Cortical Organisation and Function Flashcards
What are the layers of the cerebral cortex?
- Molecular layer
- External granular layer
- External pyramidal layer
- Internal granular layer
- Internal pyramidal layer
- Multiform layer
Describe the structures of the columns in the cerebral cortex?
- Small pyramidal neuron
- Granule (sellate) neuron
- Large pyramidal neuron
What is cytoarchitecture?
Cell size, spacing or packing density and layers
What is the role of the frontal lobe?
- Regulating and initiating motor function
- Language
- Cognitive functions (executive)
- Attention
- Memory
What is the role of the parietal lobe?
- Sensation (touch and pain)
- Sensory aspects of language
- Spatial orientation
- Self-perception
What is the role of the occipital lobe?
- Processing visual information
What is the role of the temporal lobe?
- Auditory processing
- Emotions
- Memories
- Language
What structures are included in the limbic lobe?
- Amygdala
- Hippocampus
- Mammillary body
- Cingulate Gyrus
What is the role(s) of the limbic lobe?
- Learning
- Memory
- Emotion
- Motivation
- Reward
Where is the insular cortex?
Deep within the lateral fissure
What is the insular cortex involved in?
- Visceral sensations
- Autonomic control
- Interoception
- Auditory processing
- Visual-vestibular integration
What is grey matter comprised of?
- Neuronal cell bodies
- Gilal cells
(85 million each)
What is white matter comprised of?
Myelinated neuronal axons (arranged in tracts)
What do white matter tracts do?
Connect cortical areas
What are association fibres?
White matter that connects areas in the same hemisphere
What are commissural fibres?
White matter that connects homologous structures in the left and right hemispheres.
What are projection fibres?
White matter that connects the cortex with lower brain structures (thalamus, brainstem and spinal cord)
What are the 4 main association fibres?
- short ‘u’ fibres
- Superior Longitudinal Fasciculus
- Arcuate Fasciculus
- Inferior Longitudinal Fasciculus
- Uncinate Fasciculus
What does the superior longitudinal fasciculus connect?
The frontal and occipital lobes
What does the arcuate fasciculus connect?
The frontal and temporal lobes
What does the inferior longitudinal fasciculus connect?
The temporal and occipital lobes.
What does the uncinate fasciculus connect?
The anterior frontal and temporal lobes
What are the 2 main commissural fibres?
- Corpus callosum
- Anterior commissure
What are the 2 different directions of projection fibres?
- Afferent (towards the cortex)
- Efferent (away from the cortex)
What is the corona radiata?
Projection fibres deeper to the cortex that converge through the internal capsule between the thalamus and the basal ganglia.
Characteristics of the primary cortices?
- Predictable function
- Topographical organisation
- Symmetrical
What is the role of the primary motor area of the frontal lobe?
Fine, discrete, precise and voluntary movements
descending signals for movement
What is the role of the supplementary motor area of the frontal lobe?
Involved in planning complex movements
(externally cued)
learnt movements
What is the role of the premotor area of the frontal lobe?
Involved in planning movements
internally cued
What is the role of the primary somatosensory area of the parietal lobe?
Processes somatic sensations from the rest of the body:
- Fine touch
- Vibration
- Two-point discrimination
- Proprioception
- Pain
- Temperature
What is the role of the somatosensory association of the parietal lobe?
- Interprets the significance of the sensory information
- Awareness of self and awareness of personal space
What is the role of the primary visual area of the occipital lobe?
Processing visual stimuli
What is the role of the visual association of the occipital lobe?
Provides meaning and interpretation of the visual input.
What is the role of the primary auditory region of the temporal lobe?
Processes auditory stimuli
What is the role of the auditory association in the temporal lobe?
Gives meaning and interprets the auditory input
What is the role of the prefrontal cortex?
- Attention
- Changes to social behaviour
- Planning
- Personality expression
- Decision making
What is the role of Broca’s area?
Production of language
What is the role of Wernicke’s area?
The understanding of language
What is the effect of frontal lobe lesions?
- Changes in personality
- Inappropriate behaviour
What is the effect of parietal lobe lesions?
- Contralateral neglect
- Lack of awareness of self (opposite side to site of the lesion)
- Lack of awareness of extrapersonal space
(opposite side to site of the lesion)
What is the effect of temporal lobe lesions?
- Agnosia (unable to recognise)
- Anterograde amnesia (unable to form new memories)
What is the effect of a lesion to Broca’s area?
Expressive aphasia (poor production of speech, comprehension intact)
What is the effect of a lesion to Wernicke’s area?
Receptive aphasia
poor comprehension of speech, production is fine
What is the effect of lesions to the primary visual cortex of the occipital lobe?
Blindness in the corresponding region of the visual field (opposite side of lesion).
What effect does a lesion to the visual association cortex of the occipital lobe have?
Deficits in interpretation of visual information
- prosopagnosia: unable to recognise or learn faces
- agnosia (inability to recognise colour)
What are the 2 forms of imaging cortical function?
- PET (positron emission tomography)
- fMRI (functional magnetic resonance imaging
What does a PET scan indicate?
The blood flow into the region
What does the fMRI scan show?
The blood oxygen levels in the brain region.
What are the 2 forms of encephalography used to assess cortical function?
