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The

Diencephalon

consists of the:

1-Thalamus,
2-Hypothalamus,
3-Subthalamus,
4-Epithalamus.

Prof. Dr. F. AL-Khafaji

Diencephalon & Basal Ganglia

•Learning objectives:

1- To become familiar with the

four

major anatomical

divisions of the diencephalon.
2- To understand the

main

structure, connections and

functions of the various parts of the diencephalon.
3- To become familiar with the

major

anatomical

divisions of the Basal ganglia.
4- To understand the

main

structure, connections and

functions of the various parts of the Corpus Striatum.

Prof. Dr. F. AL-Khafaji

Borders of the Diencephalon

Rostral

: plane through the optic chiasm and anterior

commissure.

Caudal

: plane through the posterior commissure and

the caudal edge of the mammillary bodies.

Medial

: wall of third ventricle, stria medullaris thalami

and massa intermedia.

Lateral

: the internal capsule, tail of caudate nucl. and stria

terminalis.

Dorsal

: the fornix and floor of the lateral ventricles.

Prof. Dr. F. AL-Khafaji

The Thalamus

•Large, egg-shaped (ovoid), 4 cm in length nuclear mass.
•It makes up about 80% of the mass of the diencephalon.
•Consists mainly of grey matter, but its sup. & lat. Surfaces are covered
by thin layers of white matter termed respectively the stratum zonale &
the external medullary lamina
•The grey matter is incompletely divided into anterior, medial &
ventrolateral nuclei by a Y-shaped lamina of white matter called the
internal medullary lamina
• Has

two

ends (Ant. & Post.) &

four

surfaces (Sup., Inf., Med. & Lat.).

•It extends:

1.Anteriorly

to the interventricular foramen;

2.Superiorly

to the transverse cerebral fissure (bet. Corpus callosum &

fornix)

3.Inferiorly

to the hypothalamic sulcus

4.Posteriorly

it overlaps the midbrain (Pulvinar).

Prof. Dr. F. AL-Khafaji

Ant. End:

Smaller than post. End
Lies behind interventricular foramen which connects the lat. Ventricle
& 3

. Ventricles

Post. End:

Large & project backwards & laterally over sup. Colliculus of midbrain &
is called the pulvinar ( )وسادة
There are two small swellings on inf. Surface of pulvinar called the med.
& lat. Geniculate bodies.

Sup. Surface:

Not clearly demarcated from lat. Surface.

Stria medullaris thalami

mark the junction between the sup. & med.

Surfaces.
Separated from the ventricular surface of caudate nucl. By the

stria

terminalis & thalamostriate vein

Divided into two areas by an impression produced by the lat. Margin of

fornix

the lat. Area is coverd by ependema & forms part of the floor of

the body of lat. Ventricle( lamina affixa) the median area is coverd by
the tela choroidea of 3

. Ventricle (double fold of pia mater)

Prof. Dr. F. AL-Khafaji

Inf. Surface:

Lies upon the subthalamic tegmental region (ie: hypothalamus,
subthalamus & midbrain (from before backwards)

Med. Surface:

Forms part of lat. Wall of 3

. Ventricle

Separated from corresponding surface of opposite thalamus by a
narrow interval
The two thalami are connected by a short band called the interthalamic
adhession

Lat. Surface:

Separated from

lentiform nucl.

By post. Limb of

internal capsule

Many fibers stream out of this surface & enter internal capsule en route
for cerebral cortex (they Form the thalamic radiation, which form a
Stratum on lat. surface called the external medullary lamina

Prof. Dr. F. AL-Khafaji

Functions of Thalamus

1.Relay station

A. Most somatic sensory pathways except olfaction.
B. few motor pathways (eg. Cerebellar)

2.Integrating center

For impulses from many sources (eg. Somatic sensory, visual,
visceral, Some motor eg. Cerebellar, corpus straital)

3.Maintenance & regulation of state of:

consciousness, alertness, attention (through influence upon
cerebral cortex)

4.Emotional connotations

(

المحتوى العاطفي

)

(which accompany most sensory experiences)

5.Crude sensations

(eg. Pain which may reach consciousness at this level even
when all connections between thalamus

& cortex are

destroyed

Prof. Dr. F. AL-Khafaji

Connections anterior nucleus

Aff. Connections
1.Cerebral cortex (gyrus cinguli)
2.Hypothalamus (mammillary nuclei)
3.Contalateral ant. nucl.
4. Other thalamic nuclei
5.Fornix

Eff. Connections
1.Cerebral cortex (gyrus cinguli)
2.Hypothalamus (mammillary nuclei)
3.Contalateral ant. nucl.
4.Other thalamic nuclei
5.Habenular nuclei

Prof. Dr. F. AL-Khafaji

Ant. Nucl.

