Practical Study Guide–Neuroanatomy

macula of utricle the neuroepithelial sensory receptor in the inferolateral wall of the utricle; hair
cells of the neuroepithelium support the statoconial membrane and have terminal arborizations of vestibular nerve fibers around their bodies; sensitive to linear acceleration in the longitudinal axis of the body and to gravitational influences.

ampullary crest an elevation on the inner surface of the ampulla of each semicircular duct; filaments of the vestibular nerve pass through the crista to reach hair cells on its surface; the hair cells are capped by the cupula, a gelatinous protein-polysaccharide mass. Syn: crista ampullaris [NA], acoustic crest, transverse septum(1).

spinothalamic tract a large ascending fiber bundle in the ventral half of the lateral funiculus of
the spinal cord, arising from cells in the posterior horn at all levels of the cord, which cross within their segments of origin in the white commissure. In their contralateral ascent, the bundle is intermingled with numerous intersegmental fibers. The spinothalamic tract continues from the spinal cord into the brainstem, occupying a ventrolateral position and issuing numerous fibers to the rhombencephalic and mesencephalic reticular formation, to the lateral part of the central gray substance of the mesencephalon, and to the deep and intermediate layers of the superior colliculus; the relatively few fibers (10 to 20%) that remain form the true spinothalamic tract which enters the diencephalon and ends in the nucleus ventralis posterior (caudal part) and intralaminar nuclei of the thalamus. In its ascent in the spinal cord the tract is composed of a dorsal part, the lateral spinothalamic tract, which conveys impulses associated with pain and temperature sensation, and a more ventral part, the anterior spinsothalamic tract, involved in tactile sensation.

solitary tract a slender, compact fiber bundle extending longitudinally through the dorsolateral
region of the medullary tegmentum, surrounded by the nucleus of the solitary tract, below the obex decussating over the central canal, and descending over some distance into the upper cervical segments of the spinal cord. It is composed of primary sensory fibers that enter with the vagus, glossopharyngeal, and facial nerves, and in part convey information from stretch receptors and chemoreceptors in the walls of the cardiovascular, respiratory, and intestinal tracts; in rostral parts of the tract impulses are generated by the receptor cells of the taste buds in the mucosa of the tongue. Its fibers are distributed to the nucleus of the solitary tract.

vestibulospinal tract a somatopically organized fiber bundle originating from the lateral
vestibular nucleus (nucleus of Deiters) which descends uncrossed into the anterior funiculus of the spinal cord lateral to the anterior median fissure; the tractus extends throughout the length of the cord, distributing fibers at all levels to the medial part of the anterior horn. Excitatory impulses conveyed by the vestibulospinal tract increase extensor muscle tone. Syn: tractus vestibulospinalis [NA], deiterospinal tract.

reticulospinal tract collective term denoting a variety of fiber tracts descending to the spinal cord
from the reticular formation of the pons and medulla oblongata. Part of these fibers conduct impulses from the neural mechanisms regulating autonomic functions to the corresponding somatic and visceral motor neurons of the spinal cord; others form links in nonpyramidal motor mechanisms affecting muscle tonus, reflex activity, and somatic movement. Syn: tractus reticulospinalis [NA].

alternating hemiplegia hemiplegia on one side with contralateral cranial nerve palsies. 

lateral lemniscus a bundle of ascending fibers that originate from the cochlear and auditory relay
nuclei of the rhombencephalon, enter the trapezoid body, a transverse fiber stratum in which about half their number decussate, and from here turn rostrally along the lateral side of the spinothalamic tract; in the midbrain, it arches dorsally and enters the inferior colliculus in which all of its fibers terminate; the auditory pathway is 	transsynaptically extended from here by the brachium of the inferior colliculus to the medial geniculate body of the thalamus, from which in turn the auditory radiation leads to the auditory cortex; intercalated in the trapezoid body and along the ascending trajectory of the lemniscus are several cell groups in which part of the fibers synapse.

inferior colliculus the ovoid, paired, inferior eminence of the laminae of mesencephalic tectum; it
receives the lateral lemniscus and projects by way of the brachium of inferior colliculus to the medial geniculate body of the thalamus, and is thus an essential way-station in the central auditory pathway.

tectospinal tract  a bundle of thick, heavily myelinated fibers originating in the deep layers of the
superior colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally, the medial lemniscus ventrally, into the anterior funiculus of the spinal cord. The tract ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during visual and auditory tracking. Throughout its course in the brainstem it is accompanied by fibers of the tectobulbar tract.

dorsolateral fasciculus a longitudinal bundle of thin, unmyelinated and poorly myelinated fibers
capping the apex of the posterior horn of the spinal gray matter, composed of posterior root fibers and short association fibers that interconnect neighboring segments of the posterior horn. Syn: Lissauer's tract,