Diencephalon Flashcards
1
Q
Describe the forebrain
A
- largest part of the brain, situated in the anterior and middle cranial fossae
- occupying the whole concavity of the vault of the skull
- contains two parts: diencephalon (above brainstem) and telencephalon (forms cerebral hemisphere)
2
Q
Describe the Diencephalon
A
- consists of symmetrical right and left solid parts and the third ventricle between them
- made up of 5 distinct components: thalamus, metathalamus, epithalamus, hypothalamus and subthalamic region
3
Q
Describe the thalamus
A
- relay station of all major somatosensory systems as well as of the extrapyramidal motor system
- every thalamic nucleus is reciprocally connected to specific cortical areas - info received by thalamus always shared with cortex, modify each other’s activity
4
Q
What can damage to the thalamus cause?
A
extensive loss of cerebral function
5
Q
Describe Thalamus
A
- large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain)
- Nerve fibers project out of the thalamus to the cerebral cortex in all directions, allowing hub-like exchanges of information.
6
Q
Function of Thalamus
A
- sensory relay - except smell
- motor integration - input from cortex, cerebellum and basal ganglia
- arousal
- pain modulation
- memory and behaviour
7
Q
Describe the structure of the thalamus
A
- large ovoid mass of grey matter, subdivided into compartments by thin septa of white matter
- anterior end is narrow and rounded - anterior tubercle
- posterior end is expanded to form pulvinar
- right and left thalami connect at the interthalamic adhesion
- medial and superior surfaces of the thalamus are exposed whereas the inferior and lateral surfaces are covered by neighbouring structures
8
Q
Describe the superior thalamic surface of the thalamus
A
- lined by a thin layer - lamina affixa, which laterally extends to the stria terminalis and the thalamostriate vein
- the latter mark the boundary of the thalamus with the caudate nucleus
- medial edge of lamina affixa - taenia choroidea, site of attachment of the tela choroidea ventriculi tertii
- lateral aspect of thalamus is separated from the lentiform nucleus by a band of white matter - capsula interna
9
Q
Describe the inferior of the thalamus
A
- dense mass of grey matter
- thin sheets of white matter (medullary laminae) divide it into individual nuclei and nuclear groups
- the internally medullary lamina separated the medial and lateral nuclear groups and splits anteriorly to enclose the anterior group of nuclei
- sevaral small intralaminar nuclei are embedded in the posterior part of the internal medullary lamina
10
Q
What does the external medullary lamina do?
A
separated the lateral group of nuclei from the posterior limb of the internal capsule and the reticular nucleus, the uppermost projection of the RF
11
Q
What are the 3 major groups of thalamic nuclei?
A
- anterior, lateral and medial
- also post, metathalamic, intralaminar and thalamic
12
Q
Anterior group of thalamic nuclei
A
- received afferents from the mammillary nuclei via the mammillothalamic tract
- also have reciprocal connections with the cingulate gyrus and hypothalamus
- integrated with the limbic system
- anteroventral, -dorsal and -medial nucleus
13
Q
Medial group of thalamic nuclei
A
- dorsomedial nucleus is the major nucleus in this group
- received input from the lateral thalamic nuclei, the hypothalamus and has a two-way connection to the prefrontal cerebral cortex in the frontal lobe
- this nucleus is said to have a role in affective behaviour, decision making, memory, judgements and integrated various somatic and visceral functions
14
Q
Lateral group of thalamic nuclei
A
- this group includes several nuclei, which are arranged in two tiers - dorsal and ventral
15
Q
Dorsal tier of lateral group of thalamic nuclei
A
- dorsal tier includes the lateral dorsal nucleus, lateral posterior nucleus and the pulvinar
- bilateral connections with other thalamic nuclei and with association cortical areas for general senses found in parietal lobe
- pulvinar has an input from the superior colliculus, play a role in saccadic ocular movements and in regulation of visual attention
16
Q
Ventral tier of lateral group of thalamic nuclei
A
- includes the ventral anterior, lateral, posterolateral and posteromedial nuclei
17
Q
- ventral anterior nucleus of lateral group of thalamic nuclei
