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Journal of the Anatomical Society of India

Comparative Anatomical Study of the Cerebellum of Man and Fowl

Author(s): Pal, B; Chowdhury, S. *Ghosh, R. K.

Vol. 52, No. 1 (2003-01 - 2003-12)

Department of Anatomy, University College of Medicine, *Faculty of Veterinary Sciences, W.B.U of A.F.S, Kolkata INDIA

Abstract

Gross anatomical and histological study on the cerebellum of man and fowl was made to find out structural differences if any, since both the species posses complex but quite different type of body movement for the maintenance of equilibrium. The shape, size, weight, volume, lobar and folial arrangement were considered under gross observation. The cerebellum of fowl was found to be heavier and more voluminous in comparison to that of man. In contrary to that of human, the cerebellum of fowl presented a well-developed lobe, which represented the vermiform lobe of human cerebellum. Histomorphology of the organ was studied with the help of slides stained with H&E and Golgi-cox method. Large flask shaped Purkinje cells in single row were observed in both the species. The sizes of the Purkinje cells were greater but the population per unit volume was lesser in case of human cerebellum. However both the species presented a common type of histological organisation.

Key words: Cerebellum, Man, Fowl,

Introduction:

Different vertebrates have different style of movements according to their living habits and gross anatomical variations. Balance and equilibrium will be different in a bipedal cursorial and quadruped. Variable limb movements are observed between flying and walking vertebrates. Movements of forelimbs (hands in case of human and wings in case of birds) are interestingly variable both as an organ of locomotion and an organ meant for prehension including fine movements.

The cerebellum is responsible for the maintenance of equilibrium of the body by making co-ordination of somatic motor activity and by regulating the muscle tone. The organ is more important in active vertebrate genera since it is intimately involved in the control and maintenance of muscle tones and thereby equilibrium. As stated by Carpenter (1995) function of the cerebellum is modified by experience and this structure plays an important role in the learning of motor tasks. Mondal (1997) mentioned that the size and shape of cerebellum is perhaps related to the animal's type of limb movement, centre of gravity and species posture. The more intricate the movement of which an animal is capable, the more developed is the cerebellum. Anatomical study on this structure has been undertaken by many workers (Pearson 1972, Turner 1891) in various vertebrates and a common pattern of cellular organisation was observed with some minor variations.

In this investigation an attempt has been made to find out the anatomical variations of cerebellum amongst human and a bird (fowl) with regard to their gross structure and histomorphological architecture, which may be helpful for better understanding of the physiology of the organ.

Materials and Methods:

Six healthy birds (fowl-white leg horn) were utilised in this investigation. The whole brain was collected from the sacrificed birds through proper aseptic procedure. The volumes and various dimensions of the whole brain and of the cerebellum were measured separately by the water displacement method and by slide calipers respectively, immediately after collection of materials. The weights of the samples were taken separately. The cerebellum as a whole was preserved in 10% buffered formalin for further processing.

Human brains were collected from six fresh, cadavers, available in the department of Anatomy of University College of Medicine, Kolkata.

After collection of the whole brain by careful dissection, weight, volume, length and width were measured in the similar manner. Pieces of cerebellum (2xlxlcm) were made by a sharp knife on desired plane and preserved in 10% buffered formalin. For histological observation, 5-6 microns thick sections were cut with the help of rotary microtome. The sections were stained with Haematoxyline and Eosin as per standard procedure.

A separate set of tissue was collected for Golgi-cox staining. The tissues were fixed in 10% buffered formalin. The Golgi-cox solution was made by mixing of 10 volumes of 5% Potasium dichromate, 10 volumes of 5% Mercuric chloride, 8 volumes of 5% Potasium Chromate with 20 volumes of distilled water. Large pieces (1cm ´ 1cm ´ 5cm) of cerebellum of each species were placed on a layer of glass wool in a large volume of Golgi-cox solution and incubated at 37°C. The solutions were changed after 48 hours. Fresh Golgi-cox solution was added and the containers were wrapped with a black paper and kept in the incubator for two months. After the incubating period the tissue samples were washed, dehydrated, cleared, wax impregnated and ultimately embedded in molten paraffin wax. 50 micron thick sections were cut with the help of rotary microtome. The sections were collected in warm water and then mounted on albumenised slides.

