Download TSM24 - Brainstem and Cranial Nerves 1

TSM24: BRAINSTEM AND CRANIAL NERVES 1
07/10/08
LEARNING OUTCOMES
Describe the gross structure of the brainstem
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The brainstem is situated inferior to the cerebrum and consists of the medulla, pons and midbrain
It contains the cranial nerve nuclei, fibres of all the ascending and descending pathways and makes up
part of the circulatory pathway of the cerebrospinal fluid (CSF)
MEDULLA OBLONGATA
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The medulla represents the transition between spinal cord and brainstem at the foramen magnum
Rostrally it broadens out and joins the pons
The ventral median sulcus extends rostrally along the midline of the ventral surface of the medulla
o There are two prominent ridges immediately lateral to the sulcus called the pyramids
o Lateral to the pyramids are two smaller oval-shaped eminences called the olives
The dorsal median sulcus extends rostrally along the midline of the dorsal surface of the medulla
o Lateral to the sulcus are the gracile and cuneate fasciculi respectively whose fibres terminate
rostrally in the corresponding nuclei in the gracile and cuneate tubercles
o The floor of the fourth ventricle on the dorsal surface narrows rostrally at the dorsal sulcus
demarking the obex
PONS
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The pons has a prominent ventral bulge divided in the midline by the basal sulcus
o Lateral to the ventral (or basal) surface are the middle cerebral peduncles which join the
pons to the cerebellum
The dorsal surface is covered almost completely by the floor of the fourth ventricle
MIDBRAIN
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The midbrain is immediately caudal to the optic tracts and the rostral-most part of the brainstem
It is divided in the ventral midline by a deep depression called the interpeduncular fossa
o The mamillary bodies are bilateral prominences at the rostral end of the fossa
The majority of the ventral surface of the midbrain is made up of the bilateral cerebral peduncles
The dorsal surface has two pairs of bilateral bulges at the rostral end, the superior and inferior
colliculi
Describe the origins of the cranial nerves from the brainstem
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CNI and CNII originate from the forebrain and so are not listed here
CNIII
Oculomotor
Arises medially from the caudal ventral surface of the midbrain
CNIV
Trochlear
Arises from the caudal dorsal surface of the midbrain immediately
inferior to the inferior colliculi
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CNV
Trigeminal
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CNVI
CNVII
CNVIII
CNIX
CNX
CNXI
Abducens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
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CNXII
Hypoglossal
Arises laterally from the ventral surface of the pons as motor and
sensory roots respectively
Arises medially from the caudal ventral border of the pons
Arises laterally to the abducens nerve
Arises laterally to the facial nerve
Arises laterally from the rostral dorsal surface of the medulla
Arises caudally to the glossopharyngeal nerve
Arises caudally to the vagus nerve as cranial and spinal roots
respectively
Arises medially and in between the vagus and cranial accessory nerves