Cortical Organisation and Structure Flashcards
What does the cerebral cortex cover?
Entire surface of the brain
What comprises the cortex?
Deep nuclei
Grey matter
What is the structure of the cortex?
Highly folded with gyri and sulci
Organised into lobes
How is the cortex organised microscopically?
Layers and Columns
6 layers
How many regions of the brain are there, based on cytoarchitecture?
52
What is region 4?
Primary motor cortex
What are regions 1,2 + 3?
Primary somatosensory cortices
What are the 4 lobes?
Frontal
Parietal Occipital
Temporal
What functions is the frontal lobe responsible for?
Regulating and initiating motor function
Language
cognitive functions (executive function [e.g. planning])
Attention
Memory
What functions is the parietal lobe responsible for?
Sensation - touch, pain
sensory aspects of language
spatial orientation and self-perception
What function is the occipital lobe responsible for?
Processing visual information
What functions is the temporal lobe responsible for?
Processing auditory information
Emotions
Memories
What is included in the Limbic lobe?
Includes the amygdala, hippocampus, mamillary body, and cingulate gyrus
What is the Limbic lobe responsible for?
learning, memory, emotion, motivation and reward
Where is the insular cortex found?
Deep within the lateral fissure
What is the insular cortex concerned with?
Visceral sensations Autonomic control Interoception Auditory processing Visual-vestibular integration
What comprises grey matter?
Neuronal cell bodies and glial cells
85 billion of each
What comprises white matter?
Myelinated neuronal axons arranged in tracts
What are the different types of white matter tracts?
Association fibres
Commissural fibres
Projection fibres
Whats are the different tracts differentiated by?
What cortical areas they connect
What do association fibres connect?
Areas within the same hemisphere
What do projection fibres connect?
Cortex with lower brain structures (e.g. thalamus, brain stem and spinal cord)
What do commissural fibres connect?
Homologous structure in left and right hemispheres
What are short association fibres also known as?
U fibres
Because of their shape
Tend to connect adjacent cortical regions
Name 4 long association fibres and what they connect
Superior Longitudinal Fasciculus connects frontal and occipital lobes
Arcuate Fasciculus - connects frontal and temporal lobes
Inferior Longitudinal Fasciculus - connects temporal and occipital lobes
Uncinate Fasciculus - connects anterior frontal and temporal lobes
Name two commissural fibres
Corpus Callosum
Anterior commissure
What are the two types of projection fibres?
Afferent – towards cortex
(Info from outside world up via the spinal cord)
Efferent – away from cortex
(Info out from the cortex down the brainstem/spinal cord)
What are the afferent/efferent projection fibres collectively known as?
Corona Radiata
What happens to the projection fibres deeper to cortex?
Radiate as the corona radiate
What happens as the projection fibres make their way down towards the spinal cord?
Converge through internal capsule between thalamus and basal ganglia
Occupying smaller spaces
Then they are congregated into a structure called the internal capsule
What does the internal capsule contain?
Both motor and sensory fibres
How are the cortices categorised functionally?
Primary cortices
Secondary/association cortices
What are the main features of primary cortices?
Function predictable (e.g. sensation in specific part of skin will cause activity in a discrete region of somatosensory cortex)
Organised topographically (body regions located in particular region of the cortex)
Symmetry between left and right
(e.g. stimulate motor region 3 cm from midline would contract the same muscle on both sides of body)
What are the main features of secondary cortices?
Function less predictable
Not organised topographically
Left-right symmetry weak or absent
Where do you tend to find secondary cortices?
Surrounding primary cortices
What are the functions of the primary motor cortex in the frontal lobe?
Motor impulse generation
Controls fine, discrete, precise voluntary movements
Provides descending signals to execute movements
What are the functions of the supplementary motor area in the frontal lobe?
Involved in planning movements (e.g. externally cued - plan to move a limb)
Orchestrates the sequence of events before the movement needs to take place
Give an example of a secondary cortex in the frontal lobe?
Supplementary area
What is the function of the pre-motor area of the frontal lobe?
Involved in planning complex movements (e.g. internally cued)
What is the primary cortex in the parietal lobe?
Primary somatosensory
What is the function of the primary somatosensory?
Processes somatic sensations arising from receptors in the body
(e.g. fine touch, vibration, two-point discrimination, proprioception, pain and temperature
What is the secondary cortex of the parietal lobe?
Somatosensory association
What is the function of the somatosensory association in the parietal lobe?
Adds significance to the sensations
Interpret significance of sensory information, e.g. recognizing an object placed in the hand.
Awareness of self and awareness of personal space
What is the primary cortex in the occipital lobe?
Primary visual
What is the function of the primary visual cortex?
Processes visual stimuli
What is the secondary cortex in the occipital lobe?
Visual association
What is the function of the visual association cortex?
Gives meaning and interpretation of visual input
Recognition of the input
What is the primary cortex of the temporal lobe?
Primary auditory
What is the function of the primary auditory cortex?
Processes auditory stimuli
What is the secondary cortex of the temporal lobe?
Gives meaning and interpretation of auditory input
Name three other secondary/association cortices
Prefrontal cortex
Broca’s area
Wernicke’s area
What are the functions of the pre-frontal cortex?
Executive functions e.g.
Attention Adjusting social behaviour Planning Personality expression Decision making
What is the function of Broca’s area?
