Back to Revision NotesQ1.
(a) Students should provide examples of three types:
i) clear examples where different parts of the brain do appear to have different functions. Two examples are sufficient, e.g. Broca's area and speech, visual cortex and vision (4 marks).
ii) examples where the function of a brain structure is unclear, e.g. amygdala, septum (2 marks).
iii) examples where the brain structure appears to have numerous functions, e.g. hypothalamus (4 marks).
(b) Students should question what is meant by a "part of the brain", citing the numerous sub-divisions of the hypothalamus and their various roles. They should also ponder on what it means to say that a brain region has a particular function; an exclusive role or merely one contribution among many? Finally some may address the issue of how any brain/function link is established (up to 10 marks for a reasonable discussion of these issues).
Alternative marking scheme: (a) list with structure & function => 14 marks + (b) discussion => 6 marks.
Book 2.
Q2.
The hippocampus appears to be involved in cognitive maps; in a loss
of declarative but not procedural memory; a loss of consolidation (old
long term memories remained, new long term memories not formed).
up
to 12 marks for making it clear what these roles are.
Could also refer to IMHV and LTP in chicks (4 marks)
There are three main pieces of evidence here: Firstly there are the human (HM) studies; secondly there are the water tank studies on rats and the effects of lesions to the hippocampus; thirdly there are the Long Term Potentiation studies both in vivo and in vitro in rats. worth 4 marks each.
Although potentially marks up to 24, limit maximum score to 20!
Books 2 & 5
The concept of fitness has helped in the context of functional explanations of behaviour, but the fact that this is but one of a number of explanatory types could be mentioned. A good answer should state what fitness is and how it can be measured (or estimated). 5 marks
Examples should range over mate choice, group living, aggression, cognition,
predator avoidance, prey capture, etc. Each example should state what the
behavioural problem is and how considering fitness has aided understanding.
up to 5 marks per example,
maximum of 15 marks.
Book 1
The 'spinal' cat experiment indicates that the spinal cord, by itself, contains the machinery for producing the rhythmically organised and sequenced movements of the four limbs that characterise walking and running. The implication then is that the forebrain motor systems then act to 'drive' the spinal cord reflex structure to produce the modulated and directed rhythmic activity that characterises normal movement. (general neurophysiology - would include sensory, motivation, etc. and not really of direct relevance; central motor & spinal cord information needed for full marks if well considered)
In contrast the movements of the arms, hands and fingers that are seen in voluntary behaviour depend upon the forebrain motor systems. The difference in nature of the behaviours is paralleled by the organisation of the descending influences upon the spinal cord from the brain.
In humans, the region of the spinal cord that controls the distal musculature of the forelimbs, the descending fibres from the pyramidal tract terminate directly upon alpha motor neurons rather than upon interneurons. Segmental organisation is also relevant
( Question is about spinal cord and central MOTOR systems, ˆ motivation voluntary etc. is not relevant. )
10 marks for:- describing the reflex; associating the sequenced and rhythmic movements of the limbs with the spinal cord;
10 marks for:- associating the form of the voluntary movements such as picking up a glass with the forebrain motor systems; relating the voluntary control of the distal musculature of the forelimbs with the termination of pyramidal tract fibres directly upon alpha motor neurons.
Book 2
(A) The receptor potential is a graded event and increases in amplitude with increasing stimulus intensity; the large the receptor potential, the more frequent the action potentials. Action potentials are all-or-nothing events, and the only possibility is to vary the frequency of firing (2 marks). Also stronger stimuli are Iikely to activate a larger number of afferent neurons (2 marks). So, increased stimulus intensity results in (i) an increased frequency of action potential firing and (ii) a greater number of responding neurons (2 marks). (max. mark limited to 4).
(B) (i) The two stimuli will activate different types of receptors. The pin prick will activate mechanoreceptors and nociceptors in the hand (3 marks); the cold object will excite thermoreceptors and mechanoreceptors on the skin of the back (3 marks).
(ii) The action potentials from these receptors will be conveyed along specific but different sets of afferent axons and be relayed in the CNS in specific pathways to the brain. The signals initiated by the pin-prick will pass via Aδ (mainly) and C- fibres (possibly) and information ascends in the spinothalamic tracts (3 marks). Information about the cold object is relayed via Aβ (touch) and Aδ (cold) fibres and ascends to the brain in the dorsal columns (touch) and spinothalamic tracts (cold) (3 marks).
(iii) These inputs will project to different parts of the somatosensory cortex (topographical representation) where they will activate different groups of modality-specific neurons. These action potential signals are interpreted in the brain as being generated by different types of stimuli applied to different regions of the body (4 marks).
