The Diencephalon[1] vvtyyyyytttttttvvv.pdf

Anatomy

1. The Diencephalon
and
Basal Ganglia

2. Introduction
•It is the developmentally unexpanded part of the forebrain,
cranial to the midbrain.
•Buried in the expansive cerebral cortex
•The 3
rd ventricle is the cavity of the diencephalon, limited
anteriorly by the lamina terminalis.
•The diencephalon has a roof, floor and 2 side walls
•The anterior wall of the diencephalon is formed by the
lamina terminalis.
•It is a thin sheet between the 2 hemispheres, from the
rostrum of corpus callosum to the optic chiasma.

4. •The roof and floor merge posteriorly and is continuous with
the midbrain in substance and cavity.
•The floor extends from the optic chiasma to the posterior
perforated substance where it blends with the tegmentum of
the cerebral peduncle.
•The tuber cinereum, infundibulum and mammillary body are
in-between
•The thalamus and hypothalamus are demarcated by the
hypothalamic groove.
•The hypothalamic groove extends from the interventricular
foramen to the aqueduct of midbrain.
•Inter-thalamic adhesion is present in 60% of brains

6. The 3
rd Ventricle
•A slit like space in the sagittal plane inferior to the fornix and corpus
callosum.
•The 2 side walls are formed by the thalamus and the hypothalamus
•The thalamus bulges into the cavity with inter-thalamic adhesion in
60% of brains.
•Inferior to the hypothalamic groove, the side walls merge with the
floor mainly as hypothalamus.
•The interventricular foramen opens into 3
rd
ventricle just posterior to
the fornix.
•It drains into the 4
th
ventricle through the aqueduct of the midbrain at
the lower posterior end.

8. The hypothalamus
•Forms the floor of the 3
rd ventricle, inferior to the thalamus,
separated by the hypothalamic groove.
•Its medial surface contributes to the wall of the 3
rd ventricle.
•Its lateral surface is in contact with the internal capsule.
•Posteriorly, it continues as the subthalamus before merging
with tegmentum of the midbrain.
•The tuber cinereum, infundibulum and mammillary body are
the inferior structures of the hypothalamus.
•The division of the hypothalamus can be medio-lateral or
anterio-posterior.

10. •It is concerned with visceral functions with connections to
the limbic system, reticular formation and autonomic centers.
•Median eminence part of tuber cinereum (infudibular base)
contain neurosecretory cell that control anterior pituitary.
•Various hypothalamic nuclei have been identified serving
different functions;
üPreoptic nucleus; located around the lamina terminalis
extending from the paraventricular to the lateral zone.
üImportant for thermoregulation, fluid and electrolyte
balance and sexual behavior
üMammillary nucleus; located in the mammillary body at
the posterior end of the hypothalamus.
üRelated to the limbic system for olfactory memory

11. üParaventricular and Suprachiasmatic
nuclei; located above the optic
chiasma in the medial zone, axons
extends to the posterior lobe of
pituitary.
üParaventricular controls oxytocin and
vasopressin production
üSuprachiasmatic controls circadian
rhythms
üOther cell possess axons that pass
through brain stem to the lateral
horn cells of preganglionic
sympathetic cells (thoracic/lumbar)
and parasympathetic (sacral)

12. The epithalamus
•This is related to the posterior part of the roof of the 3
rd

ventricle with lateral extension.
•Consists of the pineal gland, stria medullaris and posterior
commissure
•Pineal gland; It is an endocrine gland made up of
pinealocytes and neuroglia cells.
üProjects from the posterior wall of the 3
rd
ventricle above
the superior colliculus
üIt is soft and conical in shape with no BBB
üContent do calcify in the 5
th
decade of life, useful for
space occupying lesion radiodiagnosis.

13. üSecretes melatonin and other substances with
widespread endocrine effects
üThe pineal stalk is attached to the posterior and
habenular commissures via its stalk
üInnervation is by the postganglionic sympathetic
neurons

15. •Stria medullaris; a bundle of fibers at the junction between
the superior and medial surfaces of the thalamus.
üIt extends from the anterior pole of the thalamus to the
posterior end
üSome fibers cross to the opposite side through the
superior pineal stalk as habenular commissure
üThey connect the amygdala and hippocampal cortex on
both sides
•Posterior commissure; it is located in the inferior lamina of
pineal gland stalk

17. The Ventral thalamus
•It is lateral and posterior to the hypothalamus otherwise
known as the subthalamus.
•It is continuous inferiorly with the tegmentum of the midbrain
•Grey matter collections include the reticular nucleus,
pregeniculate nucleus and the Zona incerta
•Reticular nucleus; thin layer of neurons on the lateral side of
the thalamus
üSeparated by the external medullary velum
üLaterally related to the internal capsule
üTraversed by fibers from the thalamus.

