Diencephalon Flashcards
What regions comprise the diencephalon?
1) Epithalamus
2) Thalamus
3) Subthalamus
4) Hypothalamus
What comprises the epithalamus?
Pineal Gland; Habenulae
What comprises the thalamus?
Thalamus; Metathalamus
What comprises the subthalamus?
subthalamic nuclei; Zona incerta; Globus pallidus
What comprises the hypothalamus?
Tuber cinerum; Infundibulum; mammillary bodies
Where does the hypothalamus lie in relation to the thalamus?
Hypothalamus lies anteriorly, inferiorly and medially to the thalamus
Where does the subthalamus lie?
It lies obliquely between the thalamus and the hypothalamus
Where does the epithalamus lie?
It lies superior to the thalamus with the stria medullaris (a white matter tract) serving as input/output to/from habenula
What is the interthalamic adhesion?
This is a piece of grey matter that anatomically conntects the right and left thalami together - however functionally they are not connected together by this - no neurones cross over so the R and L thalami do not communicate
What is the lamina terminalis?
The anterior most border of the 3rd ventricle.
Describe the function of the pineal gland.
This is an endocrine organ which synthesises melatonin. It does not possess a blood brain barrier. Melatonin inhibits the release of pituitary hormones (inhibits puberty) and controls the circadian rhythm
What two main symptoms result with space-occupying lesions in the cranial cavity?
1) Elevated Intracranial Pressure
2) Compression of localized structures
What can pineal gland tumours result in? (2)
1) Non-communicating hydrocephalus (due to compression of cerebral acqueduct)
2) Eye movement abnormalities (due to compression of the tectum)
What are the functions of the habenula?
Integrates olfactory, visceral and somatic afferents. Involved in pain processing, reproductive behaviour, nutrition, sleep wake cycles. Part of the limbic system
To which structures is the subthalamic nucleus connected to?
The subthalamic nucleus has connections with the basal ganglia (globus pallidus) and with the subsantia nigra.
What is the gross function of the subthalamic nucleus?
To control muscle movement
What is the Zona Incerta?
It is the rostral extension of the reticular formation
What are the inputs to the zona incerta
Sensory input from the spinal cord and bainstem. Input from the cerebellum
What should the subthalamus be regarded as?
As one of the extrapyramidal nuclei
What other cell groups comprise the subthalamus?
Cranial ends of red nuclei and substantia nigra
Where exactly is the hypothalamus located?
It extends from the optic chiasm to the caudal border of the mammillary bodies. It forms the floor and lower part of the lateral walls of 3rd ventricle.
Which systems does the hypothalamus contribute to?
Autonomic system, Endocrine System, Limbic System.
What are the anterior relations of the hypothalamus?
These structures lie anterior to they hypoT.
Anterior commissure
Lamina terminalis
optic chiasm
What are the inferior relations of the hypothalamus?
These lie inferior to the HypoT
Infundibulum of the pituitary
Tubercinerum
Mamillary bodies
What are the posterior relations of the hypothalamus?
These lie posterior to hypoT
Mamillary bodies
Interpeduncular fossa
What are the superior relations of the hypothalamus?
Thalamus and hypothalamic sulcus
What is the embryological origin of the posterior pituitary? Explain,
Posterior Pituitary (neuropophysis) originates from neuroectodermal tissue (from neural tube) which invaginates and extends down.
What is the embryological origin of the anterior pituiatary?
Anterior pituitary (adenopophysis) originates from oral ectodermal tissue (from roof of mouth/pharynx) and extends upwards to form Rathke’s pouch. This later envelopes the neuropophysis
What is a craniopharyngioma?
A rare type of tumour originating from the pituitary stalk and rising up in the hypothalamus. It is often calcified to form a supracellar calcified cyst
What can you see on an MRI in the case of a Craniopharyngioma?
A calcified cyst (space-occupying lesion) above the optic chiasm)
A craniopharyngioma can cause what type of symptoms?
Elevated ICP (headaches). Visual disturbances (partial bitemporal hemianopia which developes into a complete bitemporal hemianopia if compression to the optic chiasm sustained) and specific endocrine dysfunction.
How can a craniopharyngioma be treated?
Pituitary Trans-sphenoidal surgery - since pituitary lies in the hypophyseal fossa - posterior to the sphenoidal sinus, insert an endoscope into nasal cavity, break the sphenoidal sinus, break the hypophyseal fossa, and remove tumour.
Describe the blood supply of the pituitary gland and its relation with the hypothalamus
Anterior pituitary: superior hypophyseal artery forms a primary capillary plexus on the median eminence of hypoT which drains in the hypophyseal portal vein, which then forms another fenestrated capillary plexus on the anterior lobe - hypothalamus produces release hormones and release inhibiting hormones (infundibulum and median eminence) which are released on the primary capillary plexus and drain to anterior pituitary to influence its release of hormones. Neural afferents and feedback loops alter the activity of the hypothalamus in the release of these hormones.
