Cerebral Cortex Flashcards
What are the folds within the cerebral cortex known as?
Gyri and sulci
Outline the microscopic organisation of the cerebral cortex
The cerebral cortex is arranged into layers and columns (From superficial to deep)
- Molecular layer (I)
- External granular layer (II)
- External pyramidal layer (III)
- Internal granular layer (IV)
- Internal pyramidal layer (V)
- Multiform layer (VI)
Explain briefly the classification of the cerebral cortex based on cytoarchitecture.
52 regions classified by Korbinian BRODMANN based on size, spacing or packing density and layers – regions associated with particular functions.
e.g. - Primary somatosensory cortex (1, 2 and 3); Primary motor cortex (4)
What are the functions of the frontal lobe?
Associated with regulating and initiating motor function (Primary motor
cortex)
- Language (Broca’s area).
- Cognitive function (executive function e.g. planning)
- Attention
- Memory
What are the functions of the parietal lobe?
Includes the primary somatosensory cortex responsible for processing somatic sensations:
- Touch, pain, temperature, proprioception, fine touch and vibration
- Sensory aspects of language
- Spatial orientation and self-perception-
What are the functions of the temporal lobe?
Processes auditory information including the primary auditory cortex, and Wernicke’s area (Comprehension and understanding of speech).
Emotions
Memory
What is the function of the occipital lobe?
Processes visual information, including the - Primary visual cortex and visual association area
What structures form the limbic lobe?
Amygdala, hippocampus, maxillary body and cingulate gyrus
What functions is the limbic lobe concerned with?
Memory, emotion, motivation, learning and reward
Where does the insular cortex sit in the brain and what is it concerned with?
Lies deep within the lateral fissure
Concerned with visceral sensations, autonomic control, interoception, auditory processing and visual-vestibular integration.
What is grey matter?
Neuronal cell bodies and glial cells
What is white matter?
Myelinated neuronal tracts arranged in tracts
What do white matter tracts connect?
Cortical areas
What do association, commissural and projection fibres connect respectively?
Association - connect areas within the same hemisphere
Commissural - connect homologous structure in left and right hemispheres
Projection - connect cortex with lower brain structures (e.g. thalamus, brainstem and SC)
Describe the 2 types of lengths that association fibres comprise.
Short and long
What do the following association fibre fasciculi connect: Superior longitudinal fasciculus Arcuate fasciculus Inferior longitudinal fasciculus Uncinate fasciculus
Superior longitudinal fasciculus - connects the frontal and occipital lobes.
Arcuate fasciculus - connects the frontal and temporal lobes
Inferior longitudinal fasciculus - connects temporal and occipital lobes
Uncinate fasciculus - connects the anterior frontal lobe and temporal lobes
Give 2 examples of commissural fibres
Corpus callosum
Anterior commisura
What do projection fibres deep to the cortex radiate as?
Corona radiata
What structure do projection fibres converge through and what does this structure lie between?
Internal capsule
Between thalamus and basal ganglia
What structure do projection fibres converge through and what does this structure lie between?
Internal capsule
Between thalamus and basal ganglia
Compare primary and secondary/association cortices.
Primary cortices - function predictable, organised topographically, symmetry between left and right
Secondary/association cortices - function less predictable, not organised topographically, left-right symmetry weak or absent.
List the 3 motor areas in the frontal lobe.
Primary motor cortex
Supplementary
Premotor area
What is the function of the primary motor cortex?
Controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movement.
What is the function of the supplementary motor area in the frontal lobe?
Involved in planning complex movements (e.g. internally cued - speaking)
What is the function of the premotor area?
Involved in planning movements (e.g. externally cued - seeing an object)
What is the function of the primary somatosensory cortex?
Processes somatic sensations arising from receptors in the body (e.g. fine touch, vibration, 2-point discrimination, proprioception, pain and temperature).
What is the function of the somatosensory association area in the parietal lobe?
Interpret significance of sensory information, e.g. recognise an object placed in the hand. Awareness of self and awareness of personal space.
