Diencephalon & Basal ganglia.pdf

The Diencephalon consists of the: 1-Thalamus, 2-Hypothalamus, 3-Subthalamus, 4-Epithalamus.

Prof. Dr. F. AL-Khafaji

Diencephalon & Basal Ganglia

Learning objectives: 1- To become familiar with the four major anatomical divisions of the diencephalon. 2- To understand the main structure, connections and functions of the various parts of the diencephalon. 3- To become familiar with the major anatomical divisions of the Basal ganglia. 4- To understand the main structure, connections and functions of the various parts of the Corpus Striatum.


Borders of the Diencephalon Rostral: plane through the optic chiasm and anterior commissure. Caudal: plane through the posterior commissure and the caudal edge of the mammillary bodies. Medial: wall of third ventricle, stria medullaris thalami and massa intermedia. Lateral: the internal capsule, tail of caudate nucl. and stria terminalis. Dorsal: the fornix and floor of the lateral ventricles.


The Thalamus Large, egg-shaped (ovoid), 4 cm in length nuclear mass. It makes up about 80% of the mass of the diencephalon. Consists mainly of grey matter, but its sup. & lat. Surfaces are covered by thin layers of white matter termed respectively the stratum zonale & the external medullary lamina The grey matter is incompletely divided into anterior, medial & ventrolateral nuclei by a Y-shaped lamina of white matter called the internal medullary lamina Has two ends (Ant. & Post.) & four surfaces (Sup., Inf., Med. & Lat.). It extends: 1.Anteriorly to the interventricular foramen; 2.Superiorly to the transverse cerebral fissure (bet. Corpus callosum & fornix) 3.Inferiorly to the hypothalamic sulcus 4.Posteriorly it overlaps the midbrain (Pulvinar).


Ant. End: Smaller than post. End Lies behind interventricular foramen which connects the lat. Ventricle & 3rd. Ventricles Post. End: Large & project backwards & laterally over sup. Colliculus of midbrain & is called the pulvinar ( ) There are two small swellings on inf. Surface of pulvinar called the med. & lat. Geniculate bodies. Sup. Surface: Not clearly demarcated from lat. Surface. Stria medullaris thalami mark the junction between the sup. & med. Surfaces. Separated from the ventricular surface of caudate nucl. By the stria terminalis & thalamostriate vein Divided into two areas by an impression produced by the lat. Margin of fornix the lat. Area is coverd by ependema & forms part of the floor of the body of lat. Ventricle( lamina affixa) the median area is coverd by the tela choroidea of 3rd. Ventricle (double fold of pia mater) Prof. Dr. F. AL-Khafaji

Inf. Surface: Lies upon the subthalamic tegmental region (ie: hypothalamus, subthalamus & midbrain (from before backwards) Med. Surface: Forms part of lat. Wall of 3rd. Ventricle Separated from corresponding surface of opposite thalamus by a narrow interval The two thalami are connected by a short band called the interthalamic adhession Lat. Surface: Separated from lentiform nucl. By post. Limb of internal capsule Many fibers stream out of this surface & enter internal capsule en route for cerebral cortex (they Form the thalamic radiation, which form a Stratum on lat. surface called the external medullary lamina


Functions of Thalamus 1.Relay station A. Most somatic sensory pathways except olfaction. B. few motor pathways (eg. Cerebellar) 2.Integrating center For impulses from many sources (eg. Somatic sensory, visual, visceral, Some motor eg. Cerebellar, corpus straital) 3.Maintenance & regulation of state of: consciousness, alertness, attention (through influence upon cerebral cortex) 4.Emotional connotations ( ) (which accompany most sensory experiences) 5.Crude sensations (eg. Pain which may reach consciousness at this level even when all connections between thalamus & cortex are destroyed).


