Localisation Flashcards
1
Q
What do the cerebral hemispheres consist of?
A
Include a dense core of white matter with an overlying thin layer of grey matter (cortex)
2
Q
Describe the cerebral cortex
A
- Varies in thickness from 2-4mm
- Heavily folded to increase surface area (over half the total surface area is hidden by the walls of the sulci)
- Laminar arrangement (I-IV)
- 6 layers with specific cells
- Specific sulci are used to divide the cerebral hemispheres into lobes and specific gyri
3
Q
What does the central sulcus divide? What is found on either side of the central sulcus?
A
- Divides the frontal lobe from the parietal lobes
- Precentral gyrus in front
- Postcentral gyrus behind
4
Q
Sulci and gyri view
A
5
Q
Which sulci and gyri are found on the lateral aspect of the frontal lobe?
A
2 sulci:
- Superior
- Inferior
Therefore 3 gyri:
- Superior
- Middle
- Inferior
6
Q
What does the lateral sulcus separate?
A
Separates the frontal and parietal lobes from the temporal lobe
7
Q
Which sulci and gyri are found on the lateral aspect of the temporal lobe?
A
2 sulci:
- Superior
- Inferior
Therefore 3 gyri:
- Superior
- Middle
- Inferior
8
Q
What does the parieto-occipital sulcus separate?
A
The parietal lobe from the occipital lobe
9
Q
Where is the calcarine sulcus found?
A
located on the medial surface of the occipital lobe
10
Q
Which sulcus runs parallel with the corpus callosum?
A
The cingulate sulcus
11
Q
What does the cingulate sulcus separate?
A
Separates the frontal and parietal lobes from the cingulate gyrus
12
Q
In which view of the brain is the cingulate sulcus seen?
A
Only in the medial view
13
Q
Where is the collateral sulcus found?
A
On the medial surface of the temporal lobe
14
Q
What does the collateral sulcus define?
A
Defines the position of the parahippocampal gyrus
15
Q
What is the uncus?
A
- an anterior extremity of the parahippocampal gyrus
- the most medial part of the temporal lobe
16
Q
What is the parahippocampal gyrus? What lobe is it part of?
A
A cortical region in the medial temporal lobe that surrounds the hippocampus
17
Q
Sulci and gyri: medial vs lateral view
A
18
Q
What is the limbic system?
A
- A set of brain structures located on both sides of the thalamus
- Formed mainly of the subcallosal gyrus, the cingulate gyrus, the parahippocampal gyrus, and the hippocampus.
- Deal with emotion and memory
19
Q
What part of the brain is circled in red?
A
Diencephalon
20
Q
What is an uncal herniation? What is compressed?
A
- Occurs due to rising intracranial pressure
- Uncal parts of temporal lobe herniate below the tentorium cerebelli
- Compresses midbrain
21
Q
What is a tonsillar herniation? What does it compress?
A
- Cerebellar tonsils herniate through the foramen magnum
- This compresses the medulla
22
Q
Lobes medial and lateral
A
23
Q
What is a ‘Broddman area’?
A
- A region of the cerebral cortex
- 46 areas in total
- Based on cellular organisation of cerebral cortex
- Specific areas of cortex are believed to carry out specific functions
- (you don’t have to remember numbers)
24
Q
There are primary projection areas in the brain.
- What occurs at the primary sensory areas?
- What occurs at the primary motor areas?
A
- Sensory: specific sensory pathways terminate here –> perceived sensation
- Motor: specific motor pathways originate here
25
The **primary sensory areas** have different modalities. What cortical area is associated with each modality:
* General sensation (somaesthetic)
* Visual
* Auditory
* Olfactory
* Gustatory
* Post-central gyrus
* Either side of calcarine sulcus (striate cortex) and occipital pole
* Heschl's gyrus (superior temporal gyrus)
* Uncus
* Inferior post-central gyrus
26
Which cortical area is the primary motor cortex?
