Cerebellum and its connections
Cerebellum receives afferent impulses from all receptors stimulating during locomotion (from proprioreceptors, vestibular, visual, and acoustical). Cerebellum influences onto red nucleus and reticular formation of brainstem, which send impulses to spinal cord gamma-motoneurons regulating muscle tone.
Signs of a cerebellum lesion
Static ataxy – it is infringement of statics in rest (shaking).
Dynamic ataxy – it is locomotion coordination disorder at performance of targeted movements. A tremor of extremities – so-called intentional tremor – is observed. Walking is shaky, “drunk”.
Cause of cerebellar ataxy is the disturbance of сonjugative work of muscles – agonists and antagonists, disproportion of locomotion – dysmetria. Rapid change of one locomotion by others, inverse ones – adiadohokinesis (pronation and supination) is impeded.
Asynergia – it is disturbance of mutual conjugated movements.
Atony – it is loss of muscle tone (anterior part of cerebellar posterior lobe is responsible).
Astasia – it show up in ability of muscles to realize oscillating motions (tremor, shaking) and in disabilities to conjoint tetanic contraction.
Tremor – it is oscillating motions in various body segments.
The excision of cerebellum does not cause disappearance of reflectory responses; tonic reflexes of brainstem are non-changed.
Assays (probes) for an examination of cerebellar functions
Examination of coordination and dynamic ataxy
Assay of Romberg – it is examination of equilibrium in rest. Ataxias arise at a lesion of spinal cord posterior funicles and vestibular apparatus.
In case of a cerebellar hemispheres lesion the patient is inclined to the side of the focus of a lesion.
In case of a lesion of big hemispheres cortex patient falls to the side opposite to the focus.
Phalanx walking – it is step-by-step movements sideways. In case of a lesion leg are excessively extended and are thrown out forward.
Test for an assessment of functions of a cerebellum
Examination of coordination and dynamic ataxy
Finger-nose test (digitonasal sign) – locomotor ataxia, dysmetrias, tremor of fingers are detected.
Genucalcaneal (heel-knee) test – presence of locomotor ataxia and dysmetrias of lower extremities are detected.
Diadochokinesia test – synchronism and uniformity of movements are detected. On the side of a cerebellum lesion the lag of extremities is determined.
Examination of an asynergia
Babynsky test. In reclining position with crossed arms it is necessary to get up. At a cerebellum lesion leg rise, and the body is remained to lie.
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Оzhehovsky test. Support by palms of stretched arms should be done. At sudden disappearance of support the examinated person in norm is inclined back, the patient falls forward.
Stuart-Holms test. Forearm and hand are in position of pronation, hand is clenched in fist. The doctor tries to extend patient's forearm. Healthy person's muscles-antagonists contract quickly and stroke is prevented.
In case of cerebellum lesion
Speech is slowed, explosed (loss of smoothness), scanding (accents are not on necessary syllable) (dysarthria).
Nystagmus is more often horizontal;
Hypomyotonia (muscular hypotonia). Volume of movements is enlarged;
Handwriting disorder is observed. Handwriting is irregular, bold (macrography).
Extrapyramidal part of nervous system
Strio-pallidal part.
Extrapyramidal system includes structures of big hemispheres cortex, subcortical ganglions, cerebellum, reticular formation, descending and ascending tracts.
Functions: it provides involvement of all motor systems of brain, perfects movements making them economic and automatic.
Strio-pallidal system:
Striatum (more young formation) includes caudate nucleus and putamen.
Pallidum includes globus pallidus, black matter, red nucleus, subthalamic nucleus.
Myelination of striatal tracts comes to end of 5-th month age. Newborns possess pallidal features.
Cortical center of extrapyramidal part includes premotor area (field 6), temporal and occipital areas.
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