Download Dr. Mustafa Neuroanatomy lectures (8) Diencephalon The

Dr. Mustafa
Neuroanatomy lectures (8)
Diencephalon
The diencephalon is an interbrain structure lies between the
two cerebral hemispheres. The cavity of the diencephalon is the
third ventricle.
Divisions of diencephalon:
1- Two thalami.
2- Hypothalamus.
3- Subthalamus.
4- Epithalamus.
Thalamus:
It is an important relay station has an egg shaped and it
represents a large mass of gray matter. The two thalami are
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situated on each side of the midline slit like cavity (the third
ventricle). Lateral to each thalamus is the internal capsule (white
matter).
The nuclei of the thalamus:
The thalamus is divided into numbers of nuclei. The division of
the thalamus is done by the Y- shaped white matter bundle and
it is called the internal medullary lamina which divides the
thalamus into:
a- Anterior nucleus anteriorly.
b- Medial nucleus medially.
c- Lateral group of nuclei laterally.
The lateral group of nuclei includes the following:
1- Pulvinar is the rounded posterior part of the lateral group
of nuclei of the thalamus.
2- Dorsal tire of nuclei.
3- Ventral tire of nuclei which is further subdivided into
ventro-anterior
(VA),
ventro-lateral
(VL)
and
ventro-
posterior (VP).
d- Medial and lateral geniculate bodies which are two nuclei
that are situated at the posterior part of each thalamus.
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Connections of the thalamic nuclei:
●the anterior nucleus sent information to the limbic system
(that is responsible for emotion and reaction).
●the medial nucleus sent information to prefrontal cortex
(that is responsible for thinking, behaviors and mode).
●the pulvinar and dorsal tire of nuclei send together output to
the association cortex of the temporal, parietal and occipital
lobes.
●the ventroposterior nucleus is the main sensory nucleus
that receives input from all of the sensory systems except
olfaction. It receives input from:
1- Spinothalamic tract (for pain, temperature and touch
pathway).
2- Medial
lemniscus (for
vibration and
proprioception
pathway).
3- Trigeminothalamic
tract
(for
pain
and
temperature
pathway).
4- Nucleus of tractus solitarius (for visceral sensation and
taste).
The output of the ventroposterior nucleus is to the primary
sensory areas.
●the ventroanterior and ventrolateral nuclei are motor nuclei.
They receive from: the cerebellum, red nucleus, substantia
nigra
and
the
globus
pallidus.
The
output
of
the
ventroanterior and ventrolateral nuclei are to the motor areas.
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●the medial and lateral geniculate bodies. The medial
geniculate body is connected to the auditory area. While the
lateral geniculate body is connected to the visual area.
Thus, the sensory, motor and emotional systems are all pass
through the thalamus for processing in the thalamus.
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Dr. Mustafa
The subthalamus:
It is a transitory part of the diencephalon. It lies between the
mid brain and the thalamus. The substantia nigra, red nucleus
and
superior
colliculi
have
extensions
inside
the
subthalamus.
The subthalamus has an important motor nucleus that has
connection with the basal ganglia which is called the
subthalamic nucleus of Luys.
The epithalamus:
It has two parts:
1- Pineal gland.
2- Habenular nuclei.
The pineal gland:
It secrets the melatonin hormone that is secreted in
response to darkness. It lies between the two superior
colliculi. The pineal gland or body is frequently calcified with
age and this calcification is a useful radiological landmark. Its
displacement may indicate an intracranial space occupying
lesion.
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The habenular:
They are small nuclei that responsible for visceral and
emotional response to smell.
1- Visceral response to smell like nausea and vomiting to
certain smell.
2- Emotional response to smell like increase or decrease the
emotional desire (attractive or non-attractive response).
These visceral and emotional responses to smell are
differing from one person to another.
Hypothalamus:
It is a small area lies anterior-inferior to the thalamus. It is
about 5 grams in weight, its neurons have specialized features
that make them participate in a wide range of activity. These
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neurons will control food intake, water intake, body temperature,
biological O'clock or circadian rhythm of sleep pattern; it also
controls
the
sexual
behaviors
and
reproduction.
The
hypothalamus controls the endocrine functions through its
connections with the pituitary gland (hypophysis cerebri).
The hypothalamus will control the pituitary gland through:
1- The hypothalamo-hypophyseal portal circulation, in which
venous capillary bed in hypothalamus while the other
venous capillary bed in the anterior lobe of the hypophysis
cerebri (pituitary gland) to carry the stimulatory or inhibitory
factors to pituitary gland.
2- The neural pathway through tuber cinnerum → median
eminence → infundibulum that pass through opening in the
diaphragma sellae to end in the posterior lobe of the
pituitary gland. Thus, the neuronal bodies (perikaryons) are
situated within the hypothalamus and their axons are
extended to end within the posterior lobe of pituitary gland.
This neural pathway between hypothalamus and posterior
lobe will started from the two groups of nuclei in the
hypothalamus; the paraventricular nucleus and supraoptic
nucleus. These nuclei will produce anti diuretic hormone (ADH)
and oxytocin hormone, then these hormones will be carried by
axons of these two nuclei to be stored in posterior lobe of the
pituitary gland and then release from the posterior lobe of the
pituitary gland on need into circulation.
Paraventricular and supraoptic nuclei of hypothalamus →
tuber cinnerum → median eminence → infundibulum that
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pierces through the opening of the diaphragma sellae →
posterior lobe of pituitary gland.
Limbic system
This system controls the emotional aspect of behavior and it is
composed of interconnected centers surrounding the regions where the
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two hemispheres join the diencephalon. The limbic system is divided
into two major parts:
1- The limbic cortex.
2- The subcortical structures.
The limbic cortex: it includes:
1- Cingulate gyrus which is responsible for:
a- Emotional response to pain.
b- Emotional response to touch and vision.
The emotional response to pain, touch and vision is controlled through
the autonomic nervous system.
2- Parahippocampal gyrus.
3- Hippocampal formation which is medial to parahippocampal
gyrus and has the following parts:
• hippocampus.
•dentate gyrus.
•subicullum.
The hippocampal formation is responsible for recording the memory
and then these will be carried by the parahippocampal gyrus to
different areas of the CNS. Thus, damage to hippocampal formation
will lead to improper storage of the recent memory.
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Subcortical structures: it includes:
1- Fornix and mamillary body.
The fornix is a bundle of white matter from the hippocampal
formation then loop and end in the mamillary body.
The fornix and mamillary body are responsible to transmit the
memory traces from place to place within CNS. Damage to
mamillary body will lead to Korsakoff psychosis in which there is
patchy amnesia and confabulation.
2- Amygdaloid body.
It presents in the anterior aspect of the temporal lobe inside the
uncus. It has the following functions:
a- Responsible for olfaction.
b- Emotion of aggressiveness, fear and anger.
c- Emotional control of sexual desire and tendency.
Damage to amygdaloid body will lead to Klüver-Bussy syndrome.
3- Septal area.
It is very small region in the anterior part of the cerebrum near
septum palliucidum. They are responsible for control of sense of
pleasure. The stimulation of this area leads to euphoria.
4- Habenular nuclei.
They are responsible for visceral and emotional response to smell.
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Applied anatomy of limbic system is the following psychiatric
illnesses:
1- Schizophrenia.
2- Anxiety (fear of unknown).
3- Phobia (fear of no normal ground).
4- Depression (the value of things becoming less).
The limbic system is responsible for emotional responses which are
done through the autonomic nervous system.
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