Cerebral Cortex Flashcards
What is the cerebral Cortex?
- largest, most evolved and interesting human brain region
- has 4 separate lobes - each specialised for a specific function- Functional localisation
What is functional localisation?
-Different lobes or regions which are specialised for a function
What is the cerebral cortex functional localisation for ?
- Special senses (e.g. somatic sensation or vision or hearing)
- Motor control (e.g. initiation of voluntary movements)
- Cognitive (e.g. different language or memory functions)
What are the primary areas of the cc?
-have matching pairs in each lobe and each cortical hemisphere e.g there is one primary area for a particular function in a lobe in a left cortex with a matching pair in the same lobe in the right cortex.
What is the reason of 2 primary areas in each lobe and hemisphere?
phenomenal on
- Functional Contra-laterality:
- involved with events occurring on the opposite side of the body or of external space ( left side brain controlling right side etc) - Topography: contain MAPS of the body or of external space in the primary area- primary areas contain a map of the opposite body surface or side of external space
What are the secondary association areas in the cerebral cortex ?
-lateralised to one hemisphere - known as cerebral dominance/functional asymmetry
for e.g left cc is dominant for language functions and right cc is dominated for spatial awareness/attention.
What is the old idea?
- phrenology- human beings posses 35 personality traits each of which to be ascribed to a particular region of the cc.
- idea behind phrenology- by filling around the surface of the skull- could detect bumps on it- which reflected enlargement of the gyrii of the brain undreneath- and when this was enlarged it reflected a increased development of particular characteristic to which that part of the brain was responsible
- same with the filling around the skull- there would be depressions of the bones- reflecting an underdevelopment of the gyro situated under- underdevelopment fo that personality trait
- as it happens - above the left ear- big lump of the surface of the skull- according to phrenologist - would mean you are secretive.
Where is the celebrellum ?
sticking out the back of the brain
What is the gyrii?
ridges on the surface of the cortex
What is sulci?
furrows in-between the ridges
What is the central sulcus?
major sulcus between the front and back of the brain
-divides the lobe of the cortex infront = frontal lobe from the lobe of cortex behind it called= parietal lobe
What is the frontal lobe?
- concerned with control and initiation of voluntary movements
- front
What does the parietal lobe do?
associated with somatic sensation
-back
What is the lateral sulcus?
- deep
- lateral surface of the coretx
- divides frontal and parietal lobe above from the temporal lobe below
What does the temporal lobe do?
associated with hearing / auditory functions
What is the occipital lobe?
- 4th lobe of the cortex
- situated at the back
- concerened with visual functions
What are the primary cortical areas?
-A small part of each lobe in each hemisphere, concerned with
the most basic or lowest levels of sensory or motor function;
- Primary Somatosensory (S1) Cortex (L & R parietal lobes)
- Primary Motor (M1) Cortex (L & R frontal lobes)
- Primary Auditory (A1) Cortex (L & R temporal lobes)
– Primary Visual (V1) Cortex (L & R occipital lobes)
Questions
Examine
- The organization of their detailed MAPS of the body/space
- How they acquire their specific functions (via the thalamus and long-range axon pathways in the white matter)
- Why they represent opposite side of the body/external space
- Anatomical/cellular basis of Functional Specializations
-How they acquire their specific functions (via the thalamus and long-range axon pathways in the white matter) e.g why is lumps of grey matter in occital lobes are essential for visual perception ?
they receive input from particular specialised nuclei of the thalamus that relays via long range axons projections travelling the white matter- info about vision to that particular part of the cerebral hemispheres
What is next to the central sulcus ?
continuous gyrus - long - starts at the bottom- goes all the way up lateral surface of the cortex and continues on the medial surface of the cortex where you can’t see behind the screen
Where is Postcentral gyrus ?
situated behind the central sulcus in the parietal lobe
-find the primary somatosensory (S1 cortex)
How do we know that the post central gyrus is a primary somatosensory cortex (S1 cortex)?
