Reticular Formation, Cerebellum, and Thalamus: Anatomy and Function

Posted on Jun 4, 2025 in Biology

Reticular Formation

The reticular formation (FR) is divided into:

  • Lateral FR: characterized by small neurons and short axons.
  • Medial FR: characterized by large neurons and long axons.
  • Middle FR: includes the raphe nuclei, which are serotonergic.

Bulb (Medulla Oblongata)

Key nuclei within the bulb include:

  • Parvocellular reticular nucleus
  • Nucleus gigantocellularis
  • Nucleus magnocellularis
  • Raphe nuclei: raphe pallidus, raphe obscurus, raphe magnus

Pons (Bridge)

Key areas within the pons include:

  • Lateral FR
  • Nucleus reticularis pontis oralis
  • Nucleus reticularis pontis caudalis
  • Raphe nuclei: raphe magnus (between bulb and pons) and raphe pontis

Mesencephalon (Midbrain)

Key areas within the midbrain include:

  • Midbrain reticular nuclei
  • Nucleus raphe dorsalis
  • Nucleus centralis superior

Specific Neurotransmitters

  • Serotonin: Raphe nuclei
  • Norepinephrine: Locus coeruleus
  • Dopamine: Substantia nigra pars compacta, ventral tegmental area
  • Acetylcholine: Base of the medulla

Cerebellum

Lobes

The cerebellum is divided into three lobes:

  • Anterior lobe
  • Posterior lobe
  • Flocculonodular lobe

Deep Cerebellar Nuclei

From medial to lateral, the deep cerebellar nuclei are:

  • Fastigial nucleus
  • Globose nucleus
  • Emboliform nucleus
  • Dentate nucleus

Cortical Layers

  • Molecular Layer: Sparse cell bodies, many fibers (stellate cells, basket cells). Output from Purkinje cells.
  • Granular Layer: Densely packed cell bodies (granule cells, Golgi cells)

Fiber Types

  • Nonspecific Fibers: Originating from locus coeruleus, raphe nuclei, hypothalamus (HPT)
  • Climbing Fibers: Originating from the inferior olivary nucleus, projecting directly to Purkinje cells.
  • Mossy Fibers: Originating from cerebellar nuclei, mesencephalic nuclei (ME), medulla, and pons, projecting to granule cells.

[Climbing and mossy fibers are excitatory.]

Information Passing Through Cerebellar Peduncles

  • Inferior Cerebellar Peduncle (Restiform Body): Afferent fibers from the bulb and spinal cord. Juxtarestiform body: reciprocal connections with vestibular nuclei.
  • Middle Cerebellar Peduncle (Brachium Pontis): Afferent fibers from pontine nuclei.
  • Superior Cerebellar Peduncle (Brachium Conjunctivum): Primarily efferent fibers from the deep cerebellar nuclei.

Vestibulocerebellum Module

[+ movement, balance, eye/head coordination]

  • Efferent: Fastigial nucleus -> vestibular organs -> Regulates eye/head movements.
  • Afferent: Vestibular ganglion + vestibular nuclei (ipsilateral).

Vermal Spinocerebellar Module

[Controls axial musculature]

  • Efferent: Fastigial nucleus -> thalamus -> motor cortex.

Spinocerebellar Module

[Information from EE II + SS]

  • Efferent: Globose/emboliform nuclei -> thalamus -> cortex -> (medulla [corticospinal tract], red nucleus [rubrospinal tract], reticular formation [reticulospinal tract]).

Cerebrocerebellum Module

[Planning and regulation of precise and skilled movements]

  • Afferent: Basilar pontine nuclei and inferior olivary nucleus.
  • Efferent: Dentate nucleus.

Thalamus

Sensory Nuclei

  • Taste: TE -> VPM (medial)
  • Epicritic sensation (mouth and head): Trigeminal nerve -> VPM (medial)
  • Epicritic sensation (body): Dorsal column nuclei -> VPL
  • Protopathic sensation (mouth and head): Trigeminal nerve -> PO and intralaminar VPM
  • Protopathic sensation (body): PO, VPL, and intralaminar nuclei
  • Visual Information: Lateral geniculate nucleus (LGN) -> A1
  • Auditory Information: Cochlea -> inferior colliculus -> medial geniculate nucleus (MGN) -> A1

Motor Nuclei

  • Cerebellar Input: Deep cerebellar nuclei -> VL (primarily), VA (some)
  • Reticular Input from Substantia Nigra: VA (serotonergic), VL (some)
  • Mamillary Body Input: -> Anterior nucleus [important for memory]

Associated Nuclei

  • DM (Dorsomedial Nucleus): Prefrontal cortex
  • LD (Lateral Dorsal Nucleus): Medial areas of the hemisphere
  • LP (Lateral Posterior Nucleus): Associative regions of parietal and parieto-occipital lobes
  • Pulvinar: Temporal and occipital association regions

Intralaminar Nuclei

Thalamostriatal connections

Midline Nuclei

Connections with hypothalamus, hippocampus, and amygdala

Thalamocortical Connections

Ipsilateral; Thalamus -> Cortex Layer IV -> Thalamus

Corticothalamic Connections

Ipsilateral; Cortex Layer V -> Thalamus -> Cortex Layer VI