Medulla Oblongata Anatomy

lecture 4

Abbas A. A. Shawka

Medical student

2nd grade

Subjects

• Introduction to Brainstem

• Medulla oblongata

General overview

Gross anatomy

Internal organization

Introduction to Brainstem

Introduction• Anatomy of the brainstem (

midbrain-pons-medulla ) is very complicated !!

• What you will find in each section through brainstem ?!

• 1- ascending an descending tracts that connect brain to spinal cord.

• 2- cranial nerves nuclei and their connections

• 3- Reticular formation

• 4- others ( do not classified as one of the above ) e.g ( olivary nucleus in MO , tapizus body in pons and red nucleus in MB )

Cranial nerves and nuclei

• The cranial nerves are individually named and numbered, using Roman numerals, in a rostro–caudal sequence, reflecting their order of attachment to the brain.

• Cranial nerves III–X and XII are associated with brainstem cell groupings referred to collectively as the cranial nerve nuclei

Cranial nerves and nuclei 1. A cranial nerve nuclei is a group of

cell ( gray matter ) participate in formation of CN .. ( equal for dorsal root ganglia of spinal nerves in sensory CN and to anterior horn cells of spinal nerves in motor CN )

2. Each nuclei have only ONE single function ( sensory , motor , … )

3. A cranial nerve which have ONE function is connected to ONE nucleithat served that function.

4. A cranial nerve which have many functions is connected to number of nuclei equal the number of its functions and each nuclei also served only ONE function

5. There is shared nuclei ( two CN or more can be share ONE nuclei .. )

Cranial nerves and nuclei • Since we have 3 types of general

somatic sensation ( mentioned in previous lecture ) .. Every type of these sensations have an equal nuclei in brainstem that give connections to CNV !! “ IMPORTANT “

1. Spinal nucleus of V nerve ( in MO ) is correspond to anteriorlatera system ( pain and temperature )

2. General sensory nucleus of V nerve ( in pons ) is correspond to DC-ML system ( tactile sensation )

3. Mesencephalic nucleus of V nerve is correspond to spinocerebellar tract ( proprioception )

•

Gross anatomy of medulla oblongata

Medulla oblongata • The medulla oblongata is the part

of the brainstem between the pons and spinal cord

• it extends through the foramen magnum to the level of the atlas.

• Medullar is vital for our function, without medulla we die.

• Above the foramen magnum it is embraced dorsally by the cerebellar hemispheres.

1. The lower end which contains the upward continuation of the central canal of the spinal cord is the ‘closed part of the medulla’,

2. the upper end, where the canal comes to the surface as the lower part of the floor of the fourth ventricle, is the ‘open part’.

1

2

Medulla oblongata • MO is about 3 cm ( lowest 3 cm of the

brainstem )

• it extend from the pronto-medullary junction until plane below foramina magnum for about 0.5 cm.

• Medulla spinalis have a central canal which prolonged into its lower half to open in the four ventricle at its upper half.

• CSF is encircle the MO from outside ( subarachnoid space ) and inside ( central canal ).

• MO is between the two lobes of cerebellum ( anterior cerebellar notch )

Closed part

Open part

Medulla oblongata

• Ventrally the upper part of the medulla is deeply grooved in the midline, with a bold convexity on either side, the pyramid (1) , due to the contained corticospinal fibres.

• Lateral to the pyramid is another convexity, the olive (2) , due to the underlying inferior olivary nucleus.

• Lateral to the olive the lateral surface of the medulla is formed by the inferior cerebellar peduncle, which enters the cerebellum medial to and below the middle peduncle.

12

Cranial nerves

• 2 exit from the midbrain

• 4 exit from the bones

• 4 exit from the medulla

• From medulla

1. Glossopharyngeal nerve IX

2. Vagus nerve X

3. Spinal accessory nerve XI**

4. Hypoglossal nerve XII

**although it exit through medulla it have NO nuclei in it ( note : cranial accessory nerve is consideres as part of vagus )

IX

X

XI

XII

Cranial nerves

• From the 4 cranial nerves that exit through medulla

• 1 exit between pyramid and olive XII

• The other 3 exit between olive and ICP IX,X,XI

IX

X

XI

XII

Medulla oblongata

• Dorsally the lower part of the floor of the fourth ventricle forms the upper part of the medulla , here the roof of the ventricle is ependyma and pia mater.