consequences of
-unilateral damage to that area - eg if you lose this in your left cordial hemisphere- you would lose all somatic sensation - loss of tactile, (touch) , thermal, pain & joint sensation, opposite side of body.- hemi- anaesthesia - i.e right
What is hemi-anaesthesia ?
lose all conscious sensations of the somatic senses
Why is it not just the left primary somatosensory cortex (S1 cortex)which receives sensory information from right side of body ?
because the postcentral gyrus contains a topographic representation or map of the body parts = Sensory homunculus- which is inverted and distorted
What do the neurons of the post central gyrus (S1 cortex) close to the lateral sulcus receive sensory input from ? (picture on word document)
receive input from sensory recpetors of face i.e top part of body
What do the neurons of the middle part of the post central gyrus (S1 cortex) receive sensory input from ?
from the hand and next part from arm
What do the neurons of the end part/medial surface of the post central gyrus (S1 cortex) receive sensory input from ?
medial surface of gyrus – from lower leg/foot
What does the topographic representation of the post central gyrus show? (doc) S1 cortex
map of body part is upside down – the bottom of gyrus represents top of body then the hand arm and the top of gyrus representing the lowest part of the body legs and feet represented highest up on the medial surface of the gyrus
therefore the map of the body parts are upside down and inverted.
What is the post central gyrus ?
anatomical name of where it is located
S1 cortex ?
functional name - need for conscious somatosensory perception
How is the map of the postcentral gyrus (S1 cortex) distorted in relation to body part ? - related to image on DOCUMENT
e.g
huge region containing millions of neutrons that is just interested in sensation coming from the lips
e.g huge region with millions of neutrons which is just interested in somatic sensory info coming from the hand
-in a much smaller region sensory info coming from the forax and abdomen.which is a huge part of the body and is compressed into the small region here.
What does the map show of the post central gyrus (cross section ) ?
that our hands are over represented- due to millions of neurons interested in that sensory info of the hand
-and our chest, back and abdomen are all under represented
Why is the hand over represented by the body in S1?
E.G feel a piece of material - would rub you fingertip and get a good sense of touch rather than using your whole chest or back to feel and have a sense of the material
so reason why < ?
- fingertips have millions of sensory receptors which is good in detecting quality and nature of tactile sensation whereas chest and back (much larger area off body) have fewer sensory receptors than in fingertips
- the high density in receptors in the hand and low density in the back , chest , trunk etc is maintained all the way through the somatosensory pathways through the nerves to spinal cord to the s1 cortex .
How is genitilia represented in the S1 cortex ?
-incidentally also why genitialia are represented in S 1 cortex below sole of the feet- because sensory information from your gentitalia enter the spinal cord at the lowest level - below spinal cord.- and is maintained throughout to the S1 Cortex.
What is situated in the Frontal lobes ? (infront of the central sulcus)
Pre-central gyrus (M1) cortex - runs parallel to the post central
- thick gyrus
- find primary Motor cortex
- micro-stimulation results in movements of opposite body parts
What happens if pre-central gyrus M1 cortex is damaged?
unilateral damage causes hemiplegia - paralysis, opposite side of the body - knocks out the precentral gyrus in the left central cortex which causes paralysis in the right side of body
What does the primary Motor cortex contain (M1 cortex)?
topographic represententaion or map= of the muscles in the diff parts of your body = called Homonculus
-map is inverted and distorted
What does the map of the left pre central gyrus show?
- similair to sensory map in the post central gyrus
- map of the muscles in the M1 cortex is upside down and distorted
- lower part of gyrus - when they are active- contain motor neurons that are responsible for moving muscles in your face
- then in middle part of precentral gyrus - motor neurons responsible for moving muscles in your hand , then in upper arm, forax etc
- then finally in medial surface of the precentral gyrus - motor neurons responsible for foot, limbs
- map of muscle is also upside down - distorted and similar to sensory map
What does the map show in the precentral gyrus ?
again that our hands are over represented and chest back are under represented
Why is our hands over represented in primary motor cortex in precentral gyrus ?
