Medulla oblongataMedulla oblongata

Medulla oblongataMedulla oblongata

Lower part of brainstem.Lower part of brainstem.Contains central canal in the lower part Contains central canal in the lower part

and its upper part contains IV ventricle.and its upper part contains IV ventricle.Presents pyramids on either side of the Presents pyramids on either side of the

midline anteriorly (formed by corticospinal midline anteriorly (formed by corticospinal tracts on their way to spinal cord) and olive tracts on their way to spinal cord) and olive produced by underlying inferior olivary produced by underlying inferior olivary nucleus.nucleus.

Gross features

On the back of medulla On the back of medulla are gracile and cuneate are gracile and cuneate tubercles which contain tubercles which contain nuclei of the same nuclei of the same name(2nd order neurons) name(2nd order neurons) for the fasciculi of the same for the fasciculi of the same name.name.

Fasciculus gracilis and F.cuneatusFasciculus gracilis and F.cuneatus

F.gracilis (tract of Goll) is the medial of the F.gracilis (tract of Goll) is the medial of the two. Carries fine touch, vibration and two. Carries fine touch, vibration and conscious proprioception from the lower conscious proprioception from the lower part of the body.part of the body.

F. cuneatus (tract of Burdach) is lateral to F. cuneatus (tract of Burdach) is lateral to the above tract and carries same the above tract and carries same sensations from the upper part of the sensations from the upper part of the body.body.

Tabes dorsalisTabes dorsalis

Tertiary syphilitic degeneration of posterior Tertiary syphilitic degeneration of posterior white columns which only sensory tracts.white columns which only sensory tracts.

There is loss of tactile discrimination, There is loss of tactile discrimination, vibration and position sense. vibration and position sense.

structurestructure

The characteristic appearance of grey The characteristic appearance of grey matter in spinal cord is lost in medulla.matter in spinal cord is lost in medulla.

The grey matter contains the nuclei of last The grey matter contains the nuclei of last four cranial nerves and reticular formation.four cranial nerves and reticular formation.

For the arrangement of grey and white For the arrangement of grey and white matters medulla is studied at 3 levels.matters medulla is studied at 3 levels.

Medulla at the level of pyramidal Medulla at the level of pyramidal decussationdecussation

Important features are:Important features are: 1.Spinal nucleus and tract 1.Spinal nucleus and tract

of V in line with the of V in line with the posterior horn of spinal posterior horn of spinal cord.cord.

2.Pyramidal 2.Pyramidal decussation(75%of fibers decussation(75%of fibers cross the midline and cross the midline and descend to the cord as descend to the cord as lat.corticospinal tracts.lat.corticospinal tracts.

continuedcontinued

3.corresponding to 3.corresponding to the anterior horn is the anterior horn is the spinal nucleus of the spinal nucleus of accessory.accessory.

4.diffuse zone of 4.diffuse zone of nerve cells and fibers nerve cells and fibers corresponding to the corresponding to the lateral white column lateral white column called the reticular called the reticular formation. formation. The reticular formation

SPECIAL FEATURES OF V nerveSPECIAL FEATURES OF V nerve

Has a large sensory nucleus (V1,V2 and Has a large sensory nucleus (V1,V2 and V3) and a smaller motor nucleus.V3) and a smaller motor nucleus.

Hence it extends throughout the brain Hence it extends throughout the brain stem (mesencephalic nucleus, principal stem (mesencephalic nucleus, principal nucleus and spinal tract and nucleus).nucleus and spinal tract and nucleus).

Perhaps the only cranial nerve nucleus to Perhaps the only cranial nerve nucleus to do so.do so.

Medulla at the level of sensory decussationMedulla at the level of sensory decussation

Fasciculi gracilis and Fasciculi gracilis and cuneatus end in cuneatus end in corresponding nuclei.corresponding nuclei.

Second order neurons Second order neurons begin as internal arcuate begin as internal arcuate fibres,cross the midline fibres,cross the midline and form the medial and form the medial lemniscus.lemniscus.

Olivary nucleus makes its Olivary nucleus makes its appearance.appearance.

Pyramids on either side Pyramids on either side of midline.of midline.

Sensory decussation

continuedcontinued

Central grey matter Central grey matter (close to the central (close to the central canal) containscanal) contains

1.hypoglossal nucleus 1.hypoglossal nucleus (close to the midline)(close to the midline)

2.dorsal nucleus of 2.dorsal nucleus of vagus vagus (parasympathetic)(parasympathetic)

3.nucleus of tractus 3.nucleus of tractus solitarius (taste)solitarius (taste)

Purely motor cranial nervesPurely motor cranial nerves

3rd,4th,6th and 12th 3rd,4th,6th and 12th cranial nerves lie in cranial nerves lie in the same line and the same line and have their nuclei have their nuclei close to the midline of close to the midline of the brain stem.the brain stem.

continuedcontinued

4.MLF appears just posterior to medial 4.MLF appears just posterior to medial lemniscus (this is connected to 3lemniscus (this is connected to 3rdrd,4,4thth,6,6thth,8,8thth and spinal nucleus of XI)and spinal nucleus of XI)

Spinocerebellar and lateral spinothalamic Spinocerebellar and lateral spinothalamic tracts move laterally to the lateral white tracts move laterally to the lateral white column.column.

