DIENCEPHALON PITUITARY GLAND TELENCEPHALON
DIENCEPHALON
The diencephalon , which translates as “between brain”. The diencephalon sits “atop” the brainstem. The third ventricle is situated between the two thalami. Two thalami are often connected across the midline by nervous tissue, the massa intermedia The diencephalon is situated within the brain below the level of the body of the lateral ventricles - the thalamus forms the “floor” of this part of the ventricle.
The narrow anterior pole of thalamus lies close to the midline and forms the posterior boundary of the interventricular foramen. Posteriorly, an expansion, the pulvinar , extends beyond the third ventricle to overhang the superior colliculus. The brachium of the superior colliculus (superior quadrigeminal brachium) separates the pulvinar above from the medial geniculate body below. A small oval elevation, the lateral geniculate body , lies lateral to the medial geniculate.
The superior (dorsal) surface of the thalamus is covered by a thin layer of white matter , the stratum zonale . The stratum zonale extends laterally from the line of reflection of the ependyma (taenia thalami) and forms the roof of the third ventricle . This curved surface is separated from the overlying body of the fornix by the choroid fissure , with the tela choroidea within it.
The lateral border of the superior surface of the thalamus is marked by the stria terminalis and the overlying thalamostriate vein, which separate the thalamus from the body of the caudate nucleus. The medial surface of the thalamus is the superior (dorsal) part of the lateral wall of the third ventricle. The medial surface of the thalamus is usually connected to the contralateral thalamus by an interthalamic adhesion behind the interventricular foramina.
The boundary with the hypothalamus is marked by an indistinct hypothalamic sulcus, which curves from the upper end of the cerebral aqueduct to the interventricular foramen . The diencephalon, including both thalamus and hypothalamus and some other subparts, is situated between the brainstem and the cerebral hemispheres , deep within the brain. In a horizontal section of the hemispheres, the two thalami are located at the same level as the lentiform nucleus of the basal ganglia.
THALAMUS The thalamus is usually described as the gateway to the cerebral cortex. The most thalamic nuclei that project to the cerebral cortex also receive input from that area - these are called reciprocal connections . The major function of the thalamic nuclei is to process information before sending it on to the select area of the cerebral cortex. This is particularly so for all the sensory systems, except the olfactory sense.
THALAMUS Two subsystems of the motor systems, the basal ganglia and the cerebellum , relay in the thalamus before sending their information to the motor areas of the cortex. Other thalamic nuclei are related to areas of the cerebral cortex, which are called association areas , vast areas of the cortex that are not specifically related either to sensory or motor functions. The major function of the thalamic nuclei is to process information before sending it on to the select area of the cerebral cortex.
THALAMUS THE THALAMUS
THALAMUS THE THALAMUS largest division of the diencephalon receives precortical input from all sensory systems except the olfactory system. largest input received from the cerebral cortex projects primarily to the cerebral cortex and to a lesser degree to the basal nuclei and hypothalamus plays an important role in sensory and motor system integration
THALAMUS Other parts of the DIENCEPHALON : • hypothalamus , one in each hemisphere, is composed of a number of nuclei that regulate homeostatic functions of the body, including water balance. • pineal is sometimes considered a part of the diencephalon. This gland is thought to be involved with the regulation of our circadian rhythm. Many people now take melatonin, which is produced by the pineal, to regulate their sleep cycle and to overcome jetlag. • subthalamic nucleus
THALAMUS THALAMIC NUCLEI both project to and receive fibres from the cerebral cortex . The thalamus is the major route by which subcortical neuronal activity influences the cerebral cortex , and the greatest input to most thalamic nuclei comes from the cerebral cortex. Each cortical area projects in a topographically organized manner to all sites in the thalamus from which it receives an input. Internally, the thalamus is divided into anterior , medial and lateral nuclear groups by a vertical Y-shaped sheet of white matter, the internal medullary lamina . The intralaminar nuclei lie embedded within, and surrounded by, the internal medullary lamina .
THALAMUS THALAMIC NUCLEI - ANTERIOR NUCLEUS • receives hypothalamic input from the mammillary nucleus via the mammillothalamic tract . • receives hippocampal input via the fornix . • projects to the cingulate gyrus (anterior limbic area). • part of the Papez circuit of emotion (the limbic system, control of expression). • are believed to be involved in the regulation of alertness and attention and in the acquisition of memory .