What is the function of the primary visual cortex and visual association area (both in the occipital lobe)?
Primary visual cortex - processes visual stimuli
Visual association area - gives meaning and interpretation of visual input
What is the function of the primary auditory cortex and the auditory association area (both in the temporal lobe)?
Primary auditory - processes auditory stimuli
Auditory association - gives meaning and interpretation of auditory input
What association area in the cerebral cortex is responsible for production of language?
Broca’s area
What association area in the cerebral cortex is responsible for the understanding of language?
Wernickes area
What functions is the prefrontal cortex concerned with?
Concerned with attention, adjusting social behaviour, planning, personality expression and decision making.
(N.B. Frontotemporal dementia > Difficulty in subduing inappropriate behaviour (disinhibition).)
Where is Broca’s area?
Resides within the left cerebral hemisphere in the frontal lobe
Where is Wernicke’s area?
Resides within the left temporal lobe
Symptoms if a person has a frontal lobe lesion
Changes in personality
Inappropriate behaviour
Symptoms if a person has a parietal lobe lesion
Example (lesion in right hemisphere)
- Contralateral neglect (Hemispatial)
- Lack of awareness of self on left side
- Lack of awareness of left side of extrapersonal space.
Symptoms if a person has a temporal lobe lesion.
Leads to agnosia – inability to recognise
N.B: Bilateral resection of anterior medial temporal lobe structures to cure epilepsy manifested an anterograde amnesia (cannot form new memories).
What does a patient present with if they have a lesion in Brocas area?
Expressive aphasia - poor production of speech, comprehension intact
What does a patient present with if they have a lesion in Wernicke’s area?
Receptive aphasia - poor comprehension of speech, production is fine
What does a patient present with if they have a lesion in the primary visual cortex?
Blindness in the corresponding part of the visual field
What does a patient present with if they have a lesion in the visual association area?
Deficits in interpretation of visual information e.g. prosopagnosia: inability to recognise familiar faces or learn new faces (face blindness).
Explain the use of a PET scan in assessing cortical function.
Positron emissions tomography (PET) – Blood flow directly to a brain region associated with particular active function.
Radioactively labelled glucose (fluorodeoxyglucose) is administered into circulation and a particular task is performed. Due to differences in metabolic demands, blood is directed to the area of the brain concerned with the performed action. Positron emitter annihilates electrons, releasing gamma rays in the process that are detected.
Explain the use of functional magnetic resonance imaging (fMRI) in assessing cortical function.
fMRI assesses blood oxygenation in a particular brain region (Determines the increase in oxygen being delivered to a region of the brain implies increased activity).
Subtle differences in temporal and spatial resolution of techniques.
Spatial resolution refers to the ability to zoom in onto a specific region and temporal refers to how quickly certain things are changing.
What does an EEG do and explain its use in assessing cortical function?
Measures the electrical signals produced by the brain (frequently used in the diagnosis of epilepsy and sleep disorders).
Event-evoked potentials
e.g. 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.
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 magneticencephalography measure?
Measures magnetic signals produced by the brain.
What is transcranial magnetic stimulation used for?
It assesses the functional integrity of neural circuits. The stimulator (magnetic) relies on the production of a changing electric field which gives rise to magnetic fields. Current induced in the coil stimulates production of an EM field, inducing neurones (Non- invasive). The position of the coil can be applied in specific area to narrow muscles of interest since the primary motor cortex is topographically organised.
Researched areas of TMS
TMS can be used to modulate or downregulate overactive brain regions by interfering with transmission.
- Can reduce the onset of epilepsy
- TMS in tinnitus patients
- Preventative for migraine
- Treatment in depressive disorders.
Explain how transcranial direct current stimulation works (tDCS).
Uses low direct current over the scalp to increase or decrease neuronal firing rates.
Power dimes can be used to alter the firing rates of neurones.
What is diffusion tensor imaging based on?
Diffusion of water molecules
DTI with tractography – 3D reconstruction to assess neural tracts
