Back to the debate: sternalis muscle / Volver al debate: músculo esternal

The sternalis muscle (SM) is an anatomical variant found in the anterior thoracic wall. While the attachment sites of SM are generally agreed upon, the innervation and function of this muscle are not well established. Cadaveric and surgical explorations to date report that SM is innervated by either the pectoral nerves or the anterior branches of the intercostal nerves, or a combination of both. Knowledge of SM is relevant to health care providers specialising in imaging and/or surgery of the anterior thoracic wall. This paper aims to raise awareness in the medical community of the clinical relevance of SM through two case reports and a brief literature review.

El músculo esternal (ME) es una variante anatómica en la pared torácica anterior. Mientras que los sitios de fijación del ME estan acordados, la inervación y la función de este músculo no están bien establecida. Exploraciones cadavéricas y quirúrgicas han informado que el ME está inervado por los nervios pectorales o ramos anteriores de los nervios intercostales, o una combinación de ambos. El conocimiento del SE es relevante para los proveedores de atención de salud especializada de imágenes y/o cirugía de la pared torácica anterior. Este documento tiene como objetivo crear conciencia en la comunidad médica de la relevancia clínica de ME a través de dos reportes de caso y una breve revisión bibliográfica.

[Age-related changes in sensory neurons containing calcitonin gene-related peptide under conditions of afferentation deficit in rats].

Morphological features of calcitonin gene-related peptide (CGRP)-immunoreactive neurons were studied in the sensory ganglia of the vagus and thoracic nerves in 3-, 10-, 20-, 30-, 60-, 90-, and 120-day-old rats under conditions of chemically-induced deafferentation. We found that, in rats, CGRP-containing neurons appeared in both ganglia immediately after they were born and their number decreased with aging. Most of CGRP-immunoreactive neurons were small in size, i.e., up to 600 microm2. Administration of capsaicin modified age-related changes in the number of CGRP-immunopositive neurons. In the thoracic nerve ganglion, the mean square of these cells and their number substantially decreased, whereas, in the vagus nerve ganglion, positive cells were not observed.

Efficient reinnervation of hindlimb muscles by thoracic motor neurons after nerve cross-anastomosis in rats.

OBJECT: Peripheral motor axons can regenerate through motor endoneurial tubes of foreign nerves to reinnervate different target muscles. This regenerative capacity has been brought to clinical applications for restorative surgery after nerve or root injury. In this study the authors explore the extent to which nerve cross-anastomosis between lower intercostal nerves and lumbar ventral roots would be effective in inducing reinnervation of paralyzed hindlimb muscles after spinal cord hemisection at the thoracolumbar boundary in rats. METHODS: The proximal extremities of sectioned intercostal nerves T10-12 were surgically connected to the distal extremities of sectioned ipsilateral lumbar ventral roots L3-5, respectively. Motor activity reappeared 2 months postsurgery; however, locomotion was not restored and inappropriate motor patterns persisted at 9 months postsurgery. At that time, data from electrophysiological and histological studies and horseradish peroxidase retrograde labeling demonstrated efficient regrowth of thoracic motor neuron axons that reached hindlimb muscles. They also revealed a persistent maturation defect of regrown fibers, as shown by size heterogeneity and presumable extensive axonal branching. These features are consistent with reduced neural activity subsequent to continuing inappropriate motor patterns. CONCLUSIONS: These results indicate that cross-anastomosis of intercostal nerves with lumbar ventral roots allows efficient reinnervation of paralyzed hindlimb muscles after spinal cord hemisection in rats. Stimulating the reorganization of the neuronal circuitry in the central nervous system by locomotion training or other methods would presumably result in both functional and anatomical improvements. This experimental setting provides a convenient animal model to investigate these processes.

The hypogastric and thirteenth thoracic ganglia of the rat: effects of age on the neurons and their extracellular environment.

