The thalamus is a large mass of gray matter on the lateral walls of the third ventricle forming the dorsal part of the diencephalon. Nerve fibers project out of the thalamus to the cerebral cortex in all directions, known as the thalamocortical radiations, allowing hub-like exchanges of information. It has several functions, such as the relaying of sensory and motor signals to the cerebral cortex and the regulation of consciousness, sleep, and alertness.
In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three' and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.
The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.
The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.
The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway is the major sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception from the skin and joints. It transmits this information to the somatosensory cortex of the postcentral gyrus in the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in the gracile fasciculus and the cuneate fasciculus, tracts that make up the white matter dorsal columns of the spinal cord. At the level of the medulla oblongata, the fibers of the tracts decussate and are continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.
The medial lemniscus, also known as Reil's band or Reil's ribbon, is a large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of the gracile nucleus and the cuneate nucleus. The cell bodies of the nuclei lie contralaterally.
The solitary nucleus(SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) is a series of neurons whose cell bodies form a roughly vertical column of grey matter in the medulla oblongata of the brainstem. Their axons form the bulk of the enclosed solitary tract. The solitary nucleus can be divided into different parts including dorsomedial, dorsolateral, and ventrolateral subnuclei.
In neuroanatomy, thalamocortical radiations, also known as thalamocortical fibers, are the efferent fibers that project from the thalamus to distinct areas of the cerebral cortex. They form fiber bundles that emerge from the lateral surface of the thalamus.
A cranial nerve nucleus is a collection of neurons in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei except that of the trochlear nerve supply nerves of the same side of the body.
The spinal trigeminal nucleus is a nucleus in the medulla that receives information about deep/crude touch, pain, and temperature from the ipsilateral face. In addition to the trigeminal nerve, the facial, glossopharyngeal, and vagus nerves also convey pain information from their areas to the spinal trigeminal nucleus. Thus the spinal trigeminal nucleus receives afferents from cranial nerves V, VII, IX, and X.
The dorsal column nuclei are a pair of nuclei in the dorsal columns of the dorsal column–medial lemniscus pathway (DCML) in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are situated at the lower end of the medulla oblongata. Both nuclei contain second-order neurons of the DCML, which convey fine touch and proprioceptive information from the body to the brain via the thalamus.
The ventral posterior nucleus is the somatosensory relay nucleus in thalamus of the brain.
The ventral posteromedial nucleus (VPM) is a nucleus within the ventral posterior nucleus of the thalamus and serves an analogous somatosensory relay role for the ascending trigeminothalamic tracts as its lateral neighbour the ventral posterolateral nucleus serves for dorsal column–medial lemniscus pathway 2nd-order neurons.
The ventral posterolateral nucleus (VPL) is one of the subdivisions of the ventral posterior nucleus in the ventral nuclear group of the thalamus. It relays sensory information from the second-order neurons of the neospinothalamic tract and medial lemniscus which synapse with the third-order neurons in the nucleus. These then project to the primary somatosensory cortex in the postcentral gyrus.
The spinoreticular tract is a partially decussating (crossed-over) four-neuron sensory pathway of the central nervous system. The tract transmits slow nociceptive/pain information from the spinal cord to reticular formation which in turn relays the information to the thalamus via reticulothalamic fibers as well as to other parts of the brain. Most (85%) second-order axons arising from sensory C first-order fibers ascend in the spinoreticular tract - it is consequently responsible for transmitting "slow", dull, poorly-localised pain. By projecting to the reticular activating system (RAS), the tract also mediates arousal/alertness in response to noxious (harmful) stimuli. The tract is phylogenetically older than the spinothalamic ("neospinothalamic") tract.
The ventrobasal complex (VB) is a relay nucleus of the thalamus for nociceptive stimuli received from nociceptive nerves. The VB consists of the ventral posteromedial nucleus (VPM) and the ventral posterolateral nucleus (VPL). In some species, the ventral posterolateral nucleus, pars caudalis is also a part of the VB. The VB gets inputs from the spinothalamic tract, medial lemniscus, and corticothalamic tract. The main output of the VB is the primary somatosensory cortex.
The ventral trigeminal tract, ventral trigeminothalamic tract, anterior trigeminal tract, or anterior trigeminothalamic tract, is a tract composed of second-order neuronal axons. These afferent fibers carry sensory information about discriminative and crude touch, conscious proprioception, pain, and temperature from the head, face, and oral cavity. The ventral trigeminal tract connects the two major components of the brainstem trigeminal complex – the principal, or main sensory nucleus and the spinal trigeminal nucleus, to the ventral posteromedial nucleus of the thalamus.
The trigeminal lemniscus or the trigeminothalamic tracts is a somatosensory tract containing second-order neuron fibers of the trigeminal system. It consists of the ventral and dorsal trigeminal tracts. Its second-order sensory axons convey tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities, and the eye, as well as proprioceptive information from the facial and masticatory muscles.
The dorsal trigeminal tract are uncrossed second-order sensory fibers conveying fine (discriminative) touch and pressure information from the dorsomedial division of principal sensory nucleus of trigeminal nerve to the ipsilateral ventral posteromedial nucleus of thalamus. Second-order fibers from the ventrolateral division of the principal sensory nucleus meanwhile cross-over to ascend contralaterally in the ventral trigeminal tract along with those fibers arising from the spinal trigeminal nucleus.
The parabrachial nuclei, also known as the parabrachial complex, are a group of nuclei in the dorsolateral pons that surrounds the superior cerebellar peduncle as it enters the brainstem from the cerebellum. They are named from the Latin term for the superior cerebellar peduncle, the brachium conjunctivum. In the human brain, the expansion of the superior cerebellar peduncle expands the parabrachial nuclei, which form a thin strip of grey matter over most of the peduncle. The parabrachial nuclei are typically divided along the lines suggested by Baxter and Olszewski in humans, into a medial parabrachial nucleus and lateral parabrachial nucleus. These have in turn been subdivided into a dozen subnuclei: the superior, dorsal, ventral, internal, external and extreme lateral subnuclei; the lateral crescent and subparabrachial nucleus along the ventrolateral margin of the lateral parabrachial complex; and the medial and external medial subnuclei
