NEUROANATOMY

Lecture : 3

Anatomy of the Brain Stem

Prepared and presented by:Dr. Iyad Mousa Hussein,

Ph.D in NeurologyHead of Neurology Department

Nasser Hospital

1. Morphological Subdivisions of the Brain.

2. Site, Parts, and Functions of the Brain Stem.

3. Parts of the Medulla Oblongata.

4. Connection, External, and internal Features of the Medulla

Oblongata.

5. Connection, External, and internal Features of the Pons.

6. Connection, External, and internal Features of the Midbrain.

7. Location, Connections, and Functions of the Reticular

Formation of the Brain Stem.

8. Motor and sensory pathway.

LECTURE OBJECTIVES:

1. The Cerebrum: formed of right and left cerebral

hemisphere.

2. The Cerebellum: below the posterior part of the

cerebrum.

3. The Brain Stem: formed of the following parts (from

downward):

a. Medulla oblongata.

b. Pons.

c. Midbrain.

Morphological Subdivisions of the Brain

The brain stem lying infront of the cerebellum and

occupies the posterior cranial fossa.

The brain stem formed of the following parts (from

downward):

1. Medulla oblongata.

2. Pons.

3. Midbrain.

The Brain Stem

1. It serves as a conduit for the ascending and

descending tracts.

2. It contains important reflex centers associated

with the control of cardiovascular, respiratory

systems and consciousness.

3. It contains the important nuclei of cranial nerves

III through XII.

Functions of the Brain Stem

The medulla oblongata is the lower part of the brain

stem (3 cm).

Extent:

Above: it is continuous with pons.

Below: it is continuous with the spinal cord at the

foramen magnum.

The Medulla Oblongata

Closed Medulla: it is the lower half of the medulla,

as it encloses a central canal continuous with that

of spinal cord.

Open Medulla: it is the upper half of the medulla,

as it opens into the fourth ventricle.

Parts of the Medulla Oblongata

A. Anterolateral Surface:

1. The anterior median fissure.

2. The pyramid: formed by the pyramidal

(corticospinal) tract.

3. The olive: formed by the inferior olivary nucleus.

4. The anterolateral sulci: gives exit to the hypoglossal

nerves.

5. The posterolateral sulci: gives exit to the

glossopharyngeal, vagus and cranial accessory

nerves.

6. The inferior cerebellar peduncle.

External Features of the Medulla Oblongata

B. The posterior surface of the medulla oblongata:

1. The posterior surface of the upper half (open

medulla): presents the following features from

medial to lateral:

a. The median longitudinal fissure.

b. Inferior fovea.

c. Hypoglossal trigone (triangle).

d. Vagal trigone.

e. Vestibular trigone.

2. The posterior surface of the lower half (closed

medulla): presents the following features from

medial to lateral:

a. Posterior median fissure.

b. Gracile tract.

c. Cuneate tract.

Internal Structures of the Medulla Oblongata

The main nuclei of the medulla oblongata:

1. Gracile nucleus: proprioceptive and fine touch

from the lower 1/2 of the body.

2. Cuneate nucleus: proprioceptive and fine

touch from the upper 1/2 of the body.

3. Inferior olivary nucleus: extrapyramidal

function.

4. Inferior salivary nucleus: parasympathetic

function via the glossopharyngeal nerve.

5. Spinal nucleus of trigeminal nerve: pain and

temperature sensations from the face and scalp

via the trigeminal nerve.

6. Solitary nucleus: taste sensations via the facial,

glossopharyngeal and vagus nerves.

7. Nucleus ambiguous: pyramidal and

extrapyramidal functions via motor fibers of the

glossopharyngeal, vagus and accessory nerves.

8. Dorsal nucleus of vagus nerve: parasympathetic

via the glossopharyngeal and vagus nerves.

9. Hypoglossal nucleus: motor function of the

tongue via hypoglossal nerve.

Blood Supply of the Medulla Oblongata

The medulla oblongata is supplied by:

1. The vertebral arteries.

2. The anterior spinal artery.

3. The posterior spinal arteries.

4. The posterior inferior cerebellar arteries.

5. The basilar artery.

Extent: it extends from the medulla oblongata below to

midbrain above and lies infront of the cerebellum.

The Pons

A. The anterior surface of the pons: presents the following

features:

1. The basilar groove: for basilar artery.

2. The transverse streaks: to form middle cerebellar peduncle.

3. The middle cerebellar peduncle.

4. The trigeminal nerve.

5. The abducent nerve.

6. The facial nerve.

7. The vestibule-cochlear nerve.

External features of the pons

B. The posterior surface of the pons: presents the

following features:

1. The median longitudinal sulcus: the middle line.

2. The medial eminence: produced by the abducent

nucleus.

3. The facial colliculus: it produced by the facial nucleus.

4. The medullary stria: transverse nerve fibers

which separate the posterior surface of pons from

that of medulla oblongata.

5. Superior fovea.

1. Pontine nuclei: they form part of the cortico-ponto-

cerebellar pathway.

2. Transverse fibers: pontocerebellar fibers.

3. Longitudinal fibers: which include pyramidal and cortico-

pontine fibers.

4. Nuclei of the trigeminal nerve:

a. Motor nucleus.

b. Sensory nucleus.

5. Nucleus of the abducent nerve.

6. Nuclei of the facial nerve:

a. Motor nucleus.

b. Superior salivary nucleus: parasympathetic

function.

Internal structures of the pons

7. Nuclei of the vestibulocochlear nerve.

8. Lateral lemniscus: it is a band of ascending fibers

carrying hearing impulses from both ears.

9. Spinal lemniscus: it is a band of ascending fibers

carrying pain, temperature and crude touch from the

opposite side of the body below the head.

10. Trigeminal lemniscus: it is a band of ascending

fibers carrying pain, temperature and touch and

proprioception from the opposite side of the face and scalp.

11. Medial lemniscus: it is a band of ascending fibers

carrying proprioceptive and fine touch from the opposite

side of the body below the head.

The pons is supplied by:

1. The anterior inferior cerebellar arteries.

2. The superior cerebellar arteries.

3. The basilar artery (gives pontine arteries).

Blood Supply of the Pons