Human parietal-lobe regions {motor cortex}| {area M1} {Brodmann area 4} {precentral gyrus} {pre-central gyrus} {motor strip} can have two or three million motor neurons, control purpose, initiate voluntary movements, activate habits, cause automatic movements, and specify muscle positions needed at movement completion. Pre-central gyrus contains most corticospinal motor tract neurons.
output
Motor-cortex pyramidal neurons send to extrapyramidal-motor-system alpha and gamma motor neurons, to coordinate and initiate fast and precise movements. Motor neurons excite spinal cord neurons, which excite special muscle fibers in muscle spindles. Primary motor cortex connects to basal ganglia, thalamus, and other cerebral cortex [Bullock et al., 1977].
processing
Muscles move to reach specified muscle positions, as registered by muscle sensors. Motor cortex programs movements by controlling lower-level reflexes. Once started, motor program cannot stop, only change. Motor cortex neurons align by movement direction. Neurons signal particular limb-movement direction. Actual movement is sum of vectors. Primary motor cortex M1 activity shifts with intended-arm-movement coordinates [Amirikian and Georgopoulos, 2003] [Bullock, 2003] [Dean and Cruse, 2003] [Evarts, 1968] [Miall, 2003].
In isotonic movement, motor cortex and red nucleus neurons give intense burst, at frequency corresponding to movement velocity and duration corresponding to movement duration. In isotonic movement, Purkinje cells give bursts or pauses, to inhibit positive feedback to antagonists or allow positive feedback to agonists. In isometric movement, motor cortex and red nucleus neurons give intense burst, at frequency corresponding to force and duration corresponding to force rate. Motor cortex and red nucleus neurons can also have tonic output.
Sense information selects motor-program parameters to initiate program, to define movement endpoint through proprioception, and to guide subsequent adaptive process that mediates motor learning. Sense feedback shapes motor map, and vice versa.
Y cells maintain activity after moving object crosses receptive field, using cortico-thalamic feedback.
Muscle activity initiation always begins unconsciously in cerebrum. Conscious control can affect final motor nerve signals.
damage
Damage to motor cortex does not change learned mammal behavior patterns.
voluntary movement
Mammals have voluntary behavior and move bodies and appendages to specific space points {voluntary movement}.
voluntary movement
The two million motor neurons of human parietal-lobe motor-cortex area M1 initiate voluntary movements and specify muscle positions needed after movements. Muscles move to reach specific muscle positions, as registered by muscle sensors. Motor-cortex pyramidal neurons send to spinal-cord lateral corticospinal tract, which controls voluntary muscles by controlling reflexes.
vectors
Motor-cortex neurons contract specific muscle fibers, which move in relative direction from zero length change up to maximum length change. Fiber movements have magnitude and direction and so are vectors.
vector sums
Individual cortical cells have few connections to nearby neurons, so individual-neuron activation cannot provide enough signal strength to start or maintain movements {motor act}. Motor acts require multiple neuron pathways to achieve precise movement timing. Motor acts generate large precisely coordinated temporal-signal sequences to activate muscles. In contralateral superior colliculus, average neuron vector directs eye movement, or eye and head movement, to target object, using body-centered coordinates.
Neurons for attention to target control motor neurons. Brains control movements using few independent parameters. Motor acts require coordinated temporal motor-neuron activation and inhibition. To move limbs or body parts in specific directions, motor-cortex neurons contribute fiber movement. Total limb or body-part movement is sum of vectors and moves limb or body part from starting position to final position, using body-centered coordinates. Motor cortex accounts for starting position, finds vector sum, and moves to intended final position. Proprioceptive sense information defines starting and ending positions [Amirikian and Georgopoulos, 2003] [Bullock, 2003] [Dean and Cruse, 2003] [Miall, 2003].
input
Input from attention, planning, and drive neurons goes to all motor neurons.
movement-control parameters
Movement control uses several independent parameters. For isotonic movements with constant force, motor-cortex neurons fire for duration corresponding to movement duration, at rate corresponding to movement velocity. For isometric movements with no motion, motor-cortex neurons fire for duration corresponding to force duration, at rate corresponding to force.
Biological Sciences>Zoology>Organ>Nerve>Brain>Cerebrum>Parietal Lobe
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Date Modified: 2022.0224