Thalamus and Hypothalamus

Question 1

What does the diencephalon consist of ?

Answer 1

Thalamus

Subthalamus

Hypothalamus

Question 2

Where is the thalamus found within the brain?

Answer 2

Ventral (inferior) to the lateral ventricles

Question 3

What separates the two halves of the thalamus?

Answer 3

3rd ventricle

Some people have a bridge connecting the two halves

Question 4

Describe briefly how the thalamus is organised.

Answer 4

Into discrete nuclei (=clusters of neurons with similar functions and connections)

Question 5

Which area of the thalamus receives vibration, properioception and light touch information?

Answer 5

Ventral posterior lateral nucleus (somatosensory pathway)

Question 6

What is the main function of the thalamus?

Answer 6

• It is a relay centre for numerous inputs/outputs for cortical sensory areas
• Involved in almost all sensory systems
• Enhances or restricts signals (prevents sensory overload)

Question 7

What is the only sensory function that is not represented within the thalamus?

Answer 7

Olfaction

Question 8

Describe how thalamic nuclei are named.

Answer 8

They are named based on their location within the thalamus

Question 9

Where do intralaminar nuceli of the thalamus project to ?

Answer 9

Medial temporal lobe structures: amygdala, hippocampus, basal ganglia.

Question 10

What important system are the intralaminar and reticular nuclei a part of?

Answer 10

Reticular activating system – involved in maintaining consciousness

Question 11

What types of neurons project from the intralaminal nuclei to these areas? What does loss of these neurons cause?

Answer 11

Largely glutamatergic neurons i.e. EXCITATORY

Question 12

What is loss of glutamatergic neurons in the intralaminar nuclei associated with?

Answer 12

Loss –> PSP and Parkinson’s

*PSP = progressive supranuclear palsy - rare brain disorder causing problems with walking and balance.

Question 13

What types of neurons project from the reticular nuclei mostly?

Answer 13

GABAergic i.e. INHIBITORY

Question 14

Describe how the reticular nuclei affect cortical activity.

Answer 14

• Unlike other thalamic nuclei, they don’t connect with distal regions, but with other thalamic nuclei
• Receive inputs from collaterals of their axons from thalamic nuclei
• Therefore, reticular nucleus acts to modulate thalamic activity (negative feedback)

Question 15

Describe the location of the reticular nucleus.

Answer 15

Forms the outer covering of the thalamus

Question 16

What are some of the functions of the medial temporal lobe structures?

Answer 16

Amygdala - emotions, fear, anxiety

Hippocampus - memory

Basal ganglia - movement

Question 17

What is the core of grey matter that runs through the brainstem and is involved in the reticular activating system?

Answer 17

Reticular formation - sends ascending projections from brainstem to forebrain nuclei = ARAS (ascending RAS)

Question 18

Describe the function of the reticular formation.

Answer 18

Forms the ascending reticular activating system (ARAS)

Involved in consciousness and arousal - degree of wakefulness depends on ARAS actvity (increased activity = increased wakefulness)

Question 19

What is the relationship between intralaminar nuclei, reticular nucleus and the reticular formation?

Answer 19

Both intralaminar and reticular nucleus receive inputs from ARAS (wakefulness)

Question 20

Describe the location and structure of the hypothalamus.

Answer 20

• The hypothalamus is just below the thalamus and is divided by the 3rd ventricle into two
• Collection of individual nuclei with distinct functions
• Largely ipsilareral connections with other nuclei

Question 21

What are the 4 Fs that the hypothalamus is involved with?

Answer 21

Involved in 4 Fs:

• Fighting
• Fleeing
• Feeding
• Mating

Question 22

How does the hypothalamus interact with endocrine control, ANS and behaviour?

Answer 22

It coordinates these different mechanisms to maintain homeostasis:

• Autonomic nervous system - connections from PVN to autonomic neurons in spinal cord
• Endocrine system - e.g. HPA. Posterior pituitary receives PVN and SON neurons. Anterior pituitary more likely to have tumour.
• Behaviour e.g. feeding via arcuate nucleus and PVN

Question 23

Which nucleus in the hypothalamus is involved in the circadian rhythm?

Answer 23

Subrachiasmatic nucleus - sleep wake cycle

Sits above the optic chiasm

Question 24

What are the two types of neurons in the PVN and where do they project to?

Answer 24

Parvocellular(small) –> Autonomic nervous system - vasculature, heart kidneys

Magnocellular (large) –> Posterior pituitary gland

Question 25

What is the PVN involved with?

Answer 25

Feeding behaviours

Question 26

How do we know that the PVN is important in feeding behaviour?

Answer 26

Lesions –> hyperphagia and weight gain Optogenetic stimulation of GABAergic LH neuron terminals in PVN results in feeding

Question 27

Describe the activity of the suprachiasmatic nucleus.

Answer 27

Oscillatory activity - increases during day and decreases at dark Connected to the retinal ganglia and photoreceptors. Looking at blue light disrupts its activity. Controls melatonin release.

Question 28

What is the result of lesions to the SCN? Why is this though to be important?

Answer 28

• Disrupted sleep
• Symptoms of schizophrenia - Hallucinations, delusions, confused thoughts, loss of motivation, sleep disturbances, lack of concentration..*

So suprachiasmatic nucleus could be linked to pathogenesis of schizophrenia,