Nervous system 4

1. Nervous system4 Department of Anatomy Luzhou Medical College Edited by professor Xiao

2. Ⅱ. The cerebellum • The cerebellum is the second-largest portion of the brain and occupies the inferior and posterior aspect of the cranial cavity. Specifically, it is posterior to the medulla oblongata and pons and inferior to the occipital lobes of the cerebrum. It is separated from the cerebrum by the transverse fissure and by an extension of the cranial dura mater called the tentorium cerebelli. The tentorium cerebelli partially encloses the transverse sinuses and supports the occipital lobes of the cerebral hemispheres.

3. The position of the cerebellum

4. The cerebellum is shaped somewhat like a butterfly. The central constricted area is the vermis, which means “wormshaped,” and the lateral “ wings ” or lobes are referred to as hemispheres.

5. The surface of the cerebellum called the cortex. Consists of gray matter in a series of slender, parallel ridges called follia. Beneath the gray matter are white matter tracts that resemble branches of a tree. Deep within the white matter are masses of gray matter, the cerebellar nuclei or central nuclei.

6. The tonsils of cerebellum are two elevated masses on the inferior surface of the hemispheral portion just behind the floculonnodular lobe and near by the foramen magnum. The cerebellum is attached to the brain stem by the three paired bundles of fibers called inferior, middle and superior cerebellar peduncles.

7. Ⅰ) The lobe of cerebellum • The cerebellum can also be divided by its connections and phylogeny into three portions. • ①. The flocculonodular lobeis predominantly vestibular in its connections and constitutes the oldest part of the cerebellum, so it is called the vestibulocerebellum or archicerebellum. • ②.The anterior lobeand the rostral part of the inferior vermis are predominantly spinocerebellar in its connections and is phylogenetically the next part to appear, it is also called spinocerebellum or paleocerebellum. • ③.The posterior lobeis predominantly corticopontocerebellar in its connections and constitutes the pontocerebellum or neocerebellum.

8. flocculus Peduncle of flocculus nodule Flocculonodular lobe

9. The anterior lobe and the rostral part of the inferior vermis are predominantly spinocerebellar in its connections and is phylogenetically the next part to appear, it is also called spinocerebellum or paleocerebellum.

10. The posterior lobe is predominantly corticopontocerebellar in its connections and constitutes the pontocerebellum or neocerebellum.

11. Ⅱ) The cerebellar cortex • The cerebellar cortex is uniformly structured in all parts and three layers are evident in histologic sections. From the surface to the white matter of the folium, these are the molecular layer, the Purkinje cell layer, and the granular layer. There are two types of afferent fibers to the cortex. Mossay fibers terminate in synaptic contact with cells of the granular layer, through which they affect the Purkinje cells, whereas climbing fibers enters the molecular layer and wind around the dendrites of Purkinje cells. The only fibers leaving the cortex are axons of Purkinje cells, these fibers terminate in central nuclei of the cerebellum, with the exception of some fibers from the cortex of the flocculonodular lobe that proceed to the brain stem.

12. The cerebellar cortex

13. Ⅲ. The central nuclei of the cerebellum • Four pairs of nuclei are embedded deep in the medullary center, they are fastigial, globose, emboliform, and dentate nuclei.

14. Ⅲ. The central nuclei of the cerebellum • The fastigial nucleus lies close to the midline and almost in contact with the roof of fourth ventricle. It receives the fibers from the archicerebellum. Most fibers from this nucleus of both side run directly to the brain stem through the inferior cerebellar peduncles, ending in the vestibular nuclei of both sides and in the reticular formation of medulla oblongata.

15. Ⅲ. The central nuclei of the cerebellum • The dentate nucleus is the largest one and lies most laterally, which receives the fibers from the cerebellar cortex. The efferent fibers derived from the dentate nucleus form the major part of the superior cerebellar peduncles and reach the red nucleus and the thalamus of the contralateral side.

16. Ⅳ The white matter and cerebellar peduncles • 1. The white matter • The white matter of cerebellum consists mainly of the intrinsic and projection fibers. The intrinsic fibers do not leave the cerebellum, but interconnect with different regions of the organ. The projection fibers connect the cerebellum with other parts of the brain and the spinal cord. They are grouped together into three large bundles on each side.

17. 2. The cerebellar peduncles • ⑴ The inferior cerebellar peduncles (restiform body) It is composed of the fibers from ①the inferior olivary complex ( olivocerebellar tract), ②the posterior spinocerebellar tract, ③the reticular formation in the medulla oblongata, ④the vestibular nuclei and vestibular nerve. The restiform body also contains the efferent fibers which proceed from the floculonodular lobe and fastigial nucleus to the vestibular nuclei and reticular formation in the medulla oblongata and pons.

