CHAPTER 4 - Changes in Nerves, Motor End Plates and Muscle Spindles

Abstract

This chapter discusses the changes that occur in nerves, motor end plates, and muscle spindles during pathological conditions. The ultrastructure of the terminal axons and the neuromuscular junction has been studied in various experimental animals. In the terminal axons, the synaptic vesicles may form clumps or diminish in numbers and the mitochondria undergo degenerative changes. The axons may eventually disappear and then the Schwann cell cytoplasm may lie in contact with the synaptic clefts of the muscle fiber. The Schwann cell may no longer be found in association with the synaptic cleft. Eventually, the synaptic clefts begin to disrupt and they disappear with time. Changes in the subsynaptic sarcoplasmic structures also take place and extend to the rest of the sarcoplasmic components. In myasthenia gravis—a disorder of neuromuscular transmission—changes might be expected in the motor end plates. Many authors have studied the ultrastructure of the neuromuscular junction in man under pathological conditions. It is difficult to make a correct assessment of what the changes may signify because there is considerable variation in the ultrastructure of the motor end plate in normal muscle.