Appunti neuroanatomia - De Caro

Control of Balance and Posture

Fibres in this pathway control balance and posture by innervating the 'anti-gravity' muscles (flexors of the arm, and extensors of the leg), via lower motorneurones.

The two recticulospinal tracts have differing functions: the medialreticulospinal tract arises from the pons. It facilitates voluntary movements, and increases muscle tone; the lateral reticulospinal tract arises from themedulla. It inhibits voluntary movements, and reduces muscle tone.

The rubrospinal tract originates from the red nucleus, a midbrain structure. As thefibres emerge, they decussate (cross over to the other side of the CNS), anddescend into the spinal cord. Thus, they have a contralateral innervation.

This pathway begins at the superior colliculus of the midbrain. The superiorcolliculus is a structure that receives input from the optic nerves. The neuronesthen quickly decussate, and enter the spinal cord. They terminate at thecervical levels of the spinal cord.

The tectospinal tract coordinates

movementsof the head in relation to vision stimuli.

Esopyramidal tract

It is the pathway that carries the motor control information to the cerebellumand so it is called esopyramidal or cortico-ponto-cerebellar pathway. The first-order neuron is in the cerebral cortex and its axon descends til the pons. Sincethe first-order neurons are situated in the frontal lobe, parietal, temporal andoccipital lobe, the pathway consists of more bundles. The second-order neuronis localized in the basal nuclei of pons, whose axons decussate along themedian line and enter though the middle cerebellar peduncle into the cortex ofthe cerebellar hemispheres (neocerebellum). To the cerebellum so arrives theinformation about the movement originated in the cerebral cortex, but to thecerebellar cortex arrives also the static and dynamic information brought bythe spino-cerebellar bundles and also vestibulo-cerebellar information.

Floor of 4 ventricleth

The floor of the fourth ventricle is also referred to as

The rhomboid fossa is divisible into a right and left half by the posterior median sulcus, and into a superior and inferior triangle by the striae medullares. The upper triangular part is formed by the posterior surface of the pons. The upper part of the posterior surface of the medulla and an intermediate part at the junction of the medulla and pons make up the lower triangular part. For ease of description of the floor of the fourth ventricle, the median sulcus is used as a major feature. On either side of this sulcus lies a longitudinal elevation called the medial eminence. This eminence is limited laterally by the sulcus. The area is called the vestibular area and houses the vestibular nuclei. Thus, the vestibular area lies partly in the pons and partly in the medulla.

The uppermost part of the sulcus limitans overlies an area called the locus coeruleus, deep to which there is a nucleus called the nucleus coeruleus extending into the tegmentum of the midbrain. Lower down

The sulcus limitans is a depression referred to as the superior fovea. At the level of this depression, the median eminence shows a swelling called the facial colliculus. Within the medullary part of the floor, the sulcus limitans is marked by a depression, the inferior fovea. Inferior to this inferior fovea is an oblique sulcus running towards the midline and dividing the medial eminence into two triangles called the hypoglossal and vagal triangles (or the hypoglossal and vagal trigones). The hypoglossal triangle lies medial and the vagal, lateral. These triangles house the hypoglossal and vagal nuclei respectively. The vagal triangle defines an area with the gracile tubercle called the area postrema.

The diencephalon: macroscopic anatomy of thalamus, subthalamus and hypothalamus

The diencephalon is part of the prosencephalon (forebrain), which develops from the foremost primary cerebral vesicle and differentiates into a caudal diencephalon and a rostral telencephalon. The diencephalon

The structure of the diencephalon largely corresponds to the structures that develop laterally to the third ventricle. The lateral walls of the diencephalon form the epithalamus most superiorly, the thalamus centrally, and the subthalamus and hypothalamus most inferiorly.

The thalamus is a large ovoid mass of gray matter that forms the major part of the diencephalon. It is a region of great functional importance and serves as a cell station to all the main sensory systems (except the olfactory pathway).

The anterior end of the thalamus is narrow and rounded and forms the posterior boundary of the interventricular foramen. The posterior end is expanded to form the pulvinar, which overhangs the superior colliculus and the superior brachium.