18. 2. The cerebellar peduncles • ⑵ The middle cerebellar peduncles (brachium pontis) It continues from the dorsolateral region of the pons and is composed almost exclusively of the pontocerebellar fibers.

19. 2. The cerebellar peduncles • ⑶. The superior cerebellar peduncles (brachium conjunctive) It connects the cerebellum with of the midbrain and thalamus. It consists mainly of the efferent fibers from the globose, emboliform and dentate nuclei ( the dentatorubral tract and the dentatothalamic tract). It also contains afferent fibers, such as the anterior spinocerebellar tract.

20. Ⅴ The functions of cerebellum • Functionally, the cerebellum is an area of the brain concerned with coordinating subconscious contractions of skeletal muscles. (the cerebellar peduncles are the fibers tracts that channel information into and out of the cerebellum). • The cerebellum constantly receives input signals from propriocepters in muscles, tendons, and joints, receptors for equilibrium, and visual receptors of the eyes. Such input permits the cerebellum to collect information on the physical status of the body with regard to posture, equilibrium, and all movements at joints.

21. Ⅴ The functions of cerebellum • In addition, when other motor area of the brain, such as the motor cortex of the cerebrum and basal nuclei, send signals to the skeletal muscles, they also send a duplicate set of signals to the cerebellum. The cerebellum compares this input information regarding the actual status of the body with the intended movement determined by motor areas of the brain( cerebrum and basal nuclei). If the intent of these motor areas is not being attained by the skeletal muscles, the cerebellum detects the variation and sends feedback signals to the motor areas to either stimulate or inhibit the activity of skeletal muscles. This interaction produces smooth, coordinated movements of our body’s skeletal muscles.

22. Ⅴ The functions of cerebellum • The cerebellum also functions in maintaining equilibrium and controlling posture. For example, receptors for equilibrium send nerve impulses to the cerebellum, informing it of body position. When the direction of movement changes, the cerebellum sends corrective signals to the motor neurons to skeletal muscles to reposition the body.

23. Ⅴ The functions of cerebellum • Another function of the cerebellum is related to predicting the future position of a body part during a particular movement. Just before moving a part of the body to reach its intended position, the cerebellum sends signals over motor tracts to somatic motor neurons to skeletal muscles to slow the moving part and stop it at a specific point. This function of the cerebellum is used in actions such as walking. • There is some evidence that the cerebellum may play a role in a person’s emotional development, modulating sensation of anger and pleasure, allowing normal expression and interpretation.

24. Ⅵ Damage to cerebellum • Damage to the cerebellum through trauma or disease is characterized by certain symptoms involving skeletal muscles on the same side of the body as the damage. The effects are on the same side of the body as the damaged side of the cerebellum because of a double crossing of tracts within the cerebellum. There may be lack of muscles coordination, called ataxia ( a-without taxis-order). Blindfolded people with ataxia cannot touch tip of their nose with a finger because they cannot coordinate movement with their sense of where a body part is located. Another sign of ataxia is a change in the speech pattern due to a lack of coordinating of speech muscles, cerebellar damage may also result in disturbances of gait, in which the subject staggers or cannot coordinate normal walking movements, and severe dizziness.(头晕） Ataxia共济失调

25. The diencephalon • The diencephalon, between the brain stem and the hemispheres of the cerebrum, being almost entirely surrounded by the hemispheres of the cerebrum, exposes only the ventral surface of the diencephalon to view in a diamond-shaped area containing hypothalamic structures. It consists of the • ①dorsal thalamus • ②hypothalamus • ③epithalamus • ④subthalamus • ⑤metathalamus.

27. Ⅰ. The dorsal thalamus • The thalamus is an oval structure above the midbrain that measures about 3cm in length and constitutes four fifths of the diencephalon. It consists of paired oval masses of most gray matter organized into nuclei that form the lateral walls of the third ventricle. The masses are frequently joined by a bridge of gray matter that crosses the third ventricle, called the intermediate mass. Each mass is deeply embedded in a cerebral hemisphere and is bounded laterally by the internal capsule.

28. Ⅰ. The dorsal thalamus • Although the thalamic masses are primarily gray matter, some portions are white matter. Among the white matter portions are the stratum zonale which covers the dorsal surface, the external medullary lamina covering the lateral surface and the internal medullary lamina which divides into the gray matter masses into an anterior nucleus group, a medial nuclear group, and a lateral nuclear group. The anterior nuclear group is enclosed by a bifurcation of the lamina and forms a rostromedial swelling known as the anterior tubercle.