The slides were kept in oven at 50°C for half an hour. The paraffin wax was removed by immersing the slides in xylene. The slides were passed through descending grades of alcohol and ultimately dipped in distilled water. Blackening was done by placing the sections in 5% ammonia solution for one hour and subsequently washed thoroughly in distilled water. The tissue sections were dehydrated, cleared and mounted as per usual method.

Observation and Results:

Fowl Cerebellum - gross anatomy

The cerebellum of fowl was found to be a round structure resembling a curled worm, which represents the vermiform lobe of mammals (fig-1). The rostral surface of the cerebellum, which was laterally compressed, accommodated into a V- shaped notch between the caudal poles of the cerebral hemispheres and optic lobes. In this species, the anterior end of the cerebellum was found to be closely associated to the caudal poles of the cerebral hemispheres due to the wide separation of the optic lobes on the either side. The cerebellum was found to be separated from the medulla oblongata by the fourth ventricle (fig-2). The flocculi were detected as prominent caudolateral processes at sides of cerebellum.

The middorsal surface of the cerebellum presented a series of transverse gyri and sulci. The cerebellum was connected with the midbrain rostrally and with the medulla oblongata caudally by the preduncles. In a sagittal section, it was found that the vermiform cerebellum was divided into three parts-anterior, middle and posterior by deep fissures. These parts were divided into numerous folia. Ten primary folia (number I to X) were found in sagittal section (Fig-3). The identity of individual folia or lobules i.e. lingula, central lubule, culmen, declive, folium and tuber vermis, pyramid, uvula and nodule were clearly detected.

The cerebellum enclosed a small centrally placed cavity. which was found to be continuous by a small passage with the fourth ventricle of the brain. The medullary columns were found to be extending in a radiating manner towards the cortex. Externally the cerebellum was found be covered by a thin layer of pia mater which invaginated into the fissures between the folia.

The average weight, volume, length and width of whole brain & cerebellum of fowl and the ratio between the two are depicted in table-1.

Table 1: Biometry of cerebellum in relation to the whole brain in fowl

  Whole brain
(Mean + SD)
Cerebellum
(Mean + SD)
Ratio
Weight (gm) 3.15 + .222 .791 + .042 3.9 : 1
Volume (ml) 3.00 + .163 .745 + .026 4 :1
Length (cm) 2.63 + 0.048 1.508 + .094 1.74 : 1
Width (cm) 2.05 + .064 .959 + .014 2.13 : 1

Histomorphology:

Histologically, the cerebellum of fowl was divided into an outer cortex and an inner medulla. Three distinct layers of the cerebellar cortex i.e. outer molecular layer, middle Purkinje cell layer and inner granular layer were clearly detected on microscopic examination (Fig-4). Externally the cortex was covered by pia mater, internally it overlied the white matter. Star shaped cells scattered close to periphery of the molecular layer represented stellate cells. Basket cells with their processes were observed at the depth of molecular layer (Fig-5). Thickness of molecular layer was more in the fissures than on the folial summit. The branches of processes of the basket cells of this layer encircled the Purkinje cell bodies in the form of bushes. The Purkinje cells formed a single layer at the junction between molecular and granular layers. The cells were found to be oval or round in shape and contained a centrally placed nucleus. In some places few cells were in the form of flasks with a round body and small narrow neck.

The granular layer was composed of numerous small cells together with nerve fibres. Granule cells were small and round with relatively large nuclei.