*Closely associated with the limbic system.
*Concerned with :
1-Emotional tone.
2-Mechanisms of recent memory.
*Stimulation or ablation of mammillothalamic tract causes:
1-Alteration in autonomic control.
2-Memory loss for recent events.

The Limbic Loop

Hippocampus        Fornix         Mammillary body        Ant. Thalamic Nucl.

Parahipocample gyrus                  Cingulate gyrus            Cingulum
-----------------------------------------------------------------------------------------------
NB.: Limbic system: centers that effect emotional & visceral aspects of
                                      behavior & memory processing

Prof. Dr. F. AL-Khafaji

Limbic System (

ّوفيُحلا ُزاهِجلا

)

centers that effect emotional & visceral aspects of
behavior & memory processing .

Structures with close olfactory connections

1.Paraterminal gyrus
2.Septal nuclei
3.Piriform cortex
4.Amygdaloid body

II.

Others

1.Hippocampus, fornix, hypothalamus,
cingulate gyrus, parahippocampal gyrus

Prof. Dr. F. AL-Khafaji

Connections medial nucleus (dorsomedial nucl.)

Aff. Connections
1.Cerebral cortex (prefrontal cortex)
2.Hypothalamus
3.Other thalamic nuclei
4.Amygdaloid complex
5.Piriform cortex

Eff. Connections
1.Cerebral cortex (prefrontal cortex)
2.Hypothalamus
3.Other thalamic nuclei

Prof. Dr. F. AL-Khafaji

Medial Nucl.

Provides mechanisms for the

integration

of certain

Somato-visceral impulses projecting to prefrontal cortex.

Mediate impulses of an

affective nature

which

contributes to the formation of personality.

Stimulation, disease, or surgical ablation of nucl. in man

results in

changes

in:

1- Motivational drive.
2- Ability to solve problems.
3- Consciousness level.
4- General personality.
5- Subjective feeling status (affective tone).
6- Pain perception (indifference to pain).
7- Emotional content.

Prof. Dr. F. AL-Khafaji

Types of thalamic nuclei

= Relay nucl.

= Association nucl.

= Subcortical projections

= Diffuse cortical projections

Prof. Dr. F. AL-Khafaji

Nucleus Ventralis Lateralis

*Related to

motor control system

* Makes important contribution to initiation of movements,
control of muscle tone, regulation of cortical reflexus.
* The

cerebello-Thalamo-Cortical relay system

may play an

important role in unconscious regulation of muscle tone.
(interruption of this system , at thalamic level, may be
responsible for the reduction in muscle tone following
stereotaxic surgery in Parkinsonism.
* Lesions in (VL) ameliorate some aspects of dyskinesia (due
to both cerebellar or corpus striatal lesions) by reducing
output from (VL) to motor cortex.

Prof. Dr. F. AL-Khafaji

Nucleus Ventralis Anterior

Related to

motor control system

& therefore affects

activities of motor cortex.

Regarded as important link in the final stages of the

ascending activating system (arousal reaction).

Stimulation increases Parkinsonian rigidity &

tremor.

Abalation reduces or abolish this tremor.

Prof. Dr. F. AL-Khafaji

VPI

Nucleus Ventralis

Intermedius

(R)

Vestibular Nerve

Postcentral Gyrus

(caudal portion close to junction of
Bradman's area 2,5)
(Primary vestibular area for conscious
vestibular perception)

Prof. Dr. F. AL-Khafaji

MGB

Lower auditory

center

Lat. Lemniscus

Inf. Colliculus

1-Inf. Colliculus
2-Brainstem auditory relay nuclei

Sup. Temporal gyrus (41)
(Transv. gyrus of Heschl)

1-Ventrolat. Nuclei of thalamus
2-Pulvinar

P.N: Asc. Fibs. Are paralled by desc. Fibs. Which may serve as regulatory feed-back mechanism.

Prof. Dr. F. AL-Khafaji

LGB

Lower visual

centre

Ganglion cells of retina

1-Ventrolat. Nuclei of thalamus
2-Pulvinar

Visual Cortex (Striate, 17)

1-Pretectum
2-Sup. Colliculus
3-Suprachiasmatic Nucleus
4-Zona Incerta

P.N.: LGB is the main end station of optic tract.

Prof. Dr. F. AL-Khafaji

None specific thalamic nuclei

Nuclei of midline

Intralaminar nuclei

Reticular nucl.

(SC)

Reticular Nucleus

Important final link in the diffuse Thalamo-Cortical radiation.

Produces wide spread effects on cortical activity (cortical

arousal).