29. Ⅰ. The dorsal thalamus • The medial nuclear group contains the large dorsomedial nucleus. The lateral nuclear group consists of ventral and dorsal tiers of nuclei which have been identified because of differing fiber connections. • Five nuclei are recognized in the ventral tier, i.e. the medial and lateral geniculate nuclei, the ventral posterior, ventral lateral and ventral anterior nuclei. The dorsal tier consists of the pulvinar, lateral posterior nucleus and lateral dorsal nucleus. In the central part of the thalamus, the internal medullary lamina partially encloses the intralaminar nuclei, including the well-developed centromedian nucleus. The midline nuclei lie in the periventricular gray matter of the thalamus and in the interthalamic adhesion. The thalamus also contains a intralaminar nuclear group, median nucleus, and a reticular nucleus in its reticular formation.

30. Ⅰ. The dorsal thalamus • On the basis of phylogeny, connections with other parts of the brain, and function, the thalamic nuclei may be classified into the following nuclei. • 1. Reticular nucleus • They receive collateral branches of thalamocortical and corticothalamic fibers. • 2. The midline and intralaminar nuclei • They receive afferents from the reticular formation of the brain stem and project mainly to other parts of the diencephalon. • 3. The specific thalamic nuclei • They comprise the ventral tier of the lateral nuclear mass and send fibers to sensory and motor areas of cortex. The medial geniculate nucleus (hearing), lateral geniculate nucleus (vision), and ventral posterior nucleus (general sensations) are specific sensory nuclei. The ventral lateral nucleus and the ventral anterior nucleus are specific motor nuclei, in a sense that they receive date from the cerebellum, corpus striatum, and substantia nigra, and project fibers to motor areas of cortex in the front lobe.

31. Ⅰ. The dorsal thalamus • The ventral posterior nucleus functions as a thalamic relay nucleus for general sensations. The lateral and anterior spinothalamic tracts, the medial lemniscus, and the trigeminothalamic tracts all terminate in this nucleus. The nucleus receives the fibers from the rostral part of the nucleus of solitary tract and the vestibular nuclear complex. • There is a detailed topographic projection of the opposite half of the body on the ventral posterior nucleus. The lower limb is represented in the dorsolateral part of the nucleus, the upper limb in an intermediate position, and head most medially. The medial region receiving sensory date from the head is usually referred to as the ventral posteromedial nucleus (VPM), and large lateral portion for the remainder of the body as the ventral posterolateral nucleus (VPL). Nerve fibers leave the lateral aspect of the ventral posterior nucleus in large numbers, traverse the internal capsule and medullary center of the cerebral hemisphere, and end in the general sensory area of cortex in the parietal lobe.

32. 4. The nonspecific thalamic • nuclei • They have reciprocal connections with association areas of cerebral cortex. This group includes the dorsomedial nucleus and the dorsal tier of the lateral nuclear mass, i.e., the pulvinar, lateral posterior nucleus, and lateral dorsal nucleus. The anterior nucleus is included conventionally under this heading, even though it is thalamic component of the limbic system of the brain. • Thalamic syndrome • Aside from the motor aspects of ventral lateral and ventral anterior nuclei, the thalamus is sensory part of the brain and contributes to emotional responses to sensory experience.

33. The thalamic syndrome is essentially a disturbance of these aspects of thalamic functions, subsequent to a lesion (usually vascular origin) involving the thalamus or its connections. The symptoms vary according to the location and extent of the lesion. The threshold for touch, pain and temperature is usually raised on the opposite side of the body, but when the threshold is reached the sensations are exaggerated, perverted and exceptionally disagreeable. For example, the prick of a pin may be felt as a severe burning sensation, and even music that is ordinarily pleasing may be disagreeable. There is spontaneous pain in some instances, which may become intractable颃固的to analgesics痛觉缺失. Threshold阈 exaggerate 夸张 perverted性欲倒错

35. Ⅱ. The Epithalamus It occupies the caudal roof of the third ventral together with adjacent areas. It includes the right and left habenular nuclei, each situated deep to the floor of a habenular trigone. The epithalamus also includes the habenular and posterior commissures. The pineal body, an endocrine gland in mammals, is attached to the posterior commissure on the midline.