• At the lower corner of the diamond-shaped floor the hypoglossal trigone (1) is adjacent to the midline, with the vagal trigone (2) lateral to it. Higher up and at the lateral corners of the diamond is the vestibular area and the medullary striae.

• In the lower or closed part of the medulla, the fourth ventricle has become narrowed to the tiny central canal, and the external dorsal surface shows small elevations, the gracile (3) and cuneate (4) tubercles, the former being medial to the latter.

1

2

3

4CC

Internal structure

NOTE

We will study cross section firstly in closed part then in

open part !!

Closed part of medulla

Closed part of medulla

Gray mater White mater

Spinal nucleus of V. nerve

Spinal accessory nucleus

Nucleus graciles

Nucleus cuneatus

Sensory Motor

Pyramidal decuss.Spinal tract of V nerve

Lateral ST tract

Anterior & posterior SC tract

Internal arcuate fibers*

Medial lemniscus begining*internal arcuate fibers = DC-ML system

spinal nucleus of the trigeminal nerve

• Arrow !!

• Extend from pons to C2

• Pain, temperature and crude touch from the ipsilateral H&N

• general somatic sensation corresponding to anteriolateralsystem !!!

• V, VII, IX,X have connections with it.

• Only nuclei of spinal accessory nerve XI

• Reach lower medullary levels

Spinal accessory nucleus

gracile and cuneate nuclei • The gracile and cuneate nuclei

underlie the corresponding tubercles of the dorsal surface of the lower medulla.

• They contain the cell bodies on which the incoming fibres of the gracile and cuneate tracts of the spinal cord terminate,

• the nuclei give origin to the medial lemniscus.

GC

DC-MLT

STT

ALT

Brain stem

Spinal cord

White mater – pyramidal decussation level

White mater – medial Leminscus decussation level

open part of medulla

open part of medulla

Gray mater

Inferior olivary nucleus

Arcuate nucleus

Spinal nucleus of V nerve

Nucleus ambiguius

Nuclei of solitary tract

Lateral vestibular nuclei

Cochlear nuclei

Inferior salivatory nucleus

Nucleus of hypoglossal n.

Dorsal nucleus of vagus n.

CN IX,X,XII nuclei

Will be studied in cerebellum !!

Will be studied in pons !!

Open medulla – inferior peduncle level

Modalities of CN ?• 1- motor :-

• A- to skeletal muscle

- General : muscle of somite origin GSE

- Special : muscle of branchial origin SVE

• B- to viscera ( parasympathetic ) GVE

- To glands ( secretomotor )

- To smooth muscle

• 2- sensory

• A- From body

- General : 3 types of sensation GSA

- Special : vision, hear & balance SSA

• B- From viscera

- General : visceral pain and spasm GVA

- Special : test and smell SVA

Parasympathetic CN and their nuclei and ganglion

Parasympathetic CN Nuclei Ganglion

Oculomotor nerve III Acessory oculomotor nucleus

Ciliary gangliom

Fascial nerve VII Superior salivatory nucleus Ptrygopalatine ganglia+

Submandibular ganglia

Glossopharyngeal nerve IX

Inferior salivatory nucleus Otic ganglion

Vagus nerve X Dorsal nucleus of vagusnerve

Superior and inferior ganglion of vagus nerve

Glossopharyngeal nerve IXNerve Modality Nucleus Position Distribution

Glosso-pharyngeal

nerve

SVE Nucleusambigius

Medulla Motor to stylopharyngeusthat assists withswallowing

GVE Inferior salivatorynucleus

Medulla Parasympatheticinnervation to parotidgland

GVA

Solitary nucleusLower

medulla

Visceral sensation fromparotid gland, carotidbody and sinus,pharynx, and middle ear

SVA Taste from posterior 1/3of tongue

GSA sensory nucleus of trigeminal

nerve

Pons – C2 Cutaneous sensation fromexternal earCommon sensation fromposterior 1/3 of tongue

