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Answers to Test Your Knowledge questions for
Chapter 5 - The brain
Question 5.1
A1, A2 - A1 is a dorsal (back) location and A2 a ventral (front) location. By
convention, the nervous system is usually drawn as being that of a person facing
outwards. However, you can readily check that this notation is correct by observing
the bulge of the dorsal root ganglia (Chapter 3), which houses the cell bodies of
sensory neurons. You can see this bulge towards the back.
B1, B2 - B1 is grey matter and B2 is white matter. The grey matter of the cord is made
up of large percentage of cell bodies of neurons (e.g. neurons 2, 3 and 4 of Figure
3.5), whereas the white matter is made up of a large amount of myelinated axons (e.g.
that of neuron 2). Myelin contributes to the whiteish appearance. A similar logic
applies to the white and grey matter of the brain.
C1, C2 - Of the two locations indicated, C1 is the more medial (i.e. towards the
midline) and C2 the more lateral (away from the midline).
D1, D2 - Of these two locations, D1 is the more rostral (towards the brain) and D2 is
the more caudal (towards the tail).
Question 5.2
As you can see from Figure 5.5 a and b, the superior colliculus is the more rostral
('superior') structure (towards the top end of the CNS) and the inferior colliculus is the
more caudal ('inferior') structure (far from top end of the CNS).
Question 5.3
Because, as you can see in Figure 5.9b, it is located just behind the central sulcus.
Question 5.4
As Figure 5.21 shows, the afferent side (that which brings information to the lateral
geniculate nucleus or 'LGN') is made up of the axons of retinal ganglion cells
constituting the optic nerve and the optic tract. The efferent side (that which carries
information from it to the visual cortex) is made up of the axons of neurons with cell
bodies within the LGN, labelled 'optic projection fibres'.
Question 5.5
The term 'ganglion' (pl. ganglia) is normally used to refer to a collection of cell bodies
of neurons outside the CNS (Chapter 3). In this case, the ganglia, the basal ganglia,
are within the CNS.
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Question 5.6
In answering this, we can contextualize the issue by also revising some material from
Chapter 2. Through sensory systems, the brain is informed of such things in the world
as the presence of food and water. Through detectors within the body, it is informed
of such internal states as dehydration, body temperature and level of nutrient reserves.
The brain monitors its own chemical environment (e.g. level of hydration of brain
tissue) and is informed of the physiological state of other parts of the body. The brain
integrates these sources of information to determine appropriate behavioural
strategies. When there is a deviation from homeostatic norms of, for example, body
fluid-level, behaviour is biased in favour of seeking and ingesting water. This is the
negative feedback mode of control, where, with the help of behaviour, disturbances
tend to be self-eliminating. Low levels of nutrient availability trigger feeding. Toxins
are detected by the brain and trigger vomiting, which tends to eliminate them from the
body. A memory is formed, such that toxins might be avoided in the future.
Figure 5.31 shows that information on nutrient levels and food availability is
integrated by neural systems involving the hypothalamus and solitary nucleus,
amongst other structures. Information on taste is modulated so that behaviour based
on it is appropriate to needs. At times of need, the taste of food becomes attractive.
The liver is a detector of nutrient state and supplies information to the brain. Insulin
secreted is adjusted according to needs. Neurons in some nuclei of the hypothalamus
are sensitive to hydrational level and play a role in stimulating drinking at times of
dehydration. Similarly, the secretion of arginine vasopressin from the pituitary gland
is adjusted to suit hydrational state. Neurons in other nuclei are sensitive to their
temperature and adjust behaviour and physiology in the interests of temperature
regulation. Other neurons are sensitive to events in the immune system and bias
behaviour towards rest, hence facilitating recovery from infection.
The internal physiology of the brain exhibits a form of homeostasis and negative
feedback. When a part of the brain is particularly active as a result of a high neural
activity there, the local demand for glucose and oxygen will be relatively high. By
means of changing the diameter of blood vessels, adjustments are rapidly made to the
brain's blood supply to facilitate increased supply to where it is needed.
Question 5.7
Behaviour is normally determined by a combination of external factors (stimuli in the
environment) and internal factors (cognitions, goals etc.). The term 'stimulus bound'
suggests that the weighting of control is disturbed such that the patient is more
strongly under the influence of external stimuli, relative to internal factors. The
expression that they live in the 'here and now' also describes this. Forward planning,
implying control by cognitions and goals, is more difficult.
The expression 'open to capture' suggests that stimuli that might normally be resisted
can take control of behaviour. For example, the patient of Luria came under the
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control of the physical stimulus of the lighted object and was captured such as to try
to smoke it.
Question 5.8
The notion that we employ a 'theory of mind' of the other person accords with the
kind of folk psychology that most people appear to employ in their day-to-day social
contact with others (introduced in Chapter 1, 'Introduction'). Thus, we imply motives
such as their need to impress. We infer emotional states such as anger or frustration
experienced by the other person. Thus, theories of mind lie at the basis of how we
form our calculations of the anticipated moves of others and devise our reactions.
Question 5.9
A tinkerer works on what is already available and employs trial-and-error, as opposed
to a design engineer who has some idea of the end-product. The engineer might (at
least in principle) start from nothing, though perhaps more usually he or she would
adapt some existing solution. This analogy can be applied to the hippocampus of a
caching species. It would suggest that, given first a 'basic hippocampus' to work with,
evolution has, in effect, selected increments of size since they brought a fitness
benefit in terms of foraging efficiency.
Question 5.10
As shown in Figure 5.42a, a chemical used in anterograde labelling would be taken up
by the cell body of neurons at a nucleus and transported along the axon. That is to say,
it is transported in the same direction as action potentials move. As Figure 5.21
shows, the axons of neurons in the lateral geniculate nucleus (LGN) project to the
visual cortex. Therefore, the chemical might be expected to arrive at the terminals of
these axons at the visual cortex. By the technique of retrograde labelling (Figure
5.42b), chemical taken up by axon terminals will move along the axon (in the
opposite direction to the movement of an action potential) until it reaches the cell
body. As you can appreciate from the text and Figures 5.20 and 5.21, the axons that
terminate at the LGN are those of retinal ganglion cells. Therefore, the substance
would be expected to end up in their cell bodies in the retina (As you will discover
later, the story is more complex than this since the axons of some neurons other than
ganglion cells also terminate in the LGN).
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