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anatomyphysiologyblog - Thalamus: location, relations, parts, nuclei in addition to original connections

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The Diencephalon: General Overview

Diencephalon is component of the prosencephalon (forebrain).
It corresponds largely to the structures that develop lateral to the 3rd ventricles.

The lateral walls of the diencephalon form the epithalamus most superiorly,
the thalamus (dorsal thalamus) centrally too
the subthalamus (Ventral Thalamus) and 
the hypothalamus  most inferiorly.

The epithalamus:
anterior too posterior paraventricular nuclei,
the medial too lateral habenular nuclei,
the stria medullaris thalami too
the pineal gland


The thalamus undergoes proliferation to shape numerous nuclear masses, which bring extensive reciprocal connections amongst the cerebral cortex.

The subthalamic region consists of
the subthalamic nucleus,
zona incerta too
the fields of Forel

The subthalamic nucleus is closely related to the basal nuclei.
The hypothalamic rudiment gives ascension to most of the subdivisions of the adult hypothalamus.



The Thalamus

(This banknote describes the location, relation, parts, nuclei too of import connections of thalamus.)

·   
    Thalamus is an ovoid nuclear majority nigh iv cm long  too is institute inwards relation to lateral wall of 3rd ventricle.

 
     External Features too Relations: 
      It presents:
 
    Two ends or Poles  
      Anterior too posterior

    Four surfaces 
      Medial, lateral, superior too inferior

  
    Anterior destination or Pole:
 
 It forms posterior boundary of interventricular foramen.
    
    Posterior destination or pole:  
      
    It is called Pulvinar.  

      
    

     
   Pulvinar extends beyond the 3rd ventricle too overhangs the superior colliculus (Superior colliculus is a little elevation institute on each side on the posterior facial expression of midbrain). Thus, pulvinar lies merely higher upwards too lateral to superior colliculus.
   
  Superior brachium (a ridge extending from superior colliculus) separates the pulvinar higher upwards from the medial too lateral geniculate bodies below. 

    Superior surface:
     This surface is covered past times a layer of white thing called stratum zonale.
     
    The medial component of this surface is separated from the overlying trunk of the fornix past times the choroid cleft amongst the tela choroidea inside it. 

    More laterally it forms component of the flooring of the lateral
   ventricle. 

   The lateral border of the superior surface of the thalamus is
  marked past times the stria terminalis too overlying thalamostriate vein,
  which separate the thalamus from the trunk of the caudate nucleus.

Laterally, a slender canvass of white matter, the external medullary lamina, separates the chief trunk of the thalamus from the reticular nucleus.


  Lateral to this, the thick posterior limb of the internal capsule lies betwixt the thalamus too the lentiform complex.

   
     Medial Surface:This surface forms the upper component of lateral wall
  of 3rd ventricle too is lined past times ependyma.
      
  This surface is commonly connected to the reverse thalamus past times an interthalamic adhesion/connection. 

   Inferiorly it is related to the hypothalamus separated past times an
  indstinct hypothalamic sulcus – this sulucus extends from the
  upper destination of cerebral aqueduct posteriorly to the
  interventricular foramen anteriorly.
   
  At the junction of medial too superior surfaces, the ependyma of 3rd ventricle is reflected (from the lateral wall) to the roof. The business of reflection is marked past times a business called taenia thalami, underlying which, in that place is a narrow packet of fibers called stria medullaris thalami. (Note: Stria medullares inwards the flooring of fourth ventricle are dissimilar from stria medullaris thalami)


Image from Gray's Anatomy.

     Inferior Surface:
This surfacfe is related to the hypothalamus anteriorly too subthalamus posteriorly. The subthalamus separates thalamus from the midbrain tegmentum.

Lateral Surface:
This surface is covered past times a layer of myelinated fibers called external medullary lamina.
The lamina separates lateral surface amongst the reticular nuclei.

 
Subdivisions of Thalamus
Internally, the thalamus is divided past times a vertical Y-shaped canvass of white matter, the internal medullary lamina into
  •      Anterior nuclear groups,
  •      Medial nuclear groups too
  •      Lateral nuclear groups

 
     In addition,
  •   Intralaminar nuclei prevarication embedded within, too surrounded by, the internal medullary lamina.
  •   Midline nuclei either abut the ependyma of the lateral walls of the 3rd ventricle medially, or lie adjacent to, too to closed to extent within, the interthalamic adhesion. 
  •  Reticular nuclei prevarication lateral to the chief nuclear mass, separated from it past times the external medullary lamina. (Note: reticular nuclei are straight off considered equally the component of the subthalamus or ventral thalamus)
  •   Medial too lateral geniculated bodies, previously considered equally Metathalamus, are straight off included equally component of the Thalamus.

