MEDULLA BY Dr ROBERTON GAUTAM - PowerPoint Presentation

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MEDULLA

BY Dr ROBERTON GAUTAM

SR, JNMC ALIGARH

This is stalk-like

part of the brain which

connects the forebrain with the spinal cord. It consists, from below upward, of the medulla oblongata, pons, and midbrain.The brainstem consists of nerve fibres and nerve cells.The brainstem nuclei are of the following two types:1. Nuclei of last 10 cranial nerves (i.e., 3rd–12th cranial nerves).2. Other named nuclei such as red nucleus, substantia nigra, pontine nuclei, olivary nuclei, etc.In addition to well-defined tracts and nuclei, the brainstem consists of the diffuse system of cells and fibres called reticular formation. Some of the cells of reticular formation form vital centres, viz. cardiac, respiratory, vasomotor, etc.

Brainstem

The

medulla oblongata is the direct upward continuation

of the spinal cord, extending from the foramen magnum to the upper border of the pons. It forms the lowest part of the brainstem and lies almost vertically in the anterior part of the posterior cranial fossa between the clivus in front and the vallecula of the cerebellum behind.Medulla provides attachment to the last four cranial nerves.MEDULLA OBLONGATA

The lower part of the medulla, like the spinal cord, contains the central canal.

In the upper part of the medulla, this canal widens and moves dorsally to form the lower part of the 4th ventricle.

Thus, the medulla is divided into two parts: a lower closed part of medulla and an upper open part.

Features on the Ventral

Aspect

The medulla is divided into right and left symmetrical halves - by the anterior median fissure and posterior median sulcus.Anterior median sulcus is interrupted in its lower part by the bundles of fibres crossing obliquely from one side to the other, the decussation of pyramids.The posterior median sulcus is present only in the lower half of the medulla. Above, its lips diverge to form the boundaries of a triangular area, the lower part of the floor of the 4th ventricle.

Features on the Ventral

Aspect

Each half of the medulla is marked by two sulci, anterolateral and posterolateral, which are direct upward continuations of the corresponding sulci of the cord.The anterolateral sulcus extends along the lateral border of the pyramid and along it emerge the rootlets of the XII Cranial nerve.The posterolateral sulcus lies between the olive and the inferior cerebellar

peduncle and along it emerge the rootlets of

the IX, X,

and

XI

cranial nerves.

The

ventral aspect of medulla presents the

following features:1. Pyramids.2. Olives3. Rootlets of the hypoglossal nerve.4. Inferior cerebellar peduncles5. Rootlets of the IX, X, and XI (cranial part) cranial nerves

The

closed part, on either side of the posterior

median sulcus, presents three longitudinal elevations. From medial to lateral these are: fasciculus gracilis,fasciculus cuneatus and inferior cerebellar peduncle.The upper ends of the fasciculus gracilis and fasciculus cuneatus expand to form the gracile and cuneate tubercles, respectively.Another elevation present lateral to cuneate tubercle; the tuber cinereum is produced by the spinal nucleus of the trigeminal nerve.

Features of the Closed

Part

The open part of the medulla forms

- the

lower part of the floor of the 4th ventricle.Features of the Open Part

It is studied in transverse sections (T.S.) at the

three levels

: 1. At the level of decussation of pyramids. 2. At the level of sensory decussation. 3. At the level of the olives.INTERNAL STRUCTURE

Features on the Dorsal

Aspect

The dorsal aspect of the medulla is well demarcated into lower closed and upper open parts.

Transverse section of medulla at the level

of pyramidal

decussation.The transaction at this level passes through the inferior half of the medulla.1. The nucleus gracilis and nucleus cuneatus 2. Nucleus of the spinal tract of the trigeminal nerve.3. The spinal tract of the trigeminal nerve 4. Decussation of pyramidal tracts forms the mostimportant feature of medulla at this level. 5. Each detached anterior horn divides to form the spinal nucleus of the accessory nerve and the supraspinal nucleus of the 1st cervical nerve.6. Diffuse zone appears containing a network of fibres and scattered nerve cells within it

.

1

. The

nucleus gracilis and nucleus cuneatus become more pronounced with their fibres.2. The internal arcuate fibres arising from gracile and cuneate nuclei.3. The internal arcuate fibres cut off the spinal nucleus and tract of the trigeminal nerve.4. Accessory cuneate nucleus 5. The separated spinal nucleus and tract of trigeminal Nerve.6. The lower part of inferior olivary nucleus .7. The pyramids

8. The central grey matter contains the: (a)

hypoglossal nucleus, (b) dorsal nucleus of

vagus

, and (c) nucleus of

tractus

solitarius

.

9. The

medial longitudinal bundle/fasciculus

10.

Spinocerebellar

and lateral

spinothalamic

tracts.

11.

Lateral and anterior

spinothalamic

tracts

collectively form

spinal

lemniscus.

T.S. of Medulla at the Level of Sensory

Decussation

Transverse

section of medulla at the level

of sensory decussation (1 = nucleus tractus solitarius, 2 = dorsal nucleus of vagus, 3 = hypoglossal nucleus; M = medial longitudinal fasciculus, R = reticular formation).

1

.

Hypoglossal nucleus, nucleus intercalatus, dorsal nucleus of vagus,and vestibular nuclei (inferior and medial).2. The nucleus of tractus solitarius lies ventral to vestibular nuclei.3. The nucleus ambiguus.4. On either side of the midline (paramedian region) from dorsal to ventral lie medial longitudinal fasciculus (MLF), tectospinal, medial lemniscus, and pyramidal (corticospinal) tracts.5. The

arcuate

nuclei

6

. Laterally

,

(a)

inferior

cerebellar

peduncle and

(

b)

inferior

olivary

nucleus

.

T.S. of Medulla at the Level of Olives

Transverse section of medulla at the level of olives

(M = medial longitudinal bundle, R =

reticular formation, T = tectospinal tract).

The medulla is supplied by the following arteries:

1. Two vertebral arteries.

2. Anterior and posterior spinal arteries.3. Anterior and posterior inferior cerebellar arteries.4. Basilar artery.ARTERIAL SUPPLY OF THE MEDULLA

CLINICAL

Lateral

medullary (posterior inferior cerebellar artery) syndrome of Wallenberg: It occurs due tothrombosis the of posterior inferior cerebellar artery.affecting a wedge-shaped area on the dorsolateral aspect of the medulla and the inferior surface of the cerebellum, and produces the signs and symptoms:– Contralateral loss of pain and temperature sensation in the trunk and limbs, due to involvement of spinothalamic tract.– Ipsilateral loss of pain and temperature sensation over the face, due to involvement of the spinal nucleus and tract of the trigeminal nerve.–

Ipsilateral

paralysis of muscles of palate, pharynx,

and

arynx

, due to involvement of nucleus

ambiguus

.

–

Ipsilateral

ataxia, due to involvement of inferior

cerebellar

peduncle

and cerebellum.

–

Giddiness, due to involvement of vestibular nuclei

.

Medial

medullary

syndrome: It occurs due to

involvement of the

paramedian

region of the medulla

following damage to penetrating branches of the anterior spinal branch of the vertebral artery.

It produces the following signs and symptoms:

–

Contralateral

hemiplegia

/paralysis of arm and leg, due

to damage of pyramid.

–

Ipsilateral

paralysis and atrophy of the half of the tongue, due to damage of hypoglossal nerve.

–

Contralateral

loss of position and vibration sense due

to damage of medial

lemniscus

.

THANK

YOU