Connections anterior nucleus

Aff. Connections 1.Cerebral cortex (gyrus cinguli) 2.Hypothalamus (mammillary nuclei) 3.Contalateral ant. nucl. 4. Other thalamic nuclei 5.Fornix

Eff. Connections 1.Cerebral cortex (gyrus cinguli) 2.Hypothalamus (mammillary nuclei) 3.Contalateral ant. nucl. 4.Other thalamic nuclei 5.Habenular nuclei


Ant. Nucl. *Closely associated with the limbic system. *Concerned with : 1-Emotional tone. 2-Mechanisms of recent memory. *Stimulation or ablation of mammillothalamic tract causes: 1-Alteration in autonomic control. 2-Memory loss for recent events. The Limbic Loop Hippocampus Fornix Mammillary body Ant. Thalamic Nucl. Parahipocample gyrus Cingulate gyrus Cingulum ----------------------------------------------------------------------------------------------- NB.: Limbic system: centers that effect emotional & visceral aspects of behavior & memory processing


Limbic System ( ) centers that effect emotional & visceral aspects of behavior & memory processing . I. Structures with close olfactory connections 1.Paraterminal gyrus 2.Septal nuclei 3.Piriform cortex 4.Amygdaloid body II. Others 1.Hippocampus, fornix, hypothalamus, cingulate gyrus, parahippocampal gyrus Prof. Dr. F. AL-Khafaji

Connections medial nucleus (dorsomedial nucl.)

Aff. Connections 1.Cerebral cortex (prefrontal cortex) 2.Hypothalamus 3.Other thalamic nuclei 4.Amygdaloid complex 5.Piriform cortex

Eff. Connections 1.Cerebral cortex (prefrontal cortex) 2.Hypothalamus 3.Other thalamic nuclei


Medial Nucl. * Provides mechanisms for the integration of certain Somato-visceral impulses projecting to prefrontal cortex. * Mediate impulses of an affective nature which contributes to the formation of personality. * Stimulation, disease, or surgical ablation of nucl. in man results in changes in: 1- Motivational drive. 2- Ability to solve problems. 3- Consciousness level. 4- General personality. 5- Subjective feeling status (affective tone). 6- Pain perception (indifference to pain). 7- Emotional content.


Types of thalamic nuclei R= Relay nucl. A= Association nucl. SC= Subcortical projections DC= Diffuse cortical projections


Nucleus Ventralis Lateralis *Related to motor control system. * Makes important contribution to initiation of movements, control of muscle tone, regulation of cortical reflexus. * The cerebello-Thalamo-Cortical relay system may play an important role in unconscious regulation of muscle tone. (interruption of this system , at thalamic level, may be responsible for the reduction in muscle tone following stereotaxic surgery in Parkinsonism. * Lesions in (VL) ameliorate some aspects of dyskinesia (due to both cerebellar or corpus striatal lesions) by reducing output from (VL) to motor cortex.


Nucleus Ventralis Anterior * Related to motor control system & therefore affects activities of motor cortex. *Regarded as important link in the final stages of the ascending activating system (arousal reaction). * Stimulation increases Parkinsonian rigidity & tremor. * Abalation reduces or abolish this tremor.


VPI Nucleus Ventralis

Intermedius (R)

Vestibular Nerve

Postcentral Gyrus (caudal portion close to junction of Bradman's area 2,5) (Primary vestibular area for conscious vestibular perception)


MGB Lower auditory

center

Lat. Lemniscus

Inf. Colliculus

1-Inf. Colliculus 2-Brainstem auditory relay nuclei

Sup. Temporal gyrus (41) (Transv. gyrus of Heschl)

1-Ventrolat. Nuclei of thalamus 2-Pulvinar

P.N: Asc. Fibs. Are paralled by desc. Fibs. Which may serve as regulatory feed-back mechanism. Prof. Dr. F. AL-Khafaji

LGB Lower visual

centre

Ganglion cells of retina

1-Ventrolat. Nuclei of thalamus 2-Pulvinar

Visual Cortex (Striate, 17)

1-Pretectum 2-Sup. Colliculus 3-Suprachiasmatic Nucleus4-Zona Incerta

P.N.: LGB is the main end station of optic tract. Prof. Dr. F. AL-Khafaji

None specific thalamic nuclei Nuclei of midline Intralaminar nuclei Reticular nucl.