- EEG (electroencephalography)
- MEG
(magentoencephalography)
What does a EEG measure?
The electrical signals produced by the brain
What does a MEG measure?
The magnetic signals produced by the brain
How does the EEG assess the cortical function?
- Visual evoked potentials
- Event-related potentials/evoked potentials
What is a DTI?
Diffusion tensor imaging
based on the diffusion of water molecules
What is a DTI with tractography
A 3D reconstruction used to assess the neural tracts.
What does tDCS (transcranial direct current stimulation) involve?
Using a low direct current over the scalp to increase or decrease neuronal firing rates
What has tDCS been proven as a promising treatment for?
- Drug-resistant epilepsy
- Major depressive disorder
What does TMS (transcranial magnetic stimulation) involve?
Using electromagnetic induction to stimulate neurons
What does TMS assess?
The functional integrity of neural circuts
What has TMS been seen as a promising treatment of?
- Migraines
- Depression
- Tinnitus
- Epilepsy
What can TMS be used to investigate?
- Neural interactions controlling movement following spinal cord lesions
- The responsibility of different parts of the brain
What is the cerebral cortex?
- covers the entire surface of the brain
- together with deep nuclei, contains grey matter
- highly folded with gyri and sulci
- organised into lobe
What sulcus separates the frontal and parietal lobe?
the central sulcus
What seperates the parietal and occipital lobe?
parieto-occipital sulcus
What seperates the temporal lobe from the parietal and frontal lobe?
lateral fissure
What fissure separates the 2 hemispheres?
deep longitudinal fissure
What are the characteristics of secondary cortices?
- less predictable
- not organised topographically
- left-right symmetry weak or absence
What happens if you have a lesion on the right parietal lobe?
left contralateral neglect
- lack of self-awareness and spatial awareness
What is neglect?
- lack of awareness of sensory information in the visual field
- result of parietal lobe damage
What is agnosia?
the inability to recognise objects
Where is Broca’s area?
in the frontal lobe
Where is the internal capsule?
in the subcortical area of the brain beneath the cerebral cortex
What is an Event-related potential?
- Stimulus to median nerve
- Somatosensory activity
- Thalamic activity
- Mid-cervical activity
- Impulses arriving at shoulder
- A series of waves that reflects sequential activation of neural structures along the somatosensory pathways.
What is the benefits of MEG and EEG?
- the position of the coil can be applied in specific area to narrow muscles of interest since the primary motor cortex is topographically organised.
- good temporal resolution
When are EEGs used?
in the diagnosis of epilepsy and sleep disorders
What is the checkerboard flip test?
- visual stimuli (flipped checkerboard)
- electrical signals between relevant electrodes are graphed
- height: amplitude (strength)
- width: latency (speed)
How does an EEG of somatosensory evoked potentials work?
- stimulation given to the median nerve
- series of waves that reflect sequential activation of neural structures along the somatosensory pathways
What is brain stimulation?
- use of electromagnetic induction to stimulate neurons
- (TMS)
- assesses the functional integrity of neural circuits
What is spatial resolution?
how accurately the measured activity is localised within the brain
What is temporal resolution?
the accuracy of the scanner in relation of time: or how quickly the scanner can detect changes in brain activity
What is multiple sclerosis?
is an autoimmune disorder which results in the loss of myelin from neurons of the central nervous system
What are the symptoms of Multiple Sclerosis?
- blurred vision
- fatigue
- difficulty walking
- numbness or tingling (paraesthesia) in different parts of the body
- muscle stiffness and spasms
How can we confirm that the conduction problem in MS is associated with the CNS not the PNS?
- brain stimulation (total motor conduction time = delayed)
- peripheral nerve stimulation (peripheral motor conduction time = normal)
What happens in peripheral sensory nerve stimulation?
- EEG
- Record along the path, assessing the integrity of the sensory pathway (Routinely conducted in individuals with spinal cord injury).
- Multiple peripheral nerves can be assessed –ascertain where the signal is blocked.
What does orthodromic mean?
travelling in the normal direction in a nerve fibre
What is an M wave?
the fast response to the activation of motor axons
What is a H-reflex?
induces an indirect response of the motor neurone via a monosynaptic reflex in the spinal cord
- activation of the sensory axons as well as the motor
- action potentials from nerve to spinal cord
- causing LMN in the spinal cord to be activated
- action potentials in motor axons can cause muscle contraction (twitch)
What is an F-wave?
later response (NOT REFLEX) to stimulation
- a large electrical stimulus can cause activation of the motor axons to conduct antidromically
- LMN in the spinal cord are activated
- initiating muscle contraction (twitch)
How do you produce motor-evoked potential?
Cortical motor stimulation using transcranial magnetic stimulation (TMS)
- UMNs causes action potentials to travel along the entire motor pathway (UMN and LMN) to cause muscle contraction
What is the total motor conduction time?
19.5/26.5ms
total time from primary motor cortex to muscle
What is the peripheral motor conduction time?
13.6/12.7ms
time from spinal cord to muscle along motor axon
What is the central motor conduction time?
5.9/13.9ms
What does antidromic mean?
travelling in the opposite direction to normal in a nerve fibre
What is stimulus artefact?
the interference between the electrodes
