Different Lobes Of The Brain – The cerebral cortex is very complicated; the crest of a gyrus is known as a gyrus, and the space between the two gyri is known as a groove. The sulci and gyri form a more or less constant pattern in which the surface of each cerebral hemisphere is divided into four lobes: (1) frontal, (2) parietal, (3) temporal, and (4) occipital. Two large grooves located on the lateral surface of each hemisphere distinguish these lobes. The central sulcus, or Rolando fissure, separates the frontal and parietal lobes, and the deeper lateral sulcus, or Sylvian fissure, forms the boundary between the temporal lobe and the frontal and parietal lobes.
The frontal lobe, the largest of the cerebral lobes, lies rostral to the central sulcus (ie, toward the nose from the sulcus). An important structure in the frontal lobe is the precentral gyrus, which is the primary motor region of the brain. When parts of the gyrus are electrically stimulated in conscious patients (under local anesthesia), they produce localized movements on the opposite side of the body that the patient interprets as voluntary. Lesions in part of the precentral gyrus cause paralysis in the contralateral half of the body. Part of the inferior frontal lobe (near the lateral sulcus) makes up Broca’s area, a region involved in speech (
Different Lobes Of The Brain
The parietal lobe, behind the central sulcus, is divided into three parts: (1) the postcentral gyrus, (2) the superior parietal lobe, and (3) the inferior parietal lobe. The postcentral register receives sensory input from the contralateral half of the body. The sequential representation is the same as in the primary motor area, with sensations from the head represented in the lower part of the gyrus and impulses from the lower extremities represented in the upper part. The superior parietal lobe, located caudal (ie, below and behind) the postcentral gyrus, lies above the intraparietal sulcus. This lobe is considered an association cortex, an area that is not involved in sensory or motor processing, although part of the superior parietal lobe may be involved in motor function. The inferior parietal lobe (composed of the angular and supramarginal gyri) is a cortical region involved in the integration of multiple sensory signals.
Brain Lobes In Different Colors. Isolated On White. Stock Photo By ©alexmit 18646453
In both the parietal and frontal lobes, each primary sensory or motor area is adjacent to or surrounded by a smaller secondary area. The primary sensory area receives input from the thalamus only, while the secondary sensory area receives input from the thalamus, the primary sensory area, or both. The motor areas receive information from the thalamus and the sensory areas from the cerebral cortex.
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The temporal lobe, inferior to the lateral sulcus, fills the median fossa, or hollow area, of the skull. The outer surface of the temporal lobe is an association zone consisting of the superior, middle, and inferior temporal gyri. Near the margin of the lateral sulcus, two transverse temporal gyri constitute the primary auditory area of the brain. Auditory sensations are represented here tonotopically, that is, with different frequencies represented in different parts of the area. The transverse gyri are surrounded by a less wired secondary auditory zone. A medial, or inward, bulge near the ventral surface of the temporal lobe, known as the uncus, makes up a large part of the primary olfactory area.
The occipital lobe lies caudal to the parieto-occipital sulcus, which joins the calcarine sulcus in a Y-shaped formation. The cortex on either side of the calcarine sulcus constitutes the primary visual area, receiving input from the contralateral visual field via optical radiation. The visual field is represented near the calcarine sulcus in a retinotopic fashion, that is, with the upper quadrant of the visual field disposed at the lower margin of the sulcus and the lower quadrant of the visual field represented at the upper margin. Central vision is represented primarily caudally and peripheral vision rostrally.
Radiology Quiz 46670
Not visible on the surface of the brain is the insular or central lobe, an invaginated triangular area on the medial surface of the lateral sulcus; it can be seen in the intact brain only by separating the frontal and parietal lobes from the temporal lobe. The insular lobe is believed to be involved in visceral sensory and motor functions and taste perception.
The limbic lobe is a synthetic lobe located at the medial margin (or limbus) of the hemisphere. Composed of adjacent portions of the frontal, parietal, and temporal lobes that surround the corpus callosum, the limbic lobe is involved in autonomic and somatic activities related to behavior. The limbic lobe receives input from the thalamic nucleus which is connected to parts of the hypothalamus and the hippocampal formation, a primitive cortical structure in the inferior horn of the lateral ventricle.
