The unique organization of filamentous actin in the medullary canal of the medulla oblongata.

In the central canal, F-actin is predominantly localized in the apical region, forming a ring-like structure around the circumference of the lumen. However, an exception is found in the medulla oblongata, where the apical F-actin becomes interrupted in the ventral aspect of the canal. To clarify the precise localization of F-actin, the fluorescence signals for F-actin were converted to the peroxidase/DAB reaction products in this study by a phalloidin-based ultrastructural technique, which demonstrated that F-actin is located mainly in the microvilli and terminal webs in the ependymocytes. It is because the ventrally oriented ependymocytes do not possess well-developed microvilli or terminal web that led to a discontinuous labeling of F-actin in the medullary canal. Since spinal motions can change the shape and size of the central canal, we next examined the cytoskeletons in the medullary canal in both rats and monkeys, because these two kinds of animals show different kinematics at the atlanto-occipital articulation. Our results first demonstrated that the apical F-actin in the medullary canal is differently organized in the animals with different head-neck kinemics, which suggests that the mechanic stretching of spinal motions is capable of inducing F-actin reorganization and the subsequent cell-shape changes in the central canal.

The adult macaque spinal cord central canal zone contains proliferative cells and closely resembles the human.

The persistence of proliferative cells, which could correspond to progenitor populations or potential cells of origin for tumors, has been extensively studied in the adult mammalian forebrain, including human and nonhuman primates. Proliferating cells have been found along the entire ventricular system, including around the central canal, of rodents, but little is known about the primate spinal cord. Here we describe the central canal cellular composition of the Old World primate Macaca fascicularis via scanning and transmission electron microscopy and immunohistochemistry and identify central canal proliferating cells with Ki67 and newly generated cells with bromodeoxyuridine incorporation 3 months after the injection. The central canal is composed of uniciliated, biciliated, and multiciliated ependymal cells, astrocytes, and neurons. Multiciliated ependymal cells show morphological characteristics similar to multiciliated ependymal cells from the lateral ventricles, and uniciliated and biciliated ependymal cells display cilia with large, star-shaped basal bodies, similar to the Ecc cells described for the rodent central canal. Here we show that ependymal cells with one or two cilia, but not multiciliated ependymal cells, proliferate and give rise to new ependymal cells that presumably remain in the macaque central canal. We found that the infant and adult human spinal cord contains ependymal cell types that resemble those present in the macaque. Interestingly, a wide hypocellular layer formed by bundles of intermediate filaments surrounded the central canal both in the monkey and in the human, being more prominent in the stenosed adult human central canal.

Morphological features and clinical significance of epidural membrane in the cervical spine.

STUDY DESIGN: A prospective clinical study. OBJECTIVE: To elucidate the histomorphological features and clinical significance of the epidural membrane (EM) in the cervical spine based on operative and histological findings. SUMMARY OF BACKGROUND DATA: The anatomical features of the EM have been mostly discussed on the basis of cadaver studies in the whole spine. However, the histomorphological features and clinical significance of the EM in the cervical spine based on operative findings have never been reported. METHODS: Eighty-seven patients with cervical spondylotic myelopathy who had undergone an expansive open-door laminoplasty under microscopy were evaluated with a more than 2-year follow-up period. The most damaged spinal segment was determined in each patient from the preoperative neurological and image findings along with the remaining symptoms at follow-up. The morphological features of the EM were observed and recorded in each patient during decompression. For histology, specimens of common and remarkable types of the EM obtained from 16 patients were examined. RESULTS: The age at surgery averaged 64.5 years; there were 58 men and 29 women. With regard to the most damaged spinal segment, there were 14 cases at the C3-C4 level, 37 at the C4-C5 level, 32 at the C5-C6 level, and 4 at the C6-C7 level. The EM was an adipo-fibro-vascular tissue with various histomorphologies, blending with the periradicular sheath. Some EMs showed notable findings: obstructing dural tube expansion (13 cases, 14.9%), compressing a nerve root or disturbing its mobility (4 cases, 4.6%), and the combined type (1 case, 1.1%). All of them were located at approximately the most damaged spinal segment. In addition, some EMs had interesting histological features, such as harboring many small arteries, calcified debris, and metaplastic bone fragments. CONCLUSION: The EM can develop into remarkable structures with spondylosis and aging in patients with cervical spondylotic myelopathy, affecting surgical outcomes as well as successful decompression procedures. A sound understanding of the histomorphological features of the EM is required to obtain satisfactory surgical outcomes in the limited field afforded by minimally invasive surgery.

