Loss of cells from the motor system occurs during the normal aging process, leading to reduction in the complement of motor neurons and muscle fibers. The latter age-related decrease in muscle mass has been termed “sarcopenia” and is often combined with the detrimental effects of a sedentary lifestyle in older adults, leading to a significant reduction in reserve capacity of the neuromuscular system, which is the primary subject of this review. Clear evidence of this aging effect is seen when voluntary or stimulated muscle strength is compared across the adult lifespan, with a steady decline of ∼1–2% per year occurring after the sixth decade. Interestingly, when compared with isometric contractions, the effect of aging is more pronounced for concentric movements and less for eccentric movements (i.e., muscle shortening versus lengthening). This phenomenon appears to be linked to the stiffer muscle structures and prolonged myosin crossbridge cycles of aged muscles. It is encouraging that the capability of physiological adaptations in the motor pathways remains into very old age — when an appropriate exercise stimulus is given — and long-term prevention strategies are advocated to avoid excessive physical impairments and activity restrictions in this age group. © 2002 John Wiley & Sons, Inc. Muscle Nerve 25: 17–25, 2002

Aging of the human neuromuscular system.

THE author of this book ranks as the foremost American worker on insect morphology. His contributions on the subject are notable for their clarity and originality of thought, and the appearance of a volume, embodying his ideas in comprehensive form, is sure of a hearty welcome. In its preparation, Mr. Snodgrass has incorporated the results of much first-hand study with those of many recent investigators in the same field. He has produced an outstanding book wherein knowledge of facts is combined with that of function and, at the same time, theoretical conceptions of the origins and relationships of organs and parts are not overlooked. Principles of Insect Morphology
 By R. E. Snodgrass. (McGraw-Hill Publications in the Zoological Sciences.) Pp. ix + 667. (New York and London: McGraw-Hill Book Co., Inc., 1935.) 36s. net.

Principles of Insect Morphology

We measured saccadic eye movements in 168 normal human subjects, ranging in age from 5 to 79 years, to determine age-related changes in saccadic task performance. Subjects were instructed to look either toward (pro-saccade task) or away from (anti-saccade task) an eccentric target under different conditions of fixation. We quantified the percentage of direction errors, the time to onset of the eye movement (saccadic reaction time: SRT), and the metrics and dynamics of the movement itself (amplitude, peak velocity, duration) for subjects in different age groups. Young children (5–8 years of age) had slow SRTs, great intra-subject variance in SRT, and the most direction errors in the anti-saccade task. Young adults (20–30 years of age) typically had the fastest SRTs and lowest intra-subject variance in SRT. Elderly subjects (60–79 years of age) had slower SRTs and longer duration saccades than other subject groups. These results demonstrate very strong age-related effects in subject performance, which may reflect different stages of normal development and degeneration in the nervous system. We attribute the dramatic improvement in performance in the anti-saccade task that occurs between the ages of 5–15 years to delayed maturation of the frontal lobes.

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Age-related performance of human subjects on saccadic eye movement tasks.

THINKING Young children understand the relation between objects and events in a functional manner, such that the first object is seen to go with or to operate on the second object. Complementarity criteria are an integral component of their thinking. Older children and young adults, by contrast, tend to use similarity criteria. In old age, however, the use of complementarity criteria has been found to increase once again (Reese & Rodeheaver, 1985). The reversal to complementarity in old age is thought to be caused by environmental factors rather than being attributable to changes in competence. Young children as well as the elderly are rarely required to state their thoughts in a specifically prescribed way, and complementary categorization therefore seems more natural, since such categorization groups occur naturally in time and space. Older adults do not neces-

The encyclopedia of aging

The effects of aging on eye movements are well studied in the laboratory. Increased saccade latencies or decreased smooth-pursuit gain are well established findings. The question remains whether these findings are influenced by the rather untypical environment of a laboratory; that is, whether or not they transfer to the real world. We measured 34 healthy participants between the age of 25 and 85 during two everyday tasks in the real world: (I) walking down a hallway with free gaze, (II) visual tracking of an earth-fixed object while walking straight-ahead. Eye movements were recorded with a mobile light-weight eye tracker, the EyeSeeCam (ESC). We find that age significantly influences saccade parameters. With increasing age, saccade frequency, amplitude, peak velocity, and mean velocity are reduced and the velocity/amplitude distribution as well as the velocity profile become less skewed. In contrast to laboratory results on smooth pursuit, we did not find a significant effect of age on tracking eye-movements in the real world. Taken together, age-related eye-movement changes as measured in the laboratory only partly resemble those in the real world. It is well-conceivable that in the real world additional sensory cues, such as head-movement or vestibular signals, may partially compensate for age-related effects, which, according to this view, would be specific to early motion processing. In any case, our results highlight the importance of validity for natural situations when studying the impact of aging on real-life performance.

