thalamus - jullet Flashcards
What is the diencephalon comprised of? (4)
thalamus, subthalamus, epithalamus, and hypothalamus
What is the epithalamus comprised of? (2)
habenular nuclei + pineal gland
What part of the diencephalon is the pineal gland a part of? What is its role?
epithalamus; endocrine organ that secretes melatonin in response to circadian differences in SYMPATHETIC nervous system activity.
What part of the diencephalon is the habenular nuclei a part of? What is its role?
epithalamus; limbic relay nuclei with projections to the brainstem; turns OFF the mesolimbic reward system
What is the subthalamus comprised of? (2)
subthalamic nucleus and zona incerta; functionally connected with the basal ganglia
What is the role of the subthalamus?
associated with the basal ganglia and is involved in regulating motor function or movement.
What is the functional outcome of lesions to the subthalamic nuclei (subthalamus)?
movement disorder where there is a DECREASED suppression of undesired movements
What is the chain of command that the hypothalamus follows in controlling sympathetics to the pinal gland?
hypothalamic neurons descend in the lateral brain stem and spinal cord (via IML) to the pre-ganglionic sympathetic nervous neurons in the upper thoracic spinal cord. These neurons enter and ascend in the sympathetic chain to the superior cervical ganglion (SCG), where they synapse. Post-ganglionic neurons from the SCG follow the carotid artery branches to the cranial structures (ie eye, pineal gland)
What is the IML
interomediolateral nucleus - region of gray matter in the spinal cord (T1-L2) that contains the hypothalamic projections that ultimately synapse with the sympathetic chain (to provide sympathetic innervation to cranial structures (ie eye, pineal, or other parts of the body etc)
What innervates the pineal gland?
sympathetic innervation from the superior cervical ganglion
What connects limbic structures of the brain to the habenular nuclei to the brain stem?
stria medullaris of the thalamus
Where does the habenular nucleus project to?
interpeduncular nucleus of the midbrain
What activities are the habenular nucleus involved in?
it is involved in”NEGATIVE REWARD”, where it activates systems in the midbrain that decrease activity in dopaminergic neurons, especially those in the ventral tegmental area.
T/F The habenular nucleis is functionally connected to the pineal gland.
False. It may be anatomically conneted, but it’s not functionally connected to the pineal gland
What is the dorsal thalamus? Where can it be found?
collection of nuclei in the lateral wall of the third ventricle that conveys all sensory pathways (except olfaction) from the periphery to the cortex; is the greatest source of input to the cerebral cortex (contains reciprocal connections between the cortex thalamus)
What type of neurons predominate in the dorsal thalamus? What is the role of these neurons?
GABAergic neurons - modulate the transmission of signals through the thalamus.
Thalamic neurons exsist in these two modes. What is the function of these two modes?
BURST/OSCILLATORY mode: rhythmic firing that may help to generate cortical EEG rhythms and appears with the inhibition of thalamic neurons. TONIC mode: responds to input and conveys information between cortex thalamus.
What is the role of the dorsal thalamus?
collection of nulcei that functions as a relay center that 1) filters and conveys sensory pathways (except olfaction) from the periphery to the cortex, but also acts as a 2) cortical relay center for the cerebellar, basal ganglia and limbic pathways. NOTE: each subnucleus receives reciprocal connections from the cerebral cortex.
The dorsal thalamus acts as a relay center that conveys all sensory pathways from the periphery to the cortex, except this one:
olfaction - bypasses thalamus to connect directly to the forebrain
All thalamic nuclei except for this one projects to the cerebral cortex.
reticular thalamic nucleus - never projects to the cerebral cortex, but instead it modulates the information in other nuclei in the thalamus.
What are the two basic types of input to the thalamus?
1) signals relayed from the periphery to the cortex and 2) modulatory inputfrom other thalamic nuclei (ie reticular thalamic nucleus, RTN)
What characterizes TONIC firing of thalamic neurons?
TONIC = occurs during DEPOLARIZATION, where the VG Ca2+ channels are CLOSED. Information received via afferents is linearly transferred to the cerebral cortex (more accurate/faithful transmission)
What characterizes BURST/OSCILLATORY firing of thalamic neurons?
BURST/OSCILLATORY = occurs during HYPERPOLARIZATION, where the VG Ca2+ channels are OPEN. Information received via afferents is non-linearly transferred to the cerebral cortex; more neurons are in this mode during sleep.
Give an example of how tonic and burst firing affects the perception of sensation.
If you lightly tap someone on the shoulder when they’re awake (neurons in the VPL of thalamus are in the TONIC mode), and the person will perceive the tap. However, if you tap someone when they’re in the non-REM sleep (neurons in the VPL of thalamus are in the BURST mode), a light tap will still activate afferents and the resulting signal will still reach the thalamus, but thalamic neurons the tap may elicit no response in the VPL of the thalamus. A stronger tap may elicit a burst of activity in the thalamocortical projection neurons, which activates the thalamic neurons in BURST mode to increase detection of sensory stimuli and may shift the behavior state towards greater arousal.
