Neuronal Navigation and Docking During Early Development

The stages involved in the creation of the neuronal network of the brain and spinal cord and its integration with the peripheral nerves during prenatal development are precise and apparently predetermined to a considerable degree. The first two stages are pathway selection and target selection. In humans, they are instrumental in establishing the basic groundwork of the neuronal networks and pathway systems during prenatal life. The third, the activity-dependent and experience-dependent stage,...

Myasthenia Gravis An Autoimmune Disease

Myasthenia gravis is a muscle weakness disability that is associated with defects of transmission at the motor end-plate junctions between nerve endings and the voluntary muscle acetylcholine receptors (ACh receptors). Figure 12.1. Schemata of the spinal cord to indicate the sites of lesions noted in the text. Arabic numbers refer to specific lesions. C5 to T1 indicate the cervical enlargement, the region involved with innervation of the upper extremity. 1, ventral roots of spinal nerves 2a,...

Central Autonomic Control Circuits

Central autonomic control circuits coordinate autonomic functions and the ongoing behavioral needs of the organism through the activities of the somatomotor, endocrine, and autonomic systems. These systems are represented in overlapping regions of the brain. The behavioral strategies and reflex mechanisms within these circuits act in the defense of the organism and in homeostasis, which are coordinated by interconnected groups of nuclei in the brainstem and higher forebrain centers. Three of...

Sleep Wake Cycle

A normal day is divided into waking and sleeping phases. Sleep typically occurs in repetitive cycles of different stages as eluci dated by direct observation, electrical recordings of brain waves (electroencephalogram or EEG), recordings of muscle activity (elec-tromyogam), and recordings of eye movement (electro-oculogram). Stage 1 is a transitional light sleep that lasts for but a few minutes during which muscles relax as one drifts in and out of wakefulness. The body temperature is lowered,...

Modular Organization of the Brain

An emerging view is that the brain is structurally and functionally organized into discrete units or modules' and that these components interact to produce mental activities (Gaz-zaniga, 1989). In a broad sense, the major sensory systems, such as the visual system, are complexes of modular systems. In turn, each system comprises several modules. This is expressed in the visual system, where several anatomically and physiologically documented modules, including cortical areas, are embedded...

Regulation Of Water Balance

The hypothalamus has significant roles in fluid balance by regulating both the intake (by drinking) and output (through kidneys and sweat glands) of water. Evidence indicates that a drinking or thirst center is located in the lateral hypothalamus and a thirst satiety center in the medial hypothalamus. The osmore-ceptor neurons in these hypothalamic centers respond to the osmolality (electrolyte composition) of the blood passing through these nuclei. They set off events that stimulate or inhibit...

Cerebrospinal Fluid

Cephalography

Cerebrospinal fluid is a crystal clear, colorless solution that looks like water and is found in the ventricular system and the subarachnoid space. It consists of water, small amounts of protein, gases in solution (oxygen and carbon dioxide), sodium, potassium, magnesium, and chloride ions, glucose, and a few white cells (mostly lymphocytes). The CSF, formed primarily by a combination of capillary filtration and active epithelial secretion, serves two major functional roles 1. Physical Support....

Gastrointestinal Gut Brain Peptides

These peptides were initially identified in the gastrointestinal (GI) tract and were later found in the nervous system. Secretin glucogon peptide family, an intestinal acid calcification hormone, is synthesized by the hypothalamic stress axis and cerebellum and is involved in modulating stress adaptation reactions. Vasoactive intestinal peptide (VIP) is widely distributed in the CNS and in the intrinsic neu rons of the gut. It is found in high concentrations in the cerebral cortex, hippocampus,...

Amygdala The Nodal Processing Center of the Subcortical Limbic Circuitry see Fig 222

The almond-shaped amygdala (amygdaloid complex) is located within the tip of the temporal lobe deep to the uncus and rostral to the hippocampus. The amygdala is the key structure involved in analyzing and processing the emotional and motivational significance of an array of sensory stimuli and, in turn, coordinating and activating several neuronal systems that mediate inborn and acquired responses with an emotional nuance. The amygdala receives inputs from several sources (1) Stimuli signaling...

Spinal Reflex Arcs

Reflex responses are mediated by neuronal linkages called reflex arcs or loops. The structure of a spinal somatic reflex arc can be summarized in the following manner. (1) A sensory receptor responds to an environmental stimulus. (2) An afferent fiber conveys signals through the peripheral nerves to the gray matter of the spinal cord. (3a) In the simplest reflex arc, the afferent root enters the spinal cord and synapses directly with lower motoneurons (monosynaptic reflex see Fig. 8.1). (3b) In...

