Cerebral Cortex Flashcards
What part of the neural tube forms the brain
Rostal part of the neural tube
What part of the neural tube forms the spinal cord?
Caudal part
What become the Forebrain?
What does this develop into?
Prosencephalon becomes the forebrain
It develops into the Telencephalon and Diencephalon @ 7 weeks
which go onto form the 2 cerebral hemispheres
what becomes the midbrain?
Mesencephalon
what becomes the hindbrain?
Rhombencephalon
What are the 4 lobes of the Cerebral cortex?
- Frontal
- Parietal
- Occipital
- Temporal
What can happen at the poles?
Contusion a.k.a bruising
on frontal, temporal, occipital lobes
which lobe does not have a pole?
Parietal
What are the parts of the Forebrain?
- Cerebral hemisphere
- Olfactory bulb
- Diencephalon
what are the parts of the Cerebral Hemisphere?
- Cerebral cortex
- Basal Ganglia
- Various small nuclei
What are the parts of the Diencephalon
- Thalamus
- Subthalamus
- Hypothalamus
- Epithalamuc (a.k.a Pineal gland)
Is brain shrinkage a normal process?
Yes with ageing it is
- @ 70 - 5% lost
- @80 - 10% lost
- @90 - 20% lost
Cortex
Outer layer of gray matter - 1-4mm thickness
Controls all of cognition
What is the gateway to the Cortex?
What doesn’t go through here?
The Thalamus
Only Olfaction (sense of smell) doesn’t go through here, it goes direct to the cortex
Result of Cortical Damage to
Primary Somatosensory Cortex:
- somatosensory anaesthesia (loss of touch).
- Pain remains intact (= parieto-insular supplementary area)
Result of cortical damage to
Supplementary somatosensory areas
Superior Parietal Lobe:
- contralateral somatosensory agnosia
- (inability to recognise common objects by palpation alone: = touch and proprioception)
Result of cortical damage to
Supplementary somatosensory areas
Inferior Parietal Lobule:
in the dominant hemisphere
- (Left) concerned especially with language (alexia).
Damage of non-dominant hemisphere
- = bizarre disturbances of “body image”
- known as somatosensory disregard:
- eg patients ignore parts of their body, believing they belong to someone else (contralateral to lesion) in spite of the fact that the body part is not anaesthetic to any stimulus
What is critical for memory?
where does this sit?
Hippocampus
Sits in the temporal lobe
This degenerates in Alzheimer’s pts
Homunculus
Degree of innervation is proportional to the organ size representation
larger the innervation the larger the organ size on the homunculus
Cortical Connections
Ascending Connections:
Somatosensory from the thalamus:
- (inputs from spinal cord via VPL, and trigeminal via VPM)
Auditory:
- from the thalamus (inputs from the cochlea via the medial geniculate nucleus)
Visual:
- from the thalamus (inputs from the retina via the lateral geniculate nucleus)
Smell
- (direct into the olfactory cortex) and Taste (via VPM)
Complex information from the cerebellum and basal ganglia via the thalamus
Corical connections
Descending Connections
- Motor to the spinal cord (corticospinal tract)
- Motor to the brainstem motor nuclei (cortico-bulbar tract)
- To the motor control centres (targeted to the basal ganglia and cerebellum)
- To the limbic system
Cortical connections
Connections within the cerebral cortex
On same side:
- association fibres connecting different brain regions
On opposite sides:
- commissures including the corpus callosum
Where does the visual cortex lie?
In the OCCIPITAL LOBE
Primary sensory and motor areas on the medial surface
picture
What sulcus lies on the Medial surface?
Calcarine sulcus
what does
1) a lesion in primary cortex/retina
2) damage in secondary area
cause?
Lesion in primary cortex/retina = blindness
damage in secondary area = visaul defects NOT blindness
What are the two main streams in higher-order visual processing?
- Dorsal pathway
- Ventral Pathway
Ventral pathway
the WHAT bit
- analysis of form & colour
Damage to this area leads to:
- difficulty seeing colours
- reading newspapers (due to different font sizes)
Dorsal Pathway
the WHERE
- analysis of motion and spatial relations
Damage to this area leads to:
- trouble identifying moving objects
- BUT can identify them when stationary
Facial recognition centre
Damage to this can lead to one not being able to recognise faces which can be very devastating to friends and family etc
Propagnosia = face blindness
Effects of Lesions
Retina and primary visual cortex?
Supplementary areas?
Retina and primary visual cortex:
- Blindness
Supplementary areas:
- Visual agnosia - inability to recognise everyday objects
- Visual disregard - lesion of non-dominant inferior parietal lobule contralateral hemifield can be seen but is ignored by patient (cf. somatosensory disregard)
Facial recognition - left & right hemisphere
Visual neglect
Damage on the non-dominant hemisphere
- neglect on one side of the field, usually the left
Neuroanatomy of Language 1
- Sounds processed in mid brain. Spoken language sent to Wernicke’s area in left hemisphere.
- Written language processed in visual area; sent to angular gyrus in left hemisphere. Changed to sound; sent to Wernicke’s.
- Wernicke’s area extracts meaning from language from any source. Thoughts encoded into crude linguistic outline then sent to Broca’s area in left hemisphere where refined into grammatical form.
- Broca’s then signals to motor cortex to make speech.
- Blood flow studies confirm anatomical conclusions from studies of Stroke and brain damage.
- Low frequencies sent to Wernicke’s. High frequencies giving emotional information go to right hemisphere.
Damage right hemisphere
loss of ability to interpret emotional content.
Damage Broca’s area
know what to say but can’t do it with grammar
Damage Wernicke’s area
perfect grammar but meaningless.
Same effects seen with sign language.
Commissural fibres
connect the hemispheres/cross over from one side to the other
Corpus callosum: connects hemispheres.
“Split brain” produces 2 halves.
Visual information to Right non-dominant hemisphere gets no verbal response. So can’t name objects or read words presented in left visual field.
Tumour of splenium produces alexia without agraphia - speak and write but cannot read - separation visual processing in right hemisphere from language in left dominant (e.g. of a disconnection syndrome).
Association fibres
superior longitudanal fasciculus
inf long fascic
arcuate fascic
Superior longitudanal fasciculus: connects frontal and occipital (arcuate frontal to temporal)
Inf. long. fascic: occip to temp for visual recognition
Arcuate fasciculus: Wernicke’s area to Broca’s area
What can a tumour on the corpus callosum prevent?
Can prevent information transfer from one side to another
Cortical lesions
- Focal cerebral lesions
- Bilateral cortical degeneration
- left parietal
- right parietal
- left temporal
- occipital
- single
- bilateral
Focal cerebral lesions:
- epilepsy; sensory and/or motor deficits; & psychological deficits. Left frontal lobe lesion produces “Jacksonian seizures”, contralateral hemiplegia, aphasia (alexia & agraphia)
Bilateral cortical degeneration:
- Alzheimer’s degeneration of temporal, parietal, & limbic. Loss of language and memory.
Left parietal:
- anomia, acalculia, as well as alexia and agraphia.
Right parietal:
- constructional apraxia (skilled movements)
Left temporal:
- absences, automatisms, déjà vu, Wernicke’s aphasia.
Occipital:
- single - simple visual hallucinations, contralateral field loss
- bilateral - blindness - complex
