Medulla oblongata, simplified sections of internal structure !!

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the medulla oblongata

bone superiorly with the spinal cord

inferiorly it is conical in shape it's

brought extremity being directed

superiorly the central canal of the

spinal cord continues into the lower

half of the medulla this is called the

closed middle in the upper half of the

medulla it expands as the cavity of the

fourth ventricle it forms the lower part

of the floor of the fourth ventricle on

the anterior surface of the medulla is

the anterior median fissure which is

continuous and fed early with the

anterior median fissure of the spinal

cord on each side of the median fissure

there is a swelling called the pyramid

the pyramids are composed of bundles of

nerve fibers called corticospinal fibers

because they originate in the large

nerve cells and the precentral gyrus of

the cerebral cortex so they are cortical

and spinal because they continue into

the spinal cord and form the anterior

and lateral corticospinal tracts this is

the gray matter of the spinal cord here

it's shaped or butterfly profile with

posterior horn cells anterior horn cells

a central gray commissure around the

central canal and this is the location

of the lateral corticospinal fibers and

interior corticospinal fibers this is

another section of the metal oblongata

showing the pyramids the majority of

these descending fibers they cross over

to the opposite side and they form the

decussation of the pyramids this is the

level of the decussation of the pyramids

and we can see the fibers they cross to

the opposite side about three-quarters

of these fibers they cross and form the

lateral corticospinal tract this is

also called the great motor decussation

or the de Cassation of the pyramids the

fibers that do not cross they form the

anterior cortical spinal tract and these

fibers eventually will cross to the

other side at segmental levels and

terminate on anterior horn cells of the

spinal cord

this pyramidal tract is concerned with

performing rapid skilled movements most

of the fibers they arise from the

precentral gyrus of the frontal lobe

they pass through the Kuran radiata

internal capsule and they traverse the

cerebral peduncle the ventral part of

the pons until they reach the middle

oblongata where they form the pyramids

and then most of the fibers as I said

they dicus eight at the level of the

decussation of the pyramid and the

closed part of the medulla and form the

lateral corticospinal fibers those that

do not because eight they form the

anterior corticospinal fibers and the

anterior white column of the spinal cord

and then all these fibers they terminate

into anterior horn cells of the spinal

cord

it's a crossed tract the arcuate nucleus

is a group of neurons located on the

anterior surface of the medullary

pyramids they receive fibers from

corticospinal fibers from cortical

spinal tract and send their axons

through the anterior external rq8 fibers

and the Strymon dalaras which is located

in the floor of the fourth ventricle

these fibers reach the cerebellum via

the inferior cerebellar peduncle

postural lateral to the pyramids are the

olives and these are oval elevations

they are produced by the underlying

inferior olivary nucleus the inferior

olivary nucleus is the largest nucleus

of what we call an Oliver II nuclear

complex the gray matter of this nucleus

looks like a crumpled bag

with its mouth directed medially there

are smaller dorsal and medial or every

nuclei to form the complex the cells of

the inferior olivary nucleus send fibers

medially across the midline to enter the

cerebellum through the inferior

cerebellar peduncle this is the site of

the inferior cerebellar peduncle there

are three cerebellar peduncles inferior

middle and superior cerebellar peduncles

and these they connect the brainstem

parts with the cerebellum

so the inferior connects the middle of

longa to the cerebellum the middle

connects the pons with the cerebellum

and the superior cerebellar peduncle

connects the midbrain with the

cerebellum the function of this order

very nuclear complex which is found by

the inferior olivary nucleus the smaller

dorsal and medial accessory Oliveri

nuclei is associated with voluntary

muscle movement control of voluntary

muscle movement through its connections

with the cerebellum cerebral cortex and

spinal cord here in the closed part of

the medulla the upper part of the closed

part we can see some of the remains of

the inferior olivary nucleus but the

main part of this nucleus is located in

the open part of the middle and the

groove between the pyramid and olive

emerge the reutlitz of the hypoglossal

nerve posterior to the olives are the

inferior cerebellar peduncles and in the