Table-II: Thickness of different layers and diameter and number of Purkinje cells in 1mm length (In Fowl)

Molecular Layer (m) Granular Layer (m) Ratio Purkinje Cell
  Summit Fissure Summit Fissure Summit Fissure Longitudinal Diameter (m) Tansverse Diameter (m) No. in 1mm length
Range 170-220 255-336 289-350 169-238 1:1.68 1.56:1 20-29 13-17 13.7-24.2
Mean 196 294 330 187 25.3 14.8 18.9

These cells were found to be tightly packed in this layer. Large Golgi cells were also found near the Purkinje cell layer (Fig-5). The granular layer was thicker on the folial summits and thinner in fissures.

The average thickness of molecular and granular layers at summits and fissures and their ratios along with dimensions of Purkinje cells in fowl are shown in Table-II

Cerebellum of Man:

Gross Anatomy:

The cerebellum of man was roughly spherical in shape, constricted to some extents in its median region and flattened dorso ventrally. It was lodged in posterior cranial fossa separated from the occipital lobes of the cerebral hemispheres by tentorium cerebelli. The occipital poles partly covered the cerebellum in front and it was separated from pons and medulla by the cavity of fourth ventricle. A thin layer of piamater invested the surface of the cerebellum which invaginated into the sulci. Two paramedian sulci divided the cerebellum into a middle part the cerebellar vermis and two lateral parts the cerebellar hemispheres.

The cerebellar surface was found to be divided by numerous curved trnsverse fissures, which separated its folia. Grossly the surface was laminated in appearance due to the presence of transverse fissures. Superior vermis was divided into lobules- namely central lobule, culmen, declive and folium vermis (Fig-6). The most anterior lobule of cerebellar vermis i.e. lingula was found close to most posterior lobule, the nodule. Each except lingula, was continuous bilaterally with an adjoining lobule in each hemisphere. The inferior vermis was divided into the tuber vermis, pyramid, uvula and nodule. The flocculus was found to be a small cerebellar lobule located to the tonsil and applied to the caudal surface of middle celebellar peduncle.

Average weight, volume, length and width of whole brain and cerebellum in man along with the ratio between the two are shown in Table-III.

Table III: Biometry of cerebellum in relation to the whole brain in Man

  Whole brain
(Mean + SD)
Cerebellum
(Mean + SD)
Ratio
Weight (gm) 1194 + 28.927 125.5 + 6.898 9.51 : 1
Volume (ml) 1185 + 49.867 104.1 + 8.375 10.42 : 1
Length (cm) 15.1 + .623 5.95 + .537 2.53 : 1
Width (cm) 11.25 + .75 9.25 + .547 1.21 :1

Table IV: Thickness of different layers and diameter and number of Purkinje cells in 1mm length (In Man)

Molecular Layer (m) Granular Layer (m) Ratio Purkinje Cell
  Summit Fissure Summit Fissure Summit Fissure Longitudinal Diameter (m) Tansverse Diameter (m) No. in 1mm length
Range 204-306 316-357 337-402 165-275 1:1.50 1.80:1 19.5-34 14-27.5 8-5.6
Mean 227-2 343.5 389.5 215.2 28.5 21.3 6.6

Histomorphology:

In H & E stain the appearance of whole cortex was found to be uniform microscopically. The elements of cerebellar cortex had a precise geometric order in all planes in individual folia. The cerebellar cortex was composed of three strata- an outer molecular layer, intermediate layer of large Purkinje cells and an inner granular layer (Fig-7).

The molecular layer showed a sparse population of neurons and was almost featureless in H & E sections. In Golgi-Cox stained slides the superficial stellate cells were found to be star shaped (Fig-8) and small. The larger cells located in the vicinity of Purkinje cell bodies represented basket cells. Radiating branches from large glial cells could also be seen. This layer contained the dendritic and axonal processes. Section of all these processes gave the molecular layer its finely punctate appearance.

The Purkinje cells were found in a single row between molecular and granular layer. Pear shaped large perikarya of Purkinje cells had a clear vesicular nucleus with a deeply stained nucleolus. At some places clumps of granule cells were found between Purkinje cells. The granule cells gave the appearance of closely packed chromatic nuclei in H & E stain, resembling lymphocytes. Each granule cell had a spherical nucleus and was found to contain a shell of cytoplasm. Thickness of granular layer was different in the fissures and on folial summits.

