2.2 - Cortical organisation and function

Question 1

What is the cerebral cortex?

Answer 1

• 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

Question 2

How is the cerebral cortex organised microscopically?

Answer 2

• 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

Question 3

What is the cytoarchitecture of the cerebral cortex?

Answer 3

• 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

Question 4

What are the four lobes of the cortex?

Answer 4

• frontal
• parietal
• temporal
• occipital

Question 5

What are the two additional lobes of the cortex?

Answer 5

• limbic lobe
• insular cortex

Question 6

What are the functions of the frontal lobe? (5)

Answer 6

• regulating and initiating motor function
• language
• cognitive functions (executive functions e.g. planning)
• attention
• memory

Question 7

What are the functions of the parietal lobe? (3)

Answer 7

• sensation - touch, pain
• sensory aspects of language
• spatial orientation and self-perception

Question 8

What are the functions of the temporal lobe? (3)

Answer 8

• processing auditory information
• emotions
• memories

Question 9

What are the functions of the occipital lobe?

Answer 9

Processing visual information

Question 10

What is the limbic lobe made up of? (4)

Answer 10

• amygdala
• hippocampus
• mamillary body
• cingulate gyrus

Question 11

What are the functions of the limbic lobe? (5)

Answer 11

• learning
• memory
• emotion
• motivation
• reward

Question 12

Where is the insular cortex located?

Answer 12

Lies deep within the lateral fissure (which separates frontal from temporal lobe)

Question 13

What is the insular cortex concerned with? (4)

Answer 13

• visceral sensations
• autonomic control and interoception
• auditory processing
• visual-vestibular integration

Question 14

What is grey matter?

Answer 14

Neuronal cell bodies and glial cells - around 85 billion of each

Question 15

What is white matter?

Answer 15

Myelinated neuronal axons arranged in tracts

Question 16

What do white matter tracts do?

Answer 16

Connect cortical areas

Question 17

What are the types of white matter tracts? (3)

Answer 17

• association fibres
• commissural fibres
• projection fibres

Question 18

What do association fibres do?

Answer 18

Connect areas within the same hemisphere - there are short and long fibres

Question 19

What are examples of association fibres? (4)

Answer 19

• superior longitudinal fasciculus
• arcuate fasciculus
• inferior longitudinal fasciculus
• uncinate fasciculus

Question 20

What does the superior longitudinal fasciculus connect?

Answer 20

Frontal and occipital lobes (long)

Question 21

What does the arcuate fasciculus connect?

Answer 21

Frontal and temporal lobes (long)

Question 22

What does the inferior longitudinal fasciculus connect?

Answer 22

Temporal and occipital lobes (short)

Question 23

What does the uncinate fasciculus connect?

Answer 23

Anterior frontal and temporal lobes (short)

Question 24

What do commissural fibres do?

Answer 24

Connect homologous structures in left and right hemispheres

Question 25

What are two examples of commissural fibres?

Answer 25

- corpus callosum (can be disconnected in patients with epilepsy to treat it) - anterior commissure

Question 26

What do projection fibres do?

Answer 26

- 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

Question 27

Where do projection fibres converge?

Answer 27

They converge through the internal capsule between the thalamus and basal ganglia

Question 28

What are primary cortices?

Answer 28

- function predictable - organised topographically - bits of body close to each other are closely represented on brain - symmetry between left and right

Question 29

What are secondary/association cortices?

Answer 29

- function less predictable - not organised topographically - left-right symmetry weak or absent

Question 30

What are the primary/secondary cortices in the motor area of the frontal lobe?

Answer 30

- primary motor cortex - supplementary area - premotor area

Question 31

What does the primary motor cortex do?

Answer 31

- controls fine, discrete, precise voluntary movements - provides descending signals to execute movements

Question 32

What does the supplementary area do?

Answer 32

Involved in planning complex movements (e.g. internally cued)

Question 33

What does the premotor area do?