groove between the olive and the

inferior cerebellar peduncle emerge the

roots of the glossopharyngeal vegas and

the cranial roots of the accessory

nerves so here we can see the vagus

nerve the posterior surface of the

superior half of the middle open part of

the middle oblongata it forms as I said

part of the floor or the lower part of

the floor of the fourth ventricle

however the posterior surface of the

inferior half of the medulla

is continuous with the posterior aspect

of the spinal cord and so it has a

posterior median sulcus on each side of

the median sulcus that is an elongated

swelling this is the grass aisle

tubercle produced by the underlying

nucleus gracilis

lateral to the grassle tubercle is a

similar swelling the Kuna tubercle which

is produced by the underlying unit

nucleus the physique

gracilis and fascicular skewness assent

superiorly posterior to the central gray

matter and the spinal cord

these are the central fibers of first

order neurons whose cell bodies are

located in the dorsal root ganglion and

these fibers that are carried in the

fasciculus gracilis and the fasciculus

cuny enters they are sensory fibers that

carry discriminative touch vibration and

conscious proprioception they are

uncrossed fibers here is the location of

these fibers and the lower part of the

medulla oblongata at the level of the

decussation of the pyramids the

second-order neurons in this pathway are

located in the nucleus gracilis and the

nucleus cuny ettus which are located in

the upper part of the closed medula at

the level of the decussation of the

medial lemniscus

both fasciculus gracilis and fasciculus

cuny ATIS they carry fibers that are

responsible for discriminative touch

vibration and conscious proprioception

the difference is that fibers entering

below mid thoracic level accumulate

medially and the fasciculus gracilis

while those above the mid thoracic level

are located laterally in the fasciculus

kinetise again these fibers are

first-order neurons whose cell bodies

are located in the dorsal root ganglion

of the spinal nerve and they terminate

on the cells or neurons which are

second-order neurons of the nucleus

gracilis and the nucleus cuny enters a

transverse section through the inferior

half of the medulla oblongata which is

located a short distance above the level

of the decussation of the pyramid passes

through the decussation

of the lamina sky or what we call the

great sensory

decussation here the fibers of

second-order neurons which are located

in the nucleus gracilis and the nucleus

kunis these fibers

form the internal arcuate fibers and

they cross the midline the medial

meniscus is formed by the ascending

fibers from the internal arcuate fibers

so at this level we can see the internal

arcuate fibers but at a higher level we

can see the medial lemniscus which is

the continuation upward of the internal

arcuate fibers this is at a higher level

where we can see the fibers of the

medial meniscus the substantial

gelatinous and the posterior grey column

of the spinal cord it becomes continuous

with the inferior end of the nucleus of

the spinal tract of the trigeminal nerve

this is the nucleus of the spinal tract

of the trigeminal nerve here again there

is the nucleus of the trigeminal nerve

spinal tract of the trigeminal nerve

this nucleus is one of the three sensory

nuclei of the trigeminal nerve the first

one is the messin cephalic nucleus which

is located in the midbrain the second

one is the main sensory nucleus which is

located in the pons and the other one is

the spinal nucleus of the trigeminal

nerve which is responsible for nasty

sensations including pain and

temperature sensations and it is located

in the medulla oblongata and the upper

two segments of the spinal cord this

nucleus gives rise to the spinal tract

of the trigeminal nerve

of the tract of the nucleus are situated

between the nucleus and the surface of

the medulla oblongata we can also

identify some other white matter tracts

including the anterior spinal cerebellar

and posterior spinocerebellar tract this

is the anterior spinocerebellar tract

and the posterior spinal cerebellar

tract they are located at the periphery

of the lateral column of white matter

and here they can also be identified at

the level of the decussation of the

pyramids in the lower part of the

medulla and also they can be identified

at the level of the decussation of the

medial lemniscus which is located a

little bit higher but in the lower part

closed part of the middle in the open

part of the medulla we can see the

anterior spinocerebellar tract only

because the posterior spinocerebellar

tract passes through the inferior

cerebellar peduncle heading to the

cerebellum these fibers are responsible

for unconscious proprioception