(SC) Reticular Nucleus *Important final link in the diffuse Thalamo-Cortical radiation. *Produces wide spread effects on cortical activity (cortical arousal). *Integrates intra-thalamic activities. Afferents: 1- Cerebral Cortex. 2-Other thalamic nuclei. 3-Brainstem reticular formation. 4-Globus pallidus. Efferents: 1-Other thalamic nuclei. 2-Mid-brain reticular formation. 3-Corpus striatum.


(SC, DC) CentromediansNucleus *Intra-thalamic integrating mechanism bringing the activities of various other thalamic nuclei into functional relation with each other. Afferents 1-Asc. Reticular formation. 2-Other thalamic nuclei. 3-Globus pallidus. 4-Spinal,medial & trigeminal lemnisci (collaterals). 5-Sup. Cerebellar peduncle (contribution) Efferents 1-Cerebral cortex (not directly) via collaterals to corpus straitum. 2-Corpus striatum. 3- Other none-specific thalamic nuclei. 4-VA nucleus of thalamus Nuclei of the mid-line *Lie in periventricular grey matter of dorsal 1/2 of ventricular wall & inter-thalamic adhesion. *Poorly developed in man (but well developed in many mammals). *Concerned with visceral functions & connected to hypothalamus


Hypothalamic Nuclei

Zone Nuclei 1.Supraoptic (Ant.) 1.Supraoptic nucl. 2.Paraventricular nucl. 3.Suprachiasmatic nucl.. 2.Infundibluotubular (middle) 1.Dorsomedial nucl. 2.Ventromedial nucl. 3.Arcuate nucl.(Infundibular ) 3.Mammillary (caudal) 1.Posterior nucl. 2.Mammillary nucl. 3.Mammilloinfundibular nucl.


Functions of Hypothalamus 1.Endocrine control: *Release factors Anterior pituitary *Release inhibiting factors 2.Neurosecrtion: *Vasopressin (supraoptic nucleus) Posterior pituitary *Oxytocin (paraventricular nucleus) 3.Autonomic control: Higher center for control of lower autonomic centers in brainstem & spinal cord *Ant. Region Influence parasypathetic activity *Preoptic region *Post. Region Influence sympathetic activity *Lat. Region 4.Tempereture regulation: *Ant. Region controls dissipation of heat *Post. Region controls conservation of heat Prof. Dr. F. AL-Khafaji

5.Food intake regulation: *Lat. Region (Hunger centre) initiates eating & increase food intake *Med. Region (Satiety centre) inhibits eating & reduces food intake 6.Water intake & balance: *Lat. Region (Thirst center) increase water intake PN: Vasopressin effect on distal convoluted tubules & collecting tubules of kidney 7.Emotion & behavior: Function of hypothalamus, limbic system & prefrontal cortex It generates behaviors involved in rage, aggression, escape, etc. 8.Circadian rhythms (daily rhythm of a biological function) eg.: Body temperature, Adrenocortical activity, Sleep & wakefulness (ant. Region) PN: Suprachiasmatic nucleus (aff. From retina) play a role in control of circadian rhythms (variation in intensity of light are transmitted by this nucl. To many hypothalamic nuclei.


Prof. Dr. F. AL-Khafaji Prof. Dr. F. AL-Khafaji Prof. Dr. F. AL-Khafaji


Epithalamus *Composed of : 1.Pineal body. 2.. Habenula [ :( ] ) 3.Posterior & Habenular commissures *Most dorsal, smallest, and oldest part of Diencephalon *Functionally and anatomically linked to the limbic system *It is implicated in: 1.Autonomic functions (e.g. respiratory, cardiovascular.etc.) 2.Endocrine functions (e.g. Thyroid functions) 3.Reproductive functions ( e.g. mating behavior)


Habenular Nucleus *Center for integration of olfactory, visceral & somatic afferent pathways (correlation of olfactory & somatic afferent impulses) *Ablation of this nucl. Produce changes in metabolism, endocrine regulation & thermoregulation Aff. Fibs.: 1. Amygdaloid complex (via. Stria terminalis) 2. Hippocampal formation (via. Fornix) 3. Olfactory tubercle 4. Pre-optic & septal areas (via. Stia medullaris thalami) 5. Ant. Perforated substance 6. Various hypothalamic Nuclei 7. Globus Pallidus Eff. Fibs.: 1. Interpeduncular nucl. (via. FR) 2. Medial nucl. Of thalamus 3. Tectum & reticular formation of mid-brain


