Point 4 Intro Pathway Deficit Note Overview Problems Contents Anatomy

You may remember that there is a somatotopic representation of the body in the dorsal columns (fasciculus gracilis and fasciculus cuneatus). Caudal (sacral and lumbar) body parts are represented medially, while the rostral segments (upper thoracic and cervical) are represented laterally. Nucleus gracilis receives its input from about T7 and downward, while nucleus cuneatus receives its input from spinal levels above this. There is also a somatotopic organization within the medial lemniscus. For instance, in the medullary segment of the medial lemniscus the body is represented in an upright position, so that the legs are ventral and the arms dorsal. Within the pontine portion of the medial lemniscus there is a rotation, so that the arms are represented medially and the legs laterally. Finally, in the midbrain portion of the medial lemniscus the arms are represented ventrally while the legs are represented dorsally.