Comparison of the amounts of canal encroachment between semisitting and supine position of computed tomography-myelography for vertebral fractures of the elderly involving the posterior vertebral wall.

STUDY DESIGN: A prospective radiographical trial. OBJECTIVE: To elucidate effects of loading associated with spinal canal encroachment (SCE) in patients with insufficient bone union after vertebral fractures in the elderly, using computed tomography-myelography in 2 different positions. SUMMARY OF BACKGROUND DATA: In elderly patients with vertebral fractures, influence of loading would be involved in SCE, but the details are not well understood. METHODS: Seventeen patients (mean age, 77.4 ± 8 yr; range, 62-91 yr) with various degrees of neurological deficit due to insufficient bone union at both vertebral body and posterior vertebral wall were included in this study. Computed tomography-myelography was performed in both semisitting and supine positions. Kyphotic angle, rate of dural compression, ratio of occupation by bony fragments, and posterior vertebral body height ratio were measured and compared between positions. RESULTS: Mean ratio of occupation by bony fragments was significantly higher in the semisitting position (47.9 ± 9.2%) than in the supine position (33.9 ± 10.0%, P, 0.001). Similarly, mean posterior vertebral body height ratio was significantly lower in the semisitting position (67.8 ± 10.8%) than in the supine position (76.3 ± 13.3%), indicating a significant loss of vertebral height in the semisitting position (P, 0.001). Mean rate of dural compression was likewise significantly higher in the semisitting position (48.6 ± 13.3%) than in the supine position (33.3 ± 16.5%; P, 0.001). Mean change in ratio of occupation by bony fragments, change in posterior vertebral body height ratio, and angular instability between positions were 13.9 ± 8.6%, 8.5 ± 6.7%, and 13° ± 5.7°, respectively. A significant correlation was identified between change in ratio of occupation by bony fragments and change in posterior vertebral body height ratio (P = 0.001). CONCLUSION: Our study demonstrated that collapse of the nonunited posterior vertebral wall and intracanal protrusion of vertebral fragments would occur simultaneously with axial loading, causing SCE. Computed tomographic scan obtained in semisitting position seems quite useful to evaluate the amount of SCE by an unstable posterior wall.

Characteristic features of a nerve primo-vessel suspended in rabbit brain ventricle and central canal.

Bonghan theory was proposed by Bonghan Kim to illustrate the anatomy and physiology of the acupuncture meridian system. One of his astonishing claims was the physical presence of the nerve primo-vessel, which can be involved with a regenerating system of nerves. Our previous work has shown that there is a nerve primo-vessel in brain ventricles and the central canal of the spine of a rabbit. In this study, confocal laser scanning microscopy, transmission electron microscopy, and high voltage electron microscopy demonstrated that a nerve primo-vessel comprised DNA particles, other microparticles, and rod-shaped nuclei encircled by helix-shaped actins. The nerve primo-vessel had acridine orange-stained DNA particles that varied in size and were in parallel. These characteristics of the nerve primo-vessel are crucial for a comprehensive understanding of their function in the central nervous system, which may be associated with nerve regeneration.

Clinical implications of epidural fat in the spinal canal. A scanning electron microscopic study.

BACKGROUND AND OBJECTIVES: This review of articles summarizes recent developments in relation to fat located in the epidural space and also in dural sleeves of spinal nerve roots in order to improve our understanding of the clinical effects of the epidural blockade. METHOD: Medline search was carried cross-matching of the following words: "epidural fat", "epidural space", "adipose tissue" and "fat cells" from 1966 to 2008 in which articles referring to different pathologies that alter the epidural fat were also reviewed. Techniques used by different authors included the use of samples from dissections, cryomicrotome sections, as well as light and electron microscopy. RESULTS: Fat in the epidural space has a metameric distribution along the spinal canal that can be altered in some pathological conditions. Epidural fat is not evenly distributed. At cervical level fat is absent while in the lumbar region, fat in the anterior and posterior aspects of the epidural space forms two unconnected structures. Fat cells are found also in the thickness of dural sleeves enveloping spinal nerve roots but not in the region of the dural sac. Epidural lipomatosis is characterized by an increase in epidural fat content. When a patient has a combination of kyphosis and scoliosis of the spine, the epidural fat distributes asymmetrically. Spinal stenosis is frequently accompanied by a reduction in the amount of epidural fat around the stenotic area. CONCLUSIONS: The epidural space contains abundant epidural fat that distributes along the spinal canal in a predictable pattern. Fat cells are also abundant in the dura that forms the sleeves around spinal nerve roots but they are not embedded within the laminas that form the dura mater of the dural sac. Drugs stored in fat, inside dural sleeves, could have a greater impact on nerve roots than drugs stored in epidural fat, given that the concentration of fat is proportionally higher inside nerve root sleeves than in the epidural space, and that the distance between nerves and fat is shorter. Similarly, changes in fat content and distribution caused by different pathologies may alter the absorption and distribution of drugs injected in the epidural space.

