Cortical Localisation & Subcortical White Matter Flashcards
(72 cards)
1
Q
What is meant by the “cortex”?
How can it be divided into different areas?
A
- the cortex is a thin layer of grey matter that surrounds the cerebral hemispheres
- it can be divided into 46 Brodmann’s areas based on cellular organisation
- different areas of the cortex are associated with different functions
2
Q
What is meant by somatotopic organisation?
Why are some areas represented as larger than others?
A
- areas of the body are mapped differently to the cortex and are not proportional
- areas represented as large are areas that perform highly skilled motor functions or contain many more sensory receptors
3
Q
How is sensory information coming from the face and the body relayed differently by the thalamus?
A
From the face:
- sensory information is relayed by the VPM nucleus and projected more laterally in the postcentral gyrus
From the body:
- sensory information is relayed by the VPL nucleus and projected more medially in the postcentral gyrus
4
Q
How does motor information travel differently from the precentral gyrus depending on whether it is going to the face or body?
A
To the face:
- motor information travels to the face via corticobulbar (corticonuclear) fibres
To the body:
- motor information travels to the body via the corticospinal tract
- There is no involvement of the thalamus*
5
Q
What acronym can be used to remember somatotopic organisation of the cortex?
A
FATL
- face is located most laterally, followed by the arms, trunk and legs
6
Q
Where is the primary motor cortex located?
What Brodmann’s area is this?
A
- it is located in the precentral gyrus of the frontal lobe, anterior to the central sulcus
- it is BA 4
7
Q
What fibres arise from the primary motor cortex?
What is the role of these fibres?
A
- the primary motor cortex gives rise to corticospinal and corticobulbar UMNs
- these descend via the posterior limb of the internal capsule
- the function of these tracts is to execute voluntary movement
8
Q
What muscles are supplied by corticospinal fibres from the primary motor cortex?
How do they descend to reach these muscles?
A
- corticospinal fibres cross the midline at the decussation of the pyramids
- they enter the spinal cord to stimulate the muscles of the BODY** on the **CONTRALATERAL side
9
Q
What muscles are stimulated by the fibres of the corticonuclear (corticobulbar) tract?
How do they travel to reach these muscles?
A
- corticonuclear fibres synapse with LMNs within cranial nerve nuclei in the brainstem
- the corticonuclear tract directly innervates nuclei for V, VII, IX and XII
- the corticonuclear tract innervates these nuclei bilaterally
- except for the lower facial nuclei that innervates the contralateral lower muscles of facial expression
- the fibres of the corticonuclear tract stimulate muscles of the FACE
10
Q
What is the result of a lesion in the precentral gyrus?
A
contralateral paralysis / paresis
- as the precentral gyrus is somatotopically organised, a lesion in the most medial area leads to paralysis of the legs
- a lesion more laterally will lead to paralysis of the face / tongue
11
Q
What are the association motor areas?
Where are they located?
A
- pre-motor and supplementary motor areas (BA 6)
- frontal eye field (BA 8)
- Broca’s area (BA 44, 45)
- these are all located immediately anterior to the precentral gyrus
- they do not initiate movement, but are responsible for other things related to movement
12
Q
What is the function of the premotor and supplementary motor areas (BA 6)?
A
- they both receive inputs from the VA and VL nuclei of the thalamus
- together they generate and store programmes of motor routines for skilled voluntary actions
- e.g. tying shoe laces - this action needs to be learnt
- they relay instructions to the primary motor cortex about the pattern of muscle movement needed to perform a highly skilled task
13
Q
What is the result of a lesion to BA 6 (premotor & supplementary motor areas)?
A
apraxia
- this is the inability to perform highly skilled, learned patterns of movement despite having the desire and physical ability to perform them
- there is no paralysis as the primary motor cortex is still intact
14
Q
What is the role of the frontal eye field (BA 8)?
What happens if there is a lesion?
A
- it controls voluntary conjugate eye movements to the opposite side
- a lesion causes the eyes to deviate towards the ipsilateral side
15
Q
What is the role of Broca’s area (44, 45)?
Where is it located?
A
- it is the expressive speech area that regulates the pattern of breathing and vocalisation needed for normal speech
- it is involved in the motor aspect of speech production
- it is located in the inferior frontal gyrus of the dominant hemisphere
- it consists of the opercular and triangular parts of the inferior frontal gyrus
16
Q
What is the result of a lesion to Broca’s area?
A
Expressive aphasia
- the patient is aware of what they are trying to say, but is unable to articulate their speech properly or write language down
- there is hesitant and fragmented speech with little grammatical structure
17
Q
Where is the prefrontal cortex located?
A
- it exists towards the frontal pole of the frontal lobe
- it is essentially the remainder of the frontal lobe once the primary motor cortex and association motor areas have been accounted for
18
Q
What is the role of the prefrontal cortex?