unconscious proprioception from the

trunk and lower limbs the fibers are

fibers of second order neurons which are

located in the nucleus dorsalis or

Clarke's column which is located at the

base of the posterior Horn of the spinal

cord

it receives fibers from muscles and

tendons carrying unconscious

proprioceptive sensations the cell

bodies of first order neurons are

located in the dorsal root ganglion and

they relay in the nucleus dorsalis or

Clarke's column fibers from nucleus

dorsalis that are going to form the

posterior spinocerebellar tract are

uncrossed fibers they ascend in the

posterior spinocerebellar tract of the

ipsilateral side and they terminate in

the cerebellar cortex via the inferior

cerebellar peduncle fibers of the

anterior spinocerebellar tract they have

crossed from the other side they cross

on the anterior white culture and they

ascend up in the anterior

spinocerebellar tract

and they terminate in the cerebellar

cortex after crossing via the superior

cerebellar peduncle so these fibers of

the anteater spinocerebellar tract they

cross twice other fibers that can be

seen in the medullary sections are the

fibers of the spinothalamic tract we

have lateral and anterior spinal thalmic

tracts this is the location of the

lateral spinothalamic tract and the

interior

spinothalamic tract the lateral

spinothalamic tract carries pain and

temperature sensation fibers these are

crossed fibers of neurons and the

posterior gray column including the

substantia gelatin OSA they originate

from substantial gelatin OSA and the

nucleus pro prius and they cross in the

anterior white calm sure to ascend up

fibers of the lateral spinothalamic

tract are therefore second-order neurons

the first-order neurons are located in

the dorsal root ganglion of a spinal

nerve the interior spinothalamic tract

carries fibers related to light touch

and pressure and again these fibers are

crossed fibers of neurons in the

posterior gray column including the

substantia G Latinos and the nucleus

properties sometimes the fibers of the

anterior and lateral spinothalamic tract

together are called the spinal lemon

escas together with fibers of the spinal

tectal tract so here we have the spinal

meniscus again at the level of the

decussation

of the medial lemniscus and in the

closed part of the medulla this is again

the site of the spinal a meniscus

located laterally the spino textile

tract which is included in the spinal a

meniscus is related to spinal visual

reflexes movements of the eyes and head

toward the source of stimulation

fibers terminate

in the superior colliculus of the

midbrain the superior colliculus which

is responsible for visual reflexes at

the level of the open part of the

medulla the upper part of Mandela we can

see the vestibular cochlear nuclei here

we have two groups of nuclei a

vestibular nuclear complex and the

cochlear nuclei this nuclear complex

extends from the medulla to the pons

here we have in the medulla we have the

inferior vestibular nucleus and the

medial vestibular nucleus they cause an

elevation in the floor of the fourth

ventricle located laterally which is

called the vestibular Trigon the other

nuclei the lateral and superior

vestibular nuclei are located in the

pons the cochlear nuclei we have the

posterior cochlear nucleus and interior

cochlear nucleus the interior is so

closely situated anterolateral to the

inferior cerebellar peduncle and the

posterior is located posterior to the

peduncle inferior cerebellar peduncle

the cochlear nuclei they receive

impulses concerned with sound via the

cochlear nerve from the spiral ganglion

of the cochlea via the cochlear nerve

and the vestibular nuclei they receive

impulses concerned with position and

movement of the head from the utricle

saccule and the semicircular canals via

the vestibular nerve at the upper part

of the medulla oblongata level of the

inferior olivary complex inferior

olivary nucleus there is another nucleus

which is called the nucleus ambiguus

here is the site of the nucleus ambiguus

this nucleus is the motor nucleus for

the muscles of the palate pharynx and

larynx therefore different fibers from

these this nucleus join the

glossopharyngeal vegas and the accessory

nerve the cranial root of the accessory

nerve here we can see

the fibers joining the vagus nerve this

is also the site of the reticular

formation which is a diffuse mixture of

nerve fibers and groups of nerve cells

represent a small part of the system of

the reticular system which is also

present in the pons and the midbrain

another nucleus is the hypoglossal

nucleus which is responsible for an

elevation here in the medial part of the

floor of the lower part of the fourth

ventricle hypoglossal trigon fibers from

this nucleus they provide the motor

