Movement and motor control-lower and upper motor neurons

Lower motor neuronal control of movement

1. Overview of CNS:注：motor cortex:The motor cortex is the posterior part of the frontal lobe, where our executive functions are integrating sensory, and emotion, and mnemonic signals, and devising plans for the production of behavior.
2. Overview of motor neurons:注：1.Ventral horn:contain our lower motor neurons 2.What kinds of neurons innervate skeletal muscle?—neurons in the ventral horn of the spinal cord
3. Motor units:注：Make a fist. Now squeeze harder. What just happened?——When you squeezed harder, you recruited additional larger motor units than the ones that were first activated.
4. Muscle Spindles and Myotatic Reflexes
   1. Muscle Spindles:注：Ia(movement)、II(steady state)
   2. gama fibers:the gamma motor neurons are key to adjusting the sensitivity of the muscle spindle注：Damage either to the ventral horn, the dorsal horn, the ventral root, or the dorsal root, or perhaps the spinal nerve itself all could produce a catastrophic loss of muscle tone.
5. Golgi Tendon Organs
   1. Overview：It’s sensitive to the active contraction of the muscle
   2. Where you might actually want to generate very large forces of muscle contraction. Perhaps forces that put you at some risk. And if your Golgi tendon organs are trying to minimize that risk.
   3. 问：Make a fist. Now squeeze harder. What just happened?—— Activity in the Ib afferents associated with the contracting muscles were increased substantially.
6. Spindles Versus GTOs, and Withdrawal Reflexes
   1. S VS GTO：The muscle spindle is sensitive to length but not tension. The golgi tendon organ is sensitive to tension but not length.注：What change in neural activity is associated most directly with an increase in the gain of myotatic (muscle spindle) reflexes?——Increase in the firing of gamma motor neurons
   2. Flexion-withdrawl reflex:由Adeta传入
7. Central Pattern Generation
   1. Overview：注：So in the experiments illustrated here what was discovered is that with a thorasic trans-section of the spinal cord. it was still possible to suspend this cat on a treadmill and record the rhythmical activities of extensors and flexor muscles that were consistent with locomotion.
   2. 问：Which of the following behaviors do you think is mediated by central pattern generators?——
8. Lower Motor Syndrome注：Which of the following neurological signs and symptoms would make you think that a patient you are examining probably DID NOT suffer a lower motor neuron injury?—— increased myotatic reflexes in the affected limb.