A
- stimulation to this area does NOT elicit movement
- it has a role in monitoring behaviour and controlling higher mental processes, such as judgement and foresight
- it has extensive connections with the parietal, temporal and occipital lobes via fasciculi
- the lateral portion is involved in olfaction (which can evoke a wide range of emotions)
19
Q
What is the result of a lesion to the prefrontal cortex?
A
- deficits in judgement and concentration
- patients often have a change in personality, act irrationally and demonstrate inappropriate social behaviours
20
Q
Where is the primary somatosensory cortex located?
What information does it receive?
A
- located in the postcentral gyrus in the parietal lobe (BA 1, 2, 3)
- receives sensory pathways for touch, temperature, pain, vibration and proprioception
- the dorsal column pathway carries vibration / discriminative touch / proprioception information
- the spinothalamic tract carries pain and temperature information
- this sensory information is relayed via the thalamus
21
Q
Which nuclei of the thalamus are involved in relaying sensory information to the somatosensory cortex?
Which regions do they project to?
A
- the VPL nucleus receives an input from the spinal cord, which is carrying sensory information from the body
- sensory information from the body is projected more medially within the somatosensory cortex (FATL)
- the VPM nucleus receives an input from the brainstem, which is carrying sensory information from the face
- sensory information from the face is projected more laterally within the cortex
- information from the VPM and VPL nuclei travels in the posterior limb of the internal capsule to reach the cortex
22
Q
How is information related to proprioception and cutaneous sensation carried within the internal capsule?
What type of organisation is present here?
A
Cutaneous sensation:
- projected to the cortex via the anterior part of the posterior limb of the internal capsule
Proprioception:
- projected to the cortex via the posterior part of the posterior limb of the internal capsule
- this pathway is somatotopically organised so that information relating to the face is projected more laterally
23
Q
What would be the result of a lesion to the postcentral gyrus and why?
A
hypesthesia (diminished sensation) or anaesthesia (lack of sensation) on the CONTRALATERAL side
- spinothalamic tract decussates 2-3 spinal nerve segments above the point of entry
- dorsal column pathway decussates the the level of the medulla and continues as the medial lemniscus on the contralateral side
24
Q
Where are the somatosensory association areas located?
What is their role?
A
- they surround the primary somatosensory area (BA 5 & 7)
- they are located in the superior parietal lobule on the lateral and medial surfaces
- these areas do not perceive sensation, but are involved in interpretation, understanding and recognition that gives a particular sensation meaning
25
Which areas do the somatosensory association areas (BA 5, 7) receive fibres from?
1. primary somatosensory area
2. **lateral posterior nucleus** of thalamus
3. **pulvinar nucleus** of thalamus
26
What is the result of a lesion to the somatosensory association areas?
**_tactile agnosia_**
* if someone was to close their eyes and hold a key, they could recognise the object just through touch
* someone with tactile agnosia would be **unable to name the object without a visual stimulus**
27
What is found within BA 3 and why is it significant?
**_sensorimotor strip_**
* this is a small strip of neurones within the **primary somatosensory area** that are capable of **_eliciting motor responses_**
28
Where is the primary visual area located?
How is it organised?
* it is the area located **immediately superior and inferior to the _calcarine sulcus_** that extends to the occipital pole
* it is **_BA 17_**
* it is **retinotopically organised** - retinal image is mapped onto the primary visual cortex
29
Where does the primary visual cortex receive information from?
* it receives information from the retina via the **_lateral geniculate nucleus (LGN)_** of the thalamus
* it perceives this visual information
* fibres travel via the **_geniculocalcarine tract_** (optic radiations)
30
What is the result of a lesion to the primary visual cortex (BA 17)?
* results in **_visual field defects_** - hemianopias or quadrantopias
* these are **_contralateral_** if the lesion is in one hemisphere or bilateral if both are affected
31
Where are the association visual areas located?
What are the roles of the visual association areas?
* they surround the primary visual cortex (**_BA 18, 19_**) and are involved in the **interpretation of visual information**
* 3 roles of the visual association areas:
1. relating past and present experiences
2. recognition of what is being seen
3. appreciation of the significance of what is being seen
32
What is meant by the "where?" and "what?" streams?
**_"Where?" dorsal stream:_**
* describes areas located **more superiorly** towards the **parietal lobe**
* this stream is involved in **_analysis of motion_** and **_spatial awareness_**
**_"What?" ventral stream:_**
* describes are towards the **inferior aspect** of the **temporal lobe**
* this stream is involved in **_identifying colours_** and **_familiar shapes / faces_**
33
What is the result of a lesion to the association visual areas?
**_visual agnosias_**
* we are still able to see objects, but are unable to give meaning to the visual information being perceived
34
What is the blood supply to the dorsal "where?" stream?