A
- receives input from the globus palludus and substantia nigra
- its efferent fibers terminate in the motor area of the cerebral cortex
- relay station in the extrapyramidal circuit: cortex, striatum, pallidum, thalamus, cortex
18
Q
Ventral lateral nucleus of lateral group of thalamic nuclei
A
- similar connections to ventral anterior
- also received a major input from cerebellum and a minor input from red nucleus
- sends output to the premotor and motor cortical area
- it is integrated in the cortico-cerebellar extrapyramidal circuitry
19
Q
Posterior nuclear group of thalamus
A
- suprageniculate nucleus (SG)
- nucleus limitans (Lim)
- posterior nucleus (PO)
20
Q
Intralaminar nuclei
A
- embedded in internal medullary lamina
- receives afferents from the RAS, collaterals from ascending sensory pathways, other thalamic nuclei, cerebral cortex and the striatum
- they are believed to influence levels of consciousness and alertness, and to integrate sensory information, prior to the projection of the latter to the cortex
rostral intralaminar nuclei - central lateral/medial and paracentral
caudal intralaminar nuclei - centro-median nucleus
21
Q
Thalamic radiation
A
- the vast reciprocal connections of the thalamic nuclei with the cerebral cortex pass lateral to the thalamus and are components of the internal capsule
- grouped to 4
- anterior TR: connects medial and anterior nuclei with the frontal lobe
- superior TR: - connects the ventral nuclei with parital lobe
- posterior TR: connects with the pulvinar with occipital lobe
- inferior TR: connects with the pulvinar with temporal lobe
22
Q
Input of thalamus
A
- medial lemniscus, spinothalamic tracts
- trigeminothalamic tract
23
Q
Thalamic reticular nucleus
A
cerebral cortex –> TRN –>
24
Q
Clinical syndromes of Thalamus
A
- posterolateral thalamic syndromes - sensory disorders
- medial thalamic syndromes - disorders of consciousness
- anterolateral thalamic syndromes - motor disorders
25
Describe the Metathalamus
- comprise the two geniculate bodies - corpus geniculatum **mediale** and corpus geniculatum **laterale**, which adhere to the postero-inferior aspect of the pulvinar
26
Corpus geniculatum laterale
- relay center along the vision pathway
- reached by fibers of the optic tract in such a manner that, it gets information from the contralateral visual field
- its efferents form the optic radiation, which terminates in the visual cortical area in the occipital lobe around the calcarine sulcus
- dorsal and ventral nucleus
27
Corpus geniculatum mediale
- relay center along the auditory pathway
- receives afferent fibers from the inferior colliculus via brachium colliculi inferioris
- info which the medial geniculate body receives is from both ears, but predominantly from the opposite one
- its efferent projections form the acoustic radiation, which passes through the posterior limb of the capsula interna and reaches the primary auditory complex in the superior temporal gyrus - the gyrus of Heschl
28
Epithalamus
- includes several small structures
- these are the striamedullaris thalami, posteriorly terminate with a triangular enlargement - trigonum habenulae
- the habenilla; the two habenulae, left and right, connect by the habenular commissure, with the pineal gland (epiphysis) attached to it
29
What is inside each triangle in epithalamus
- two habenular nuclei - medial and lateral which belongs to the limbic system
function of the nuclei is vague - maybe connect olfactory brain, hypothalamus and limbic system with brainstem
30
What does the epiphysis produce? (pineal gland)
- melatonin, a hormone which regulates circadian rhythm
- production is stimulated by darkness and inhibited by light
- also produces serotonin
- regulated by the retino-hypothalamic pathway - includes retina, suprachiasmatic nucleus (projecting the upper sympathetic outflow in the lateral grey horn of T1-3 spinal segments) and the superior cervical sympathetic ganglion (whose postganglionic fibers reach the pineal gland)
31
Hypothalamus
- part of the diencephalon
- receives and integrates sensory information from the internal environment and directs actions to control homeostasis
- these actions are accomplished by an output to the autonomic nervous system and by regulating the endocrine activity of the hypophysis
32
Where is the hypothalamus located?
