Brainstem Anatomy: Medulla, Pons, Cerebellum

Medulla, Pons, Cerebellum Overview

• Covers external anatomy, fiber tracts, sections, major blood supply and vascular syndromes of the brainstem

Brainstem Anatomy - Inferior View

• Includes crus cerebri (cerebral peduncles) and pons (brachium pontis)
• Characterized by pre- and post-olivary sulci, olivary eminence and pyramids
• Contains the restiform body

Key Features of the Brainstem - Inferior View

• Posterior median, intermediate and lateral sulci, along with anterior and anterolateral sulci

Cranial Nerve Exit Points from Brainstem

• Pons: CN IV (dorsal exit) and pons/medulla: CN VI, VII, VIII
• Cerebello-pontine angle provides an interface of pons, medulla, and cerebellum (CN VII, VIII)
• Medulla: CN IX, X exit from the post olivary sulci; CN XII exit from the pre-olivary sulci

Brainstem Anatomy - Superior View

• Includes the vermis, anterior and posterior lobes and primary fissure
• Cerebellar hemisphere is made up of intermediate and lateral parts
• Includes superior and inferior colliculi and crus cerebri (cerebral peduncles)
• Characterized by the restiform body, the gracile and cuneate tubercles

Brainstem Landmarks - Superior View

• Includes striae medullares, vagal trigone, hypoglossal trigone and facial colliculus

Cerebellum - External Anatomy

• Divided into anterior and posterior lobes
• Composed of the Vermis, intermediate and lateral hemispheres and tonsils

Cerebellar Fissures

• Primary, horizontal, and posterolateral

Cerebellar Lobes

• Flocculo-nodular lobe with nodulus and flocculus components

Descending Pathways - Corticospinal Tract (CST)

• Pathway begins with the cortical upper motor neurons
• Traverses the internal capsule before reaching the crus cerebri (cerebral peduncles)
• Continues as the pontine CST and medullary CST (pyramids)
• Decussation leads to the lateral corticospinal tract (LCS) in the lateral funiculus
• Non-decussating fibers become the anterior corticospinal tract (ACS) in the anterior funiculus
• Ends at the ventral horn lower motor neurons

Descending Pathways - Rubrospinal Tract

• Begins at the red nucleus
• Performs ventral tegmental decussation in the midbrain
• Descends through the lateral funiculus
• Terminates at the proximal limb flexor lower motor neurons

Ascending Pathways - Dorsal Column Medial Lemniscus (DCML)

• DCML deals with tactile and proprioceptive information
• Composed of two dorsal columns (fasciculi): gracile (lower extremities) and cuneate (upper extremities)
• Gracile and cuneate are the two medullary nuclei, which then decussate via internal arcuate fibers
• Medial lemniscus carries information to the ventral posterolateral nucleus of the thalamus and then the somatic sensory cortex

Ascending Pathways - Anterolateral System (ALS)

• ALS deals with pain and temperature sensation
• Uses two lateral columns with fibers from dorsal horn interneurons and undergoes prior decussation via anterior white commissure (AWC)
• ALS includes dorsal and ventral spinothalamic tracts
• ALS approaches medial lemniscus and reaches the ventral posterolateral nucleus (VPL) of the thalamus before reaching the somatic sensory cortex

Trigeminal System

• Both the DCML and ALS are systems for the head and face
• Projects to the ventral posteromedial nucleus (VPM) of the thalamus and then the somatic sensory cortex

Spinal Cord - Rostral Region

• Contains a dorsal horn, spinal accessory nucleus, spinal trigeminal tract, posteromarginal nucleus and substantia gelatinosa
• Intermediate horn contains dorsal nucleus of Clarke
• Includes anterior horn
• Lateral and Medial motor columns

Funiculi of the Spinal Cord

• Posterior funiculus is made up of the gracile and cuneate fasciculi
• Lateral funiculus consists of the rubro-spinal tract, lateral cortico-spinal tract, anterolateral system and spinocerebellar tracts
• Anterior funiculus has anterior cortico-spinal tract and medial longitudinal fasiculus