Table: Functional segmentation of major thalamic nuclei
      Type
            Nucleus
         Sensory
Ventral posterolateral
Ventral posteromedial
Lateral geniculate
Medial geniculate
         Motor
Ventral anterior
Ventral lateral
         Limbic
Anterior
Dorsomedial
         Multimodal
Lateral dorsal (dorsolateral)
Lateral posterior (posterolateral)
Pulvinar
  
       
      ANTERIOR GROUP OF THALAMIC NUCLEI too THEIR CONNECTIONS
 
      These nuclei lies betwixt the limbs of Y.
      Three subdivisions are recognized.
  •      Anteroventral nucleus,
  •      Anteromedial too
  •      Anterodorsal nuclei
    They are collectively called equally Anterior Nucleus

Important Connections:
Afferents:
- receives fibers from the mamillary trunk through mamillothalamic tract.

Effecrents:
- shipping fibers mainly from medial surface of the hemisphere, - the areas are mainly anterior component of limbic organization (anterior too inwards front end of corpus callosum), cingualte gyrus, parahippocampal gyrus
- the connections are reciprocal

Functions:
- the regulation of alertness too attention, emotional tone too the acquisition of recent memory
       

     MEDIAL GROUP OF THALAMIC NUCLEI too THEIR CONNECTIONS

•The unmarried too largest element of this grouping of nuclei is Medial dorsal (mediodorsal or dorsomedial)       nucleus.
•lies betwixt intralaminar nuclei laterally too midline nuclei medially

subdivided into:  
•anteromedial magnocellular component too
•posterolateral parvocellular part

Main connection:
•Reciprocal connections to prefrontal cortex, likewise to anterior cingulated too medial frontal gyri
•Receives olfactory inputs from pyriform too following cortex, ventral pallidum  (part of globus pallidus) too amygdale
•Interconnected amongst all other thalamic nuclei

Functions:
•involved inwards olfactory information, inwards controlling one’s emotional too subjective state
•Damage may Pb to a decrease inwards anxiety, tension, aggression or obsessive thinking (reflecting the defects similar to harm to prefrontal cortex)
      

   LATERAL GROUP OF THALAMIC NUCLEI (The lateral nuclear complex)
 
•The largest major segmentation of thalamus
•are lateral to the internal medullary lamina,
•divided into dorsal too ventral tiers of nuclei.

The Dorsal tier of Nuclei (from earlier backwards)
•    Lateral dorsal (or dorsolateral)
•    Lateral posterior
•    Pulvinar

Important Connections
 
•Lateral dorsal too lateral posterior nuclei mainly have afferents from superior colliculus.
•Efferents from these 2 nuclei accomplish parietal lobe too component of prahippocampus too cingulated gyri
•Lateral posterior nucleus has reciprocal connexion amongst superior parietal lobule
•The Pulvinar likewise receives afferents from superior colliculus.
•The inferior component of pulvinar likewise receives conduct fibers from the retina.
•The efferents are projected to association areas inwards parieto-temporal cortex too visual too visual association areas inwards the occipital too posterior component of temporal cortex
•Also connects amongst component of cingulated gyrus, hippocampal gyrus too prefrontal cortex.

Functions:
  The complexity of functions of the association areas to which it projects beside visual areas, especially inwards the temporal lobe (e.g. perception, knowledge too memory), propose the role of the pulvinar inwards modulating these functions.

The Ventral Tier of Nuclei (from earlier backwards)
  •       Ventral anterior
  •       Ventral lateral too
  •       Ventral posterior
    •       Ventral posterior medial or ventral posteromedial
    •       Ventral posterior lateral or ventral posterolateral

Ventral anterior Nucleus
 Also called ventral anterior (VA) complex
  consists of a principal component (VApc) too a magnocellular component (VAmc)

Main Connections:
Afferents
•Internal component of globus pallidus – to VApc
•pars reticulate of substantia niagra – to VAmc
•premotor cortex (area 6) – to VApc
•frontal oculus champaign (area 8) – to VAmc

Efferents
•Motor areas of Frontal cortex
•Anterior component of parietal lobe
•Intralaminar thalamic nuclei

Function:
•Unclear, may influence motor cortex

Ventral lateral (VL) nucleus
•Consists of anterior segmentation or pars oralis (VLo) too posterior segmentation or pars caudalis (VLc)

Connections:
 
Afferents 
  •From internal component of globus pallidus (ipsilateral) – to VLo
  •From deep cerebellar nuclei (contralateral) – to VLc
  •From precentral motor areas (area iv too 6)
  •Spinothalamic tract too vestibular nuclei

Efferents
  •To supplementary motor cortex too premotor cortex (from VLo) too to primary motor surface area (from VLc)

Function:

    •Probably influences the motor activity
  •Stereotactic surgical physical care for of ventral lateral nucleus is sometimes     used inwards the handling of essential tremor.

