Anatomy and Physiology of Thalamus

DM input info destination

prefrontal assoc cortex general arousal, modulation of thalmic input to the cortex prefrontal assoc cortex

Thalamus

the brain's sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla

internal capsule brain

the internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons, going to and coming from the cerebral cortex.

Thalamic projection neurons have Two Physiological States

tonic and busrt mode tonic mode is normal relay and burst mode is innaccuarte one

Medial nuclear group -

Medial nuclear group - mood & emotion

corticalthalmic pathways

from cotrex to thalmus

Anterior -input -info destination

hippocampus mamillary body memory cingulate cortex

VL/VA input: info: destination:

input: basal ganglia, cerebellum info: motor destination: motor cortex

NOTE: pain of face vs. pain of body (trigmeinal pathway vs. DCML) lack of oxygen injury circuit reorganizes abnormally chronic pain Numbness & tingling - blank pathway Temperature - blank pathway Mechanical -blank pathways

...Numbness & tingling - DCML VPL sensory cortex Temperature - spinothalamic VPL sensory cortex Mechanical - DCML, trigeminal VPL & VPM motor cortex

Cerebral cortex receives inputs via:

1. Thalamus sends specific information to restricted cortical areas 2) Diffuse, modulatory inputs that set the general level of excitability of broad cortical areas

has 5 pathways

1. anterior limb 2. genu 3. posterior limb 4. sunlenticula part 5. retrolenticular part

Almost all thalamic nuclei have rich reciprocal connections with the

Almost all thalamic nuclei have rich reciprocal connections with cerebral cortex

Anterior nuclear group -

Anterior nuclear group - part of limbic sys

LGN -Input -Info -Destination

CN II Vision Calcarine sulcus (visual cortex)

dorsomedial nucleus

Controls aggression; animal instincts

GABAergic

Describing neurons or synapses that produce and release gamma-aminobutyric acid.

Thalamic association nuclei Receives information from the association cortex, and distribute it back to association cortex

Dorsomedial nuclei Pulvinar

Clinical Research

ET is the most common motor disease. It affects activities of daily living and is a prominent public health issue.

A fundamental difference between pathways entering the cortex and pathways leaving the cortex

Efferent pathways (e.g., the corticospinal, corticobulbar and corticopontine tracts) can go directly from the cortex to their destinations. They DO NOT go through the Thalamus

Afferent vs. efferent pathways

Efferent pathways carry signals away from the central nervous system. Essentially, they are signals that your brain sends to tell your body to do something, like blinking. Afferent signals come from outside stimuli and tell your brain what they are sensing, such as temperature.

Intralaminar nuclei -

Intralaminar nuclei - cerebral cortex activation

cingulate gyrus

It receives inputs from the thalamus and the neocortex, and projects to the entorhinal cortex via the cingulum. It is an integral part of the limbic system, which is involved with emotion formation and processing,[1] learning,[2] and memory.[3][4] The combination of these three functions makes the cingulate gyrus highly influential in linking motivational outcomes to behavior (e.g. a certain action induced a positive emotional response, which results in learning).[5] This role makes the cingulate cortex highly important in disorders such as depression[6] and schizophrenia.[7] It also plays a role in executive function and respiratory control.

Largely similar circuits: Start - blank Intermediate centers - e.g. blank Thalamus - specific blank Neocortex -

Largely similar circuits: Start - activation of peripheral sensory receptors Intermediate centers - e.g. brainstem Thalamus - specific nucleus Neocortex - specific region & specific layers

Burst mode

Long refractory period of calcium channels Reduction in action potentials May underlie absence epilepsy

Blood Supply anterior IC

MCA AND ACA branches (lenticulostriate branches and recurrent a of heubner

posterior interior capsule

MCA and ICA branches (lenticulostriate branches and anterior choroid artery)

Note: reticular nucleus is blank and DOES NOT project to cortex. All other nuclei are blank and project to the cortex.

Note: reticular nucleus is GABAergic and DOES NOT project to cortex. All other nuclei are glutaminergic and project to the cortex.

Functional Overview

Nuclei that transmit general and special sensory information corresponding to regions of sensory cortices Nuclei that receive impulses from cerebellum and basal ganglia and interface with motor regions of frontal lobe Nuclei that have connections with associate and limbic areas of cerebral cortex

Blood Supply to the Thalamus just one

Posterior Cerebral Artery: small branches supply most of the thalamus Posterior communicating artery Anterior choroidal artery: lateral geniculate body

Reticular nucleus -

Reticular nucleus - receives collaterals from thalmocortical and corticothalamic fibers

Thalamus Reticular Nucleus

Samples the activity in fibers Sends inhibitory (GABA) projections back to adjacent parts of the thalamus. Directs attention sleep-wakefulness cycles thalamic reticular nucleus is part of the ventral thalamus that forms a capsule around the thalamus laterally. However, recent evidence from mice and fish question this statement and define it as dorsal thalamic structure.[1][2] It is separated from the thalamus by the external medullary lamina. Reticular cells are GABAergic, and have discoid dendritic arbors in the plane of the nucleus.

thalamic nuclei

Size of Sensory Thalamic Nuclei. The thalamus is a neural structure found in all vertebrates, located at the dorsal end (top) of the brain stem. It consists of 30 to 40 "nuclei", or interconnected groups of neurons. "Sensory" thalamic nuclei connect sensory input to the cerebral cortex.