18. •Pregeniculate nucleus; it is
related to visual functions
and movement of eyeball
•Zona Incerta; thin layer of
grey matter continuous
with reticular nucleus

19. Dorsal thalamus
•Largest mass of grey matter, it is wedge shaped
•Contributes to 3
rd ventricle walls
•It has anterior and posterior poles, and 4 surfaces
•Anterior pole is just posterior to the interventricular foramen
while the posterior pole is supero-lateral to the superior
colliculus.
•Medial surfaces alongside hypothalamus form the 3
rd
ventricular walls.
•The 2 medial walls are parallel anteriorly, inter-thalamic
adhesions in 60% of brains.

20. •Posterior end of medial surfaces diverge from each other
expanding to form the pulvinar.
•The medial and lateral geniculate bodies are related to the
midbrain and pulvinar
•Hypothalamic sulcus runs from interventricular foramen to
the aqueduct of midbrain.
•Lateral surface is beveled and separated from the lentiform
nucleus by the internal capsule.
•Superior surface is convex and triangular in outline, tapering
anteriorly from pulvinar

21. •Superior surface (laterally) is separated from the body and tail
of caudate nucleus by stria terminalis and thalamostriate vein.
•The superior surface (lateral) and caudate nucleus form the
floor of the central part of lateral ventricle.
•The tela choroidea and fornix separates the medial part of
superior surface from the lateral ventricle.
•Inferiorly, thalamus is related to the hypothalamus and ventral
thalamus anterio-posteriorly.
•Ventral thalamus separates the thalamus from the tegmentum
of the midbrain.
•Thalamic nuclei receives afferents from the medial, spinal and
trigeminal lemnisci and reticular formation, they are projected
to the sensory area of cortex.

22. •Afferents from dentate nucleus and Globus pallidus are
projected to the motor cortex
•Afferents from the hypothalamus, corpus striatum are
reciprocally projected to the frontal lobe, they are concerned
with memory and emotional functions
•The medial and lateral geniculate bodies are concerned with
hearing and vision respectively.

24. •Thalamus consists mainly of grey matter.
•A strip of white matter lines the superior surface (stratum
zonales) and the lateral surface (external medullary lamina)
•Internal medullary lamina is a Y shaped white matter sheet
dividing the thalamus into medial, lateral and anterior parts.
•Anterior part; anterior nucleus collectively
•Medial part; medial dorsal nucleus divisible into
magnocellular (anterio-medial) and Parvocellular (posterior-
lateral).

26. •Lateral part; further divided into ventral and lateral groups
üVentral group; anterior, intermediate and posterior nuclei
(posteriolateral and posterior-medial).
ØAnterior; anteriolateral end of the thalamus.
ØIntermediate; also known as ventral lateral nucleus.
ØPosterior; receives input from sensory pathways from
spinal cord and brain stem.
üLateral group; Dorsolateral, lateral posterior and Pulvinar

28. •THE BASAL GANGLIA consist of the caudate nucleus,
lentiform nucleus, amygdaloid body and claustrum.
•The lentiform nucleus consist of an outer putamen and an
inner globus pallidus.
•The caudate and putamen form the striatum; the larger part
of the basal ganglia and its afferent part.
ØCaudate nucleus; It is a comma shaped structure with a
demonstrable bulbous head, body and tail attached to the
amygdaloid body.

30. •The convexity of the caudate nucleus projects into the
ventricle.
•The internal capsule fibres run in the concavity of the
nucleus.
ØThe lentiform nucleus; consist of the putamen and globus
pallidus.
•It is biconvex in shape with the putamen lateral and smaller
medial globus pallidus.
•The caudate nucleus and the putamen are joined by many
interconnecting fibre running through the anterior part of
the internal capsule (corpus striatum)

32. •Amygdaloid body; a group of grey matter at the tip of the
tail of the caudate nucleus
•It lies on the roof of the inferior horn of the lateral ventricle.
•It has numerous neurons that connects it to the frontal,
temporal and olfactory lobes.
•Its efferent bundle (stria terminalis) runs parallel to the
concavity of the caudate nucleus.
•The claustrum; a saucer shaped thin lamina of grey matter,
lateral to the putamen.

34. •The corpus striatum is the afferent centre of the basal
ganglia receiving fibres from the cortex, thalamus and
substantia nigra.
•The globus pallidus is the efferent pathway of the basal
ganglia sending fibres to the thalamus, subthalamic nucleus,
substantia nigra etc
•The basal ganglia offers supraspinal control over skeletal
muscle movement, modulating the rate, range and
coordination.
FUNCTIONAL ANATOMY

35. •Several neurotransmitter are involved in the different
pathways such as the acetylcholine, dopamine, glutamate,
serotonin etc
•Parkinsonism is the most common anomaly of the basal
nuclei.
•Involving a decrease in dopamine in the nigrostriatal
pathway following destruction of dopaminergic cells of
the substantia nigra.
•Huntington's disease is as a result of destruction of the
neurons in the striatum.