Reticular area

Figure 12 14. The reticular activation system. As indicated by the curved arrows, the RAS emanates upward from the reticular areas of the mesencephalon.

Reticular area is the projection of the unit cell on to a surface plane and can effectively be thought of as the 2D unit cell at the surface. Reticular area (S ) is calculated fiom the ratio of the unit cell volume (F ) to the d-spacing (d ) as shown in Equation 8.1. The concept will be utilised later whai describing the surfaces of particles. 

I Typical number of steps in X, Y and Z directions are 8x8x8 I One probe molecule explores every grid point on a reticular area m... 

The ER has a reticular morphology which provides a large surface area, which presumably is required for the synthesis and transport of proteins and lipids and for the storage of calcium. The ER is associated with microtubules, and the two are highly interdependent structures. Terasaki et al. (1986) found that when microtubules in the cell are depolymerized by colchicine, the ER network slowly retracts toward the center of the cell. If the microtubules are repolymerized, the ER network is restored to its original morphology, thereby suggesting that the MTs participate in the formation and maintenance of the ER. 

Patients of varying skin types (1-V) having striae distensae alba on the abdomen or thighs can apply topical 20% glycolic acid daily to the entire treatment area. In addition, these patients apply 10% L-ascorbic acid, 2% zinc sulfate, and 0.5% tyrosine to half of the treatment area and 0.05% tretinoin emollient cream to the other half of the treatment area. The creams are applied on a daily basis for 12 weeks. Improvement is evaluated at 4 and 12 weeks with increased elastin content within the reticular and papillary dermis [14]. 

B9 Nucleus prosupralemniscus B1 and B3 Neurons of the lateral paragigantocellular nucleus and the intermediate reticular nuclei Cells in the area postrema... 

The slow (deep sleep) -waves probably originate in the eortex beeause they survive separation from, or lesions of, the thalamus. However, the rhythm and appearanee of spindles in earlier phases of the sleep eyele do depend on links with the thalamus (see Steriade 1999). Unlike stimulation of the specific sensory relay nuclei in the thalamus, which only affects neurons in the appropriate sensory areas of the cortex, the nonspecific nuclei can produce responses throughout the cortex and may not only control, but also generate, cortical activity. Certainly, in vitro studies show that neurons of the non-specific reticular thalamic nucleus (NspRTN) can fire spontaneously at about 8-12 Hz (equivalent to EEG a-rhythm) or lower, and that low-frequency stimulation of this area can induce sleep. 

Figure 22.5 Pathways involved in cortico-thalamic synchrony and EEG arousal. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and midbrain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). Its stimulation is followed by EEG arousal. It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state...

Figure 4.2 Model of the network responsible for paradoxical sleep onset and maintenance Abbreviations DRN, dorsal raphe nucleus 5-HT, serotonin LC, locus coeruleus NA, noradrenaline LDT, laterodorsal tegmental nucleus Ach, acetylcholine Me, magnocellular reticular nucleus Gly glycine DPMe, deep mesencephalic reticular nucleus PAG, periaqueductal gray DPGi, dorsal paragigantocellular reticular nucleus PPT, pedunculopontine nucleus PRN, pontine reticular nucleus SLD, sublaterodorsal nucleus Glu, glutamate Pef/HLA perifornical/lateral hypothalamic area Hcrt, hypocretin (i.e. orexin).

The neural structures involved in the promotion of the waking (W) state are located in the (1) brainstem [dorsal raphe nucleus (DRN), median raphe nucleus (MRN), locus coeruleus (LC), laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT), and medial-pontine reticular formation (mPRF)] (2) hypothalamus [tuberomammillary nucleus (TMN) and lateral hypothalamus (LH)[ (3) basal forebrain (BFB) (medial septal area, nucleus basalis of Meynert) and (4) midbrain ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) (Pace-Schott Hobson, 2002 Jones, 2003). The following neurotransmitters function to promote W (1) acetylcholine (ACh LDT/PPT, BFB) (2) noradrenaline (NA LC) (3) serotonin (5-HT DRN, MRN) (4) histamine (HA TMN) (5) glutamate (GLU mPRF, BFB, thalamus) (6) orexin (OX LH) and (7) dopamine (DA VTA, SNc) (Zoltoski et al, 1999 Monti, 2004). 

The midbrain (mesencephalon) is the top of the brain stem. The dorsal midbrain is the tectum, which is involved in eye movements and reflexive reactions to sensory stimuli. The mesencephalic reticular formation projects upward to the forebrain and is involved in arousal and attention. The periaqueductal gray area surrounds the cerebral aqueduct, and integrates analgesic, defensive/aggressive, sexual, and autonomic responses. The red nucleus and substantia nigra are important structures in motor function. 

---