- lies below the level of the hypothalamic sulcus, found on the medial surface of the diencephalon
- on the basal brain surface, it extends from the opic chiasm anteriorly to the posterior border of the mammillary bodies posteriorly
- it includes: chiasma opticum, tuber cinereum with inf. projection infundibulum and mammillary bodies
33
optic chiasma of hypothalamus
- site fo partial crossing of the fibers of the optic nerves
- these fibers then continue as the optic tracts and terminate in the lateral geniculate bodies
34
mammillary bodies of hypothalamus
- two round pea-like structures, situated just behind the post. perforated substance
- each one consists of a white matter exterior and two grey matter nuclei inside - medial and lateral mammillary nuclei
- the mammillary bodies belong to the limbic system
35
tuber cinereum of hypothalamus
- basal eminence in the midline, situated just behind the optic chiasma
- inferiorly, it continues into the infundibulum
- the latter passes through an opening in the diaphragma sellae and connects to the hypophysis
36
White matter tracts in the hypothalamus
- crossed by two thick white matter tracts
- pars tecta of the column of the fornix
- mammillo-thalamic tract
- both lie in one sagittal plane and divide the hypothalamus into medial and lateral parts
- the hypothalamus is packed with nuclei of various nature, function and affiliations
37
The supraoptic and paraventricular nuclei
- both nuclei are structurally similar, containing large bipolar neurons
- they synthesise the hormones vasopressin (antidieuretic) and oxytocin, which pass along the axons, attached to carrier proteins called neurophysins
- they are released at the axon terminals into the capillary blood-stream of the post. lobe of the hypophysis - neurohypophysis
38
What does vasopressin do?
- causes increased reabsorption of water in the distal convoluted tubules of the nephron
- it also carries arterial vasoconstriction and elevation of blood pressure
39
What does oxytocin do?
- causes contraction of the uterine smooth muscle and the myoepithelial cells in the breast
- towards the end of the pregnancy, it is released in large amounts and stimulates labor contractions of the uterus
40
Collective role of Vasopressin and Oxytocin
- essential for appropriate social interactions, maternal care and closeness
- role in modulating fear, anxiety responses and sexual behaviour
41
Dorsomedial and Ventromedial nuclei of hypothalamus
- contain neurosecretory cells which produce releasing and release-inhibitory hormones
- these hormones are transported along the axons of these neurons and are released into the bloodstream at the upper end of the hypophysial portal system
- they are carried to and regulate the function of the anterior lobe of the hypophysis
- the latter, in turn, produce hormones which regulate the function of all endocrine glands in the body
42
What is the anterior nucleus of hypothalamus involved in?
thermoregulation
43
What is the suprachiasmatic nucleus in hypothalamus involved in?
- circadian rhythm regulation - ensures proper function of biological clocks
- receives input bilaterally from the retina and sends output to other hypothalamic nuclei as well as to the pineal gland to regulate melatonin synthesis in it via the retino-hypothalamic pathway
44
What does the arcuate (infundibular) nucleus do in hypothalamus?
