Connections of strio-pallidal system.
1. Tract connecting to ending motor tract and muscle.
2. Mutual connections with various parts of extrapyramidal system and big hemispheres cortex
3. Afferent pathways:
- rubrospinal tract of Monakov
- reticulospinal tracts
- tegmental-spinal tract from corpora quadrigemina
- tracts to motor nuclei of cranial nerves.
Afferent signals from thalamus, cerebellum, reticular formation, great brain cortex create continuous corrective flow.
Signs of a pallidum lesion.
Lesion of pale globule and black matter causes parkinsonism – hypertonic-hypokinetic syndrome.
It occurs at a lesion of pale globule, black matter. Total restraint, hypoexpressions of movements (hypokinesia), muscle rigidity are characteristics. Static tremor is present. The person has face like mask. Beginning of arbitrary movements is difficult. Walking is with shallow steps. Voice is quiet, monotonic. Handwriting is small.
Signs of a striate body lesion. Striatic syndrome.
Hyperkinetic-hypotonic syndrome includes hypotonia or dystonia and different non-arbitrary violent excessive movements – hyperkinesias.
Chorea is lesion of midbrain tegmentum, lentiform and caudate nuclei. Unrhythmic fibrillations are typical.
Myoclonias are unrhythmic and unsynchronic contractions of various muscles of trunk, abdomen.
2. Study aims:
To know: cerebellum mopho-functional peculiarities; cerebellum connections with CNS other parts; clinical picture of cerebellum disorders.
To be able to: to perform movement co-ordination investigation.
3. Pre-auditory self-work materials.
3.1.Basic knowledge, skills, experiences, necessary for study the topic:
|Histology||Cerebellum, intermediate brain and basal ganglia histological structure||Recognize intermediate brain main parts, cerebellum and basal ganglia preparations|
|Anatomy||Morphology and connections of cerebellum, intermediate brain and basal ganglia||Draw cerebellum nuclei and fibers|
|Biochemistry||Dophamine origin and role in human organism, hypothalamic hormones and melatonin biochemistry|
|Neurology||Cerebellum, intermediate brain and basal ganglia morphology, physiology||Analize human organism functions disorders features and explain their mechanisms (particularly at cerebellum pathology, parkinsonism and thalamic syndrome)|
|Dentistry||Maxillary-facial region disorders features at cerebellum and basal ganglia pathology|
INTERMEDIATE BRAIN PHYSIOLOGY
It consists of:
Thalamus is a large ovoid mass of gray matter, situated bilaterally in diencephalon. Thalamus on both sides, lie close together in their rostral two thirds and are slightly separated by third ventricle. The caudal thirds are more widely separated by corpora quadrigemina.
Nuclei: Thalamus on each side is divided into five main nuclear groups by means of internal medullary septum.
A. Midline nuclei
B. Intralaminar nuclei
С.Medial mass of nuclei
D. Lateral mass of nuclei
E. Posterior group of nuclei
Thalamic radiation is the collection of nerve fibers connecting thalamus and cerebral cortex. It contains both inalamocortical and corticothalamic fibers. All these fibers between thalamus and cerebral cortex pass through internal capsule.
Thalamic radiations are divided into four groups, which are called thalamic peduncles or thalamic stalks.
Anterior (frontal) peduncle or radiation: connects the frontal lobe of cerebral cortex with medial and lateral thalamic nuclei. This contains mostly motor nerve fibers.
Superior (centrolateral) peduncle or radiation - the fibers of this peduncle connect post central gyrus (somesthetic area) of parietal lobe and adjacent area in frontal cortex with lateral mass of thalamic nuclei. This contains mostly sensory fibers.
Posterior (occipital) peduncle or radiation - connects occipital lobe of cerebral cortex with pulvinar and lateral geniculate body. This contains the nerve fibers concerned with vision.
Inferior (temporal) peduncle or radiation - fibers of this peduncle connect temporal lobe and insula with pulvinar and medial geniculate body. This peduncle contains the nerve fibers concerned with hearing.
Thalamus is primarily concerned with somatic functions and it plays little role in the visceral functions. The various functions of thalamus are:
The impulses of almost all the sensations (except olfactory) reach the thalamic nuclei, particularly in the ventral posterolateral nucleus. After being processed in the thalamus, the impulses are carried to cerebral cortex through thalamocortical fibers. Thus, thalamus forms the relay center for sensations.