Prediction of spinal canal expansion following cervical laminoplasty: a computer-simulated comparison between single and double-door techniques.

STUDY DESIGN: Laminoplasty was simulated using a computer-assisted technique to assess the amount of canal expansion. OBJECTIVES: This study was designed to clarify the relationship between laminoplasty opening size and increase in sagittal canal diameter, increase in canal area, and the angle of the opened lamina following laminoplasty, and to determine whether a spinous process-splitting laminoplasty achieves the similar canal expansion as a single open-door method. SUMMARY OF BACKGROUND DATA: Single and double-door cervical laminoplasty (SDCL and DDCL, respectively) have been widely used in the treatment of multilevel stenotic conditions. However, the relationship between laminoplasty opening size and spinal canal expansion following laminoplasty, and the comparison of postoperative spinal canal expansion between single and double-door techniques have not been well investigated. METHODS: SDCL and DDCL, based on preoperative computerized tomography scans of 34 patients who had undergone the laminoplasty surgery, were simulated using a computer-assisted technique. Laminoplasty with an opening size of 6, 8, 10, 12, 14, 16, and 18 mm were simulated to determine the amount of canal enlargement with the various opening size. RESULTS: Sagittal diameter, canal area, and lamina angle were increased steadily following either single or double-door laminoplasty with the door opened from 6 to 18 mm. Significant positive correlation was found between laminoplasty opening size and increase in sagittal diameter (R2 = 0.969 and P = 0.001 in SDCL; R2 = 0.926 and P < 0.001 in DDCL), increase in canal area (R2 = 0.961 and P < 0.001 in SDCL; R2 = 0.937 and P < 0.001 in DDCL), and lamina angle (R2 = 0.959 and P < 0.001 in SDCL; R2 = 0.943 and P < 0.001 in DDCL). No significant correlation was observed between preoperative sagittal diameter and increase in sagittal diameter of the spinal canal, whereas significant positive correlation was found between preoperative cross-section area and increase in cross-section area of the spinal canal. The differences between postoperative canal increase in sagittal diameter and canal area for the single versus double-door technique were statistically significant when the door was opened by more than 12 mm (P < 0.05). CONCLUSIONS: Our investigation provides insight into canal expansion after laminoplasty. The increased amount of canal following laminoplasty can be predicted by the regression equations. This may allow preoperative determination of the optimal size of the opening needed to establish adequate canal space for the spinal cord. Both single and double-door techniques of laminoplasty provide sufficient room for posterior migration of the spinal cord, although gaining different canal expansion.

Immunocytochemical localization of zinc transporter 3 in the ependyma of the mouse spinal cord.

We report, for the first time, the light microscopical and ultrastructural appearance of ZnT3-immunoreactivities in the ependymal cells of the central canal of the mouse spinal cord. Light microscopy revealed the presence of ZnT3-immunoreactive (Ir) ependymal cells in 1 microm thick epon sections stained by the ABC method. The ZnT3-Ir cells were observed at all levels of the spinal cord, but were a little more numerous in lumbosacral segments than in cervicothoracic segments. The ZnT3-Ir cells had large, ovoid nuclei with abundant cytoplasm, and protruded into the lumen of the central canal. Our ultrastructural findings suggest that the ZnT3-Ir ependymal cells possess secretory activity directed towards the central canal. We propose that they may play a role in the trans-ependymal mechanism responsible for zinc homeostasis between cerebrospinal fluid and the central area of the gray matter.

