Thalamus and Hypothalamus Flashcards
What does the diencephalon consist of ?
Thalamus
Subthalamus
Hypothalamus
Where is the thalamus found within the brain?
Ventral (inferior) to the lateral ventricles
What separates the two halves of the thalamus?
3rd ventricle
Some people have a bridge connecting the two halves
Describe briefly how the thalamus is organised.
Into discrete nuclei (=clusters of neurons with similar functions and connections)
Which area of the thalamus receives vibration, properioception and light touch information?
Ventral posterior lateral nucleus (somatosensory pathway)
What is the main function of the thalamus?
- 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)
What is the only sensory function that is not represented within the thalamus?
Olfaction
Describe how thalamic nuclei are named.
They are named based on their location within the thalamus
Where do intralaminar nuceli of the thalamus project to ?
Medial temporal lobe structures: amygdala, hippocampus, basal ganglia.
What important system are the intralaminar and reticular nuclei a part of?
Reticular activating system – involved in maintaining consciousness
What types of neurons project from the intralaminal nuclei to these areas? What does loss of these neurons cause?
Largely glutamatergic neurons i.e. EXCITATORY
What is loss of glutamatergic neurons in the intralaminar nuclei associated with?
Loss –> PSP and Parkinson’s
*PSP = progressive supranuclear palsy - rare brain disorder causing problems with walking and balance.
What types of neurons project from the reticular nuclei mostly?
GABAergic i.e. INHIBITORY
Describe how the reticular nuclei affect cortical activity.
- 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)
Describe the location of the reticular nucleus.
Forms the outer covering of the thalamus
What are some of the functions of the medial temporal lobe structures?
Amygdala - emotions, fear, anxiety
Hippocampus - memory
Basal ganglia - movement
What is the core of grey matter that runs through the brainstem and is involved in the reticular activating system?
Reticular formation - sends ascending projections from brainstem to forebrain nuclei = ARAS (ascending RAS)
Describe the function of the reticular formation.
Forms the ascending reticular activating system (ARAS)
Involved in consciousness and arousal - degree of wakefulness depends on ARAS actvity (increased activity = increased wakefulness)
What is the relationship between intralaminar nuclei, reticular nucleus and the reticular formation?
Both intralaminar and reticular nucleus receive inputs from ARAS (wakefulness)
Describe the location and structure of the hypothalamus.
- 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
What are the 4 Fs that the hypothalamus is involved with?
Involved in 4 Fs:
- Fighting
- Fleeing
- Feeding
- Mating
How does the hypothalamus interact with endocrine control, ANS and behaviour?
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
Which nucleus in the hypothalamus is involved in the circadian rhythm?
Subrachiasmatic nucleus - sleep wake cycle
Sits above the optic chiasm
What are the two types of neurons in the PVN and where do they project to?
Parvocellular(small) –> Autonomic nervous system - vasculature, heart kidneys
Magnocellular (large) –> Posterior pituitary gland
What is the PVN involved with?
Feeding behaviours
How do we know that the PVN is important in feeding behaviour?
Lesions –> hyperphagia and weight gain Optogenetic stimulation of GABAergic LH neuron terminals in PVN results in feeding
Describe the activity of the suprachiasmatic nucleus.
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.
What is the result of lesions to the SCN? Why is this though to be important?
- 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,
