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.