Posterior pituitary has a capillary plexus formed by the inferior hypophyseal artery which receives the nervous axons from the supraoptic and paraventricular nuclei which release ADH and oxytocin respectively. the SON and PVN are found in the hypothalamus.
Mention how the hypothalamus regulates autonomic function.
The anterior domain sends nerve fibers to the 4 parasympathetic nuclei in the brainstem and to the lumbosacral region of the spinal cord, where they synapse with preganglionic parasympathetic nerves to regulate parasympathetic function.
The posterior domain sends nerve fibers to the thoracic spinal cord to synapse with preganglionic sympathetic fibers to regulate sympethetic function
Mention how the hypothalamus regulates neuroendocrine function in direct and indirect ways
Direct: production of oxytocin and ADH (mamillary gland development, uterine contractions and osmolality)
Indirect: production of release hormones and release inhibiting hormones
Hence, mention one general function of the hypothalamus
preserves body homeostasis by regulating autonomic and neuroendocrine systems.
What is the pre-optic nucleus responsible for?
Regulation of body temperature (36.6-37*C)
What is the supra-chiasmatic nucleus responsible for?
Regulation of circadian rhythms, sleep-wake cycle
What is the mamillary body responsible for?
Regulation of emotions and memory (receives inputs from hippocampal fornix)
What are the lateral hypothalamus and ventromedial nuclei responsible for?
Regulation of foot intake (hunger centre, satiety centre) and water intake (thirst centre)
Mention the 4 general functions of the thalamus
1) regulates sensory information going to the somatosensory/primary visual cortex
2) involved in motor circuitry with the cerebellum, basal ganglia and motor cortex
3) sends information to the cingulate gyrus (involved in emotion and limbic system)
4) regulates arousal and alertness via the reticular system
pacemeaker of the brain
Describe the appearance and location of the thalamus
it is completely covered by the telencephalon, egg shaped ovoid mass, and has 2 ends (anterior and posterior) and 4 surfaces (superior inferior medial lateral)
What is the anterior end of the thalamus related to?
The interventricular foramen of monroe
What is the posterior end of the thalamus related to
Overlies the midbrain and the tectum
What is the lateral surface of the thalamus related to?
the posterior limb of the internal capsule
What is the antero-lateral surface of the thalamus related to?
the caudate nucleus
What is the medial surface of the thalamus related to?
Third ventricle and the opposite thalamus
What is the superior surface of the thalamus related to?
Lateral ventricle floor and tela choroidea (superior surface laterally) roof of the third ventricle and fornix (superior medially)
What is the inferior surface related to of the thalamus?
Inferoanteriorly - hypothalamus inferioposteriorly - subthalamus
Which 2 structures divide the thalamus?
Internal Medullary Lamina and External Medullary Lamina
What does the internal medullary lamina divide the thalamus into? where is it located and describe the shape/
Internal medullary lamina is Y shaped, found in the thalamus, divides it into the anterior, lateral and medial groups.
What does the external medullary lamina divide the thalamus into? where is it located?
External medullary lamina is located out of the thalamus and separates the thalamus from the reticular nuclei
What structures comprise the internal medullary lamina
Thin sets of fibers (afferents efferents connecting thalamic nuclei) and the intralaminar nuclei
What comprises the external medullary lamina
Thalamocortical and cortico-thalamic fibers
Describe the anterior blood supply of the thalamus
Posterior communicating artery
Describe the posterior blood supply of the thalamus
Posterior cerebral artery
Describe the symptomology of lesions in the ventral posterior nucleus (VPM and VPL)
Sensory loss (negative) - decreased sensation Pain paraesthesias (positive) - increased sensation
Lesions ALWYAS contralateral to site of symptoms
What is thalamic pain syndrome?
Lesions in the Ventral posterior nucleus. extreme pain is felt with slight touch.
Describe the symptomology of lesions in the ventral anterior and ventral medial nuclei
Motor disturbances (no muscle paralysis since the primary motor cortex is intact) - abnormal movements (hemiataxia + action tremors + choreoathetosis) - these are explained in NV lecutre
How do disturbances of alertness/consciousness come about?
Lesions in intralaminar nuclei
Affective disturbances, apathy disinterest and lack of drive come about from lesions in the…
Anterior and Medial group of thalamic nuclei
Memory disturbances arise from lesions in…
dorsomedial nucleus of thalamus
Lesions in the lateral geniculate body cause…
visual disturbances, homonymous hemianopia
Lesions in the medial geniculate body cause…
hearing deficits
