Chromatophilic substance (Nissi bodies) Dendrites Cell Body Neurofibrils Nucleus Axon hillock Direction of Nodes of Ranvier Impulse Nucleus Axon Myelin (cut) FIGURE 25.1 Label this diagram of a multipolar motor neuron.
The Correct Answer and Explanation is:
Based on the provided diagram of a multipolar motor neuron, here are the correct labels for the numbered parts:
- Dendrite
- Nucleus
- Schwann cell
- Cell Body (Soma)
Explanation of the Multipolar Motor Neuron Anatomy
A multipolar motor neuron is a highly specialized cell that serves as a fundamental component of the nervous system, responsible for transmitting efferent signals from the central nervous system to effector organs like muscles and glands. Its intricate structure is precisely adapted for this function of high-speed communication.
The main biosynthetic and metabolic center of the neuron is the Cell Body (6), also known as the soma. This region houses the essential organelles required to maintain the neuron’s life and function. Prominently located within the cell body is the Nucleus (2), a large, spherical organelle containing the cell’s genetic material. The nucleus directs all cellular activities, including the synthesis of proteins and neurotransmitters crucial for neural signaling. Also visible within the cytoplasm of the cell body are the Chromatophilic substance (Nissl bodies), which are concentrations of rough endoplasmic reticulum and free ribosomes, indicating a high rate of protein synthesis.
Extending from the cell body are numerous branching processes called Dendrites (1). These structures serve as the primary receptive regions of the neuron. Their extensive branching pattern, or arborization, dramatically increases the surface area available for receiving signals from other neurons. Dendrites convey incoming electrical signals, known as graded potentials, toward the cell body for processing.
The long projection extending from the axon hillock is the axon, which transmits nerve impulses away from the cell body. In many motor neurons, the axon is myelinated. This myelination is accomplished by Schwann cells (4) in the peripheral nervous system. Each Schwann cell wraps its plasma membrane tightly around a segment of the axon, forming the myelin sheath. This lipid-rich sheath acts as an electrical insulator, preventing the leakage of electrical charge and forcing the action potential to “jump” between the unmyelinated gaps, or Nodes of Ranvier. This process, called saltatory conduction, significantly increases the velocity of nerve impulse transmission, ensuring rapid and efficient communication with distant targets.
