Medulla, Pons, and Cerebellum Anatomy

• Lecture covers the medulla, pons, and cerebellum, including external anatomy, fiber tracts, sections, major blood supply, and vascular syndromes of the brainstem.

Anatomical Overview

• Inferior brainstem anatomy includes the crus cerebri (cerebral peduncles), pons (brachium pontis), pre- and post-olivary sulci, olivary eminence, pyramids, and restiform body.
• Superior brainstem anatomy shows superior and inferior colliculi, the crus cerebri, restiform body, and gracile and cuneate tubercles.
• Key brainstem exit points are: Pons: IV (dorsal exit), V; Pons/medulla: VI, VII, VIII; Cerebello-pontine angle (interface of pons, medulla, and cerebellum): VII, VIII; Medulla: post olivary IX, X pre-olivary sulci XII.

Cerebellum Anatomy

• Cerebellum features include: Anterior lobe, Posterior lobe, Vermis, Intermediate hemisphere, Lateral hemisphere, and Tonsils.
• Key fissures of the cerebellum are: Primary fissure, Horizontal fissure, and Postero-lateral fissure.
• Flocculo-Nodular lobe includes the Nodulus and Flocculus.

Major Descending Pathways - Corticospinal Tract (CST)

• Cortical Upper Motor Neurons (UMNs) pass through the Internal Capsule and Crus Cerebri (cerebral peduncles).
• The CST descends via the Pontine CST and Medullary CST (Pyramids).
• The CST decussates and becomes the Lateral Corticospinal Tract (LCS) in the lateral funiculus; fibers that don't decussate become the Anterior Corticospinal Tract (ACS) in the anterior funiculus, and both innervate Ventral horn LMNs.
• The Rubrospinal Tract originates in the Red Nucleus, undergoes Ventral tegmental decussation in the midbrain, and descends in the Lateral funiculus to influence Proximal limb flexor LMNs.

Major Ascending Pathways - Dorsal Column Medial Lemniscus (DCML)

• DCML is responsible for tactile and proprioceptive sensation
• Two dorsal columns (fasciculi): Gracile (lower extremities) and Cuneate (upper extremities).
• Relays in two medullary nuclei: gracile and cuneate
• The DCML decussates via internal arcuate fibers.
• Travels in the medial lemniscus (white matter) to the Ventral Posterolateral Nucleus of the Thalamus (VPL) and then to the Somatic Sensory Cortex.

Antero Lateral System (ALS)

• Carries pain and temperature information.
• ALS consists of fibers from dorsal horn interneurons.
• Fibers decussate via the Anterior White Commissure (AWC) and ascend as dorsal and ventral spinothalamic tracts (= Antero Lateral System).
• ALS ascends and approaches the medial lemniscus, eventually reaching the VPL of the thalamus and projecting to the Somatic Sensory Cortex.
• Trigeminal System (head/face) uses both DCML and ALS pathways.

Spinal Cord Anatomy

• Structures in the rostral spinal cord include the Dorsal Horn, Spinal accessory nucleus, Spinal trigeminal tract, posteromarginal nucleus, and substantia gelatinosa.
• Intermediate Horn contains the Dorsal nucleus of Clarke.
• Anterior Horn consists of Lateral and Medial motor columns.
• Posterior Funiculus includes the Gracile and Cuneate fasiculus.
• Lateral Funiculus includes the Rubro-spinal tract, Lateral cortico-spinal tract, Anterolateral system, and Spinocerebellar tracts.
• Anterior funiculus contains the Anterior cortico-spinal tract and Medial longitudinal fasiculus, along with the Vestibulo-, Tecto-, reticulo-spinal tracts

