6. Thalamus and Hypoothalamus Flashcards
Where is the thalamus found within the brain?
It is right in the middle the brain just under the posterior half of the corpus callosum
What separates the two halves of the thalamus?
3rd ventricle
Some people have a bridge connecting the two halves
(Its called vestigeal structure)
Describe the connections of the thalamus with the forebrain.
Each half of the thalamus has ipsilateral connections with the forebrain
3 components of diencephalon
Thalamus, subthalamus and hypothalamus
What is the main function of the thalamus?
[[[It is a relay centre between the cerebral cortex and the rest of the CNS, to cortical sensory areas]]]
Enhances and restricts signals
Connection is reciprocal
Integration and modification of information as it goes through thalamus
nucleus for every functional system in NS but not for olfaction
What is the only 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
What is the classification of thalamic nuclei based on and what are the four different classes?
The classification is based on the connections of the thalamic nuclei with the cortex
SPECIFIC – connected to primary cortical areas
ASSOCIATION – connected to association cortex
INTRALAMINAR – connected to ALL cortical areas
RETICULAR – not connected to the cortex
Describe somatosensory pathway
Vibration/propioception/light touch TO dorsal root ganglion TO posterior dorsal columns TO primary sensory neuron TO gracile nucleus seen in medulla and sensory decussation (cuneate nucleus maybe) TO thalamus VPLN via secondary sensory neurone TO primary somatosensory cortex via tertiary neuron.
Which nuclei connect with the motor cortex (primary, premotor and supplementary)?
Ventral lateral
Ventral anterior
Which nuclei relay sensory information from different parts of the body?
Head – Ventral posteromedial
Below the neck – Ventral posterolateral
Which nucleus is connected to the primary visual cortex?
Lateral geniculate nucleus
Which nucleus is connected to the primary auditory cortex?
Medial geniculate nucleus
The association cortex can be divided into three areas based on thalamic function. What are these three areas?
Prefrontal Cortex
Parieto-tempero-occipital Cortex
Cingulate Cortex
What do the anterior, lateral dorsal and dorsomedial nuclei connect with?
Prefrontal and Cingulate Cortex
What do the lateral posterior and pulvinar nucleus connect with?
Prefrontal and Parieto-tempero-occipital Cortex
What important system are the intralaminar and reticular nuclei a part of?
Reticular activating system – involved in maintaining consciousness
Describe intralaminar nuclei
Project to various medial temporal lobe structures (e.g. amygdala-emotion, hippocampus-memory and basal ganglia-movement) Mostly glutamergic (excitatory) Loss of neurons in this region associated with supranuclear palsy(problem walking and balance) and Parkinsons
Describe how the reticular nuclei affect cortical activity.
The reticular nuclei don’t have any direct connections with the cortex but they do have widespread intrathalamic connections with all other thalamic nuclei so it can influence the flow of information from the other nuclei to the cortex
What is the core of grey matter that runs through the brainstem and is involved in the reticular activating system?
Reticular formation
What forms outer covering of thalamus?
Reticular nucleus
What is the reticular formation?
Set of interconnected pathways in the brain stem, ascending projections to forebrain nuclei- aRAS
consciousness and arousal
Intralaminar and reticular nucleus receives input from aRAS
How do the intralaminar nuclei modulate the activity of the cortex?
The reticular formation projects up to the thalamus to the intralaminar nuclei and the intralaminar nuclei, because of their diffuse cortical projections, can modulate the activity of the cortex
What is thalamic syndrome?
NOT IN PP
Syndrome that develops after thalamic stroke
The symptoms depend on which part of the thalamus has been affected
What three main changes occur in thalamic syndrome? NOT IN PP
CHANGE IN SENSATION – reduced, exaggerated, altered
PAIN – central, non-localised (not easily treated because normal analgesics have no effect – may need to use opioids or anti-convulsants/anti-depressants)
EMOTIONAL DISTURBANCE – the nuclei that transmit information to and from the association cortex are associated with the limbic system
Describe the location and structure of the hypothalamus and its involvement in homeostasis
The hypothalamus is just below the thalamus and is divided by the 3rd ventricle
It also has ipsilateral connections with the forebrain
It coordinates these different mechanisms to maintain homeostasis:
• Autonomic nervous system
• Endocrine system
• Behaviour
State some forebrain structures that the hypothalamus has very close connections with
Olfactory system
Limbic system
List some structures of the limbic system.
Hippocampus
Amygdala
Cingulate Cortex
Septal Nuclei
What does the behavioural control exerted by the hypothalamus include?
4Fs
fight, flee, feeding, mating
Eating and drinking Expression of emotion Sexual behaviour Circadian rhythm Memory
Which nucleus is involved in the circadian rhythm?
SuPrachiasmatic nucleus
Discuss the paraventricular nucleus
Shape of a balloon just when you start blowing it, furthest away from optic chiasm
Sends projections to ANS and neurohypophysosis(magnocellular and parvocellular nuclei for oxytocin and ADH) and feeding behaviour
What are effects of lesions of SuPrachiasmatic nucleus
disturbance of sleep pattern
Hypothalamic tumour EARLY and LATE symptoms
EARLY
Polydipsia, polyuria, absent menses
LATE
labile motions, rage, inappropriate sexual behaviour, memory lapses, temp fluctuation, thyroid, adrenal cortex and gonadal function decrease, hyperphagia
How is our behaviour directed towards homeostatic goals?
There is a pleasure centre within the limbic system, which, whenever you’ve achieved homeostasis (e.g. eating food when you’re hungry), the activity of the pleasure centre increases
