Cerebral Cortex - from cells to function Flashcards
What is the principle axonal target?
The dendritic spines
What is a unipolar neuron?
Single extension: There is a peripheral sprout that collects sensory information and there is a central sprout.
What is a bipolar neuron?
There is a single dendrite which senses and sends info to the cell body and there is an axon
What is a multipolar neuron?
Lots of dendrites and a single axon
What is an interneuron?
- A type of multipolar neuron
- local processing
- Short axon
What is a pyramidal cell?
• Multipolar cell with a long axon
Describe myelination in the PNS
- Schwann cells make a wrapping around a single axon
- you can find the nucleus
- One Schwann cell builds one internode
Describe myelination in the CNS
- Oligodendrocytes have multiple processes to wrap around different neurones
- One oligodendrocyte builds a number of internodes
Describe the non myelinated neurones in both the CNS and the PNS
- In the CNS: unmyelinated neurones are not associated with any glial cells
- In the PNS: Schwann cells envelope the unmyelinated axons, contacting one or more of the axons
Describe conduction in non myelinated neurones
- Continuous conduction because of passive current flow
* example: sensory fibres carrying pain, itch and temperature
What is multiple sclerosis?
- A phasic disease which results in demyelination
- Caused by an immune attack/ inflammation of T cells (macrophage mediated)
- This can result in a conduction block (slowing of propagation) and cross talk
- Paraesthesia and crosstalk
- Some re-myelination can occur
- There will be some permanent loss (due to cell death/axonal loss)
- Plaques and lesions will be seen throughout the CNS
What is white matter?
Collection of nerve fibres, many of which are coated with insulating fatty myelin
What is grey matter?
Contains neuron cell bodies, synapses and processes
What are the glial cells of the CNS?
- Oligodendrocytes
- Astrocytes
- Microglia
- Ependyma (lining cells of the CNS cavities)
What are the glial cells of the PNS?
- Schwann cells
* Satellite cells (support the cells in the ganglia)
What are astrocytes?
- ‘star cells’
* They offer metabolic and structural/mechanical support
What are the roles of astrocytes?
- Water distribution
- Potassium buffering
- ROS (reactive oxygen species) Scavenging
- Define architecture
- Regulate migration/pruning of synapses/synaptogenesis
- Help maintain (but don’t make up) the blood brain barrier
What type of astrocyte is present in white matter?
Fibrous astrocyte
What type of astrocyte is present in grey matter?
Protoplasmic astrocyte
What is the blood brain barrier?
A barrier composed of endothelial cells and their tight junctions
What is the integrity of the blood brain barrier highly dependent on?
The ‘end feet’ (or foot processes) of astrocytes
What are microglia?
• Resident macrophages of the central nervous system
What are the functions of microglia?
- Phagocytosis and antigen presentation (immune response)
* Synaptic pruning
Where do microglial cells originate?
• They are blood series cells (unlike the other glial cells, they don’t originate from the epithelium in the neural tube)
What are ependymal cells?
- Ciliated cuboidal epithelial cells that line the ventricle as part of a plexus and secrete and reabsorb CSF
- Specialised ependyma secrete CSF on the choroid plexus
What are the lobes of the brain and where are they located
- Frontal (anterior superior part of the brain)
- parietal (middle superior part of brain)
- Occipital (posterior part)
- Temporal (middle inferior part of the brain)
What is the neocortex?
Part of the cerebral cortex (which is the external grey matter)where the cells are arranged into 6 layers
How many cell layers are there in the paleocortex?
3
How many layers are there in the archicortex (hippocampus)?
4
What are the 6 layers in the neocortex?
- Molecular layer
- External granular layer
- External pyramidal layer
- Internal granular
- Internal pyramidal layer
- Multiform layer
Describe the granular layer of the neocortex
- Contain granule (stellate) neurones which are multipolar with short axons
- Local processing occurs
- There is more receiving in this layer
Describe the pyramidal layer of the neocortex
- Contain pyramidal cells
- Multipolar neurones with long axons
- More output/sending in this layer
What gives a striated appearance to the primary visual (striate) cortex?
The fourth layer is well developed (layers vary in thickness with function from region to region)
Describe column/barrel representation in the somatosensory cortex
- Columns appear as functional units linked to sensory input
- Columns are associated with different modalities of sensation for a given part of the body
- The barrels have more information flow up and down as opposed to side to side
- their size is not fixed and is determined on the extent of the input
- Columns arise from experience, not pre existing subunits
Where is the primary visual cortex located?