Morphometric analyses of the neurons and microvessels of perfusion-fixed hypogastric (HG) and 13th thoracic (T13) ganglia have been performed in male Wistar rats aged 4, 24 and 30 mo. Estimations of HG volume employing the Cavalieri principle have also been performed and showed that the size of the aged HG is increased by 42%. Routine histological staining of the ganglia with Masson's trichrome indicated that this may be due to the increased amount of interstitial connective tissue which was apparent in the aged animals. The number of neurons per unit area progressively decreased by 38% between ages 4 and 24 mo and by 16% between ages 24 and 30 mo in the HG and by 25% (4 and 24 mo) and 2% (24 and 30 mo) in the T13 ganglion. The total number of neurons in the HG however, estimated by a physical disector analysis, was constant with age. The number of microvessels per unit area, microvessel diameter, neuronal and nuclear areas did not differ significantly between the 3 age groups studied. This observed increase in ganglionic volume and decrease in neuronal packing density may be associated with changes in the extracellular matrix, in particular in glycosaminoglycans whose presence was indicated by metachromasia of the ganglia with toluidine blue. The extracellular matrix was therefore characterised using a panel of monoclonal antibodies against glycosaminoglycans and laminin. Chondroitin-6 sulphate and chondroitin-4 sulphate were present in the interstitial connective tissue, and there was an increase in the expression of both these epitopes at 24 mo, noteably surrounding neuron cell bodies. The expression of chondroitin-4 sulphate/dermatan sulphate was unchanged, thus implying a decreased expression of dermatan sulphate with age. Keratan sulphate and the native chondroitin sulphate epitopes were absent from the ganglia at both ages. Laminin expression was increased in the aged ganglia. It is therefore clear that the constituents of the extracellular matrix are not constant throughout the adult lifespan and that the extracellular matrix may influence neuronal survival in old age. This is the first report characterising age-related changes in the extracellular matrix of autonomic ganglia.

Comparison of 180-degree and 360-degree skeletal muscle nerve cuff electrodes.

Use of skeletal muscle for cardiac augmentation is a promising technique for treatment of end-stage cardiac failure. An electrode woven through the latissimus dorsi that recruits nearby nerve fibers is commonly used to pace skeletal muscles both in clinical practice and in the laboratory. A proximally placed nerve cuff electrode offers potential advantages in improved recruitment of muscle fibers and low threshold for stimulation. We tested the effectiveness of a nerve cuff electrode passed directly about the proximal thoracodorsal nerve. Our report looks at the efficacy of nerve cuff electrode stimulation and compares electrical and histologic characteristics of a 180-degree wrap of the thoracodorsal nerve to a 360-degree wrap in dogs over 3 months. Threshold voltage at the commonly used pulse width of 200 microseconds was typically in the range of 400 to 600 mV for each electrode after 3 months. Statistical analysis revealed no significant difference (p < 0.05) in threshold voltage or current between the 180-degree and 360-degree nerve cuff electrode either at acute evaluation or after 3 months. Even contraction of latissimus dorsi was achieved with all implants. Adenosine triphosphatase staining revealed 100% conversion of type II to type I fibers in all stimulated muscles. Histologic examination of the thoracodorsal nerve and latissimus dorsi muscle revealed no abnormalities grossly or by light microscopy. Thus, a carefully applied nerve cuff electrode is an atraumatic, effective method for skeletal muscle stimulation. The 180-degree and 360-degree nerve cuff configurations are equally effective.

Morphometric evidence from C-synapses for phased Nissl body response in alpha-motoneurones retrogradely intoxicated with diphtheria toxin.

Diphtheria toxin (DTX) kills cells by inactivating ribosomal translocation and when used to retrogradely intoxicate cat intercostal motoneurones produces marked morphological alterations in Nissl bodies, including those specifically sited postsynaptic to C-type axon terminals. Here, qualitative examinations of 'intoxicated' postsynaptic Nissl bodies reveal a progressive structural alteration marked by rER dilatation, rER lamellae fragmentation but retention of both the highly ordered multilamellate organization and ribosomal attachment until final stages of Nissl body dissolution. Morphometric results identified 3 broad phases to the postintoxication response which differed in the degree of rER cisternal dilation, and the numerical and spatial relationships between rER-lamellae, rER-bound ribosomes and rER-associated polyribosomes. These phases reflect the known molecular basis of diphtheritic toxicity and contrast with the fast developing Nissl body reaction associated with the neurotoxin ricin which also invokes ribosomal dysfunction and has been used to mimic certain features of motor neurone disease. The cytopathology of DTX and ricin are compared in the Discussion.

Electronmicroscopic and electrophysiological studies of the teat branch of the XIII thoracic nerve: relationship with lactation in the rat.