In fact, very little information about the somatosensory function is sent to cerebral cortex directly without being processed by the thalamic nuclei. Because of this, thalamus is usually called a "Functional gateway" for cerebral cortex.
CENTER FOR INTEGRATION OF SENSORY IMPULSES
Thalamus forms the major center for the integration and modification of peripheral sensory impulses before the impulses are projected to specific areas of cerebral cortex. Generally, this function of thalamus is called the processing of sensory information.
Thalamus is also the center determining the quality of sensations.
Usually the sensations have two qualities:
a). The discriminative nature: ability to recognize the type, location and other details of the sensations - the function of cerebral cortex.
b). The affective nature: capacity to determine whether asensation is pleasant or unpleasant and agreeable or disagreeable - the function of thalamus.
CENTER FOR SEXUAL SENSATIONS
Thalamus forms the center for perception of sexual sensations.
ROLE IN AROUSAL AND ALERTNESS REACTIONS
Because of its connections with nuclei of reticular formation, thalamus plays an important role in arousal and alertness reactions.
CENTER FOR REFLEX ACTIVITY
Since the sensory fibers relay here, thalamus forms the center for many reflex activities.
CENTER FOR INTEGRATION OF MOTOR FUNCTIONS
Through the connections with cerebellum and basal ganglia, thalamus serves as a center for integration of motor functions.
Fig.23. Connections of thalamus.
2) brain anterior comissure;
Epiphysis is endocrine gland secreting hormone melatonin. It provides regulation of:
1. biological rhythms;
2. endocrine function;
Shortly, melatonin is necessary for organism adaptation to different conditions of enlighting and organism biorhythms. Its main effect is gonadotropine secretion decreasing by adenohypophysis. Enlighting decreasing reducel sympathetic influencings activity breaking cavn to epiphysis and thus melatonin synthesis decreasing.
Hypothalamus is a diencephalic structure. It is situated just below thalamus in the ventral part of diencephalon. It is formed by groups of nuclei scattered in the walls and floor of third ventricle. It extends from optic chiasma to mamillary body.
Hypothalamus consists of scattered nuclei, which are divided into three groups, anterior or supraoptic group, middle or tuberal group and posterior or mamillary group.
|Anterior or supraoptic group||Middle or tuberal group||Posterior or mamillary group|
|1. Preoptic nucleus 2. Paraventricular nucleus 3. Anterior nucleus 4. Supraoptic nucleus||1. Dorsomedial nucleus 2. Ventomedial nucleus 3. Lateral nucleus 4. Tuberal nucleus||1.Posterior nucleus 2. Mamillary body|
Afferent connections to hypothalamus:
1)Medial forebrain bundle: From rhinencephalon (limbic cortex) to preoptic nucleus, lateral nucleus and mamillary body.
2) Fornix: From hippocampus to mamillary body.
Efferent connections from hypothalamus:
1. Mamillothalamic tract: From mamillary body to anterior thalamic nuclei.
2. Mamillotegmental tract: From mamillary body to the tegmental nuclei of midbrain.
3. Periventricular fibers: Fibers from posterior, supraoptic and tuberal nuclei of hypothalamus pass through periventricular gray matter and reach the following:
a. Reticular formation in brainstem and spinal cord,
b. Dorsomedial nucleus of thalamus and
c. Frontal lobe of cerebral cortex.
4. Hypothalamo-hypophyseal tract: From supraoptic and paraventricular nuclei of hypothalamus to posterior pituitary.
Hypothalamus is the important part of brain concerned with homeostasis of the body. It regulates many vital functions of the body like endocrine functions, visceral functions, metabolic activities, hunger, thirst, sleep, wakefulness, emotion, sexual functions, etc. It is considered to be the highest vegetative center.