In the occipital lobe, localised in a small area medially
What is the function fo the primary visual cortex?
It responds to simple visual stimuli/simple patterns
What makes up most of the occipital lobe?
The association cortex - for higher order processing
Describe the visual cortex dorsal and ventral dual stream model
• There are 2 pathways, one is vision for action (movement) superiorly, and one for vision perception (recognition) towards the temporal lobe (where and what pathways)
• The vision for action pathway:
- integrates motion vs object locations
- co-ordinates visual guided action for skilled movements
- guides visual attention
• Vision perception:
- recognition (inferno-temporal cortex)
- Distinguishes spatial patterns, objects and faces
- stores visual memory
- recognises the significance of both objects and faces
Where is the primary motor cortex?
- Pre-central gyrus
* Frontal lobe just before the central sulcus
What is the function of the primary motor cortex?
- It has more direct control of motor activity than any other motor area
- It is the director of force, speed and direction of muscle contraction
Describe somatotopy
- Body regions ‘map’ onto the motor cortex
* Certain parts of the body will have an enlarged representation e.g. the hand and the face (fine motor)
What makes up the motor association cortex?
- Supplementary motor area
- Premotor cortex
- Posterior parietal complex
Describe the function of the supplementary motor area
- Simple movement
- Planning complex movement (especially with 2 hands)
- Mental reversal of complex movement
- Practice related, sequential movements
Describe the function of the premotor cortex
- Preparation for action
- Posture and gait
- Integration of spatial awareness and planned movement
Describe the function of the posterior parietal complex
• Integrates visual information to formulate motor commands
Broadly, what is the motor association cortex responsible for?
•The integration and complex processing of cognate primary cortex info. There are 2 types recognised:
- Unimodal (one type of modality)
- Polymodal (multiple modal input e.g. vision and somatic sensation in the dorsal stream)
Where is the primary somatosensory cortex?
• Postcentral gyrus - motor and sensory are close together
What are the functions of the association somatosensory cortex?
- Awareness/perception in space (orientation)
- Rearrangement of memories
- Organising grasping movement
- Number processing
- Mirror neurons (fires both when doing and observing)
What would damage to the superior parietal lobe lead to?
Problems with visumotor integration (optic integration)
What would damage to the inferior parietal lobe lead to?
Contralateral neglect (patient ignores half of their body) and/or astereognosis (inability to recognise objects by touch)
What are the functions of the pre-frontal region association cortex?
- Morality
- Contributes to attention
- Planning
- Working memory
- Conscious decision making
- Social behaviour regulation
What are the features of pre-frontal lobe damage?
- Personality changes
- Deficits in planning
- Perseveration (repetition of a response)
- Primitive reflexes (suckling reflex)
- Abuloa (slowness of intellect)
What would happen as a result of a lesion in Broca’s area ?
- Expressive aphasia
- Language is reduced to disjointed words and sentence structure is poor
- Comprehension is ok
Where is Broca’s area?
In the frontal lobe next to the temporal lobe
What would happen if there was a lesion in Wernicke’s area?
- It could lead to repetitive aphasia
* Inability to understand/generate meaningful language
What connects Broca’s area and Wernicke’s area?
DTI of arcuate fasciculus
What would happen if there was damage to the DTI of arcuate fasciculus?
Conduction aphasia (difficulty repeating words/phrases)
Where does 96% of language processing occur?
In the left hemisphere
Dorsal stream of language specialisation
Maps acoustic speech to articulatory networks in the frontal lobe
Ventral stream of language specialisation
Comprehension, bilateral
What does repeated stimulation of neuronal pathways do?
Modifies dendritic spines
What is long term potentiation
Synapses become strengthened
Describe the specialisation of the hemispheres
- Right: better at language and calculation
* Left: better at drawing, music and spatial perception
Describe the feel the keys experiment
The left hand feels a set of keys and the right cortex recognises this but cannot activate the language centres in the left hemisphere to speak the word ‘keys’
What are the 3 ways in which communication in the Brian occurs?
- Commissural: cortex to cortex - crosses over the midline
- Association: cortex to cortex - stays on the same side
- Projection: communicates with the other structures inside and outside the brain
What is the largest commissural bundle?
The corpus callosum
