Thalamus

KURSK STATE MEDICAL UNIVERSITYDEPARTMENT OF NORMAL PHYSIOLOGYProfessor AV Zavyalov

THE THALAMUS

Thalamus localizationThalamus (Greek) means inner chamber or meeting placeThe thalamusis a structure in the middle of the brain. It is located between the cerebral cortex and the midbrain.Part of the forebrain, below the corpuscallosum.

Division of Brain Thalamus localization

Thalamus

Localization of Thalamus at DiencephalonDorsal-posterior structuresEpithalamusThalamus (Largest component of the diencephalon)MetathalamusMedial geniculate body auditory relayLateral geniculate body visual relay

Ventral-anterior structureHypothalamus

Thalamus localizationThe thalamus is sitting at the top of the brain stem

Composed of two parts, often referred to as lobes, that are symetrical

Thalamus localization

The thalamus surrounds the third ventricle. It is a subdivision of part of the brain called the diencephalon

One of the largest structures derived from the diencephalon during embryonic development.

Thalamus localizationThe thalamus lies at the top of the brain stem near the centre of the brain from where nerve fibres project out towards the cerebral cortex.

The thalamus is divided into two prominent bulb shaped masses of around 5.7 cm in length and positioned symmetrically on each side of the third ventricle.

Thalamus localization

Thalamus localization

Thalamus

Thalamus blood supplyThe thalamus is supplied with blood by four branches of the posterior cerebral artery, namely the polar artery, paramedian thalamic-subthalamic arteries, thalamogeniculate arteries and the posterior choroidal arteries.

Thalamus Physiology

Primarily a relay station that modulates and coordinates the function of various systems

Locus for integration, modulation, and intercommunication between various systems

Has important motor, sensory, arousal, memory, behavioral, limbic, and cognitive functions

Thalamus Physiology

The largest source of afferent fibers to thalamus is cerebral cortex and cortex is the primary destination for projection fibres from the Thalamus

Characteristically, thalamic connections are reciprocal, that is, the target of the axonal projection of any given thalamic nucleus sends back fibers to that nucleus. Nevertheless, thalamocortical projections are often larger than their corticothalamic counterparts

Summary functions of thalamusRelay of sensation (Except olfactory system)Spatial senseRegulation of consciousnessRegulation of sleepand alertness

Main largest product of embryonic diencephalonGreat sensory gateway to cerebral cortexDamage to thalamus can lead to permanent coma

Summary functions of thalamusSensory integration relay station for all sensory pathway (Except olfaction)

Capable of recognition of pain, thermal & tactile sensations

Influences voluntary movements through basal ganglia & cerebellum cerebral cortex cortico-nuclear / cortico-spinal pathways

Through ascending activating system maintains state of wakefulness and alertness

Impulses received from hypothalamus projected o prefrontal & cingulate gyrus Determination of mood

Recent memory and emotions

Influences electrical activity of cerebral cortex (EEG)

Thalamus

Nuclei of ThalamusIt is subdivided into the following major nuclear groups on the basis of their rostrocaudal and mediolateral location within the thalamus:

AnteriorMedialLateralIntralaminar and reticularMidlinePosterior

Nuclei of Thalamus Anterior groupInternal medullary lamina divides the thalamus into medial and lateral groups of nuclei

Anterior nuclear group consists of two nuclei: principal anterior and anterodorsal.

Nuclei of Thalamus Anterior group

The anterior group of thalamic nuclei has reciprocal connections with the hypothalamus (mamillary bodies) and the cerebral cortex (cingulate gyrus).

The anterior group also receives significant input from the hippocampal formation of the cerebral cortex

Nuclei of ThalamusMedial nuclear groupThe dorsomedial nucleus is reciprocally connected with the prefrontal cortex via the anterior thalamic peduncle, and with the frontal eye fieldsReceives inputs from the temporal neocortex (via the inferior thalamic peduncle)amygdaloid nucleus and substantia nigra pars reticulataadjacent thalamic nuclei (lateral and intralaminar groups)

Concerned with affective behavior, decision making and judgment, memory, and the integration of somatic and visceral activity.

Nuclei of ThalamusDorsomedial NucleusBilateral lesions of the dorsomedial nucleus result in a syndrome of lost physical self-activation, manifested by apathy, indifference, and poor motivation. The reciprocal connections between the prefrontal cortex and the dorsomedial nucleus can be interrupted surgically to relieve severe anxiety states and other psychiatric disorders. This operation, known as prefrontal lobotomy is rarely practiced nowadays, having been replaced largely by medical treatment

Nuclei of ThalamusLateral nuclear group is subdivided into two groups: dorsal and ventral

The pulvinar is a relay station between subcortical visual centers and their respective association cortices in the temporal, parietal, and occipital lobes. Has a role in selective visual attention. Plays a role in speech mechanisms. Stimulation of pulvinar of dominant hemisphere has produced nominal aphasia Has role in pain mechanisms.