Ultrastructural characterization of the accessory lobes of Lachi in the lumbosacral spinal cord of the pigeon with special reference to intrinsic mechanoreceptors.

The lumbosacral spinal cord of birds is unique among vertebrates in that segmentally organized accessory lobes protrude from the ventrolateral spinal cord into the vertebral canal. Recently, it has been suggested that these lobes may be part of an extralabyrinthine sense organ of equilibrium. For a better understanding of such a function, a complete analysis of the structural basis was performed by means of electron microscopy. The lobes consist of multipolar neurons, myelinated and unmyelinated axons, glia-derived glycogen cells, glial cells, and capillaries. The dorsal part of the lobe is covered by a loose mesh of pia mater. Ventrolaterally, an arachnoidal trabecle is in close contact with the lobe. Extracellular lacunae extend from the periphery deep into each lobe. The lacunae are separated from the subarachnoidal space by a loose mesh of processes of the glycogen cells with its basal lamina. The lacunae are filled by a network of processes of glycogen cells, glial cell, dendrites, and small axons. Both neuronal somata and dendrites are contacted by numerous axon terminals that form rather uniform synapses. Finger-like processes emerge from both the somata and the dendrites. The dendrites branch deeply into the extracellular lacunae and form lateral ramifications, which consist of narrow stalks with serially arranged bulbous portions, from which finger-like processes emerge. Finger-like processes are well-known elements in mechanotransduction. Glycogen cells and lacunae may contribute to transmission of hydrostatic pressure changes during movements of the body.

Complex expression pattern of the SCO-spondin gene in the bovine subcommissural organ: toward an explanation for Reissner's fiber complexity?

Bovine SCO-spondin is a glycoprotein secreted by the subcommissural organ (SCO), an ependymal derivative located in the roof of the third ventricle. It shows homology with developmental molecules involved in directional axonal growth. Using SCO-spondin cDNAs as probes, we analysed the specific expression of the corresponding gene in the bovine SCO by Northern blot and in situ hybridization (ISH). A strong expression was detected in the secretory ependymal and hypendymal cells of the SCO and the main transcripts showed a large size 14 kb. A single copy gene was revealed by Southern blot analysis of bovine genomic DNA. The presence of additional transcripts suggested a transcriptional regulation of the SCO-spondin gene. A comparative analysis of the results obtained by molecular and immunological techniques (immunoblotting and immunopurification) pointed to the presence of several SCO-spondin related proteins in the SCO encoded by the same gene. The presence in the cerebral hemispheres (CH) of a 54-kDa glycoprotein with a common epitope is discussed as a putative cleaved SCO-spondin product carried by the cerebrospinal fluid, that may act on neuronal development.

The ventriculus terminalis and filum terminale of the human spinal cord.

Serial sections of the conus medullaris and the filum terminale of 23 randomly selected human spinal cords were studied by light and electron microscopy, and following immunoperoxidase staining for glial fibrillary acidic protein (GFAP), vimentin, neuron-specific enolase (NSE), amyloid beta protein, and S-100 protein. The intradural portion of the filum contains bundles of GFAP-positive glial fibers, scattered silver- and NSE-positive neurons, segments of peripheral nerve, blood vessels, fibrous connective tissue, and fat. Glial cell clusters varying from five to 100 cell layers thick at times constitute the bulk of the filum. The periependymal glial cells possess moderate amounts of eosinophilic cytoplasm and relatively uniform round to ovoid nuclei containing evenly distributed chromatin. They are distributed diffusely with no specific pattern of organization, although some of them showed a tendency to form acinar structures. A minority of the glial cells showed GFAP immunoreactivity, and some were immunoreactive for vimentin. Electron microscopy demonstrated the presence of periependymal cells showing cilia, microvilli, and the formation of intercellular junctional complexes, as well as cells containing bundles of glial filaments within the cytoplasm. Degenerated NSE-positive neurons and degenerated neurites resembling neuritic plaques were also demonstrated. However, immunoperoxidase staining for amyloid beta protein was negative in these structures. Thus, the filum terminale is endowed with an abundance of glial cells and neurons and is not simply a fibrovascular tag. Periependymal glial cells in the filum terminale should not be mistaken for neoplasm. The presence of neuropil with profuse astroglial and neuronal components within the filum terminale suggests a possible functional role for these structures.

