Brain subdivisions

Histamine receptors were first divided into two subclasses Hi and H2 by Ash and Schild (1966) on the basis that the then known antihistamines did not inhibit histamine-induced gastric acid secretion. The justification for this subdivision was established some years later when Black (see Black et al. 1972) developed drugs, like cimetidine, that affected only the histamine stimulation of gastric acid secretion and had such a dramatic impact on the treatment of peptic ulcers. A recently developed H2 antagonist zolantidine is the first, however, to show significant brain penetration. A further H3 receptor has now been established. It is predominantly an autoreceptor on histamine nerves but is also found on the terminals of aminergic, cholinergic and peptide neurons. All three receptors are G-protein-coupled but little is known of the intracellular pathway linked to the H3 receptor and unlike Hi and H2 receptors it still remains to be cloned. Activation of Hi receptors stimulates IP3 formation while the H2 receptor is linked to activation of adenylate cyclase. 

Anatomically, the human nervous system may be divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The major subdivision of the central nervous system is into the brain and spinal cord. The peripheral nervous system is divided into the motor or efferent system (efferent = away from ), and the sensory or afferent (afferent = toward ) nervous systems (Figure 2.1). 

Anatomically, the nervous system is divided into the central nervous system (CNS) consisting of the brain and the spinal cord and the peripheral nervous system comprised of neural cells forming a network throughout the body. The peripheral system is itself subdivided into two sections the somatic system, where control of skeletal muscles allows movement and breathing, and the autonomic system which controls the actions of smooth muscle, cardiac muscle and glandular tissues. Further subdivision of the autonomic system based on anatomical and biochemical factors creates the sympathetic and parasympathetic nervous systems. 

The term central nervous system is sometimes used as a synonym for the brain, but it also includes the spinal cord. Indeed, the word system implies the entirety of the tissues working together to achieve a single function. Usage, however, has validated its division into the central and peripheral nervous systems, and even the subdivision of the latter into the autonomic nervous system and the voluntary nervous system. 

The nervous system is conventionally divided into the central nervous system (CNS the brain and spinal cord) and the peripheral nervous system (PNS neuronal tissues outside the CNS). The motor (efferent) portion of the nervous system can be divided into two major subdivisions autonomic and somatic. The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life. The somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity. 

Part III lays the groundwork for understanding the brain as the physical basis of consciousness. It describes the regional, cellular, and molecular mechanisms that may contribute to alterations of conscious states. Chapter 6 begins to tease apart the major subdivisions of the brain-mind and to describe their interaction in normal conscious state alteration. In chapter 7, we meet the neuromodulatory chemical systems that appear to be causative of those alterations. 

Figure 2.15 Position of the V4 complex. It consists of V4 at the back and V4o in front. (Redrawn from Figure 1 (page 1373) S. Zeki and A. Bartels. The clinical and functional measurement of cortical (in)activity in the visual brain, with special reference to the two subdivisions V4 and V4a) of the human colour centre. Proceedings of the Royal Society of London. Series B, 354, pp. 1371-1382, The Royal Society, 1999, used by permission.)...

Zeki S and Bartels A 1999 The clinical and functional measurement of cortical (in)activity in the visual brain, with special reference to the two subdivisions (V4 and V4a) of the human colour centre. Proceedings of the Royal Society of London B 354, 1371-1382. 

CNS—brain and spinal cord—and two separate pathways within the peripheral nervous system (PNS) for two-way communication with the peripheral organs. The PNS subdivisions are the somatic and autonomic nervous systems (Figure 11.2). The latter is further divided into sympathetic and parasympathetic divisions (Figure 11.3). 

Figures 4-6 show the cytoarchitectonic subdivisions which contain dopaminergic cells in the ventral midbrain tegmentum, as illustrated in stereotaxic atlases of the rat and mouse brain. These atlases nowadays represent common laboratory tools, especially for young researchers (who may not be necessarily experts in sophisticated neuroanatomical subdivisions and nomenclature). The SN and its different subdivisions (described in Section 2.2.2) are clearly delineated in Figures 4-6. Medially to the SN, the emphasis on the parcellation (or lack of parcellation) into different nuclei varies slightly according to the authors. The VTA is obviously indicated in all atlases, but its extent is rarely delineated, though the boundaries of this region are outlined at rostral levels in Swanson s...

Hentschel K, Moore KE, Lookingland KJ (2000) Effects of prolactin on expression of Fos-related antigens in tyrosine hydroxylase-immunoreactive neurons in subdivisions of the arcuate nucleus. Brain Res 557 110-118. Hesketh R (1995) The Oncogene Facts Book, pp. 105-160. Academic Press, New York. 

Molinari HH (1987) Ultrastructure of the gracile nucleus projection to the dorsal accessory subdivision of the cat inferior olive. Exp. Brain Res., 66, 175-184. 

Luiten, P.G.M., Gaykema, R.P.A., Traber, J. and Spencer Jr., D.J. (1987) Cortical projection patterns of magnocellular basal nucleus subdivisions as revealed by anterogradely transported Phaseolus vulgaris leucoagglutinin. Brain Res., 413, 229-250. 

Puelles, L., Milan, J.F., Martinez-de-la-Torre, M. 1996. A segmental map of architectonic subdivisions in the diencephalon of the frog Rana perezi acetylcholinesterase-histochemical observations. Brain Behav. Evol. 47, 279-310. 

EAA postsynaptic receptors have been divided into three types. One subtype is NMDA activated, one is activated by kainic acid, and the third by quisqualic acid. However, this separation has already been challenged by newer experiments that suggest additional subdivisions based on apparent pharmacological differences at different brain sites. 

Glutamate or a structurally-similar chemical is an excitatory neurotransmitter in many areas of the brain. EAA receptors are generally divided into N-methyl-D-aspartate, quisqualate and kainate receptors, named for agonists that bind to each type of receptor. Further subdivision of classes is currently underway. Stimulation of EAA receptors increases cation conductance, leading to depolarization, or stimulates phosphatidyl inositol turnover. 

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