Cerebral cortex from cells to function Flashcards
What are the components of a neuron and their function?
Dendrites which direct stimulus towards cell
Dendritic spines principal axon target
Nucleus + (nucleolus)
Cell Body
Axon hillock
Axons direct unitary digital output away from the cell
What are neurons used for?
Neurons are used for;
- Networking
- Vectorial impulse transmission/propagation
- Dissociative secretion/synapse formation
- Chemical Transmission
- Inhibitory or excitatory
How are neurons classified and what is the main neuron we have and its function?
Based upon how many processes they have
Pseudo-Unipolar Cell (dorsal root ganglion) - they bring conduction towards the cell body (structurally this is an axon as its got a myelin sheath but functionally its a dendrites as its bringing information to a cell body)
- has a peripheral and central process
We also have “Modified” bipolar cells - commonly found in ear, eyes and nose
What is a multipolar neuron, its features and 2 types of it?
Multipolar - lots of dendrites with 1 single axon
Interneuron (local processing)
- Has a SHORT axon
- Can be inhibitory or excitatory
Pyramidal cell (sending info from cerebral cortex)
- Has a LONG axon
What is the Schwann cells job?
It builds only 1 internode in the PNS
They all envelope unmyelinated axons contacting 1 or more axons (cf myelinating ones)
What is the Oligodendrocyte cells job?
It builds multiple internodes in the CNS
What are some features of unmyelinated axons in the CNS + examples?
- They are not associated with myelinating cells (not embedded)
- Have continuous conduction f action potentials due to passive current flow (low conduction speed)
Examples - sensory fibres carrying pain, temp and itch
What occurs in multiple sclerosis ?
Phasic disease
Demyelination
Inflammation (T cell/macrophage mediated)
Conduction block (slowing propagation)
Cross talk (paraesthesia - burning sensation)
Some re-myelination can occur
Permanent loss (due to cell death/axonal loss)
Can see white spots on MRI - signs of demyelination
More common in northern hemispheres that lack Vit D
What is white matter?
Collections of nerve fibres many of which are coated in insulating fatty myelin
White matter also contains neuron processes Schwann/oligodendrocyte cells and myelin
What is grey matter?
Processing
Contains: Neuron cell bodies, processes and synapses
What are the Glial cells of the CNS?
Oligodendrocytes (myelination)
Astrocytes
Microglia
Ependyma (lining cells of the CNS cavities)
What are the Glial cells of the PNS?
Schwann Cells (myelination)
Satellite Cells (support cells in ganglia)
What are astrocytes and their function?
Astrocytes are star shaped cells and they appear in the white matter as fibrous astrocytes (longer and more extended) and as protoplasmic astrocytes in the grey matter (looks blobby)
They provide metabolic and mechanical support (and in the CNS scar tissue also).
Details;
- Control water distribution
- Potassium buffering
- ROS scavenging (Reactive oxygen species)
- Define architecture
- Regulate migration / pruning /synaptogenesis
- Help maintain but do not take upper the BBB
What are astrocytes role in the BBB?
BBB is a barrier composed of endothelial cells and their tight junctions
Integrity is highly dependent on astrocyte ‘end feet
So the barriers consists of endothelial cells and their tight junctions and the astrocytes help to maintain it
What is the function of microglial cells?
Microglial cells are described as the resident macrophages of the CNS
Their role is for;
- Phagocytosis and antigen presentation (immune response)
- Synaptic pruning
What is the function of Ependymal cells?
Ependymal cells are ciliated cuboidal cells, that line the ventricle as part of a plexus and secrete (also reabsorb) CSF
What its CSF?
CSF (cerebrospinal fluid)
- Clear, cell-free fluid partly produced in specialised ependyma on choroid plexus
What are the 4 main lobes of the cerebrum and what separates them?
Frontal, parietal, temporal and occipital
Central sulcus separates the frontal and parietal lobes
Lateral sulcus/fissure separates the frontal and parietal lobes from the temporal lobe
Preoccipital notch separates the Occipital lobe from the Parietal and Temporal lobe
Parieto-occipital sulcus separates the parietal and occipital lobes
Calcarine sulcus separates the occipital lobe into two parts:
1) lingual gyrus (inferior part)
2) cuneus (superior part)
How is the cerebral cortex sorted into layers?
