Thalamas Flashcards
what composes the diencephalon *
thalamus subthalamus hypothalamus
describe the subthalamus nucleus *
target for deep brain stimulation for Parkinson’s electrode placed in the nucleus and when turned on the tremor stops
describe the location of the thalamus *
either side of the midline, towards the back of he brain it is beneath the lateral ventricles thalamus is divided down the midline by the 3rd ventricle very closely associated with the midbrain above the substantia nigra encapsulated by the corticospinal tract
describe the thalamic organisation *
it is organised into discrete nuclei
overall function of the thalamus *
relay site for numerous inputs/outputs between cortex and other parts of CNS key relay centre to cortical sensory areas involved in most sensory systems - except olfactory modulates signals - either restrict or enhance signal depending on part of the thalamus
describe the somatosensory pathway *
vibration, proprioception, light touch sensory neurons have cell bodies in the dorsal root ganglion which is near the spinal cord (it is in the CNS) the neurons go into the dorsal horn and then up the dorsal columns to the gracile nucleus here it synapses and the secondary sensory neuron goes across the sensory decussation to the other side of the spinal cord it then travels to, and synapses in, the thalamic ventral posterior lateral nucleus where all the sensory info is processed the tertiary sensory neuron goes to the primary somatosensory cortex
where is the primary somatosensory cortex *
in post ccentral gyrus behind the central sulcus in the parietal lobe
where are the intralaminar nuclei *
in the lamina [image]
describe the intralaminar nuclei *
they project to various medial temporal lobe structures eg the hippocampus, amygdala and basal ganglia involved in the limbic system for emotion eg amygdala - emotions, fear anxiety - lots of connections here so the pathways can be neurodegenerative ? hippocampus - short term memory basal ganglia - movement and control of initiation of movement mostly glutaminwergic neurons so excitatory
describe the location of the hhippocampus and amygdala *
in medial temporal lobe hippocampus line floor of ventricle amygdala is in the anterior part of the temporal lobe ? [image]
effect of loss of neurons in the intralaminar nuclei region *
motor disorders eg parkinsons and progressive supranuclear palsy which is a rare brain disorder causing problems with walking and balance
describe the reticular nucleus *
forms the outercovering of the thalamus - connect with other thalamic nuclei rather than distally, ie involved in local circuitry they receive inputs from collateral of their axons from the thalamic nuclei. therefore they are involved in internal regulation and modulation of the thalamus providing a -ve feedback loop majority of neurons are GABAergic - inhibitory
describe the reticular formation *
it is a set of interconnected pathways in the brain that have an ambiguous function. It sends ascending projections to the forebrain nuclei (intralaminar and reticular) this is the ascending reticular activating system which is involved in consciousness and arousal - increased activity of the ARAS means more wakefulness
how are the intralaminar, reticular nuclei and reticular formation related *
all together they form the reticular activating system
describe the position of the hypothalamus
it forms the wall and the floor of the 3rd ventricle - 3rd ventricle divides the hypothalamus into 2 its nuclei go up to the level of the thalamus it is directly connected to the pit gland
what is the function of the hypothalamus *
it is a collection of nuclei with distinct functions
largely has ipsilateral connections with other nuclei
controls behaviour via connection with forebrain structures
involved in the 4 Fs: fighting, fleeing, feeding and mating
fight and flight are part of the limbic system
it has neuroendocrine functions - hypothalamic pituitary axis
it has direct connections with the ANS
circadian rhythms
memory
expression of emotion
describe the hypothalamic connections with the ANS *
it controls the ANS response to the outside world neurons in the hypothalamic parvoventricular nucleus have direct projections to pre-autonomic neurons in the spinal cord
describe how the hypothalamus controls feeding *
hypothalamic peptides eg leptin control appetite GLP1 acts on hypothalamic nucleus and supresses appetite - inhibitory neurons the paraventricular nucleus is also involved in feeding - if there are lesions here the inhibitory neurons are lost causing hyperphagia and weight gain. It also receives input from hypothalamic nuclei involved in feeding the arcuate nucleus is involved in it too optogenetic stimulation of the GABAergic neuron terminals in PVN causes feeding.
describe the organisation of the thalamus *
it is a collection of individual nuclei with separate functions and connections with forebrain structures
describe how the hypothalamus controls ANS *
the paraventricular nucleus has parvocellular nuclei in it that send projections into the spinal cord, which then send projections out to the ANS `
describe how the hypothalamus links to the endocrine system *
in the paraventricular nucleus the magnocellular neurons send projections to the posterior pituitary
describe the suprachiasmatic nucleus *
it is involved in the circadian rhythms - the sleep-wake cycles it connects to the paraventricular nucleus which controls ANS also connects to and innervates the pineal gland which sits on the roof of the brain secreting melatonin also links to the reticular formation and is involved in arousal. Therefore it affects mood and behaviour - ANS, melatonin and arousal.
effect of lesions in the suprachiasmatic nucleus *
disrupt the sleep wake cycle - sonogram can map the sleep activity this is the basis of sleep disturbance - hypofunction
describe how Parkinson’s can affect the sleep wake cycle *
it spreads through the brain and affects the reticular activating system this causes REM based sleep behaviour disorder (RBD) affecting the sleep cycle 80% of people with RBD go on to get Parkinsons
what are specific nuclei in the thalamus *
they have reciprocal innervations with a primary cortical area ie they have a clearly defined function
what are the association nuclei in the thalamus *
they have more diffuse reciprocal functions with the association nuclei The anterior, lateral dorsal and dorsomedial nuclei connect with parts of the limbic system The lateral posterior and pulvinar nuclei connect with the association cortex at the junction of the parietal, temporal and occipital lobes and the prefrontal cortex.
what structures are the hypothalamic nuclei associated with
olfactory system
limbic system - hippocampus, amygdala, cingulate cortex, spetal nucleu
behaviour directed to the reward system and well being triggers