PN.:The Stria Medullaris Thalami, Habenula, & Fasciculus Retroflexes form segments of Visceral Eff. Pathways which carry impulses to parts of brainstem & spinal cord (eg. Tectotegmentospinal Tracts & Dosal Longitudenal Fasciculus which connect with autonomic preganglionic centers


Nucleus Subthalamicus Aff. Fibs.: 1.Globus Pallidus 2.Motor cortex (precentral) 3.Pedunclopontine Nucl. Eff. Fibs.: 1.Globus Pallidus 2.Contrlateral Globus pallidus 3.Substantia Nigra 4.Opposite Subthalamic nucl.

Zona Incerta Aff. Fibs.: 1.Motor cortex (precentral ) Eff. Fibs.: 1.Mid-brain reticular formation

Nucleus Subthalamicus *Lies medial to internal capsule *Continuous with substantia nigra Function Important site for integration of a number of motor control centers Especially through its connections with the corpus striatum & midbrain Tegmentum Lesions of one subthalamic nucl. Results in condition called Hemiballismus (Subthalamic Dyskinesia) Zona Incerta *Thin strip of gray matter *Lies between thalamic & lenticular fasciculei *Continuous with thalamic reticular nucl. Functionally associated with the Zona Incerta are the Nucl. of prerubral field & Entopeduncular nucl.


Basal Ganglia (Nuclei)

(Concerned with somatic motor function)

Amygdaloid nuclear complex (Archistriatum) (oldest) (Component of Limbic system) Ie. visceral, endocrine, behavioral

Neostriatum (Striatum)

Paleostiatum


Caudate Nucleus *C-shped structure, related to lateral ventricle. *The head lies rostral to thalamus & protrude into ant. Horn of lat. Vent. *The body is slender & elongated & arches along dorsolateral border of thalamus (lat. To stria terminalis) *The tail lies caudal to thalamus in roof of inferior horn of lat. Vent. (in relation to amygdaloid nuclear complex)

Putamen *Largest & most lateral part of corpus striatum *Medial to external capsule *Traversed by striopallidal fibers *Rostrally & ventrally is continuous with head of caudate nucl. *But in more dorsal regions, is connected to caudate nucl. by strial bridges (passing between fibers of internal capsule)


Globus Pallidus *Phylogentically older than striatum *Smaller inner part of lentiform nucl. *Lies med. To putamen *Dorsomedial margin borders the post. Limb of internal capsule *Has a thin lat. Medullary Lamina (between it & putamen) *Has Med. Medullary Lamina which divide globus pallidus into med. & lat. Segments *Has less distinct Accessory Medullary Lamina which divide med. segment into inner & outer portions


Caudate Nucleus Afferents: 1- Cerebral Cortex Efferents: 1- Globus Pallidus (mainly)

Putamen Afferents: 1- Cerebral Cortex 2- Caudate Nucl. Efferents: 1- Globus Pallidus

Globus Pallidus Afferents: 1- Caudate Nucl. 2- Putamen 3- Subustantia Nigra 4- Subthalamic Nucl.

Efferents: 1- Thalamus (VL,VA,Centomedian) 2- Subthalamus 3- Substantia Nigra 4- Hypothalamus 5- Reticular formation 6- Habenular nuclei

Lentiform Nucleus


Diseases of corpus striatum

Various types of abnormal involuntary movements (Dyskinesia ) eg. Tremor, athetosis, chorea, ballism

Disturbances of muscle tone (usually increased muscle tone) eg. Rigidity of Parkinson disease

PN: Cerebral cortex must play an important role in dyskinesia Evidence: 1- All forms of abnormal involuntary movements cease during sleep 2- Abolished by general anesthesia 3- Exaggerated by excitement & anxiety 4- Ablation of motor cortex & interruption of corticospinal tract at various levels abolishes dyskinesia (may suggests that impulses from centers responsible for dyskinesia must be transmitted to segmental levels via the corticospinal tract Prof. Dr. F. AL-Khafaji

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Diencephalon & Basal ganglia.pdf