NEUROANATOMY

Lecture : 5

Anatomy of the Diencephalon, Limbic System Pituitary Gland &

Prepared and presented by:Dr. Iyad Mousa Hussein ,

MD, Ph.D in NeurologyHead of Neurology DepartmentNasser Hospital

1. Definition, Site, Surfaces, and Subdivisions of the Diencephalon.

2. Definition, site, Parts, nuclei, and functions of the Thalamus.

3. Definition, Site, Parts, and Nuclei and functions of the Hypothalamus.

4. Definition, Site, Structures, and functions of the Epithalamus.

5. Definition, Site, and Structures of the Metathalamus.

6. Definition, Site, and Structures of the Subthalamus.

7. Anatomy and Functions of the Pituitary Gland.

8.Definition, Site structures, Connections and functions of the

Limbic System.

9. Pathway of upper and lower motor neuron.

10. Pathway of th superfacial and deep sensation.

LECTURE OBJECTIVES:

Definition and Site:

It is the part of the brain located above the midbrain and

between the lower parts of the two cerebral hemispheres.

Embryological Origin: from forebrain → prosencephalon.

Cavity of the diencephalon: is the third ventricle.

The Diencephalon

1. Two lateral surfaces: each lateral surface related to the

internal capsule.

2. The Lower surface:

a. The middle (largest) part: is the subthalamus, which

located upper the midbrain.

b. The anterior part: is formed by the hypothalamus

and is connected with pituitary gland.

C. The posterior part: is formed by the metathalamus.

3. Upper surface: it is formed by the two thalami and the third

ventricle in the middle.

Surfaces of the Diencephalon

It is subdivided into five parts:

1. Thalamus (bilateral): the largest part.

2. Subthalamus: it lies directly above midbrain.

3. Hypothalamus: it lies infront of the subthalamus.

4. Metathalamus (bilateral).

5. Epithalamus.

Subdivisions of the Diencephalon

The Thalamus

Definition: it is a large, egg-shaped mass of gray

matter lying in the middle of the cerebrum.

Site: it is located on each side of the third ventricle,

immediately above the subthalamus and medial to the

internal capsule.

Parts of the Thalamus:

1. Anterior part.

2. Medial part.

3. Lateral part.

1. Sensory Function: the thalamus is the great sensory

relay station on the pathway of all sensations to cerebral

cortex (except smell).

2. Consciousness level.

3. Emotional function.

Functions of the Thalamus

1. Medial group.

2. Lateral group.

3. Anterior group.

Nuclei of the Thalamus

1. Anterior nucleus.

2. Dorsomedial nucleus.

3. Lateral posterior nucleus.

4. Lateral dorsal nucleus.

5. Lateral pulvinar nucleus.

6. Ventral anterior nucleus.

7. Ventral posterior nucleus (Ventral Posterolateral &

Posteromedial nuclei).

8. Ventral lateral nucleus.

9. Inttralaminar nucleus.

10.Midline reticular nucleus.

Nuclei of the Thalamus

Definition and Site:

It is the part of the diencephalon located infront of

subthalamus and anterioinferior to the thalamus.

The hypothalamus, although small (0,3 % of the total

brain), is very important part of the central nervous

System called Neuroendocrine organ.

The Hypothalamus

1. Optic part: immediately related to optic chiasma. It

consists of two nuclei:

a. Supraoptic nucleus.

b. Paraventricular nucleus.

2. Tuberal part: it consists of three nuclei:

a. Ventromedial nucleus.

b. Dorsomedial nucleus.

c. Tuberal nucleus.

3. Mamillary part: it consists of two nuclei:

a. Posterior nucleus.

b. Lateral nucleus.

4. Posterior perforated substance.

Parts and Nuclei of the Hypothalamus

A. Afferent fibers:1. Somato and Visceral afferents.2. Visual afferents.3. Olfaction.4. Auditory afferents.5. Thalamohypothalamic fibers.6. Amygdaloidhypothalamic fibers.7. Tegmental fibers: from midbrain.

B. Efferent fibers:1. Descending fibers to the brain stem and spinal cord.2. To the limbic system.3. To the pituitary gland.

Connections of the Hypothalamus

Hypothalamus has important regulatory functions:

1. Temperature.

2. Emotional regulation.

3. Growth (via thyroid stimulating hormone).

4. Hunger and thirst.

5. Sexual behaviour.

6. Control of various endocrine and activity

rhythms (via hormones).

7. Memory (visual and verbal memory).

Functions of the Hypothalamus

1. The hormones vasopressin (antidiuretic hormone) and

oxytocin are synthesized in the hypothalamus → the

posterior lobe of the pituitary gland.

2. The hypothalamus is play important role in the

production of the releasing hormones and release-

inhibitory hormones.

Connections of the Hypothalamus with the Hypophysis (Pituitary Gland)

The Hypothalamic Releasing and Inhibitory Hormones

Hypothalamic Regulatory Hormones Anterior Pituitary

Hormones

Growth hormone-releasing hormone (GHRH)

Growth hormone (GH)

Growth hormone-inhibiting hormone (GHIH) or Somatostatin

Growth hormone (reduced production)

Prolactin-releasing hormone (PRH) Prolactin hormone

Prolactin-inhibiting hormone (PIH) Prolactin hormone (reduced production)

Corticotropin-relasing hormone (CRH) Adrenocorticotropic hormone (ACTH)

Thyrotropin-relasing hormone (TRH) Thyroid-stimulating hormone (TSH)

Lutenizing hormone-relasing hormone (LHRH)

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH)

Definition and Site: it is a part of the diencephalon

which is attached to posterior end of the upper

surface of the diencephalon.

