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17Cell Motility, Neurons and Muscle Contraction

All living cells, from bacteria to plants and animals, utilize various mechanisms to achieve movement. Examples of these mechanisms include the flagellar movement of bacteria, the cytoplasmic streaming of plant cells, ciliary and flagellar movements of animal cells, contraction motion of muscle cells, and intracellular transport of materials. Except for the flagellar movement in bacteria, all of these are carried out using energy produced by the hydrolysis of ATP. The basic underlying mechanism involves harnessing the energy obtained from ATP hydrolysis to alter the three-dimensional structure of proteins; this serves as the driving force behind the cellular movements. This chapter discusses the basic mechanism behind cellular movements.

In animals, stimulation from the external environment is sensed by sensory and nerve cells. The information is then sent to the muscle cells of motor organs, resulting in muscle cell contraction. This chapter also discusses the process of neuronal excitation, how this excitation is then transmitted, and the mechanism by which excitatory information is transmitted to the muscle cells to cause contraction.

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