- not down to size of muscle but their number - in hadn’t lots of small muscle- capable of moving - 25 degrees of freedom - but although back is bigger has less muscle and can just move in about 6 degrees of freedom
- thats why there is lots more motor neurons in the lowest bit of the precentral gyrus for the hands face etc on the map and less in the top part for the back, trunk etc.
What is the front side of central sulcus ?
precentral gyrus of the leg and foot which represents the primary motor cortex
What is the back side of central sulcus?
postcentral gyrus which repsresntes the primary sensory cortex
What is the corbiscolosum ?
200 million axons
takes information from left cortex to right and vice ever
What is right at the back of the cortex ?
occipital lobe-
What is the occipital lobe (visible on the medial surface )?
- it is divided from parietal lobe infront of it on this medial surface by a deep sulcus - called the parieto-occiptal sulcus
- running 90dgeress to this is the calcarine sulcus- in the grey matter of upper and lower bank which we find V1 -primary visual cortex - this region contains a map of our opposite half of the visual; field
What does primary visual cortex contain (V1)?
a map of opposite half of the visual field- heavy field
-looking at right V1 - this tissue in calcarine sulcus contain a map of the left half which is the opposite half which is inverted and distorted
What does the tissue upper and lower depths of the calcarine sulcus show ?
contain a map of the left half which is the opposite half of space which is inverted and distorted
What does it mean when map is inverted in V1 ?
- top part of V1 contains a lower paRt of the opposite side of the visual field
VICE VERsa
-same with S1 and M1
How is the hemi field map in the V1 cortex?
- it is distorted
- large region devoted to processing info from. the Central 15 degrees of your visual field of the opposite side- corresponds to where the fovea and macula are looking with all the rest of the visual field crammed into the anterior bit to the calacrine sulcus - near the parietal occipital sulcus
?
-over representation of fovea and macula compared to under representation of the periphery is down to what’s going on in the retina
What are the reason for overrepresentation of the fovea and macula and underrepresentation of peripheral?
- fovea and macula of the retina contain high density of photoreceptors and retinal ganglion cells compared to peripheral parts of retina which contain fewer
- this relationship is maintained throughout the visual pathways.
Q1 - How do different primary areas acquire their different function ?
= via long-range axon pathways that relay in the THALAMUS
Q2- Why do Primary Areas deal with only the opposite side of the body/space?
= because axons cross the midline (a.k.a. ‘decussate’) once, somewhere along their pathway in the CNS
Q3- Are there anatomical differences between different Primary Areas that relate to their Functional Specialization?
= subtle differences in their cellular structure (‘cyto-architecture’)
Q1 explanation - what are the pathways inside CNS ?
are continues nerves but consist of
- Seperate nuclei in the grey matter - which operate as relay stations- they receive information from lower down and they process information and pass it on
- via other long range axon pathways in the white matter and transfer to next relay in system
- This applies to both sensory (ascending) & motor
(descending) pathways in the brain and spinal cord
Q1- What do these pathways relay in a large part of ?
the thalamus
What is the thalamus?
- top of brain stem - mass of nuclei
- have thalamus on left and right Side of brain
- have central brain location
- pear structure
- separated by narrow 3rd ventricle containing CSF
- left and right thalamus comprises many nuclei
- Receive input from specific sensory or motor pathways these then relay to
- ‘Relay’ to specific Areas of Cerebral Cortex, via axons in the Internal Capsule
- ‘Primary’ Relay Nuclei (VL, VP, MG, LG)
What does the primary nuclei do ?
send info to the primary areas in the each of the corticol lobes
What is VP?
Ventral posterior nucleus
-relays somatosensory info up to s1 cortex
-
What is VL?
ventral lateral nucleus
-relays motor signals up to the primary motor cortex
What is MG?
medial geniculate nucleus - relasys a auditory info about hearing up spot eh primary auditory cortex
What is LG
Lateral geniucalte nucleus
-relay that’s end info from eye up to the V1 - primary visual cortex
What does the thalamus do?
