Nervous and Sensory Systems
The nervous system of sea anemones consists of environment-monitoring superficial sensory neurons, motorneurons that active effectors such as muscles or cnidocytes, and interneurons that join the sensory receptors to the motorneurons. Interneurons also function to control the intensity and quality of signal conduction by forming networks and ganglia. The sensory neurons are usually bipolar, with a transmitting axon and one end and a receptive dendrite at the other. Interneurons and motorneurons may be bipolar or multipolar, with each cell of the latter usually having several dendrites and one axon.
The nervous system of sea anemones is made up of at least one epidermal and one gastrodermal intraepithelial nerve net that join together at the pharynx, mesentery insertions on the oral and pedal disc, and across the mesoglea1. Microscopic studies have indicated that relatively thick and bipolar nerve fibers innervate fast-contracting muscles like the retractors (see Skeleton and Musculature), while slow muscles such as the circular muscles of the column and diffuse radial muscles of the mesenteries are overlaid by few relatively slender, multipolar nerve cells3,4.
The epidermis contains the highest concentration of sensory cells. However, sensory tissues or organs are absent1. Additionally, most of the microscopial sensory structures in sea anemones have a cilium or several cilia, and sensory cells such as nematocytes often bear a ciliary cone (see Defense Mechanisms)1. Lastly, no photoreceptor structure or pigment has been identified in any sea anemones despite the importance of light in their biology2.
1Ruppert, Fox & Barnes 2004
2Shick 1991
3Robson 1961a
4Robson 1963
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