The pons is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
The brainstem is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.
The ventral spinocerebellar tract conveys proprioceptive information from the body to the cerebellum. It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract. Both these tracts involve two neurons. The ventral spinocerebellar tract will cross to the opposite side of the body first in the spinal cord as part of the anterior white commissure and then cross again to end in the cerebellum, as compared to the dorsal spinocerebellar tract, which does not decussate, or cross sides, at all through its path.
The dorsal spinocerebellar tract conveys proprioceptive information from proprioceptors in the skeletal muscles and joints to the cerebellum.
The cerebellar vermis is located in the medial, cortico-nuclear zone of the cerebellum, which resides in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior surface of the cerebellum, dividing it into anterior and posterior lobes. Functionally, the vermis is associated with bodily posture and locomotion. The vermis is included within the spinocerebellum and receives somatic sensory input from the head and proximal body parts via ascending spinal pathways.
The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.
The dentate nucleus is a cluster of neurons, or nerve cells, in the central nervous system that has a dentate – tooth-like or serrated – edge. It is located within the deep white matter of each cerebellar hemisphere, and it is the largest single structure linking the cerebellum to the rest of the brain. It is the largest and most lateral, or farthest from the midline, of the four pairs of deep cerebellar nuclei, the others being the fastigial nucleus and the globose and emboliform nuclei which together are referred to as the interposed nucleus. The dentate nucleus is responsible for the planning, initiation and control of voluntary movements. The dorsal region of the dentate nucleus contains output channels involved in motor function, which is the movement of skeletal muscle, while the ventral region contains output channels involved in nonmotor function, such as conscious thought and visuospatial function.
The interposed nucleus is part of the deep cerebellar complex and is composed of the globose nucleus and the emboliform nucleus. It is located in the roof of the fourth ventricle, lateral to the fastigial nucleus. It receives its afferent supply from the anterior lobe of the cerebellum and sends output via the superior cerebellar peduncle to the red nucleus.
The fastigial nucleus is located in the cerebellum. It is one of the four deep cerebellar nuclei, and is grey matter embedded in the white matter of the cerebellum.
The flocculus is a small lobe of the cerebellum at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule. Like other parts of the cerebellum, the flocculus is involved in motor control. It is an essential part of the vestibulo-ocular reflex, and aids in the learning of basic motor skills in the brain.
In the medulla oblongata, the arcuate nucleus is a group of neurons located on the anterior surface of the medullary pyramids. These nuclei are the extension of the pontine nuclei. They receive fibers from the corticospinal tract and send their axons through the anterior external arcuate fibers and medullary striae to the cerebellum via the inferior cerebellar peduncle.
Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side:
The posterior thoracic nucleus, is a group of interneurons found in the medial part of lamina VII, also known as the intermediate zone, of the spinal cord. It is mainly located from the thoracic vertebra T8 to lumbar L3-L4 levels and is an important structure for proprioception of the lower limb.
Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex. This cortex is typically represented as a sensory homunculus which orients the specific body parts and their respective locations upon the homunculus. Areas such as the appendages, digits, penis, and face can draw their sensory locations upon the somatosensory cortex. The areas which are finely controlled have larger portions of the somatosensory cortex whereas areas which are coarsely controlled have smaller portions. Areas such as the viscera do not have sensory locations on the post central gyrus.
The cerebellothalamic tract or the tractus cerebellothalamicus, is part of the superior cerebellar peduncle. It originates in the cerebellar nuclei, crosses completely in the decussation of the superior cerebellar peduncle, bypasses the red nucleus, and terminates in posterior division of ventral lateral nucleus of thalamus. The ventrolateral nucleus has different divisions and distinct connections, mostly with frontal and parietal lobes. The primary motor cortex and premotor cortex get information from the ventrolateral nucleus projections originating in the interposed nucleus and dentate nuclei. Other dentate nucleus projections via thalamic pathway transmit information to prefrontal cortex and posterior parietal cortex. The cerebellum sends thalamocortical projections and in addition may also send connections from the thalamus to association areas serving cognitive and affective functions.
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 "microzones". At the microscopic level, each module consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry.