Deep within the white matter of the cerebral hemispheres are cavities filled with cerebrospinal fluid that form the ventricular system. These cavities include a pair of C-shaped lateral ventricles with anterior, inferior, and posterior “horns” arising from the frontal, temporal, and occipital lobes, respectively. Most cerebrospinal fluid is produced in the ventricles, and about 70 percent is secreted by the choroid plexus, a collection of blood vessels in the walls of the lateral ventricles. Fluid drains through interventricular orifices or openings into a slit-shaped third ventricle that, located along the midline of the brain, separates the symmetrical half of the thalamus from the hypothalamus. From there, the fluid passes through the cerebral aqueduct in the midbrain and into the fourth ventricle in the rhombencephalon. The opening in the fourth ventricle allows cerebrospinal fluid to enter the subarachnoid space that surrounds both the brain and spinal cord.
Deep in the cerebral hemispheres, large gray masses of nerve cells, called nuclei, form the components of the basal ganglia. Four basal ganglia can be distinguished: (1) the caudate nucleus, (2) the putamen, (3) the globus pallidus, and (4) the amygdala. Phylogenetically, the amygdala is the oldest of the basal ganglia and is often referred to as the archistriatum; The globus pallidus is known as the paleostriatum, and the caudate nucleus and putamen together are known as the neostriatum, or simply the striatum. Together, the putamen and adjacent globus pallidus are called the lentiform nucleus, while the caudate nucleus, putamen, and globus pallidus form the striatum.
Your Brain: An Introduction To Its Anatomy
The caudate nucleus and putamen are continuous rostral and ventral, and have the same cellular composition, cytochemical characteristics, and function, but slightly different connections. The putamen is deep in the cortex of the insular lobe, while the caudate nucleus has a C-shaped configuration parallel to the lateral ventricle. The head of the caudate nucleus arises from the anterior horn of the lateral ventricle, the body lies above and lateral to the thalamus, and the tail lies on the roof of the inferior horn of the lateral ventricle. The tail of the caudate nucleus terminates in relation to the tonsillar nuclear complex, located in the temporal lobe below the cortex of the uncus.
There are enormous numbers of neurons in the caudate nucleus and putamen; They have two basic types: spiny and aspinous. Spiny striatal neurons are medium-sized cells with extending dendrites dotted with spines. The axons of these cells project beyond the border of the caudate nucleus and the putamen. All nerves supplying information to the caudate nucleus and putamen terminate on the dendritic spines of spiny striatal neurons, and all output signals are via the axons of the same neurons. Chemically, the spiny neurons of the striatum are heterogeneous; that is, most have more than one neurotransmitter. Gamma-aminobutyric acid (GABA) is the main neurotransmitter found in spiny neurons of the striatum. Other neurotransmitters found in spiny striatal neurons include substance P and enkephalin.
Aspiny striatal neurons have smooth dendrites and short axons confined to the caudate nucleus or putamen. The small spiny neurons of the striatum secrete GABA, neuropeptide Y, somatostatin, or some combination of these. The largest aspiny neurons are evenly distributed neurons that also secrete neurotransmitters and are important in maintaining dopamine and GABA balance.
Because the caudate nucleus and putamen receive varied and diverse inputs from multiple sources using different neurotransmitters, they are considered receptive components of the striatum. Most of the input comes from the region of the cerebral cortex, with connected corticostriatal fibers that contain the excitatory neurotransmitter glutamate. In addition, afferent fibers from a large nucleus located in the middle of the brain called the substantia nigra or the intralaminar thalamic nucleus project to the caudate nucleus or putamen. Neurons in the substantia nigra are known to synthesize dopamine, but the neurotransmitter secreted by thalamostriatal neurons has not been identified. All striatal afferent systems terminate in patchy areas called striosomes; the area that does not receive terminals is called the matrix. Spiny striatal neurons containing GABA, substance P, and enkephalin project in a specific pattern to the globus pallidus and substantia nigra.
Lobes Of The Brain
The globus pallidus, which has two cytologically similar wedge shapes
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