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
What is the physiological criteria for sleep?
x
What are the stages of sleep?
x
How does a single sleep cycle appear?
x
How many sleep cycles occur during a night’s sleep?
x
How do we maintain consciousness?
Reticular activating system controls it -> with the lateral hypothalamus promoting wakefulness and ventrolateral preoptic nucleus promoting sleep
What controls the synchronisation of sleep/wake cycle?
Suprachiasmatic nucleus synchronises sleep with falling light level
Is seep necessary?
Most/all animals sleep as sleep deprivation is detrimental and sleep is regulated accurately
What are the effects of sleep deprivation?
Sleepiness, irritability, performance decrements/increased risk of errors and accidents, concentration/learning difficulties, glucose intolerance, reduced leptin/increased appetite, hallucinations (after long sleep deprivation), death (rats in 14-40d; humans with fatal familial insomnia)
How is sleep regulated after sleep loss?
Reduced latency to sleep onset, increase of slow wave sleep (NREM), increase of REM sleep (after REM sleep deprivation)
What is the function of sleep?
Restoration and recovery (but active individuals don’t sleep more), energy conservation (10% drop in BMR but lying still is just as effective), predator avoidance, specific brain functions
When do dreams occur?
REM (most frequent and more easily recalled) and NREM sleep
What causes dreams?
Brain activity in limbic system higher than in frontal lobe during dreams -> contents of dreams are more emotional than real life
What is the function of dreams?
Safety valve for antisocial emotions, disposal of unwanted memories, memory consolidation -> NREM sleep = declarative memory; REM = procedural memory
What is insomnia?
High prevalence with most cases being transient -> sleep disorder
What are the causes of chronic insomnia?
Physiological (sleep apnoea, chronic pain); Brain dysfunction (depression fatal familial insomnia, night working)
How do you treat insomnia?
Most hypnotics enhance GABAergic circuits
What is narcolepsy?
Falling asleep repeatedly during the day and disturbed sleep during the night; cataplexy, dysfunction of control of REM sleep
What is the cause of narcolepsy?
Orexin deficiency either genetic or autoimmune
How does night working affect sleep?
Causes physiological processes to become desynchronised -> leading to sleep disorders, fatigue and an increased risk for conditions such as obesity, diabetes and cancer
How does the nervous system develop?
x
What does the wall of the neural tube (neuroepithelium) make up?
CNS
What do the neural crest cells make up?
PNS
What does the neuroepithelium differentiate into?
Neuroblasts (All neurones with cell bodies in the CNS), glioblasts (Astrocytes, oligodendrocytes), ependymal cells (Lining ventricles and central canal) - microglia form from immune cells not from the neural cells
What do the neural crest cells differentiate into?
Sensory neurones of dorsal root ganglia and cranial ganglia, postganglionic autonomic neurones, schwann cells, non-neuronal derivatives (melanocytes)
How does the neuroepithelium differentiate?
Divides into neuroblast and a stem cell in the ependymal layer -> the neuroblast then differentiates into a neurone which orientates itself into grey and white matter
What are the layers of the neural tube?
x
What controls differentiation of tissues in the nervous system?
Signalling molecules secreted by surrounding tissues, interact with receptors on neuroblasts; control migration and axonal growth by attraction and repulsion, depends on concentration gradient and timing
How does the developing spinal cord appear?
x
What is the dorsal-ventral patterning?
Notochord and ectoderm secrete different concentration gradients of signalling molecules and create different parts of the spine
What are the 3 primary vesicles of the brain?
x
What are the 5 secondary vesicles of the brain?
x
How do the secondary vesicles of the brain develop into the adult brain?
x
How does the brain fold at 4 weeks?
x
How does the brain fold from 4 wks to 8 wks?
x
How does the spinal cord develop?
x
How does the brainstem develop?
x
How does the cerebral cortex form?
Neurones with axons -> cell bodies attach to process of radial glial cells and move up the process so grey matter is outside of white matter forming a cortical plate
What are the developmental disorders of the NS?
Neural development involves several complex, timed processes; may be disrupted by genetic or environmental abnormalities -> occurs early in gestation
What is consciousness?
Consciousness is the brain state that enable us to experience the world around us and within one-self. Distinct from automatic behaviours that occur in a rather unconscious manner. Consciousness is not equal to be alert or attentive
What is the reticular formation’s actions?
Regulates many vital functions -> degree of activity associated with alertness/levels of consciousness -> projects to thalamus and cortex so sensory signals reach cortical sites of conscious awareness such as frontoparetal cortex. Cholinergic neurones in RF boost level of activity in cerebral cortex vis the thalamus
What are the types of waves that can be seen in an EEG at different levels of arousal?
Delta at sleep, theta at drowsiness, alpha at relaxed/eyes closed, beta at normal/waking consciousness. Increased frequency of natural oscillations are associated with creation of conscious contents in focus of minds eye via thalamo-cortical feedback loops
What are the causes of coma?
Damage to RF/thalamus and massive bilateral cortical insult can lead to coma/persistent vegetative state and brain death. Also metabolic = hypoxia, hypoglycaemia, intoxication
What is the GCS?
Eyes open /4, verbal response /5, motor response /6 -> 3 = severe brain injury and brain death
What are the different kinds of brain injuries leading to altered states of consciousness?
Contusion (focal lesion), concussion (more spread, with microlesions = more damaging) can lead to diffuse axonal injury
What are the tests for visual neglect syndrome?
Bunny rabbit in different quadrants of visions, line bisection and computorised test -> all with lesioned side being unfavoured, even ignored -> this should be distinguished from hemianopia
What is the neural correlate of consciousness?
Activity of many cortices in the brain, all acting together -> no single neural correlate -> feed-forward processing (subliminal/non-conscious), top-down recurrent processing (conscious access)
What is blindsight pts?
Pts who are ‘blind’ of visual field due to damage of visual field due to occipital damage but can respond to visual stimuli
