Olfactory and Limbic Systems Flashcards
What does the olfactory system include?
- epithelium in the nose
- nerves
- bulb
- tract
- cortex
Where are olfactory neurons located?
in the olfactory mucosa, restricted to the upper part of the nasal cavity
What does the olfactory epithelium contain?
olfactory neurons, supporting cells, and basal cells
What do basal cells do?
renew the bipolar neurons throughout life
Where do olfactory neurons in the olfactory epithelium send their axons?
through the cribriform plate to synapse on mitral cells in the olfactory bulb
What do axons of the olfactory neurons constitute?
the olfactory nerve (cranial nerve I)
What do axons of the mitral cells constitute?
the olfactory tract
What does the olfactory tract split into?
the medial and lateral olfactory striae
Where do the medial olfactory stria terminate?
- septal nuclei
- anterior perforated area
Where do the lateral olfactory stria terminate?
- cerebral cortex of uncus
- amygdala
What is involved in the interpretation of smell?
- septal nuclei
- anterior perforated area
- cortex of the uncus
What is the limbic system concerned with?
- feeding behaviour
- control of aggression
- emotion
- sexual arousal
- memory
How are structures in the limbic system arranged?
in a ring-like manner, between the diencephalon and the telencephalon
What are the 3 gyri associated with the limbic system?
- parahippocampal gyrus
- subcallosal gyrus
- cingulate gyrus
Give examples of nuclei in the limbic system
- hippocampal formation
- amygdala
- basal forebrain
- septal nuclei
What are many of the nuclei of the limbic system connected to and why?
the hypothalamus for regulation of body homeostasis and autonomic responses
What are the 4 components of the hippocampus formation?
- entorhinal cortex
- subiculum
- hippocampus proper
- dentate gyrus
What is the hippocampus formation made up of?
a special type of cerebral cortex rolled into the medial aspect of the temporal lobe
What is the hippocampus proper?
the actual structure of the hippocampus divided into CA fields 1-3
What are the principal cells of the hippocampus?
pyramidal neurons
What does the dentate gyrus contain?
dentate granule neurons formed throughout life via neurogenesis
What do the dendrites of both granule and pyramidal cells contain?
large numbers of dendritic spines
What does the hippocampal formation receive input from?
other association areas of the cortex via the entorhinal cortex
Describe the hippocampal trisynaptic circuit
- entorhinal cortex projects to dentate granule neurons (perforant path)
- dentate granule neurons project to pyramidal neurons in CA3 (mossy fibres)
- CA3 pyramidal neurons project to CA1 pyramidal neurons (Shaffer collaterals)
What is LTP?
the cellular substrate for learning and memory dependent on calcium entry via the NMDA glutamate receptor
What do CA1 pyramidal neurons project to?
the subiculum which projects to the entorhinal cortex which in turn projects to other association areas of the cortex
Where do axons sent from the hippocampus that form the fornix terminate?
in the mammillary bodies of the hypothalamus
What is the hippocampus essential for?
explicit/declarative memory
What does bilateral damage or removal of both hippocampi cause?
anterograde amnesia
What is anterograde amnesia?
the absence of conscious recall of newly acquired information for more than a few minutes
How can the hippocampus be damaged?
global ischemia, AD and epilepsy
How can dentate gyrus neurogenesis be decreased?
stress and depression
How can dentate gyrus neurogenesis be increased?
- maternal choline intake (eggs and beef liver)
- enriched environment
- physical exercise
- antidepressant drugs
Where is the amygdala located?
in the anterior part of the temporal lobe
What inputs does the lateral nucleus of the amygdala receive?
olfactory, visual, auditory, tactile and visceral
Where does the central nucleus of the amygdala project?
- hypothalamus
- brainstem
What do central nuclei of the amygdala projecting to the brainstem do?
activate neurons that influence respiratory rate and autonomic activity to facilitate defensive/evasive activity
What is the amygdala concerned with?
mood and emotion; it interprets and recalls emotional content of visual inputs and events
What are autonomic responses of the amygdala?
heart rate, respiration, blood pressure, and gastric motility
What does removal of the amygdala in monkeys and rats cause?
a greatly increased sexual drive
What does damage to the amygdala result in?
- loss of fear and aggression
- hyperorality (excessive attention to stimuli with oral tendencies)
- hypersexuality
What is the basal forebrain?
the grey matter in and around the anterior perforated substance
What are the cholinergic nuclei of the basal forebrain?
- nucleus basalis of Meynert, which projects to all parts of the neocortex
- septal nucleus, which projects to the hippocampus
What does the cholinergic supply from the nucleus basalis in the neocortex contribute to?
the awake pattern on EEG recordings since it is tonically active
What are drugs used to treat AD?
acetylcholine esterase inhibitors that prolong the effect of ACh
Where are septal nuclei located?
next to the septum pellucidum, separating the lateral ventricles
What do septal nuclei receive afferents from?
- medial olfactory stria
- hippocampus
- amygdala
- brainstem monoaminergic neurons
What do septal nuclei send efferents to?
- the habenular nucleus to affect the sleep-wake cycle
- hippocampus via the septo-hippocampal pathway
What do the septal nuclei affect?
rhythm in the hippocampus, which is important for formation of memories
What does lesion of the septal nuclei in animals produce?
signs of extreme displeasure
What does electrical stimulation of the human septal area produce?
sexual sensations similar to orgasm
