial to the restiform body.

One of four vestibular nuclei. Receives fibers from the vestibular component of thevestibulocochlear (CN VIII) nerve and projects fibers to the cerebellum via the

restiform body and to nuclei of extraocular movement via the medial longitudinal

fasciculus.

Facial (CN VII) nerve:Coursing ventrolaterally to emerge at the lateral border ofthe pons.

Facial nucleus:Located medial to the facial nerve. Axons of neurons in the facial

nucleus course medially and dorsally to reach the floor of the fourth ventricle


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(genu of facial nerve) before turning laterally and ventrally to exit from the lateral

surface of the pons.

Abducens nerve: Rootlets of the abducens nerve are seen coursing in the

tegmenturn of the pons. They arise from the medial aspect of the nucleus and exitfrom the ventral surface at the caudal border of the pons. Supply the lateral rectusmuscle of the eye.

Medial lemniscus:Continuation of the same structure seen at more caudal andmore rostral levels.

Pontocerebellar tract:Continuation of the same structure seen at more caudallevels. Axons of pontine nuclei destined for the cerebellum.

Pontine nuclei:Scattered between pontocerebellar fibers and the corticospinal,corticopontine, and corticobulbar fibers. Relay station between the cerebral cortexand cerebellum.

Corticospinal, corticopontine, corticobulbar tracts:Long descending fibersystem originating in the cerebral cortex. Sectioned transversely as it passes

through the basal portion of the pons.

Abducens nucleus: Located in a paramedian position in the floor of the fourthventricle. Axons of neurons in this nucleus emerge from the medial aspect of the

nucleus to form the abducens nerve. Lesions of the abducens nucleus result inipsilateral paralysis of lateral gaze. The abducens nucleus and the adjacent genu offacial nerve together form the facial colliculus, a paramedian elevation in the floor

of the fourth ventricle.

Brachium pontis: A massive bundle of fibers connecting the basal portion of thepons with the cerebellum. Also known as the middle cerebellar peduncle.

Restiform body: Continuation of the same structure seen at more caudal levels.Seen entering the cerebellum.

Dentate nucleus: The largest of the deep cerebellar nuclei. Axons of this nucleus

are major components of the brachium conjunctivum.

Facial colliculus:A paramedian elevation in the floor of the fourth ventricleoverlying the abducens nucleus and the genu of the facial nerve.


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PONS

Trigeminal nerve coronal


Fourth ventricle: The anterior part of the fourth ventricle overlying the pons.

Brachium conjunctivum: Massive outflow tract from the cerebellum seen at thislevel prior to decussation. Lesions in this area will result in a disorder of

coordinated movement. Note the change in position of this structure in more rostral

sections (seePlates 337,338and339).

Principal (main) sensory nucleus of trigerninal (CN V) nerve:Located lateral

to the motor nucleus of the trigeminal. Receives touch sensations from theipsilateral face via the trigeminal nerve.

Motor nucleus of trigerninal (CN V) nerve:Located in the dorsal part of thetegmentum. Axons form the motor root of the trigerninal nerve and supply musclesof mastication, and the tensor tympani, tensor palati, mylohyoid, and the anterior

belly of the digastric muscles.

Brachium pontis:Also known as the middle cerebellar peduncle. A massive

bundle of fibers connecting the basal portion of the pons with the cerebellum.

Contains pontocerebellar fibers.
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Pontocerebellar tract: Axons of pontine nuclei destined for the cerebellum via the

brachium pontis.

Corticospinal, corticopontine, corticobulbar tracts: Long descending fiber

system originating in the cerebral cortex. Sectioned transversely as it passesthrough the basal portion of the pons. Note the horizontally oriented

pontocerebellar tract.

Medial lemniscus:Continuation of the same system seen in more caudal levels.

Trigeminal nerve:Sensory-motor cranial nerve. Seen coursing in the lateral part

of the pons.

Central tegmental tract:Compact fiber bundle located in the tegmenturn of the

pons. Carries fibers from midbrain tegmentum, red nucleus, and periaqueductalgray matter to the inferior olivary complex.

