1
Q
Where is the retina located?
What are the first 3 neurones of the visual pathway located in the neural layer of the retina?
A
- the retina is located at the very inferior aspect of the eye
- the first 3 neurones of the optic pathway are located in the neural layer of the retina:
- photoreceptors (rods & cones)
- bipolar cells
- ganglion cells
- the photoreceptors absorb light and connect to bipolar cells
- bipolar cells then connect to ganglion cells
- the axons of the ganglion cells collect together at the back of the retina as the optic nerve
2
Q
Where is the optic disc located?
What vessels are found here? What cells are not found here?
A
- the optic disc is the point at which the optic nerve exits the retina
- the central retinal artery and vein are found at the optic disc
- it is called the “blind spot” as there are no photoreceptors located here
- these are the cells that absorb light - so we are blind to any light information that falls on the optic disc
3
Q
What is the macula lutea and where is it located?
What is the centre of it called and why is this significant?
A
- it is an area adjacent to the optic disc that has a high concentration of photoreceptors
- it is located along the visual axis
- the fovea is the area at the very centre of the macula that contains a high concentration of cone cells
- the fovea is the centre of the visual field and is the point of highest visual acuity
4
Q
What is significant about the optic nerve being an extension of the diencephalon?
A
- as the optic nerve is an extension of the diencephalon, it is surrounded by meninges
- there is a subarachnoid space containing CSF surrounding the optic nerve
- if there is an increase in CSF pressure at the level of the brain, this can translate to the optic nerve and cause it to swell (papilloedema)
5
Q
What is papilloedema?
What typically causes it and what are the symptoms?
A
- papilloedema is swelling of the optic disc
- it is caused by increases in CSF pressure by space-occupying lesions or a failure to drain CSF
- the increase in CSF pressure compresses the central retinal vein, preventing drainage of blood from the eye and increasing the pressure even further
Symptoms:
- headaches
- drowsiness
- blurred vision
- vomiting
6
Q
What are the structures involved in the visual pathway starting from the optic nerve?
A
- the optic nerve travels inferiorly to reach the optic chiasm
- at the chiasm, some fibres will cross and some will not
- from the chiasm, fibres travel to the lateral geniculate nucleus (LGN) of the thalamus via the optic tract
- this is underlying the lateral geniculate body (LGB)
- the LGN gives rise to optic radiations, which travel to the primary visual cortex in the occipital lobe
7
Q
Locate the structures of the visual pathway
A
- the optic tract radiates around the midbrain to reach the LGN of the thalamus
- the primary visual cortex is the area of grey matter that surrounds the calcarine sulcus
8
Q
What is an alternative name for the optic radiations?
A
geniculocalcarine tract
- they are passing from the geniculate nucleus to the area surrounding the calcarine sulcus
- the area of grey matter surrounding the calcarine sulcus is the primary visual cortex (striate cortex)
9
Q
Identify the following structures
A
10
Q
In which part of the internal capsule do the optic radiations travel in?
A
- the optic radiations travel mostly through the retrolenticular part of the internal capsule
- this is a radiation away from the posterior limb
- some fibres also travel in the sublenticular parts of the internal capsule
11
Q
What are the 3 main parts of the internal capsule and their anatomical relationships?
A
Anterior limb:
- located lateral to the head of the caudate nucleus
Genu:
- named as it bends like a knee
Posterior limb:
- located lateral to the thalamus and medial to the lentiform nucleus
12
Q
How do the sublenticular and retrolenticular limbs of the internal capsule travel and what fibres do they contain?
A
Sublenticular limb:
- fibres travel underneath / below the lentiform nucleus
- contains auditory radiations and some fibres that are part of the optic radiations
Retrolenticular limb:
- fibres arch behind the lentiform nucleus
- contains the majority of the optic radiations
13
Q
What is labelled 1-5 in this diagram?
What must be removed to expose the internal capsule?
A
- sublentiform part
- retrolentiform part
- posterior limb of IC
- genu
- anterior limb of IC
- the lentiform nucleus must be removed to allow for exposure of the entire internal capsule
14
Q
How can the primary visual cortex be further subdivided?
What is the role of this area and what is its BA?
A
- the primary visual cortex (BA 17) is where we consciously perceive visual information, but we do not interpret it
- it can be further subdivided into:
- upper bank of calcarine sulcus (superior to sulcus)
- lower bank of calcarine sulcus (inferior to sulcus)
- occipital pole (tip of occipital lobe)
15
Q
What are the roles of the visual association cortex?
How can this be divided into 2 streams?
A
- visual association areas (BA 18, 19**) surround the primary visual cortex and **give meaning to the visual information we perceive
dorsal “where” stream:
- involved in analysis of motion and spatial relationships
ventral “what” stream:
- involved in analysis of letters, shapes, faces, colours, etc.
16
Q
What is the difference between the visual field and the retinal field?
A
visual field:
- this describes what we are seeing when looking at something
retinal field:
- this is the part that gets projected onto the retina
- when images are inverted onto the retinal field, they are flipped upside-down and mirror-reversed
17
Q
How is the visual field divided?
What is the fixation point?
A
- each visual field is divided into hemi-fields by a vertical line
- they are then divided into quadrants by a horizontal line
- the point where these lines transect is the fixation point
- this corresponds to light that is reaching the fovea
18
Q
How is information projected from the visual fields to the hemiretinas?
A
- information from the temporal visual field (outermost visual field) is projected to the nasal hemiretina
- information from the nasal visual field (innermost visual field) is projected to the temporal hemiretina
- the nasal hemiretina is the area medial to the fovea
- the temporal hemiretina is the area lateral to the fovea
19
Q
Which fibres cross at the optic chiasm?
