Thalamus Flashcards
Pineal gland
Modified photoreceptors - not important in humans
Sympathetic input:
light -> super-chiasmatic nucleus -> hypothalamus -> spinal cord -> sympathetic chain -> post-ganglionic sympathetics follow arteries -> pineal
Produces melatonin -> regulated sleep, sex
-> have to destroy SNS chain bilaterally to disrupt circadian rhythm
Diencephalon
(Dorsal) thalamus - relay and association -> cortex
Hypothalamus - metabolic/hormonal control
Subthalamus - associated with basal ganglia
Epithalamus
- pineal gland - SNS input -> circadian rhythm
- habenula - limbic -> stria thalami medullaris -> habenula -> suppresses mesolimbic dopamine reward
Overview of thalamus function
Essential for cortical functioning
- every thalamic nucleus except reticular projects primarily to cortex (and has reciprocal)
Relay - sensory (except olfactory indirect), motor feedback, limbic
- filtering - lots of inhibitory neurons
- modulation from cortex, brain stem (locus ceruleus, raphe), other thalamic nuclei
- ex VPL, VPM, medial and lateral geniculate
Association - primary cortex -> association cortex (pre-frontal, posterior temporo-parietal, anterior occipital)
- ex synthesizing sensory, integrating motor, attention
- modulatory input from brain stem (5HT, NE)
Regulation - mediodorsal, anterior, intralaminar nuclei
- emotional regulation
- excitability, alertness
Thalamic neuron function
Projections to cortex in two modes
- rapid transition between modes based on stimuli
Burst/oscillatory mode - inhibitory input -> basal output
- hyperpolarization -> special Ca channels -> burst of AP’s
- slow, rhythmic, large-amplitude waves -> cortical waves (alpha, delta, sleep)
Tonic mode - excitatory input -> meaningful signal
- fast, high activity (AP’s), irregular
Thalamus anatomy
Medial - third ventricle
Lateral - internal capsule
Subthalamus, midbrain (reticular formation)
Internal medullary lamina divides into ant nucleus, medial, lateral groups
- lateral divided into ventral (relay) and dorsal groups
Pulvinar - anatomic, caudal portion
- contains metathalamus = medial and lateral geniculate
Ventral posterior nuclei
Includes VPM and VPL - both sensory relay
VPL - input from medial lemniscus, spinothalamic tract
-> primary somatosensory cortex (postcentral gyrus)
VPM - input from trigeminal
Intermediate and ventral - vestibular -> inf parietal (and operculum)
Ventral lateral nucleus
Relay
Input from cerebellum (mostly dentate nucleus), some basal ganglia
Output to primary motor (precentral gyrus) and some to premotor
Planning, initiating, correcting movements
Ventral anterior nucleus
Relay
Input - basal ganglia (medial globus pallidus, substantia nigra, pars reticulata)
Output - premotor (supplementary frontal motor)
Planning and initiating movements
Metathalamus
Both relay nuclei
Lateral geniculate
- optic tract (contralateral visual field) via superior colliculus -> primary visual cortex (aka calcarine, striate)
Medial geniculate
- auditory via inferior geniculate -> primary auditory (sup temporal)
Dorsal nuclei
Pulvinar (most caudal segment) and lateral posterior
- both association
Input: association cortex and superior colliculus
Output: secondary visual, parieto-temporal-occipital association area (lateral to parietal)
Visual attention, perception, eye movements
Anterior nucleus
Association
Between rostral arms of internal medullary lamina
- lateral dorsal similar function
Input: hippocampus via mammilary bodies
Output: posterior cingulate cortex
Emotional learning?
Mediodorsal nucleus
Lateral portion
- input superior colliculus, olfactory cortex, ventral pallidum
- output - frontal eye fields, anterior cingulate
- eye movements, attention, emotional
Medial portion
- input solitary nucleus, substantia nigra reticulata, amygdala, ventral pallidum
- output frontal cortex (orbital, medial), insular
- autonomic regulation, emotion, memory (EtOH -> Wernicke-Korsakoff)
“Nonspecific” nuclei
Includes intralaminar and midline
Input: midbrain reticular formation
Output: broad projections in brain
Alertness, sleeping
Part of ascending reticular activating system (ARAS)
ARAS
Ascending reticular activating system
Responsible from changes: sleeping, resting, alert
Involved midbrain reticular formation, thalamic nuclei (intralaminar), diffuse cortex
Disfunction -> coma, persistant vegetative state
? Deep brain stimulation for coma -> doesn’t work
Reticular nucleus
Thick shell around nucleus
Input: cortex, brain stem (reticular formation), thalamic nuclei
Output: inhibitory to all thalamic nuclei (GABA)
Key for regulating thalamic activity, excitability