THALAMUS THALAMIC NUCLEI - DORSOMEDIAL NUCLEUS (MEDIODORSAL NUCLEUS) This most important nucleus relays information from many of the thalamic nuclei as well as from parts of the limbic system (hypothalamus and amygdala) to the prefrontal cortex
THALAMUS THALAMIC NUCLEI - DORSOMEDIAL NUCLEUS (MEDIODORSAL NUCLEUS) • reciprocally connected to the prefrontal cortex . • has abundant connections with the intralaminar nuclei . • receives input from the amygdala , the temporal neocortex , and the substantia nigra . • part of the limbic and striatal systems . • when destroyed results in memory loss (Wernicke–Korsakoff syndrome). • plays a role in the expression of affect , emotion , and behavior (limbic function). • damage may lead to a decrease in anxiety, tension, aggression or obsessive thinking. • there may also be transient amnesia, with confusion developing over time.
THALAMUS THALAMIC NUCLEI - INTRALAMINAR NUCLEI intralaminar, midline, and reticular nuclei - these nuclei receive from other thalamic nuclei and from the ascending reticular activating system, as well as receiving fibers from the “slow” pain system; they relay to widespread areas. THALAMIC NUCLEI - INTRALAMINAR NUCLEI • receive input from the brainstem reticular formation, the ascending reticular system, and other thalamic nuclei. • receive spinothalamic and trigeminothalamic input. • project diffusely to the neocortex. • projects to the dorsomedial nucleus.
THALAMUS THALAMIC NUCLEI - INTRALAMINAR NUCLEI 1. Centromedian nucleus largest of the intralaminar nuclei reciprocally connected to the motor cortex (area 4) receives input from the globus pallidus projects to the striatum projects diffusely to the neocortex 2. Parafascicular nucleus projects to the striatum and the supplementary motor cortex (area 6)
THALAMUS THALAMIC NUCLEI DORSAL TIER NUCLEI 1. Lateral dorsal nucleus 2. Lateral posterior nucleus 3. Pulvinar
THALAMUS THALAMIC NUCLEI - DORSAL TIER NUCLEI 1. Lateral dorsal nucleus • a posterior extension of the anterior nuclear complex • receives mammillothalamic input • projects to the cingulate gyrus • has reciprocal connections with the limbic system 2. Lateral posterior nucleus • located between the lateral dorsal nucleus and the pulvinar • has reciprocal connections with the superior parietal cortex (areas 5 and 7) 3. Pulvina This nucleus is part of the visual relay, but relays to visual association areas of the cortex, areas 18 and 19
THALAMUS THALAMIC NUCLEI - DORSAL TIER NUCLEI 3. Pulvinar • the largest thalamic nucleus • has reciprocal connections with the association cortex of the occipital, parietal, and posterior temporal lobes • receives input from the lateral and medial geniculate bodies and the superior colliculus • concerned with the integration of visual, auditory, and somesthetic
THALAMUS THALAMIC NUCLEI VENTRAL TIER NUCLEI include primarily specific relay nuclei: 1. Ventral anterior nucleus 2. Ventral lateral nucleus 3. Ventral posterior nucleus a. Ventral posterolateral (VPL) nucleus b. Ventral posteromedial (VPM) nucleus c. Ventral posteroinferior (VPI) nucleus
THALAMUS THALAMIC NUCLEI - VENTRAL TIER NUCLEI 1. Ventral anterior nucleus • receives input from the globus pallidus and the substantia nigra • projects diffusely to the prefrontal and orbital cortices • projects to the premotor cortex (area 6)
THALAMUS THALAMIC NUCLEI - VENTRAL TIER NUCLEI 2. Ventral lateral nucleus • receives input from the globus pallidus, substantia nigra, and the cerebellum (dentate nucleus) • projects to the motor cortex (area 4) and to the supplementary motor area (area 6) • influences somatic motor mechanisms via the striatal motor system and the cerebellum • stereotactic destruction reduces Parkinsonian tremor
THALAMUS THALAMIC NUCLEI - VENTRAL TIER NUCLEI 3. Ventral posterior nucleus the nucleus of termination of general somatic afferent (GSA; pain and temperature) and special visceral afferent (SVA; taste) pathways
THALAMUS THALAMIC NUCLEI - VENTRAL TIER NUCLEI 3. Ventral posterior nucleus contains three subnuclei: a. Ventral posterolateral (VPL) nucleus b. Ventral posteromedial (VPM) nucleus c. Ventral posteroinferior (VPI) nucleus
Recommend
More recommend
