Chapter 7 Flashcards
What does cortex mean?
The cortex means the outer layer.
What area of the rodent cortex is buried in humans? What is this area concerned with?
The insula is buried by other cortical areas in humans, and is responsible for taste and gut control.
What are spines and why are they important?
Spines are tiny extensions of the dendrite that extend out for synaptic connections. They are only found in excitatory neurons. They are the basis of plasticity. They can grow or retract within several hours.
What are sulcus and gyrus?
Sulcus is the groove or the part that folds inside while sulcus is a fold in the outside.
What can be said about the cellular arrangement of the cerebral cortex?
The cerebral cortex is very uniform. It is called the neocortex, the most recently developed part of the brain and also as isocortex due to its uniformity. All the cortical regions have the same types of cells in the same layers. The only distinction is between the motor cortex and sensory cortex. The sensory cortex has a granular layer, which is filled with spiny stellate cells which gives it a grainy appearance, this layer is present in the motor cortex, however it does not contain any spiny stellate cells. Scientists have tried classifying these areas by measuring the difference in thickness, which is really hard as these areas often merge with their neighbours.
What neurons makes up most of the cortical region?
The most common neurons in the cortex are excitatory neurons(glutamate or aspartate). Especially, pyramidal cells and spiny stellate cells make up the cortex.
Describe the pyramidal cell.
The pyramidal cell is conical in shape with one large dendrite arising from the apex and many other smaller dendrites arising from the base of the cone. The axon also arises from the base of the cone. The dendrites are covered in spines.
The axons may branch out to the nearby cortex, to the opposite cortex or to structures outside the cerebrum to structures like the thalamus, brainstem and spinal cord.
How much cells in the cortex are inhibitory and what neurotransmitter do they use?
20% of the cerebral cortex is made up of GABAergic neurons. Their functions vary upon their arrangement and the specific types of inhibition
What is some examples of how different inhibitory cells act on other neurons?
The basket and clutch cells send their axons to the cell bodies of other neurons, whilst the chandelier cell gives rise to processes that wraps around the initial segment of the axon hillock and instantly cancels any action.
Hay many layers make up the neocortex and olfactory cortex?
The neocortex and olfactory cortex is made up of 6 and 3 layers respectively. The layers are numbered from the outside to the inside.
Why did Golgi and Cajal receive a Nobel prize?
Golgi developed a silver stain that first allowed researches to see the full anatomy of the neurons in detail. Cajal used this staining method to make meticulous pen and ink drawing of neurons from all parts of the brain.
What stain did Broadmann use to do his pioneering research?
He had to use the Nissl stain and examined subtle differences in the parts of cortex and classified into different regions.
Write a small description of each layer in the neocortex.
Layer 1 is a dense mat of fibres. The neurons carry specialised neurotransmitter such as noradrenaline and dopamine from the hindbrain, distributing them throughout the cortex.
Layer 2 consists of small pyramidal cells and small inhibitory cells, which acts in local circuits to process input.
Layer 3 consists of larger and numerous pyramidal cells, and basket and other inhibitory cells. The pyramidal send excitatory outputs to other parts of the cortex, either nearby or in the opposite cortex. The inhibitory neurons act on their neighbouring cells as part of cortical processing.
Layer 4 is the granular or agranular layer that distinguishes sensory from motor cortex. The thalamus sends the sensory input to this layer. The layer is split into sublayers
Layer 5 has the largest pyramidal cells and Betz cells. The pyramidal cells their output to the striatum or the spinal cord. The Betz cell forms the corticospinal tract in the motor cortex.
Layer 6 has small pyramidal cells that projects to the thalamus , which in turns supplies input to the cortex. This allows for a feedback loop to regulate the incoming thalamic activity.
What is the theory of Vernon Mountcastle and why was it disregarded?
Vernon Mountcastle suggested that the cortex has mini columnar units due to the high evidence pointing at columnar activity. However, other researchers disagree because researches show the size of the columns is not consistent throughout the cortex, and can be formed due to need and is not necessarily permanent.
What suggests high columnar activity?
Most neural connections in the cortex are with the cells above and cells below. There are however few cells that make connections with adjacent cells as part of cortical processing.
Why are inhibitory neurons important in the cortical areas?
The inhibitory neurons prevent from a storm of electrical activity or otherwise known as hyper excitation. This is the basis of epilepsy. The interneurons control the activity in a coordinated manner to prevent this.
What are the effects of neurotransmitters such as dopamine, noradrenaline and serotonin in the cortex?
The neurotransmitter have modulators functions rather than direct excitation or inhibition of neurons.
Describe the connectivity of the cortex.
The neurons are connected like tapestry in the cortical regions. The sophisticated connections allows it to cooperatively analyse the inputs. However, the connection to the rest of the brain is quite circumscribe. The cortex sends feedback to the thalamus which is actually bigger than the input. To direct the rest of the nervous system, the cortex connects to the thalamus, hypothalamus, hippocampus, brainstem and spinal cord.
How is the tactical receptor of mice whiskers represented in its brain?
Each whisker is represented by a barrel shaped part in the cortical area. This was discovered by Woolsey and van der Loos in 1969. This was not discovered because of the routine use of the coronal section. It was obvious in a mid saggital view.
What is somatotopy and its importance?
Somatatopy for the touch system is the map of the skin of the body transmitted to the cortex in proper spatial order. This topographic representation provides ability to compare activity from adjacent patches of the skin or finding the edges of visual objects. Example, retinotopic organisation for retinal map and tonotopic organisation for auditory system
What was the limitation of Broadmann’s area?
Broadmann’s mapping work only the surface of the gyrus and not walls of the grooves. However, realising the importance of the structure like the auditory cortex, Wernicke’s area and the insula, he mapped the surface that was buried between the frontal lobe and the temporal lobe.
Why is it difficult to ascertain the functions of certain areas of the cortex?
All the information known about the cerebral cortex comes from people who have damaged their brain. These studies have been supported by the modern day imaging in the past few decades.
However, these regions only give us a large scale understanding of the process. Electrodes which are capable of detecting things at smaller scale has not been put in use for research yet.
The another problem is that the cortex receives different inputs and the information is processed in one area and in other cases, one input is analysed in many parts of the cortex. This integration of neurons that allows us to do these wide range of skills still remains as a mystery.
For example, the parietal lobe receives information from touch, vision and proprioception receptors. The input mix depends on the area, as in like the Wernicke’s area gets sound processed by the auditory cortex and is also strongly connected to the speech motor area.
What are primary, secondary and tertiary cortical association areas?
The primary association regions are parts of the cortex that are dealing with sensory information and motor movement at a basic level. The secondary regions are the regions that utilises these information to get meaning out of it. The tertiary regions which produces more abstract capabilities like reasoning and emotions.
The primary association regions are extremely well studied and their functionings are well understood. The secondary regions functions are known but the molecular workings behind it is really complex and yet is not worked out. Very little or almost nothing is known about the tertiary association regions
What can damage to the association regions cause?
People may lose the ability to combine types of information, such as the ability to read maps, or they might have something as large as loss of complete colour perception. In the frontal lobe, subtle damage can reflect deficits in planning and organisation. There might also be inappropriate behaviour in a social setting.
