2.2 - Cortical organisation and function Flashcards
What is the cerebral cortex?
- covers entire surface of brain
- together with deep nuclei, contains grey matter (cell bodies and glial cells)
- highly folded with gyri and sulci
- organised into lobes
How is the cerebral cortex organised microscopically?
- organised into layers and columns
- six layers (I most superficial and VI most deep) and multiple cortical columns
- entire cortex only 2-3mm thick and has cell bodies which makes it look grey
What is the cytoarchitecture of the cerebral cortex?
- cytoarchitecture is cell size, spacing or packing density and layers
- German neurologist Brodmann identified 52 regions of the cortex using this
- 1,2,3 = primary somatosensory cortex
- 4 = primary motor cortex
- many areas are related to their function
What are the four lobes of the cortex?
- frontal
- parietal
- temporal
- occipital
What are the two additional lobes of the cortex?
- limbic lobe
- insular cortex
What are the functions of the frontal lobe? (5)
- regulating and initiating motor function
- language
- cognitive functions (executive functions e.g. planning)
- attention
- memory
What are the functions of the parietal lobe? (3)
- sensation - touch, pain
- sensory aspects of language
- spatial orientation and self-perception
What are the functions of the temporal lobe? (3)
- processing auditory information
- emotions
- memories
What are the functions of the occipital lobe?
Processing visual information
What is the limbic lobe made up of? (4)
- amygdala
- hippocampus
- mamillary body
- cingulate gyrus
What are the functions of the limbic lobe? (5)
- learning
- memory
- emotion
- motivation
- reward
Where is the insular cortex located?
Lies deep within the lateral fissure (which separates frontal from temporal lobe)
What is the insular cortex concerned with? (4)
- visceral sensations
- autonomic control and interoception
- auditory processing
- visual-vestibular integration
What is grey matter?
Neuronal cell bodies and glial cells - around 85 billion of each
What is white matter?
Myelinated neuronal axons arranged in tracts
What do white matter tracts do?
Connect cortical areas
What are the types of white matter tracts? (3)
- association fibres
- commissural fibres
- projection fibres
What do association fibres do?
Connect areas within the same hemisphere - there are short and long fibres
What are examples of association fibres? (4)
- superior longitudinal fasciculus
- arcuate fasciculus
- inferior longitudinal fasciculus
- uncinate fasciculus
What does the superior longitudinal fasciculus connect?
Frontal and occipital lobes (long)
What does the arcuate fasciculus connect?
Frontal and temporal lobes (long)
What does the inferior longitudinal fasciculus connect?
Temporal and occipital lobes (short)
What does the uncinate fasciculus connect?
Anterior frontal and temporal lobes (short)
What do commissural fibres do?
Connect homologous structures in left and right hemispheres
What are two examples of commissural fibres?
- corpus callosum (can be disconnected in patients with epilepsy to treat it)
- anterior commissure
What do projection fibres do?
- connect cortex with lower brain structures (e.g. thalamus, brain stem, spinal cord)
- afferent fibres take info towards cortex
- efferent fibres take info away from cortex
- deeper to cortex - radiate as the corona radiata (anatomical, fan out)
i.e. corona radiata are a type of projection fibre
Where do projection fibres converge?
They converge through the internal capsule between the thalamus and basal ganglia
What are primary cortices?
- function predictable
- organised topographically - bits of body close to each other are closely represented on brain
- symmetry between left and right
What are secondary/association cortices?
- function less predictable
- not organised topographically
- left-right symmetry weak or absent
What are the primary/secondary cortices in the motor area of the frontal lobe?
- primary motor cortex
- supplementary area
- premotor area
What does the primary motor cortex do?
- controls fine, discrete, precise voluntary movements
- provides descending signals to execute movements
What does the supplementary area do?
Involved in planning complex movements (e.g. internally cued)
What does the premotor area do?
