CEREBELLUM

 In man, after the cerebral hemispheres, it is the most voluminous encephalic organ (see brain ). It presents on the surface a layer of gray matter applied over a central mass of white matter, in continuity with this. The gray cortex covers all the inequalities determined by the particular architecture of the organ, which results from lobules, which in turn are formed by laminae and these lamellae.

The connections of the cerebellum with other parts of the nervous system are made by means of bundles of fibers, and peduncles, which are in continuation of the central mass of white matter, the medullary body, contained in the organ. The inferior cerebellar peduncles connect the cerebellum to the medulla oblongata; the middle of the peduncle to the bridge; the peduncles superior to the lamina quadrigemina.

The nerve pathways of the cerebellum are classified into afferent and efferent. Afferents come from other nerve centers and terminate in the cerebellum; conversely, the efferents arise in the cerebellum and are directed to other nerve centers.

Various fiber systems arrive at the cerebellum via the inferior cerebellar peduncle from gray matter nuclei of the spinal cord, medulla oblongata, and pons. These gray nuclei are in turn directly or indirectly related to the termination of the sensory roots of spinal nerves and cerebral nerves. Important are the connections that are thus established between the vestibule and the semicircular canals of the organ of hearing, on the one hand, and the cerebellum on the other, by means of the vestibular nerve (of the acoustic), which is the nerve of the 'equilibrium.

An important system of afferent pathways reaches the cerebellum via the middle cerebellar peduncle. They have their first origin in the cortex of one cerebral hemisphere; they break off in gray nuclei found in the basal part of the pons, and terminate for the most part after crossing the median line; thus they mainly reach the cerebellar cortex of the side opposite to that of their origin.

The main efferent pathway of the cerebellum results from a system of fibers that originates in the cortex of the organ and, with the intermission of a nucleus of gray matter ( nucleus dentate ), contained in each cerebellar hemisphere in the middle of the white matter, passes into the superior cerebellar peduncle, heading towards the midbrain. It reaches it after crossing, and for the most part, it ends in a nucleus located in the dorsal part of the midbrain ( red nucleus ). Some of its fibers go up to the optic thalamus; others descend to the dorsal part of the pons and perhaps even further down to the spinal cord. Another efferent pathway, moving from the cerebellar cortex, reaches one of the terminal nuclei of the vestibular nerve of the acoustic.

In order to understand the importance of the various connections that the efferent pathways of the cerebellum acquire at their termination, it should be kept in mind that from all the nuclei of gray matter, to which they arrive, fibers depart, which relate to nuclei of origin of nerves cerebral and spinal motors.

In summary, it must be admitted, on the basis of anatomical data, that the functional activity of the cerebellum can be determined by sensory stimuli that reach it from the spinal cord, medulla oblongata, and pons; from those coming from the vestibule and the semicircular canals of the organ of hearing; finally from those that come from the cortex of the cerebral hemispheres. The reactions of the cerebellum to these various stimulations are felt almost exclusively indirectly on nuclei of cerebral and spinal motor nerves, and thus ultimately on the muscular apparatus.

The association fibers which go from one point to another of the cerebellar cortex, and the others which join this to some nuclei of gray matter contained in the organ, establish a functional solidarity between the various parts of the cerebellum.

Diseases of the cerebellum.

 - The cerebellum, due to family hereditary causes, can be tarnished by a particular fragility (cerebellar heredoataxia, Friedreich's disease); it may be involved in an infectious process (malaria, abdominal typhus) or toxic (alcoholism, uremia), or present lesions in diseases of other parts of the brain (tumors, multiple sclerosis, tabes, paralytic dementia, etc.).

Diseases of the cerebellum proper can be acquired during fetal life (agenesis) or after birth; manifest with a characteristic syndrome (dizziness, staggering gait, dysmetria, intentional or kinetic tremors, static tremor, nystagmus, speech disturbances, asynergy, adiadochokinesia, hypotonia, hypoesthesia, etc.).

Developmental anomalies consist of a complete (very rare) lack of the entire organ (total agenesis) or a partial lack (unilateral or bilateral agenesis). Atrophies are divided into primary (unilateral or bilateral) and associated (cerebello-cerebral, cerebello-spinal, cerebro-cerebello-spinal). Léjonne and Lhermitte described olivorubrocerebellar atrophy; A. Thomas, lamellar atrophy; Dejerine and Thomas, olivopontocerebellar atrophy.

Acquired diseases.

 - Traumatisms: wounds and fractures of the skull can directly or indirectly damage the various lobes of the organ and compromise its function definitively or temporarily; in general they have a very serious prognosis.

Hemorrhage:

 they are due to arteriosclerosis, infectious arteritis and above all syphilis. Hemorrhagic foci may not give rise to any clinical symptoms, those of a certain size manifest themselves with an apoplectic stroke mostly not followed by hemiplegia.

Softenings:

 they are even rarer than hemorrhages and are mostly due to thrombosis due to arteriosclerosis or luetic arteritis. The cerebellar-type symptomatology is more or less rich according to the extent and extension of the disease and begins progressively, rarely with a stroke.

Tumors:

 from a clinical point of view they include: neoplasms or blastomas (gliomas, sarcomas, psammomas, lipomas, endotheliomas, etc.), granulomas (gums, tuberculomas), cysts (parasitic, inclusion, serous) and vascular tumors ( aneurysms, angiomas) extremely rare. General symptoms: early and often predominantly occipital headache, painful craniopercussion, vomiting, stasis papilla, mental numbness, radiographic signs of intracranial hypertension, cerebrospinal fluid hypertension and albumin-cytological dissociation, etc. Localization symptoms: vertigo in the form of a sensation of movement of the body or surrounding objects, or as an indefinable feeling of lightheadedness ( giddily feeling), asthenia and atony of the limbs, asynergy, dysmetria, etc. In tumors of the cerebellar vermis, balance disorders predominate, the signs of cerebellar deficit are bilateral and, according to Duret, opisthotonus can be found. Proximity symptoms for indirect compression: deficits of the cranial nerves and more frequently of the abducens, common oculomotor, facial, trigeminal and acoustic nerves.

Abscesses:

 very often otitic or traumatic in origin, mostly single; they can be encysted or diffluent, of very variable volume and site in individual cases; are due to ordinary pyogenic germs or anaerobes. Warning symptoms: facial and abducens nerve paralysis, labyrinthitis following purulent otitis media. Premonitory symptoms: fever, easy irritability, apathy, depressive state. General symptoms of the state period: depressive headache, now continuous, now intermittent, tenderness on percussion and compression on the occipital region, neck stiffness, vomiting, fever, bradycardia, hypertension and cerebrospinal fluid lymphocytosis. Brain symptoms: as in tumors.