A
- fibres travelling from the nasal hemiretina will CROSS at the optic chiasm
- fibres travelling from the temporal hemiretina will NOT CROSS at the optic chiasm
- fibres from both hemiretinas will reach the optic chiasm via the optic nerve
20
Q
At the level of the optic tract, how is each visual field represented?
A
- from the optic chiasm, visual information reaches the LGN via the optic tract
- information then travels to the primary cortex via the optic radiations
- at the level of the optic tract (and beyond this), each visual field is represented in the contralateral cortex
- the left half of the visual field is completely on the right side of the cortex, and vice versa
21
Q
How can the optic radiations be divided?
What is the purpose of this?
A
- the optic radiations are divided into:
- superior trajectory
- inferior trajectory (Meyer’s loop)
- this is necessary as information from the superior and inferior quadrants of the visual field is carried slightly differently from the LGN to the cortex
22
Q
What type of information is carried by the superior and inferior trajectories of the optic radiations?
A
Superior trajectory:
- carries information from the lower visual field** to the **upper bank of the calcarine sulcus
- information from the lower visual field reaches the upper part of the retina as it is turned upside-down as it is projected onto the retinal field
Inferior trajectory (Meyer’s loop):
- carries information from the upper visual field to the lower bank of the calcarine suclus
23
Q
How are the macula and fovea represented at the level of the primary visual cortex?
What about more peripheral areas?
A
- the fovea is the very centre of the visual field, and this is the centre of the macula
- the macula is represented most posteriorly in the striate cortex - at the occipital pole
- more peripheral areas are located more anteriorly in the striate cortex
- (red = macula at occipital pole*
- orange = areas surrounding the macula (more anterior)*
- yellow = periphery of visual field (most anterior)*
24
Q
What is the result of a lesion to the upper bank of the calcarine sulcus with sparing of the occipital pole?
What is another name for this presentation?
A
- upper bank of the calcarine sulcus receives visual information from the lower field of the contralateral eye
- if there is a lesion in the right hemisphere, there will be loss of the left lower quadrant
- the occipital pole is intact so there is macular sparing
- they are still able to see the very centre of the visual field
- this is known as “pie in the floor” with macular sparing
25
How does the superior trajectory travel to the primary visual cortex?
What information is it carrying?
* it passes around the lateral ventricle
* it then curves posteriorly within the **_retro-lenticular part**_ of the internal capsule to reach the _**upper bank_ of the calcarine sulcus**
* it is carrying information from the **_lower half_ of the visual field**
26
How does the inferior trajectory travel to the primary visual cortex?
What information is it carrying?
* some fibres travel over the temporal horn of the lateral ventricle
* these fibres are travelling within the **_sublenticular part_** of the internal capsule to reach the **_lower bank_ of the calcarine sulcus**
* they are carrying information from the **_upper half of the visual field_**
27
What is a scotoma?
* this is a **_localised patch of blindness_**
* it can be located within the centre of the visual field or in the periphery
28
What is an anopia?
How can this be further classified?
* the **_loss of one or more quadrants_** of the visual field
* **_hemianopia_** is the **loss of half** of the visual field
* **_quadrantopia_** is the **loss of a quarter** of the visual field
* **_homonymous_** describes visual field losses that are **similar on both sides**
* **_heteronymous_** describes visual field losses that are **different on each side**
29
What is meant by macular sparing?
* this describes a condition in which the **central visual field is maintained**
30
What visual defect to pituitary tumours often lead to and why?
* pituitiary tumours **_impinge on the optic chiasm_** to disrupt the fibres in the **very centre**
* *these are the fibres that are crossing over*
* this results in **_bitemporal hemianopia_** (heteronymous hemianopia)
* the **temporal visual fields** on both sides are lost as it is the **nasal hemiretina fibres** crossing at the optic chiasm that are affected
* there is loss of the left visual field in the left eye, and of the right visual field in the right eye
31
How many layers is the lateral geniculate nucleus divided into?
**_6 layers_**
* layers **1-2** are the **magnocellular layers** (ventral)
* layers **3-6** are the **parvocellular layers** (dorsal)
32
What are the ventral layers of the LGN?
What is their role and which part of the primary visual cortex do they project to?
**_magnocellular_ (large cell) layers**
* information reaching and being relayed to this area is related to **location** and **movement**
* this information is projected via the **_dorsal "where" stream_**
* it reaches the **_superior occipital_** and **_posterior parietal cortex_**
* *this region analyses information related to motion and spatial relationships*
33
What cells are found in the dorsal LGN?
Where is this information projected to?
**_parvocellular_ (small cell) layer**
* information reaching this area is related to **colour** and **visual form**
* it is projected via the **_ventral "what" stream_**
* it reaches the **_inferior occipital_** and **_temporal cortex_**
* *these areas can identify colours and familiar shapes*
34
Neuroanatomy
flashcards
Decks in class (16)
# Cards
-
Development of the Nervous System85
-
Spinal Cord14
-
Blood Supply to the Brain56
-
Cranial Nerves - V & VII49
-
Cranial Nerves - IX, X, XI & XII27
-
Cranial Nerves - Blood Supply & Reflexes41
-
Cranial Nerves - III, IV & VI41
-
Cortical Localisation & Subcortical White Matter72
-
Diencephalon53
-
Visual Pathway34
-
Auditory Pathway34
-
General Sensation43
-
Descending Pathways34
-
Cerebellum42
-
Basal Ganglia51
-
Limbic System41
