6. 3 PARTS
• MID BRAIN
• PONS
• MEDULLA
• Present in the Posterior Cranial fossa.
• Connects narrow spinal cord with the
expanded Forebrain.
7. Broad functions
1. It serves as a conduit for the ascending tracts
and descending tracts connecting the spinal
cord to the different parts of the higher
centers in the forebrain
2. Inportant reflex centers present - respiration,
cvs and control of consiousness
3. Nuclei for CN 3 to 12
8. MEDULLA OBLONGATA
• Connects Pons with Spinal cord
• Conical in shape
• The central canal in lower half continues as that of
spinal cord while the upper half expands as the
cavity of fourth ventricle
• The region between the anterior median sulcus
and the antero lateral sulcus is occupied (on
either side of the midline) by an elevation called
the pyramid.
• The elevation is caused by a large bundle of fibres
that descend from the cerebral cortex to the spinal
Cord (corticospinal fibres)
9. • Some of these fibres cross from one side to the
other in the lower part of the medulla,
obliterating the anterior median fissure. These
crossing fibres constitute the decussation of the
pyramids.
• The posterior surface of the superior half of
medulla forms the lower part of the floor of the
fourth ventricle
• The posterior surface of the inferior half of the
medulla is continuous with posterior aspect of the
spinal cord and has POSTERIOR MEDIAN SULCUS
11. PONS
• The Pons is anterior to the cerebellum and connects the medulla with the
midbrain.
• 1 inch
• Anterior surface has basilar groove which lodges the basilar artery.
• Connected to cerebellum via Middle cerebellar peduncle.
12. • On either side of the lower part of the Pons there is a region called the
cerebello-pontine angle. This region lies near the lateral aperture of the
fourth ventricle. The facial, vestibulocochlear and Glossopharyngeal
nerves, the nervus intermedius, and sometimes the labyrinthine arteries
lie in this region.
• The pons is divisible into a ventral part and a dorsal part
• The ventral (or basilar) part contains numerous transverse and vertical
fibres. Amongst the fibres are groups of cells that constitute the pontine
nuclei.
• When traced laterally the transverse fibres form the middle cerebellar
peduncle.
• The vertical fibres are of two types. Some of them descend from the
cerebral cortex to end in the pontine nuclei. Others are corticospinal fibres
that descend through the pons into the medulla where they form the
pyramids.
14. MIDBRAIN
• 0.8 inch in length
• Connects Pons and cerebellum with the forebrain
• The midbrain is traversed by NARROW CHANNEL, THE CEREBRAL
AQUEDUCT, filled with CSF
• Posterior surface- 4 colliculi- Corpora Quadrigemina
• Superior colliculi- Visual
• Inferior colliculi- auditory
• In the midline below the Inferior colliculus- trochlear nerves emerge
• When the midbrain is viewed from the anterior aspect, we see two large
bundles of fibres, one on each side of the middle line. These are the crura
of the midbrain
15. • The crura are separated by a deep fissure. Near the pons the fissure is narrow,
but broadens as the crura diverge to enter the corresponding cerebral
hemispheres. The parts of the crura just below the cerebrum form the
posterior boundary of a space called the interpeduncular fossa. The
oculomotor nerve emerges from the medial aspect of the crus of the same
side.
• Each colliculus is related laterally to a ridge called the brachium.
• The superior brachium (also called the superior quadrigeminal brachium, or
brachium of superior colliculus) connects the superior colliculus to the lateral
geniculate body.
• Similarly, the inferior brachium (also called the inferior quadrigeminal
brachium or brachium of inferior colliculus) connects the inferior colliculus to
the medial geniculate body.
• Just below the colliculi, there is the uppermost part of a membrane, the
superior medullary velum, which stretches between the two superior
cerebellar peduncles, and helps to form the roof of the fourth ventricle.
16. • For convenience of description, the midbrain may be divided as follows
A. The part lying behind a transverse line drawn through the cerebral
aqueduct is called the tectum. It consists of the superior and inferior
colliculi of the two sides.
B. The part lying in front of the transverse line is made up of right and left
halves called the cerebral peduncles.
• Each peduncle consists of three parts. From anterior to posterior side
these are the
1. crus cerebri (or basis pedunculi),
2. the substantia nigra and
3. the tegmentum.