Glossopharyngeal nerve IX Nerve Modality Nucleus Position Distribution

Vagusnerve

SVE**

Nucleus ambigius Medulla Motor to constrictor muscles of pharynx, intrinsic muscles oflarynx, muscles of palate (except tensor veli palatini), and striatedmuscle in superior two thirds of esophagus

GVE Dorsal vagus nuclei Medulla Smooth muscle of trachea, bronchi, and digestive tract,cardiacmuscle

GVA Solitary nucleus Lower medulla

Visceral sensation from base of tongue, pharynx, larynx, trachea,bronchi, heart, esophagus, stomach, and intestine

SVA Taste from epiglottis and palate

GSA Sensory nucleus of trigeminal nerve

Pons – C2 Sensation from auricle, external acoustic meatus, and dura materof posterior cranial fossa

**Cranial part of accessory nerve XI

Spinal accessory nerve

• Two parts

1. Cranial part ( from N ambigius ) X

2. Spinal part

- Ascend from upper cervical cord

- Enter F. magnum to join the cranial part.

- Separate just below the Jagularforamina.

- PCT supply platysma and SCM !!

Hypoglossal n.

• Hypoglossal nucleus

lies in lower medulla

• Give XII nerve fibers

Medullary autonomic centers• Cardiovascular centers :-

• 1- cardioinhibitary and cardiostimulatory centers affect the rate and force of cardiac contraction.

• 2- vasomotor centers affect the smooth muscle fibers tone.

• Respiratory centers :-

• Recive input from pons

• Others :-

• Emesis

• Deglutition

• Coughing

• Hiccupping

• Sneezing

Blood supply of medulla• The medulla is supplied

ventrally by branches of the vertebral and basilar arteries, and laterally and dorsally by the posterior inferior cerebellar artery.

• The veins drain dorsally to the occipital sinus and ventrally into the basilar plexus of veins and the inferior petrosal sinus.

• The medullary veins communicate with the spinal veins.

Posterior inferior cerebellar a.

Blood supply of medulla

Aertery distribution Loss of supply lead to

Anteriorspinal artery ( branch of vertebral a. )

supply the region next to the midline i.e. the part containing the pyramid, medial lemniscusand hypoglossal nucleus

medial medullary syndrome

Posterior inferior cerebellar a. ( branch of vertebral a. )

Lateral and dorsal sides of the MO

lateral medullary syndrome ‘syndrome of the posterior inferior cerebellar artery’.

Medial medullary syndrome • Due to loss of blood supply to ventral

side of MO … ( by anterior spinal a. )

• Structures will be affected :-

1. Pyramid

2. Medial lemniscus

3. Hypoglossal nucleus

• It will lead to :-

• IPSILATERALLY

• paralysis of the tongue on the same side ( due to damaged hypoglossal nuclei hypoglossal nerve )

• CONTRALATERALY

• hemiplegia ( crossed pyramid damage)

• loss of touch and kinaesthetic sense on the opposite side ( medial lemniscus damage )

Which side is affected ?!

Lateral medullary syndrome • Due to loss of blood supply to lateral

area of MO ( posterior inferior cerebellar a. )

• Structures will be affected :-

1. Nucleus ambiguus

2. Spinal tract of trigeminal n. ( uncrossed )

3. Spinal lemniscus ( crossed ) :-upper continuation of anteriolateral system

4. Hypothalamospinal fibres of the sympathetic system

5. Vestibular nuclei

• The loss of nucleus ambiguus function paralyses laryngeal, palatal and pharyngeal muscles on that side, causing dysphonia and dysphagia.

• Loss of the uncrossed spinal tract of the trigeminal and of the crossed spinal lemniscus results in loss of pain and temperature sensation on the same side of the face and opposite side of the body.

• There will also be a Horner’s syndrome on the ipsilateral side due to interruption of descending hypothalamospinal fibres of the sympathetic pathway.

• Involvement of the vestibular nuclei causes vertigo and nystagmus with nausea and vomiting.

Thank youThank you