Pre-central gyrus
27
Medial and lateral view of primary motor and sensory areas
28
What are secondary association areas?
Lie near the primary projection areas and are associated with further processing
29
What is the function of 2ary sensory areas?
* Receive input from 1ary sensory areas
* Involved in interpretation/understanding
* 1ary areas **perceive** info
* 2ary areas **interpret** info (give it meaning)
30
What is the function of the 2ary motor areas?
* Sends output **to** 1ary motor area
* Organises patterns of movement
* Organises instruction and then sends to 1ary area
* 1ary area then sends command to move that body part
31
The **secondary** sensory areas have different modalities. Which cortical area is associated with:
* General sensation (somaesthetic)?
* Visual?
* Auditory?
* Superior parietal lobe
* Pre-striate area
* Lateral fissure/superior temporal gyri
32
The 2ary motor areas have different modalities. What cortical area is associated with:
* Premotor area?
* Supplementary motor area?
* Frontal eye field?
* Anterior to precentral sulcus on lateral surface
* Anterior to precentral sulcus on medial surface
* Anterior to premotor
33
What is function of primary motor cortex in pre-central gryus?
* Sends **descending motor fibres** through brainstem, through spinal cord via specific tracts to perform muscle contractions
* Controls **voluntary contraction** of specific muscles
* Somatotopically organised
34
Where are the associated motor areas located?
Anterior to primary motor cortex
35
What are the association motor areas?
* Supplementary motor (sm)
* Pre-motor (pm)
* Frontal eye field (8)
* Broca's area (44, 45)
36
Where are the supplementary motor and pre-motor association areas located? What is their function?
* Located anteriorly to primary motor cortex (pre-central gyrus)
* Sm located more medially
* Pm located more laterally
* Function: learned complex motor activities and storage of those activities
* Organise instructions to perform a complex motor activity and send it to the pre-central gyrus to execute this movement
* E.g. learning to tie shoelaces
* Storage of those activities (so can perform activity again)
37
Where is the frontal eye field located? What is its function?
* Frontal lobe (8)
* Controls voluntary scanning movements of the eyes
38
Where is Broca's area located? What is its function?
* Located in **inferior frontal gyrus**
* Localised to dominant hemisphere (left in most people)
* Function: regulates pattern of **breathing** and **vocalisation** needed for **normal speech**
39
What is result of injury to pre-central gyrus?
Paresis (impaired movement) or even paralysis (if severe)
40
What is result of injury to association motor area?
* Still able to move body parts
* Lost ability to perform highly skilled movement e.g. tieing shoelace
41
What does the primary somatosensory cortex located in the post-central gyrus do?
* **Receives** sensory pathways for touch, temperature, vibration, pain, proprioception
* Sensory receptors all round body project to spinal cord, through specific tracts and **ascends** to the post-central gyrus
* HOWEVER, this info stops in the **thalamus** and is then relayed to the primary somatosensory cortex
* Thalamus = relay station
* *Somatotopically organised*
42
What is the VPL and VPM?
* There are 2 subdivisions VPL (ventral posterolateral nucleus):
* Lateral VPL
* Medial VPL
* VPN: ventral posteromedial nucleus
These are nuclei of the thalamus which are part of the somatosensory system.
43
Function of VPL?
* Lateral VPL: receives input from **leg** and projects to **midline**
* Medial VPL: recives input from **arm** and projects to **lateral region**
44
Function of VPM?
Receives input from the **face** and projects to **lateral** region
45
Where does the lateral VPL receive info from? Where does it project to?
* Receives from leg
* Projects to midline
46
Where does the medial VPL receive info from? Where does it project to?
* Receives from: arm
* Projects to: lateral region
47
Where does the VPM receive info from? Where does it project to?
* Receives from: face
* Projects to: lateral region
48
Somatotopic organisation:
Pre-central gyri: pink
Post-central gyri: blue
49
Organisation explained: pre-central gyrus
* Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system.