Medulla

• Sectional anatomy highlights the Cerebellar vermis, Cerebellar tonsil, Foramen of Magendie, Inferior cerebellar peduncle, Cerebellar cortex, and Medial lemniscus.
• Sectional anatomy highlights Cortico-spinal tract, Medullary pyramids and Inferior olivary nucleus.
• Caudal medulla contains: Hypoglossal nucleus, Dorsal vagal motor nucleus, Nucleus ambiguus, Solitary nucleus and tract, Spinal trigeminal nucleus and tract.
• Other features of the Caudal medulla: Reticular formation, DCML, Internal arcuate fibers, MLF, ALS, Spinocerebellar tracts, Inferior olivary nucleus, and Corticospinal tract/pyramids.
• Rostral medulla contains: Hypoglossal nucleus*, Vestibular nuclei, Cochlear nuclei, Dorsal vagal motor nucleus*, Solitary nucleus, and tract, Nucleus ambiguus*, Spinal trigeminal nucleus, and tract.

Key Structures in Rostral Medulla

• Reticular formation
• Cerebellar peduncle (inferior)
• Medial Lemniscus
• MLF
• ALS
• Spinocerebellar tracts
• Inferior olivary nucleus
• Corticospinal tract / pyramids

Pons

• Sectional anatomy of the pontine region includes Superior medullary velum, 4th ventricle, Superior Cerebellar peduncle, Medial Lemniscus, Pontine Reticular formation, Middle Cerebellar peduncle, and Cortico-spinal Tract.
• Caudal pons: abducens nucleus, facial motor nucleus, vestibular & spinal trigeminal nuclei, dentate, interposed and fastigial cerebellar nuclei and also: cerebellar peduncles, reticular formation, medial and lateral lemniscus, MLF, ALS, spinocerebellar and superior olivary tracts, and also corticospinal, pontine and bulbar tracts.
• Mid-pons features: Principal sensory and Trigeminal motor nuclei, Mesencephalic nucleus and tract, Reticular formation, Superior cerebellar peduncles, Medial and Lateral Lemniscus, MLF, DLF, ALS, Spinocerebellar tracts, Superior olivary nuclei, and Corticospinal, pontine, bulbar tracts.

Brainstem Vascular Supply - General Concepts

• Vertebral artery feeds the Basilar artery
• The AICA, PICA and SCA all contribute to the blood supply.
• Basilar artery branches include: Paramedian branches and Long & short cirucumferential branches.

Vascular Syndromes of the Brainstem

• Wallenberg (lateral medullary) syndrome: common after an infarction of the brainstem, caused by vertebral & PICA artery occlusion
• Features Ipsilateral Vertigo (vestibular nuclei), decreased facial pain & temperature sensation (trigeminal nuclei/tract), decreased taste (solitary nucleus), dysphagia/hoarseness (nucleus ambiguus).
• Other features: Anterolateral system (ALS), ataxia (cerebellar peduncle)
• Ptosis and miosis indicate a disruption of sympathetic fibers.
• Medial Medullary Syndrome (Dejerine's): localizing sign is tongue weakness and contralateral hemiparesis/loss touch and proprioception.
• Brainstem Syndromes - Pons: Medial, Lateral & Superior

Medial (Foville Syndrome)

• Paramedian branches of basilar artery affect CN VI, paramedian pontine reticular formation (pprf*), and the medial longitudinal fasciculus that connect eyemotor nuclei.
• Horizontal gaze palsy and internuclear ophthalmoplegia can result.

Lateral (Gubler Syndrome)

• AICA or superior cerebellar artery
• Affects CN VII, cerebellar peduncle, CN V and spinothalamic tract
• Facial paralysis, ataxia, jaw weakness, facial and contralateral body pain/Temp loss.
• Also results in decreased taste, tinnitus, deafness, solitary and cochlear nuclei are affected

Lecture on the anatomy of the medulla, pons, and cerebellum with a focus on external anatomy, fiber tracts, and blood supply. Key areas include the crus cerebri, olivary eminence, pyramids, and cerebellar lobes and fissures. Vascular syndromes of the brainstem are also covered.