2: Thalamus Flashcards
Describe the anatomical organization of the thalamus.
Located in lateral wall of 3rd ventricle
Internal medullary lamina: white matter tract running anterior to posterior with “Y” anterior that divides it into 3 main nuclei (medial, lateral, anterior)
–Contains intralaminar nuclei: central median, parafascicular nuclei
Lateral region: most complex
- Ventral tier: contains most of the relay nuclei
- —>(caudal->rostral): VPM, VPL, ventral lateral nuclei, ventral anterior nuclei - Dorsal tier: contains association nuclei
- —>(caudal->rostral): pulvinar & two others that are unimportant
Metathalamus: medial and lateral geniculate nuclei (in back)
Anterior region: anterior nucleus
Medial region: mediodorsal nucleus, midline nuclei
What are the two broad types of thalamic nuclei?
Relay nuclei and association nuclei
What does the diencephalon consist of? (4)
Epithalamus
Subthalamus
Hypothalamus
(Dorsal) thalamus
What are the two components of the epithalamus? Describe them.
Pineal gland:
- -Endocrine organ
- -Releases melatonin
- -Circadian rhythm controlled by sympathetics
Habenular nuclei:
- -Limbic relay nuclei with projections to brainstem
- -Involved in negative reward (suppression of the mesolimbic dopamine reward system) -> extinction
What is the subthalamus associated with?
The basal ganglia
What is the (dorsal) thalamus?
A collection of nuclei in the lateral wall of the 3rd ventricle
The greatest source of input to the cerebral cortex
—ALL sensory pathways (except olfaction) relay in thalamus before reaching cortex
—Relays cerebellar, basal ganglia, and limbic pathways
What do reciprocal connections from the cortex to the thalamus do?
Regulate thalamic input back to the cortex
Discuss the two physiological states of thalamic projections nuclei and the importance of these states.
“Burst mode:” rhythmic firing, oscillatory
- -Cell is HYPERPOLARIZED: Ca channel opens -> cell depolarizes -> AP -> Ca channel closes -> hyperpolarization -> repeat
- -May help generate cortical EEG rhythms
- -Appears with inhibition of thalamic neurons
“Tonic mode:” neuron responds to excitatory input and conveys information
–Fires off many irregular APs -> barcode for how particular stimulus activated that cell
NOVEL STIMULI -> conversion
What are specific relay nuclei? From where do they receive input?
Thalamic nuclei that filter sensory information
-Includes VPL, VPM, VL, VA, metathalamus
–Receive specific input, input from a different thalamic nucleus, regulatory input from cortex, and modulatory input from brain stem
What are association nuclei? From where do they receive input?
Thalamic nuclei that project to association cortex
- -Interconnect back and forth with cortex to regulate activity
- -Involved in complex functions like attention, memory, and eye movement
- -Necessary for normal activity - regulates excitability of association/processing areas of the cortex
–Receive input from multiple parts of the cerebral cortex, as well as some modulatory input from the brain stem (NO sensory/motor input)
What thalamic nuclei are connected with limbic areas of the cortex?
Anterior nucleus (along with LD) Mediodorsal (along with midline)
What are intralaminal nuclei? What is the ARAS? What happens when it is damaged?
Less focused thalamic outputs to cortex (nonspecific nuclei)
- -Some involvement in Ascending Reticular Activation System: essential for maintaining normal levels of consciousness, going from inattentive -> alert state
- -Reciprocal connections with the basal ganglia and limbic system
- -Can affect most cortical function
- -Damage = coma
**What is the only thalamic nucleus that does not send its major output to the cortex?
Reticular thalamic nucleus (an INHIBITORY feedback nucleus)
- -Like the shell on the outside of the thalamic “robin’s egg”
- -Regulates thalamic excitability
What are the two ways in which the thalamus influences the cerebral cortex?
- Relay of sensation or motor feedback (involved in filtering that input)
- Providing internal circuitry that maintains normal levels of cortical activity
Can affect excitability of all cortical regions
Why is the thalamus so important?
Filters information relayed to cerebral cortex
- -Helps us not be overwhelmed by sensations
- -Example: olfaction skips the thalamus, so certain smells are very hard to ignore/filter out
