#6 GUSTATORY AND OLFACTORY SYSTEMS, THALAMUS .Gustatory System (186-187)
1.All taste fibers from the tongue and epiglottis terminate in the rostral part of the nucleus solitarius. This nucleus surrounds the tractus solitarius (T4AL (labeled), T3L (unlabeled) or H5-11). The nucleus projects to the VPM nucleus of the thalamus (T9CL or H5-30) via the central tegmental tract (T5L, T6HighL or H5-13, H5-17, H5-20). The cortical representation of taste is in the insular cortex and in the postcentral gyrus.
1.Examine the inferior surface of the frontal lobe on the gross brain or the brain stem and note the olfactory bulb in the olfactory sulcus. Trace the olfactory tract backward and note the olfactorytrigone (H2-23) from which three stria can be traced. The medial olfactory stria should be followed into the septal area. The medial olfactory stria reaches the contralateral olfactory tract via the anterior commissure (T11L, T12L or H5-35).
2.The intermediate stria or tract disappears beneath the surface of the anterior perforated substance (H2-23). Identify the parahippocampal gyrus (H2-14). It ends anteriorly in a hook-like expansion, the uncus (H2-17). Underlying the uncus is the amygdaloid nucleus (H3-6) The gray matter of the amygdaloid nucleus lies deep to the upper surface of the uncus. It should also be located on gross sections through this region in which it will be found to occupy the roof of the anterior end of the inferior horn of the lateral ventricle (H4-3). The lateral olfactory stria can be traced along the border of the anterior perforated substance. It dips into the lateral sulcus to enter the temporal lobe reaching as far back as the cortex of the uncus (piriform area). Axons in the lateral stria reach the piriform cortex (T11L) on the surface of the uncus, the entorhinal cortex in the parahippocampal gyrus (T9BL) and the amygdaloid nucleus (T10L or H5-34).
1.Use the axial and frontal (coronal) sections of the gross brain to confirm the general position of the thalamus between the third ventricle and internal capsule (H4-6, H4-12). The pulvinar (H4-8, H3-7) can be seen on the gross brain as the large mass partially covering the geniculate bodies.
2.Study the thalamic nuclei (T9AL, T10L, T11L, T12L, S1L, S2L, S3L, S4L, & S5L). The position of the thalamus relative to the third ventricle should be reviewed. Caudally, the pulvinar is the first nucleus seen. Note just lateral to the pulvinar (T9AL) the visual and auditory relay nuclei, the lateral and medial geniculate bodies (H5-26). The pulvinar is particularly well shown in sagittal sections (S3L, S4L & S5L, 163-169). The pulvinar is involved in integration of sensory information and projects to association cortical areas but its role is largely unknown. The internal medullary lamina separates the medial from the lateral nuclei. Although it has not been identified on our sections, it may be seen as a thin band of fibers between dorsomedial and VL nuclei (T10L, T11L or H5-31). The centromedian nucleus (S3L, S4L or H5-30) is situated within the lamina. The anterior group of nuclei, anterior and ventral anterior nuclei (T12L or H5-33), can be viewed best on slides of all sagittal sections (155). The anterior is involved in the limbic system and the ventral anterior receives input mainly from basal ganglia and projects to the motor cortex. The lateral group is divided into lateral and ventral nuclei. Identify the lateral posterior nucleus (T9CL). This nucleus is involved in emotional expression. The lateral dorsal nucleus (T10L, T11L, S3L or H5-31) is part of the limbic system. The ventral lateral nucleus (T10L, T11L or H5-31 and all sagittal sections) receives input mainly from the cerebellum and projects to the motor cortex. The dorsomedial nucleus (T9AL, T10L, T11L, S2L, S3L or H5-31, H5-32 & H5-33, 163-167) is also involved in the limbic system. The general sensory relay nuclei are ventralposterolateral and ventralposteromedial nuclei (T9CL, S4L or H5-30).
3.Review the 1 cm. transverse sections of the head. On the slides identify:
a.NG13falx cerebri, the superior sagittal sinus, gray matter, white matter, subarachnoid space.