Question

You are sitting in a chair and decide to get up and cross the room to the kitchen to get something to eat (a snack). Describe the neural processes and networks involved in this process. Make sure you include everything from the cortical areas to the midbrain, cerebellum and spinal cord. And don’t forget alpha motor neurons and motor pools

Answer 1

The premotor cortex ( Betz cells) is responsible for some aspects of motor control, possibly including the preparation for movement, the sensory guidance of movement, the spatial guidance of reaching, or the direct control of some movements with an emphasis on control of proximal and trunk muscles of the body

The primary motor cortex is the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement.

The supplementary motor area (or SMA), has many proposed functions including the internally generated planning of movement, the planning of sequences of movement, and the coordination of the two sides of the body such as in bi-manual coordination.

PYRAMIDAL SYSTEM

The pyramidal motor system start in the motor center of the cerebral cortex. There are upper and lower motor neurons in the corticospinal tract. The motor impulses originate in the giant pyramidal cells or Betz cells of the motor area; I.e. precentral gyrus of cerebral cortex. These are the upper motor neurons (UMN) of the corticospinal tract. The axons of these cells pass in the depth of the cerebral cortex to the corona radiata and then to the internal capsule passing through the posterior branch of internal capsule and continue to descend in the midbrain and the medulla oblongata. In the lower part of Medulla oblongata 90 to 95% of these fibers decussate (pass to the opposite side) and descend in the white matter of the lateral funiculus of the spinal cord on the opposite side. The remaining 5 to 10% pass to the same side. Fibers for the extremities (limbs) pass 100% to the opposite side. The fibers of the corticospinal tract terminate at different levels in the anterior horn of the grey matter of the spinal cord. Here the lower motor neurons (LMN) of the corticospinal cord are located. Peripheral motor nerves carry the motor impulses from the anterior horn to the voluntary muscles.

The role of midbrain in motor functions.

substantia nigra is a large pigmented cluster of neurons that consists of two parts, the pars reticulata and the pars compacta. Cells of the pars compacta contain the dark pigment melanin; these cells synthesize dopamine and project to either the caudate nucleus or the putamen, both of which are structures of the basal ganglia and are involved in mediating movement and motor coordination.

The role of cerebellum in motor movement:

Strong inputs from a single climbing fiber serve as a teaching signal to change the strength of impulses from the corresponding group of parallel fibers.Four principles of cerebellum function have been identified. They include: feedforward processing, divergence and convergence, modularity, and plasticity.

Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction.

While their cell bodies are found in the central nervous system (CNS), α motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles.

An alpha motor neuron and the muscle fibers it innervates is a motor unit. A motor neuron pool contains the cell bodies of all the alpha motor neurons involved in contracting a single muscle.