CEREBELLUM BRAINS BLOOD SUPPLY THE CEREBELLUM CEREBELLUM The - PowerPoint PPT Presentation

CEREBELLUM BRAIN’S BLOOD SUPPLY

THE CEREBELLUM

CEREBELLUM The principal function of the cerebellum is to regulate and maintain balance, and to co-ordinate timing and precision of body movements . The cerebellum has multiple connections with the cerebral cortex , reticular formation in the brainstem, thalamus and vestibular nuclei . Through these intricate connections, the cerebellum constantly monitors proprioceptive sensory input from joints, muscles and tendons, and accordingly refines and co-ordinates the contractions of skeletal muscles. However, unlike the cerebral cortex of the primary motor area, the cerebellum is incapable of initiating movement, nor is the cerebellum involved in the conscious perception of somatic or visceral sensations.

CEREBELLUM The cerebellum is located dorsal to the pons and the medulla. The fourth ventricle is found between the cerebellum and the dorsal aspect of the pons. The cerebellum functions in the planning and finetuning of skeletal muscle contractions . The cerebellum performs these tasks by comparing an intended with an actual performance.

CEREBELLUM The cerebellum consists of a midline vermis and 2 lateral cerebellar hemispheres . The cerebellar cortex consists of multiple parallel folds that are referred to as folia. The grey and white substance of cerebellum on the sagittal section form a typical structure called “ arbor vitae - the tree of life “.

CEREBELLUM The cerebellum is connected to the brain stem by three peduncles The cerebellar peduncles: Superior cerebellar peduncle - primary output of the cerebellum with mostly fibers carrying information to the midbrain. Middle cerebellar peduncle - carry input fibers from the contralateral cerebral cortex. Inferior cerebellar peduncle - receives ipsilateral proprioceptive information from the spinal cord.

CEREBELLUM The cerebellar cortex contains several maps of the skeletal muscles in the body. The topographic arrangement of maps of the skeletal muscles: • the vermis controls the axial and proximal musculature of the limbs, • the intermediate part of the hemisphere controls distal musculature, • the lateral part of the hemisphere is involved in motor planning, • the flocculonodular lobe is involved in control of balance and eye movements

CEREBELLUM Major input to the cerebellum travels in the inferior cerebellar peduncle (ICP) and middle cerebellar peduncle (MCP) . Major outflow from the cerebellum travels in the superior cerebellar peduncle (SCP) .

CEREBELLUM The 3 cell layers of the cortex are: • the molecular layer • the Purkinje layer • the granule cell layer The molecular layer is the outer layer and is made up of basket and stellate cells as well as parallel fibers, which are the axons of the granule cells. The extensive dendritic tree of the Purkinje cell extends into the molecular layer.

CEREBELLUM The Purkinje layer is the middle and most important layer of the cerebellar cortex. All of the inputs to the cerebellum are directed toward influencing the firing of Purkinje cells , and only axons of Purkinje cells leave the cerebellar cortex. A single axon exits from each Purkinje cell and projects to one of the deep cerebellar nuclei or to vestibular nuclei of the brain stem.

CEREBELLUM The granule cell layer is the innermost layer of cerebellar cortex The granule cell is the only excitatory neuron within the cerebellar cortex . All other neurons in the cerebellar cortex, including Purkinje, Golgi, basket, and stellate cells, are inhibitory .

CEREBELLUM From medial to lateral, the deep cerebellar nuclei in the internal white matter are the fastigial nucleus , interposed nuclei , and dentate nucleus . Two kinds of excitatory input enter the cerebellum in the form of climbing fibers and mossy fibers . Both types influence the firing of deep cerebellar nuclei by axon collaterals.

CEREBELLUM These afferent fibers (mossy and climbing) reach the cerebellum via the inferior and middle cerebellar peduncles, which connect the cerebellum with the brain stem. These afferent fibers (mossy and climbing) are excitatory and project directly or indirectly via granule cells to the Purkinje cells of the cerebellar cortex.

CEREBELLUM The axons of the Purkinje cells are inhibitory. The axons of the Purkinje are the only outflow from the cerebellar cortex. The axons of the Purkinje cells project to and inhibit the deep cerebellar nuclei (dentate, interposed, and fastigial nuclei) in the medulla.

