Sensory system nerves

Peripheral nervous system Nerve tissues lying outside the brain and spinal cord, functions include the transmittal of sensory information such as touch, heat, cold, and pain, and the motor impulses for limb movement. 

Nervous system disorders are diagnosed by examining the patient s mental status, cranial nerve function, motor system reflexes, and sensory systems. An electroencephalogram (EEG) tests higher brain and nervous system functions. 

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. 

In all sensory systems, this afferent pathway consists of at least three neurons (nerve cell and nerve fiber) arranged in a continuous chain. The transfer of nervous signals from one neuron to the next occurs in well-defined loci called synapses. 

Vertebrates possess three primary chemosensory systems gustation ( taste ), trigeminal, and olfaction ( smell ) but only one of these, the olfactory system, mediates responses to pheromones. Chemicals that stimulate the olfactory system are known as odorants and comprise one type of biological cue (any entity that stimulates a sensory system). Bouquets of odorants that can be discriminated as specific entities are termed odors. The olfactory system contains olfactory receptor neurons (ORNs) that comprise cranial nerve I and project directly to the forebrain. ORNs are now known to express only one to a few olfactory receptor proteins ( receptors ), which means that the chemoreceptive range of each neuron can be very narrow. The olfactory system also has several subcomponents including the vomeronasal organ, which is described below. 

Human perception is the active reception and coordination of information received through our sensory systems in order to make sense of the environment and to behave effectively within it. In contrast with the direct and immediate sensations actually received and transmitted, perception is the transformation of that information into nerve cell activity that is transferred to the brain where further processing occurs. Our perceptual systems do not passively receive stimuli from the world, instead they actively select, organize, interpret, and sometimes distort sensory information. The real world then may not be the same as the one we perceive. Broadly, perception can be said to be the study of the human organism s relation to the physical world. 

Nervous system abnormalities. Balali-Mood et al. (2005) conducted smdies on peripheral neuropathic processes in victims exhibiting severe late manifestations of mustard poisoning using electromyography and nerve conduction velocity. Seventy percent of the patients demonstrated disturbances in the peripheral nervous system. Nerve conduction abnormalities were more common in sensory nerves and more prevalent in lower extremities than in upper extremities. Forty percent of the patients exhibited incomplete interference patterns in electromyographic studies. 

Subsequent to these early observations, scientists discovered that transplantation of a mouse sarcoma tumor Into a chick led to a marked Increase In the numbers of certain types of neurons. This finding Implicated the tumor as a rich source of the presumed trophic factor. To Isolate and purify this factor, known simply as nerve growth factor (NGF), scientists used an In vitro assay In which outgrowth of neurltes from sensory ganglia (nerves) was measured. Neurltes are extensions of the cell cytoplasm that can grow to become the long wires of the nervous system, the axons and dendrites... 

Muscles, for example, can develop increased aerobic or anaerobic metabolic capacity. Furthermore, muscular responses are characterized in the model as a series of cascading mechanical and physiological events. The local changes (system responses), such as deformation and the yielding of connective tissues within the muscle, are conveyed to the central nervous system by sensory afferent nerves and cause corresponding sensations to effort and discomfort, often referred to as perceived fatigue. 

The skeletomotor system provides the structure and drives to move the body and Kmbs relative to the surroundings and to maintain the posture in space. The motor systems act on the environment by transforming neural information and metabolic energy into movement. Changes in external events or in the internal environment, signaled by the sensory systems, set up commands that are transmitted to the skeletal muscles by nerve impulses. The muscles convert the neural information into a command that transforms chemical into mechanical energy by generating a contractile force. 

Demski, L. S., and Northcutt, R. G., 1983, The terminal nerve a new chemo-sensory system in vertebrates . Science, 220 435. 

Evoked EEG Potentials. When a stimulus is applied to the brain through the sensory system, such as a tone burst in the ear, a flash of light to the eye, or a mechanical or electric stimulus to the skin or nerve, there is a subtle response in the EEG. TTiis is known as an evoked response, and it reflects... 

Sensory systems There have been reports of nerve injury after mandibular nerve block [24" ] and ocular complications after inferior alveolar nerve block PS ]. 

The diverse physiological actions of capsaicin described in the previous sections have motivated numerous, equally diverse, in vivo and in vitro studies in search of biochemical correlates. The most attention, however, has been focused on the sensory system since a direct effect of capsaicin on sensory nerves has been suspected for a long time. More recent observations of capsaicin-induced sensory neuron degeneration in neonatal animals have added further impetus to determine the resultant neurochemical deficits of this lesion. It is perhaps fortunate that the small type B neurons of dorsal root ganglia which appear anatomically to succumb to capsaicin after both neonatal and adult treatment are also among the neurons for which putative neurotransmitter markers have been identified. Accordingly, these markers, two of which are the peptides somatostatin and substance P, have provided both a means to assess the neurotoxic potential of capsaicin, and to some extent relate anatomical with neurochemical investigations. For the sake of coherence the biochemical aspects of some reports cited in the previous sections are discussed here. The major conclusions in these reports will be summarized in Section 13. 

In addition, after nerve and tissue destruction, regenerative sprouts rewire the afferent sensory system, where non-noxious stimuli can cause pain (allo-dynia). Schwann cells in damaged nerves produce increased mRNA for NGF and their receptors for regenerative events. Damaged axons often express adrenoreceptors, which cause discharges in response to circulating epinephrine and norepinephrine (NE). 

It is widely assumed that tramnatic injiuy to the nerve is the major cause of post-operative neiu-opathlc pain, but it is probably more complicated than this suggestion. It is also likely that the particular procedure and sensory systems in the surgical field contribute. Additionally, in some patients, continuous inflammatory responses, such as after inguinal hernia repair, drive the chronic response. However, it is the role of peripheral nociceptor sensitization that seems to be at the center of this issue. 

Sensory systems Vision Transient scintillating scotomata have been observed in the visual fields of both eyes in nine patients receiving paclitaxel infusions in doses of 175 and 225 mg/n [4T]. Involvement of the optic nerve was confirmed, and this is likely to have been related to optic nerve conduction abnormalities associated with the neurological effects of paclitaxel. The abnormalities were not progressive and there was some degree of recovery, although one patient had permanently impaired vision. 

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