Parts of the Epithalamus:

1. Right and left Habenular nucleus.

2. Habenular commissure.

3. Posterior commissure.

4. Pineal body.

The Epithalamus

Definition and Site:

It is the part of the diencephalon which is attached to

posterior part of the inferior surface of the thalamus.

Parts of the Metathalamus:

1. Lateral geniculate body (LGB): visual function.

2. Medial geniculate body (MGB): auditory

function.

The Metathalamus

Definition and Site: it is the part of the diencephalon which located

between the thalamus and midbrain.

Parts of the Subthalamus:

A. Posterior smaller part: containing of five bundles:

1. Medial lemniscus.

2. Spinal lemniscus.

3. Trigeminal lemniscus.

4. Reticuo-thalamic tract.

5. Superior cerebellar peduncle.

B. Anterior larger part: containing of five bundles.

1. The upper end of the red nucleus.

2. The upper end of the substantia nigra.

3. The subthalamic nucleus.

4. The ansa lenticularis bundle.

5. The fasciculus lenticularis.

The Subthalamus

Site: it lies below the hypophyseal fossa below the diaphragm sella.Shape: it is an avoid body, its transverse diameter is 12mm and its anteroposterior diameter is 8mm.Relation:

1. Above: diaphragm sella which separates the gland from optic chiasma.

2. Below: body of sphenoid and sphenoid sinus separating the gland from nasopharynx.

3. On each side: cavernous sinus and its contains.Connection: with hypothalamus.Components:

1. Anterior lobe (Adenohypophysis).2. Posterior lobe (Neurohypophysis).

Pituitary Gland (Hypophysis or Master Gland)

Production of the following hormones:

A. Anterior pituitary hormones (from anterior lobe):

1. Growth hormone (GH).

2. Prolactin hormone.

3. Adrenocorticotropic hormone (ACTH).

4. Thyroid-stimulating hormone (TSH).

5. Luteinizing hormone (LH).

6. Follicle-stimulating hormone.

B. Posterior pituitary hormones (from posterior lobe):

1. Vasopressin (Antidiuretic hormone).

2. Oxytocin.

Functions of the Pituitary Gland

Definition and Site: It is the number of cortical and

subcortical structures lying between the cerebral

cortex and the hypothalamus.

The Limbic System (Emotional Brain)

Structures of the Limbic System

1. Cingulate gyrus.

2. Parahippocampal gyrus.

3. Uncus.

4. Hipocampal formation.

5. Mammilary bodies.

6. Septum pollucidum.

7. Amygdaloid nucleus.

8. The fornix.

1. Cerebral cortex.

2. Thalamus.

3. Hypothalamus.

4. Epithalamus.

Connections of the Limbic System

1. Control the endocrine system.

2. Control the emotional behavior.

3. Recent memory (hippocampus).

4. There is no evidence that the limbic system has

an olfactory function.

Functions of the Limbic System

From Betz cells in motor area 4 (precentral gyrus of

frontal lobe) → descends in the corona radiata → pass

in the internal capsule → descends in mid brain, pons

and medulla oblongata, some fibers of the pyramidal

tract (cortico-nuclear fibers) supply the motor nuclei of

the cranial nerves of both sides except the lower 1/2 of

facial nuclei & the hypoglossal nuclei which are supplied

only from opposite pyramidal tract.

In the lower medulla 80% of fibers decussate to

descend → in the lateral column of the opposite side of

the spinal cord, while the another fibers (20%) descend

directly → in the anterior column of the same side.

All fibers are terminate at different level of anterior

horn cells (AHCs).

Pathway of the Upper Motor Neuron (Pyramidal or Cortico-Spinal tract)

From AHCs of the spinal cord →

fibers exit from the spinal cord as

the anterior roots of the same side

→ peripheral nerves → motor end

plate → voluntary muscles .

Pathway of the Lower Motor Neuron System(Spino-muscular fibers)

All somatic sensation (superficial and deep) pass through three order neurons

from receptors in the skin & deep structure to reach cortical sensory area.

1. The first order neuron (muscular-spinal neuron): started from receptors in

the skin → peripheral (spinal) nerves → posterior roots & ganglion cells.

2. The second neuron (spino-thalamic neuron):

started from posterior ganglion cells → posterior horns → decussating

(crossing) to the opposite side of the spinal cord:

a. For pain and temperature sensations: ascends in the lateral column of the

spinal cord (lateral spino-thalamic tract).

b. For crude touch sensation: ascends in the ventral column of the spinal cord

(ventral spino-thalamic tract).

Both lateral & ventral spino-thalamic tracts ascends through spinal cord →

medulla oblongata → pons → mid brain → ends in the thalamus.

3. The third order neuron (Thalamo-cortical neuron): from the thalamus,

sensation ascends through the internal capsule to reach cortical sensory area (1,

2, 3) in the postcentral gyrus of the parietal lobe.

Pathway of the Superficial Sensations)Pain, Temperature & Crude Touch(

1. The first order neuron (muscular-spinal tract): started from

receptors in the skin → peripheral (spinal) nerves → posterior roots &

ganglion cells.

2. The second neuron (Gracile & Cuneate tract): from the posterior

roots, fibers pass directly into the posterior column of the same side of

the spinal cord reaching the Gracile and Cuneate nuclei in the medulla

→ decussating (crossing) to the opposite side of the medulla

oblongata and ascends through pons → mid brain → ends in the

thalamus.

3. The third order neuron (Thalamo-cortical tract): from the thalamus,

sensation ascends through the internal capsule to reach cortical

sensory area (1, 2, 3) in the postcentral gyrus of the parietal lobe.

Pathway of the Deep & Fine Touch Sensation