**Voluntary Movement: Instructions from Cerebral Cortex** - Dorsolateral Prefrontal Cortex: directs movement of our limbs (as in reaching) and movements of our fingers. - Actual signal for movement must go through pre-motor cortex, then motor cortex. - From motor cortex, signal travels down spinal cord eventually reaching the alpha motor neuron. - But, the instructions for this movement ultimately comes from our Parietal lobe, which receives sensory input. ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image95.png]] It is important to note in the picture that the **Posterior Parietal Association Cortex** is the location where all these sensory information are integrated, as well as the point of origin of the decision to perform a particular movement. | ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image96.png]] | ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image97.png]] | |---|---| In the **Premotor Cortex** the sequence of muscles to be activated is planned. Then, in the **Primary Motor Cortex** all the muscles needed to perform a particular movement are "read" and the exact contractions and relaxation information are calculated. ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image98.png]] Where is the best place to implant electrodes to read impulses and try to decode the intentions of an individual, which can be used to actuate prosthesis? There are **two school**: - **Primary Motor Cortex** to read the output signals of the brain, but that's already very difficult as the inputs are already decomposed and spread around the area. - **Parietal Cortex** in order to read the high-level commands of the movements that the individual would like to perform. **Control of Movement by Motor Cortex** - **Micro-stimulation Studies**: in MI movements of particular contralateral joints (e.g., distal finger) can be elicited by micro-stimulation; in MII contractions of groups of muscles sequentially to produce overall movements of limbs, often bilaterally. - **Electrical Activity During Movement**: corticospinal neurons active just before initiation of a movement; activity related to amount of force necessary to produce movement; directionally-sensitive corticospinal neurons; higher-order motor cortex involved in calculating trajectories in space (probably in close communication with cerebellum) and in planning larger-scale movements (probably in close communication with the basal ganglia). - **Imaging Studies in Humans**: random movements of digits activates MI (precentral gyrus); planned movements activate MI and supplemental motor cortex; thinking about planned movements activates supplemental motor cortex, but not MI. There has been a lot of work done about thinking of movements, which leads to an activation of this area that are usually involved in planning. It involves mirror neurons, which is a population of neurons shown to be active in humans/animals when they observe someone else performing a particular movement, which are the same neurons that activate when someone plans the same movement. Hypothesis consider them involved in the process of learning by imitation and they are considered to be very important in the process of learning language. Activation of different cortical areas involved in performing a sequence of actions that has been well practiced. Compared to performing a sequence of actions that has not been extensively practiced | ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image99.png]] | ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image100.png]] | |---|---| **Of course, this is really too simple...** Other brain areas are involved in movement: - **Ventromedial Frontal Cortex** - involved in body control, posture and whole body movements. - **Cerebellum** - **Basal Ganglia** - **Brainstem** - **Frontal Eye Fields** are involved in control of saccadic movements, and they can be found in the frontal part of the brain In the end, all movement funnels through the alpha motor neuron (final common path). **Motor Hierarchy and Loops** ![[ETH/ETH - Systems Neuroscience/Images - ETH Systems Neuroscience/image101.png]] **Disorders of the Motor System** - **Amyotrophic Lateral Sclerosis** - motor neurons of the brainstem & spinal cord are destroyed. - **Huntington's Disease** - progressive destruction of the basal ganglia (GABA). - **Muscular Dystrophy** - biochemical abnormality affecting the utilization of Ca++ causing wasting away of muscles. - **Myasthenia Gravis** - autoimmune disorder that destroys Ach receptors (starts with head as in drooping eyelids then progresses to swallowing & respiration). - **Parkinson's Disease** - degeneration of neurons in the striatum due to loss of cells in the substantia nigra that synthesis/release dopamine.