Upper motor neuronal control of movement

1. Primary motor cortex
   1. Overview about Motor systems: 注：1.The lateral pathways are primarily associated with a major projection from the cortex to the spinal cord that we call the lateral corticospinal tract. And this is a collection of axons that, as it runs through the brain stem, and specifically in the medulla, forms a structure that we call the medullary pyramid（pyramidal pathway） 2.Corticospinal obviously refers to projections from the cortex to the spinal cord. And for some authors, it means specifically the projections to the cranial nerve nuclei, that are expressing motor behavior. So those would be our somatic motor nuclei and our branchial motor nuclei.
   2. Motor cortex:注：1.PMC(which is found in the anterior bank of the central sulcus, including much of the crest of the precentral gyrus. and then just in front of that primary motor cortex）2. PC(We find a premotor cortex. And these areas extend into the midline hemispheric surface.) 3.We can identify two nuclei at the thalamus that are primarily responsible for projections to the motor cortex. They are the ventral anterior nucleus and the ventral lateral nucleus. Sometimes, we refer to them together as the VA-VL complex of the thalamus. In addition to input from the thalamus, these divisions of the motor cortex receive important projections from other parts of the cerebral cortex.
   3. PMC:问：What features best differentiates the body map in the precentral gyrus (primary motor cortex) from the post central gyrus (primary somatic sensory cortex)?—The body map in the precentral gyrus is actually not a map of the body and its parts per se, as it is in the postcentral gyrus, but a map of movement intention.
2. The premotor cortex 1. The mosaic: reflecting the encoding of ethologically important motor behaviors注：1. In the banks of the cingulate sulcus, they seem to be involved in the expression of emotional behavior. 2.FEF:this is a part of the premotor cortex that helps to orient our attention, and therefore what we’re looking across the midline to some location in the contralateral visual hemifield.注：绿色部分与social communication有关 2. 问：Consider what you would do should you be driving a motor vehicle and you approach a typical, international 3-color traffic light, and the light changes from green to yellow. I trust that the well-practiced motor response in this circumstance is a gentle application of the brake (not the accelerator!) so that you come to a stop in advance of the anticipated change in color from yellow to red. With this scenario in mind, here’s the question: which division of the premotor cortex was chiefly engaged with planning to execute the appropriate motor response given the color change in the traffic light?——the lateral division of the premotor cortex
3. Motor control centers in the brainstem: 1. Brainstem:注：1. The vestibular nuclei and descent and terminate in the spinal cord: the sensory signal is going to be some kind of an acceleration, or movement of the head) 2. The lateral vestibulospinal pathway（无预判，如跑步中摔倒）:for upper motor neuronal control of posture, and the more proximal muscles of the limbs 3.短跑运动员在准备过程中需要依赖reticular formation(有预判) 2. 问：Imagine that you are a runner at the starting line of a race and you are anticipating the sound of the starter’s signal. You are in the “ready … set” posture awaiting the “go” signal. Your body is ready for action at the sound of that signal. Which descending tract provides the appropriate signals that prepare the body for action in advance of the “go” signal?——reticulospinal tract.
4. Emotional motor system:
   1. 
   2. 问：You are trying your best to smile for a camera, but you are not all that happy about having your picture taken. Which part of the motor cortex is likely governing that forced smile?——the inferior segment of the precentral gyrus, just inferior to where the “S-shaped” bend is typically found in the central sulcus
5. Control of Facial Expressions：
   1. 问：（1）What cranial nerve innervates the muscles of facial expression?—CN VII. （2）Where would you find the facial motor nucleus?—Pons
   2. Motor Control:
6. Upper Motor Neuron Syndrome:
   1. Syndrome:
   2. 问：Consider a patient who is now in the so-called “chronic” phase (after the first 3 months or so have passed) following a stroke involving the right anterior cerebral artery. What signs and symptoms would you expect to discover in this patient?—weakness in the left lower leg, with ankle clonus and a positive Babinski sign, all on the left
7. Corticospinal and Corticobulbar Pathways
   1. Upper motor neuronal pathways:
   2. C & C pathways:注：Red是CS（near the middle of the precentral gyrus）注：Yellow是Cb(It grows out of a neuron in the inferior and lateral part of the precentral gyrus.)
   3. 问：
      1. Where would you find most of the synapses made by axons in one medullary pyramid?——contralateral ventral horn.
      2. Damage to one medullary pyramid would impact which “activity of daily living” most significantly?——writing using the contralateral hand.

Eye movements:

1. Muscles and Nerves
   1. Overview of eye movements:注：All of the alpha motor neurons, except for these trochlear motor neurons, supply ipsilateral muscles, the third cranial nerve supplies ipsilateral extraocular muscles.
      1. Saccades:注：A saccade is a quick, ballistic eye movement that allows us to change fixation from one target to another.
      2. Smooth Pursuit:
      3. Optokinetic nystagmus:注：I’m activating the horizontal canal on the left side of my head, that’s driving excitatory signals that are going to cross the midline. That’s going to activate the motorneurons on the medusa’s nucleus, which will innervate the lacteral rectus and pull that eye towards the left. Meanwhile there are inter-nuclear neurons that will project from one of the dusons nucleus to the contra lateral ocular motor nucleus and then that drive the contraction of the medial rectus muscle and the other eye to produce the synergistic rotation.
      4. Convergence:注：b-a是convergence; b-c是divergence.
      5. Amplitude and direction:注：1. PPRF: This paramedian pontine reticular formation is what we call the horizontal gaze center. 2.In midbrain:it has a gaze center that coordinates vertical eye movements.
      6. Neural Control of Saccades:FEF(Brodmann’s area 8) — Just be aware that the frontal eye field is directing voluntary shifts of attention across the mid-line to the opposite side of the visual field.
      7. 问：When looking up into the night sky (while standing), a bolt of lightning struck somewhere off in the far distance to your right and you quickly turn to look at the lightning. What just happened in your brainstem?—The left superior colliculus directed a shift of your gaze to the distant right side of your visual field, in the direction of the lightning strike.