Fine structural analysis of the neuromuscular junction in the venomous organ of the spider, Agelena limbata (Araneae: Agelenidae)

Fine structure of the neuromuscular junction in the venomous organ of the spider, Agelena limbata, was studied using high magnification electron microscope. The motor nerve endings at neuromuscular contact area composed of neurons and neuroglial cells were located between musculature and extracellular sheath of the venom gland. At the synaptic contact between a motor axon and a muscle fiber in the musculature, spherical synaptic vesicles were prominent in the nerve terminal. The sarcoplasm beneath the neuromuscular synapse has a granular appearance and lacks myofilaments. And the main axon gives off a branch between the muscle fibers. The synaptic regions of this organ are located close to the myofilaments unlike to other chelicerate classes. Moreover the postsynaptic complex of vesicles and membrane invaginations present in other synaptic regions are absent from these regions in this venomous organ.