The average thickness of molecular and granular layers at summit and fissures and their ratios along with dimensions of Purkinje cells in man are depicted in Table-IV.

Discussion:

Although the cerebellum of both the species presented a common anatomical disposition but exhibited wide variations so far their gross morphology is concerned. In the birds the whole structure was found to be almost rounded in shape, but in human it is roughly spherical. Cerebellum of fowl was found to be relatively greater in size and weight in comparison to that of human. In fowl the cerebrum was four times greater than that of cerebellum but in human the cerebrum was ten times greater than that of cerebellum. Parker and Haswell (1963) mentioned that the relatively greater size of the cerebellum of birds was associated with centre of equilibrium, which was important in flying animals. Messer (1958) reported that the cerebellum of birds was found to be situated forwardly to meet the cerebrum and to cover the diencephalon dorsally. In the fowl the cerebellum was situated caudal to cerebral hemisphere and dorsal to pons and medulla oblongata, whereas in human it is caudodorsal in position. This positional difference may be due to the variations in axis of the bodies of these two species. In both the species fourth ventricle was situated between the cerebellum and brain stem.

Two well developed cerebellar hemispheres and an ill developed vermis which were observed in human were absent in case of fowl.The cerebellum of fowl had a large median portion called the vermis and two small lateral portion the flocculi. This is in agreement with the statement of Carpenter (1995) in human and Nickel et al (1977) in birds. Ranson and Clark (1959) stated that vermis was highly developed in birds which fly as compared to the flightless one.

According to Kappers et al (1936) greater size of corpus cerebelli in birds was associated with increased number of spino-cerebellar fibre bundles.

The sulci, which divided the surface of the cerebellum of the both the species were found to be finer in case of human and coarser in case of birds. The ten numbers of folia, which were found only on the superior and inferior part of the vermiform lobe of the human, were also clearly detected in the sagittal section of the whole cerebellum in fowl. The arrangement of lobules as has been recorded in superior and inferior sequence could not be detected in case of birds. This is in accordance with the statement of Larsell and Whitelock (1952) who observed ten different lobules in avian cerebellum. In sagittal section of the cerebellum it was found that the lobes were made up of ten primary folia or lobules which were arranged antero-posteriorly, They represent lingula, central lobule, culmen, declive, folium vermis, tuber vermis, pyramid, uvula and nodulus having resemblance to those of mammals (Nickel et al 1977).

Histologically the basic cellular organisation of the cerebellum was found to be similar in both the species under this investigation. Pearson (1972) stated that throughout all vertebrate genera the organisation of cells and axons within the cerebellum had a similar and distinctive appearance.

A number of small star shaped cells found in a scattered manner close to the periphery of molecular layer represented stellate cells. In the deeper part of this layer a different type of cells were detected. These were basket cells whose processes were arranged like bushes around some of the Purkinje cells. According to Nickel et al (1977), the molecular layer was found to contain thinly myelinated nerve fibres originating from the nerve cells situated within this layer and also dendrites of Purkinje cells from the layer below. The large Purkinje cells formed a single layer at the junction between the molecular and granular layers. The cells were flask or pear shaped with a centrally placed nucleus. This finding is in agreement with Pearson (1972), who reported that Purkinje cells formed a single layer of large flask shaped cells at the junction of molecular and granular layer in birds. The granular layer was the innermost layer of the cortex and was situated between the Purkinje cell layer and medullary layer of white matter. This is in agreement with Hodges (1974) and Nickel et al (1977) in birds. This layer was composed of numerous small granule cells together with nerve fibres. Granule cells had a relatively large nucleus. Large Golgi cells were also found in the granular layer near the Purkinje cell layer. This finding is in accordance with the statement of Pearson (1972), Hodges (1974) and Nickel et al (1977) in avian species.

