Chapter 1 - Upper and Lower Motor Neurons

Abstract

Publisher Summary This chapter presents an overview of the upper and lower motor neurons. Anterior horn cells and their peripheral processes (axons), which innervate striated muscle, constitute anatomic and physiologic units referred to as the final common motor pathway or the lower motor neuron. The concept of the lower motor neuron is not limited to spinal cord. Motor cranial nerve nuclei, which innervate muscles in the head and neck, also are classified as lower motor neurons. Anterior horn cells, which are the prototype for all motor neurons, lie in cell columns in the anterior gray horn of the spinal cord. Several distinct cell columns are evident in the anterior horn. A medial cell column extending throughout the length of the spinal cord, which is divisible into cell groups, innervates the long and short axial muscles. The lateral cell column innervates the remaining body musculature. In the thoracic region, the lateral cell column is small and innervates the intercostal and anterolateral trunk musculature. All the descending fibers systems that can influence or modify activities of the lower motor neuron constitute the upper motor neuron.