Pain/temperature (limb):

·       Spinothalamic tract

·       Crosses within 2 segments, projects to thalamus and post-central gyrus

Strength (limb):

·       Corticospinal tract (et al.)

·       Originates in pre-central gyrus, crosses in medulla

Position/vibration (limb):

·       Dorsal column/medial lemniscus pathway

·       Crosses in medulla, projects to thalamus and post-central gyrus

Pain/temperature (face):

·       Trigeminothalamic tract

·       Enters at pons, descends to C1/2, crosses, projects to thalamus and post-central gyrus

Strength (face):

·       Corticobulbar tract

·       Crosses in high pons; additional uncrossed pathway supplying forehead muscles

Vision:

·       Optic nerve/tract/radiation

·       Medial retinal representation (lateral visual field) crosses at chiasm; lateral retinal representation uncrossed (THUS: right brain ↔ left visual field)

Pupillary constriction to light:

·       Optic nerve/tract → bilateral oculomotor (3rd) nerve

(enters at the midbrain)

Pupillary dilation:

·       Sympathetic pathway

·       Hypothalamus → T1 spinal cord → sympathetic chain → ascends with carotid → trigeminal (5th) nerve

(does not cross midline, descends to C8/T1 before exiting)

Eye movements:

·       Gaze centers/oculomotor pathways

·       Cortical gaze centers project to brainstem gaze centers, which project to nuclei of cranial nerves 3 (oculomotor), 4 (trochlear), and 6 (abducens)

(enters at the pons)

Hearing:

·       Auditory pathway

·       Enters at pons, immediately becomes bilateral

Reflexes

·       Local arc: IA afferent → dorsal horn → ventral horn → motor neuron → muscle

·       Inhibitory input from contralateral cortex, crosses in the medulla

(LMN lesion = diminshed relfex; UMN lesion = exaggerated reflex)