36. Ⅲ. The Subthalamus The subthalamus is situated immediately ventral to the dorsal thalamus, in part lateral the hypothalamus, and emerges caudally with the tegmentum of midbrain. The region includes the rostral extension of the red nucleus and substantia nigra, the prominent subthalamic nucleus (nucleus of Luys). The latter, located beneath the dorsalthalamus and medial to the internal capsule, has the shape of the thick biconvex lens. Caudally the medial part of the nucleus overlies the dorsal portion of the substantia nigra. It is a component of the extrapyramidal system.

37. Ⅳ. The Metathalamus The metathalamus is located posterolateral to the thalamus. It includes lateral geniculate body and medial geniculate body. In lateral geniculate body the lateral geniculate nucleus is located, the lateral geniculate nucleus then gives rise to optic radiation In medial geniculate body the medial genicullate nucleus is located, the medial geniculate nucleus then gives rise to the acoustic radiation.

39. Ⅴ. The Hypothalamus The hypothalamus, occupying only a small part of the brain weighed about 4G, has a functional importance that is quite out proportion to its size. The hypothalamus surrounds the third ventricle ventral to the hypothalamic sulci. The mammillary bodies are distinct swellings on the ventral surface. The region bounded by the mammillary bodies, optic chiasma, and beginning of the optic tracts is kwon as the tuber cinereum. The infundibular stem arises from the median eminence just behind the optic and expands to form the infundibular process. The median eminence, pars infundibularis and pars nervosa constitute the neurohypophysis.

41. Regions • The hypothalamus is divided into four major regions. • ①.The supraoptic region: • This anterior region lies above the optic chiasma and contains the paraventricular nucleus, supraoptic nucleus and anterior hypothalamic nucleus.

42. ②The tuber region • The middle region is the widest portion of the hypothalamus. On its ventral surface are tuber cinereum, infundibulum and median eminence.

43. ③The mammillary region • This region is posterior to the tuberal region and contains mammillary bodies and posterior hypothalamic nucleus.

44. ④The preoptic region • This region is in front ofthe supraoptic region and is usually considered as a part of the hypothalamus because it functions in regulating certain autonomic activities in conjunction with the hypothalamus. The preoptic region contains the preoptic periventricular nucleus, medial preoptic, nucleus and lateral preoptic nucleus.

45. Hypophyseal portal system

46. The chief functions of the hypothalamus are as follows • 1. It controls and integrates the activities of the autonomic nervous system, which regulates the contraction of the smooth muscle and cardiac muscle and secretions of many glands. • 2. It is the principal connection between the nervous system and the endocrine system ( the two major control systems of the body). The hypothalamus lies just above the pituitary when the hypothalamus detects certain changes in the body, it release chemicals called regulating hormones that stimulate or inhibit specific cells in the anterior pituitary gland.

47. The chief functions of the hypothalamus are as follows • The anterior pituitary then releases or holds back hormones that various physiological activities of the body. • 3. It is associated with feeling of rage and aggression. • 4. It controls normal body temperature. • 5. It regulates food intake through the feeding center and the satiety center. • 6. It is one of the centers that maintains the waking state and sleep pattern.

48. The third ventricle • The diencephalic part of the ventricular system consists of the narrow third ventricle. The anterior wall if this ventricle is formed by the lamina terminalis, the anterior commissure crosses the midline in the dorsal part of the lamina terminalis. The rather extensive lateral wall is marked by the hypothalamic sulcus, separating the thalamus from the hypothalamus. A massa intermedia (interthalamic adhesion) bridges the ventricle in 70% of brains. The floor of third ventricle is bounded with the optic chiasma, infundibulum, tuber cinereum, and mammillary bodies. The membranous roof of the third ventricle is attached along striae terminalis, and a pair of choroid plexuses is suspended from the roof. Cerebrospinal fluid enters the third ventricle from each lateral ventricle by way of the mesencephalic aqueduct, through which it reaches the fourth ventricle. From the latter it passes through the apertures on the ventricle into the subarachnoid space surrounding the brain and spinal cord.

49. Third ventricle

50. The telencephalon • The telencephalon, also called cerebrum, consists mainly of two large cerebral hemispheres. Two hemispheres are almost completely separated by the cerebral longitudinal fissure. At the bottom of this fissure a large bundle of transverse fibers, the corpus callosum, crosses between the hemispheres. The cerebrum and the cerebellum are completely separated by the cerebral transverse fissure. • Each cerebral hemispheres is composed of an outer layer of grey matter, termed the cortex, and inner white matter, the medullary substance. Within the hemisphere, there are several masses of grey matter known as the basal nuclei and a cavity, the lateral ventricle.