The cerebellum is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or even larger. In humans, the cerebellum plays an important role in motor control and cognitive functions such as attention and language as well as emotional control such as regulating fear and pleasure responses, but its movement-related functions are the most solidly established. The human cerebellum does not initiate movement, but contributes to coordination, precision, and accurate timing: it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity. Cerebellar damage produces disorders in fine movement, equilibrium, posture, and motor learning in humans.
The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions, ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers, and therefore deals with the autonomic functions of breathing, heart rate and blood pressure as well as the sleep–wake cycle. "Medulla" is from Latin, ‘pith or marrow’. And "oblongata" is from Latin, ‘lengthened or longish or elongated'.
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The brainstem is the stalk-like part of the brain that connects the forebrain with the spinal cord. In the human brain, the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch.
In neuroanatomy, a neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable neurotransmission. Neurons are connected by a single axon, or by a bundle of axons known as a nerve tract, or fasciculus. Shorter neural pathways are found within grey matter in the brain, whereas longer projections, made up of myelinated axons, constitute white matter.
The inferior olivary nucleus (ION) is a structure found in the medulla oblongata underneath the superior olivary nucleus. In vertebrates, the ION is known to coordinate signals from the spinal cord to the cerebellum to regulate motor coordination and learning. These connections have been shown to be tightly associated, as degeneration of either the cerebellum or the ION results in degeneration of the other.
The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. The structure is located in the tegmentum of the midbrain next to the substantia nigra and comprises caudal magnocellular and rostral parvocellular components. The red nucleus and substantia nigra are subcortical centers of the extrapyramidal motor system.
The pontine nuclei are all neurons of the ventral pons collectively. Corticopontine fibres project from the primary motor cortex to the ipsilateral pontine nucleus; pontocerebellar fibers then relay the information to the contralateral cerebellum via the middle cerebellar peduncle.
Climbing fibers are the name given to a series of neuronal projections from the inferior olivary nucleus located in the medulla oblongata.
The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.
Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side:
The basilar part of pons, also known as basis pontis, is the ventral part of the pons; the dorsal part is known as the pontine tegmentum.
The myoclonic triangle is an important feedback circuit of the brainstem and deep cerebellar nuclei which is responsible for modulating spinal cord motor activity.
The spino-olivary tract is located in the anterior funiculus of the spinal cord and provides transmission of unconscious proprioception and is involved in balance. This tract carries proprioception information from muscles and tendons as well as cutaneous impulses to the inferior olivary nuclei, located in the olivary bodies, also known as the olives. The olivary bodies are located in the medulla oblongata in the brainstem. Other tracts that carry proprioception are the DSCT, cuneocerebellar tract, dorsal column–medial lemniscus pathway, and the VSCT.
The juxtarestiform body is the smaller, medial subdivision of each inferior cerebellar peduncle.
The pontocerebellar fibers are the second-order fibers of the corticopontocerebellar tract. They arise from the nuclei pontis as the second leg of the path of the corticopontocerebellar tract, and deecussate (cross-over) in the pons before passing through the middle cerebellar peduncle to reach and terminate in the contralateral posterior lobe of cerebellum (neocerebellum). It is part of a pathway involved in coordination of voluntary movements.
The central tegmental tract is a structure in the midbrain and pons.
Corticopontine fibers are projections from the cerebral cortex to the pontine nuclei of the ventral pons. They represent the first link in a cortico-cerebello-cortical pathway mediating neocerebellar control of the motor cortex. The pathway is especially important for voluntary movements.
The anatomy of the cerebellum can be viewed at three levels. At the level of gross anatomy, the cerebellum consists of a tightly folded and crumpled layer of cortex, with white matter underneath, several deep nuclei embedded in the white matter, and a fluid-filled ventricle in the middle. At the intermediate level, the cerebellum and its auxiliary structures can be broken down into several hundred or thousand independently functioning modules or compartments known as microzones. At the microscopic level, each module consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry.
