The nervous system of the nematode worm Ascai contains about 250 nerve cells; of these, the motoneurons consist of five segmental sets, each containing 11 cells. Morphologically, the motoneurons can be divided into seven different types. Their geometry is simple: some are unbranched, others have one branch point, and the most complex have two. There is no neuropil in the nerve cords; synapses are made by axo-axonal contact or onto short spines. These features enable us to study the anatomy and physiology of the system with a degree of completeness that would be difficult in other systems. The physiological activity of five of the motoneurons has been investigated, three being excitatory and two inhibitory. The excitatory motoneurons receive input from intersegmental interneurons. The inhibitory motoneurons do not receive input from the interneurons; instead they receive their input from the excitatory motoneurons in a circuit that can mediate reciprocal inhibition between the dorsal and the ventral musculature.One of the outstanding problems in neurobiology is to understand the capabilities of assemblies of neurons in terms of the properties of the cells of which they are composed. In vertebrate nervous systems this problem has been approached in situations in which small numbers of cell types are arranged in a repeating pattern (e.g., cerebellum, retina); by studying the smallest fundamental repeating unit in these systems, the logical principles by which information is transformed might be inferred.An alternative approach is to select an invertebrate system in which there is only a small number of neurons. A number of interesting results have already emerged from the study of small assemblies of neurons in invertebrates (1-7). However, these assemblies still contain a large number of interacting components, and the geometry of the neurons in many cases is as complex as that found in vertebrates.In this paper we will describe the motor nervous system of the large parasitic nematode Ascaris lumicdes. This system has a small number of neurons with extremely simple geometry. This allows us to study the physiology and anatomy of the system with a degree of completeness that would be difficult in other systems.The salient advantages of the Ascaris nervous system are threefold.(i) Cell number. The entire nervous system contains only about 250 neurons; the motor nervous system that we will describe here is divided into five segments, each containing 11 motoneurons, and there are six nonsegmental interneurons traversing the segments. By contrast, in truly segmented animals such as the crayfish and the leech, each segmental ganglion contains several hundred cells and there are hundreds or thousands of neurons impinging upon each ganglion from other centers.

We present a patient with old traumatic right brachial plexus injury, who developed progressive neurological deterioration 4 years after the initial injury. On magnetic resonance imaging (MRI), herniation of the upper dorsal cord was noted into a post-traumatic pseudomeningocele. Though the herniation of cord into a post-traumatic pseudomeningocele is very rare, it should be suspected in cases of delayed progressive myelopathy. A three dimensional (3-D) T2-weighted sequence such as Sampling Perfection with Application optimized Contrasts using different flip angle Evolution (SPACE) or constructive interference in steady state (CISS) provides optimal visualization of the herniated cord and helps in surgical planning.

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Giant cell tumour of the bone (GCT) is a rare locally aggressive primary bone tumour with an incidence of 3% to 5% of all primary bone tumours. The most common location for this tumour is the long bone metaepiphysis especially of the distal femur, proximal tibia, distal radius, and the proximal humerus. Involvement of distal ulna is rare accounting for 0.45% to 3.2%. Considering local aggressive nature and high recurrence, wide resection is the treatment recommended. Instability of ulnar stump and ulnar translation of the carpals are known complications following resection of distal ulna. To overcome these problems, we attempted a newer technique of distal ulna reconstruction using proximal fibula and TFCC reconstruction using palmaris longus tendon following wide resection of giant cell tumour of distal ulna in a 44-year-old male. This technique of distal radioulnar joint reconstruction has excellent functional results with no evidence of recurrence after one-year followup.

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