Thalamus

Thalamus

gray matter, a collection of nuclei distinguished from one another by the pattern of connections (comprises bulk of diencephalon)

Thalamus Location

rostral most part of diencephalon

superior margin forms part of the floor of lateral ventricles, and sits on midbrain

Thalamus

gray matter, a collection of nuclei distinguished from one another by the pattern of connections (comprises bulk of diencephalon)

Thalamus Location

rostral most part of diencephalon

superior margin forms part of the floor of lateral ventricles, and sits on midbrain

What lies above and behind the thalamus?

Epithalamus

What lies between the thalamus and midbrain substantia nigra?

Subthalamus

Massa intermedia (interthalamic adhesion)

joins the 2 thalami

Kinds of nuclei in thalamus

Relay, Association, Non-specific

What lies anterior and ventral to the thalamus?

Hypothalamus

All thalamic nuclei communicate with _____ _____ except ____ _____, which provide intrathalamic connections

cerebral cortex; reticular nuclei

Thalamus function

Relays information and receives corticothalamic feedback that likely regulates thalamocortical input

Relay nuclei

single system/function

-bidirectional connections with sensory cortices

-connections with motor cortices as part of motor control circuits

(sometimes part of motor networking, sometimes bidirectional connections send and receive info)

Association nuclei

-networking

-connections with limbic and association cortices

-help monitor networking in brain

Non-specific nuclei

-arousal

-intrathalamic connections

-help regulate overall level of alertness (connected from themselves to other thalamic nuclei)

Relay sensory nuclei (specific)

-VPL

-VPM

-Lateral geniculate

-VP

-Medial geniculate

Relay motor nuclei

-VA/VL

Relay limbic nuclei

-Anterior/LD/MD

What descending fibers run in internal capsule

-corticobulbar (posterior; ascending/third order neuron fibers from sensory paths)

-cerebrospinal tract (anterior fibers)

Thalamus is the _______ of our _______ pathways

gateway; sensory

The gate is the _____ the gatekeeper is the ______

cortex; thalamus

Principal neurons

-glutamatergic

-synapse in cortex

-convey sensory input to thalamus from various receptor organs

thalamic regulatory inputs

influence physiological state of thalamus (open/shut gate)

3 neuron sensory pathways (ST, ML, out in periphery)

1st: detect sensory input

2nd: pick message up and synapse into thalamic nuclei

3rd: pick message up and take to cortex

3rd relay: principal neurons

-axon leaves area where soma is

-leaves thalamus, goes to cortex through internal capsule (myelinated on the way)

Glutamatergic

neurotransmitter the 3rd order neuron releases onto recipient neurons in cortex is glutamate; cortex neurons have EPSPs (excitation from glutamate)

Functions related to relay nuclei

Sensory: vision, hearing, somatic sensation from contralateral body and face

Motor: initiating/planning movement, motor control and motor learning

Functions related to association nuclei

Limbic: alertness, episodic memory, learning, spatial organization; affective behavior, active memory, decision making, judgment, nonspecific pain/perception arousal

Multimodal: visual perception, sensory integration, eye movements related to attention; visual processing; memory, attention, spatial processing

Functions related to nonspecific nuclei

Intralaminar: GABAergic cells, regulates interthalamic nuclear activity, affects cognitive and motor functions involving thalamic nuclei; nonspecific arousal system, cognitive, limbic, sensory, motor function

Tonic firing

More sensitive, more likely for APs

from relatively depolarized membrane potentials, occurs most frequently during wakefulness

Burst firing

Less sensitive, less likely for APs

from hyperpolarized potentials, occurs most frequently during sleep, drowsiness, inattention (also some during wake)

G-protein coupled receptor

3rd order thalamic relay neurons take info to cortex in state-dependent way (tonic/burst)

neuromodulation moves from one to the other because of the g-protein inside cell (ran off and did things to channels; they act on ion channels)

Receptors g-proteins belong to

glutamate, norepinephrine, dopamine

Ligands for g-protein receptors come from ______, which come from the _________ ______

vesicles; pre-synaptic neuron

Thalamic regulatory input

some neuron (ret. form., cortex, or other thalamic) releasing ligands onto 3rd order thalamic relay neuron; neurons not part of sensory pathways (3rd party neurons) release neuromodulatory neurotransmitters onto thalamic relay neurons - switch them from tonic to burst or vise-versa

In fight or flight mode, we want info passed faithfully to our cortex, so __________ turns neurons _____ to facilitate

norepinephrine; tonic

The info that needs to get to cortex will when we are awake, but when we are asleep, the info has to be _____ _____ to make it to the cortex

enough stimulus

Thalamic syndrome presentation

-contralateral face/body poor/absent sensation

-sensory based ataxia

-cortex interprets something is wrong (bc of no sensory input), so it gives the experience of pain

-body activates immune response to pain in absence of injury (swelling and redness where stroke happened)

-neuropathic (pain from brain response): symptom of allodynia (light touch now hurts)