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L14 Olfactory system and limbic system
Terms in this set (29)
What is the olfactory system for in animals?
how is the human's different from animals?
A developed system of smell
- for many animals such as amphibians, birds and dogs
closely connected to drive to
- locate food
- distinguish friend from foe
- attract opp sex
Humans rely on smell much less
- the pathways related to the olfactory system remains, and probably the most complex of the nervous system
What does the olfactory system comprise of?
- olfactory epithelium in nose
- olfactory nerves
- olfactory bulb
- olfactory tract
- olfactory cortex
Describe the location of the olfactory neurons
- what is signifiant about this?
- how is it different about it's location as compared to other neurons?
olfactory neurons are in the olfactory mucosa
- only at the upper part of the nasal cavity
- only this part is sensitive to smell
different from other neurons because
- the entire neuron itself is located in the mucosa
- other neurons have the neuron in the dorsal root ganglion and have processes coming out
What are the different components of the olfactory epithelium?
what does this allow the olfactory epithelium to do?
olfactory epithelium contain
- olfactory neurons
- supporting cells
- basal cells
(basal cells are like stem cells)
- they renew the bipolar neurons throughout life
Describe the pathway of the olfactory system
-> olfactory neurons in olfactory epithelium
-> send their axons through Cribriform plate (skull bone)
-> synapse with mitral cells in olfactory bulb (part of CNS)
-> axons of mitral cells constitute the olfactory tract (cranial nerve I)
-> olfactory tract travles posteriorly
-> divides into medial and lateral olfactory striae
medial olfactory striae terminates
-> Septal nuclei
-> anterior perforated area
lateral olfactory striae
-> cerebral cortex of uncus
What is the function of the olfactory system?
which part control the functions?
what can it lead to?
Interpretation of smell by
- Septal nuclei
- anterior perforated area
- cerebral cortex of uncus
smell can lead to
- trigger memories
- emotion and related reflexes
e.g smell of perfume -> sexual arousal
e.g odors elicit long-forgotten memories
How is the sense of smell tested?
Tested separately in each nostril
Close one nostril and then successively pass vials
containing various substances, such as pine oil,
coffee, and perfume. Ask the patient whether he
smells the substance and can identify it.
What are olfactory ensheathing cells?
why is it significant
who are they used for?
A group of cells of the olfactory system
- can continually regenerate
olfactory system is part of CNS
- but yet can regenerate
- paralytic patients
What is the olfactory system closely linked to?
what are the functions of this system? (For Christ Sake Manage)
concerned with emotions and autonomic response
- Feeding behaviour
- control of aggression
- sexual arousal
Where does the limbic system comprise of?
where are they generally located?
Limbic system includes the parahippocampal gyrus, subcallosal gyrus, and cingulate gyrus and
- Septal nuclei
- hippocampus formation
- Basal forebrain
generally arranged in ring like manner
- between diencephalon and telencephalon
What are most of the nuclei of limbic system connected to
What is it for?
give one example
2 ways/ tracts in which it controls it
Most nuclei of limbic system connected to
- regulation of body homeostasis
- autonomic response
- rat smell cat -> limbic system -> hypothalamus -> autonomic system -> sympathetic pathway -> flight or flight (heart rate increase)
2 ways ways that hypothalamus control
-> hormonal tract
(release hormones via pituitary gland)
-> Neuronal tract
(hypothalamus connected to motor neuron and reticular formation of brainstem via Dorsal longitudinal fasciculus)
What does the hippocampus comprise of?
where is it located?
- entorhinal cortex
- Hippocampus proper
- dentate gyrus
located and rolled into the
- medial aspect of temporal lobe
Describe more of the hippocampus
- what is special about the cerebral cortex that makes it up
- how is it split up?
- what is the main type of cell? (what other cells)
- what is the main thing that it contains? (what is it able to do?)
