Thalamus and hypothalamus Flashcards
1
Q
diencephalon structures
A
- thalamus
- subthalamus (contains the subthalamic nucleus= target for deep brain stimulation for Parkinson’s treatment)
- hypothalamus
Diencephalon is in close association with the midbrain
2
Q
Thalamic organisation
A
- occupies most of diencephalon
- ventral to the lateral ventricles (underneath)
- sits either side of the midline towards the back of the brain
- divided into right and left thalamus by the third ventricle
- main corticospinal tracts encapsulate thalamus on the midline
- hypothalamus just below thalamus and basal ganglia as a more anterior midline structure
- organised into collections of discrete nuclei (thalamic nuclei) with separate functions and connections with ipsilateral forebrain structures
- connections also present between the different thalamic nuclei
3
Q
Function of the thalamus
A
- relay site for numerous inputs/outputs for nearly all brain functions (converge on the thalamus)=between cerebral cortex and other parts of the CNS
- key relay centre to cortical sensory areas
- involved in almost all sensory systems (except olfactory system->no direct connection to thalamus)
- can enhance or restrict signals (role in modulation->excitatory or inhibitory depends on the part of the thalamus)
4
Q
Intralaminar nuclei
A
- project to various medial temporal lobe structures/cortical areas (eg: amygdala, hippocampus and basal ganglia)
- receive inputs from the reticular formation of the brainstem
- mostly glutamatergic neurons->excitatory output
- loss of neurons in this region associated with motor disorders->progressive supranuclear palsy (PSP=rare brain disorder causing walking and balance problems) and Parkinson’s disease
5
Q
Reticular formation
A
- set of interconnected pathways in the brainstem
- sends ascending projections to forebrain nuclei (Ascending Reticular Activating System=ARAS)
- Both intralaminar and reticular nucleus receive inputs from ARAS located in the brainstem
- ARAS involved in consciousness and arousal (allows reaction to circumstances in the outside world) , thus degree of wakefulness is dependent on ARAS activity (controls level of brain arousal by modulating cerebral cortex activity level)
- increased ARAS activity=increased wakefulness
6
Q
Hypothalamus structure
A
- located just below thalamus
- has direct pituitary gland connection->closely involved in neuroendocrine function (hypothalamic-pituitary axis)
- divided into left and right hypothalamus by the third ventricle
- collection of individual nuclei with distinct functions=nuclei present all the way up to the level of the thalamus
- largely ipsilateral (same side) connections with other nuclei/forebrain structures
7
Q
The 4 F’s (function of the hypothalamus)
A
DOWN TO DIFFERENT HYPOTHALAMIC NUCLEI
- Fighting (part of fight or flight response)
- Fleeing (part of fight or flight response)
- Feeding
- Mating
8
Q
Function of the hypothalamus
A
COORDINATES HOMEOSTATIC MECHANISMS BY:
- direct connections (brainstem and spinal cord) with autonomic nervous system (regulation of autonomic response to outside world)
- connections with endocrine systems (acting as endocrine organ via pituitary gland)
- control of behaviour (eg: feeding behaviour) via connections with forebrain structures
9
Q
Paraventricular nucleus
A
Located at the top of the third ventricle
- Sub areas within paraventricular nucleus: parvocellular neurons (small cells) and magnocellular neurons (large cells)
- Function: sends projections to autonomic nervous system and posterior pituitary gland
- Parvocellular neurons involved with autonomic nervous system (vasculature, heart, kidneys etc=CVS/renal effects)
- Magnocellular neurons involved with posterior pituitary gland (secretory function)-> synthesise Vasopressin and Oxytocin
Also closely involved in feeding behaviour
- paraventricular nuclei lesions result in loss of inhibitory neurones to give hyperphagia and hence weight gain
- Optogenic stimulation of GABAergic LH neuron terminals in paraventricular nucleus results in feeding behaviour
- paraventricular nucleus receives input from hypothalamic nuclei (eg: arcuate nucleus) involved in feeding->other nuclei involvement depicts functional network
10
Q
Suprachiasmatic nucleus
A
- Immediately above optic chiasm in hypothalamus
- involved in circadian rhythm controlling sleep wake cycles
- disturbances in sleep wake cycle often down to pathology in suprachiasmatic nucleus
- nucleus connected to paraventricular nucleus and thus controls autonomic outflow (ANS link)
- nucleus also innervates/connects to pineal gland (sits on roof of midbrain)-> controls melatonin secretion from gland, with melatonin controlling the light dark cycle
- lesions of the suprachiasmatic nucleus can cause disrupted sleep cycles
11
Q
Nuclei in neuroanatomy
A
Cluster/collection of neuronal cell bodies with similar functions and connections in the CNS
-exception of basal GANGLIA which is in the CNS
12
Q
Ganglia in neuroanatomy
A
Cluster/collection of neuronal cell bodies with similar functions and connections in the PNS
13
Q
Reticular nucleus
A
THALAMIC NUCLEUS
- forms outer covering of thalamus
- receives inputs from reticular formation
- majority of neurons are GABAergic->inhibitory output
- don’t connect/project with distal regions like other thalamic nuclei, projecting to other thalamic nuclei only
- receive inputs from axon collaterals from thalamic nuclei->thus reticular nucleus regulates information flow to cortex and acts to modulate thalamic activity with negative feedback loop
14
Q
Thalamic nuclei classification
A
CLASSIFICATION INTO GROUPS ACCORDING TO HOW THEY CONNECT WITH THE CEREBRAL CORTEX
Specific nuclei:
- Ventral lateral and ventral anterior->motor cortices
- Ventral posterolateral->Somatosensory (body)
- Ventral posteromedial->Somatosensory (head)
- Lateral geniculate->visual
- Medial geniculate->auditory
Association nuclei:
- Anterior, lateral dorsal and dorsomedial nuclei-> limbic system parts (cingulate cortex and prefrontal cortex)
- Lateral posterior and pulvinar->association cortex at junction of the parietal, temporal and occipital lobes and the prefrontal cortex
15
Q
Specific nuclei
A
-have reciprocal connections with a primary cortical area (ie: clearly defined function)
