Olfactory and limbic systems, basal ganglia, association and projection fibres Flashcards
What are the two main roles of the limbic system?
- role in learning
- role in regulation and translation of emotional state into appropriate behaviour
what system is the limbic system related to?
olfactory
what connects the limbic system?
Papez circuit
what structure was not in the original Papez cirucit?
amygdala
what areas are involved with the limbic system?
cingulate gyrus, hippocomapl formation, parahippocampal gyrus, anterior perforated substance, septal nuclei, uncus and amygdala
what is the cingulum bundle?
continuous bundle of fibres between cingulate gyrus and parahippocampal gyrus
what type of fibres is the cingulum bundle?
association fibres (connect cortical regions in same hemisphere)
what is an example of projection fibres thats found behind and above the corpus callosum?
internal capsule
what are projection fibres?
connect cortical and subcortical regions
what does olfactory tracts divide into?
medial olfactory striae and lateral olfactory striae
where does majority of lateral olfactory striae project to?
uncus (hook like structure at anterior end of parahippocampl gyrus)
where is primary olfactory cortex situated?
uncus
where do the rest of the projections from the lateral olfactory striae go?
hippocampus and orbito-frontal cortex by the thalamus
what is lateral olfactory striae important for?
initial perception and recognition of smells
where do medial olfactory striae project to?
- septal nuclei in hypothalamus
- olfactory sensors connected by the anterior commissure (allow for odorant gradients)
what is the largest bundle of association fibres?
superior longitudinal fasciculus
where is choroid plexus found?
- lateral ventricles (CSF production)
what sits in floor of lateral ventricles medially?
hippocampus
what is the caudate nucleus?
part of basal ganglia
- has head, body and tail following the curve of the lateral ventricles
what is the striae terminalis?
bundle of white fibres accompanying the curve of the caudate around into the temporal horn of the ventricle and connecting the amygdala with the septal nuclei and hypothalamus
where is the amygdala found?
tip of inferior horn of lateral ventricles
overlies the hippocampus
what are fimbria?
- efferent fibres form the hippocampus heading to the fornix forming a flattened longitudinal bundle of white matter
what are the basal ganglia important for?
control of movement
what is caudate attached to and whats its importance?
tail of caudate attached to amygdala
important for fear responses
role of hippocampus?
long term memories and emotional repsonses
which area of brain is most severely affected in AD?
hippocampus
what is the pes hippocampi?
anterior part of hippocampus with shallow grooves
- gives it appearance of paw/foot
what happens if there are lesions in limbic system?
- depends on location
- anterograde amnesia
- generation of emotions in absence of external stimuli
- inappropriate emotional responses
what is hyrocephalus?
- blockage of CSF flow in ventricles (eg. tumour) or subarachnoid space (eg. adhesions following meningitis or trauma)
- causes increase in pressure and ventricles swell
what are the signs and symptoms of hydrocephalus?
- increased intracranial pressure: headache, unsteadiness and mental impairment
what is treatment for hydrocephalus?
pressure relieved by insertion of a shunt connecting the ventricular system to the peritoneum or jugular vein
what makes up the basal ganglia?
Forebrain: caudate nucleus, putamen, globus pallidus
Diencephalon: Subthalamic nuceli
Midbrain: substantia nigra
what does fornix split and go down to form?
mammillary bodies
what is the lentiform nucleus?
putamen
globus pallidus
where is internal capsule located?
between striatum and thalamus
what is the layering of basal ganglia going laterally to medially?
extreme capsule -> claustrum -> external capsule -> lentiform nucleus (putamen, Gpe, Gpi)
what is putamen and globus pallidus separated by?
lateral medullary lamina
what separates the external and internal globus pallidus?
medial medullary lamina
what is corpus striatum made up of?
caudate and putamen
what is the claustrum?
strip of grey matter
- receives inputs from and projects to the cerebral cortex
- responds to visual, auditory and sensory stimuli
- function poorly understood
what is internal capsule?
- projection fibres carrying motor and sensory fibres to and from the cortex
what is the nucleus accumbens?
where caudate and putamen meet
what does nucleus accumbens do?
- reward centre
- dopaminergic input from VTA in midbrain
what does anterior limb of internal capsule separate?
caudate and putamen
what does posterior limb of internal capsule separate?
thalamus from putamen
what is forceps minor?
passes through genu of corpus callosum
what is foreceps major?
passes through splenium of corpus callosum
Symptoms of PD?
- cog-wheel rigidity
- pill-rolling tremor at rest (thumb and forefinger)
- shuffling, festinant gait (difficulty starting and stopping)
- bradykinesia (slowness of movement)
- loss of facial expressions
what causes PD?
- degeneration of DA neurons in substantia nigra pars compacta
- depletion of DA levels
what is HD?
- autosomal dominant ingerited genetic disorder
symptoms of HD?
- chorea (overshooting, unintentional movements)
- personality change
- depression
- progressive dementia due to degeneration of corpus striatum and cerebral cortex
what is lacunar stroke?
- most common type of ischaemic stroke
what causes lacunar stroke?
occlusion of small penetrating arteries that provide blood to deep structures of brain
what is a common site for lacunar stroke to occur?
lenticulostriate arteires (branch of middle cerebra arteries) that supply internal capsule
what can stroke affecting internal capsule cause?
- hemiparesis typically affecting half the face (ipsilateral) or one arm or leg (contralateral)
- ataxic hemiparesis (combo. cerebellar and motor symtpims) most commonly affecting the leg
- mixed sensorimotor stroke if the thalamus is also affeted
what is an example of a specific basal ganglia disorder?
PD
what makes up the Papez circuit?
Hippocampus -> fimbrie -> fornix -> mammillothalamic tract -> mamillary bodys -> projection fibres -> cingulate gyrus -> parahippocampal gyrus -> hippocampis
whats the role of the thalamus?
filter, relay, independent nuclei
role of basal ganglia?
- initiation and control of ongoing movement
- acquisition and expression phases of motor learning
- avolition (motivational outcomes/goal directed activity)
- repetitive, inflexible patterns of attention, emotion, planning and cognition
what makes up the basal ganglia?
putamen, caudate and globus pallidus
whats the role of the limbic system?
sexual and emotional aspects of behaviour, motivation and memory processing
what is cingulate gyrus important for?
- gives meaning to things
relevance of cingulate gyrus in surgery?
- can remove cingulate gyrus in surgery to help with pain (pathology here can cause increased pain as it is constantly being brought to consciousness)
what is reticular formation?
- diffuse nervous tissue in tegmentum and core of brainstem
