Thalamus (dorsal thalamus)

External Features

Two ends (or poles)

Narrow

Anteriorly: interventricular foramen.

Posterior (Pulvinar)

broader

Inferior and medially: superior colliculus

separated from the geniculate bodies by the brachium of the superior colliculus.

Four surfaces

Superior

Lateral portion:

Thalamocaudate groove

Contains

A bundle of efferent nerve fibres from amygdala called the stria terminalis
Thalamostriate vein lie in this groove.

Body of caudate nucleus
Floor of the central part of the lateral ventricle formed by

The lateral part of superior surface of thalamus AND
The body of caudate nucleus

Medial portion

Separated from the ventricle by the fornix and by a fold of pia mater called the tela choroidea.

Inferior

Adjacent

Hypothalamus
Ventral thalamus

The ventral thalamus separates the thalamus from the tegmentum of the midbrain

Medial

Forms the greater part of the lateral wall of the 3rd ventricle

Lined by ependyma

Interconnected by interthalamic adhesion: a mass of grey matter

inferior portion

is separated from the hypothalamus by the hypothalamic sulcus.

This sulcus runs from the interventricular foramen to the cerebral aqueduct

At the junction of the medial and superior surfaces of the thalamus,

Taenia thalami is present

The ependyma of the third ventricle is reflected from the lateral wall to the roof.
Underlying it there is a narrow bundle of fibres called the stria medullaris thalami (stria habenularis).

Lateral

Adjacent to internal capsule, which separates it from the lentiform nucleus

Internal structure

Consist of mainly grey matter and a small amount of white matter:

White Matter

Outer surface

Superiorly: covered by Strarum zonale: a thin layer of white matter

Laterally: external medullary lamina: a thin layer of white matter

Of note: medially it is covered by the ependyma of 3rd ventricle

Internally a ‘Y’ shaped bundle of white matter called internal medullary lamina divides the grey matter of thalamus into three major groups of nuclei:

anterior group

medial group

lateral group

Grey Matter

Main thalamic nuclei

Sensation from the face is received by which thalamic nucleus?

Ventroposteromedial (VPM) nucleus.
Ventroposterolateral (VPL) nucleus receives sensory input from the body

Other Thalamic Nuclei

Intralaminar nuclei

Embedded within the internal medullary lamina.
There are several nuclei in this group.

Centromedian nucleus

Most important

Parafascicular nuclei
Rostral intralaminar nuclei

Midline nuclei

consist of scattered cells that lie between the medial part of the thalamus and the ependyma of the third ventricle.

Medial and lateral geniculate bodies (aka metathalamus)


graph LR
    A[Thalamus] --> B[Anterior]
    A --> C[Medial]
    A --> D[Lateral]

    B --> B1[Anterior nucleus]
    C --> C1[Medial dorsal nucleus]

    D --> D1[Dorsal group]
    D --> D2[Ventral group]

    D1 --> D1a[Lateral dorsal]
    D1 --> D1b[Lateral posterior]
    D1 --> D1c[Pulvinar]

    D2 --> D2a[Ventral anterior nucleus]
    D2 --> D2b[Ventral lateral nucleus]
    D2 --> D2c[Ventral posterior nucleus]

    D2c --> D2c1[Ventral posteromedial nucleus]
    D2c --> D2c2[Ventral posterolateral nucleus]

Connections of Thalamus

General

The thalamus is the gateway to the cerebral cortex: all major sensory pathways, except olfactory, relay in the thalamus before ascending to the cortex.

Afferent

From subcortical centres converge on the thalamus

Type of impulse	From	Through	To
Exteroceptive impulses and proprioceptive impulses	ㅤ	Medial lemniscus, Spinothalamic tracts Trigeminothalamic tract.	Cerebellum, Cortex
Visual impulses	Retina	Optic tract	Lateral geniculate bodies
Auditory impulses	Cochlear	CN8 → lateral lemniscus/inferior colliculus	Medial geniculate bodies
Sensations of taste	Tongue	CN12 → Solitariothalamic fibres	Primary somatosensory cortex.
Olfactory impulses	Nasal mucosa	CN1 → Indirectly through amygdaloid complex (thalamus does not receive direct olfactory impulses)	Anterior olfactory nucleus, Piriformis cortex
Visceral information	ㅤ	Reticular formation from the hypothalamus	ㅤ