The spinal cord is pretty small, but its importance is out of proportion to its size. It's the home of all the motor neurons that work your body, and of a large percentage of the autonomic motor neurons as well. It's also the recipient of nearly all the sensory information taken in by your body. Beyond that, many of the organizing principles of spinal cord reflexes…
Neural traffic to and from the CNS travels in peripheral nerves . The afferent fibers in these peripheral nerves either have endings that respond to physical stimuli (making them primary afferents that are also sensory receptors ) or carry information from separate sensory receptor cells in the periphery. The efferent fibers end on muscle fibers, autonomic ganglia, or glands. Receptors Encode the Nature, Location, Intensity, and…
In contrast to the way in which information travels within individual neurons as electrical signals, information is usually transmitted between neurons through the release of neurotransmitters at specialized junctions called synapses . And in contrast to unvarying, always-depolarizing action potentials, a wide variety of slow graded potentials may be produced at the synapses on an individual neuron—some depolarizing, some hyperpolarizing, some milliseconds in duration, others seconds,…
Neurons share many properties with other cells, including their complement of organelles, an electrical potential across their surface membranes, and an ability to secrete various substances. What distinguishes neurons is the ways in which they have adapted these common properties for their roles as information-processing and information-conveying devices. For example, neurons have specialized configurations of organelles to support their extended anatomy (see Chapter 1 ). Similarly,…
The central nervous system (CNS) is tremendously active metabolically—relative to its weight, it uses much more than its share of the available oxygen and glucose. Corresponding to this metabolic activity, it has an abundant and closely regulated arterial supply and a large venous drainage system. Also, for its proper functioning, the CNS depends on carefully controlled extracellular ion concentrations. Part of the basis for this control…
The ventricular system , the remnant of the space in the middle of the embryonic neural tube (see Fig. 2.5 ), is an interconnected series of cavities that extends through most of the central nervous system (CNS). The Brain Contains Four Ventricles There is a pair of lateral ventricles in the telencephalon (one for each cerebral hemisphere), a midline third ventricle in the diencephalon, and a…
The meninges form a major part of the mechanical suspension system of the CNS, necessary to keep it from self-destructing as we move through the world. In addition, one layer of the meninges participates in the system of barriers that effectively isolates the extracellular spaces in the nervous system from the extracellular spaces in the rest of the body. There Are Three Meningeal Layers: The Dura…
A useful way to start studying the brain is to learn some of the vocabulary that refers to its major parts, and to understand in a vague way what they do. These major parts can then serve as reference points to build on in later chapters. The Long Axis of the CNS Bends at the Cephalic Flexure Most creatures move through the world with their spinal…
Understanding a little bit about the embryology of the brain helps clarify the way it's put together in adults. The central nervous system (CNS) starts out as a simple ectodermal tube that develops some folds and bulges. The cavity of the tube persists as the ventricles, and the folds and bulges determine the shape and layout of many parts of the CNS. The Neural Tube and…
The brain seems bewilderingly complex the first few times you look at it. One way to ease the bewilderment is to have an overview of some vocabulary and organizing principles, which the first three chapters of this book attempt to provide. Chapter 1 is a quick introduction to the parts of the nervous system and the cells that make it up, Chapter 2 is an overview…
In order to survive, there must be continual biochemical and physiological adjustments to preserve the internal environment of the body in a balanced and stable state (homeostasis). Interoceptor signals from the internal organs and body fluids initiate homeostatic responses to achieve this end and the hypothalamus is the structure responsible for orchestrating the task. Exteroceptive information concerning the outside world strongly influences behaviour. This is relatively…
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Within the cerebral hemisphere lie a number of nuclear masses. Apart from the thalamus ( Chapter 12 ), the most prominent of these are the caudate nucleus , putamen and globus pallidus, which lie in close proximity to the internal capsule and are collectively referred to as the basal ganglia, basal nuclei or corpus striatum ( Figs 14.1 , 14.2 ; see also Figs 13.3 –…
The cerebral hemisphere is derived from the embryological telencephalon ( Chapter 1 ). It is the largest part of the forebrain and it reaches the greatest degree of development in the human brain. Superficially, the cerebral hemisphere consists of a layer of grey matter, the cerebral cortex, which is highly convoluted to form a complex pattern of ridges ( gyri ; singular, gyrus ) and furrows…
Rostral to the midbrain lies the forebrain (prosencephalon, cerebrum; see Fig. 1.13 ). The forebrain consists of the bilaterally paired diencephalon and cerebral hemisphere on each side and is by far the largest derivative of the three basic embryological divisions of the brain. The diencephalon is continuous with the rostral part of the midbrain and lies between the brainstem and the cerebral hemisphere. From dorsal to…
The cerebellum is the largest part of the hindbrain. It originates from the dorsal aspect of the brainstem and overlies the fourth ventricle. The cerebellum is connected to the brainstem by three stout pairs of fibre bundles, called the inferior , middle and superior cerebellar peduncles ( Figs 11.1, 11.4 ; see also Fig. 9.1, Fig. 9.2, Fig. 9.3 ); these join the cerebellum to the…
There are 12, bilaterally paired, cranial nerves. These carry afferent and efferent nerve fibres between the brain and peripheral structures, principally of the head and neck. The cranial nerves are individually named and numbered (Roman numerals I–XII) according to the rostrocaudal sequence in which they attach to the brain ( Fig. 10.1 and Table 10.1 ): I olfactory II optic III oculomotor IV trochlear V trigeminal VI abducens VII facial VIII vestibulocochlear IX glossopharyngeal X vagus…
The brainstem consists of the medulla oblongata, pons and midbrain. The archaic term ‘bulb’ is applied to the brainstem in compound anatomical names given to nerve fibres originating from, or terminating in, the brainstem (e.g. ‘corticobulbar’ refers to axons that arise in the cerebral cortex and terminate in the brainstem). It is also used clinically to denote the medulla in such terms as ‘bulbar palsy’ and…
The spinal cord and its associated spinal nerves are of immense functional importance. These structures act to: Receive afferent fibres from sensory receptors of the trunk and limbs Control movements of the trunk and limbs Provide autonomic innervation for most of the viscera The internal organisation of the cord permits many functions to operate in an automatic or reflex fashion. In addition, extensive connections with the…
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