Medial longitudinal fasciculus:Ascending component of a fiber systemoriginating in vestibular nuclei and destined to synapse with neurons in nuclei ofextraocular movement (CN III, IV, and VI). Concerned with control of eye

movement.

Superior medullary velum:Forms the anterior (superior) part of the roof of thefourth ventricle.


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PONS

Trigeminal nerve coronal


Brachium conjunctivum:Also known as superior cerebellar peduncle. Contains

axons of deep cerebellar nuclei destined for the red nucleus and thalamus. Formspart of the lateral wall of the fourth ventricle.

Central tegmental tract: A compact fiber bundle located dorsal to the lateral partof the medial lemniscus. Carries fibers from midbrain tegmentum, red nucleus, and

periaqueductal gray matter to the inferior olivary complex.

Brachium pontis:Also known as the middle cerebellar peduncle. Massive bundleof fibers connecting the basal portion of the pons with the cerebellum. Contains

pontocerebellar fibers from the contralateral half of the pons. Some pontocerebellar

fibers from the ipsilateral half of the pons are also contained in the brachium pontis.

Trigeminal (CN V) nerve: A mixed nerve with a larger sensory component(portio major) and a smaller motor component (portio minor).

Pontine nuclei:Located in the basal part of the pons. Continuous caudally with

arcuate nuclei in the medulla oblongata. Receive corticofugal fibers and project

(pontocerebellar tract) mainly to the contralateral cerebellum.

Corticospinal, corticopontine, corticobulbar tracts:A long descending fiber

system sectioned transversely as it courses through the basal part of the pons.


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Pontocerebellar tract:Axons of pontine nuclei destined for the cerebellum.

Constitutes the major component of the middle cerebellar peduncle (brachium

pontis).

Medial lemniscus:Continuation of the same fiber system noted in several morecaudal levels. Note the change of orientation of this fiber bundle from a verticalorientation in the medulla to a horizontal orientation at this level.

Lateral lemniscus:Continuation of trapezoid body. Conveys auditory impulses.

Medial longitudinal fasciculus:The ascending component of this fasciculus.

Contains fibers from the vestibular nuclei destined for the nuclei of extraocularmovement. Lesions of the medial longitudinal fasciculus at this level will result in

a characteristic clinical picture known as internuclear ophthalmoplegia.


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PONS- MESENCEPHALIC JUNCTION

Trochlear nerve coronal


Brachium conjunctivum:Massive outflow tract of the cerebellum. Fibers are

seen just prior to and beginning decussation. Fibers project, after decussation, intothe red nucleus and ventrolateral nucleus of the thalamus. Lesions in this tractresult in a disorder of coordinated movement.

Pontocerebellar tract:The same structure seen at more caudal levels.

Corticospinal, corticopontine, corticobulbar tracts:The same structures seen at

more caudal levels. Cut in cross section as they descend to lower caudal levels.

Pontine nuclei:Scattered between pontocerebellar fibers and the corticospinal,

corticopontine, and corticobulbar tracts.

Brachium pontis:Axons of pontine nuclei on their way to the cerebellum.

Medial lemniscus:Continuation of the same structure seen at more caudal levels.

Spinal lemniscus:Continuation of the same structure seen at more caudal levels.

Contains spinothalamic and spinotectal fibers.

Lateral lemniscus: Contains cochlear fibers. Located laterally and dorsally on its

way to the inferior colliculus and medial geniculate body. Concerned with audition.


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Trochlear (CN IV) nerve: Seen exiting from the dorsal aspect of the midbrain

after decussating. The fourth cranial nerve supplies the superior oblique

extraocular muscle. The only cranial nerve to decussate (cross) completely prior toleaving the neuraxis.

Central tegmental tract:Compact fiber bundle located medial to the brachiumconjunctivum. Carries fibers from the midbrain tegmentum, red nucleus, and

periaqueductal gray matter to the inferior olivary complex. Note change in position

of this tract in more caudal levels.

Medial longitudinal fasciculus:Continuation of same structure seen at more

rostral and more caudal levels.