Nuclei of ThalamusVentral Subgroup

Share the following characteristics:

They receive a direct input from the long ascending tracts.They have reciprocal relationships with specific cortical areas.They degenerate on ablation of the specific cortical area to which they project

Nuclei of ThalamusVentrolateral group

Ventral anterior and ventral lateral nuclei together comprise MOTOR THALAMUS.

AFFERENT FIBERS TO THE VENTRAL LATERAL NUCLEUS: Deep cerebellar nuclei Globus pallidus (internal segment) Primary motor cortex (area 4)

Nuclei of ThalamusVentrolateral group

Ventral anterior and ventral lateral nuclei together comprise MOTOR THALAMUS

EFFERENT FIBERS mainly go to primary motor cortex nonprimary somatosensory areas in the parietal cortex (areas 5 and 7) premotor and supplementary motor cortices

Nuclei of ThalamusVentroposterior group

Receives the long ascending tracts conveying sensory modalities (including taste) from the contralateral half of the body and face.The ventral posterior nucleus is made up of two parts:ventral posterior medial (VPM) nucleusreceives the trigeminal lemniscus and taste fibersventral posterior lateral (VPL) nucleusreceives the medial lemniscus and spinothalamic tracts. Both nuclei also receive input from the primary somatosensory cortex

The output from both is to primary somatosensory cortex (area 1, 2, and 3). The VPL and VPM nuclei collectively comprise - ventrobasal complex

Nuclei of ThalamusIntralaminar group

The Intralaminar nuclei- divided into caudal and rostral groups. The Caudal group includes the centromedian and parafascicular nucleiThe Rostral group includes the paracentral, centrolateral, and centromedial nuclei

Nuclei of ThalamusIntralaminar group

Afferent connections Reticular formation of the brain stem (major input) Cerebellum : The dentatorubrothalamic system Spinothalamic and trigeminal lemniscusGlobus pallidus Cerebral cortex

Efferent ConnectionsOther thalamic nuclei (influences cortical activity via other thalamic nuclei)The striatum (caudate and putamen)

Nuclei of ThalamusReticular group

Is a continuation of the reticular formation of the brainstem into the diencephalon.Afferents from the cerebral cortex and other thalamic nuclei.The former are collaterals of corticothalamic projections, and the latter are collaterals of thalamocortical projections.Efferent projections to other thalamic nuclei. The inhibitory neurotransmitter in this projection is GABA. It plays a role in integrating and gating activities of thalamic nuclei

Nuclei of ThalamusMetathalamus

Medial Geniculate NucleusThis is a relay nucleus in the auditory system. It receives fibers from the lateral lemniscus directly or, more frequently, after a synapse in the inferior colliculus. efferent outflow from the MG nucleus forms the auditory radiation of the internal capsule (sublenticular part) to the primary auditory cortex in temporal lobe (areas 41 and 42)

Nuclei of ThalamusMetathalamus

Lateral Geniculate NucleusThis is a relay thalamic nucleus in the visual system. It receives fibers from the optic tract conveying impulses from both retinaeThe efferent outflow from the lateral geniculate nucleus forms the optic radiation of the internal capsule (retrolenticular part) to the primary visual cortex in the occipital lobe

Nuclei of ThalamusThe motor group receives motor inputs from the basal ganglia (ventral anterior, ventral lateral) or the cerebellum (ventral lateral) and projects to the premotor and primary motor cortices.The sensory group receives inputs from ascending somatosensory (ventral posterior lateral and medial), auditory (medial geniculate), and visual (lateral geniculate) systems.The limbic group is related to limbic structures (mamillary bodies, hippocampus, cingulate gyrus).

Nuclei of Thalamus

Functional Specific Group:

Nuclei of Thalamus

Functional Non-Specific Group:

Nuclei of Thalamus

Reticular Group:

Damage of ThalamusDamage to the thalamus may result in a number of problems related tosensory perception. Thalamic syndrome is condition that causes an individual to experience excessive pain or a loss of sensation in limbs. Damage to areas of the thalamus that are associated with visual sensory processing can cause visual field problems. Damage to the thalamus can also result in sleep disorders, memory problems, and auditory issues.

Refernciashttp://brainmadesimple.com/thalamus.htmlhttp://www.news-medical.net/health/What-is-the-Thalamus.aspxhttp://study.com/academy/lesson/thalamus-definition-functions-location.htmlhttp://www.neuroanatomy.wisc.edu/coursebook/thalamus.pdfhttp://biology.about.com/od/anatomy/p/thalamus.htmhttp://biology.about.com/od/anatomy/p/thalamus.htm