Chapter Fourteen Homework

1. You are a neurologist presented with a patient who has the following symptom: an inability to independently wiggle the toes on the left foot, but with all other movements (walking, independent finger movement) apparently intact. You suspect a lesion in the spinal cord. Where?

For this patient I would suspect a lesion in the lateral pathways of the spinal cord. A lesion in the corticospinal and rubrospinal tract would render the patients ability make fractionated movements such as being able to independently wiggle their toes. However, the patient would still be able to walk independently because their ventromedial pathway would still be intact which is responsible for posture.

2. Pet scans can be used to measure blood flow in the cerebral cortex. What parts of the cortex show increased blood flow when a subject is asked to think about moving her right finger?

The areas of the cerebral cortex that show increased blood flow when a subject is asked to think about moving her right finger are the somatosensory, the posterior parietal areas, and parts of the prefrontal cortex, specifically areas 6, 8 and 4. These areas play a role in generating intention to move and converting that intention into an execution. However, when asked to only mentally move her right finger area 6 of the prefrontal cortex is active while area 4 is inactive.

3. Why is L-dopa used to treat Parkinsons disease? How does it act to alleviate the symptoms?

L-dopa is used to treat Parkinsons disease because it is a precursor to dopamine. Parkinsons is the depletion of dopamine, which closes the funnel that feeds activity to the SMA via the basal ganglia and VLo, it also inhibits the neurons in the striatum that sends inhibitory output via the indirect pathway to the GPe. The goal of Parkinsons is to increase or enhance the levels of dopamine delivered to the caudate nucleus and putamen. Therefore, L-dopa is often prescribed to treat Parkinsons, it crosses the blood-brain barrier and boosts the production of DA in the remaining alive cells in the substantia nigra therefore alleviating some of the symptoms.

4. Individual Betz cells fire during a fairly broad range of movement directions. How might they work together to command a precise movement?

The Betz cells project to pools of lower motor neurons and excite them monosynaptically. However, the same corticospinal axons can branch and excite local inhibitory interneurons. Therefore, by controlling selected groups of motor neurons and interneurons, a single corticospinal neuron can generate coordinated effects on antagonist muscles.