Thalamus – that’s given rise to 250 milliosn axons that are travelling to different parts of the cerebral cortex
Relays info to the frontal lobe, then occipital lobe etc parietal lobe
What are the bundles of very well organised axons called ?
corona radiator – radiating crown of axons travelling from internal capsule to different areas of the cerebral cortex
What is the multistage route for the visual information EXAMPLE INCLUDED ?
- Retina is Brighton- get on train corresponding to retinal ganglion cells - travel along a particular railway track(this is an axon pathway-opposite pathway) - to a relay station which is clapham junction which Is the Lateral geniculate nucleus
- At clapham junction you get off train and walk across platform and get on another train means you have crossed the synapse in the LG
- on the second train you travel along the internal capsule - another railway track - relay - and end up at Victoria station - which is the cerebral cortex.
What is the multistage route for for the S1 cortex ?
- This is the relay station for somatosensory pathway
- begin in Paris (SKIN) and end up in St.Pancras (S1 CORTEX)
- TRAVEL FROM Paris travel through France get off another station which is leal-(spinal cord) get off the train and cross the platform and get on another train which heads to ventral posterior thalamus- then get off again and walk to another platform and get on another and travel on a separate railway line through the internal capsule ending up at St Pancras- cerebral cortex- S1.
What is the multistage for the M1 cortex ?
-VL nucleus - sends primary motor cortex (M1) - which then has its own railway lines some end up in the brainstem and some in spinal cord and further railway lines which innovate particular involuntary muscles that cause them to contract etc.
Q2 - Why do areas of the cortex are concerned with the opposite side of the body/space?
the motor and sensory pathways cross the middline- (defaccate)
Q2- so what happens in SQ 1 (in the sensory cortex) ?- CHECK POWERPOINT FOR PICS
This is where you have your sensory receptors on the right side of your body for e.g in your fingertips- which have axon which make direct connections to neurons sensory neurons in the spinal cord on the same side (right side)
-Those spinal neurons have axons which travel up the spinal cord and at some point cross the midline- make connections with the neurons VP nucleus on the left side of the thalamus which makes the connections with the somatosensory cortex on the left
Due to spincal sensory neuron having an axon that crosses the midline, the sensory info on the right side of your body ends up being perceived on your left primary somastosensory cortex (S1).
Q2- What happens in the Motor cortex ?- CHECK POWERPOINT FOR PICS
Similarily the motor neruons in the pre-central gyrus in the primary cortex on the left have axons which travel down the brain – at some point inside the CNS they cross the midline and travel down the right side to innovate spinal motor neurons on the right whos axons come out and innovate muscles on the right side of your body.
it is because this neuron in the motor cortex that has an axon that crosses the midline, an activity in your left motor cortex causes muscles on the right side of your body to contract.
Q3- Are there anatomical differences between different Primary Areas that relate to their Functional Specialization?
Yes
How can we stain to see through the cerebral cortex ?
Nissl stain-
What does nil stain do on the cerebral cortex?
it attaches itself to the DNA and RNA IN THE cell bodies of the neurons within the cerebral cortex
- Al the blue dots are the cell bodies of the corticol neurons
- neurons in cerbeal cortex are laid down in separate layers
What is the common structural plan of the cerebral cortex when shown in the nissl stain ?
-the common structural plan of the cerebral cortex – doesn’t matter where you look- there is 6 layers of cells within the corticol gray metter- they extend from layer 1 down to layer 6 which is deepest in the corticol gray matter right next to the underlye white matter
What is layer 1 of the cerebral cortex?
- those 6 layers of cortex- are labelled in roman numerals
- Layer 1 – external
What is layer 6 of the cerebral cortex?
Layer 6 is more internal near to the white matter
What can another dye be used to stain the cerebral cortex?
- golgi stain
- each of those corticol layers contains different populations of corticol neurons
What do golgi stains do?
