key concept 44.4 Neurons and Glia Form Information-Processing Circuits

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Nervous systems can process information because their neurons are organized into neural networks. These networks include three functional categories of neurons that are responsible for input, output, and integration:

  1. Afferent neurons carry sensory information into the nervous system. That information comes from specialized sensory cells that transduce (convert) various kinds of sensory stimuli (e.g., light, heat, pressure) into APs.

  2. Efferent neurons carry commands to physiological and behavioral effectors such as muscles and glands.

  3. Interneurons integrate and store information and communicate between afferent and efferent neurons.

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  • From invertebrates to vertebrates, nervous systems have evolved with increasing complexity from simple nerve nets to clusters of neurons (ganglia) to the development of anterior brain structures.

  • The knee-jerk reflex involves a simple circuit with input from sensory neurons stimulating interneurons and motor neurons in the spinal cord that trigger the quadriceps to contract.