The lateral geniculate body forms a small elevation on the under aspect of the lateral portion of the pulvinar. The medial surface of the thalamus forms the superior part of the lateral wall of the third ventricle and is usually connected to the opposite thalamus by a band of gray matter.

theinterthalamic connection (interthalamic adhesion). The lateral surface of thethalamus is separated from the lentiform nucleus by the very important bandof white matter called the internal capsule. In addition to being divided intoanterior, medial and lateral parts by the internal medullary lamina, the nucleiof the thalamus are further subdivided into those that are dorsal and those thatare ventral. Together there are sixteen nuclei that are found in the thalamus.Most of these cell bodies are located in the larger lateral part of the thalamus.The subthalamus lies inferior to the thalamus and,therefore, is situatedbetween the thalamus and the tegmentum of the midbrain; craniomedially, it isrelated to the hypothalamus. The structure of the subthalamus is extremelycomplex, and only a brief description is given here. Among the collections ofnerve cells found in the subthalamus are the cranial ends of the red nuclei andthe substantia nigra. The subthalamic nucleus has the shape of a

The nucleus has important connections with the corpus striatum; as a result, it is involved in the control of muscle activity. The subthalamus also contains many important tracts that pass up from the tegmentum to the thalamic nuclei; the cranial ends of the medial, spinal, and trigeminal lemnisci are examples.

The hypothalamus is that part of the diencephalon that extends from the region of the optic chiasma to the caudal border of the mammillary bodies. It lies below the hypothalamic sulcus on the lateral wall of the third ventricle. The hypothalamus controls and integrates the functions of the autonomic nervous system and the endocrine systems and plays a vital role in maintaining body homeostasis. It is involved in such activities as regulation of body temperature, body fluids, drives to eat and drink, sexual behavior, and emotion.

The telencephalon: macroscopical anatomy

The cerebral hemispheres are the largest part of the human brain. They each have a highly convoluted external cortex,

Beneath which lies an extensive internal mass of white matter that contains the basal ganglia. Each hemisphere also contains a lateral ventricle, continuous with the third ventricle through the interventricular foramen. They are separated by a deep midline sagittal fissure, the longitudinal cerebral fissure. The fissure contains the sickle-shaped fold of dura mater, the falx cerebri, and the anterior cerebral arteries. In the depths of the fissure, the great commissure, the corpus callosum, connects the hemispheres across the midline. A second horizontal fold of dura mater separates the cerebral hemispheres from the cerebellum and is called the tentorium cerebelli. To increase the surface area of the cerebral cortex maximally, the surface of each cerebral hemisphere is thrown into folds or gyri, which are separated from each other by sulci or fissures. For ease of description, it is customary to divide each hemisphere into lobes, which are named according to the cranial bones under which they lie.

The central and parieto-occipital sulci and the lateral and calcarine sulci are boundaries used for the division of the cerebral hemisphere into frontal, parietal, temporal, and occipital lobes.

Organization of WM in the telencephalon: associative and non-associative bundles

The white matter is composed of myelinated nerve fibers of different diameters supported by neuroglia. The nerve fibers may be classified into three groups according to their connections: (1) commissural fibers, (2) association fibers, and (3) projection fibers. Commissure fibers essentially connect corresponding regions of the two hemispheres. They are as follows: the corpus callosum, the anterior commissure, the posterior commissure, the fornix, and the habenular commissure. The corpus callosum, the largest commissure of the brain, connects the two cerebral hemispheres. It lies at the bottom of the longitudinal fissure. It is divided into the rostrum, the genu, the body, and the splenium. The anterior commissure is a small

bundle of nerve fibers that crosses the midline in the lamina terminalis. The posterior commissure is a bundle of nerve fibers that crosses the midline immediately above the opening of the cerebral aqueduct into the third ventricle. The commissure of the fornix consists of transverse fibers that cross the midline from one column to another just before the formation of the body of the fornix. The function of the commissure of the fornix is to connect the hippocampal formations of the two sides. The habenular commissure is a small bundle of nerve fibers that crosses the midline in the superior part of the root of the pineal stalk.

Association fibers are nerve fibers that essentially connect various cortical regions within the same hemisphere and may be divided into short and long groups. The uncinate fasciculus connects the first motor speech area and the gyri on the inferior surface of the frontal lobe with the cortex of the pole of the temporal lobe. The cingulum is a long, curved fasciculus lying

Within the whitematter of the cingulate gyrus. It connects the frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions.

The superior longitudinal fasciculus is the largest bundle of nerve fibers. It connects the anterior part of the frontal lobe to the occipital and temporal lobes.

The inferior longitudinal fasciculus runs anteriorly from the occipital lobe, passing lateral to the optic radiation, and is distributed to the temporal lobe.

The fronto-occipital fasciculus connects the frontal lobe to the occipital and temporal lobes. It is situated deep within the cerebral hemisphere and is related to the lateral border of the caudate nucleus.

Afferent and efferent nerve fibers passing to and from the brainstem to the entire cerebral cortex must travel between large nuclear masses of gray matter within the cerebral hemisphere. At the upper part of the brainstem, these fibers form a compact band known as the intern