Anatomy - Medullary Region (Human Brain)

• The region contains the cerebellar vermis, tonsil and cortex
• The region contains inferior olivary nucleus, cortico-spinal tract & medullary pyramids
• Also the foramen of Magendie, inferior cerebellar peduncle and medial lemniscus

Caudal Medulla - Cranial Nerve Nuclei

• Includes nuclei for hypoglossal, dorsal vagal motor, ambiguus, solitary tract and spinal trigeminal

Caudal Medulla - Other Features

• Includes reticular formation, DCML and internal arcuate fibers

Rostral Medulla - Cranial Nerve Nuclei

• Hypoglossal, vestibular and cochlear nuclei as well as dorsal vagal motor, solitary, ambiguus and spinal trigeminal nuclei

Rostral Medulla - Other Features

• Reticular formation, inferior cerebellar peduncle and medial lemniscus

Blood Supply of Brainstem and Cerebellum

• Vertebral and basilar arteries supply the brainstem and cerebellum
• Anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA) and superior cerebellar artery (SCA) are also key arteries that supply the region

Basilar Artery Branches

• Paramedian branches and long and short circumferential branches feed the area

Wallenberg Syndrome (Lateral Medullary) - Characteristics

• Caused by infarction of the lateral medulla in the brainstem
• Includes vertigo from vestibular nuclei, decreased facial pain/temperature sensation from trigeminal nuclei involvement
• Decreased taste from solitary nucleus involvement and dysphagia/hoarseness from nucleus ambiguus involvement (CN IX, X)

Dejerine Syndrome (Medial Medullary)

• Stroke leads to tongue weakness, contralateral hemiparesis, and loss of touch/proprioception

Wallenberg - Additional Symptoms and signs

• Body pain/temperature sensation is decreased (anterolateral system)
• There is also ataxia (cerebellar peduncle involvement)
• Ptosis and miosis (Horner's syndrome involves sympathetic fibers)

Tonsillar Herniation

• Can result in Apnea (reticular area), hypertension/hyperventilation. Blackouts, and cardio-respiratory issues

Anatomy - Pontine Region (Human Brain)

• In the region are the superior medullary velum and fourth ventricle
• Includes the Medial Lemniscus, Pontine Reticular formation and Middle/Superior Cerebellar peduncles
• Also the Cortico-spinal Tract and Locus Ceruleus

Caudal Pons - Cranial Nerve Nuclei

• Abducens, facial motor and vestibular nuclei, and spinal trigeminal nucleus

Caudal Pons - Cerebellar Nuclei

• Dentate, Interposed and fastigial

Caudal Pons - Features

• Cerebellar peduncles, reticular formation, Medial and Lateral Lemniscus and the MLF

Mid-Pons - Cranial Nerve Nuclei

• Principal sensory nucleus and trigeminal motor nucleus as well as mesencephalic Nucleus

Mid-Pons - Features

• Reticular formation, superior cerebellar peduncles, Medial and Lateral Lemniscus, MLF, and DLF

Brainstem Syndromes - Pons - General

• Strokes involving CN VI, medial longitudinal fasciculus lead to horizontal gaze palsy
• Strokes involving the internuclear ophthalmoplegia (INO)
• Facial paralysis, ataxia, jaw weakness, and facial numbness if strokes involve CN VII, cerebellar peduncle and CN V

Brainstem Syndromes - Pons - Medial vs. Lateral

• Medial strokes involve paramedian branches of basilar artery, CN VI, pprf which can cause horizontal gaze palsy
• Lateral strokes involve AICA/Superior/Cerebellar artery leading to facial paralysis, ataxia and deafness

Overview of the brainstem, focusing on the medulla, pons, and cerebellum. Covers external anatomy, fiber tracts, and blood supply. Also discusses cranial nerve exit points and key features.