Neuro 14 - Cerebral cortex and Limbic system Flashcards
What are the 3 types of cerebral white matter?
- Association fibres (in cortex) - connect areas within same hemisphere
- Commissural fibres - connect left hemisphere to right hemisphere. Largest commissural pathway = corpus callosum (joining the 2 hemispheres).
- There is also anterior commissural pathway (basal forebrain)
- Smaller posterior commissural pathway - join the 2 hippocampi posteriorly - Projection fibres - connect cortex with lower brain structures (e.g. thalamus), brainstem and spinal cord. Biggest projection fibre pathway is the corticospinal tract
How many layers does the neocortex have?
Describe the lateral arrangement
6 (for majority of cortex)
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from thalamus
Layers 5 and 6 = connections with subcortical, brainstem and spinal cord
The neocortex is arranged in layers (lamina structure) and?
Columns - dense vertical connections. This formed the basis for topographical organisation - neurones with similar properties connected in same column
The posterior border of the frontal cortex is?
Central sulcus
Whatolder part of the cortex can be seen if you retract the frontal, parietal and temporal lobes?
Insula
Describe primary cortices
- Predictable function
- Organised topographically
- Left right symmetry - NB lt part controls right side of body
Where is the primary somatic sensory cortex?
Parietal lobe
Where is the visual cortex
Occipital lobe
Where is the auditory cortex?
Temporal lobe
All taste sensation goes to a single nucleus in the brainstem - the ?
Nucleus solitarius (has CN input from CN7, 9, little bit of 10)
Describe association cortices
- Less predictable function
- Not organised topographically
- Left-right symmetry weak or absent
e.g. language - largely a left based function
Where is the auditory association area?
On the auditory cortex (which is on the superior temporal gyrus)
Where is the visual association area?
Surrounding the visual cortex (calcarine) in the occipital lobe
Where is the sensory association area
Sensory association area provides sensory information from skin and viscera (and taste buds)
Located in parietal lobe
Where is the prefrontal association area
Frontal lobe - quite diffuse
Prefrontal association area involved in behaviours, coordinating information from other areas, etc
Where is motor association area?
Anterior to central sulcus
Motor association area involved in SkM movement
What are the 2 visual pathways (once the PVC has occurred)
- “where” pathway (spatial relationships) - dorsal stream
2. “what” pathway (colour, form)- ventral stream
What may lesions in the visual posterior association area (fusiform gyrus) lead to
Prosopagnosia - inability to recognise familiar faces or learn new faces
What may frontal lobe lesions result in
Lack of planning, disorganised behaviour, diminished concentration and attention span, impaired self-control
What may parietal cortex lesions result in
Post. parietal association cortex = creates spatial map of body in surroundings from multi-modality information
Injury - may cause disorientation, inability to read maps/understand spatial relationships, apraxia (inability to carry out programmed movements), hemispatial neglect
What may temporal cortex lesions cause
Agnosia, receptive aphasia
Temporal lobe involved in language, object recognition, memory, emotion
Patients who have had a callosotomy (removed corpus callosum) have?
Lateralised deficits in function
as commissural pathways compromised, which links the 2 hemispheres
Which hemisphere is dominant for verbal processing?
Left
What is TMS
Transcranial Magnetic Stimulation (TMS)
Magnetic filed induces electric current in cortex –> causing neurones to fire
Can be used to test whether a specific brain area is responsible for a function (e.g. speech)
What is TDCS
Transcranial direct current stimulation (TDCS)
Changes local excitability of neurones - increasing/decreasing firing rate (but it doesn’t actually induce firing)
Parkinsons patients have a deficit in?
Dopamine
Distinguish MEG and EEG
MEG = measures magnetic fields
EEG = measures electric fields
Both give noisy signals - large numbers of trials needed so avg can be used
What can fMRI be used for
Can check areas of higher blood flow - presumed to be due to increased electrical activity in those areas
White matter is a bit more deep than grey matter
Y
Describe the olfactory system progression
Olfactory epithelium —> bipolar olfactory neurones (which pass through the cribriform plate - ethmoid bone) —> sustentacular cells (support cells) —> basal cells
(There is also a progressive loss of olfaction with age)
Where does the olfactory bulb lie?
Inferior surface of frontal lobe (above cribriform plate from sagittal view)
What are second-order olfactory neurons also known as?
Mitral cells
Olfactory bulb (mitral cells) —> olfactory tract —> olfactory stria. What are the stria present and what are the highest cortical functioning areas for olfaction?
Medial and lateral olfactory striae
Highest functioning olfactory areas = Piriform cortex (temporal lobe) and orbitofrontal cortex
Both piriform and orbitofrontal cortex connected to brainstem and can promote autonomic responses
What is a clinical deficit in smell called
Anosmia
In Parkinson’s disease, what is affected quite early on
Olfactory bulb
What is the limbic system
System responsible for processes aimed at survival of the individual:
- Maintenance of homeostasis, modulating pituitary hormone release and initiation of feeding and drinking (hypothalamus = part of limbic system)
- Agonistic behaviour
- Sexual and reproductive behaviour
- Memory
Where is the amygdala present
Temporal lobe
Describe the parts of the limbic system
Frontal lobe Thalamus Hippocampus Amygdala Hypothalamus Olfactory bulb
Describe the emotional experience circuit (Major part of Papez circuit - other parts involve emotional colouring and emotional expression)
Cingulate cortex — (cingulum bundle) –> Hippocampus 000 (fornix) –> Hypothalamus (mammillary bodies) –(MTT - Mammillo-thalamic tract)
—> Anterior nucleus of thalamus —> back to cingulate cortex
Emotional colouring of a memory is a ……. response
Neocortical
Our response/emotional expression is …..
Hypothalamic
What are the main connections of the hippocampus
Afferent = perforant pathway (input from entorhinal cortex)
Efferent = fimbria / fornix (to hypothalamus)
Hippocampus vital in memory and learning
Clinical problems with hippocampus may cause
Alzheimers disease / epilepsy
Mammillary bodies are present at the base of the diencephalon. Where can the hippocampi be found
Inferior horn of lateral ventricle (temporal lobe)
the amygdala is buried in the white matter of anterior temporal lobe
What is a radiological sign of Alzheimers
Atrophic hippocampus
Describe the anatomical progression of Alzheimers
Early: hippocampus and entorhinal cortex, shorter memory problems
Moderate:
parietal lobe, dressing apraxia
Late:
frontal lobe, loss of executive skills
Describe the structure infront of hippocampus, buried in the white matter
Amygdala (temporal lobe)
Afferent connections: olfactory cortex, septum, temporal neocortex, hippocampus, brainstem
Efferent: stria terminalis (goes to hypothalamus)
Functions: fear and anxiety, fight or flight
Clinical dysfunction - Kluver-Bucy syndrome
Describe Kuver-Bucy syndrome
Person defers to basic instincts
Hyperorality
Loss of fear
Visual agnosia
Hypersexuality
What parts of the brain are involved in aggression
- Hypothalamus
- Brainstem (periaqueductal grey matter)
- Amygdala
5-HT main NT in raphe nuclei
What divides the lateral ventricles. Describe this structure
Septum
Afferent:
Amygdala, olfactory tract, hippocampus, brainstem
Efferent: stria medularis thalami, hippocampus, hypothalamus
Functions: reinforcement and reward
Aside from septal nuclei, what else is thought to be involved in reward behaviour
Nucleus accumbens
Most recreational drugs increase DA release in nucleus accumbens
Describe the mesolimbic dopamine pathway
Midbrain (VTA) neurones (Median forebrain bundle MFB) projecting to cortex, nucleus accumbens and amygdala
