[Music] representatives sections from each region of the spinal cord sacral lumbar thoracic and cervical can be seen here in each the area of white matter between the dorsal horns the dorsal columns is emphasized in color cell bodies of sensory neurons from either proprioceptors or xterra receptors reside in the dorsal root ganglion sensory neurons from the lower extremities enter the spinal cord and descend in the dorsal columns in a bundle known as fasciculus gracilis collateral branches of these sensory axons enter the dorsal horns where they synapse with inter neurons that mediate reflex activity such as the stretch reflex on axons at lumbar levels behave in an identical manner giving off collaterals and ascending in the fasciculus gracilis from the trunk enter thoracic spinal cord segments and ascend in the dorsal columns laterally to exons from the sacral and lumbar segments sensory neurons innervate the upper extremities and neck enter the cord at the cervical levels along with neurons carrying information from the upper trunk these axons form the most lateral section of the dorsal columns the fasciculus cuny Attis fasciculus gracilis and fasciculus cuny ADA's passed through the spinal cord medulla junction keep in mind that within the DC ml tract axons are grouped both by their function and the area of the body from which they originate Austral to the motor decussation is the sensory decussation where the fibers of fasciculus gracilis and fasciculus cuny ADIS synapse with second-order neurons the axons of neurons in nucleus chrysalis and nucleus CUNY Attis then past ventrally in the tegmentum of the medulla and crossed the midline these deca sating axons are known as the internal arcuate fibers and form the medial lemniscus tract the somatic toppy from the spinal cord shifts from a medial lateral pattern to a ventral dorsal pattern with the previously medial sacral axons becoming the most ventral from this point on only two axons will be illustrated in each medial lemniscus one represents the axons of all the second-order neurons in nucleus gracilis and the other the axons from all the second-order neurons in nucleus CUNY Attis as the medial lemniscus ascends its orientation and position change previously dorsal fibers become medial and the pattern of somatic topic changes so that it is opposite to the pattern in the spinal cord as the caudal midbrain is reached the horizontally oriented medial lemniscus changes its orientation yet again the fibers of the medial lemniscus pass through the rostral midbrain and immediately enter the ventral posterior lateral nucleus of the dorsal thalamus there they synapse with third order neurons the axons of the third-order neurons in the MVP L travel through a white matter area of the forebrain called the internal capsule and terminate in the primary somatosensory cortex of the post central gyrus so matatabi for discriminatory tactile information and conscious proprioception is maintained in the primary somatosensory cortex [Music] [Music]