Afferent system

Another method employed rather frequently by neuropharmacologists involves measurement of transmission in sensory systems by the so-called evoked potential technique. A sense organ, e.g. the eye or the ear, is stimulated by a light flash or a loudspeaker click, and an afferent volley of nerve impulses is produced. This volley travels first through peripheral sensory nerve fibers and then through the afferent systems in the CNS to reach finally the so-called projection area of the cerebral cortex. 

Directional Afferent system by sensory neurons, which carry impulses from a somatic receptor to the CNS. Efferent system by motor neurons, which carry impulses from the CNS to an effector. Relay system by interneurons (also called relay neurons ), which transmit impulses between the sensory and motor neurons (in both the CNS and the PNS). 

Depending on the visual acuity and visual fields, one determines how quickly intervention is needed. If the patient has no afferent system loss, the first step in the treatment of PTC is to remove any agent that caused it (e.g., tetracycline). If the patient is obese, as is usually the case, then loss of excess weight may reverse... 

The (central) cerebellar nuclei and the lateral vestibular nucleus of Deiters receive the axons of the Purkinje cells of the cerebellar cortex and serve as the main output stations of the cerebellum. The vermis and the flocculus also project to other vestibular nuclei, but here the Purkinje cell axons compete with vestibular root fibers, intrinsic and commissural vestibular connections and projections from the medial cerebellar nucleus and, therefore, are not the dominant afferent system. 

Afferent systems of the inferior olive have been reviewed by Brodal and Kawamura (1980) for the cat and by Martin et al. (1980) for the opossum. For the rat the tabulated summary of its afferent connections in the paper of Brown et al. (1977) and the review by Flumerfelt and Hryccyshyn (1985) are useful. Afferent systems of the inferior olive can be subdivided into three groups (1) the GABAergic nucleo-olivary and vestibulo-olivary projections (2) the monoaminergic and cholinergic projections to the inferior olive (3) the specific projections from the spinal cord, certain brain stem nuclei and the cerebral cortex will not be considered in this chapter. Their neurotransmitters are not known. 

Bernocchi G (1986) Cytochemical variations in Purkinje neuron nuclei of cerebellar areas with different afferent systems in Rana esculenta. Comparison between activity and hibernation. Z. Hirnforsch., 26, 659-665. 

Border BG, Kosinski RJ, Azizi SA, Mihailoff GA (1986) Certain basilar pontine afferent systems are GABA-ergic combined HRP and immunocytochemical studies in the rat. Brain Res. Bull, 17, 169-179. 

Cummings S, King JS (1990) Coexistence of corticotropin releasing factor and enkephalin in cerebellar afferent systems. Synapse, 5, 167-174. 

Cummings S, Sharp B, Elde R (1988) Corticotropin-releasing factor in cerebellar afferent systems A combined immunohistochemistry and retrograde transport study. J. Neurosci., 8, 543-554. 

Saper CB (1984) Organization of cerebral cortical afferent systems in the rat. II. Magnocellular basal nucleus. J. Comp. Neurol., 222, 313-342. 

Storm-Mathisen, J. and Blackstad, T. W. (1964) Cholinesterase in the hippocampal region. Distribution and relation to architectonics and afferent systems. Acta anat. (Basel), 56, 216-253. 

The results of the RREP, PET, and fMRl studies indicate common areas are activated by multiple respiratory modalities, suggesting convergent neural pathways for respiratory perception that can lead to specific respiratory sensations. The differences in brain activations with the different respiratory sensory modalities are likely due to the afferent systems activated. Each respiratory sensory modality has a unique convergent and divergent afferent input to the central nervous system and a unique temporal pattern of afferent activity. Despite well-known afferent responses to respiratory stimuli, it remains unknown which of the fMRI- and PET-imaged activated central neural structures are essential to produce specific respiratory sensations. 

Shirahata M, Ishizawa Y, Rudisill M, Schofield B, Fitzgerald RS. Presence of nicotinic acetylcholine receptors in cat carotid hody afferent system. Brain Res 1998 814 213-217. 

---