![]() The cell body contains a specialized structure, the axon hillock that integrates signals from multiple synapses and serves as a junction between the cell body and an axon. Once a signal is received by the dendrite, it then travels passively to the cell body. There is great diversity in the types of neurons and glia that are present in different parts of the nervous system. ![]() Although glia have been compared to workers, recent evidence suggests that also usurp some of the signaling functions of neurons. Glia can be compared to the workers at the electric company who make sure wires go to the right places, maintain the wires, and take down wires that are broken. A neuron can be compared to an electrical wire-it transmits a signal from one place to another. Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.” Regardless of the animal, the nervous system is made up of neurons, specialized cells that can receive and transmit chemical or electrical signals, and glia, cells that provide support functions for the neurons by playing an information processing role that is complementary to neurons. Some organisms, like sea sponges, lack a true nervous system. ![]() Nervous systems throughout the animal kingdom vary in structure and complexity, as illustrated by the variety of animals shown in Figure 1.
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