Brainstem

Brainstem

The stalk-like part of the CNS that connects the spinal cord with the forebrain; includes the medulla oblongata, pons, and midbrain; houses essential nuclei and relays for many cranial nerves.

Medulla oblongata

Lower part of the brainstem; continuous with the spinal cord; contains the pyramids and olives, fourth ventricle floor, and nuclei for several cranial nerves.

Pons

Middle part of the brainstem between medulla and midbrain; contains pontine nuclei, transverse pontocerebellar fibers, and the middle cerebellar peduncle; separates basilar/tegmental regions.

Midbrain (mesencephalon)

Upper part of the brainstem; contains cerebral peduncles (crus cerebri), tegmentum, substantia nigra, and tectum with the superior and inferior colliculi.

Foramen magnum

Large skull opening where the medulla Continues as the spinal cord.

Central canal

CSF-filled canal in the spinal cord that continues upward into the medulla and expands into the fourth ventricle.

Fourth ventricle

Ventricular cavity between the brainstem and cerebellum; its floor and roof relate to medulla and pons.

Pyramid

Ventral medullary column containing corticospinal tract fibers; forms the bulges known as pyramids on the ventral surface.

Pyramidal decussation

The crossing point of most corticospinal fibers at the caudal medulla, yielding contralateral control of the body.

Olives (Inferior olivary nucleus)

Bulges on the ventrolateral medulla formed by the inferior olivary nucleus; relay to the cerebellum and involved in motor coordination.

Anterolateral sulcus

Ventral surface groove where cranial nerve roots (including IX–XI) emerge along the anterolateral medulla.

Posterolateral sulcus

Lateral ventral surface groove on the medulla marking pathways/roots border; landmark for neural exits.

Gracile tubercle

Dorsal medulla bulge over the gracile nucleus; part of the dorsal columns conveying fine touch and proprioception from the lower body.

Cuneate tubercle

Dorsal medulla bulge over the cuneate nucleus; carries fine touch and proprioception from the upper body.

Inferior cerebellar peduncle

Fiber tract connecting the medulla to the cerebellum; carries afferent information to cerebellum.

Posterior median sulcus

Dorsal midline groove on the medulla (and spinal cord).

Area postrema

Medullary area on the floor of the fourth ventricle; chemoreceptor trigger zone; contributes to vomiting reflex.

Hypoglossal nucleus

Motor nucleus for the hypoglossal (CN XII) nerve, located in the medulla near the midline.

Nucleus ambiguus

Medullary nucleus giving rise to motor fibers of CN IX and X (and portions related to XI); involved in swallowing and voice.

Nucleus of spinal tract of trigeminal nerve

Medullary nucleus processing facial pain and temperature information.

Nucleus gracilis

Medullary nucleus receiving fine touch/proprioception from the lower body; forms part of the gracile pathway.

Nucleus cuneatus

Medullary nucleus receiving fine touch/proprioception from the upper body; forms part of the cuneate pathway.

Medial lemniscus

Ascending somatosensory tract carrying discriminative touch and proprioception from body to thalamus.

Decussation of pyramids

Crossing of corticospinal fibers at the caudal medulla, producing contralateral motor control.

Decussation of lemnisci (great sensory decussation)

Crossing of dorsal column fibers to form the medial lemniscus before reaching the thalamus.

Vestibular nuclei

Group of nuclei (medial, inferior, lateral, superior) in the medulla processing balance and gaze stabilization signals.

Cochlear nuclei

Auditory processing nuclei that receive input from the cochlear nerve; located in the medulla/brainstem junction area.

Dorsal vagal nucleus

Parasympathetic nucleus of the vagus (CN X) providing autonomic output to thoracic and abdominal organs.

Nucleus of tractus solitarius

Visceral sensory nucleus in the medulla—receives autonomic and taste information and initiates reflexes.

Medial longitudinal fasciculus (MLF)

Bilateral fiber tract coordinating conjugate eye movements by linking CN III, IV, and VI pathways.

Tectospinal tract

Descending tract from the superior colliculus that guides head/neck movements in response to visual stimuli.

Crus cerebri (cerebral peduncles)

Anterior part of the midbrain containing major descending corticospinal and corticonuclear tracts.

Substantia nigra

Midbrain motor nucleus rich in melanin; connected to basal nuclei; critical for movement control; degenerates in Parkinson’s disease.

Red nucleus

Midbrain motor nucleus interfacing with cerebellum and cortex to influence limb movement; located between the aqueduct and substantia nigra