Neuroscience/Objectives/Lecture 19

From PhysioWiki

Brainstem organization

List the major anatomical subdivisions of the brainstem.

From caudal to rostral:

• Medulla oblongata (myelencephalon)
• Basilar pons (ventral metencephalon)
• Midbrain (mesencephalon)

Contrast the basic organizational features of the brainstem to that found in the spinal cord.

At the level of the closed medulla, the brainstem shares its overall structure with the spinal cord. Thus in general, nuclei are deep to the more superficial fiber tracts. In the open medulla, the posterior aspect of the midbrain rotates laterally (opening like a book).

Describe the gross (i.e. external) morphologic features of each of the major subdivisions of the brainstem as seen from the dorsal and the ventral surfaces.

• Medulla oblongata
  • Dorsal
    • Dorsal columns
      • Cuneate tubercle
      • Gracile tubercle
    • Hypoglossal trigone (hypoglossal nerve)
    • Vagal trigone (dorsal motor nucleus of CN X)
    • Facial colliculus (facial nerve wrapping around abducens nucleus)
  • Ventral
    • Pyramids
    • Olives
    • CN IX, X, XI, XII
• Basilar pons
• Midbrain

(List is incomplete.)

Identify those structures within the brain that contribute to the distinct external features of the brainstem.

• Abducens nucleus + facial nerve → facial colliculus
• Hypoglossal nucleus → hypoglossal trigone
• Dorsal motor nucleus of CN X → vagal trigone
• Vestibular nuclei → vestibular area
• Superior + inferior colliculi → corpora quadrigemina
• Gracile nucleus → gracile tubercle
• Cuneate nucleus → cuneate tubercle

Name and identify the locations of the cranial nerves that emerge from or enter the brainstem.

Identify the location of the ventricular system throughout the brainstem and its relationships to other brainstem structures.

The fourth ventricle begins in the closed medulla at the level of the obex. The medial foramen of Magendie exits at this point, allowing cerebrospinal fluid to escape from the ventricular system and into the cisterns. The rostral open medulla feeds into the pons, which is associated with the major part of the fourth ventricle. At the widest part of the fourth ventricle are the lateral foramina of Luschka, which also permit CSF to escape into the cisterns. The fourth ventricle ascends to become the cerebral aqueduct in the midbrain, and separates the midbrain tegmentum from tectum.

Draw the outline of a coronal section representative of medulla, pons, and mesencephalon. Within each outline, draw the major ascending and descending axonal pathways and indicate the locations of cranial nerve nuclei and other major structures, such as the reticular formation, inferior olive, etc.

See Haines.

Identify the locations of the three cerebellar peduncles and describe their relationship to the cerebellum.

The cerebellar peduncles are fiber pathways that connect the pons and cerebellum. The middle peduncle (brachium pontis) is most lateral and also the largest of the three; the inferior peduncle (restiform and juxtarestiform bodies) is inferior and medial to the middle peduncle; the superior peduncle (brachium conjunctivum) is superior and medial to the middle peduncle.

Describe the general functions of the brainstem.

• Integration of sensory information
• Motor control for head muscles (contains cranial nerve motor nuclei and parasympathetic nuclei)
• Regulation of autonomic functions essential for homeostasis
• Regulation of general activity of higher cognitive brain centers (e.g. via somatosensory relay nuclei)