Movement
An effector is a part of the body that can be moved. An alpha motor neuron takes place between the muscles and the nervous system, which is the primary interaction between the two. It start at the spinal cord and exits through the ventral root and finally ends in the muscle fibers. In order for a muscle to move and excitatory signal is activated and the other is accompanied by inhibitory signals.
Sherrington
He damaged the spinal cords in cats and dogs, which disconnected the peripheral motor structures. He wanted to see if the animals were able to move without the higher level commands. The stretch reflexes remained intact. He saw that they could alternate the movements of their hind limbs. For example: one leg flexed and the other was extended, then the first leg extended while the other flexed.
Thomas Brown
He found that movements did not require sensory signals. He sectioned spinal cords and the dorsal root and animals could still make walking movements. He called these the central pattern generators. These are neurons in the spinal cord that can carry out a sequence of actions with no external feedback signals.
Emilio Bizzi
He experimented with deafferented monkeys. They were trained in a pointing experiment, but a torque motor counteracted their movements, but the monkeys were unaware this. When the torque motor was on the limb stayed in the same place and could not move. However, if it was off the limb would quickly move to the correct location.
Apostolos Georgopoulos
He tested monkeys on the center-out task. First, the monkey had to love the lever to the center. Then a light illuminated one of the eight target positions. Then the monkey had to move the lever to the illuminated position in order to get the reward. While the monkeys were carrying out this task Georgopoulos was recording cell activity. He found that activity in the cell in the motor cortex is strongly correlated to movement rather than location and it was even the activity was even stronger when the animal moved the lever towards itself.
Brain Machine Interface (BMI)
Monkeys have learned to move computer cursors and even prosthetic limbs just by thinking. This revolutionary idea can be a great help to those with amputated limbs. However, it is hard to move from animals to humans.
Rizzolatti
He studied monkeys and studied whether or not neurons activated while observing someone carry out an action. The neurons in monkeys responded similarly when the monkey cracked the peanut itself, watched someone crack it, watch someone crack it but could not hear it and could hear the peanut being cracked but could not see it. He called these mirror neurons.
Planning and Execution of Movement
Individuals were taught a complex sequence of finger movements. When TMS is used to disrupt the motor cortex the individual knew what to do but something stopped them. When the supplementary motor area was disrupted they lost track and could not remember the goal. However, activation depends on how much it is based on memory. How well you know a certain action changes in the brain. A novel action start in the PMC but when you start to know something better it moves to the SMA.
Apraxia
Apraxia is a loss of motor skills. These individuals are not able to turn their thoughts into actions. One example is of a patient with bilateral lesions of the parietal lobes. She was a fish filleter and one days she started to cut the fish when she all of a sudden stopped. She remembered how she needed to finish the task but she just could not execute it.
Ideomotor apraxia is when the individual has an idea of the action but they cannot execute it properly. Ideation apraxia is more severe. It is when the patient's knowledge of an action is disrupted.
Basal Ganglia
The basal ganglia consists of five nuclei: caudate nucleus, putamen, globus pallidus, subthalamic nucleus and the substantia nigra. In Parkinson's disease the pathway from the substantia nigra to the striatum is destroyed. The substantia nigra produces most of the body's dopamine. This produces more excitation from the thalamus to the cortex, when then causes uncontrollable movements. There are two kinds of dopamine receptors, when one has Parkinson's the dopamine cannot cross the blood brain barrier. The medication one can take is called L-dopa. It is one step back from dopamine so it is able to cross the blood brain barrier.
Those with Parkinson's have a motor impairment as well as a cognitive impairment. Steven Keele tested patients in a shifting test. They had to learn two 3 movement sequence. Then they were asked to produce a six element sequence from the two movement sequences that they learned initially. Parkinson's patients had a hard time when they had to transition between sequences. This shows that they have a motor control impairment. Then they were tested on their cognition. They had to discriminate between either shapes or colors and they reaction time was recorded. Again, they were slow when they had to shift.
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