In human cerebellum the cortex was clearly divided in outer molecular layer,middle Purkinje cell layer and inner granular layer. In H & E stained slides the molecular layer was found to be almost featureless. The star shaped cells located near the periphery were the stellate cells and deeper cells close to Purkinje cell layer were basket cells. This observation is in accodance with Williams et al (1995). In this study it was observed that this layer was primarily composed of dendritic arborisation of cells of deeper layers and numerous thin axons coursing parallel to the long axis of folia. Similar observation was made by Helmut (1977) and Carpenter (1995) in human. The Purkinje cell layer was found in a single row of cells between molecular and granular layer in this study. The cells were pear shaped or flask shaped with clear vesicular nucleus with deeply stained nucleolus. This observation is in accordance with Kuhlenbeck (1975). Carpenter (1995) stated that the unique feature of the Purkinje cells was their monoplaner shape which was demonstrated in the section stained by Golgi-Cox technique in this study. The cells of the granular layer in H & E stained slides appeared similar to lymphocyte because of large chromatic nucleus. The granule cells were found in this zone in a closely packed manner. However some cell-free zones were also located in between. This is in accordance with Kappers et al (1936). The Golgi cells were located at the junction between granular layer and Purkinje cell layer.

Under the gray matter of the cerebellum, white matter formed the medullary layer. Externally the cortex was covered by pia mater. White matter formed the inner bulk of the organ. Similar observation were made by Williams et al (1995).

References:

  1. Carpenter's Human Neuroanatomy 9th Edn. Williams & Wilkins, Baltimore USA : pp 538-622. (1995)
  2. Helmut, L., Translated by Winstaley, D. P. : In : human Histology, Cytology and microanatomy. George Thieme publishers' stuttgart. Germany : pp231-234. (1977)
  3. Hodges, R. D. : The Nervous System. In : The Histology of Fowl. Academic Press, New York, San Francisco : pp. 612.616. (1974)
  4. Kappers C. U. A. et al : The cerebellum. In the comparative Anatomy of the Nervous system of vertebrates including man Vol. II. Haffner Publishing Company, New York : pp 696-860. (1936).
  5. Kuhlenbeck, H : The Central Nervous System of vertebrates, Vol 4. Spinal cord and Deuterencephalon, S karger. Basel : pp 625-768. (1975)
  6. Larsell, O., and Whitelock, D. G. (1952) : Further observations on the cerbellum of birds Journal of comparative Neurology.97 : 545-566.
  7. Messer, H.M. The Nervous System. In: An Introduction to veterinary Anatomy. The Macmillan Company, New York : pp 374-380. (1958)
  8. Mondal, R.K. (1997): Comparative gross anatomical and histomorphological studies on cerebellum of Fish, Amphibia, Reptilia and Mammalia. Ph D. Thesis W B univ of Animal and Fisheries science cal - 37.
  9. Nickel R. et al. In: Anatomy of Domestic Birds. Verlag Paul Parey. Berlin; pp 118-121. (1977)
  10. Parker, T.J. and Haswell, W.A. : Textbook of Zoology In : Vertebrates Vol-2, 7th Edn. Macmillan & Co. Ltd, London. pp 312, 410, 542, 592, 681. (1963):
  11. Pearson, R : The Avian Brain. In : The Cerebellum, Academic press, London and New York, pp 235-278. (1972)
  12. Ranson, S.W. and Clark, S.I: (1972). The Anatomy of the Nervous System - its development and function 10th Edn. W.B Saunders Co. Philadelphia. PP 43-45 and 286-287. (1959)
  13. Turner, C.H. (1891): The morphology of Avain brain Journal of . comp. Neurology 1 : 39-92.
  14. Williams P. L., et al: 38th Edn. Gray's Anatomy In: Nervous System. Churchill Livingstone, London, pp 1028-1065. (1995)

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Fig.1

Photograph of the whole brain of fowl.

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Fig.2

Sagittal Section of the cerebellum of fowl showing disposition of its various folia.

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Fig.3

Close up photograph of the sagittal section of cerebellum of fowl showing all the labules (I to X).

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