1. Ventricular enlargement in this patient is a consequence of loss of neural tissue. Because the volume of the skull is fixed, as brain tissues decrease in volume due to a neurodegenerative process, there is a corresponding increase in ventricular volume.
2. The cerebral cortex and hippocampal formation are severely affected. By contrast, brain stem structures are not.
3. The hippocampal formation is important for consolidating memories. The patient shows profound degeneration of the hippocampal formation. The patient is able to repeat the words initially, pointing to preserved linguistic capabilities at this stage of his condition, but unable to remember the words.
4. Acetylcholine is an excitatory neurotransmitter, and with its loss due to neuronal degeneration, there is a reduction in the activity of cortical neurons. This impairs cortical neuron function. Key neurons that use acetylcholine as their neurotransmitter are located in a brain region called the basal forebrain.
5. High densities of amyloid plaques and neurofibrillary tangles are essentially pathognomonic for Alzheimer disease.
1. Both the dorsal column-medial lemniscal pathway and the corticospinal tract decussate within the ventral portion of the medulla. Without these decussations, the two sides of the ventral medulla become somewhat separated, and a sulcus forms. CSF is present where the decussating axons should be. Axons important for coordinating eye movements normally decussate in the dorsal pons. Without this decussation, the two sides of the dorsal pons also become somewhat separate, as revealed by the presence of CSF and the formation of a shallow sulcus.
2. No, the corpus callosum is an example of a midline structure with intact decussating axons.
3. No DTI reveals bundles of many thousands of axons. The resolution of MRI is insufficient to reveal individual neurons and their components. The image reflects the properties of hydrogen ions in water associated with neural pathways.
4. The impairments are more likely due to a genetic disorder. This is because there are localized structural changes along the midline of the medulla and pons and functional impairments are selective for the horizontal eye movement system. Typically, traumatic injury will affect many functions within the damaged brain region. By contrast, a developmental impairment produced by a genetic defect can be remarkably selective if the affected gene has a limited set of brain functions.
1. The proximal portion of the middle cerebral artery became occluded. This affected both deep branches to subcortical white matter and superficial branches supplying the cerebral cortex.
2. Since all descending motor control axons converge within the internal capsule, damage to this structure alone can produce the major limb and facial motor signs seen in this patient.
3. Whereas the lower facial muscles receive contralateral control by the cortex, ...