Distinguishing between scar and recurrent herniated disk in postoperative patients: value of contrast-enhanced CT and MR imaging.

Twenty patients with failed back surgery syndrome were analyzed prospectively with MR imaging. In addition, 10 of these patients were analyzed with high-dose contrast-enhanced CT or gadopentetate dimeglumine-enhanced MR imaging. Imaging results were compared with surgical and pathologic findings in all cases. In the 10-patient subset, abnormal epidural soft-tissue specimens were also assessed with light and electron microscopy for vascular density, size of the extracellular space, and collagen orientation and thickness. The average vascular density of epidural fibrosis on light microscopy was found to be 1.19%; the average size of the extracellular space on electron microscopy was 4.29%. Scar 4 months of age or less had a larger extracellular space than did older scar; high- (grade 4 or 5) intensity scar had a larger extracellular space than did less intense scar on long TR/short TE images. Scar 1 year old or less enhanced more intensely on CT than did older scar. The MR signal intensity and CT enhancement characteristics of epidural scar were also found to differ according to epidural location. The percentage of scar that was hyperintense on long TR/TE images was as follows: anterior, 82%; lateral recess, 70%; lateral, 47%; and posterior, 20%. However, no relationship was found between the degree of CT enhancement of scar and vascular density. Gap junction status and extracellular space size, therefore, are more important than vascular density in predicting the degree of enhancement. The accuracy of contrast-enhanced CT and unenhanced MR in separating scar from herniated nucleus pulposus is 80%. This accuracy is related to the partial overlap in imaging characteristics of scar and recurrent herniated nucleus pulposus.

Reissner's fiber and the wall of the central canal in the lumbo-sacral region of the bovine spinal cord. Comparative immunocytochemical and ultrastructural study.

Reissner's fiber (RF) of the subcommissural organ (SCO), the central canal and its bordering structures, and the filum terminale were investigated in the bovine spinal cord by use of transmission electron microscopy, histochemical methods and light-microscopic immunocytochemistry. The primary antisera were raised against the bovine RF, or the SCO proper. Comparative immunocytochemical studies were also performed on the lumbo-sacral region of the rat, rabbit, dog and pig. At all levels of the bovine spinal cord, RF was strongly immunoreactive with both antisera. From cervical to upper sacral levels of the bovine spinal cord there was an increasing number of ependymal cells immunostainable with both antisera. The free surface of the central canal was covered by a layer of immunoreactive material. At sacral levels small subependymal immunoreactive cells were observed. From all these structures sharing the same immunoreactivity, only RF was stained by the paraldehyde-fuchsin and periodic-acid-Schiff methods. At the ultrastructural level, ependymal cells with numerous protrusions extending into the central canal were seen in the lower lumbar segments, whereas cells displaying signs of secretory activity were principally found in the ependyma of the upper sacral levels. A few cerebrospinal fluid-contacting neurons were observed at all levels of the spinal cord; they were immunostained with an anti-tubulin serum. The lumbo-sacral segments of the dog, rat and rabbit, either fixed by vascular perfusion or in the same manner as the bovine material, did not show any immunoreactive structure other than RF. The possibilities that the immunoreactive ependymal cells might play a secretory or an absorptive role, or be the result of post-mortem events, are discussed.

The ependyma of the cat central canal, with particular reference to its mitochondria-containing bulbs.

The ultrastructure of the ependyma in the central canal of adult cats was examined in both the scanning and the transmission electron microscopes (SEM and TEM). The same morphological details were seen in the ependyma of the central canal as have so frequently been described in the ependyma of the brain ventricular system, for example bundles of cilia, single cilia, microvilli and occasional small cytoplasmic protrusions. The supraependymal cells and supraependymal nerve fibers found in the central canal also resembled those seen in the ventricular system. The most striking feature of the canal ependyma were the large, spherical bodies containing numerous mitochondria. They are therefore called mitochondria-containing bulbs. In sections the bulbs were seen to be connected by long, slender stalks to neurons in subependymal position. In some respects the mitochondria-containing bulbs resemble the processes of cerebrospinal fluid-contacting neurons.

Descriptive studies of occlusion and reopening of the spinal canal of the early chick embryo.

