This pathway consists of A & A fibers characterised with high velocity (30 to 110 m/sec) of impulse conduction. The dorsal column-lemniscal pathway has also high degree of spatial orientation of the nerve fibres; particularly the medial fibers convey the information from the lower parts of the body while the lateral fibers related to higher segments.
The spasticity in the muscles is related to the pyramidal insufficiency. This condition can occur if pyramidal pathways controlling voluntary movements are damaged by the mechanic or other agents. Intoxications, chronic neurodegenerative diseases, traumas, and metabolic disorders can play role in the origin of muscular spasticity.
The attenuation reflex is important protective mechanism providing the best sound perception. The contraction of the stapes muscle protects the inner ear from damaging. The role of outer ear structures is important also - they can reduce resonance in the middle ear.
Summation is a process of gradual release of the transmitter and the transmission of the impulse from several presynaptic neurones to one postsynaptic neurone (spatial summation) or from only one presynaptic and one postsynaptic neurone (temporal summation). The summation leads to the release of sufficient the impulse is transmitted across the synaptic cleft.
The pain control system of CNS is represented by three major components: the periaqueductal grey and the nucleus raphe magnus (in the brain) and the pain inhibitory neurons of the dorsal horns in medulla spinalis. The opioid receptors of these structures are activated by endorphins or exogenous opiates and block the spreading of pain impulses.
3.3 Why is it difficult to localize slow, chronic pain (2)
Chronic pain usually irradiate to other areas thus its localisation could be difficult. Furthermore, the efferent pain stimuli are conducted to CNS