Brain Internal Structure Dr. Nimir Dr. Safaa

Objectives Describe the types of fibers in the internal capsule. Identify the basal ganglia nuclei. Identify main parts of the diencephalons and name the main functions of each part Briefly describe the brain ventricles and meanings. Describe the organization of the cerebral cortex. (Layers and columnar organization). Locate the motor, sensory and other cortical areas. Describe the cortical areas related to the written and spoken language. Identify the structures in coronal, sagittal and horizontal sections of brain.

Internal capsule It has : Anterior limb Genu Posterior limb. It is medial to lentiform nucleus and lateral to the thalamus and cuadate nucleus. It contains projection fibers.

Basal ganglia are masses of gray matter situated deep within each cerebral hemisphere. They are: Corpus striatum. Amygdaloid nucleus. Claustrum. Corpus striatum is divided by internal capsule, into caudate nucleus and lentiform nucleus( putamen & globus pallidus).

Diencephalon The diencephalon consists of the third ventricle and the structures that form its boundaries. It is divided into: Thalamus. Subthalamus. Hypothalmus. Epithalamus.

Ventricular System: The ventricles are four cerebrospinal fluid-filled cavities located within the brain. Two lateral ventricles. Third ventricle. Fourth ventricle. Lateral ventricles communicate through interventricular foramina (of Monro) with third ventricle. The third is connected to the fourth by cerebral aqueduct (of Sylvius).

Meninges: Brain and spinal cord are surrounded by three membranes (meninges). Dura mater. Arachnoid mater. Pia mater.

Cortical layers Molecular layer (plexiform layer). External granular layer. External pyramidal layer. Internal granular layer. Internal pyramidal (ganglionic ) layer. Multiform layer (layer of polymorphic cells).

Columnar organization Cortex is organized into vertical columns of functional activity Extends from the cortical surface to the white matter. Each column possesses: o Afferent fibers o Internuncial neurons o Efferent fibers

Cortical areas Frontal lobe:  Precentral area includes: 1. Precentral gyrus 2. Paracentral lobule 3. Posterior parts of : Superior,middle and inferior frontal gyri.

 Motor area( primary motor area, or Brodmann area 4) occupies posterior part of precentral gyrus and paracentral lobule.  Premotor area (secondary motor area, or Brodmann area 6,8, 44, and 45) occupies the anterior part of precentral gyrus and posterior parts of superior, middle, and inferior frontal gyri.

 Supplementary motor area is anterior to paracentral lobule. Frontal eye field extends from the facial area of precentral gyrus into middle frontal gyrus (parts of Brodmann areas 6, 8, and 9).  Motor speech area of Broca is located in the inferior frontal gyrus.

 Prefrontal cortex lies anterior to the precentral area. It includes: Greater parts of superior, middle, inferior frontal gyri & orbital gyri. Most of medial frontal gyrus, and anterior half of cingulate gyrus (Brodmann areas 9, 10, 11, and 12).

Movement areas of the body are represented in inverted form in the precentral gyrus.

Parietal lobe: Primary somesthetic area (primary somatic sensory cortex) occupies postcentral gyrus and posterior part of paracentral lobule (Brodmann areas 3, 1, and 2). Secondary somesthetic area (secondary somatic sensory cortex ) is in superior part of lateral fissure. Somesthetic association area occupies superior parietal lobule and extending onto medial surface (Brodmann areas 5 and 7).

Occipital lobe Primary visual area (Brodmann area 17) is situated in walls of posterior part of calcarine sulcus and around occipital pole onto the lateral surface. Secondary visual area (Brodmann areas 18 and 19) surrounds the primary visual area. Occipital eye field exists in secondary visual area.

Temporal lobe: Primary auditory area (Brodmann areas 41,42) includes the gyrus of Heschl is situated in inferior wall of the lateral sulcus. Secondary auditory area ( association) is posterior to primary area and in superior temporal gyrus (Brodmann area 22). Sensory speech area of Wernicke is in dominant hemisphere, mainly in superior temporal gyrus, with extensions into the parietal region. Wernicke area is connected to Broca area by arcuate fasciculus.

Other cortical areas: Taste & smell area (gustatory) is in lower end of postcentral gyrus in the insula. Vestibular area lies opposite auditory area in the superior temporal gyrus. Primary sensory and primary motor areas form only a small part of cortical surface area. Remaining areas are association areas which concerned with behavior, discrimination, and interpretation of sensory experiences.

Brain sections