Brain Motor Centers and Pathways
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
There are four vestibular nuclei on each side, located in the rostral medulla and caudal pons (Figure 12.17): superior, lateral, medial, and inferior. The lateral vestibular nucleus is also known as Deiters’ nucleus. Cerebellar afferents to the vestibular nuclei project ipsilaterally from the vermis of the anterior lobe to the lateral vestibular nucleus, from the flocculonodular lobe to the other three vestibular nuclei, and bilaterally from the fastigial nucleus to the lateral and inferior vestibular nuclei. The vestibular nuclei integrate a broad range of visual and somatosensory inputs, including inputs from the spinal cord, particularly neck proprioceptive information, inputs from subcortical visual centers, and inputs from the cerebral cortex, including premotor head movement commands.
Motor Function and ControlDescending Tracts
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The descending motor pathways have been classified into the pyramidal tracts, which originate from the cerebral cortex, and the extrapyramidal tracts, which arise from brainstem nuclei (Table 9.1). The pyramidal tract is the most important motor pathway for motor control and consists of axons of pyramidal cells in layers III and V of the premotor, precentral and postcentral gyrus of the cortex (Figure 9.3). The corticospinal tract descends through the posterior part of the internal capsule on the lateral side of the thalamus and passes through the midbrain, pons and medulla. In the ventral medulla, the axons (90%) cross to the contralateral side and proceed to the spinal cord. Approximately 10%–15% of the axons do not cross to the contralateral side and supply the thoracic respiratory muscles. The corticospinal tract controls the muscles responsible for precise movements (fingers and hands) and the laryngeal muscles. The corticobulbar tract fibres terminate on the lower motor neurons in the brainstem and control facial muscle movements.The extrapyramidal tract is formed by the rubrospinal, vestibulospinal, tectospinal and reticulospinal tracts. These tracts maintain postural tone and direct voluntary movement. The rubrospinal tract arises from cells in the red nucleus, crosses contralaterally in the brainstem, receives input from the cerebral cortex and runs down the spinal cord. The lateral vestibulospinal tract arises from the lateral vestibular nucleus and does not cross to the contralateral side. The reticulospinal tract originates from the reticular system in the pons and medulla. The extrapyramidal system receives inputs from the cerebral cortex and cerebellum (Figure 9.4).
The Vestibular System: An Overview of Structure and Function
Kenneth J Ottenbacher, Margaret A Short Degraft in Vestibular Processing Dysfunction in Children, 2013
The vestibular nuclear complex makes up a large portion of the dorsolateral brainstem in the region of the pontomedullary junction. It consists of four major vestibular nuclei and a number of smaller accessory nuclei. The major inputs to these nuclei arise from the following sources: primary afferent fibers from vestibular receptors, the reticular formation, and the cerebellum which comprises the largest component. The superior vestibular nucleus (SVN) is the most rostral of the main nuclei. It is made up of cells of various sizes. Primary afferent fibers, largely from the vertical semicircular canals, terminate in the central region of the SVN, where its larger cells are concentrated. 13 Horizontal canal units and otolith-sensitive cells are present, but fewer in number than vertical canal units. Fibers from the cerebellar fastigial nucleus tend to terminate in the peripheral part of the SVN. Cells from all areas of the nucleus give rise to fibers that ascend in the brain stem. The SVN also has extensive commissural connections with the contralateral SVN. The lateral vestibular nucleus (L VN) lies ventral to SVN and lateral to the medial vestibular nucleus (MVN). LVN is frequently called Deiters' nucleus in reference to the giant cells of Deiters found here. The L VN also contains many smaller neurons, the giant cells being more abundant in the caudal portion of the nucleus. The LVN receives a modest number of primary afferents from the labyrinth, and their termination is restricted to the ventral part of the nucleus. The majority of these primary fibers are from the otolith organs. 14 Commissural fibers are reported to be absent in the LVN . 15 Cells of the LVN have a specific and important relationship with both the spinal cord and cerebellum but, as noted above, have very limited direct contact with the end organ. The medial vestibular nucleus (MVN) lies just below the floor of the fourth ventricle medial to the LVN and inferior vestibular nucleus (IVN). Many primary afferents terminate in its rostral portion, mainly from the semicircular canals. Primary afferents from the saccule and utricule tend to terminate caudally., along the border shared with the IVN. MVN neurons from this same border region project axons to the ipsilateral flocculus, nodulus and uvula of the cerebellum. Commissural fibers enter the MVN from the contralateral SVN, MVN and IVN. The inferior vestibular nucleus (IVN) is the most caudally located of the four major vestibular nuclei. This nucleus receives the greatest number of primary afferents, mainly from the saccule and utricule. The greatest representation is from the saccule and the least from the semi-
Vestibular function in children with generalized epilepsy and treated with valproate
Published in Expert Review of Clinical Pharmacology, 2022
Sherifa Ahmed Hamed, Amira Mohamed Osiely
The vestibular system is divided into peripheral and central components. The peripheral component is composed of the semicircular canals, otolith (saccule and utricle) organs and the superior and inferior vestibular nerves. The central component begins from the point of entrance of vestibular nerves to the brainstem, the medial and lateral vestibular nuclei and the central inter-relations and connections to the thalamus and cerebral cortex. The semicircular canals sense horizontal angular head accelerations. Their afferents project to the medial vestibular nuclei via the vestibulo-ocular reflex (VOR). They provide reflexive ocular motor responses for maintenance of gaze stability. The otolith organs sense linear acceleration and static tilt in relation to gravity. Their afferents project to the lateral vestibular nucleus via the vestibulo-spinal reflex (VSR) for postural control and via connections to the cerebellar neurons, thalamus, and higher-cortical areas for balance, self-motion, and gravity direction [14].
Related Knowledge Centers
- Abducens Nerve
- Anterior Funiculus
- Axon
- Cranial Nerve Nucleus
- Oculomotor Nerve
- Trochlear Nerve
- Vestibular Nerve
- Spinal Cord
- Medial Longitudinal Fasciculus
- Multipolar Neuron