Decussation of trochlear (CN IV) nerve: Axons of neurons in the trochlear

nucleus seen decussating prior to exit from the dorsal surface of the neuraxis.


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MESENCEPHALON

Inferior colliculus coronal


Aqueduct of Sylvius: Connecting the third and fourth ventricles. Sylvius (JacquesDubois) was a sixteenth -century French anatomist.

Trochlear (CN IV) nucleus:Motor neurons located in a paramedian position

dorsal to the medial longitudinal fasciculus. Axons of neurons in trochlear nucleusdecussate prior to leaving the neuraxis (seePlate 337).

Inferior colliculus:Ovoid cellular mass in the tecturn of the mesencephalon.Belongs to the auditory system.

Lateral lemniscus:Located laterally and dorsally as it enters the inferiorcolliculus. Concerned with audition.

Spinal and medial lemnisci: Continuation of the same structures seen at morecaudal levels.

Corticospinal, corticopontine, corticobulbar tracts:Sectioned transversely ontheir way to pontine nuclei, cranial nerve nuclei, and motor neurons of the spinal

cord.

Pontocerebellar tract:Axons of pontine nuclei on their way to the cerebellum.
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Decussation of brachium conjunctivum: Massive outflow tract of the cerebellum

seen decussating at this level. Fibers project, after decussation, into the red nucleus

and ventral lateral nucleus of the thalamus.

Tract of the mesencephalic nucleus of trigerninal (CN V) nerve:Processes ofpseudounipolar neurons in the mesencephalic nucleus of the trigeminal nerve.Neurons are sparsely scattered on each side of the tract.

Medial longitudinal fasciculus:Continuation of the same structure seen at morerostral and more caudal levels.


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MESENCEPHALON

Inferior colliculus coronal


Inferior colliculus: Ovoid cellular mass belonging to the auditory system.Receives fibers from the lateral lemniscus and is reciprocally connected to themedial geniculate body.

Central (periaqueductal) gray: An area of gray matter surrounding the aqueduct

of Sylvius. Contains scattered neurons, several nuclei, and some finely myelinatedand unmyelinated fibers. Recent interest in this area has focused on its role in pain.

The neuropeptide enkephalin has been identified in the central gray.

Spinal lemniscus (spinothalamic and spinotectal tracts):Continuation of thesame fiber system seen at more caudal levels.

Medial lemniscus:Continuation of the same fiber system seen at more caudal

levels.

Central tegmental tract:A compact fiber bundle located in the dorsal part of the

mesencephalon dorsal to the decussation of brachiurn conjunctivurn. Carries fibers

from the midbrain tegmentum, red nucleus, and periaqueductal gray matter to the

inferior olivary complex. Note how the position of this tract changes in morecaudal levels (seePlates 333 and335,336,337).
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Decussation of brachium conjunctivum: Massive outflow tract of the cerebellum

seen crossing in the tegmenturn of the midbrain. Fibers project, after decussation,

into the red nucleus and the ventral lateral nucleus of the thalamus. Lesion resultsin a disorder of coordinated movement.

Basis pontis:Basal part of pons. Contains pontine nuclei as well as corticospinal,corticobulbar, corticopontine, and pontocerebellar fibers.

Cerebral peduncle:Descending corticofugal fiber system. Lesion results inweakness (paresis) or paralysis of the contralateral half of the body, including theface.

Medial longitudinal fasciculus:The ascending component of this bundle.

Connects vestibular nuclei with nuclei of extraocular movement (CN III, IV, VI).

Trochlear (CN IV) nucleus: Lies in the V-shaped ventral part of the central gray.Axons arch around the central gray, cross in the anterior medullary velum, andemerge from the dorsal aspect of the mesencephalon. Axons supply the superior

oblique extraocular muscle.

Brachium of inferior colliculus:Also known as inferior quadrigeminal brachium.

A bundle of nerve fibers from the lateral lemniscus and the inferior colliculus on

their way to the medial geniculate body. This fiber bundle conveys auditoryimpulses from the midbrain to the thalamus.


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neuroanatomy brain stem

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