Electrical stimulation of the XIII thoracic nerve (the 'mammary nerve') causes milk ejection and the release of prolactin and other hormones. We have analysed the route of the suckling stimulus at the level of different subgroups of fibres of the teat branch of the XIII thoracic nerve (TBTN), which innervates the nipple and surrounding skin, and assessed the micromorphology of the TBTN in relation to lactation. There were 844 +/- 63 and 868 +/- 141 (S.E.M.) nerve fibres in the TBTN (85% non-myelinated) in virgin and lactating rats respectively. Non-myelinated fibres were enlarged in lactating rats; the modal value being 0.3-0.4 micron 2 for virgin and 0.4-0.5 micron 2 for lactating rats (P greater than 0.001; Kolmogorov-Smirnov test). The modal value for myelinated fibres was 3-6 micron 2 in both groups. The compound action potential of the TBTN in response to electrical stimulation showed two early volleys produced by the A alpha- and A delta-subgroups of myelinated fibres (conduction velocity rate of 60 and 14 m/s respectively), and a late third volley originated in non-myelinated fibres ('C') group; conduction velocity rate 1.4 m/s). Before milk ejection the suckling pups caused 'double bursts' of fibre activity in the A delta fibres of the TBTN. Each 'double burst' consisted of low amplitude action potentials and comprised two multiple discharges (33-37 ms each) separated by a silent period of around 35 ms. The 'double bursts' occurred at a frequency of 3-4/s, were triggered by the stimulation of the nipple and were related to fast cheek movements visible only by watching the pups closely. In contrast, the A alpha fibres of the TBTN showed brief bursts of high amplitude potentials before milk ejection. These were triggered by the stimulation of cutaneous receptors during gross slow sucking motions of the pup (jaw movements). Immediately before the triggering of milk ejection the mother was always asleep and a low nerve activity was recorded in the TBTN at this time. When reflex milk ejection occurred, the mother woke and a brisk increase in nerve activity was detected; this decreased when milk ejection was accomplished. In conscious rats the double-burst type of discharges in A delta fibres was not observed, possibly because this activity cannot be detected by the recording methods currently employed in conscious animals.(ABSTRACT TRUNCATED AT 400 WORDS)

The non-myelinated fibers of the phrenic and the intercostal nerves in the cat.

The aim of this work was obtaining quantitative data relative to the non-myelinated fibers of some thoracic nerves of the cat. The study has been done both through the utilization of the light and the electron microscope. A comparative analysis of the results obtained from the muscle nerves (external intercostal nerve and phrenic nerve), cutaneous nerve (lateral collateral branch of the internal intercostal nerve) and mixed nerves (internal intercostal) has been made. The C muscle fibers have a smaller diameter than the C cutaneous fibers. Some of the non-myelinated fibers of the phrenic nerve are probably involved in the innervation of the pleura or of the peritoneum. The relative number of non-myelinated fibers varies according to the nerves. The factor linking the diameter of the non-myelinated fibers to their conduction velocity is approximately equal to 0.7.

Ultrastructural identification of afferent fibers of cardiac origin in thoracic sympathetic nerves in the dog.

While cardiac afferent nerve activity has been recorded from the ventrolateral (VLCN) and ventromedial (VMCN) cardiac nerves, left dorsal and ventral ansae subclaviae, and left upper thoracic white rami communicantes, little anatomical evidence for the existence of afferent fibers in these nerves has been reported. This study was designed to characterize the normal ultrastructure of the above nerves and to identify afferent fibers in them through Wallerian degeneration produced by dorsal root ganglionectomy. Laminectomies followed by dorsal root ganglionectomies were performed on left thoracic roots T1-T4 in six mongrel dogs. The nerves to be examined were removed from two animals at 1, 2, and 3 weeks following ganglionectomy and prepared for electron microscopy. Control nerves were obtained from two normal dogs. Degenerating nonmyelinated fibers were characterized by watery axoplasm containing clumps of electron-dense material. Degenerating myelinated fibers were distinguished by the separation of their myelin lamellae, producing characteristic whorls. After three weeks, afferent nonmyelinated axons had degenerated in all nerves, leaving only layered processes of Schwann cells in these areas. Approximately 5-15% of the fibers in each nerve degenerated, indicating their afferent nature. Of these fibers, 85-90% were nonmyelinated C fibers and the remainder myelinated Adelta fibers. These results indicate participation of both Adelta fibers and a large population of C fibers in transmission of cardiac afferent activity.