|1. Control of anterior pituitary||Releasing hormones Inhibitory hormones||Discrete areas|
|2. Secretion of posterior pituitary hormones||Oxytocin ADH||Paraventricular nucleus Supraoptic nucleus|
|3. Control of adrenal cortex||CRH||Paraventricular nucleus|
|4. Control of adrenal medulla||Catecholamines during emotion||Posterior and dorsomedial nuclei|
|5. Regulation of ANS (autonomic nervous system)||Sympathetic Parasympathetic||Posterior and lateral nuclei Anterior nuclei|
|6. Regulation of heart rate||Acceleration Inhibition||Posterior and lateral nuclei Preoptic area|
|7. Regulation of blood pressure||Pressor effect Depressor effect||Posterior and lateral nuclei Preoptic area|
|8. Regulation of body temperature||Heat gain center Heat loss center||Posterior hypothalamus Anterior hypothalamus|
|9. Regulation of food intake||Feeding center Satiety center||Lateral nucleus Ventromedial nucleus|
|10. Regulation of water intake||Thirst center Water retention by ADH||Lateral nucleus Supraoptic nucleus|
|11. Regulation of sleep and wakefulness||Sleep wakefulness||Anterior hypothalamus Mamillary body|
|12. Regulation of behavior and emotion||Reward center Punishment center||Ventromedial nucleus Posterior and lateral nuclei|
|13. Regulation of sexual function||Sexual cycle||Tuberal and posterior nuclei|
|14.Regulation of response to smell||Autonomic responses||Posterior hypothalamus|
|15. Role in circadian rhythm||Rhythmic changes||Supraoptic and anterior nuclei|
1. SECRETION OF POSTERIOR PITUITARY HORMONES
Hypothalamus is the source of secretion for the posterior pituitary hormones. Antidiuretic hormone (ADH) and oxytocin are secreted by supraoptic and paraventricular nuclei. These two hormones are transported by means of axonic or axoplasmic flow through the fibers of hypothalamo-hypophyseal tracts to the posterior pituitary.
2. CONTROL OF ANTERIOR PITUITARY
Hypothalamus controls the anterior pituitary gland by secreting releasing hormones and inhibitory hormones. It secretes seven hormones.
1. Growth hormone releasing hormone (GHRH).
2. Growth hormone releasing polypeptide (GHRP).
3. Growth hormone inhibitory hormone (GHIH) or somatostatin.
4. Thyrotropic releasing hormone (TRH).
5. Corticotropin releasing hormone (CRH).
6. Gonadotropin releasing hormone (GnRH).
7. Prolactin inhibitory hormone (PIH).
These hormones are secreted by discrete areas of hypothalamus and transported to the anterior pituitary by the hypothalamo-hypophyseal portal blood vessels.
3. CONTROL OF ADRENAL CORTEX
The adrenal cortex is regulated by adrenocorticotropic hormone (ACTH). ACTH secretion is in turn regulated by corticotropic releasing hormone (CRH) which is secreted by the paraventricular nucleus of hypothalamus.
4. CONTROL OF ADRENAL MEDULLA
Dorsomedial and posterior hypothamic nuclei are excited by emotional stimuli. These hypothalamic nuclei, in turn, send impulses to adrenal medulla through sympathetic fibers and cause release of catecholamines, which are essential to cope up with emotional stress.
5. REGULATION OF BODY TEMPERATURE
Hypothalamus has two centers, which regulate the body temperature. These centers are the heat loss center and the heat gain center. Heat loss center is in anterior hypothalamus and heat gain center is in posterior hypothalamus.
Mechanism of Temperature Regulation
In addition to temperature receptors present in skin, abdomen and other structures, there are some heat sensitive nerve cells in the preoptic area of hypothalamus. The heat sensitive nerve cells are called thermoreceptors.
When body temperature increases, blood temperature also increases. When blood with increased temperature passes through hypothalamus, it stimulates the thermoreceptors present in the preoptic area. The thermoreceptors of hypothalamus are stimulated and cause heat loss in two ways.
1. Preoptic thermoreceptors stimulate sweat glands and increase the secretion of sweat. When more sweat is secreted, more water is lost from skin. Along with water, heat is lost from body.
2. The preoptic thermoreceptors inhibit the posterior hypothalamus, which controls the sympathetic nervous system. This decreases the activity of vasomotor center so that the vasomotor tone to cutaneous blood vessels is decreased. This leads to cutaneous vasodilatation and increase in blood
6. REGULATION OF AUTONOMIC NERVOUS SYSTEM
Hypothalamus controls the autonomic nervous system (ANS). The sympathetic division of ANS is regulated by posterior and lateral nuclei of hypothalamus. The parasympathetic division of ANS is controlled by anterior group of nuclei. Cerebral cortex also influences ANS but, only through hypothalamus.