They are sorted into layers by lamination during tissue development
The cerebral cortex external grey matter - convoluted shaped gyro increased packing per volume
Most cerebral cortex 6 layered neocortex (recent evolution) - e.g hippocampus has less layers
There is much less area within the 3rd and 4th layers as evolutionary they are old
What are the 2 main neurons found in the main layers?
Stellate interneurons mostly in granular layers 2 + 4 - For inputs and local processing
Pyramidal neurons in pyramidal layers 3 + 5 - For outputs to local and distant targets
What are the different layers of the cerebellum called from 1 - 6 and what functions and neurons would you find here?
Layer 1) - Molecular layer
Layer 2) - External Granular - INPUT from other cortex
Layer 3). External Pyramidal - OUTPUT local to other cortex
Layer 4). Internal Granular - INPUT from thalamus
Layer 5). Internal pyramidal - OUTPUT to brainstem and spinal cord
Layer 6). Multiform layer
External layers nearer brain, internal further away from brain!
How do the layers of the cerebellum vary from region to region of the cerebellum?
Layers vary in thickness/cellular composition and also function from region to region
Stellate cells (interneurons) are more numerous in the sensory cortex (in layer 4) - more input
(also in primary visual cortex layers 4 is well developed/prominent and makes a striped appearance and this is why we call it the striate cortex!)
Whereas in the motor cortex you will see more pyramidal cells (layer 5) - more output
What its brodmann’s areas ?
Its a map based on histological differences in structure across the cerebral cortex. It relates closely to function.
E.g motor function in area 4 (primary motor cortex) and area 1 (primary visual cortex) for input
Tell me about the primary visual cortex and its association cortex
Primary visual cortex is located on the median area of the occipital lobe, receives input and does simple processing
The association visual cortex is adjacent to the primary visual cortex and carries out more complex processing of visual information (in rest of occipital lobe and beyond)
E.g Motion, object recognition, depth, binocular, patters and faces
Can get an impairment called Prosopagnosia which is a blindness for faces
Describe the dual stream mode of the visual cortex?
The dual stream mode of the visual cortex starts off in the primary visual cortex then splits off into dorsal and ventral streams of visual information processing (by association cortexes);
Dorsal Stream runs along the posterior parietal lobe;
- Vision for action (movement, spatial)
- Integrates motion vs object locations
- Coordinates visual guided action for skilled movements
- Guides visual attention
(basically more awareness)
Ventral stream;
- Vision perception (object recognition)
- Recognition inferno-temporal cortex
- Distinguishes spatial patters, objects and faces
- Stores visual memory
- Recognises significance of objects and faces
(Basically more recognition of objects and faces)
What are the general principles for function localisation across the cerebral cortex?
The cerebral cortex can be split into primary and association cortex (majority of cerebral cortex in humans is association cortex)
The primary motor cortex is the principle exit in motor and entry points in sensory
In the association cortex there is integration, complex processing often cognate primary cortex info
What are the 2 types of modes that you can get from the association cortex?
Unimodal - one top of modality input/output
Polymodal - multiple modal input (e.g vision and somatic sensation in the dorsal stream)
What is the function of the primary motor cortex and where is it located?
The primary motor cortex is located just anterior to the central sulcus.
It has more direct control of motor activity than other motor areas
Force, direction and speed of muscle contraction
What do body region maps show (homunculus)?
This is called homunculus
Areas of the brain showing how much of it controls what body parts. Certain parts are enlarged to show fine sensory and motor skills and the quantity needed e.g hands
Where are the association cortex regions for the primary motor cortex and what do they do?
- Supplementary motor area
- Premotor cortex
- Posterior parietal cortex
Where is the Supplementary motor area and what is its function?
Supplementary motor area;
- Planning complex tasks!
- Simple movement
- Complex movement (especially two hand movements)
- Mental rehearsal of complex movement
It is located on the midline surface of the hemisphere just in front of (anterior to) the primary motor cortex and superior to the premotor cortex
Where is the Premotor cortex and what is its function?
Its just anterior to the Primary motor cortex and inferior to the supplementary motor area.
Its function is;
- to prepare for action
- Posture and gait
- Integration of spatial information
- Planned movement
- Grasping
Where is the Posterior parietal cortex and what is its function?
Its located in the superior region of the parietal lobe
Its function is;
- To integrate visual information to formulate motor commands (hence why is in parietal!)
What is the function of the primary somatosensory cortex and where is it located?
