Brain Stem Anatomy

Comprehensive vocabulary flashcards covering the external features, internal divisions, cranial nerve exits, and arterial supply of the medulla oblongata, pons, and midbrain.

Brain stem

The lowermost part of the brain formed from below upwards of medulla oblongata, pons, and midbrain; continuous above with the diencephalon and below with the spinal cord.

Medulla oblongata

The lowermost, conical part of the brain stem measuring $3\,cm$ long, continuous above with the lower border of the pons and below with the spinal cord.

Closed medulla

The lower half of the medulla oblongata, traversed by the central canal which is continuous with that of the spinal cord.

Open medulla

The upper half of the medulla oblongata, which forms the lower half of the floor of the $4^{\text{th}}$ ventricle.

Pyramid (Medulla)

An elongated elevation on the ventro-lateral surface of the medulla produced by corticospinal fibers of the pyramidal tract.

Olive (Medulla)

An oval elevation posterolateral to the upper part of the pyramid, produced by the inferior olivary nucleus.

Antero-lateral sulcus (Medulla)

The sulcus separating the pyramid from the olive on the ventro-lateral surface of the medulla, serving as the exit site for the hypoglossal nerve ($12^{\text{th}}$ cranial nerve).

Postero-lateral sulcus (Medulla)

The sulcus separating the olive from the inferior cerebellar peduncle, serving as the exit site for the glossopharyngeal ($9^{\text{th}}$), vagus ($10^{\text{th}}$), and cranial root of accessory ($11^{\text{th}}$) cranial nerves.

Inferior cerebellar peduncle (I.C.P)

A bundle of nerve fibers on the posterolateral aspect of the medulla connecting the medulla oblongata with the cerebellum.

Gracile tract and tubercle

Elevations located on each side of the posterior median sulcus on the dorsal surface of the lower half of the medulla, overlying the gracile nucleus.

Cuneate tract and tubercle

Structures located lateral to the gracile tract on the dorsal surface of the lower half of the medulla, overlying the cuneate nucleus.

Tuberculum cinereum

An elevation on the dorsal surface of the lower half of the medulla located lateral to the cuneate tubercle, overlying the spinal nucleus of the trigeminal nerve.

Inferior fovea

An inverted V-shaped depression on the dorsal surface of the open medulla that separates three triangular elevations: hypoglossal trigone, vagal trigone, and lower vestibular eminence.

Hypoglossal trigone

A medial triangular elevation on the floor of the $4^{\text{th}}$ ventricle in the open medulla, overlying the hypoglossal nerve nucleus.

Vagal trigone

A triangular elevation caudal to the inferior fovea in the open medulla, overlying the dorsal nucleus of the vagus nerve.

Lower vestibular eminence

A lateral elevation on the floor of the $4^{\text{th}}$ ventricle in the open medulla, overlying the inferior and lower part of the medial vestibular nuclei.

Pons

The middle part of the brain stem measuring $1\text{ inch}$ ($2.5\,cm$) long, located between the medulla and midbrain, lying between the basilar part of the occipital bone and the cerebellum.

Basilar groove

A median shallow groove on the ventral (basilar) surface of the pons that lodges the basilar artery.

Transverse pontine fibers

Thick ridges on the ventral surface of the pons that collect on each side to form the middle cerebellar peduncle (M.C.P), connecting the pons to the cerebellum.

Facial colliculus

An elevation at the lower end of the medial eminence on the dorsal surface of the pons, produced by the abducent nucleus and encircling facial nerve fibers.

Sulcus limitans (Pons)

A longitudinal groove lateral to the medial eminence on the dorsal surface of the pons, whose lower part lies lateral to the facial colliculus and is called the superior fovea.

Upper vestibular eminence

An area lateral to the sulcus limitans on the dorsal surface of the pons that overlies the superior, lateral, and upper part of the medial vestibular nuclei.

Midbrain

The uppermost and shortest part of the brain stem measuring $2\,cm$ long, located between the pons and diencephalon within the tentorial notch of the tentorium cerebelli.

Cerebral aqueduct of Sylvius

A narrow canal passing through the midbrain that connects the $3^{\text{rd}}$ and $4^{\text{th}}$ ventricles, dividing the midbrain into an anterior two-thirds (cerebral peduncles) and a posterior one-third (tectum).

Interpeduncular fossa

A depression between the two cerebral peduncles on the ventral surface of the midbrain containing the posterior perforated substance and the exit of the oculomotor nerve ($3^{\text{rd}}$ cranial nerve).

Corpora quadrigemina

The four rounded elevations (colliculi) on the dorsal surface of the midbrain composed of gray matter, consisting of two superior colliculi and two inferior colliculi.

Superior colliculi

The two upper rounded elevations on the dorsal surface of the midbrain that serve as centers for visual reflexes.

Inferior colliculi

The two lower rounded elevations on the dorsal surface of the midbrain that serve as centers for auditory reflexes.

Trochlear nerve ($4^{\text{th}}$ cranial nerve)

The cranial nerve emerging from the midbrain below the inferior colliculus, notable as the only cranial nerve that emerges from the back of the brain stem.

Brachia quadrigemina

The superior and inferior brachia on the lateral surfaces of the midbrain that connect the superior and inferior colliculi with the lateral and medial geniculate bodies, respectively.

Transverse section of the midbrain

An anatomical cross-section showing the posterior tectum, middle tegmentum containing the periaqueductal gray matter surrounding the cerebral aqueduct, red nuclei, and substantia nigra, and the anterior crus cerebri (cerebral peduncles).