7. REGULATION OF HEART RATE
Hypothalamus regulates heart rate through vasomotor center in the medulla oblongata. Stimulation of posterior and lateral nuclei of hypothalamus increases the heart rate. Stimulation of preoptic area decreases the heart rate.
8. REGULATION OF BLOOD PRESSURE
Hypothalamus regulates the blood pressure also by acting on the vasomotor center. Stimulation of posterior and lateral hypothalamic nuclei increases arterial blood flow to the skin. Due to increased blood flow through skin, more heat is lost from the skin directly or indirectly through sweat.
9. REGULATION OF FOOD INTAKE
To regulate the food intake, hypothalamus has two centers namely the feeding center and satiety (satiation) center.
It is in the lateral hypothalamic nucleus. The stimulation of this center in animals leads to increased food intake (hyperphagia), and uncontrolled hunger. It causes obesity. The destruction of feeding center leads to loss of appetite-anorexia.
It is in the ventromedial nucleus of the hypothalamus. Stimulation of this in animals causes cessation of food intake. Destruction of satiety center leads to hyperphagia. Normally, the feeding center is always active and its activity is inhibited by satiety center after food intake.
Mechanism of Regulation of Food Intake
There are some receptors called glucostats in the ventro-medial nucleus of hypothalamus. The glucostats give response to increased glucose content in blood. During food intake, the blood glucose level is increased. The glucostats are activated and stimulate the satiety center. This, in turn, inhibits the feeding center causing stoppage of food intake. But in diabetes, because of deficiency of insulin, hyperglycemia occurs. Hyperglycemia cannot stimulate the satiety center. So, tne satiety center will not inhibit the feeding center. This increases the frequency of food intake - polyphagia.
Few hours after meals, the blood glucose level is reduced. Now, the glucostats are not excited, and thus the satiety center is not activated. This causes release of inhibition over feeding center leading to hunger and food intake.
10. REGULATION OF WATER BALANCE
Hypothalamus regulates water content of the body by two mechanisms:
1. Thirst mechanism
2. ADH mechanism
1. Thirst center is in the lateral nucleus of hypothalamus. There are some osmoreceptors in the areas adjacent to this nucleus. When the blood circulating volume decreases, the osmolality of blood increases. This stimulates the osmoreceptors which, in turn, activate the thirst center. Now, the person feels thirsty and drinks water. Water intake increases volume and decreases osmolality of blood.
2. Simultaneously, when the volume of blood decreases with increased osmolality, the supraoptic nucleus is stimulated and ADH is released. ADH causes retention of water by reabsorption in the renal tubules. This brings the osmolality back to the normal level. When fluid volume is more, the supraoptic nucleus is not stimulated and ADH is not secreted. In the absence of ADH, more amount of water is excreted through urine and the volume of blood is brought back to normal.
11. REGULATION OF SLEEP AND WAKEFULNESS
Stimulation of anterior hypothalamus or the lesion of mamillary body leads to sleep and the stimulation of mamillary body causes wakefulness. Mamillary body in the posterior hypothalamus is considered as the wakefulness center.
12. ROLE IN BEHAVIOR AND EMOTIONAL CHANGES
The behavior of animals and human beings is mostly affected by two opposing responding systems, which involves hypothalamus and other structures of limbic system.
These responding systems are concerned with affective nature of sensations, i.e. whether the sensations are pleasant or painful. These two qualities are called the Reward/Satisfaction and Punishment/Aversion or avoidance. The two centers in hypothalamus involved in the behavior and' emotional' changes are:
A. Reward center and
B. Punishment center.
Electrical stimulation of medial forebrain bundle and ventromedial nucleus of hypothalamus in animals, pleases or satisfies the animals. These areas are called reward centers.
The electrical stimulation of posterior and lateral nuclei of hypothalamus leads to pain, fear, defense, escape reactions and other elements of punishment. These centers are called punishment centers.
Role of Reward and Punishment Centers
The importance of the reward and punishment centers lies in the behavioral pattern of the individuals. Almost all the activities of day-to-day life depend upon reward and punishment. While doing something, if the person is rewarded or feels satisfied, he or she continues to do so. If the person feels punished or unpleasant, he or she stops doing so. Thus, these two centers play an important role in the development of the behavioral pattern of a person.