What structures border the medial, lateral, and caudal side of the thalamus?
medial: 3rd ventricle, lateral: internal capsule, caudal: rostral portion of the midbrain reticular formation and other subthalamic structures
What makes up one of the walls of the 3rd ventricle?
thalamus
What is the internal medullary lamina?
it is a band of white matter running through the thalamus that divides anteriorly and creates a lateral, medial, and anterior group of nuclei.
What two nuclei are contained within the internal medullary lamina?
1) intralaminar nuclei. 2) centramedian nuclei
How is the thalamus divided into regions? What are these regions?
the internal medullary lamina is a band of white matter that runs through the thalamus and divides anteriorly to create a lateral, medial, and anterior group of nuclei. The MEDIAL region contains the medialdorsal (MD) nucleus and adjacent intralaminar nuclei (rostral continuation of periaqueductal gray matter). The LATERAL region contains ventral and dorsal tiers, each which contain subnuclei.
How is the lateral group of the thalamus subdivided? (3 groups)
VENTRAL TIER (rostral to caudal): ventral anterior -> ventral lateral, and ventral posterior. DORSAL TIER (rostral to caudal): lateral dorsal, lateral posterior, pulvinar. METATHALAMUS: medial (auditory) and lateral (visual) geniculate
What two structures form the metathalamus?
medial geniculate (auditory) and lateral geniculate (visual) geniculate.
What is the medial geniculate involved in?
auditory - it is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus and the auditory cortex
What is the lateral geniculate involved in?
visual - part of the visual thalamus and represents the thalamic relay center for visual information received from the retina of the eye.
What forms the anterior thalamic region? (3)
1) anterior nucleus (flanked by the internal medullary lamina), 2) intralaminar nuclei (centromedian and parafascicular nuclei) within the internal medullary lamina, 3) reticular nucleus (thin shell of neurons that cover the entire lateral part of the thalamus).
What is the reticular thalamic nucleus? What is its function?
it’s a thin shell of inhibitory neurons that cover the entire lateral aspect of the thalamus, but its GABA neurons project into the thalamus and is involved in the “gating” of the thalamus.
What separates the reticular nucleus from the thalamus?
external medullary lamina
There are 3 types of thalamic nuclei. What are they?
1) relay nuclei. 2) association nuclei. 3) non-specific nuclei
What are the 3 relay nuclei?
lateral tier, ventral tier, and metathalamus.
What roles do relay nuclei of the thalamus have?
receives well-defined input, filters input, and projects to functionally distinct areas of the cortex; there are also feedback projections from the cerebral cortex to the thalamic nucleus.
What roles do association nuclei of thalamus have?
receives input from multiple parts of the cortex, processes and filters it, and output to association cortexes (prefrontal cortex and tempo-parietal cortex)
What two portions are involved in integrating sensory inputs and other cortical activity and generating appropriate responses?
prefrontal cortex and tempo-parietal cortex (both association cortexes)
Where are the association cortexes usually located?
it makes up for the majority of the cortex and surrounds primary sensory cortexes. Ex: transverse gyri of Heschl receives and figures out what the input is (ie sound - what is it, what is the meaning associated with it)
What is the cingulate gyrus involved in?
emotions, how we interact and react to the world. Abnormalities to this area result in anxiety, depression, chronic pain, etc.
What is the Wernicke-Korsakoff syndrome?
destruction in the medial mediodorsal (MD) + midline nuclei (all association nuclei) that results in impaired memory - since it projects to the limbic system, it also affects personality, motivation, and mood.
What type of nuclei is the ventral posterior lateral (VPL) nuclei?
relay nuclei
What part of the thalamus is the ventral posterior lateral (VPL) nuclei?
lateral group
What is the input/output of the ventral posterior lateral (VPL) nuclei?
INPUT: medial leminiscus input and spinothalamic tract OUTPUT: primary somatosensory area - postcentral gyrus (areas 3, 1, 2)
What type of info is relayed by the ventral posterior lateral (VPL) nuclei?
somatosensory from trunk and feet
What type of nuclei is the ventral posterior medial (VPM) nuclei?
relay nuclei
What part of the thalamus is the ventral posterior medial (VPM) nuclei?
lateral group
What is the input/output of the ventral posterior medial (VPM) nuclei?
INPUT: trigeminothalamic input. OUTPUT: inferior portion of the postcentral gyrus
What type of info is relayed by the ventral posterior medial (VPM) nuclei?
somatosensory from face
What type of nuclei is the ventral lateral nucleus?
relay nuclei
What part of the thalamus is the ventral lateral nucleus ?
lateral group
What is the input/output of the ventral lateral nucleus?
INPUT: cerebellum afferents (mainly from dentate nucleus) and basal ganglia (rostrally) OUTPUT: primary motor areas (area 4) of precentral gyrus and premotor (area 6)
What type of info is relayed by the ventral lateral nucleus ?
motor - planning, initiating and correcting (cerebellum + basal ganglia)
What type of nuclei is the ventral anterior nucleus ?
relay nuclei
What part of the thalamus is the ventral anterior nucleus ?
lateral group
What is the input/output of the ventral anterior nucleus?