Ventral posterior (VP) nucleus
  •  is the principal thalamic relay for the somatosensory  pathways
  •   consists of 2 major divisions
    •   ventral posterior lateral or ventral posterolateral (VPl)
    •   ventral posterior medial or ventral posteromedial (VPm)

Connections:
 
Afferents
 
•from medial leminscal too spinothalamic pathways  to VPl
•from trigeminothalamic too solitariothalamic (gustatory) pathways to VPm

Topographic representation – sacral laterally too cervical medially on VPl too confront on VPm following to cervical surface area of representation on VPl
Taste fibres most anteriorly too ventromedially inside the VPl

Efferents
 
•Passes through posterior limb of internal capsule equally Superior thalamic radiations
•To the primary somatosensory surface area (area 3,2,1)
•Also to secondary somatosensory surface area located at the lower destination of postcentral gyrus inwards the parietal     operculum (or superior lip o posterior ramus of lateral sulcus)


 

     
     Medial  too Lateral Geniculate bodies
•Small rounded elevations situated below the posterior component of the thalamus

Medial Geniculate body
•relay station for auditory pathway
•consists of medial, ventral too dorsal nuclei

Connections
Afferents
•receives fibres from the lateral laminiscus (part of the auditory pathway) conduct or after relay inwards the inferior colliculus via the inferior brachium
•also receives fibers from the auditory surface area of cerebral cortex

 
Efferents
•To primary auditory cortex (from ventral nucleus) via the acoustic radiations which passes through the sublentiform component of internal capsule 

Tonotopic representation of dissimilar frequencies of audio inwards the ventral nucleus of medial geniculate trunk – depression to high frequencies from lateral to medial component of the nucleus.

•To auditory areas (from other nucleus) surrounding the primary auditory area

Lateral geniculate trunk or nucleus
•Relay station for visual pathway

Connections;
Afferents
•From both retinae
•Also receives fibers from the primary visual cortex, secondary visual cortex, superior colliculus too reticular formation of pons too medulla

Efferents
•Optic radiations that passes through the retrolentiform component of internal capsule to primary visual areas
•May projection to surrounding cortex also

Intralaminar nuclei
•These are the neurons inside the inermedullary lamina
•Consists of anterior too posterior subgroups – centromedian nucleus is component of posterior subgroups

Connections:
Afferents
•From the trunk through spinothalamic tracts
•Also receives fibers from the reticular formation, cerebellar nuclei too the substantia niagra
•Centromedian nucleus receives fibers from globus pallidus

Efferents
•Those from the anterior grouping are diffuse too accomplish the many parts of the cerebral cortex
•Those from the posterior grouping projection to the motor, premotor too supplement motor areas equally good equally striatum

Functions
•Precise functional role is unclear
•May mediate cortical activation from the encephalon stalk reticular formation (thus may influence the levels of consciousness too alertness inwards an individual), too play a component inwards sensorimotor integration

 
Midline nuclei
•Consists of several little grouping of neurons

Connections:
Afferents
•from the hypothalamus, the periaqueductal grayness thing of the midbrain, the spinothalamic tract too the medullary too pontine reticular formation
•from ascending noradrenergic too serotoninergic axons from the locus coeruleus too raphe nuclei respectively (from brainstem)
•also have a cholinergic input from the midbrain.

Efferents
•To the hippocampal formation, the amygdala too the nucleus accumbens.
•Also to cingulate, too perhaps orbitofrontal cortex

Functions
•Closely related to limbic organization too may play a role inwards retentiveness too arousal

Reticular nuclei (part of the ventral thalamus or subthalamus)
•Made upwards of a sparse layer of neurons
•Covers the lateral facial expression of thalamus separated past times extramedullay lamina
•Laterally it is related to internal capsule


Connections
Afferents
•Collaterals from thalamocoritcal, corticothalamic, thalamostriatal too pallidothalamic fibers
•Also receives cholinergic fibers from reticular formation of midbrain
•Thus reticular nucleus receives somatic, visual too auditory impulses

Efferents
•To the trunk of the thalamus (mostly reciprocal)


REFERENCES: 
     Gray’s Anatomy, 39th Edition 
     Snell’s Clinical Neuroanatomy seventh Edition 
     Lange Clinical Neuroanatomy 25th Edition