Involved in planning movements (e.g. externally cued)
What are the primary/secondary cortices in the parietal lobe?
- primary somatosensory
- somatosensory association
What does the primary somatosensory cortex do?
Processes somatic sensations arising from receptors in the body (e.g. fine touch, vibration, two-point discrimination, proprioception, pain and temperature)
What does the somatosensory association area do?
- interprets significance of sensory information e.g. recognising an object placed in the hand
- also awareness of self and awareness of personal space
What are the primary/secondary cortices of the occipital lobe?
- primary visual
- visual association
What does the primary visual cortex do?
Processes visual stimuli
What does the visual association cortex do?
Gives meaning and interpretation of visual input
What are the primary/secondary cortices of the temporal lobe?
- primary auditory
- auditory association
What does the primary auditory cortex do?
Processes auditory stimuli
What does the auditory association cortex do?
Gives meaning and interpretation of auditory input
What other association areas are there? (3)
- prefrontal cortex
- Broca’s area
- Wernicke’s area
What does the prefrontal cortex do? (5)
- attention
- adjusting social behaviour
- planning
- personality expression
- decision making
What does Broca’s area do?
Production of language
What does Wernicke’s area do?
Understanding of language
What do frontal lobe lesions cause? (2)
- changes in personality
- inappropriate behaviour
What do parietal lobe lesions do?
- contralateral neglect
- e.g. for a lesion in right hemisphere:
- lack of awareness of self on left side
- lack of awareness of left side of extrapersonal space
- e.g. no shaving/clothing on left side, forgotten about left
What do temporal lobe lesions do?
- leads to agnosia - inability to recognise (lateral lesion)
- a patient had a bilateral resection of anterior medial temporal lobe to cure epilepsy and was left with anterograde amnesia (couldn’t form new memories - medial lesion)
What do lesions to Broca’s area do?
Expressive aphasia - poor production of speech, comprehension intact
What do lesions to Wernicke’s area do?
Receptive aphasia - poor comprehension of speech, production is fine
What does a lesion to the arcuate fasciculus cause?
Inability to repeat speech (this tract links Broca’s to Wernicke’s)
What does a lesion to the primary visual cortex do?
Blindness in the corresponding part of the visual field
What does a lesion to the visual association cortex do?
Deficits in interpretation of visual information e.g. prosopagnosia (inability to recognise familiar faces/learn new faces - face blindness)
Imaging - what does positron emission tomography (PET) do?
Looks at blood flow directly to a brain region by seeing how glucose (radioactive isotope used) is taken up by different parts of the brain
Imaging - what does functional magnetic resonance imaging (fMRI) do?
Looks at amount of blood oxygen in brain region
Imaging - what is diffusion tensor imaging (DTI)?
Based on diffusion of water molecules
Imaging - what is DTI with tractography?
3D reconstruction to assess neural tracts
Encephalography - what does electroencephalography (EEG) do?
- measures electrical signals produced by brain since brain works on AP travelling around it
- different electrodes stuck over scalp and each electrode measures its own thing
- evoked potentials = seen as peaks
Encephalography - what does magnetoencephalography (MEG) do?
Measures magnetic signals produced by brain
Encephalography - how are somatosensory evoked potentials measured?
- put electrodes along a certain neural pathway and see if there are any issues
- we can see a series of waves that reflect sequential activation of neural structures along the somatosensory pathways
Encephalography - what do somatosensory evoked potentials help us measure?
Nerve degradation and which point it has happened
Brain stimulation - how does TMS (transcranial magnetic stimulation) work?
- uses electromagnetic induction to stimulate neurones
- assess functional integrity of neural circuits
What can brain stimulation be used to measure?
- investigate neural interactions controlling movement following spinal cord injury
- investigate whether a specific brain area is responsible for a function e.g. speech
Brain stimulation - what is transcranial direct current stimulation (tDCS)?
Uses low direct current over the scalp to increase or decrease neuronal firing rates
