Brain cerebrum

The mesencephalon, or midhrain, serves as a bridge between the higher areas of the brain (cerebrum and diencephalon) and the brainstem. The brainstem consists of the pons and the medulla oblongata. In addition to serving as a pathway between the higher brain and spinal cord, the midbrain and brainstem are the locations of centers responsible for controlling respiration and cardiovascular function (vasomotor center). 

Tumor, infarction (stroke/ischemia), haemorrhage (bleeding/ ischemia) and infection (abscess) are the example of brain lesions that are affected in the brain cerebrum. In 2006, it was reported that tumor and brain diseases such as brain infarction and haemorrhage were the third and fourth leading cause of death in Malaysia [1]. The incidence of brain tumor in 2006 was 3.9 among males and 3.2 among females per 100,000 populations with a total of 664 cases reported by the Minister of Health Malaysia. In the United States, the combined incidence of primary brain tumor was 6.6 per 100,000 persons per year with a total of 22,070 new cases in 2009 [2], while brain infarction affects approximately 750,000 new cases per year [3]. 

The spinal cord is the most anatomically inferior portion of the CNS and its functions are at the lowest level of sophistication (see Table 6.1). As mentioned earlier, the spinal cord receives sensory input from the periphery of the body and contains the cell bodies of motor neurons responsible for voluntary and involuntary movements. Once again, the involuntary and neurologically simple reflexes are processed entirely at the level of the spinal cord. Voluntary, deliberate movements are initiated and controlled by thought processes in the cerebrum. The second important function of the spinal cord is to transmit nerve impulses to and from the brain. Ascending pathways carry sensory input to higher levels of the CNS and descending pathways carry impulses from the brain to motor neurons in the spinal cord. 

The brain is the integrative portion of the nervous system that serves to receive, process, and store sensory information and then plan and orchestrate the appropriate motor response. It is divided into several anatomically and functionally distinct regions (see Table 6.2). The forebrain consists of the cerebrum, basal ganglia, thalamus, and hypothalamus. The midbrain, along with the pons and the medulla of the hindbrain, composes the functional region referred to as the brainstem. The cerebellum is also considered a component of the hindbrain but is functionally distinct from the brainstem. 

Figure 6.2 Frontal section of the brain. The cerebrum is composed of two types of tissue internal white matter and external gray matter which forms the cerebral cortex. Embedded within the cerebral hemispheres are other masses of gray matter, basal ganglia, and thalamus. The ventricles are filled with cerebrospinal fluid (CSF).

Named for the bones of the cranium under which they lie, the lobes are conspicuously defined by prominent sulci of the cortex, which have a relatively constant position in human brains. Each lobe is specialized for different activities (see Figure 6.3). Located in the anterior portions of the hemispheres, the frontal lobes are responsible for voluntary motor activity, speaking ability, and higher intellectual activities. The parietal lobes, which are posterior to the frontal lobes, process and integrate sensory information. The occipital lobes, located in the posterior-most aspects of the cerebrum, process visual information, and the temporal lobes, located laterally, process auditory information. 

The gray matter is composed of nerve cell bodies and unmyelinated intemeuron fibers. The location of the gray matter in the spinal cord is opposite to that of the brain. In the brain, the gray matter of the cerebrum and the cerebellum is found externally forming a cortex, or covering, over the internally located white matter. In the spinal cord, the gray matter is found internally and is surrounded by the white matter. 

Fig. 9.4 Evolutionary change in the zones of vertebrate brains. Note that the figures are related here to the cerebrum cortex so that in man the hindbrain appears twisted downwards to allow for human upright stance.

Fig. 9.5 A midsagittal section through the human brain. Note that in this type of section half of the brain is cut away so that structures normally covered by the cerebrum are exposed.

It may be noted that the retina represents an outlying portion of the brain itself. It arises as a protrusion from the prosencephalon (anterior portion of the cerebrum), and, being a constituent part of the brain, presents the same anatomical and physiological problems as does the central nervous system elsewhere. The more or less complete spatial separation of the synapses from the cell bodies makes the retina eminently suitable for finding out whether a known biochemical constituent is located in the cell bodies, axons, dendrites or at the synapses, and the information so obtained may perhaps be applicable to other parts of the nervous system, where the cell bodies and the synapses are all too intimately mingled for a proper analysis. 

Cerebrovascular Pertaining to the blood vessels of the cerebrum, or brain. [EU]... 

Cerebrospinal fluid is produced in chambers within the brain called ventricles. Two lateral ventricles and a midline third ventricle are contained within the cerebrum, while the fourth ventricle exists within the brain stem. CSF is produced by the choroid plexus in the lateral and third ventricles. It flows out through the ventricles by a series of aqueducts and into subarachnoid space. CSF supports the brain and spinal cord, ab-... 

As we move forward, it will prove helpful to get some basic aspects of the human nervous system in place. An enormous amount of work has gone into making associations between brain anatomy and function. Starting with the three main parts of the brain, we know that the cerebrum is the seat of consciousness. It is divided into two hemispheres, which are linked by the corpus callosum. In a very general sense, the left hemisphere is associated with intellectual and the right hemisphere with emotional responses. Within the cerebrum, one can associate a number of brain areas (the prefrontal, frontal, temporal, parietal, and occipital lobes, for example) with functions including vision and hearing. One can make crude maps in which function is mapped onto brain structure. 

The central nervous system consists of the brain and spinal cord. The average adult brain weighs 1250-1380 grams. The brain is divided into three gross parts the brainstem, the cerebrum, and the cerebellum. Structurally, the brain may be likened to a bouquet of flowers with the cerebrum (as two cerebral hemispheres) blossoming outwards above the brainstem the cerebellum is attached at the back of the brainstem. 

Figure 4.4 General structure of the brain the central nervous system consists of the spinal cord and the brain. The brain consists of the brain stem (medulla oblongata, cerebellum, pons, mesencephalon, diencephalon) and the cerebrum (cerebral hemispheres, subcortical white matter, basal ganglia).

The anatomy of the brain and spinal column is very complex. The outer, most visible portion of the brain is known as the cerebrum. The cerebrum accounts for about 80% of the mass of the brain. Covered with a layer of grey matter known as the cerebral cortex, the cerebrum is divided into two hemispheres -left and right. 

Tire anatomy of the brain is quite complex, and only a few terms will be defined here. Tire cerebrum, which is made up of two hemispheres, accounts for the largest part of the brain. Tire deeply folded outermost layer, the cerebral cortex, consists of gray matter, a mass of cell bodies, and fine unmyelinated nerve fibers. Beneath this lies a layer of white matter made up of myelin-covered axons connecting the cerebral cortex with other parts of the brain. Tire two cerebral hemispheres are connected by the corpus callosum, a band of 2 x 108 nerve fibers. Remarkably, these fibers can be completely severed with a relatively minimal disruption of the nervous system. In the past the corpus callosum was sometimes cut to control almost incessant epileptic seizures that could not be prevented by drugs. The "split-brain" patients suffered relatively little disability as long as both eyes functioned normally. Studies of these patients provided some insights into the differing functions of the two hemispheres of the cerebrum.395... 

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