- it gets inside neuron cell bodies and fills up the cell body and also extends into the dendrites that come out of the cell body and into its axon
- can see characteristics of neurons
What does layer 1 of the cerebral cortex look like when stained with nissl?
layer 1 - looks white in cerebral cortex- as it contains no neuron cell bodies at all -that pick up the dye
Whats in layer 1 of the cerebral cortex?
have synaptic connections on the dendrites of corticol neurons no cell bodies at all.
What does layer 4 show in the nissl stain ?
-is very dark blue
Why is layer 4 stained so dark in the nissl stain of the cerebral cortex ?
- reason for that- is stuffed full of neurone cell bodies at really high density -
- the neurons are called granule/stellate cells.
Where are stellate/granule cells found?
- in the layer 4 only
- these are the neurons which receive direct input from the thalamic nucleus which supplies input to the region of the cerebral cortex
What do the stellate cells do in layer 4 ?
they -recieve input from the thalamus and they relay that information on to neurones and layers above and below.
-these neurons are excitatory - receive excitatory signals from the thalamus- they are like local circuits neurons they have short axons which travel into the layers above and below and excite the cells in layers 2 3 or 5 6 below
What is the main type of neuron above and below ?
- pyramidal cells
- shape of their cell body is like a pyramid - triangular- they are long range projection cells
- the axons of pyramidal cells leave this region of grey matter and enter the white matter below and travel to parts of the brain
Where is pyramidal cells in the cerebral cortex?
main occupants of layers 2 and 3 and 5 and 6
What are the 4 types of corticol connections ?
- Thalamic input - layer 4- granule cells receive input from the thalamus
- Inter-corticol association projections- layer 2 nd 3- - Pyramidal cells -Make connections with the other areas of the cerebral cortex- such as inter-corrtical association
- Subcortical descending projections (layers 5 & 6)
- Pyramidal cells in layers 5 and 6- send their axons down subcortically – e.g neurons in layer 6 make of V1 make connections with the lateral geniculate nucleus .
What did brodmann do ?
- got material of cerebral cortex
- stained with blue dye to look at distribution of neuron cell bodies in the 6 layers
- he identified 52 discrete areas of human cerebral cortex, based on differences in layer thickness, cell size & distribution (i.e., cytoarchitecture)
What is brodmann area 4 ?
is the grey matter of the pre central gyrus where you find primary motor cortex
- says this is unique because the pyramidal cells in layer 5 are huge - they have cell bodies which are 1/10th mm across- big fro a neuron - huge neurons in layer 5.
- those neurons in layer 5 or area 4 are source of pathways which go all the way into the spinal cords and activate motor neurosn that move your muscles. - M1
What is area 17 of brodmann?
corresponds to primary V1
=unique - layer 4 in this area is the widest.
What is very first evidence of functional specialisation in the cerebral cortex ?
- came from px which had localised damage to secondary areas of the cortex
- Paul Broca discovered this
- encountered px who had a stroke - px lost ability to speak— Left hemisphere of his patient ‘Tat’ who could understand language but could not speak. The patient died,1861.
- *Focal lesion in the inferior Frontal Lobe
- damage to localised section
- he deduced that it was result of damage of the signal region of the inferior frontal gyrus in left hemisphere- this condition is called Expressive Aphasia
What is Wernickes complementary finding?
Receptive Aphasia
- Carl Wernicke (1848-1905) Neurologist
- *Focal lesion in left superior Temporal Lobe of a patient in the LEFT cerebral HEMISPHERE Too- who - like Wernicke’s (1874) - could speak, but could not understand spoken language.
- damage to this region is inability to understand spoken language.
What hemisphere is the most dominant for language ?
left hemisphere
-true for people who are right handed - but also true for people of left hand - only few left handed might not.
What happens with damage to the prefrontal cortex ?
- the motor cortex causes loss of working memory and damage to medial part of temporal lobe and underlying hippocampus and can’t form new life memories
- called Anterograde Amnesia -unable to form new long-term personal memory of any autobiographical life events