- plays a role in maintaining energy homeostasis
- integrates signals from the brainstem and the periphery
- its neurons have leptin (satiety hormone) and ghrelin (hunger hormone) receptors
- they project to other hypothalamic nuclei, brainstem, cortical areas and reward pathways, all of which influence food intake
45
Other hypothalamic nuclei role
- water intake, growth regulation, blood pressure and heart rate, metabolic rates
46
Input of Hypothalamus
- has numerous reciprocal connections with other parts of the CNS
- receives input from:
- ascending portion of the dorsal longitudinal fasiculus (DLF) - originates from the nuclei of the RF (conveying general visceral sensations) and from the nucleus of the solitary tract in the medulla (which conveys taste and general visceral sensation)
- some nuclei of the thalamus
- structures of the limbic system
47
Output of Hypothalamus
- main output is to the ANS and the limbic system
- descending fibers from the hypothalamus form the descending portion of the dorsal longitudinal fasciculus DLF
- passes through PAG (periaqueductal gray?) and reaches the spinal cord
- on its way, it carries info from the hypothalamus to:
- midbrain PAG for pain modulation
- medullary autonomic centers for HR, BP and respiration
- brainstem parasympathetic nuclei (dorsal nucleus of the vagus nerve, salivatory nuclei and edinger-westphal nucleus)
- thoraco-lumbar preganglionic sympathetic neurons
- lumbo-sacral preganglionic parasympathetic neurons
48
Mammillary nuclei
- integrated in the limbic system
- project to the anterior nucleus of the thalamus via the mammillo-thalamic tract
- further this pathway is relayed to the gyrus cinguli
- the mammillary nuclei also project to the reticular nuclei in the tegmentum mesencephali via the mammillo-tegmental tract
49
Hypothalamus as a higher nervous center
- for the control of lower autonomic centers in the brainstem and spinal cord
- its role is to preserve the body homeostasis
- regulates body temp, food and water intake, circadian rhythms, hormonal balance, BP, HR, sexual function
- its reciprocal connections with the limbic system and with the thalamus suggest that the hypothalamus is the integrator of vast afferent information, and plays a role in higher brain functions, such as behavioural patterns
50
Subthalamic region
- region situated inferolaterally to the hypothalamus and medial to the internal capsule
- contains two nuclei - subthalamic and zona incerta, and several white matter bundles - subthalamic fasciculus, ansa lenticularis and fasciculus lenticularis
51
The subthalamic nucleus
- extends inferiorly to the substantia nigra and merges with its rostral end
- nucleus is integrated with the extrapyramidal motor system and is reciptocally connected to the globus pallidus via the subthalamic fasciculus
52
Ansa lenticularis of subthalamic region
connects medial segment of the pallidum to the thalamus and passes inferior to the SN
- also contains efferents from the substantia nigra
53
Fasciculus lenticularis
- connects the lateral pallidum to the thalamus and passes superior to the STN
- towards the thalamus these bundles, together with the dentothalamic tract form the fasciculus thalamicus, which projects to the ventral anterior nucleus of the thalamus
54
Zona inseta of subthalamic region
- superior continuation of the mescencephalic RF
- contains GABA-ergic neruons
- suspected to be involved in the control of voluntary movements, because stimulation has been shown to suppress limb tremor
- has vast reciprocal connections with neocortex, thalamus, brainstem, basal ganglia, cerebellum, hypo, basal forebrain and spinal cord
55
Third Ventricle
- narrow space between the two diencephalons
- anteriorly, communicates with the lateral ventricles, via interventricular foramen (of monro)
- inferiorly, with the fourth ventricle, via cerebral aqueduct
56
Structure of anterior wall of third ventricle
- anterior wall is a thin narrow lamina - lamina terminalis
- anterior commissure is a round bundle of commissural nerve fibers, running across the lamina terminalis, anterior to the columns of the fornix
- contains fibers connecting the olfactory bulbs; the rest of its fibers connect the right and left amygalda
- ant. commissure and columns of fornix form the boundaries of the triangular recess, in the ant. part of the ventricle
57
Inferior wall of third ventricle
- formed by optic chiasma, the tuber cinereum and infundibulum
- two funnel shapes recesses are formed here - recessus opticus recess and recessus infundibuli
58
Lateral wall of third ventricle
- formed by the medial surface thalamus and the hypothalamus
- limited superiorly by the stria medullaris thalami
- two lateral walls are connected via the interthalamic adhesion
59
Superior wall of third ventricle
- formed by the tela choroidea of third ventricle
- derives from pia mater, which during embryonic devel. folds and penetrates into the ventricular system through telodiencephalic fissure
- covered by a layer of ependymal cells
- inferiorly, along the two sagittal lines it gives rise to the choroid plexus of third ventricle
- sup. to the roof of the ventricle is the body of the fornix
60
Posterior wall of third ventricle
- contains opening of the cerebral aqueduct, the pineal recess with a superior boundary - the habenular commissure, and an inferior boundary - the posterior commissure
