Chapter 7

Question 0

What does cortex mean?

Answer 0

The cortex means the outer layer.

Question 1

What area of the rodent cortex is buried in humans? What is this area concerned with?

Answer 1

The insula is buried by other cortical areas in humans, and is responsible for taste and gut control.

Question 2

What are spines and why are they important?

Answer 2

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.

Question 3

What are sulcus and gyrus?

Answer 3

Sulcus is the groove or the part that folds inside while sulcus is a fold in the outside.

Question 4

What can be said about the cellular arrangement of the cerebral cortex?

Answer 4

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.

Question 5

What neurons makes up most of the cortical region?

Answer 5

The most common neurons in the cortex are excitatory neurons(glutamate or aspartate). Especially, pyramidal cells and spiny stellate cells make up the cortex.

Question 6

Describe the pyramidal cell.

Answer 6

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.

Question 7

How much cells in the cortex are inhibitory and what neurotransmitter do they use?

Answer 7

20% of the cerebral cortex is made up of GABAergic neurons. Their functions vary upon their arrangement and the specific types of inhibition

Question 8

What is some examples of how different inhibitory cells act on other neurons?

Answer 8

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.

Question 9

Hay many layers make up the neocortex and olfactory cortex?

Answer 9

The neocortex and olfactory cortex is made up of 6 and 3 layers respectively. The layers are numbered from the outside to the inside.

Question 10

Why did Golgi and Cajal receive a Nobel prize?

Answer 10

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.

Question 11

What stain did Broadmann use to do his pioneering research?

Answer 11

He had to use the Nissl stain and examined subtle differences in the parts of cortex and classified into different regions.

Question 12

Write a small description of each layer in the neocortex.

Answer 12

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.

Question 13

What is the theory of Vernon Mountcastle and why was it disregarded?

Answer 13

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.

Question 14

What suggests high columnar activity?

Answer 14

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.

Question 15

Why are inhibitory neurons important in the cortical areas?

Answer 15

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.

Question 16

What are the effects of neurotransmitters such as dopamine, noradrenaline and serotonin in the cortex?

Answer 16

The neurotransmitter have modulators functions rather than direct excitation or inhibition of neurons.

Question 17

Describe the connectivity of the cortex.

Answer 17

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.

Question 18

How is the tactical receptor of mice whiskers represented in its brain?

Answer 18

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.

Question 19

What is somatotopy and its importance?

Answer 19

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

Question 20

What was the limitation of Broadmann’s area?

Answer 20

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.

Question 21

Why is it difficult to ascertain the functions of certain areas of the cortex?

Answer 21

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.

Question 22

What are primary, secondary and tertiary cortical association areas?

Answer 22

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

Question 23

What can damage to the association regions cause?

Answer 23

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.

Question 24

What did Alexander Luria discover?

Answer 24

He studied the people who escaped the war with small time head injuries and discovered damage to a specific part cause the person to be unable to express himself. He named it aphasia. However, his research was ignored due to Cold War politics until the 1970.

Question 25

How important is the cerebral cortex in terms of survival?

Answer 25

Rats whose cerebral cortex removed can still able to feed, drink, and avoid threats. However, this has a profound effect on the behaviour of humans.

Question 27

Is cerebral cortex not so important in the cortex?

Answer 27

The basic behaviours and learned movements need less of cortical inputs. However, even a small damage to the cortical area can have impact on personality and behaviour. The cortex was regarded as silent areas as their functions were unknown, however they carry sophisticated functions like analysing, predicting and responding to environmental events based on prior experience and information from different sensory systems and mental states to make future predictions. This is still not completely measurable in clinical situations.

Question 27

What is the overall role by the cortex?

Answer 27

To be able to analyse, predict and respond to environmental events based on our past experiences. The cortex learns from the previous experiences tying together information from different sensory systems and mental states to make a more accurate prediction of the future events and plan accordingly.

Question 28

Why was the cerebral cortex expensive to run?

Answer 28

It is expensive to run in terms of metabolic energy, as its cells are near constant active during awake behaviour.

Question 29

What did Arcimboldo and Dr. Mike Gazzaniga discover?

Answer 29

Arcimboldo drew a painting of face composed of vegetables. He used this painting to demonstrate the different ways the right and left hemisphere of the brain perceived the same picture. This was supported by Dr. Mike Gazzaniga’ s research in which he showed the same painting to split brain patients, and found out that the right hemisphere sees the bigger picture, the face, and the left hemisphere sees the components, the vegetables.

Question 30

How is extremely debilitating epilepsy that does not respond to drug is treated?

Answer 30

The two hemispheres are surgically separated to prevent the spread of the epilepsy to over a wider region. This involved the section one of the corpus callosum.

Question 31

What have researchers such as Mile Gazzaniga and Roger Sperry study?

Answer 31

They studied split-brain patients as in how their the right brain and left brain worked differently when they could not combine the information processed from both sides

Question 32

What are some of the functions that specialised to one of the two hemispheres?

Answer 32

The main language areas, Broca’s region and Wernicke’s region, and calculations is lateralised exclusively to the left hemisphere. Similarly, the right hemisphere was important for spatial awareness.

Question 33

Explain a simple test done by researchers to prove the difference in the right and left hemisphere in split-brain patients.

Answer 33

Left hemisphere showed to focus on the components of the stimulus, while the right hemisphere tried to view it as the whole. For example, in a piece of music the left hemisphere may track the melody of the individual notes, while the right hemisphere tries to interpret the whole composition.

Question 34

Where is the Broca’s and Wernicke’s region located and what are their functions?

Answer 34

In right handed people, these areas are exclusively in the left. While left handed people can have these areas on either side of the brain. Broca’s region was first discovered and associated with speech problems by Paul Broca. The Wernicke’s area was named after Broca’s contemporary, Carl Wernicke. The Broca’s region found in the frontal lobe whilst the Wernicke area is found in the temporal lobe next to the auditory cortex.

The Broca’s region is associated with the expression of language through spoken or written words. Wernicke’s area is concerned with the comprehension of the words and its meaning, and also producing speech.

Question 35

What happens when Broca’s and Wernicke’s region are damaged?

Answer 35

If the Broca’s region is damaged, the person is unable to express themselves either through speech or writing. If Wernicke’s region is damaged, the person completely loses the ability to associate words with their meanings, therefore their comprehension is impaired. Broca’s aphasia is known as an expressive aphasia and Wernicke’s aphasia is known as a receptive aphasia.

Question 36

What did Norman Geschwind find?

Answer 36

He found out that by measuring the lateral fissure using a ruler was enough to find out the dominant side in human postmortem bodies.

Question 37

How rapidly the cortex has expanded?

Answer 37

From 450 cm cubed to 1350 cm cubed in a period about 4 million years ago.

Question 38

Why has the cortex expanded?

Answer 38

The increasing social interactions and the complexity of society is promoting the cerebral cortex to grow.

Question 39

What is the effect of chronic stress?

Answer 39

The chronic stress has profound effect on the person’s mental and physical health.