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Effects of aging on eye movements in the real world

In the 1-day old larva, the brain and other ganglia, seen in the full grown larva, are already developed. Besides the brain and the suboesophageal ganglion, there are 3 thoracic and 8 abdominal ganglia. The pointed ends of the brain rotate, and by the end of 1st instar these become anteriorly directed. As the larva passes from instar to instar, all the ganglia gradually increase in size. In the pre-pupal stage, a gradual shortening of the connectives between the metathoracic and the 1st abdominal ganglion and of the crura cerebri starts. A black rod-like pigmented mass appears in the anterolaterally pointed regions of the brain from which arise the optic nerves. In the late pupa, the 1st and 2nd abdominal and the meso- and metathoracic ganglia fuse to form the thoracoabdominal ganglionic mass. The crura cerebri virtually disappear and the suboesophageal ganglion comes in direct contact with the brain. The ganglionic swelling of the 3rd abdominal ganglion disappears. The entire nerve cord becomes covered with a layer of connective tissue which is thicker dorsally than ventrally. In the adult, besides the brain, there are 2 thoracic and 4 abdominal ganglia only.

Anatomical changes in the nervous system of the castor silk moth, Philosamia ricini hutt. (Lepidoptera: Saturniidae) during metamorphosis

The morphology of the larval and adult brain of Philosamia ricini , and changes during pupal period have been described. In the larva, each mushroom body has 2 calyces, a stalk with a feebly developed outer and a well-developed inner root, the latter extending posterolaterally to the central body, and joined with each other. The elongated central body has fibrous connectoins with the deutocerebrum. Optic commissures join the 3 laterally situated optic ganglia. The corpora ventralia are joined with each other by a paired ventral commissure (single in adult). Antennal nerves arise from the posteroventrally situated deutocerebral lobes, and the antennal commissure joins the 2 opposite lobes. The small, paired, glomerular tritocerebrum is placed posteroventrally to the deutocerebrum, and fibres from these travel to the crura cerebri. During metamorphosis, apart from general increase in size, changes are observed in the mushroom body, central complex, optic ganglia and deutocerebrum. In addition, certain structures such as the antennal cortex, ellipsoid body and chiasmata between optic ganglia are also observed. In the adult, behind the well-developed central body, is an ellipsoid body. The swollen pons cerebralis joins the 2 protocerebral lobes. The medulla interna is divided into 2 smaller lobes, and the deutocerebral lobes are differentiated into cortical and medullary zones.

Structure and metamorphic changes in the brain of castor silk moth, philosamia ricini hutt. (Lepidoptera: Saturniidae)

The present paper deals with the development of secondary malpighian tubules of Chrotogonus trachypterus in its nymphal stages. There are 12 groups of malpighian tubules in the adult C. trachypterus, each group opening into the alimentary canal at the junction of the midgut and hindgut through an ampulla derived from the hindgut. But, while in the male each group has only 5 tubules, in the female each group has 11 tubules, so that the male has 60 tubules and the female has 132 tubules. The early 1st nymphal instar has only 18 well-developed malpighian tubules in both sexes. Sexual dimorphism starts in the 2nd nymphal instar. In the males, the secondary malpighian tubules are added in the sequence of 6, 12 and 24 tubules in the 1st, 2nd and 3rd numphal instars respectively; in the 4th and 5th instars there is no further addition. In the females, they are added in the sequence of 6, 24, 36, 24 and 24 in the 1st, 2nd, 3rd, 4th and 5th instars respectively. The development of a secondary malpighian tubule comprises successively the phases of initial development, mitosis and cell enlargement. The increase in the number of secondary malpighian tubules is apparently related to the increased excretory requirement brought about by the growth of the body.

U.S. Srivastava

Papers

Anatomical changes in the nervous system of the castor silk moth, Philosamia ricini hutt. (Lepidoptera: Saturniidae) during metamorphosis

Structure and metamorphic changes in the brain of castor silk moth, philosamia ricini hutt. (Lepidoptera: Saturniidae)

Development of secondary malpighian tubules in Chrotogonus trachypterus blanch (Orthoptera: Acrididae)