GlrFIG 4: Muscle arms of the head muscles.
A. Diagram showing two stylized head muscle arms (dark green) approaching nerve ring. Muscle arms from the 32 muscles in the head and neck project onto the inside surface of the nerve ring in a highly ordered fashion. Their terminal branches lie between the processes of GLR cells (golden yellow) on the inside and the motor neurons of the nerve ring (dark red and purple) on the outside. Arms from the somatic head muscles run posteriorly until they reach the posterior nerve ring region. The arms from each muscle row then make an anterior arc of about 45° and extend inward to reach between the outside surface of the GLRs and the inner surface of the neural plate. This inward turn involves close apposition to the GLR cell bodies (see GlrFIG 3). In the neck, somatic muscles extend arms both to the nerve ring and to either the ventral or dorsal nerve cords where they receive additional synapses (not shown). (Light green) pharynx; (orange) basal lamina.
B. Graphic rendition of the structure of the nerve ring and interior muscle plate. The muscle arms (dark green) innervated by RIML/R (purple) make four small spurs that may pierce through the basal lamina to access these neurons. Other motor neuron processes (only RME neurons are indicated) are located adjacent to the inner surface of the nerve ring, where they make NMJs with the muscle arms. Only a few cells on the right side are labeled. (Based on White et al., 1986.)
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