Production of language
What is the function of Wernicke’s area?
Understanding of language
Where is Broca’s area found?
Sits directly in front of the motor regions
It is a motor region with respect to language
How you formulate your mouth and generate the motor commands to produce speech
Where is Wernicke’s area found?
Temporal lobe - so is a sensory region in relation to language
What symptoms are common in frontal lobe lesions?
Changes in personality
Inappropriate behaviour
What are classic symptoms of parietal lobe lesions?
Loose aspects of self-awareness and personal space
What would happen to a patient with a lesion in the right parietal lobe?
Contralateral neglect (themselves and the world)
e. g. would neglect to shave left side of factor or put left arm into t-shirt
e. g. would not eat food on the left side of plate
Lack of awareness of self on left side
Lack of awareness of left side of extrapersonal space
What are classic symptoms of temporal lobe lesions?
Leads to agnosia (inability to recognise)
What happened to the case of HM who had a bilateral resection of anterior medial temporal lobe?
Could not form new memories - anterograde amnesia
What would a lesion to Broca’s area lead to?
Expressive aphasia – poor production of speech, comprehension intact
Can understand reading/speech
What would a lesion to Wernicke’s area lead to?
Receptive aphasia – poor comprehension of speech, production is fine
What would a lesion in the primary visual cortex (occipital lobe) lead to?
Blindness in the corresponding part of the visual field
As signals can not reach cortex from retina
What would a lesion to the visual association cortex (occipital lobe) lead to?
Deficits in interpretation of visual information e.g. prosopagnosia: inability to recognise familiar faces or learn new faces (face blindness)
What can be used to assess cortical function?
Imaging
Encephalography
What imaging can be used to assess cortical function?
Position emission tomography (PET)
Functional magnetic resonance imaging (fMRI)
How does PET work?
Radioactive glucose injected into blood and the person is placed in scanner and asked to undertake a task
Examines blood flow directly to brain region
Regions that consume glucose will light up on scan
e.g. if reading visual cortex will light up
if speaking Broca’s area will light up
How does fMRI work?
Used to understand brain function when carrying out tasks e.g. responding to emotional stimuli
Used to understand connection between brain regions
Amount of blood oxygen in a brain region is monitored
Assesses oxygenated vs. deoxygenated blood in an area
Increased oxygen being delivered equals increased activity
What should be considered before a scan?
Is the radiation that PET exposes the patient to necessary
Differences in temporal and spatial resolution
What does electroencephalography measure?
Electrical signals produced by the brain can reach the surface and be detected by electrodes all over the brain
Comparing the signals from different regions of the brain over time can give you an insight into what regions were active at the time of a stimulus or task
Frequently used for sleep disorders or epilepsy
What doe magnetoencephalography measure (MEG)?
Magnetic signals produced by the brain
More recent
How are electrodes placed?
Electrodes are numbered and have a specific position
Universal system
What potentials are observed?
Visual evoked potentials
Event-related potentials
Evoked-Potentials
With brain activity 50-100 stimuli are needed to elicit a waveform
How do you know which signal corresponds to which electrodes?
e.g LO-Fz shows the signals between the electrodes LO and Fz
How can we assess the integrity of the sensory pathway?
Record along the path from an impulse when it arrives along the entrance point of a peripheral nerve up to the brain
Routinely carried out in people with spinal cord injuries
To confirm where along the pathway any injury has occurred
What is recorded when using somatosensory evoked potentials?
Series of waves that reflect sequential activation of neural structures along the somatosensory pathways
Can track the pathway of a peripheral nerve from start to end
To ascertain where within the nervous system there is an issue and the signal gets blocked
What is the path that should be recorded when using somatosensory evoked potentials?
E.g. Median nerve
Impulses arriving at shoulder
Mid-cervical cord activity
Thalamic activity
Somatosensory activity
Each will generate a trace
How can we asses cortical function using brain stimulation (non-invasive)?
Assess functional integrity of neural circuits
Using transcranial magnetic stimulation
Electromagnetic induction stimulated neurons
Hold a magnetic coil over head. Current is passed through the coil causing a EM field to be induced.
The EM field produces a field in a nerve or the brain
How can TMS be used in practice?
Investigate neural interactions controlling movement following spinal cord injury
Investigate whether a specific brain area is responsible for a function e.g. speech
Could be used in modulating activity e.g turning down overactivity
Research being conducted into whether it can reduce/prevent epilepsy, used in tinnitus, migraines
What is tDCS?
Transcranial direct current stimulation
What does tCDS do?
Uses low direct current over the scape to increase or decease neuronal firing rates
What is DTI?
Diffusion tensor imaging
What is DTI used for?
Assessing structure of the brain
Based on the diffusion of water molecules
What is DTI with tractography used for?
3D reconstruction to assess neural tracts
What are the main symptoms of MS?
Fatigue Vision problems Numbness and tinglign Mobility issues Pain Anxiety and Depression Sexual problems Bladder problems
What is MS?
Multiple Sclerosis: autoimmune condition of the CNS. Demyelinates nerves in a particular set of neurons, disrupting these nerves from conducting impulses. It is not directly inherited but there is a genetic component. It usually begins in early adulthood between the ages of 20 and 40.
What is a M-wave
Small preceding wave to any motor response, muscle twitches
Direct activation of motor neuron towards muscles