Integrates intra-thalamic activities.

Afferents:

1- Cerebral Cortex.
2-Other thalamic nuclei.
3-Brainstem reticular formation.
4-Globus pallidus.

Efferents:

1-Other thalamic nuclei.
2-Mid-brain reticular formation.
3-Corpus striatum.

Prof. Dr. F. AL-Khafaji

(SC, DC)

Centromedians

Nucleus

*Intra-thalamic integrating mechanism bringing the activities of various
other thalamic nuclei into functional relation with each other.

Afferents

1-Asc. Reticular formation.
2-Other thalamic nuclei.
3-Globus pallidus.
4-Spinal,medial & trigeminal lemnisci (collaterals).
5-Sup. Cerebellar peduncle (contribution)

Efferents

1-Cerebral cortex (not directly) via collaterals to corpus straitum.
2-Corpus striatum.
3- Other none-specific thalamic nuclei.
4-VA nucleus of thalamus

Nuclei of the mid-line

*Lie in periventricular grey matter of dorsal 1/2 of ventricular wall &
inter-thalamic adhesion.
*Poorly developed in man (but well developed in many mammals).
*Concerned with visceral functions & connected to hypothalamus

Prof. Dr. F. AL-Khafaji

Hypothalamic Nuclei

Zone Nuclei

1.Supraoptic (Ant.)                                          1.Supraoptic nucl.
                                                                            2.Paraventricular nucl.
                                                                            3.Suprachiasmatic nucl..

2.Infundibluotubular (middle)                       1.Dorsomedial nucl.
                                                                             2.Ventromedial nucl.
                                                                             3.Arcuate nucl.(

Infundibular

)

3.Mammillary (caudal)                                    1.Posterior nucl.
                                                                             2.Mammillary nucl.
                                                                             3.Mammilloinfundibular nucl.

Prof. Dr. F. AL-Khafaji

Functions of Hypothalamus

1.Endocrine control:

*Release factors
Anterior pituitary
*Release inhibiting factors

2.Neurosecrtion:

*Vasopressin   (supraoptic nucleus)
                                                                              Posterior pituitary
*Oxytocin         (paraventricular nucleus)

3.Autonomic control:

    Higher center for control of lower autonomic centers in brainstem & spinal cord
*Ant. Region
                                     Influence parasypathetic activity
*Preoptic region

*Post. Region
                                Influence sympathetic activity
*Lat. Region

4.Tempereture regulation:

*Ant. Region controls dissipation of heat
*Post. Region controls conservation of heat

Prof. Dr. F. AL-Khafaji

5.Food intake regulation:

*Lat. Region (Hunger centre) initiates eating & increase food intake
*Med. Region (Satiety centre) inhibits eating & reduces food intake

6.Water intake & balance:

*Lat. Region (Thirst center) increase water intake

PN:

Vasopressin effect on distal convoluted tubules & collecting

tubules of kidney

7.Emotion & behavior:

Function of hypothalamus, limbic system & prefrontal cortex
It generates behaviors involved in rage, aggression, escape, etc.

8.Circadian rhythms

(daily rhythm of a biological function)

eg.:

Body temperature, Adrenocortical activity,

Sleep & wakefulness (ant. Region)

PN:

Suprachiasmatic nucleus (aff. From retina) play a role in control of

circadian rhythms (variation in intensity of light are transmitted by this
nucl. To many hypothalamic nuclei.

Prof. Dr. F. AL-Khafaji

Epithalamus
*

Composed of :

1.Pineal body.
2.. Habenula

نانِعلا

(

بنية تشريحية تشبه لجام الفرس

[ )

أعنة

]

3.Posterior & Habenular commissures

Most dorsal, smallest, and oldest part of Diencephalon

Functionally and anatomically linked to the limbic system

It is implicated in:

Autonomic

functions (e.g. respiratory, cardiovascular….etc.)

Endocrine

functions (e.g. Thyroid functions)

Reproductive

functions ( e.g. mating behavior)

Prof. Dr. F. AL-Khafaji

Habenular Nucleus

Center for integration of olfactory, visceral & somatic afferent

pathways (correlation of olfactory & somatic afferent impulses)

Ablation of this nucl. Produce changes in metabolism, endocrine

regulation & thermoregulation

Aff. Fibs.:

1. Amygdaloid complex (via. Stria terminalis)
2. Hippocampal formation (via. Fornix)
3. Olfactory tubercle
4. Pre-optic & septal areas (via. Stia medullaris thalami)
5. Ant. Perforated substance
6. Various hypothalamic Nuclei
7. Globus Pallidus

Eff. Fibs.:

1. Interpeduncular nucl. (via. FR)
2. Medial nucl. Of thalamus
3. Tectum & reticular formation of mid-brain

Prof. Dr. F. AL-Khafaji

PN.:The Stria Medullaris Thalami, Habenula, & Fasciculus
Retroflexes form segments of Visceral Eff. Pathways which
carry impulses to parts of brainstem & spinal cord
(eg. Tectotegmentospinal Tracts & Dosal Longitudenal
Fasciculus which connect with autonomic preganglionic
centers

Prof. Dr. F. AL-Khafaji

Nucleus Subthalamicus

Aff. Fibs.:

1.Globus Pallidus
2.Motor cortex (precentral)
3.Pedunclopontine Nucl.