Occlusion and reopening of the lumen of the spinal cord, two processes believed to be involved in early brain enlargement, were examined in chick embryos to determine what morphological features characterize these events. Occlusion begins at a particular craniocaudal level near the time that the neural folds become apposed in the dorsal midline and blocklike somites form from the segmental plates. During occlusion, the apical sides of the lateral walls of the neural tube are in close apposition. Interdigitating apical surface protrusions, cross-luminal intercellular junctions, and abundant cell-surface materials are lacking. Reopening has occurred by about stage 20 throughout most of the craniocaudal extent of the spinal cord. A lumen suddenly appears during this process, but correlated structural changes that might account for such a dramatic change in morphology were undetectable. Reopening involves the release of the forces that previously maintained occlusion, or the generation of new forces that overcome those causing occlusion, but what these forces are remains to be determined. Observations suggest that forces generated outside of the neural tube might be largely responsible for occlusion, and experiments are in progress to test this possibility.

An electron microscopic study of the development of the ependyma of the central canal of the mouse spinal cord.

The central canal of the adult mouse spinal cord is lined for most of its extent by ependymal cells which are rich in microfilaments and whose apical surface is covered with matted, broad microvilli. The canal itself is filled with amorphous material containing glycogen granules. Two forms of this material are present, a dark form rich in glycogen, and a light form containing a few glycogen granules. Each type appears to be surrounded by a membrane. The upper cervical region, however, has a large empty lumen and the ependymal cells in this region have only scattered, narrow microvilli. During development, the floor and roof plates are at first composed largely of ependymoglial cells, unlike the lateral walls, where undifferentiated neuroepithelial cells predominate. By E15 few undifferentiated neuroepithelial cells remain. At E17 the morphology of the ependymal cells changes. Their apical surface becomes covered with matted, club-shaped microvilli and the central canal is filled with glycogen-containing material. By P5 microfibrils are present in large bundles in the ependymal cells. The piaglial surface opposite the roof and floor plates has finger-like projections unique to these regions and these persist at the surface of the dorsal median septum until myelination is well advanced after P5. The fibres forming the dorsal median septum are at first pale processes containing scattered glycogen granules and microtubules. By P5 microfibrils are present and at P150 the processes are packed with masses of microfibrils.

A study of experimental syringomyelia by scanning electron microscopy.

Experimental hydromyelia and syringomyelia, induced by kaolin in dogs, has been investigated by scanning electron microscopy. This study demonstrated that communication between the 4th ventricle and the spinal central canal is normally occluded by a plug of acellular material lying within the central canal. This plug is broken down following the onset of hydrocephalus and communication is rapidly established between the ventricles and the central canal. The canal distends and ruptures dorsally into the spinal gray matter with the development of extensive intramedullary cavities, lined by glial and neuronal elements. The morphological changes demonstrated are consistent with a physical destructive process of the cord resulting from CSF dissection.

[The cerebrospinal fluid contact processes in the central canal of the spinal cord. A scanning and transmission electron microscopic study of the rabbit]. / Die Liquorkontaktfortsätze im Zentralkanal des Rückenmarkes. Eine raster- und transmissionselektronenmikroskopische Untersuchung am Kaninchen

The surface of the central canal of the rabbit spinal cord was investigated with scanning and transmission-electron microscopy. On the ventral wall of the central canal, a long cranio-caudally oriented area carries a row of bulbs (about 630 per millimeter of length). The bulbs are spinal ventricular processes of cerebrospinal fluid contacting nerve cells. Its cytoplasm contains mitochondria, smooth- and rough-surfaced endoplasmic reticulum and vesicles of various size and contents. The bipolar or multipolar nerve cells are situated below the ependymal cells of the central canal. The perikaryon has the general cytological structure of a neuron. Some nerve fibres are shown to be running in the cranio-caudal direction within the central canal. Axons containing synaptic vesicles (diameter 400 A) form synapses on some of the ventricular processes. Two main types of ventricular processes can be observed, they differ in the size and structure of the end bulb, in the shape of its sterocilia, and in the number of mitochondria. Big globular processes are filled with a great number of mitochondria, whereas stereocilia are lacking. On the contrary, small processes with numerous stereocilia extending radially into the cerebrospinal fluid contain a number of mitochondria. A third type takes the mid position between the two main types. The ventricular processes have no "sensory cilia". On the basis of these morphological differences the possible role of mitochondrial movements in the function of the ventricular processes and the question of the identity of the three types of processes are discussed.