Neurology 19 - Limbic System Flashcards
List the qualities of the olfactory system
- 2000-4000 different odours
- Molecular mechanism largely unknown
- Olfactory epithelium includes bipolar olfactory neurons, sustentacular cells, basal cells
- Progressive loss with age
List the components of the olfactory system
- Olfactory bulb (mitral cells)
- Olfactory tract
- Olfactory stria
- Piriform (medial temporal lobe) and orbitofrontal cortex (frontal cortex, next to the orbit)
- Connections to brainstem
What happens to the nose in Parkinsons?
- Loss of smell is an early indication of parkinson’s and Alzheimer’s
- Patients with parkinsons have abnormal protein accumulation in the olfactory bulb
What is the limbic system?
- Rim or limbus of the cortex adjacent to the corpus callosum and diencephalon
- Structurally and functionally interrelated areas, considered as a single functional complex
List the functions of the limbic system
Responsible for processes aimed at survival of the individual
- Maintenance of homeostasis via activation of visceral effector mechanisms
- Modulation of pituitary hormone release
- Initiation of feeding and drinking
- Agnostic behavious
- Sexual and reproductive behaviour
- Memory
List the components of the limbic system
- Frontal lobe
- Thalamus
- Hippocampus (floor of the inferior horn of the lateral ventricle in the temoral lobe)
- Amygdala (anterior to hippocampus in the white matter of the temporal lobe)
- Hypothalamus
- Olfactory bulb
Describe the Papez circuit
- Hippocampus main output pathway is the fornix, which goes forward and down to terminate in the mamillary bodies of the hypothalamus
- Mamillary bodies have a mamillothalamic tract, which project to the anterior nucleus of thalamus
- Thalamus projects to the cingulate cortex
- The cingulate cortex then projects to the hippocampus by the cingulum bundle
- The neocortex inputs to the cingulate cortex (emotional colouring - how does this relate to what has happened before)
- The emotional expression is mainly performed by the hypothalamus
List the main connections of the hippocampus
- Afferent: perforant pathway
- Efferent: fimbria (called this when still physically attached to the hippocampus)/fornix (called this when it breaks off from the hippocampus)
List the functions of the hippocampus
Memory and learning
List the clinical diseases that occur when hippocampus function is impaired
- Alzheimers disease
- Epilepsy
What is seen in the brain in Alzheimers?
- Cortical atrophy and enlargement of the ventricles
- Plaques
- Tangles
List the stages of anatomical progression of Alzheimers
Early
- Hippocampus and entorhinal cortex
- Short term memory problems
Moderate
- Parietal lobe
- Dressing apraxia
Late
- Frontal lobe
- Loss of executive skills
List the connections of the amygdala
Afferent:
- Olfactory cortex
- Septum
- Temporal neocortex
- Hippocampus
- Brainstem
Efferent: Stria terminalis
List the functions of the amygdala
- Fear and anxiety
- Fight or flight
Give an example of a disease caused by loss of function of the amygdala
Kluver-Bucy syndrome
What is Kluver-Bucy syndrome?
- Seen in monkeys with bilateral temporal lobectomy, clinically traumatic damage to both of the temporal lobes
- Symptoms include hyperorality, loss of fear, visual agnosia, and hypersexiality
List the structures associated with aggression
- Hypothalamus
- Brainstem (periaqueductal grey)
- Amygdala
- 5-HT in raphe nuclei
List the main connections of the septal nuclei
Afferent:
- Amygdala
- Olfactory tract
- Hippocampus
- Brainstem
Efferent
- Stria medularis thalami
- Hippocampus
- Hypothalamus
List the functions of the septal nuclei
Reinforcement and reward
What occurs in drug dependence?
- Mesolimbic pathway (dopamine)
- Opiods, nicotine, amphetamines, ethanol and cocaine all increase dopamine release in the nucleus accumbens
- Stimulate midbrain neurons, promotes dopamine release or inhibits reuptake
[- Modified by other neurotransmitters]
What is the name of the clinical deficit of the olfactory system?
Anosmia
What are prodromal auras?
- Some people with epilepsy will know they are going to have a seizure when they smell a distinctive smell
- Prodromal aural - temporal lobe
What is the septum?
The membrane lining the anterior horns of the lateral ventricles in the midline
What is the septal nuclei related to?
- Nucleus accumbens
- Involved in the mesolimbic pathway
Describe the mesolimbic pathway
- Dopaminergic - origionates in the midbrain ventral tegmental area
- Up to the nucleus accumbens, cortex and amygdala
What is a risk in dopamine treatments?
- Obsessive compulsive behaviours
- Eg. obsessive gambling