Answer 33

Involved in planning movements (e.g. externally cued)

Question 34

What are the primary/secondary cortices in the parietal lobe?

Answer 34

- primary somatosensory - somatosensory association

Question 35

What does the primary somatosensory cortex do?

Answer 35

Processes somatic sensations arising from receptors in the body (e.g. fine touch, vibration, two-point discrimination, proprioception, pain and temperature)

Question 36

What does the somatosensory association area do?

Answer 36

- interprets significance of sensory information e.g. recognising an object placed in the hand - also awareness of self and awareness of personal space

Question 37

What are the primary/secondary cortices of the occipital lobe?

Answer 37

- primary visual - visual association

Question 38

What does the primary visual cortex do?

Answer 38

Processes visual stimuli

Question 39

What does the visual association cortex do?

Answer 39

Gives meaning and interpretation of visual input

Question 40

What are the primary/secondary cortices of the temporal lobe?

Answer 40

- primary auditory - auditory association

Question 41

What does the primary auditory cortex do?

Answer 41

Processes auditory stimuli

Question 42

What does the auditory association cortex do?

Answer 42

Gives meaning and interpretation of auditory input

Question 43

What other association areas are there? (3)

Answer 43

- prefrontal cortex - Broca's area - Wernicke's area

Question 44

What does the prefrontal cortex do? (5)

Answer 44

- attention - adjusting social behaviour - planning - personality expression - decision making

Question 45

What does Broca's area do?

Answer 45

Production of language

Question 46

What does Wernicke's area do?

Answer 46

Understanding of language

Question 47

What do frontal lobe lesions cause? (2)

Answer 47

- changes in personality - inappropriate behaviour

Question 48

What do parietal lobe lesions do?

Answer 48

- 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

Question 49

What do temporal lobe lesions do?

Answer 49

- 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)

Question 50

What do lesions to Broca's area do?

Answer 50

Expressive aphasia - poor production of speech, comprehension intact

Question 51

What do lesions to Wernicke's area do?

Answer 51

Receptive aphasia - poor comprehension of speech, production is fine

Question 52

What does a lesion to the arcuate fasciculus cause?

Answer 52

Inability to repeat speech (this tract links Broca's to Wernicke's)

Question 53

What does a lesion to the primary visual cortex do?

Answer 53

Blindness in the corresponding part of the visual field

Question 54

What does a lesion to the visual association cortex do?

Answer 54

Deficits in interpretation of visual information e.g. prosopagnosia (inability to recognise familiar faces/learn new faces - face blindness)

Question 55

Imaging - what does positron emission tomography (PET) do?

Answer 55

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

Question 56

Imaging - what does functional magnetic resonance imaging (fMRI) do?

Answer 56

Looks at amount of blood oxygen in brain region

Question 57

Imaging - what is diffusion tensor imaging (DTI)?

Answer 57

Based on diffusion of water molecules

Question 58

Imaging - what is DTI with tractography?

Answer 58

3D reconstruction to assess neural tracts

Question 59

Encephalography - what does electroencephalography (EEG) do?

Answer 59

- 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

Question 60

Encephalography - what does magnetoencephalography (MEG) do?

Answer 60

Measures magnetic signals produced by brain

Question 61

Encephalography - how are somatosensory evoked potentials measured?

Answer 61

- 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

Question 62

Encephalography - what do somatosensory evoked potentials help us measure?

Answer 62

Nerve degradation and which point it has happened

Question 63

Brain stimulation - how does TMS (transcranial magnetic stimulation) work?

Answer 63

- uses electromagnetic induction to stimulate neurones - assess functional integrity of neural circuits

Question 64

What can brain stimulation be used to measure?

Answer 64

- investigate neural interactions controlling movement following spinal cord injury - investigate whether a specific brain area is responsible for a function e.g. speech

Question 65

Brain stimulation - what is transcranial direct current stimulation (tDCS)?

Answer 65

Uses low direct current over the scalp to increase or decrease neuronal firing rates