The Spinal Cord

Anatomic Organization Spinal Roots and Peripheral Nerves Laminae of the Spinal Cord Pathways and Tracts The spinal cord is a slender cylindrical structure less than 2 cm in diameter composed of gray and white matter that is located in the upper two-thirds of the vertebral canal and is surrounded by the bony vertebral column. It is the central processing and relay station (1) receiving input via peripheral nerves from the body and via descending tracts from the brain and (2) projecting output...

Schizophrenia and the Limbic System

Schizophrenia is a mental disorder that features a disturbance of cognitive and sensory processes leading to hallucinatory experiences, delusions, and disturbances of thought. In addition, the illness shares many features such as paranoia, suspiciousness, and unrealistic thinking. This serious disorder is characterized by a loss of contact with reality (psychosis). Patients with lesions of the prefrontal cortex have behaviors indicative of a diminished ability to plan and to organize daily...

Internal Capsule

The internal capsule is a massive bundle of nerve fibers, which contains almost all of the fibers projecting from the subcortical nuclei to the cerebral cortex and from the cerebral cortex to subcortical structures in the cerebrum, brain-stem, and spinal cord (Fig. 13.4). It is divided into an anterior limb, genu, and posterior limb (Fig. 1.8). Retrolenticular and sublenticular parts of the posterior limb are recognized (Figs. 1.8 and 23.3). The anterior (caudatolenticular) limb is located...

Referred Transferred Pain

Pain of visceral origin usually is vaguely localized. The site of visceral irritation and the locale where the pain is felt are not necessarily the same. The pain can be referred (transferred) from the visceral source to a corresponding dermatomal segment on the body, extremity, or head. Referred pain can also apply to pain from a somatic source. The brain and the parenchyma of visceral organs do not have pain receptors. Such receptors are primarily in the walls of arteries, meninges, and all...

Circuit 5 Substantia Nigra

Striatum substantia nigra thalamus (VA and VL nuclei) portions of the motor cortex (see Figs. 24.2 and 24.4). This circuit involves the substantia nigra. In brief, the substantia nigra (1) receives input from the ipsilateral striatum, subthalamic nucleus, and globus pallidus and (2) projects to the ipsilateral VL and VA thalamic nuclei (see Fig. 24.5) as well as back to the striatum (see Fig. 24.2). The substantia nigra is divided into the ven-trally located pars reticularis, or SNr (adjacent...

Level of the Inferior Colliculus see Fig 1314

The distinguishing features at this level include the inferior colliculi and the decussa-tion of the superior cerebellar peduncle. The ventricular system is represented by the narrow cerebral aqueduct. The large nucleus of the inferior colliculus is a major processing station in the auditory pathways. It receives input from ascending auditory fibers of the lateral lemniscus and from descending fibers from the medial geniculate body it projects influences (1) rostrally to the medial geniculate...

Structure Of Peripheral Nerves And Ganglia

Peripheral nerves include both cranial and spinal nerves. Peripheral ganglia are collections of cell bodies associated with the peripheral nerves. Each nerve consists of three basic tissue elements (1) axons, (2) Schwann cells (neurolemma) and myelin sheaths (interstitial element), and (3) endoneurium, perineurium, and epineurium (connective tissue component). A peripheral ganglion consists of the same three elements (1) neuronal cell bodies and axons, (2) inner satellite cells (interstitial...

Neuron As An Integrator

Peripheral Nerve Microtubules

Each neuron is an integrator of stimuli (neu-rotransmitters) streaming into its dendritic field and onto its cell body (Fig. 3.11). Some of the receptive patches (subsynaptic membranes) on the dendrites and cell body are excitatory others are inhibitory. In addition, as will be described, presynaptic inhibitory activity could indirectly affect some excitatory receptive sites. At any one moment, a neuron might receive hundreds or even thousands of stimuli on its excitatory and inhibitory...

Ventral Nuclear Group

The ventral nuclear group comprises the ventral anterior, ventral lateral and ventral posterior nuclei, as well as the medial and lateral geniculate bodies, which are a caudal extension. Ventral Anterior Nucleus. The ventral anterior (VA) and ventral lateral thalamic nuclei are motor relay nuclei associated with the somatic motor system. The VA nucleus is divided into two subdivisions (1) parvocellular (principal) part (VApc) and (2) magnocellular part (VAmc). Each part receives input from...