the cerebellum of the brain
The cerebellum is the second largest structure of the brain after the cerebrum and about 11% of the brain's total mass. It is found dorsal to the pons and medulla and inferior to the occipital lobes of the cerebral hemispheres. The cerebellum receives input from the cerebral motor cortex, various brain stem nuclei, and sensory receptors, then provides the precise timing and appropriate patterns of skeletal muscle contraction for smooth, coordinated movements and agility. We have no conscious awareness of its functioning.
Anatomy
Bilaterally symmetrical, the cerebellum's two cerebellar hemispheres are connected medially by the vermis, which is highly wormlike in appearance. The surface is very convoluted, with fine, transversely oriented pleatlike gyri called folia. Each hemisphere is further divided by deep fissures into anterior, posterior, and flocculonodular lobes. The flocculonodular lobes are deep to the vermis and therefore invisible from a surface view. They receive inputs from the equilibrium apparatus of the inner ears, and adjust posture to maintain balance.
The cerebellum is much like the cerebrum in that it has a thin outer cortex of gray matter surrounding an interior of white matter. It also has small, deeply situated denate nuclei. Some of the most well-known neurons of the cerebellar cortex are the Purkinje cells, which are the only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum. As a result, the white matter resembles a branching tree, the pattern of which is referred to as the arbor vitae.
The cerebellum is regionally tied to the body in that its medial aspects influence activities of the trunk and girdle, while the intermediate aspects influence the more distal areas of the body. It is believed that the lateralmost parts of the cerebellum are more involved in planning rather than executing movements.
The cerebellum is much like the cerebrum in that it has a thin outer cortex of gray matter surrounding an interior of white matter. It also has small, deeply situated denate nuclei. Some of the most well-known neurons of the cerebellar cortex are the Purkinje cells, which are the only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum. As a result, the white matter resembles a branching tree, the pattern of which is referred to as the arbor vitae.
The cerebellum is regionally tied to the body in that its medial aspects influence activities of the trunk and girdle, while the intermediate aspects influence the more distal areas of the body. It is believed that the lateralmost parts of the cerebellum are more involved in planning rather than executing movements.
cerebellar peduncles
Three paired fiber tracts, known as the cerebellar peduncles, connect the cerebellum to the brain stem. Unlike the fibers to and from the cerebral cortex, however, almost all of these fibers connect to the same side of the body on which they are found in the cerebellum; that is to say, they are not contralateral. The superior cerebellar peduncles connect the cerebellum and midbrain and carry instructions from the deep cerebellar nuclei to the cerebral cortex via the thalamic relays. The cerebellum has no direct cerebral connection. The middle cerebellar peduncles carry one-way communication from the pons to the cerebellum, advising it of voluntary motor activities controlled by the motor cortex via relays in the pontine nuclei. The inferior cerebellar peduncles connect the medulla and cerebellum. Their function is to convey sensory information to the cerebellum from muscles throughout the body and vestibular nuclei in the brain stem.
cerebellar processing and cognitive function
The cerebellum follows a repeatable series of steps in its processing for motor activity:
1) The motor areas of the cerebral cortex notify it of their intent to initiate voluntary muscle contractions. This notification first passes through relay nuclei in the brain stem.
2) The cerebellum simultaneously receives this information and information from proprioceptors throughout the body regarding tension in muscles and tendons, as well as joint position, and from visual and equilibrium pathways. It uses this information to perform a full analysis of body position and momentum.
3) The cerebellar cortex calculates the best way to coordinate force, direction, and extent of muscle contraction to prevent overshoot, maintain posture, and ensure smooth, coordinated movements.
4) The superior peduncles send this plan for coordinating movement to the cerebral motor cortex. Cerebellar fibers also send information to brain stem nuclei, which influence motor neurons of the spinal cord.
The cerebellum also recognizes and predicts sequences of events so that it may adjust for multiple forces exerted on a limb during complex movements involving several joints. It also appears to be involved in word association and puzzle solving.
1) The motor areas of the cerebral cortex notify it of their intent to initiate voluntary muscle contractions. This notification first passes through relay nuclei in the brain stem.
2) The cerebellum simultaneously receives this information and information from proprioceptors throughout the body regarding tension in muscles and tendons, as well as joint position, and from visual and equilibrium pathways. It uses this information to perform a full analysis of body position and momentum.
3) The cerebellar cortex calculates the best way to coordinate force, direction, and extent of muscle contraction to prevent overshoot, maintain posture, and ensure smooth, coordinated movements.
4) The superior peduncles send this plan for coordinating movement to the cerebral motor cortex. Cerebellar fibers also send information to brain stem nuclei, which influence motor neurons of the spinal cord.
The cerebellum also recognizes and predicts sequences of events so that it may adjust for multiple forces exerted on a limb during complex movements involving several joints. It also appears to be involved in word association and puzzle solving.