Cerebellum Anatomy PDF

Cerebellum: [Learning outcomes:] - Identify and describe the gross morphological features of the cerebellum. - Identify and describe the superior, middle and inferior cerebellar peduncles and what pathway(s) they contain. - Identify and describe the functional regions of the cerebe...

Cerebellum: [Learning outcomes:] - Identify and describe the gross morphological features of the cerebellum. - Identify and describe the superior, middle and inferior cerebellar peduncles and what pathway(s) they contain. - Identify and describe the functional regions of the cerebellum. - Identify and describe the internal structures of the cerebellum (cortex, its cellular components and connections, white matter and deep cerebellar nuclei). - Describe the mossy fibres and climbing fibres. - Describe the cerebellar pathways (inputs and outputs). - Describe the function of the cerebellum as well as signs and symptoms following a lesion/injury to the cerebellum. [Finger-to-nose test:] Finger-to-nose test \| - cerebellar lesions or intoxication = not being able to do this test [Where is the cerebellum?]  - cerebellum = 4 - lies behind the brain stem [Anatomy of the cerebellum:] - has two hemispheres - hemispheres are connected via the vermis - Surface -- highly convoluted (ridges or folds): Folia (singular: folium) A close-up of a brain Description automatically generated [Cerebellar peduncles:]  - 3 pairs of cerebellar peduncles = superior, middle (largest) and inferior - cerebellar peduncles = nerve fibres/pathways that travel in or out of the cerebellum [superior cerebellar peduncle:]  - almost entirely an efferent pathway - most of the fibres that form the peduncle are efferent fibres - deep cerebellar nuclei = deep in the white matter of the cerebellum - send projections to the thalamus + superior colliculus via the superior peduncle. - thalamus primary motor + premotor cortex. - superior colliculus neurons deep within the colliculus [middle cerebellar peduncle:]  - An afferent pathway - most of the cell bodies that give rise to this pathway - the pontine nuclei (contralateral pons). - basilar part of the pons -- grey matter that is spread across this region = pontine nuclei - cortex sends projections to the pontine nuclei via corticopontine fibres - corticopontine fibres synapse at the pontine nuclei - neurons in the pontine nuclei project neurone fibres (transverse pontine fibres) out - transverse pontine fibres travel to the contralateral cerebellum via the middle cerebellar peduncle [Inferior cerebellar peduncle:] - smallest peduncle but most complex - Contains both afferent and efferent pathways - Afferent (arrive from) pathways - Vestibular nuclei - Spinal cord - Brainstem - Efferent (project into) pathway - Vestibular nuclei - Reticular formation [lobes of the cerebellum:] - anterior lobe - middle (posterior) lobe -- largest lobe - folcculonodular lobe  - primary fissure = separates the anterior + middle lobe - horizontal fissure -- no significance but can help divide the surface into superior + inferior regions. cerebellum can be divided into different lobes based on anatomy, but it can be divided into functional lobes depending on their sources of input. [which lobe is the most primitive (oldest)?] = flocculondular lobe (vestibulocerebellum)  - vestibular nuclei project into the flocculondular lobe [Function regions of the cerebellum:] - not the same as the divisions using anatomy A diagram of a brain Description automatically generated - Archicerebellum (Vestibulocerebellum) - receives input from the vestibular nuclei. - maintain balance (equilibrium) + involved in vestibulo-ocular regulation - Paleocerebellum (spinocerebellum) - muscle tone and posture - receives projections + proprioceptive information from the spinal cord - median zone (vermis)- control/movement of proximal muscles (e.g. head, neck & trunk) - paramedian zone (intermediate zone) - movement of distal muscles (e.g. hands & feet - Neocerebellum (cerebrocerebellum) - project into the cerebellum indirectly - well developed in primates and particularly prominent in human. - receives input indirectly from the cerebral cortex - involved in more complex movement i.e.: - coordination of movement - planning and execution of movement  [Neocerebellum (cerebrocerebellum)] A diagram of a structure Description automatically generated - cortex sends corticopontine fibres to the pontine nuclei in the basilar part of the pons + synapse with the fibres in this region. - transverse pontine fibres are projected across the midline to contralateral cerebral cerebellum via the middle cerebellar peduncle. [Vestibulo-ocular reflex] = a mechanism which maintains the eyes on a visual target when the head is moving. - Enables clear vision