NMH; Lecture 15, 16, 17 and 18 - Olfaction and the limbic system, Introduction to conciousness, Sleep, Development of Nervous System Flashcards
What is the size of the olfactory system?
2000-4000 different odours
What is the olfactory epithelium made up of?
Bipolar olfactory neurons, sustentacular cells (supporting neural cells), basal cells (help generate turnover cells) -> progressive loss with age
How does the smell move down into the olfactory tract?
Olfactory receptor cells project through the cribriform plate into the secondary order olfactory neuron then forming the olfactory tract
How does the smell continue from the olfactory bulb to the cortex?
Olfactory bulb -> tract -> stria -> piriform and orbitofrontal cortex
What is special about smell and the brainstem?
Connections to brainstem promote autonomic responses
What is a clinical deficit in smell called?
Anosmia
What occurs in some epileptic patients in smell?
Some can smell the increase in electrical activity so know when a fit is about to come one -> prodromal auras
What degenerative diseases can have anosmia as a symptom?
In parkinson’s and alzheimer’s
What is the limbic system?
Structurally and functionally interrelated areas considered as a single functional complex -> rim or limbus of cortex adjacent to corpus callosum and diencephalon
What is the function of the limbic system?
System responsible for processes aimed at survival of individual -> maintenance of homeostasis via activation of visceral effector mechanisms, modulation of pit hormone release and initiation of feeding and drinking; agonistic behaviour; sexual and reproductive behaviour; memory
What are the features of the limbic system?
Hippocampus -> memory function; hypothalamus affects the system according to previous memories of situations; amygdala is
What is the Papez circuit?
Specifically projects to mamillary bodies from fornix; (MTT=mamillothalamic tract); cingulate cortex lies above corpus callosum; cingulum bundle runs on the top of the corpus callosum. Emotional colouring is the previous emotional experience, emotional experience is current emotion and emotional expression is how the emotion comes out
What are the main connections of the hippocampus?
Afferent: Perforant pathway. Efferent: Fimbria still attached to hippocampus)/fornix (not attached)
What is the function of the hippocampus?
Memory & learning (every experience ever passes through and here is where the experience is encoded); short term memory and memory recall
In which clinical situations is the hippocampus relevant?
Alzheimer’s disease, epilepsy
What are the main features of the hippocampus?
Enterinal cortex (receives input from every other part of the cortex), fimbria and perforant path
What is cortical atrophy?
General atrophy, can be seen in the size of the ventricles and the hippocampus (R is alzheimer’s patient)
What happens to Tau protein in alzheimer’s?
It is hyperphosphorylated which causes the membrane to rupture which causes the neuron to die
What are senile plaques made from?
Present in hippocampus and Alzheimer’s -> extracellular deposits of amyloid beta in the grey matter of the brain
What is the anatomical progression of Alzheimer’s disease?
Early: Hippocampus and entorhinal cortex so short term memory problems but long term memory is good; Moderate: parietal lobe (store procedural memories) and dressing apraxia; Late: Frontal lobe and loss of executive skills/reasoned decisions, forget people/loss of cognitive function
What are the main connections of the Amygdala?
Afferent: olfactory cortex, septum, temporal neocortex, hippocampus, brainstem. Efferent: stria terminalis (hypothalamus)
What is the function of the amygdala?
Fear/Anxiety/Rage/Aggression, so fight or flight
What is Kluver-Bucy syndrome?
Post trauma, after temporal has been bashed causing bilateral amygdala damage; symptoms are: hypersexuality, disinhibition, visual agnosia, loss of fear and hyperorality (explore things using their mouth)
Where is the amygdala located?
x
What structures are associated with aggression?
Hypothalamus, brainstem (periaqueductal grey), amygdala, 5-HT in raphe nuclei
What are the main connections of the septum?
Afferent: amygdala, olfactory tract, hippocampus, brainstem. Efferent: stria medularis thalami, hippocampus, hypothalamus
What is the function of the septum?
Reinforcement and reward
What is the mesolimbic pathway (DA)?
When the pathway is from the midbrain to the nucleus accumbens DA release and stimulation of neurons in area and reward feeling
Which drugs increase release in DA in nucleus accumbens?
Opioids, nicotine, amphetamines, ethanol and cocaine -> stimulate midbrain neurones, promoting DA release or inhibit DA reuptake
What is consciousness?
Brain state that enables us to experience the world around us and within oneself -> distinct from automatic behaviours that occur in a rather unconscious manner -> NOT equal to being alert or attentive
What are the behavioural criteria for sleep?
Stereotypic/species specific psoture, minimal movement, reduce responsiveness to external stimuli, reversible with stimulation unlike coma, anaesthesia or death