In the pons, the primary sensory axons terminate either in the principalsensorynucleus of V (or chief sensorynucleus) (#6197) or turn caudally to form the descending tract of V (or spinal tract of V) (#4621) (fig 6b).
Unlike the other secondary sensory axons that have been studied, these are ipsilateral, i.e., the left nucleus solitarius projects to the left VPM.
Is this tract efferent or afferent to the descending nucleus?
It is the principalsensorynucleus and the mesencephalic nucleus of V. The pontine nucleus or principalsensorynucleus is placed lateral to the motor nucleus in the pontine tegmentum.
It then forms a genu which sweeps across the dorsal surface of the abducent nucleus in order to reach the lateral aspect of the pontine tegmentum where it runs a ventral course to escape at the cerebellopontine angle, medial and inferior to the point of escape of the abducent nerve.
This nerve has its nucleus buried in the facial colliculus, a little ventral to the nucleus of the abducent nerve.
The first stage of auditory information processing occurs in the cochlear nucleus, where the relatively uniform discharge of auditory nerve fibers is transformed into a set of distinct ascending parallel pathways that emphasize different features of the sensory environment.
The auditory system has two principal advantages over the other sensory systems for the study of information processing mechanisms:
Our fundamental interest is to understand the mechanisms used by the nervous system to process and analyze information about the sensory environment.
The medial fillet passes upward in the ventral part of the formatio reticularis through the medulla oblongata, pons and mid-brain to the principalsensorynucleus of the ventro-lateral region of the thalamus.
The posterior root fibers conducting these impulses pass into the fasciculus cuneatus and the collaterals from them to the nucleus dorsalis are said to come almost exclusively from the middle area of the fasciculus cuneatus.
The cerebellar reflex are is supposed to be completed by the fibers of the superior peduncle which pass from the cerebellum to the red nucleus of the mid-brain where some of their terminals and collaterals form synapses with neurons whose axons descend to the spinal cord in the rubrospinal fasciculus.
principal trigeminal sensorynucleus, nucleus of the trapezoid
Mugnaini E, Oertel WH (1985) An atlas of the distribution GABAergic neurons and terminals in the rat CNS as revealed by GAD immunohistochemistry.
Pardo CA, Xu Z, Borchelt DR, Price DL, Sisodia SS, Cleveland DW (1995) Superoxide dismutase is an abundant component in cell bodies, dendrites, and axons of motor neurons and in a subset of other neurons.
Lee, J.I., Dougherty, P.M., Antezana, D., and Lenz, F.A. Responses of neurons in the region of human thalamic principal somatic sensorynucleus to mechanical and thermal stimuli graded into the painful range.
Dashed arrows indicate nociceptive or endogenous physiological factors that influence pain sensation and unpleasantness.
of pain are often more intense than other types of somatic sensations.