Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Functions of the vestibular system • Semicircular The supraspinal control of movements canals • Recognition of angular acceleration of the head • Activation occurs only at the beginning and at the end of rotation – dynamic receptor • do not respond to rotation at constant velocity • Otolith organ • Utricle and saccule • Recognition of the position of the head in space as well as sensing the gravitation („graviceptor”) • Recognition of linear acceleration • Continuously active – static receptor Nystagmus The vestibuloocular reflex (VOR) • When do we see nystagmus? • Aim – To maintain retinal fixation, even if the head turns • Causes nystagmus • The reflex arch: 1. 2. 3. 4. 5. Sensor: Afferent pathway: Centre: Efferent pathway: Effectors: Semicircular canals 8th cranial nerve Brain stem 3rd and 6th cranial nerves medial and lateral rectus Only at the onset and offset of the rotation, not during the rotation (unless the eyes are open). When the rotation stops, opposite nystagmus is observed. • How to give the direction of the nystagmus? • Is it possible to evoke nystagmus without rotating the head? Yes, e.g. optokinetic nystagmus. Regulation of the mucle tone and maintaining erect posture Significance of nystagmus • Slow component: – Requires intact brain stem Cerebral cortex GP Cerebellar cortex • Fast component: Red nucleus – Requires intact cortex • Stimulation of the semicircular canals (e.g. Caloric stimulation): – Everything is O.K.: Full nystagmus – Cortical damage: Only the slow component – Brain stem damage: No eye movement Substantia nigra Cerebellar roof nuclei Otolith organ Inhibitory reticular formation Lateral vestibular nucleus α motoneurones γ motoneurones 1 Cerebellum Cerebellar lesions • Medial part – Coordination of trunk muscles • Necessary for walking and maintaining balance – Coordination of the extraocular muscles • Lateral part (Hemispheres) • Medial part: – Trunk and gait ataxia (swaying towards the lesion) – Nystagmus (more severe when the patient looks towards the side of the lesion) – Coordination of highly skilled voluntary movements (Review the histology of the cerebellar cortex) Cerebellar lesions 2. • Hemispheres – Ataxia – Dysmetria – Intention tremor – Dysarthria (scanning speech) – Dysdiadochokinesis – Adiadochokinesis – Alterations in the muscle tone – Dyssynergia (Decomposition of movements) – Rebound phenomenon Symptoms of basal ganglia disorders • Plus (or hyperkinetic) symptoms – TREMOR – RIGIDITY – CHOREA – ATHETOSIS – BALLISMUS • Minus (or hypokinetic) symptoms – AKINESIA Significance of the basal ganglia • Important points: • Basal ganglia are involved in the planning and preparation of the movements, as well as in ensuring the motivation • Incoming information reaching the basal ganglia arrives from the cerebral cortex, and after processing this information, they relay it mainly to the cerebral cortex • Their descending projections target the red nucleus, thus they are involved in the regulation of the muscle tone, too Parkinson’s disease (paralysis agitans) • Parkinson’s trias: – Akinesia – Rigidity – Tremor • Reason: – Damage of the dopaminergic nigrostriatal pathways • Treatment: – Application of L-DOPA 2 Huntington’s chorea • Incidence is 5-10/100,000 • Autosomal dominant with complete penetrance. • The mutant gene is found on the 4th chromosome • Characterised by the loss of GABA-ergic neurones Significance of the cortical motor areas (1) • Primary motor cortex – Actual performance of the motoric tasks • Premotor cortex – The activity of this region always preceds that recorded from the primary motor cortex – Involved in the „preparation” phase of the voluntary movements – Isolated lesion: apraxia (inability to perform complex motor tasks) Cortical areas involved in the motor function • Primary motor cortex • Precentral gyrus • Brodmann’s 4 area • Motoric „homunculus” • Praemotor area • „Non-primary” motor cortex • Brodmann’s 6 area • „True” preemotor area • Supplementary motor area Significance of the cortical motor areas (2) • Supplementary motor cortex – Organisation of complex motor movements, planning of the movement • True premotor area – It projects to the brain stem and spinal cord mainly – Particularly important at the beginning of the motor activity, it is responsible for ensuring and maintaining the appropriate posture, necessary for completing the motor required motor activity The corticospinal (pyramidal) tract • Composition – – – – 2×106 axons ~60%: primary motor cortex ~20%: premotor cortex ~20%: somatosensory cortex • Target – Grey matter of the spinal cord on the contralateral side α-motoneurones – Direct – monosynaptic – Indirect – polysynaptic γ-motoneurones – polysynaptic 3