Chapter 2. Functional Regional Anesthesia Anatomy
Which of the following descriptions is correct about the structure of the neuron?
A. A typical neuron consists of a cell body, which is also called the soma, with a small or absent nucleus.
B. Many dendrites branch out from the cell body; their main function is to spread out outgoing messages.
C. A typical neuron consists of several axons, which carry outgoing messages. They can vary in length and are also called nerve fibers.
D. Most neurons are incapable of dividing under normal circumstances and have limited ability to repair themselves after injury.
D is correct. In adults, most neurons are incapable of dividing under normal circumstances and have limited ability to repair themselves after injury.
A is incorrect. The cell body of the typical neuron has a large nucleus.
B is incorrect. The function of dendrites is to receive incoming messages.
C is incorrect. A typical neuron has only one axon.
The structure of a typical peripheral nerve is as follows:
A. The endoneurium is a resistant layer of connective tissue surrounding each axon; its main function is to deliver strength to the peripheral nerve.
B. The nerve fascicle is surrounded by the perineurium. It protects the neural tissue from the surrounding tissue, functioning as a blood–nerve barrier.
C. Fascicular bundles are continuous throughout the peripheral nerve. Because of this, axons starting in one quadrant of the nerve keep the same position distally.
D. The peripheral nerve is composed of three parts: (1) somatosensory or efferent neurons, (2) motor or afferent neurons, and (3) autonomic neurons.
B is correct. The nerve fascicle is surrounded by the perineurium, which imparts mechanical strength to the peripheral nerve. In addition to its mechanical strength, the perineurium functions as a diffusion barrier to the fascicle, isolating the endoneural space around the axon from the surrounding tissue. This barrier helps to preserve the ionic milieu of the axon and functions as a blood–nerve barrier.
A is incorrect. The endoneurium is a thin and delicate layer of loose connective tissue surrounding each fiber.
C is incorrect. The fascicular bundles are not continuous throughout the peripheral nerve. They divide and anastomose with one another as frequently as every few millimeters.
D is incorrect. The peripheral nerve is composed of three parts: (1) somatosensory or afferent neurons, (2) motor or efferent neurons, and (3) autonomic neurons.