INPUT: motor input from basal ganglia (medial globus pallidus and substantia nigra pars reticulata) OUTPUT: pre-motor cortex (area 6), including supplementary motor cortex
What type of info is relayed by the ventral anterior nucleus ?
motor - planning and initiating
What type of nuclei is the lateral geniculate ?
relay nuclei
What part of the thalamus is the lateral geniculate ?
metathalamus
What is the input/output of the lateral geniculate?
INPUT: visual input from optic tract (input from the homonomous visual world) OUTPUT: primary visual area (area 17, aka striate or calcarine cortex)
What type of info is relayed by the lateral geniculate ?
vision
What type of nuclei is the medial geniculate ?
relay nuclei
What part of the thalamus is the medial geniculate ?
metathalamus
What is the input/output of the medial geniculate?
INPUT: auditory afferents from the inferior colliculus via the brachium of the inferior colliculus
OUTPUT: primary auditory cortex (areas 41 and 42, heschel’s gyrus) on superior tempoeral lobe in lateral fissure
What type of info is relayed by the medial geniculate ?
audio
What type of nuclei is the pulvinar nucleus ?
association nuclei
What part of the thalamus is the pulvinar nucleus ?
lateral group, dorsal tier
What is the input/output of the pulvinar nucleus?
INPUT: superior colliculus and association cortex OUTPUT: secondary visual areas (area 18 and 19), and to the parieto-temporo-occipital association area
What type of info is relayed by the pulvinar nucleus ?
attention and eye movements
What type of nuclei is the lateral posterior nuclei?
association nuclei
What part of the thalamus is the lateral posterior nuclei ?
lateral group, dorsal tier
What is the inputs/output of the lateral posterior nuclei?
INPUT: superior colliculus and association cortex OUTPUT: association areas of the parietal lobe
What type of info is relayed by the lateral posterior nuclei?
attention and eye movements
What type of nuclei is the lateral dorsal nucleus and anterior nucleus?
association nuclei
What part of the thalamus is the lateral dorsal nucleus and anterior nucleus?
dorsal tier and anterior
What is the input/output of the lateral dorsal nucleus and anterior nucleus?
INPUT: afferents from hippocampus and mammillary bodies (via mammillothalamic tract) OUTPUT: posterior cingulate cortex (area 23)
What type of info is relayed by the lateral dorsal nucleus and anterior nucleus?
hearing and emotions (limbic connections)
What type of is the lateral mediodorsal (MD) ?
association nuclei
What part of the thalamus is the lateral mediodorsal (MD) ?
medial group
What is the input/output of the lateral mediodorsal (MD)?
INPUT: afferents from superior colliculus, piriform (olfactory) cortex, and ventral pallidum. OUTPUT: frontal eye fields and anterior cingulate (area 24) cortex of frontal lobe
What type of info is relayed by the lateral mediodorsal (MD) ?
eye-head control and attention
What type of nuclei is the medial mediodorsal (MD) ?
association nuclei
What part of the thalamus is the medial mediodorsal (MD) ?
medial group
What is the input/ouput of the medial mediodorsal (MD)?
INPUT: afferents from solitary nucleus, substantia nigra (reticulata), amygdala, and ventral palladium. OUTPUT: limbic areas of the cortex (insula, orbitofrontal, and subcallosal cortex)
What type of info is relayed by the medial mediodorsal (MD) ?
autonomic regulation and emotion; destruction damages memory, personality, mood, and motivation.
What type of nuclei is the intralaminar nuclei and midline nuclei ?
non-specific nuclei
What part of the thalamus is the intralaminar nuclei and midline nuclei ?
medial group
What is the input/output of the intralaminar nuclei and midline nuclei?
INPUT: midbrain reticular formation. OUTPUT: diffuse projections into the cortex via ascending reticular activating system (ARAS)
What type of info is relayed by the intralaminar nuclei and midline nuclei ?
alertness, sleep rhythms (damage to pathway can result in coma)
What is the ascending reticular activating system (ARAS)?
a set of nuclei that is responsible for regulating arousal and sleep-wake transitions; pathways originate in the upper brainstem reticular core and project through synaptic relays in the rostral intralaminar and thalamic nuclei to the cerebral cortex. Damage can result in a coma.
What is the centromedian nucleus?
intralaminar nucleus that receives input from the globus pallidus that projects to area 4 and to the entire neocortex. Part of the basal ganglia feedback and mayb e involved in motor functions.
What is unique about the reticular thalamic nucleus?
Reticular Thalamic nucleus (**only thalamic nucleus that does not project primarily to the cortex)
What is the function of the reticular thalamic nucleus?
regulates thalamic excitability, signal transmission, and function (also impt for sleep/wake cycles)
What is the input/output of the reticular thalamic nucleus?
input: cortex and brainstem output: inhibitory output to thalamic nuclei (GABAergic neurons)