Lateral and anterior spinothalamic tracts Lateral and anterior spinothalamic tracts lie close to each other and form “spinal lie close to each other and form “spinal lemniscus”.lemniscus”.

Upper medulla (open part)Upper medulla (open part)

central canal opens central canal opens into IV ventricle.into IV ventricle.

along with XII, along with XII, vestibular nuclei(2 of vestibular nuclei(2 of the 4) appear here.the 4) appear here.

nucleus ambiguus nucleus ambiguus (common motor (common motor nucleus for 9nucleus for 9thth,10,10thth and 11and 11thth cranial cranial nerves) is present.nerves) is present.

Medulla (clinical aspects)Medulla (clinical aspects)

Cranial nerves IX, X, XI and XII originate from the medulla.

2) control of visceral motor reflexes, e.g., coughing, swallowing, salivating,

vomiting, secretion, sneezing; the medulla also receives taste and other

visceral sensations.

Functions of the medulla include: 1) control of somatic motor reflexes

of the larynx, pharynx and tongue which are important in speech and swallowing. (nucleus ambiguus)

3) the MLF contains fibers for the 3) the MLF contains fibers for the regulation of the position of the head and regulation of the position of the head and neck and for coordinated eye movements; neck and for coordinated eye movements;

4) the medulla is a relay for the cochlear 4) the medulla is a relay for the cochlear and vestibular responses;and vestibular responses;

5) the reticular formation regulates a 5) the reticular formation regulates a variety of functions including skeletal variety of functions including skeletal motor activity, consciousness, visceral motor activity, consciousness, visceral functions, conduction of sensation, etc.functions, conduction of sensation, etc.

The features of medullary syndromes reflect The features of medullary syndromes reflect its anatomy and physiology, i.e., the its anatomy and physiology, i.e., the ascending sensory tracts, the descending ascending sensory tracts, the descending motor systems, cranial nerves IX - XI motor systems, cranial nerves IX - XI exiting at this level, and the cranial nerves exiting at this level, and the cranial nerves that are associated at or near this level, that are associated at or near this level, viz., CN VIII viz., CN VIII

Lateral medullary syndromeLateral medullary syndrome(PICA) of Wallenberg (PICA) of Wallenberg

Dorsolateral aspect of Dorsolateral aspect of medulla is supplied by medulla is supplied by PICA.PICA.

In this area In this area spinothalamic tract, spinothalamic tract, spinal nucleus and spinal nucleus and tract of V, nucleus tract of V, nucleus ambiguus, inferior ambiguus, inferior cerebellar peduncle, cerebellar peduncle, vestibular nuclei are vestibular nuclei are situated.situated.

Effects

Nucleus ambiguus Nucleus ambiguus Paralysis of vocal cord and Paralysis of vocal cord and pharyngeal muscles on the pharyngeal muscles on the side of the lesion side of the lesion

Inferior cerebellar peduncle Inferior cerebellar peduncle

Ipsilateral ataxia; also vertigo Ipsilateral ataxia; also vertigo from interruption of from interruption of connections of vestibular connections of vestibular nuclei nuclei

Spinal tract of trigeminal Spinal tract of trigeminal Loss of pain and Loss of pain and temperature sensation, temperature sensation, same sidesame side of face of face

Spinothalamic tract Spinothalamic tract Loss of pain and Loss of pain and temperature sensation, temperature sensation, opposite sideopposite side of the body of the body

Medial medullary syndromeMedial medullary syndrome(hypoglossal alternating hemiplegia)(hypoglossal alternating hemiplegia)

Due to thrombosis of Due to thrombosis of vertebral artery vertebral artery branches supply branches supply paramedian regions paramedian regions of medulla.of medulla.

Structures present Structures present here are: pyramid, here are: pyramid, hypoglossal nerve, hypoglossal nerve, medial lemniscus.medial lemniscus.

Effects

Medial Medial lemniscuslemniscus

Contralateral loss of Contralateral loss of position and vibration senseposition and vibration sense

pyramidpyramid Contralateral hemiplegiaContralateral hemiplegia

Hypoglossal Hypoglossal nucleusnucleus

Ipsilateral paralysis and Ipsilateral paralysis and atrophy of atrophy of halfhalf of tongue of tongue (when protruded, the tip (when protruded, the tip deviates to the same side of deviates to the same side of lesion)lesion)