supply for the muscles of the tongue

through the hypoglossal nerve lateral to

this nucleus lateral to the hypoglossal

nucleus is the dorsal nucleus of the

vagus which is responsible for another

elevation the vagal trigon and the floor

of the fourth ventricle this dorsal

nucleus of the vagus is the source of

the preganglionic parasympathetic motor

fibers for the involuntary muscles that

are supplied by the vagus nerve like the

cardiac muscles the smooth muscles of

the trachea bronchial tree and the

smooth muscles of the GI tract another

nucleus is the nucleus of the tractus

solitarius and this is located in the

medulla extends up also on the pons this

is the nucleus that receives taste

fibers so it receives from the vagus

glossopharyngeal and from the facial

nerve in the pons here it is shown to

receive fibers from the vagus nerve here

these fibers have originated from the

posterior third of the tongue again at

the level of the olive we can see the

medial lemniscus fibers conveying

sensory information which are now

crossed fibers from the nucleus gracilis

and kunis these fibers are heading to

the thalamus they pass through the pons

midbrain and go into the thalamus where

third-order neurons will carry these

sensations to the postcentral gyrus

dorsal to the medial meniscus there is

another fasciculus which is called the

medial longitudinal fasciculus this

fasciculus contains ascending and

descending fibers that connect the

vestibular and cochlear nuclei with the

nuclei controlling extraocular muscles

like the oculomotor nucleus trochlear

nucleus which are located in the

midbrain and the abducens nucleus which

is located in the pons

the textural spinal tract arises from

nerve cells in the superior colliculus

of the midbrain

most of the fibers they cross the

midline they pass through the brainstem

close to the medial longitudinal

fasciculus

we can see them here and in the lower

part of the medulla

they are very close to the middle

then they descend through the anterior

white column of the spinal cord and the

upper cervical segments of the spinal

cord and terminate by synapsing with

inter neurons they control by the

reflexes in response to visual stimuli

to complete the picture here are some

descending attracts of the spinal cord

which constitute the extra pyramidal

fibers including the vestibular spinal

tract rubra spinal Olivos spinal in

addition to the textual spinal &

reticulospinal tracts it should be

expected that all these tracts travel

through the medulla in lateral medullary

syndrome or Vallon burg syndrome which

is a vascular disorder affecting the

medulla oblongata resulting from

thrombosis of the posterior inferior

cerebellar artery or thrombosis of the

vertebral artery this will affect the

lateral part of the medulla thus if the

spinothalamic tract is affected then

there will be analgesia and thermal

anesthesia and the trunks and limps on

the contralateral side of the body

involvement of the vestibular nuclei

will result in vertigo nausea vomiting

and nystagmus involvement of the nucleus

and spinal tract of the trigeminal nerve

result in analgesia and thermo

anesthesia in the head Epps allotted to

the lesion involvement of the nucleus

ambiguus results in dysphagia and

dysphonia because this nucleus is the

motor nucleus of the muscles of the

pharynx larynx and palate and

involvement of the inferior cerebellar

peduncle will result in ataxia so all

these structures will be affected

because they are located in the lateral

part of the medulla in another vascular

disorder which is called the medial

medullary syndrome the medial medullary

syndrome results from thrombosis of the

medullary branch of the vertebral artery

and this will effect

the pyramidal tract therefore and result

in hemiparesis contralateral to the

lesion because these pyramidal fibers

corticospinal fibers are going to dicuss

it later on at either at the medullary

decussation

which is located lower down or the

fibers that are going to form the

anterior corticospinal tracts are going

to dicuss a tad segmental levels so

involvement of the pyramid will result

in contralateral hemiparesis involvement

of the medial meniscus which is also

located medially results in impaired

sensation of position movement and

tactile discrimination because this is

the modality of sensation that is

carried by the medial lemniscus

it will also affect the contralateral

side of the body because these fibers

have already dica sated in the lower

part of the medulla at the level of the

medial meniscal decussation involvement

of the hypoglossal nerve will result in

FC lateral paralysis of the muscles of

the tongue lower motor neuron lesion on

the same side of the body and when the

tongue is protruded it will deviate to

the same side of the lesion.....