When the punishment centers in posterior and lateral hypothalamus are stimulated in animals, a violent and aggressive emotional state is caused. This is called rage. Following are the reactions of rage:
1. Development of a defense posture
2. Extension of limbs
3. Lifting of tail
4. Hissing and spitting
6. Wide opening of eyeballs
7. Dilation of pupil
8. Severe savage attack, even by mild provocation.
In physiological conditions, the animals and human beings maintain a balance between the rage and the opposite state called the calm emotional state. Major irritations make even a normal person to loose the temper. However, the minor irritation are usually overcome or ignored. This is because of inhibitory influence of cerebral cortex on hypothalamus. But in animals or human beings with brain lesions, the balance is altered. In some lesions, even the mild stimulus evokes a violent and angry reactions of rage. This type of rage is called sham rage. This can occur in decorticated animal also.
Sham rage is due to release of hypothalamus from the inhibitory influence of cortical control.
13. REGULATION OF SEXUAL FUNCTION
In animals, hypothalamus plays an important role in maintaining the sexual functions, especially in females. A decorticate female animal will have regular estrus cycle provided the hypothalamus is intact. In human being also, hypothalamus regulates the sexual functions by secreting gonadotropin releasing hormones. Tuberal and posterior hypothalamic nuclei are involved in the regulation of sexual functions.
14. REGULATION OF RESPONSE TO SMELL
Posterior hypothalamus along with other structures like hippocampus and brainstem nuclei, is responsible for the autonomic responses of body to olfactory stimuli. The responses include feeding activities and emotional responses like fear, excitement and pleasure.
15. ROLE IN CIRCADIAN RHYTHM
The body rhythm to 24 hours dark - light cycle is called circadian rhythm. The supraoptic and anterior nuclei of hypothalamus play an important role in regulation of circadian rhythm.
Cerebellum consists of a narrow, worm like central body called vermis and two lateral lobes, the right and left cerebellar hemispheres.
Cerebellar hemispheres are the extended portions on either side of the vermis.
DIVISIONS OF CEREBELLUM
On the basis of structure, the whole cerebellum is divided into three portions.
This lobe includes lingula, central lobe and culmen. It is separated from posterior lobe by the primary fissure.
This consists of lobulus simplex, declive, tuber, pyramid, uvula, paraflocculi and the two portions of hemispheres-ansiform lobe and paramedian lobe.
This includes nodulus and the lateral extension on either side called flocculus. It is separated from rest of the cerebellum by posterolateral fissure.
Depending upon phylogeny, the cerebellum is divided into two divisions.
This is the phylogenetically oldest part of cerebellum. It includes two divisions, archicerebellum and paleocerebellum proper.
a). Archicerebellum—Flocculonodular lobe
b) Paleocerebellum proper—It includes lingula, central lobe, culmen, lobulus simplex, pyramid, uvula and paraflocculi
This is the phylogenetically newer portion of cerebellum. It includes declive, tuber and lateral portions of hemispheres, lobulus ansiformis and lobulus paramedianus.
Based on the functions, the cerebellum is divided into three divisions.
This includes flocculonodular lobe that forms the archi-cerebellum.
This includes lingula, central lobe, culmen, lobulus simplex, declive, tuber, pyramid, uvula and paraflocculi and medial portions of cerebellar hemispheres.
This includes the lateral portions of hemispheres.
Cerebellum is made up of outergray matter or cerebellar cortex and an inner white matter. The white matter is formed by afferent and efferent nerve fibers of cerebellum. The gray masses called cerebellar nuclei are located within white mater.
Gray matter or cerebellar cortex is made up of structures arranged in three layers. Each layer of gray matter is uniform in thickness and appearance throughout cerebellum. The three layers of gray matter are:
1. Outer molecular or plexiform layer
2. Intermediate Purkinje layer and
3. Inner granular layer
1. Molecular or Plexiform Layer
It is the outer most layer of cortex having the cells arranged in two strata. The superficial stratum contains few star shaped cells known as stellate cells. The deep stratum contains basket cells. In addition to stellate and basket cells, the molecular layer has the following structures:
a) Parallel fibers, which are the axons of granule cells, present in granular layer
b) The terminal portions of climbing fibers.
c) Dendrites of Purkinje cells and Golgi cells.