* I.e. specific regions within **pre-central gyrus** that controls specific areas of the body
* Info to move the hands starts more laterally than info to move the toes
* General rule:
* Legs (most medially)
* Then trunk
* Then arms
* Then face (most laterally)
50
Organisation explained: post-central gyrus
* Sensory info coming from body reaches the thalamus
* The thalamus knows where the info has come from and then projects this info to specific parts of **post-central gyrus**
* General rule:
* Face located (more laterally)
* Then arms
* Then trunk
* Then leg (more medially)
51
What is a motor homunculus?
* It's important to notice that the size of the area of the pre-central gyrus does not correspond to the size of the body parts
* A motor homunculus represents a **map of brain areas** dedicated to motor processing for different anatomical divisions of the body.
* Hand so big as we perform many specific actions with our hands --\> many motor commands go here
52
What is a sensory homunculus?
* The sensory homunculus is a map along the cerebral cortex of where each part of the body is processed.
* Many sensory receptors in hand and face (especially lips and tongue)
53
Where is the somatosensory association cortex (areas 5 and 7) located? What is its function?
* Directly posterior to the sensory cortex in the **superior parietal lobes.**
* Function: interpretation, understanding and recognition
* Gives meaning to those sensations
* If your arm is being stroked, your 1ary somatosensory cortex knows you are being stroked BUT your somatosensory association cortex knows what kind of stroke (e.g. kind, feather, unpleasant, burning etc)
54
What is result of injury to 1ary somatosensory cortex (post-central gyrus)?
* Diminished sensation --\> Hypoesthesia
* Absent sensation --\> Anaesthesia
55
What is result of injury to association somatosensory area?
Tactile agnosia
56
What is tactile agnosia?
the loss of the ability to recognise objects, faces, voices, or places despite intact elementary tactile perceptions.
57
Where is the primary auditory cortex (BA 41, 42) located? What is its function?
* Located in the **superior temporal gyrus** (Heschl's gyrus)
* Function: Conscious perception of sound
* Perceives sound but doesn't know meaning of sound as only a 1ary area
58
What part of the thalamus does the primary auditory receive input from?
From the **medial geniculate nucelus (MGN)**
59
How is the primary auditory cortex organised?
Tonotopically organised:
* Lower frequences are projected more medially into gyrus
* Higher frequences are projected more laterally/posteriorly into gyrus
60
what is tonotopic organisation?
Tonotopic organisation means that cells responsive to different frequencies are found in different places at each level of the central auditory system, and that there is a standard (logarithmic) relationship between this position and frequency. Each cell has a characteristic frequency (CF).
61
Where is the **association** auditory cortex (BA 22) located?
* Surrounds 1ary auditory cortex
* In the posterior section of the superior temporal gyrus
* Called **Wernicke's area** (in the dominant hemisphere - typically left)
* Function: interprets and gives significance to auditory information
* I.e. decides if noise is pleasant/unpleasant etc
62
What is Wernicke's area? How does it differ from Broca's area?
* Interpretation of written or spoken word
* Wernicke's area is the region of the brain that is important for language development. It is located in the temporal lobe on the left side of the brain and is responsible for the comprehension of speech, while Broca's area is related to the production of speech.
63
Where is the primary visual area (BA 17) located?
* Area around **calcarine sulcus** and **occipital pole**
* Function: receives info from retina
* Optic nerve sends input from retina to lateral geniculate nuleus of thalamus
* Info them sent to primary visual cortex in occipital lobe
64
Which is the only sense that isn't relayed in the thalamus?
Smell
65
Which part of the thalamus relays auditory info?
medial geniculate nucleus
66
Which part of the thalamus relays visual info?
lateral geniculate nucleus
67
How is the primary visual cortex organised?
Retinotopically
68
Where is the association visual cortex (BA 18, 19) located? Function?