CEREBELLUM From the deep nuclei , efferents project mainly through the superior cerebellar peduncle and drive the upper motor neurons of the motor cortex . The efferents from the hemisphere project through the dentate nucleus , to the contralateral ventral lateral/ventral anterior nuclei of the thalamus, to reach the contralateral precentral gyrus . Right side of Cb controls muscles on right side of the body

CEREBELLUM These influence contralateral lower motor neurons via the corticospinal tract . Lesions of the cerebellum give rise to symptoms and signs on the same side of the body . Unilateral lesions of the cerebellum will result in a patient falling toward the side of the lesion .

CEREBELLUM Hallmarks of cerebellar dysfunction include ataxia , intention tremor , dysmetria , and dysdiadochokinesia . ATAXIA is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes and abnormalities in eye movements. DYSMETRIA is a type of ataxia - lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye.

CEREBELLUM DYSDIADOCHOKINESIA often abbreviated as DDK , is the medical term for an impaired ability to perform rapid, alternating movements Thrombosis of the posterior inferior cerebellar artery (PICA) gives rise to a characteristic syndrome ( PICA syndrome ) marked by ataxia and hypotonia of the ipsilateral limbs owing to involvement of the inferior cerebellar peduncle and cerebellar cortex, signs of cranial nerve involvement (V to X) and contralateral loss of pain and thermal sensibility (spinothalamic tract involvement).

CEREBELLUM Examination of cerebellar function: TAXIS - the finger-to-nose test and heel-to-shin test with and with out eye control. Damage of neocerebellum leads to ipsilateral problems with taxis.

CEREBELLUM Examination of cerebellar function:

CEREBELLUM Examination of cerebellar function: REBOUND PHENOMENA – inability to stop the movement after removing the contra-pressure which is generated by examiner.

CEREBELLUM Examination of cerebellar function: TEST OF TRUNK RETROFLEXION (GROSS ASYNERGY ) - standing patient, examiner performs a dorsal pull which is normally followed by flexion of lower limbs - in disease of cerebellum this synergy is impaired and patient usually falls in the direction of the pull.

CEREBELLUM Examination of cerebellar function: SMALL ASYNERGY - patient is unable to sit up from a supine position without the help of his/her upper limbs and the elevation of the lower limb on the side of the lesion. DIADOCHOKINESIS - fast alternation of antagonist movements (pronation and supination, flexion and extension) of upper limbs simultaneously. We search for asymmetry, rhythm disruptions and movement slowness.

ARTERIAL SUPPLY OF THE BRAIN

ARTERIAL SUPPLY The arterial supply of the brain is derived from the internal carotid and vertebral arteries , which lie, together with their proximal branches, within the subarachnoid space at the base of the brain. The INTERNAL CAROTID ARTERY arises from the bifurcation of the common carotid artery, ascends in the neck and enters the carotid canal of the temporal bone. The INTERNAL CAROTID ARTERY ascends in the neck and enters the carotid canal of the temporal bone.

ARTERIAL SUPPLY The INTERNAL CAROTID ARTERY has petrous , cavernous and intracranial parts .

ARTERIAL SUPPLY PETROUS PART The petrous part of the internal carotid artery ascends in the carotid canal. The petrous part of the internal carotid artery curves anteromedially and then superomedially above the cartilage that fills the foramen lacerum, and enters the cranial cavity. The petrous part of the ICA lies at first anterior to the cochlea and tympanic cavity The petrous part of the ICA is separated from the latter and the pharyngotympanic tube by a thin, bony lamella that is cribriform in the young and partly absorbed in old age.

ARTERIAL SUPPLY PETROUS PART Further anteriorly, petrous part of the ICA is separated from the trigeminal ganglion by the thin roof of the carotid canal, although this is often deficient. The petrous part of the ICA is surrounded by a venous plexus and by the carotid autonomic plexus, derived from the internal carotid branch of the superior cervical ganglion.

ARTERIAL SUPPLY PETROUS PART The petrous part of the ICA gives rise to two branches : • caroticotympanic artery • pterygoid artery The caroticotympanic artery is a small, occasionally double, vessel which enters the tympanic cavity by a foramen in the carotid canal and anastomoses with the anterior tympanic branch of the maxillary artery and the stylomastoid artery. The pterygoid artery is inconsistent: when present, it enters the pterygoid canal with the nerve of the same name, and anastomoses with a (recurrent) branch of the greater palatine artery.