Spinal Cord Tracts and Brainstem Nuclei Anatomy

Ascending Tracts of the Spinal Cord

Propriospinal: These tracts integrate multiple segments of the spinal cord, surrounding the gray substance.

Fasciculus Gracilis and Cuneatus: Responsible for epicritic sensation. They involve Laminae I and II; pathways are ipsilateral (ascending to the bulb) and contralateral (from the bulb). The sequence involves: 1st node (spinal ganglion), 2nd core (posterior Cordner/column), and 3rd (thalamus).

Anterolateral System (Neospinothalamic): Responsible for protopathic sensation. It involves Laminae III and IV; it crosses contralaterally (within 2 segments). The sequence involves: 1st node, 2nd node at Lamina VII of the posterior horn, and 3rd node (left thalamus, fibers to the reticular formation, midbrain roof/mesencephalon, and hypothalamus).

Paleospinothalamic: Responsible for pain sensation. It involves Lamina IV bilaterally (via interneurons and the channel surrounding the ependymal area). It is multisynaptic, projecting to the reticular formation and hypothalamus.

Posterior Spinocerebellar: Responsible for muscle tone. It involves Laminae I and II; it is ipsilateral. The sequence involves: 1st node, 2nd node at the accessory cuneate nucleus in the medulla (T1 to L2 is the Nucleus of Clarke).

Anterior Spinocerebellar: Located at L5 - S8; it travels contralaterally through the anterior spinocerebellar fasciculus to the superior cerebellar peduncle and into the cerebellum.

Descending Spinal Cord Pathways

Propriospinal: Located on the lateral and medial cords.

Medial Vestibulospinal: Originates in the medial vestibular nucleus (NV) bilaterally; synapses in Laminae VII and VIII. It does not descend below the cervical or upper thoracic levels.

Lateral Vestibulospinal: Originates in the medial vestibular nucleus (NV) ipsilaterally; synapses in Laminae VII to IX.

Pontine Reticulospinal (Medial): Originates in the pons; travels ipsilaterally through the medial cord; synapses in Laminae VII and VIII to facilitate extensor tone.

Bulbar Reticulospinal (Lateral): Originates in the bulb; travels laterally and bilaterally; synapses in Laminae VII and VIII to facilitate flexor tone.

Raphe-Spinal: Originates in the Raphe nuclei. It modulates the entry of pain and secretes serotonin bilaterally at Laminae VII and VIII.

Tectospinal: Originates in the superior colliculus; travels contralaterally to Laminae VII and VIII for repositioning and rotating movements.

Rubrospinal: Originates in the Red Nucleus; travels contralaterally to Laminae V-VII. It provides minor movement and is of little importance in lower mammals.

Hypothalamo-Spinal: Originates in the hypothalamus; travels ipsilaterally through the lateral cord.

Corticospinal Pathway: Originates in the cerebral cortex; directs voluntary movement. 90% of fibers are lateral (crossed) and 10% are direct (anterior).

Brainstem Nuclei: Truncus Encephali

Motor Nuclei of the Basal Plate

MSG (Somatic Efferent): Includes Cranial Nerves III, IV, VI (pons; ipsilateral cerebellopontine angle), and XII (bulb; ipsilateral preolivary furrow).

MVG (General Visceral Efferent): Parasympathetic supply to the head. Includes the Edinger-Westphal nucleus, Superior Salivatory nucleus (pons, accompanying the chorda tympani of CN VII), Lacrimomuconasal nucleus (pons; ipsilateral cerebellopontine sulcus), Inferior Salivatory nucleus (bulb; retro-olivary furrow), and the Dorsal Motor Nucleus of the Vagus (bulb; retro-olivary furrow).

MVE (Special Visceral Efferent): Includes the Masticatory nucleus (pons; trigeminal exit), Facial Motor nucleus (ipsilateral cerebellopontine furrow), Nucleus Ambiguus (bulb; retro-olivary furrow in three forms: IX, X, and adjacent to the vagus), and the Spinal Accessory nucleus (CN XI).

Sensory Nuclei of the Alar Plate

SSG (General Somatic Afferent): Includes the sensory trigeminal nuclei (spinal portion: oral, intermediate, and caudal; principal nucleus; and mesencephalic nucleus).

SVG (General Visceral Afferent): Medial solitary tract (accompanying the vagus and glossopharyngeal nerves).

EVS (Special Visceral Afferent): Lateral solitary tract (fibers of CN IX and X).

SE (Special Somatic Afferent): Vestibular and cochlear nuclei.