Molecular layer also contains the following cellular junctions:
a) The dendrites of stellate cells and basket cells synapse with parallel fibers, which are the axons of granule cells
b) The axons of stellate cells end on the dendrites of Purkinje cells. However, the axon of basket cell descends down into the Purkinje layer and forms the transverse fiber that ends on the soma of Purkinje cells
c) The dendrites of Purkinje cells synapse with climbing fibers and parallel fibers
d) The dendrites of Golgi cells situated in granular layer enter the molecular layer and end on parallel fibers.
2. Purkinje Layer
It is situated in between outer molecular layer and inner granular layer. It is the thinnest layer having a single layer of flask shaped Purkinje cells. The Purkinje cells are the largest neurons in the body. The dendrites of these cells ascend through the entire thickness of molecular layer. These dendrites terminate either on climbing fibers or the parallel fibers. The axons of the basket cells form the transverse fibers and end on the soma of Purkinje cells. The axons of Purkinje cells descend into the white matter and terminate on the cerebellar nuclei and vestibular nuclei via cerebellovestibular tract. The Purkinje cells are termed as "Final common path" of cerebellar cortex because the impulses from different parts of cerebellar cortex are transmitted to other parts of brain only through Purkinje cells.
Fig.24. Structure of cerebellar cortex. (+) = Excitation, (-) = Inhibition
3. Granular Layer
This layer is placed in between Purkinje layer and the white matter. It is formed by interneurons namely granule cells and Golgi cells. The total number of interneurons in this layer is about half the number of all neurons in the whole nervous system.
The axon of the granule cell ascends into molecular layer and forms the parallel fiber, which synapses with dendrites of Purkinje cells, stellate cells, basket cells and Golgi cells. The dendrites of granule cells and the axon and few dendrites of a Golgi cell synapse with mossy fiber. The synaptic area of these cells is called the glomerulus and it is encapsulated by the processes of glial cells.
Afferent Fibers to Cerebellar Cortex
The cerebellar cortex receives afferent signals from other parts of brain through two types of nerve fibers.
1. Climbing fibers
2. Mossy fibers
Climbing fibers: they arise from the neurons of inferior olivary nucleus situated in medulla and reach the cerebellum via olivocerebellar tract. The inferior olivary nucleus relays the output signals from motor areas of cerebral cortex and the proprioceptive signals from different parts of the body to the cerebellar cortex via climbing fibers. The proprioceptive impulses from different parts of the body reach the inferior olivary nucleus through spinal cord and vestibular system.
After reaching the cerebellum, the climbing fibers ascend into the molecular layer and terminate on the dendrites of Purkinje cells. While passing through cerebellum, the olivocerebellar tract sends collaterals to cerebellar nuclei. Because of this, the impulses from cerebral cortex and proprioceptors of the body are conveyed to not only the cerebellar cortex but also the cerebellar nuclei by the climbing fibers. Each climbing fiber innervates one single Purkinje cell.
Mossy fibers: Unlike climbing fibers, the mossy fibers have many sources of origin namely motor areas of cerebral cortex, pons, medulla and spinal cord. Fibers arising from all these areas send collaterals to the cerebellar nuclei before reaching the cerebellar cortex. So, like climbing fibers, the mossy fibers also convey afferent impulses to both cerebellar nuclei and cerebellar cortex. Some of the mossy fibers arise from cerebellar nuclei. After reaching the granular layer of cerebellar cortex, the mossy fiber divides into many terminals. Each terminal enters the glomerulus and ends in a large expanded structure that forms the central portion of the glomerulus. The dendrites of granule cells and the axon and dendrites of Golgi cells synapse on the mossy fiber giving a thick bushy appearance. The word “mossy” refers to the appearance of a plant called moss, which grows into dense clumps, and hence, the name mossy fibers is given to these fibers.
Neuronal Activity in Cerebellar Cortex and Nuclei
The functions of cerebellum are executed mainly by the impulses discharged from the cerebellar nuclei. However, the cerebellar cortex controls the discharge from the nucleus constantly via the fibers of Purkinje cells. This is done in accordance with the signals received by the cerebellar cortex from different parts of brain and body via climbing and mossy fibers. The entire process involves a series of neuronal activity as mentioned in Table .
Дата добавления: 2018-02-15; просмотров: 1038;