Neurology 6 - Thalamus and Hypothalamus

Question 1

Describe the location of the thalamus

Answer 1

• Sits ventral to the lateral ventricles
• Thalamus divided in two by 3rd ventricle
• Organised into discrete nuclei (clusters on neurons with similar functions and connections)
• Towards the back of the brain in the midline

Question 2

List the function of the thalamus

Answer 2

• Relay site for numerous inputs/outputs (for nearly all brain function)
• Key relay centre to the cortical sensory areas
• Involved in almost all sensory systems (except olfactory/smell)
• Enhances or restricts signals (modulatory)

Question 3

What is the intralaminar nuclei? (location, function, connections)

Answer 3

• Located in the lamina of the thalamus
• Projects to various medial temporal lobe structures (amygdala - fear/anxiety, hippocampus - memory, basal ganglia - movement)
• Mostly glutamatergic neurons (excitatory)
• Loss of neurons in this region associated with progressive supranuclear pals (walking and balance) and Parkinsons

Question 4

What is the reticular nucleus? (Location, function, connections)

Answer 4

• Forms the outer covering of the thalamus
• Most neurons are GABAergic (inhibitory)
• Don’t connect with distal regions, but with other thalamic nuclei
• Recieve inputs from collateral of their axons from thalamic nuclei
• Therefore, reticular nucleus acts to modulate thalamic activity - negative feedback

Question 5

What is reticular formation?

Answer 5

• Set of interconnected pathways in the brainstem (send ascending projections to forebrain nuclei - ascending reticular activating system [ARAS])
• Involved in consciousness and arousal - degree of wakefulness depends on ARAS
• Both intralaminar and reticular nucleus recieve inputs from ARAS

Question 6

Describe the location of the hypothalamus

Answer 6

• Divided in two by 3rd ventricle - makes the walls and the floor of the third ventricle
• Collection of individual nuclei with distinct functions

Question 7

List the connections and functions of the hypothalamus

Answer 7

• Ipsilateral connections with other nuclei (same side)
• 4 f’s (feeding, fleeing, fighting, mating)
• Directly connects with ANS
• Connects with endocrine systems (hypothalamo-pituitary axis)
• Control of behaviour (feeding)

Question 8

Describe the structure of the paraventricular nucleus

Answer 8

• Sends projections to the autonomic nervous system and posterior pituitary gland
• Parvocellular (small cells) and magnocellular (large cells)

Question 9

List the functions of the paraventricular nucleus

Answer 9

• Involved in feeding behaviour
• Innervates vasculature, heart and kidney (magnocellular)
• Parvocellular causes vasopressin and oxytocin release

Question 10

What is damage to the suprachiasmatic nucleus associated with? What does the normal suprachiasmatic nucleus control?

Answer 10

• Disturbed sleep cycle
• Normally it is involved in circadian rhythm
• Links to the pineal gland - causes release of melotonin

Question 11

What is present in the diencephalon?

Answer 11

• Thalamus
• Subthalamus (stimulated by electrodes to treat parkinsons - Subthalamic nucleus of the basal ganglia)
• Hypothalamus

Question 12

Where does the somatosensory pathway go (anatomically)?

Answer 12

• Cell bodies in the dorsal route ganglion
• Enters the dorsal horn of the spinal cord, and travels up the dorsal columns to the gracile nucleus
• Crosses over the midline (sensory decussation) and travels up to the thalamus, ventral posterior lateral nucleus, and then to the primary somatosensory cortex

Question 13

Describe the location of the suprachiasmic nucleus.

Answer 13

It is just above the optic chiasm, next to the supraoptic nucleus (above the optic nerve)