What happens if there is a lesion to this region?
* blood supply is via the **_middle cerebral artery_**
* there are usually **bilateral lesions** of the **superior parietal lobe**
* lesions to this area lead to **_visual disorientation_** as there is **difficulty interpreting motion** and **spatial awareness**
35
What is the blood supply to the ventral "what?" stream?
What happens if there is a lesion here?
* supplied by the P3 and P4 branches of the **_posterior cerebral artery_**
* there is usually a lesion to the **inferior temporal lobe** anterior to the occipital lobe
* this leads to **_acquired achromatopsia_** (loss of colour vision in the contralateral halves of the visual field)
* there is also **_prospagnosia_** (inability to recognise faces)
36
Where is the primary auditory cortex located?
What is its role?
* located within the **_transverse temporal gyri_** (***Heschl's convolutions***)
* located in the ventral wall of the lateral fissure in the **superior temporal gyrus** (**BA 41, 42**)
* the primary auditory cortex is invovled in the **_conscious perception of sound_**
37
What nucleus of the thalamus is associated with the primary auditory cortex (BA 41, 42)?
* information about sound is projected to the brainstem via the **cochlear nerve**
* it is projected to the **_medial geniculate nucleus (MGN)_** of the thalamus, and then to the primary auditory cortex
38
How is the primary auditory cortex organised?
**_tonotopically organised_**
* **lower frequency** sounds are perceived by more **anterolateral aspects** of the primary auditory cortex
* **higher frequency** sounds are interpreted more **posteromedially**
39
What happens if there is a unilateral and bilateral lesion to the primary auditory cortex?
**_Unilateral lesion:_**
* there is a ***slightly decreased ability to perceive sound*** as auditory information is projected to **_both MGNs_**
**_Bilateral lesion:_**
* leads to ***cortical deafness***
40
Where is the association auditory cortex located?
What is its role?
* it is the **_planum temporale_** - located in the **superior temporal gyrus** and extends slightly into the **parietal lobe**
* it is involved in the **interpretation of auditory information**, which gives it meaning
* in the dominant hemisphere, **_BA 22 is Wernicke's area_**
41
What is the role of Wernicke's area (BA 22)?
What happens if there is a lesion to this area?
* it is the **_receptive language area_** that is involved in the ability to **understand and interpret** both **written and spoken language**
* a lesion leads to **_receptive aphasia_**
* the patient is able to produce speech, but they cannot understand spoken/written language
* **_speech is fluent_**, but it **_makes little sense_**
42
Where is the primary taste cortex located?
* it is located in the region of the **_insula_** (**BA 43**)
* it extends from the **inferior margin of the postcentral gyrus** and is adjacent to the general sensory area for the tongue
43
Which fibres and nuclei are involved in delivering information to the primary taste cortex (BA 43)?
* cranial nerve afferents carry taste information to the **_rostral solitary nucleus_** (VII, IX and X)
* this information is projected to the **_VPM of the thalamus_** via the **ipsilateral tegmental pathway**
* from the VPM nucleus, **thalamocortical fibres** complete the pathway to BA 43
44
What is the result of a lesion to the primary taste cortex (BA 43)?
* a lesion to the taste cortex is usually accompanied by **_lack / diminished sensation in the tongue_** due to the close proximity of the **tongue area of the postcentral gyrus**
* if the lesion extends **more anteriorly**, it may affect the **tongue area of the precentral gyrus** and lead to **_motor deviations of the tongue_**
45
Where is the olfactory cortex located?
What is significant about this sensory pathway?
* olfactory fibres end in the area surrounding the **_uncus_** and its neighbouring area (**BA 28, 34**)
* the olfactory pathway is the only sensory pathway that has **_no thalamic involvement_**
* *fibres travel directly from the olfactory tract to the olfactory cortex*
46
What are the roles of the additional association cortex?
What are the 2 parts?
* involved in more complex aspects of **behavioural** and **intellectual functioning**
* not specific to giving meaning to one sensation, but **_integrate multiple modalities_**
* **_prefrontal cortex_** and **_parieto-temporal cortex_** make up the additional association cortex
47
What is the role of the prefrontal cortex?
* it **_regulates moods and feelings_** and is involved in **higher cognitive functions**
* it has a role in **_conceptualisation, planning and judgement_**
* flexible and complex behavioural patterns are constructed using experience
48
What is the role of the parieto-temporal cortex?
* it **_integrates analysed information_** from **different sensory association areas** to give a comprehensive understanding of the immediate environment
* it has a **_role in memory_** and allows us to retrieve specific information
* *e.g. the memory of someone's face, how they smell, what they sound like etc.*
49
Why is the left hemisphere called the "talking hemisphere"?
Why might a lesion to this hemisphere be more severe?