* Surrounds 1ary visual cortex (shown in orange)
* Funcion: Interpretation of visual information
* Recognise faces, objects, trees etc
69
What does an injury to the association visual cortex result in?
Prosopagnosia
70
What is prosopagnosia?
Neurological disorder characterised by the **inability to recognise faces.** Prosopagnosia is also known as **face blindness** or facial agnosia.
71
Where is the taste cortex located?
Extends from inferior margin of postcentral gyrus into the insula
72
What are is the general association cortex?
Involved in **more complex aspects** of behavioural and intellectual functioning
Examples:
* Prefrontal cortex
* Parieto-temporal cortex
73
What is the function of the prefrontal cortex?
* Is a general association cortex
* Regulates moods and feelings
* Involved in higher order cognitive functions
* Conceptualisation, planning, judgement
74
What is the function of the parieto-temporal cortex?
* Is a general association cortex
* Integrates information from different modalities (e.g. vision, hearing) and gives it meaning
* Involved in memory
75
What can damage to the prefrontal cortex result in?
* Tend to perform poorly on tasks that require the use of long-term strategies and the inhibition of impulses.
* Become impulsive
* Lose ability to make sound judgements
* Lose inhibition of impulsive behaviour
* Often display short-term memory deficits, which may help to explain some of their difficulties in planning.
76
What is cerebral dominance?
The ability of one cerebral hemisphere (left or right) to **predominately control specific tasks** --\> i.e. lateralisation of the brain
77
What is the dominant hemisphere for language in most people?
The left --\> two language areas are located within dominant hemisphere
78
What can damage to language areas result in?
Aphasia
79
What is aphasia?
An inability to comprehend or formulate language because of damage to specific brain regions.
80
What are the 2 main language areas?
1. **Broca's area:** inferior frontal lobe
2. **Wernicke's area:** superior temporal lobe
81
What does damage to Wernicke's area result in?
Sensory/fluent aphasia: inability to understand language BUT words come out fluently but make no sense
(applies to written language as well as spoken language)
82
What can damage to Broca's area result in?
Motor/non-fluent aphasia: inability to correctly articulate speech BUT can understand language
83
What is dysphasia?
Difficulty speaking
84
What connects the Broca's area and the Wernicke's area in the brain?
* The arcuate fasciculus
* A bundle of axons (white matter)
* Is an **association fibre tract** connecting caudal temporal cortex and inferior frontal lobe.
85
What can damage to the arcuate fasciculus result in?
Conduction aphasia:
* Impaired repetition as connection lost
* Comprehension and fluency intact
* Wernicke's and Broca's area intact
86
Cortical organisation summary:
* Some areas have precise sensory or motor function
* Other areas have progressively more associative or integrative function
* As ascends “hierarchy” of cortical function, lateralisation of some functions
* Dominant hemisphere (typically left)
* Linguistic function
* Numerical skills
* Non-dominant hemisphere
* Spatial awareness
87
What is the dominant hemisphere associated with?
* Linguistic function
* Numerical skills
88
What is the non-dominant hemisphere associated with?
Spatial awareness
89
Damage to **secondary sensory** areas leads to?
Agnosia - disorders of understanding:
* Awareness of sensation persists but significance of this sensation is lost
* E.g. eyes closed, handed scissors, can't recognise
90
Damage to **secondary motor areas** leads to?
Apraxia - Inability to carry out purposive movements, although there is no paralysis
* Leads to inability to perform learned movements
91
_Case Study:_
* 20 year old woman fainted, unconscious for several hours.
* Once awake, unable to speak apart from saying ‘damn’ repeatedly due to frustration of loss of speech.
* Able to print words with L hand. R hand limp and paralysed.
* Months later: Loss of speech persisted, R arm and hand weak.
Locate the lesion. Structures involved? Vessel involved?
* Hemisphere: left
* Location of lesion: inferior pre-central gyrus and Broca's area
* Vessels: Middle cerebral artery
