In addition to the dorsal and ventral horns, two structures especially obvious in the thoracic cord are the dorsal nucleus of Clarke and the lateral extension of the ventral horn. Slide 66a View Virtual Slide shows a section of thoracic spinal cord. Remember that the perikaryon is the metabolic support center for each neuron, so, therefore, motor neurons require much larger perikarya. Neurons in the dorsal horn are essentially interneurons that project to other regions of the CNS (e.g., motor neurons in the spinal cord or sensory input to the brain), so they have much smaller overall volume and therefore much less metabolic demand compared to motor neurons which project to target muscles that may be more than a meter away. Why are perikarya of dorsal horn neurons smaller than those in the ventral horn? The perikarya of large somatic motor neurons slide 065-2 View Image located in the ventral horn of the cord innervate the skeletal muscles of the limbs and trunk, which are embryologically derived from somites (hence, somatic muscles). In these slides, dorsal happens to be "up," but you should be able to tell dorsal and ventral horns based on morphology and the cells present rather than the orientation. You should also identify the dorsal and ventral horns in slide 65-1N stained with Masson trichrome. At low magnification, differentiate inner gray from outer white matter and identify dorsal and ventral horns of the gray matter. Examine the cross section of the lumbar spinal cord in slide 065-2. Review the organization of the spinal cord using your atlas. Slide 066a thoracic spinal cord thoracic spinal cord luxol blue cross View Virtual Slide Slide 065-1 spinal cord lumbar H&E cross View Virtual Slide Slide 065-2 spinal cord lumbar H&E cross View Virtual Slide Slide 065-1N spinal chord Masson cross View Virtual Slide
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