Fibers
- Ia: 10-20 μm / 80-120 m/s / Proprioceptors: Muscle spindles 1, 5, 6, 7, 9
- Ib: 10-20 μm / Proprioceptors: Golgi tendon organ 5-8, 7 - <9
- II: 6-2 μm / 50 m/s / Cutaneous mechanoreceptors + Proprioceptors: Muscle spindle 2º / 3-4, 7
- III: 1-5 μm / 5-30 m/s / Free nerve endings / 1.5, 6 - <9
- IV: 0.5-1.5 μm / 1 m/s / Free nerve endings, cutaneous and visceral / 2
Ascending Pathways of the Spinal Cord
- Posterior Pathway (PP): Integrates multiple segments of the spinal cord, surrounding the substantia gelatinosa.
- Posterior Column Pathway (CP): Fine touch information; Gracile (always) / Cuneate (T7 and above) - Ipsilateral - Medulla - Contralateral
- Spinothalamic Anterior Lateral Pathway (SAL): Crude touch information; Posterior horn - Contralateral (2 segments); Reticular Formation (RF), Mesencephalon (MSC), Thalamus (T), Hypothalamus (HIP)
- Posterior Spinocerebellar Tract (PET): Pain information, many interneurons, bilaterally (around the ependymal canal + Lamina II, RF, HIP)
- Anterior Spinocerebellar Tract (ECP): Muscle state information; Clarke's nucleus (below the neck) / Cuneate nucleus (cervical) - Ipsilateral
- Spinocerebellar Tract (ECA): Highly processed information; L7 - Bilateral.
Descending Pathways of the Spinal Cord
- Propriospinal: Same as ascending.
- From You:
- Anteromedial Group
- Lateral Vestibulospinal Tract (VEL): Maintains posture; Lateral Vestibular Nucleus -> VII ipsilateral
- Medial Vestibulospinal Tract (VEM): Maintains upright posture; Medial Vestibular Nucleus -> VIII; bilateral
- Pontine Reticulospinal Tract (REM): + Extensor muscles; Pons -> VIII; ipsilateral
- Medullary Reticulospinal Tract (REL): + Flexor muscles; Medulla oblongata -> VII; bilateral
- Tectospinal Tract (TE): Eye/head movement; Mesencephalon -> VII/VIII, contralateral (not lower cervical nerves)
- Lateral Group
- Rubrospinal Tract (RUE): Important in mammals - humans, Thalamus, muscle -> VII; contralateral
- Raphespinal Tract (RAE): Pain input; Tectum -> VII + anterior horn; Bilateral (Neurotransmitter: Serotonin)
- Hypothalamic-Spinal Tract (HIP ESP): Hypothalamus -> Lateral horn; bilateral (synapse with motor neurons)
- Corticospinal Tract (CORTEX ESP): Movement of extremities; Cortex -> Lamina IX; contralateral.
Cranial Nerve Nuclei
Engines of the Basal Plate:
- General Somatic Motor (MSG): Oculomotor (III), Trochlear (IV), Abducens (VI), and Hypoglossal (XII)
- General Visceral Motor (MVG): Edinger-Westphal (ciliary), Superior Salivatory, Lacrimomucosal, Inferior Salivatory, Dorsal Motor Nucleus of the Vagus (X)
- Special Visceral Motor (MVE): Masticatory (part of V), Facial Motor (VII), Ambiguous (combined IX, X, XI)
Midbrain:
- Oculomotor (III): Ipsilateral (eyelid lift [bilateral] / superior rectus [contralateral]); exits via the interpeduncular fossa
- Trochlear (IV): Contralateral; exits via the posterior region
- Ciliary: Ipsilateral
Pons:
- Lacrimomucosal: Ipsilateral; exits via the cerebellopontine angle [as a thickening: facial colliculus]
- Superior Salivatory: Terminates in the pterygopalatine ganglion; accompanies the Facial nerve (VII); exits via the cerebellopontine angle
- Masticatory: Forms part of the Trigeminal nerve (V)
- Facial: Ipsilateral; before surrounding the Abducens nerve (VI); exits via the pontocerebellar angle
Medulla Oblongata:
- Hypoglossal (XII): Ipsilateral; exits via the preolivary sulcus
- Inferior Salivatory: Terminates in the otic ganglion; accompanies the tympanic nerve; exits via the retro-olivary sulcus
- Ambiguous: Exits via the retro-olivary sulcus (fibers [+ head: Glossopharyngeal (IX)] [Intermediate: Vagus (X)] [+ caudal: Spinal Accessory (XI)])
- Dorsal Motor Nucleus of the Vagus: Terminates in intramural ganglia; exits via the retro-olivary sulcus.