[possibly pin-prick does not equate with pain, so could omit nociceptors]
Books 2 & 3
(a) The statement is of course a reductionist one. First, it
assumes that there is a unitary phenomenon which can be diagnosed as depression
(the essay may distinguish between depression and manic-depression, and
between endogenous and exogenous explanations of depression). Second, it
assumes that the cause for any such phenomenon must lie in the biology
of the individual - in some disorder of the cellular or molecular structure
and processes of the brain. Finally, it emphasises that the "ultimate"
underlying cause for any such condition lies in the genes. This is the
type of "nothing-but" statement that characterises reductionism and forms
the theoretical presupposition of the statement.
4 marks.
(b) Evidence:
First, the biochemical statement that the condition is characterised by disordered neurotransmitter metabolism. The evidence is derived partly from the analysis of blood platelets from depressed individuals, which show decreased levels of serotonin binding activity, and post-mortem analyses of brains from depressed individuals. But could this be a consequence rather than a cause of the depression?
Drugs which alleviate depression can be shown in experimental animals to interact with neurotransmitters and particularly with serotonin - but the fact that a drug interacts with a particular system doesn't mean that the cause of the problem is a disorder of that system (the aspirin and toothache analogy). Also, animal models of depression also show changes in serotonin metabolism - but once again cause or consequence? 6 marks
Second, the claim that the condition is genetic. Thus, some forms of depression seem to run in families, but this could be a consequence of the environment. Claims that genetic linkage has been shown for one form of depression (manic-depressive psychosis) are discussed in the text - and also the retraction of the claims. Genetic explanations need to be able to explain the epidemiology - for instance that twice as many women as men are diagnosed as depressed and that the precipitating factors in the social environment that can predict depression include childhood "vulnerability" and adult economic and emotional insecurity (the Brown and Harris study). 6 marks
For "critical discussion" - 4 marks
Book 6
This question is aimed squarely at Tinbergen's four answers. Thus there are evolutionary, functional, developmental and causal explanations - what are they and what do they mean? 10 marks (must mention all four for maximum marks).
The remainder of the marks are available for the extent to which the
student elaborates on these four themes and provide examples. Could go
into genetic differences, different mating systems, and the balance of
costs and benefits on males and females, different hormonal environments
during development and responsiveness to different stimuli as adults. 10
marks
Book 1
(a) The basic idea of plasticity is that the nervous system is seen as dynamic and capable of change in a way that a "hard-wired" system is not. The distinction needs to be made, though, between the principal pathways and tracts which are relatively permanent, and the micro-structure of the nervous system where the changes can be seen. Examples of plasticity include axon sprouting (e.g. after an axon innervating a muscle or sense organ has been cut), denervation supersensitivity, and physiological effects of training. There is also the restructuring of dendritic trees in ageing; changes in dendrites and synapses during learning, alteration in receptive field characteristics after nerve section, and changes in nerve-muscle synapses over time.
For a competent description of an appropriate range of processes - 8 marks.
(b) A good answer will distinguish between repair of structure and restitution of lost function. It will raise questions about the formation of new pathways or the strengthening of existing pathways and the replacement of 'information' lost with the loss of pathways as a result of damage. There is also the distinction between repair in the central nervous system, which is limited because of the nature of the glial cells (oligodendrocytes) and that is the peripheral nervous system where the glial cells (Schwann cells) allow considerable growth. Even where growth occurs it may be limited by glial scars, absence of myelin tubes, growing down inappropriate myelin tubes or contacting an inappropriate target. Within the central nervous system, recovery of function seen e.g. after a stroke, is more the result of the amelioration of secondary trauma rather than of physiological repair and reconstruction.
For a competent discussion - 12 marks.
Book 4
10 marks for:-
In essence the student has to link Homeostasis: the maintenance of a
variable within narrow limits with
Motivation: that class of reversible internal processes responsible
for variations in response to external stimuli.
The simplest link is that departures from homeostatic norms usually trigger motivation. Should consider four features of motivation: 1) changing responsiveness to constant stimulus; 2) goal directed behaviour; 3) decisions, choosing between behaviours (motivation as common currency); 4) selectively potentiate certain species-specific behaviours.
10 marks for examples and discussion:-
(a) To a considerable extent, motivation is aroused in the service of maintaining homeostasis. Thus a loss of body fluids is associated with drinking motivation which plays a role in the search for water.
(b) An example at variance with this is egg incubation by hens and loss of body weight, the function of the behaviour takes precedence over homeostasis.
(c) Some behaviours cannot be viewed as serving the regulation of physiological variables crucial for survival (e.g. defence, sex), so called non-homeostatic systems.
(d) Where there is conflict between two motivational systems both motivational systems cannot gain full expression in behaviour, thus neither physiological system is optimally maintained, e.g. hungry lizards on hot sand.
(e) An animal's reactivity to a substance varies in a way that is appropriate for the animal's physiological state, e.g. taste reactivity test, temperature of object and core temperature.
(f) Influence of circadian rhythm on homeostatic set point, e.g. timing of meals.
Alternatively, 12 marks for homeostasis concepts & examples, 8 marks for motivation concepts & examples
Plus 4 marks for genuinely attempting to pull the examples together (but limit max. marks awarded to 20!)
Books 1 & 5
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