olfaction and the limbic system

Question 1

describe the anatomy of the olfactory system *

Answer 1

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

Question 2

describe human’s ability to smell *

Answer 2

ability decreases with age

relatively bad at it

detect 2000-4000 different odours

chemical basis of differentiation of smell is largely unknown

Question 3

describe the path of neurons from the olfactory bulb *

Answer 3

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

Question 4

what is clinical deficit of olfaction called and what are potential causes *

Answer 4

anosmia

alzheimers and parkinsons

midface trauma - shear off the olfactory epi

Question 5

what are prodromal auras *

Answer 5

when people with epilepsy get a warning smell

if the epilepsy is based in the temporal cortex around the piriform cortex

Question 6

what is different about the brain in parkinson’s that affects olfaction*

Answer 6

there is an abnormal accumalation of proteins

Question 7

what is the limbic system*

Answer 7

rim of cortex adjacent to corpus callosum and diencephalon - structurally and functionally related areas considered as a single functional complex

Question 8

what are the roles of the limbic system *

Answer 8

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

Question 9

what is the anatomy of structures involved in the limbic system *

Answer 9

hippocampus - floor of inferior horn of the lateral ventricle in temporal lobe

amygdala is anterior to the hippocampus

Question 10

why is diffusion tensor imaging good for assessing the limbic system

Answer 10

the issues are to do with functional connectivity =- there are no visual changes to the structure

Question 11

describe the papex ciruit *

Answer 11

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

Question 12

what are the main connections to the hippocampus *

Answer 12

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

Question 13

what lobe is teh hippocampus in *

Answer 13

the medial temporal lobe

Question 14

what are the functions of the hippocampus*

Answer 14

memory and learning

Question 15

what clinical conditions involve the hippocampus *

Answer 15

alzhheimer’s disease

epilepsy

Question 16

diagram of the location of the hippocampus *

Answer 16

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Question 17

what type of neuronal tissue is the amygdala in *

Answer 17

white matter

Question 18

describe the hippocampal circuitary*

Answer 18

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

Question 19

describe alzheimer’s and the brain*

Answer 19

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

Question 20

describe te anatomical progression of alzheimer’s and the effect at each stage *

Answer 20

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

Question 21

what are the main connections of teh amygdala *

Answer 21

afferent - olfactory cortex (eg when there is a gas leak), septum, temporal neocortex, hippocampus, brainstem

efferent - stria terminalis to anterior hypothalamus

Question 22

what are the functions of the anygdala *

Answer 22

fear and anxiety centre

fight and flight

Question 23

what clinical condition involves the amydala- describe it 8

Answer 23

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)

Question 24

describe the anatomy of the amydala *

Answer 24

grey matter nucleus in white matter of the temporal lobe

in front of the lateral ventricles

different nuclei have different suseptibility to neurodegeneration

Question 25

what structures in the brain are involved in aggression *

Answer 25

hypothalamus

brainstem (periaqueductal grey - grey matter around teh aqueduct)

amygdala

5HT (serotonin NT) in raphe nucleus - in brainstem down the midline

Question 26

what is the part of the brain involved in reinforcement and reward *

Answer 26

septal nuclei - below the lateral ventricles

the septal membrane is between the lateral ventricles anteriorly

Question 27

what are the main connections with the septal nuclei *

Answer 27

afferent - amygdala, olfactory tract, hippocampus and the brain stem

efferent - stria medularis thalami, hippocampus, hypothalamus

Question 28

what can you clinically use the septal nuclei for *

Answer 28

stimulation gives good feeling - maybe stimulate in chronic depressives not been trials yet

treat tremor with electrodes in the subthalamic nucleus

Question 29

desribe the dopaminergic pathway *

Answer 29

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

Question 30

describe drug dependance and the dopaminergic pathway *

Answer 30

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

Question 31

how can you use dopamine in parkinson’s

Answer 31

give dopamine - quell motor problem

but becomes ineffective so give dopamine agonist

se - stimuate nucleus accumbens = obsessive compulsive disorder

Question 32

pictures of different parts of the limbic system *

Answer 32

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