Its located just posterior to the central sulcus
It senses touch, pain, etc
It has different modalities, based upon the depth of the gyrus. The deepest part is for tactical info/muscle spindle, more superficially is for basic processing, even more superficially is for size, shape and texture and more posteriorly is for motion, direction and orientation!
What is the function of the association somatosensory cortex and where is it located ?
Its located in the parietal lobules superior and inferior
Its mainly responsible for awareness and perception in space (orientation)
It is also responsible for rearrangement of memories, organising grasping reaching movement, number processing, mirror neurons here!
What happens if the association somatosensory cortex is damaged?
If you damage the inferior parietal lobule you will deny an existence of your left hand side of body, will draw a clock with one side missing
To do with awareness of self in space
Also asterognosis (inability to recognise objects by touch)
Damage in superior parietal lobule will cause problems with visuomotor integration (optic ataxia - affects co-ordination, balance and speech).
What happened in the Boston Crow Bar Case?
A guy was tamping on the railway and the rod bounced and managed to go through the mans skull and brain and he still somehow lived!
The rod had been driven through his frontal lobe hence how he still lived but there was a huge change in his personality and motivation which are functions associated with the frontal lobe
What can damage to the frontal lobe cause?
- Personality changes
- Deficits in planning
- Perseveration
- Primitive reflexes
- Abulia (slowlessness of intellect)
What are the functions of the prefrontal lobes?
- Contributes to attention
- Morality
- Planning
- Working memory
- Conscious decision making
- Social behaviour regulation
What did Paul Pierre Broca discover?
He had a patient called Tan (or so he thought as this is all the patient could mutter) and he suffered from Expressive Aphasia -
Language is reduced to disjointed words and instance construction is poor but comprehension is okay.
Once Tan died Broca dissected Tan’s brain and discovered a lesion in an area that is now called Broca’s area and it is for executing speech.
It is located in the inferior frontal gyrus of the frontal lobe
Where is Wernicke’s area and what is its function?
Wernicke’s area is fo comprehension of speech
Wernicke’s area is located in the posterior section of the superior temporal gyrus (STG), usually in the left cerebral hemisphere.
This area encircles the auditory cortex on the lateral sulcus, the part of the brain where the temporal lobe and parietal lobe meet
What would a lesion to Wenicke’s area cause?
Receptive aphasia - unable to understand/generate meaningful language
Where is the primary auditory area and what is its function?
Used for hearing; integrating and processing complex auditory signals, which includes language comprehension
The primary auditory cortex is located on the superior temporal gyrus in the temporal lobe
What connects Wernicke and Broca’s areas together and what does damage to this cause?
Wernicke and Broca’s areas are connected together by DTI of acute fasciculus (association bundle).
Damage to this area causes conduction aphasia (difficulty repeating words/phrases)
How was the classical model wrong about right and left handers and the side of the brain they use?
Most processing does happen in left even in left and right handers
4% there’s usually damage
Most have a dominant left hemisphere
Language processing 96% in left
How does the dual stream mode work in language specialisation?
The stream starts in Wernicke’s area and the Dorsal stream (sensorimotor) maps acoustic speech to articulatory networks through the angular and supra marginal gyrus to the the frontal lobe and Broca’s area for Articulation
The ventral stream is for comprehension bilaterally. It starts in Wernicke’s area and travels into the primary auditory cortex for word sound recognition.
How do we know specialisation of the hemispheres occurs and what different things do they do?
Hemispheres are specialised
Left is mostly dominant where language and calculation is done
Right is mainly drawing, music and spatial perception
In 96% of the population…
We know this due to corpus callosum slicing
People get corpus callosum cut when they have really bad epilepsy
If you ask someone with split brain to feel their keys in their pockets the left hand feels and the right cortex recognises but cannot activate the language centres too speak the word keys as they are in the left hemisphere.
Why does a small percentage of people have rights sided language control?
Many of the 4% with right sided language control have damaged left hemisphere or it can b completely missing. Therefore hemispheric specialisation can switch sides
What is important in stroke recovery?
Brain plasticity
How do brain cells and regions talk to one another?
Commissural - cortex to cortex cross over the midline (largest commissural bundle of fibres is the corpus callosum)
Association - cortex to cortex cross “stay”on the same side
Projection - communicate with other structures inside and outside the brain
- By projections fibres lik bundle of nerve fibres in internal capsule and corona radiata
What happens to the corticospinal tract after corona radiata stroke?
You get a reduced corticospinal tract as projections don’t work the same