MGN -Input -Info -Destination

Superior olive and inferior colliculus of tectum Hearing Auditory cortex of temporal lobe

Ventral/Posterior Thalamic Lesions and Central Post Stroke Pain Syndrome(Dejerine-Roussy syndrome) (vpl injury) what would happen?

Syndrome of neuropathic pain due to thalamic lesions. Occurs in ~10% of stroke patients Initially paresthesias (numbness & tingling) Followed in weeks to months by allodynia (ordinarily painless stimuli cause pain) Pain described as temperature (hot, burning, cold) Pain described as mechanical sensation (dull, aching, squeezing)

Thalamus is divided into 3 principal nuclear masses (blank, blank, blank) by the internal medullary lamina (also contains intralaminar nuclei)

Thalamus is divided into 3 principal nuclear masses (anterior, medial, lateral) by the internal medullary lamina (also contains intralaminar nuclei)

Thalamus is the largest component of blank, lies between brainstem & cerebral hemisphere

Thalamus is the largest component of diencephalon, lies between brainstem & cerebral hemisphere

genu

The genu is the flexure of the internal capsule. It is formed by fibers from the corticonuclear tracts. The fibers in this region are named the geniculate fibers; they originate in the motor part of the cerebral cortex and after passing downward through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the motor nuclei of the cranial nerves of the opposite side. It contains the corticobulbar tract, which carries upper motor neurons from the motor cortex to cranial nerve nuclei that mainly govern motion of striated muscle in the head and face.

Thalamic nuclei: Lateral group

The lateral division is divided into several nuclei.

reticular nucleus

The thalamic reticular nucleus is part of the ventral thalamus that forms a capsule around the thalamus laterally. However, recent evidence from mice and fish question this statement and define it as dorsal thalamic structure.[1][2] It is separated from the thalamus by the external medullary lamina. Reticular cells are GABAergic, and have discoid dendritic arbors in the plane of the nucleus. Input and output. The thalamic reticular nucleus receives input from the cerebral cortex and dorsal thalamic nuclei. Most input comes from collaterals of fibers passing through the thalamic reticular nucleus. ... Its function is modulatory on signals going through thalamus (and the reticular nucleus).

Thin blank nucleus lies on lateral aspect of thalamus

Thin reticular nucleus lies on lateral aspect of thalamus

VPL -Input -Info -Destination

VPL Spinothalamic & dorsal columns/medial lemniscus Pain, temperature; pressure, touch, vibration, proprioception Somatosensory cortex

VPM -Input -Info -Destination

VPM Trigeminal & gustatory pathway Face sensation, taste Somatosensory cortex

pulvinar nucleus

a mass of neurons in the posterior thalamus that have widespread reciprocal connections with areas across the cerebral cortex

Relay nuclei

a nucleus of the brain that serves primarily to relay stimuli from lower receptor centers to coordinating cortical centers -Anterior nuclei (A/LD) -Ventral anterior, ventral lateral nuclei (VA/VL) -ventral posterolateral (VPL) -Ventral posteromedial (VPM) -Medial Geniculate (MGN) -Lateral Geniculate (LGN)

anterior limb of internal capsule orgin and output (has two)

anterior nucleus-> cingulate gyrus MD-> prefrontal cortex

Thalamocortical pathways

auditory receptors in cochlea-> brain stem neurons-> MGN-> Auditory cortex or photoreceptors in eye-> other retinal neurons lgn-> visual cortex

Dicenphalon

composed of: thalmus, hypothalmus, epithalmus

Sublenticular

lgn->visual cortex (optic radiation) mgn->auditory cortex (auditory radiation)

Lateral nuclear group function

located ventrally; general and special senses

Posterior limb orgin and outputs

motor cortex-> spinal cord (corticospinal tract) motor cortex -> brainstem (coricobulbuar and corticopontine tract) vpl/vpm-> postcentral gyrus (somatosensory radiation)

Pulvinar input and output

parietal, occipital, temporal assoc cortex general arousal modulation of thalmic input to cortex parietal, occipital, temporal assoc cortex

retrolenticular

pulvinar-> association cortex lgn->visual cortex (optic radiation)

Association nuclei

receive specific inputs mainly from association cortex, and project back to related areas of association cortex. -Dorsomedial (DM) -Pulvinar (P/LP)