Cerebellum
The cerebellum is a structure highly involved at ensuring the movement plans are refined, realistic (eg in line with the current body position), and general coordination.
Voluntary movements can occur without the cerebellum but they are clumsy and disorganised. (drunken gait for example is similar)
Anatomy of the cerebellum
The cerebullum has 2 hemispheres demarcated by the anterior cerebellar incisure, posterior cerebellar incisure, and the vermis. each hemisphere has 2 lobes, the anterior and posterior. However the functional divisions lie across different boundaries.
There are 3 main divisions of the hemispheres,
- Spinocerebellum This is the medial 50% of the cerebellum and works to balance the posture and movement of the trunk and limbs
- Cerebrocerebellum This is the lateral portions of the cerebellum and are important for planning movement
- Vestibulocerebellum The is is the flocculi and the nodulus which do balance, head and eye movements
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- deep nuclei The deep nuclei are 3 pairs of nuclei, the dentate, interposed and fastigial, which act to do calculations to refine the
Cerebellum physiology
There are 3 peduncles which connect the cerebellum to the brainstem, there is the superior, middle and inferior. These dont really look like distinct structures and are more sections of one large peduncle.
The SCP is most efferent information away from the cerebellum, and the MCP is mainly afferent to the cerebellum. The ICP does both directions.
Inputs: Inputs to the cerebellum are sensory data from the limbs, and motor plans from the motor cortex and premotor cortex.
Outputs: outputs to the spinal cord and the brainstem which directly influence motor control. and outputs tot he motor areas in the thalamus and the brainstem which helps refine movements.
Cerebellar cortex vs DCN
The cerebellar cortex is involved with comparing sensory data to motor data but the movement refinement, on the go correction as well as learning is chiefly handled by the DCN.
Some symptoms of cerebellar dysnfucntions are loss of cooridination in muscle activity which can present as:
- Ataxia Inaccuracy in the speed force and distance of a movement.
- Tremor Involuntary oscillation of the limbs or trunk
- Nystagmus Rhythmic involuntary oscillation of the eyes
- Headache & vomiting
Cerebellar dysfunction
Brainstem
The brainstem is made of 3 parts: the midbrain, pons and medulla oblongata.
It is a compact and intricate structure with lots of tracts and pathways as well as nuclei for processing. It is also where 10 of the 12 cranial nerves emerge from.
The brainstem is made of 3 sections, the midbrain, pons and medulla.
The midbrain
The midbrain is immediatly below the diencephalon and is a big bridge for motor sensory and autonomic function (basically everything).
Important superficial structures are:
- Cerebral peduncles Crus Cerebri - little feet of cerebrum NOT cerebellar peduncles these are fibres descending from the cores to the brainstem and spinal cord. They also help anchor the cerebrum to the brainstem.
- Corpora quadrigemia Quadruplets This is a group of 4 colliculi (hills), a pair of superior colliculi which deals with certain visual signals (like fast moving or flying objects) and the inferior colliculi which deals with reflexive responses to noises which startle you.
- Substantia nigra Black substance These are neurons which contain melanin, as it is a chemical precursor to dopamine. They are involves with dopamine release and are thus atrophied in parkinsons disease. It is functionally linked to the basal nuclei
- Red nucleus This has extensive blood supply, leading to its red colour. it is a relay nucleus in some motor pathways.
- Cerebral aquaduct This is the passage from the 3rd to 4th vetnricle
- superior cerebellar peduncles These are 1 of 3 peduncles and connect the cerebellum to the brainstem and CNS
The pons
The pons means bridge, and it is a major connection between the cerebral cortex, cerebellum and spinal cord. It also had nuclei involved with breathing sleep-wake cycles and arousal. it also the origin of 4 cranial nerves, 5-8.
it had the pontine nuclei and the pneumotaxic centre, together with the medullary centre
The medulla
The medulla connects the pons to the spinal cord and the cerebellum to the spinal cord. It has the pyramidal decussation and 4th ventricle. It also is the origin of cranial nerves 9-12. It has many reflex centres which are important in controlling heart beat, vasocular tone, breathing as well as more refelxes.