olfaction and the limbic system Flashcards
describe the anatomy of the olfactory system *
olfactory bulb is very small
have the olfactory epithelium - within this have the bipolar olfactory neurons which have the receptive component externally, then cell body, then project throug cribiform plate in the etmoid bone to reach the olfactory bulb - here synapse with mitral cells in glomerular organisation - 2nd order neurons go to brain via olfactory tract
in the epi also have substentacular cells - support cells and basal cells that give potential for turnover of olfactiry neurons
describe human’s ability to smell *
ability decreases with age
relatively bad at it
detect 2000-4000 different odours
chemical basis of differentiation of smell is largely unknown
describe the path of neurons from the olfactory bulb *
mitral cells in olfactory bulb go to brain via olfactory tract
this spilts into olfactory stria which goes to piriform and orbitofrontal cortex
connections to brainstem promote the autonomic response eg salvation when smell cooking
what is clinical deficit of olfaction called and what are potential causes *
anosmia
alzheimers and parkinsons
midface trauma - shear off the olfactory epi
what are prodromal auras *
when people with epilepsy get a warning smell
if the epilepsy is based in the temporal cortex around the piriform cortex
what is different about the brain in parkinson’s that affects olfaction*
there is an abnormal accumalation of proteins
what is the limbic system*
rim of cortex adjacent to corpus callosum and diencephalon - structurally and functionally related areas considered as a single functional complex
what are the roles of the limbic system *
it is responsible for processes aimed at survival of the individual:
maintain homeostasis via activation of visceral effector mecanisms, modification of pit ormone release and initiation of feeding and drinking
agonistic behaviour - fight and flight
sexual and reproductiv behaviour
memory - perception of world coloured by previous experience
what is the anatomy of structures involved in the limbic system *
hippocampus - floor of inferior horn of the lateral ventricle in temporal lobe
amygdala is anterior to the hippocampus
why is diffusion tensor imaging good for assessing the limbic system
the issues are to do with functional connectivity =- there are no visual changes to the structure
describe the papex ciruit *
the main output pathway from the hippocampus is the fornix - goes forward and down and terminantes in the mamillary body of the hypothalamus
then the mammilothalamic tract projects from the mamillary body to the anterior nucleus of the thalamus
projections from the thalamus go to the cingulate cortex which is above the corpus callosum
longitudinal fibres called the cingulum bundle project to the hippocampus
all cortical areas feed into this circuit
have emotional experience - interaction with the environment and lay down memory - this has emotional colouring from other areas of the cortex
this forms an emotional expression - reaction to outside world is largely hypothalamic
what are the main connections to the hippocampus *
afferent - perforant pathway from the entorhinal cortex (every part of the cortex has connections to the enterhinal cortex)
efferent - finbria/fornix - fimbria when physically attached to the hippocampus
what lobe is teh hippocampus in *
the medial temporal lobe
what are the functions of the hippocampus*
memory and learning
what clinical conditions involve the hippocampus *
alzhheimer’s disease
epilepsy
diagram of the location of the hippocampus *
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what type of neuronal tissue is the amygdala in *
white matter
describe the hippocampal circuitary*
has 2 interlocking Cs - dentate gyrus and major pyramidal cells
inputs from all cortical areas go into the enterhinal cortex
the perforent pathway leads to different subfields of the hippocampus
describe alzheimer’s and the brain*
enlargement of the ventricles
atrophy of the hippocampus
pathology begin in the transenterhinal cortex - defect in tau (microtubule associated protein) = neuronal cytoskeleton is disrupted = tangles
there are plaques
describe te anatomical progression of alzheimer’s and the effect at each stage *
early - hippocampus and enterhinal cortex affected - sshorrt term mem problems
moderate - parietal lobe = disorientation and dressing ataxia
late = frontal lobe = loss of executive skills - personality change and loss of decision making
what are the main connections of teh amygdala *
afferent - olfactory cortex (eg when there is a gas leak), septum, temporal neocortex, hippocampus, brainstem
efferent - stria terminalis to anterior hypothalamus
what are the functions of the anygdala *
fear and anxiety centre
fight and flight
what clinical condition involves the amydala- describe it 8
kluver-bucy syndrome
caused by bilateral damage to the anterior temporal lobe eg in trauma
have more basic view of world - loss of fear and hightened orality - put things in mouth, hypersexuality, visual agnosia (impairment in recognition)
describe the anatomy of the amydala *
grey matter nucleus in white matter of the temporal lobe
in front of the lateral ventricles
different nuclei have different suseptibility to neurodegeneration
what structures in the brain are involved in aggression *
hypothalamus
brainstem (periaqueductal grey - grey matter around teh aqueduct)
amygdala
5HT (serotonin NT) in raphe nucleus - in brainstem down the midline
what is the part of the brain involved in reinforcement and reward *
septal nuclei - below the lateral ventricles
the septal membrane is between the lateral ventricles anteriorly
what are the main connections with the septal nuclei *
afferent - amygdala, olfactory tract, hippocampus and the brain stem
efferent - stria medularis thalami, hippocampus, hypothalamus
what can you clinically use the septal nuclei for *
stimulation gives good feeling - maybe stimulate in chronic depressives not been trials yet
treat tremor with electrodes in the subthalamic nucleus
desribe the dopaminergic pathway *
it is the mesolimbic pathway
originates in the ventral tegmental nucleus in the midbrain (A10) goes via the median forebrain bundle to the cortex, nucleus accumbens, amygdala
describe drug dependance and the dopaminergic pathway *
opiods, nicotine, amphetamines, ethanol, and cocaine increase dopamine release in nucleus accumbens
the drugs stimulate the dopaminergic midbrain neurons and promote dopamine release or inhibit uptake (cocaine inhibits uptake)
other neurotransmitters are involved
how can you use dopamine in parkinson’s
give dopamine - quell motor problem
but becomes ineffective so give dopamine agonist
se - stimuate nucleus accumbens = obsessive compulsive disorder
pictures of different parts of the limbic system *
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