during head movements by producing compensatory eye movements. - A simple form of motor learning & adaptation [Structures of the cerebellum:] A diagram of a brain Description automatically generated - white matter is inside and grey matter on the outside - the white matter contains intracerebellar nuclei or deep cerebellar nuclei - 3 layers of the cerebellar cortex: - molecular layer -- outermost layer - Purkinje cell layer - granular layer -- have a lot of granule cells [Cerebellar Cortex:]  - granular layer appears denser + darker on histological staining - lots of granular cells packed. [Molecular layer:] Contains two cell types - Stellate cells - Star-shaped - receive input from the parallel fibres and provides input to the Purkinje cells - Basket cells - projects very long axons and synapse with Purkinje cells [Purkinje cell layer:] Contains Purkinje cells: - **only the output cells** of the cerebellar cortex -- send projections out. - Extensively branched dendritic tree extend into the molecular layer. - Receive input from parallel fibres and climbing fibres. - Long axons -- synapse with cells of one of the intracerebellar nuclei (deep within the white matter) https://upload.wikimedia.org/wikipedia/en/6/68/BasketCellsCerebellum.jpg [Granular layer:] Contains: - Granule cells - Granule cells: granular layer is packed with granule cells. - Each cell give rise 4-5 dendrites which make claw like ending - Synapse with **mossy fibres** - project axons into the molecular layer + bivariate (split into two) = creating "**parallel fibres**" which synapse with Purkinje cells - Golgi cells - Not as many as granule cells - Receive input from the parallel fibres - provide an inhibitory feedback to the granule cells [Cerebellar cortex] - Each layer contains different neurons which have different functions. [Cerebellar inputs (afferent pathways):] Cerebellum has two main inputs: - - 1. Mossy fibres - Originate from the spinal cord, brainstem (including the axons from the pontine nuclei). - Mossy -- resembling moss because of the appearance of their synaptic terminals. - Synapse on granule cells and send projections to the deep cerebellar nuclei. 2. Climbing fibres - arise in the contralateral inferior olivary nucleus. - each Purkinje cell receives numerous synaptic contacts from a single climbing fibre -- one fibre makes several contacts - also send input to the deep cerebellar neurones.  - two main inputs are mossy fibres + climbing fibres - embedded in the white matter - 4 paired nuclei (from lateral to medial) - Dentate nucleus - associated with the middle cerebellum - largest, shape of a crumpled bag - Emboliform nucleus - Globose nucleus - Fastigial nucleus - the last three nuclei cannot be seen with the naked eye [Neocerebellum:] A diagram of a structure Description automatically generated  - neocerebellum -- occupies the lateral parts of the cerebellar hemisphere. - punkinje cells in this region send projections to dentate nucleus send fibres out aceoss the midline to the thalamus via the superior cerebellar peduncle [Cerebellar pathways:] - Input (afferent) http://bme2.aut.ac.ir/%7Etowhidkhah/MotorControl/Notes/Cerebellum-Vahdat/Book/fulltextservice/ct%7B06b9ee1beed594190674f1983457a7dd32af6a0d5a4c9892%7E49/da6c42ff3.gif.png - Spinal cord - Brainstem - Cortex (via brainstem) - Middle of the vermis = Visual & auditory inputs -- provide additional sensory signals that supplement the proprioceptive information regarding body position and motion. - median zone (vermis) + paramedian zone form the spinal cerebellum -- proprioceptive information from face and spinal cord terminates here - Output (efferent) - The axons of the neurons that form the deep cerebellar nuclei constitute the efferent outflow from the cerebellum. - Shows output pathway: Functions of the cerebellum: - influences/regulates voluntary movement - controls the maintenance of balance, posture & muscle tone - motor co-ordination; coordinates movement - involved in motor learning and behaviour Cerebellum monitors movement and detect errors: - graduates and harmonise muscle tone, maintain normal body posture. - Permits voluntary movement to take place smoothly with precision and efficiency (least required effort but effective). - Not able to initiate muscle movement. lesions of the cerebellum: - **Intention tremor:** occurs when attempting to perform movement - Tremor: involuntary, rhythmic muscle contraction. - **Hypotonia**: decreased muscle tone. - **Cerebellar ataxia:** - ataxic gait (walking) -- staggering, wide-based & unsteady. (ataxia: lack of voluntary coordination of muscle movement) - **Dysarthria** - slowness of speech - scanning of speech: spoken words are broken up into separate syllables, separated by a noticeable pause.