The nervous system is a lot less able to repair itself after damage than some other organs are, but that doesn't mean it can't change. There's extensive adjustment of connections during development, but even in adult brains, synapses all over the nervous system modify their strength over timescales ranging from seconds to years. Some of these modifications are the basis of normal learning and memory. There…

There is a whole sphere of mental activity that goes beyond simple perception of stimuli and logical formulation of responses. We have drives and urges, and most of our experiences are emotionally colored. This emotional coloring and its relationship with basic drives is the province of the limbic system . The hypothalamus regulates autonomic function and drive-related behavior, and limbic structures serve as bridges between the…

The cerebral cortex is ultimately the part of the CNS that makes us human. Other parts of the CNS like sensory pathways bring in raw data, the reticular activating system adjusts levels of excitability, but the cortex is where events are analyzed, plans are hatched, and responses are formulated. The cerebral cortex is a big sheet of repeated functional modules , with the operations of different…

Photoreceptors throughout the animal kingdom use G protein–coupled transduction mechanisms for added sensitivity, but they pay a price in speed: images need to stay still on the retina for a tenth of second or so at a time to be seen clearly. And for animals with a fovea (like us), images need to stay still on precisely that small part of the retina. All animals with…

The cerebellum helps coordinate movement by sampling most kinds of sensory information, comparing current movements with intended movements, and issuing planning or correcting signals. The comparisons are made in a uniform, precisely organized, cerebellar cortex, and the planning or correcting signals are issued through a set of deep cerebellar nuclei. Because its output is concerned with coordination of movement and not with perception, cerebellar lesions cause…

Historically, the basal ganglia have been considered as major components of the motor system. In fact, they have a much broader role than that and are probably involved to some extent in most forebrain functions. However, their relationship to movement is their best understood aspect, and that is what shows up clinically in disorders like Parkinson disease and Huntington disease. The interrelationships of the basal ganglia…

The firing rates of our motor neurons, and therefore the states of contraction of our muscles, are determined by multiple influences. Simple reflex arcs like the stretch reflex and more complex motor programs like the basic pattern generator for walking are built into the spinal cord and brainstem. Various descending pathways influence these reflex arcs and motor programs, as well as the motor neurons themselves. Finally,…

The visual system is the most studied sensory system, partly because we are such a visually oriented species and partly because of its relative simplicity. In addition, the visual pathway is highly organized in a topographical sense, so even though it stretches from the front of your face to the back of your head, damage anyplace causes deficits that are relatively easy to understand. The Eye…

The diencephalon is a relatively small, centrally located part of the cerebrum that, like the spinal cord and brainstem, is functionally important way out of proportion relative to its size. It is subdivided into four general regions, each with the term “thalamus” as all or part of its name. The Diencephalon Includes the Epithalamus, Subthalamus, Hypothalamus, and Thalamus Key Concepts The epithalamus includes the pineal gland.…

The previous four chapters presented various aspects of the brainstem and its cranial nerves bit by bit. This chapter summarizes the major points, using as a vehicle the same series of drawings of brainstem sections used in Chapter 11 but with additional structures and brief descriptions added. A few of the structures (e.g., substantia nigra) are dealt with more fully in later chapters. FIG 15.1 Levels…

The eighth nerve is the nerve of hearing and equilibrium. All of its receptive functions are accomplished by variations on a common theme; the different sensory information carried by different fibers in the nerve is simply the result of slight differences in the mechanical arrangement of receptors and accessory structures. Auditory and Vestibular Receptor Cells Are Located in the Walls of the Membranous Labyrinth Key Concept…

The Perception of Flavor Involves Gustatory, Olfactory, Trigeminal, and Other Inputs When we eat food or drink a beverage, we have a unified perception, centered on the tongue, of some mixture of flavors. However, this unified perception actually results from the CNS combining multiple kinds of information—somatosensory inputs reflecting things like temperature, texture, and fizziness, as well as inputs about the chemical makeup of the food…

Cranial nerves and their central connections often look bewilderingly complicated, but for the most part they are actually arranged systematically. Cranial Nerve Nuclei Have a Generally Predictable Arrangement Key Concept The sulcus limitans intervenes between motor and sensory nuclei of cranial nerves. The olfactory nerve (I) is a series of thin filaments that attach directly to the olfactory bulb, part of the telencephalon. Fibers of the…

The Brainstem Has Conduit, Cranial Nerve, and Integrative Functions The brainstem is another part of the CNS whose importance is out of proportion to its size. All of the long tracts traverse the brainstem on their way to or from the spinal cord, so the brainstem has conduit functions. In addition, through connections with cranial nerves , the brainstem takes care of the same basic sensory…

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…