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PMU Anatomy > Diencephalon > Flashcards

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)
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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
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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
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4
Q

What can damage to the thalamus cause?

A

extensive loss of cerebral function

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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.
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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
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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
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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
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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
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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

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11
Q

What are the 3 major groups of thalamic nuclei?

A
  • anterior, lateral and medial
  • also post, metathalamic, intralaminar and thalamic
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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
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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
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14
Q

Lateral group of thalamic nuclei

A
  • this group includes several nuclei, which are arranged in two tiers - dorsal and ventral
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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
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16
Q

Ventral tier of lateral group of thalamic nuclei

A
  • includes the ventral anterior, lateral, posterolateral and posteromedial nuclei
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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
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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
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19
Q

Posterior nuclear group of thalamus

A
  • suprageniculate nucleus (SG)
  • nucleus limitans (Lim)
  • posterior nucleus (PO)
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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

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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
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22
Q

Input of thalamus

A
  • medial lemniscus, spinothalamic tracts
  • trigeminothalamic tract
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23
Q

Thalamic reticular nucleus

A

cerebral cortex –> TRN –>

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24
Q

Clinical syndromes of Thalamus

A
  • posterolateral thalamic syndromes - sensory disorders
  • medial thalamic syndromes - disorders of consciousness
  • anterolateral thalamic syndromes - motor disorders
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25
Q

Describe the Metathalamus

A
  • comprise the two geniculate bodies - corpus geniculatum mediale and corpus geniculatum laterale, which adhere to the postero-inferior aspect of the pulvinar
26
Q

Corpus geniculatum laterale

A
  • 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
Q

Corpus geniculatum mediale

A
  • 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
Q

Epithalamus

A
  • 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
Q

What is inside each triangle in epithalamus

A
  • 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
Q

What does the epiphysis produce? (pineal gland)

A
  • 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
Q

Hypothalamus

A
  • 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
Q

Where is the hypothalamus located?

A
  • 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
Q

optic chiasma of hypothalamus

A
  • 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
Q

mammillary bodies of hypothalamus

A
  • 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
Q

tuber cinereum of hypothalamus

A
  • 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
Q

White matter tracts in the hypothalamus

A
  • 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
Q

The supraoptic and paraventricular nuclei

A
  • 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
Q

What does vasopressin do?

A
  • causes increased reabsorption of water in the distal convoluted tubules of the nephron
  • it also carries arterial vasoconstriction and elevation of blood pressure
39
Q

What does oxytocin do?

A
  • 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
Q

Collective role of Vasopressin and Oxytocin

A
  • essential for appropriate social interactions, maternal care and closeness
  • role in modulating fear, anxiety responses and sexual behaviour
41
Q

Dorsomedial and Ventromedial nuclei of hypothalamus

A
  • 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
Q

What is the anterior nucleus of hypothalamus involved in?

A

thermoregulation

43
Q

What is the suprachiasmatic nucleus in hypothalamus involved in?

A
  • 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
Q

What does the arcuate (infundibular) nucleus do in hypothalamus?

A
  • 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
Q

Other hypothalamic nuclei role

A
  • water intake, growth regulation, blood pressure and heart rate, metabolic rates
46
Q

Input of Hypothalamus

A
  • 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
Q

Output of Hypothalamus

A
  • 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
Q

Mammillary nuclei

A
  • 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
Q

Hypothalamus as a higher nervous center

A
  • 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
Q

Subthalamic region

A
  • 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
Q

The subthalamic nucleus

A
  • 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
Q

Ansa lenticularis of subthalamic region

A

connects medial segment of the pallidum to the thalamus and passes inferior to the SN

  • also contains efferents from the substantia nigra
53
Q

Fasciculus lenticularis

A
  • 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
Q

Zona inseta of subthalamic region

A
  • 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
Q

Third Ventricle

A
  • 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
Q

Structure of anterior wall of third ventricle

A
  • 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
Q

Inferior wall of third ventricle

A
  • formed by optic chiasma, the tuber cinereum and infundibulum
  • two funnel shapes recesses are formed here - recessus opticus recess and recessus infundibuli
58
Q

Lateral wall of third ventricle

A
  • 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
Q

Superior wall of third ventricle

A
  • 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
Q

Posterior wall of third ventricle

A
  • contains opening of the cerebral aqueduct, the pineal recess with a superior boundary - the habenular commissure, and an inferior boundary - the posterior commissure

PMU Anatomy (19 decks)

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