* it is the dominant hemisphere in 95% of people, which is responsible for **language** (and calculations)
* a left-sided lesion is more serious due to the potential added deficit of **_aphasia_**
50
Which structure is larger in the left hemisphere compared to the right?
**_planum temporale_**
* it is larger in the left hemisphere as it is part of **Wernicke's (receptive language) area**
51
What are the main roles of the right hemisphere?
* spatial and dimensional awareness
* perception
* nonverbal ideation
* it is not involved in written or spoken language, but has roles in other aspects of language (e.g. perception of body language)
52
What are the 3 different types of nerve fibres found in the white matter of the cerebral hemispheres?
1. association fibres
2. commissural fibres
3. projection fibres
53
What is the purpose of association fibres?
What are the 2 different types?
* they **interconnect areas within the _same hemisphere_** and **adjacent gyri** within a hemisphere
* there are **_long_** and **_short_ association fibres**
54
What are the 6 main long association fibres?
1. cingulum
2. superior longitudinal fasciculus
3. inferior longitudinal fasciculus
4. perpendicular fasciculus
5. superior occipitofrontal fasciculus
6. inferior occipitofrontal fasciculus
55
What structures are connected by the cingulum?
What is its purpose?
* it is the fasciculus of the **_limbic system_** that allows for communication between its different components
* it interconnects the ***cingulate gyrus***, ***parahippocampal gyrus*** (of temporal lobe) and the ***septal area*** below the ***genu of the corpus callosum***
56
What structures are connected by the superior longitudinal fasciculus?
What is its role?
* it runs **_above the insula_** to connect the **parietal, temporal** and **occipital lobes** with the **frontal lobe**
* it is a pathway for sensory information to influence appropriate motor function
57
What structures are connected by the inferior longitudinal fasciculus?
What is its function?
* it connects the **_temporal and occipital lobes_**
* thought to be involved in functions linked to the **_ventral "what?" stream_**, such as **object recognition** and **face perception**
58
Which structures are connected by the perpendicular fasciculus?
the parietal and occipital lobes
59
What structures are connected by the superior & inferior occipitofrontal fasciculus?
Which part involves the temporal lobe?
* it connects the **_occipital lobes_** to the **_frontal lobes_**
* it passes backwards from the frontal lobe, along the lateral border of the caudate nucleus and onto the medial aspect of the corona radiata
* the **_uncinate fasciculus_** is part of this that **sweeps around the lateral sulcus** to the temporal lobe
* the uncinate fasciculus connects the **orbital and anterior temporal cortex**
60
What is the role of short association fibres?
short association fibres connect **_adjacent areas of cortex**_ within the _**same hemisphere_**
61
What is the role of commissural fibres?
What are the 4 main commissural fibres?
they interconnect areas **_between hemispheres_**
1. corpus callosum
2. anterior (rostral) commissure
3. posterior commissure
4. habenular commissure
62
What are the following commissural fibres?
63
What are the 4 parts of the corpus callosum?
What is it derived from?
1. rostrum
2. genu
3. body
4. splenium
* it is derived from the **lamina terminalis**
* the rostrum is continuous with the lamina terminalis (anterior wall of IIIrd ventricle)
64
What are the 2 major radiations from the corpus callosum that interconnect the 2 hemispheres?
**_Forceps minor / frontalis:_**
* this connects the **lateral and medial surfaces of the _frontal lobes_**
* it crosses the midline via the **_genu_** of the corpus callosum
**_Forceps major / occipitalis:_**
* this connects the **_occipital lobes_**
* it crosses the midline via the **_splenium_** of the corpus callosum
65
What structures are connected by the anterior commissure?
* it interconnects the **_middle and inferior temporal gyri_** and the **_olfactory bulbs_**
* derived from the lamina terminalis
66
What structures are connected by the posterior commissure?
* it interconnects posterior cortical regions, 2 sides of the rostral midbrain and the pretectal area
* fibres are involved in the pupillary light reflex and coordinating vertical eye movements
67
What structures are connected by the habenular commissure?
the habenular nuclei of the epithalamus
68
What structures are connected by the fornix?
* also called the hippocampal commissure as it connects the hippocampi
69
What is the function of projection fibres?
they **interconnect the cerebrum** with the **_rest of the CNS_**
70
What do projection fibres begin with?
What is this continuous with and what passage does it take to reach its target?
* projection fibres begin as the **_corona radiata_**, which are **continuous with the _internal capsule_**
* the internal capsule passes between the **head of the caudate** and the **lentiform nuclei**
* it connects to the **cerebral peduncles**, **ventral pons** and **medullary pyramids**
71
What are the 5 parts of the internal capsule?
1. anterior limb
2. genu
3. posterior limb
4. sublentiform part
5. retrolentiform part
72
How is the internal capsule organised?
it is somatotopically organised