Eff. Fibs.:

1.Globus Pallidus
2.Contrlateral Globus pallidus
3.Substantia Nigra
4.Opposite Subthalamic nucl.

Zona Incerta

Aff. Fibs.:

1.Motor cortex (precentral )

Eff. Fibs.:

1.Mid-brain reticular formation

Nucleus Subthalamicus

*Lies medial to internal capsule
*Continuous with substantia nigra
Function
Important site for integration of a
number of motor control centers
Especially through its connections with
the corpus striatum & midbrain
Tegmentum
Lesions of one subthalamic  nucl.
Results in condition called Hemiballismus
(Subthalamic  Dyskinesia)

Zona Incerta

*Thin strip of gray matter
*Lies between thalamic & lenticular fasciculei
*Continuous with thalamic reticular nucl.
Functionally associated with the Zona Incerta are
the Nucl. of prerubral field & Entopeduncular nucl.

Prof. Dr. F. AL-Khafaji

Basal Ganglia (Nuclei)

(Concerned with somatic motor function)

Amygdaloid nuclear
complex

(Archistriatum) (oldest)
(Component of Limbic system)
Ie. visceral, endocrine, behavioral

Neostriatum

(Striatum)

Paleostiatum

Prof. Dr. F. AL-Khafaji

Caudate Nucleus
*

C-shped structure, related to lateral ventricle.

The

head

lies rostral to thalamus & protrude into ant. Horn of lat. Vent.

The

body

is slender & elongated & arches along dorsolateral border of

thalamus (lat. To stria terminalis)

The

tail

lies caudal to thalamus in roof of inferior horn of lat. Vent.

(in relation to amygdaloid nuclear complex)

Putamen
*

Largest & most lateral part of corpus striatum

Medial to external capsule

Traversed by striopallidal fibers

Rostrally & ventrally is continuous with head of caudate nucl.

But in more dorsal regions, is connected to caudate nucl. by strial

bridges (passing between fibers of internal capsule)

Prof. Dr. F. AL-Khafaji

Globus Pallidus
*

Phylogentically older than striatum

Smaller inner part of lentiform nucl.

Lies med. To putamen

Dorsomedial margin borders the post. Limb of internal

capsule

Has a thin

lat. Medullary Lamina

(between it & putamen)

Has

Med. Medullary Lamina

which divide globus pallidus

into med. & lat. Segments

Has less distinct

Accessory Medullary Lamina

which divide

med. segment into inner & outer portions

Prof. Dr. F. AL-Khafaji

Caudate Nucleus

Afferents:

1- Cerebral Cortex

Efferents:

1- Globus Pallidus (mainly)

Putamen

Afferents:

1- Cerebral Cortex
2- Caudate Nucl.

Efferents:

1- Globus Pallidus

Globus Pallidus

Afferents:

1- Caudate Nucl.
2- Putamen
3- Subustantia Nigra
4- Subthalamic Nucl.

Efferents:

1- Thalamus (VL,VA,Centomedian)
2- Subthalamus
3- Substantia Nigra
4- Hypothalamus
5- Reticular formation
6- Habenular nuclei

Lentiform Nucleus

Prof. Dr. F. AL-Khafaji

Diseases of corpus striatum

Various types of abnormal involuntary
movements (

Dyskinesia ةَك

َ رَحلا ُلَل َخ

) eg.

Tremor, athetosis, chorea, ballism

Disturbances of muscle tone

(usually increased muscle tone)
eg. Rigidity of Parkinson disease

PN:

Cerebral cortex must play an important role in dyskinesia

Evidence:
1- All forms of abnormal involuntary movements cease during sleep
2- Abolished by general anesthesia
3- Exaggerated by excitement & anxiety
4- Ablation of motor cortex & interruption of corticospinal tract at
     various levels abolishes dyskinesia (may suggests that impulses from
     centers responsible for dyskinesia must be transmitted to segmental
     levels via the corticospinal tract

Prof. Dr. F. AL-Khafaji