- Cerebral cortex is 3 layers rather then normal 6
split up into cornu ammonia (CA) fields
- CA1, CA2, CA3
- pyramidal neurons (excitatory)
- inhibitory neurons (GABA)
- dentate gyrus which contains dentate neurons
- able to have neurogenesis throughout life
Describe the trisynaptic circuit through the hippocampus
(afferent and efferent connection to hippocampus)
Other association area of cortex send input
-> entorhinal cortex
-> [performant path] -> dentate granule neurons
-> [Mossy fibers] -> CA3 Pyramidal neurons
-> [Shaffer collaterals] -> CA1 pyramidal neurons
-> entohinal cortex
-> back to association areas of cortex
What is the trisynaptic circuit for?
What is one common reason for damage to this
which part of the pathway is used to study long term potentiation
- formation of new memories
Common damage by
- Alzheimer's disease
Shaffer collaterals from CA3 to CA1
- use electrodes to study long term potentiation
What is long term potentiation
how does it occur
Persistent increase in synaptic strength due to stimulation
(this is the cellular substrate for learning and memory)
- dependent on Ca2+ entry via NMDA glutamate receptors
NMDA receptors allow more CA2+ to enter neuron
-> CA2+ kinase
-> activity of AMPA glutamate receptor
-> LTP due to more physical contacts between axons and dendrites
What is another pathway for hippocampus?
-> large bundle of axons (Fornix)
-> terminates in maxillary bodies of hypothalamus
What is the function of the hippocampus?
what is the effect of damage of hippocampus?
what can cause it?
for consolidation of short term memory -> long term memory
for explicit/ declarative memory
Bilateral damage or removal of both hippocampi leads to
- anterograde amnesia
- cannot remember anything from lesion till now
(only remember remote past and immediate present)
- no emotional strain since problem cannot be recognised by patient (but more and more confused)
- Alzheimer's disease
- global ischemia
Where is adult neurogenesis?
What can increase and decrease it?
Dentate gyrus -> dentate granule neurons
dentate grus neurogenesis affected by
Where is the amygdala located?
Anterior part of temporal lobe
What are the inputs/ afferent connections to the amygdala
Describe the pathway
what are the physiological effects of its stimulation
Lateral nucleus of amygdala receives
- olfactory input
- visual input
- auditory input
- tactile input
- Visceral input
- central nucleus projects to hypothalamus and
- brainstem (respiratory rate and autonomic rate for defensive/ evasive activity)
What is the function of amygdala?
Mood and emotion
- interpret and recall emotion content
(especially fear and stress)
e.g even unlearning of fear e.g dogs do not bite
- heart rate
- blood pressure
- gastric motility
What happens when amygdala is removed for
- monkey and humans
- and cats
Monkey and humans
- docile animal, somnolent
- aggressive behaviour in unprovoked situations (sham rage)
what happens when amygdala is damaged for
- monkeys and rats
Monkey and rates
- increased sexual drive
- Kluver-Bucy syndrome
-> loss of fear and aggression
-> hyperorality (excessive attention to stimuli with oral tendencies)
-> hyper sexuality
What is the basal forebrain made up of?
where is it?
pathway and what neurotransmitters it uses
Made up of
- gray matter
- nucleus basalis of Meynert
- Septal nucleus
where is it
- around anterior perforated substance
- nucleus basalis of Meynert -> all parts of neocortex
- septal nucleus -> projects to hippocampus
(cholinergic - uses acetylcholine)
how does Alzheimer disease affect basal forebrain? and what does drugs for it do?
Alzheimer's disease destroy half the neurons of
- nucleus of basalis of Meynert
- Septal nuclei
- they are acetylcholine esterase inhibitors
- prolong the effect of acetylcholine
describe the location of septal nuclei
Located next to septum pellucidium
separating the lateral ventricles
Describe the pathway of the septal nuclei
- input from
- projection to
recieve input from
- Medial olfactory stria
- brainstem monoaminergic neurons
- habenular nucleus (affect sleep-wake cycle)
- [septohippocampal pathway] to hippocampus
what are the effects or function of septal nuclei
effect of damage
effect of stimulation
- affect sleep wake cycle
- theta rhythm in hippocampus (for formation of memories)
effect of damage
- signs of extreme displeasure
effects of stimulation
- sexual sensation similar to orgasm
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