Back to Revision NotesNote: In this exam there is a slightly greater emphasis on Book
6 (Questions 1,3 & 7) than in previous years, but two of the questions
(3 & 7) involve integrating material from more than one book, so they
are not exclusively reliant on one book. Other questions that integrate
material are 2 & 8.
Q1.
(mostly Book 6)
The study needs to be put in the context of Parkinson's disease and
the progressive loss of neurons in the substantia nigra. These cells release
dopamine into the striatum and it is this loss of dopamine that is the
cause of the muscle rigidity and movement poverty of Parkinson's. One possible
treatment is to put new dopamine releasing cells into the brain, and the
paper in question examines whether the treatment works. Short and long-term
survival refers to the grafts; can the cells withstand the transplant process?
Short and long-term function of the grafts; if the cells do survive, can
they effect a change in the subject? It is clearly important to know whether
the treatment is a short-term measure (weeks, months) or long term (years).
Unilateral refers to the fact that most parts of the brain have a left
and a right part. Treating one side of the brain, say the left, should
produce measurable effects on the contralateral side of the body, the right.
The untreated side of the brain, the right, in contrast should effect no
change in its contralateral side, the left. This is a good clinical design.
Intrastriatal means within the striatum; the new cells are put directly
into the striatum (caudate nucleus + putamen), the area to which cells
in the substantia nigra project and in which they release their dopamine.
"Grafts" refers to the cells that are introduced into the brain. The title
is a pretty good guide to what is in the subsequent paper.
The answer should focus on "relevance" - total mark could be only up
to 8 if not made relevant to the paper/study.
4 marks Style: an essay was requested.
12 marks Content: are the terms in the title correctly explained
with their relevance made clear?
4 marks Understanding: the whole essay must convey the student's
grasp of the issues.
(Books 1, 4 & 5)
Variation may be discrete or continuous with the former more likely
to result in polymorphism. Variation arises because of differences between
the genotypes of conspecifics (e.g. Tfm mutation; AJ and CFW mice); differences
in the local cellular environment in which that genotype is expressed (e.g.
quantity of testosterone/oestrogen; temperature affecting castes); differences
in the stimuli to which the animals are exposed (e.g. other conspecifics
during development; smells; experience of success/failure at fighting;
stress). It is important because without variation there would be nothing
upon which natural selection could act.
4 marks Style
12 marks Content: 7 for genetics; 7 for environment; 7 for natural
selection
4 marks Understanding
(Books 2, 5 & 6)
Some regions of the brain are clearly anatomically identifiable either
as structures comprising whole neurons (e.g. cerebellum, thalamus, cortex)
or as axonal pathways (e.g. fornix, corpus callosum). The regions may themselves
be subdivided by their cellular composition (e.g. Brodman's areas). Different
regions of the cortex, thalamus and hippocampus have different functions,
as demonstrated by the LGN and visual cortex for vision, medial hypothalamus
and defensive aggression; CAl region and LTP. This would lend some support
to the notion that that each separate region has a separate function. However,
many regions are involved in vision, speech, and aggression. The probability
is that each region plays a different even unique role but that several
regions contribute to each function.
4 marks Style
6 marks Anatomical regions
6 marks Functional regions
4 marks Understanding
(Book 2)
Not an essay but a coherent, logical account is needed. The account
should focus on synaptic potentials which are graded and decay with distance
from the synapse, temporal and spatial summation. However, some thought
should be given to what the inputs are (e.g. inhibitory and excitatory)
and their quantity. The key to the whole process is the extent of depolarisation
at the axon hillock and the effect on the voltage gated sodium channels
located there.
4 marks Style
12 marks Content
4 marks Understanding
(Book 4)
Direction: chemotropic substances released by target; signpost
cells; pathways (e.g. adhesion cues - NCAM, other axons, barriers); temporally
specific responsiveness; temporally specific cues; deterrent properties
of some substances (e.g. glutamate on hippocampal dendrites). On arrival
appropriate chemotrophic substance and enough of it; functional
synapses (implies some reciprocity).
4 marks Style
12 marks Content
4 marks Understanding
(Book 3)
The question is in two parts (and so should be the answer):
a) The output from one receptor is compared with that of adjacent receptors via a comparator cell. If the receptor in question excites the comparator cell and adjacent receptors inhibit the comparator cell the output of the comparator cell will reflect the balance between inhibition and excitation; it will in effect compare the two types of input. Assuming that the system is wired up appropriately so that equal stimulation of the receptors evokes a nil response from the comparator, then any response from the comparator will mean a luminance discontinuity across the receptors. [Bk. 3: 4.3.2]
b) Largely. Colour: bipolar cells and opponency; motion: the basic motion detector receives input from two receptors in neighbouring retinal positions (delayed inhibition; velocity gradients: detectors add together the responses from neighbouring individual motion detectors which are selective for opposite directions of motion); stereopsis: comparison of the images of the two eyes [Bk. 3: 4.4, 4.5, 4.6]
a) 12 marks
b) 8 marks
plus 4 marks for understanding (up to max total of 20!)
(Book 6 and Experimental strand)
Perceptual acuity declines with knock-on effects for cognition. Both
long-term and short-term memory are affected. In working memory the amount
of information that can be held in consciousness is reduced. Retrieval
from long-term memory becomes more difficult. There is a decline in speed
of processing and in multi-tasking.
Difficulties in studying revolve around cross sectional studies with
associated cohort effects and longitudinal studies with problems of practice
effects and fatigue, as well as uncontrolled drop out. There is also the
problem of very large variation in the effect of ageing. There are financial
and practical problems in maintaining a research program over many years.
Also other aspects: e.g. laboratory vs. "home environment", animal models,
etc.
4 marks Style
12 marks Content: 8 psychological effects; 8 methodological
4 marks Understanding
(Books 1 & 3)
A good answer will integrate examples with their relevance to the question.
Selecting a mate of the same species can be down to species specific odours/sounds/colourings/light
patterns used by one party and tuned sensors of the other. A particular
individual may not be selected (it is merely an appropriate stimulus set
encountered during sexual receptivity). Or, partner selection may be based
on movement, subtle differences in the stimuli presented, fighting ability,
territory occupied.
4 marks Style
12 marks Examples (clarity and range)
4 marks Understanding
(Book 5)
Stress is the prolonged inability to remove a source of danger. It
is accompanied by physiological responses (i.e. SNS activity, release of
the catecholamines adrenaline/noradrenaline from the adrenal medulla) which
initially prepare the animal for fight or flight. In the absence of effective
action these hormones remain elevated as do their consequences, e.g. high
heart rate. Prolonged SNS activity can lead to atherosclerosis and high
blood pressure. Another physiological system enhances glucose availability
(i.e. CRH increase -> ACTH increase -> corticosteroids
increase -> CRH decrease, etc.). Similarly, in the absence of effective
action high corticosteroid levels can reduce the number of corticosteroid
receptors and so diminish their own negative feedback effect. This results
in continued high levels of corticosteroids, including cortisol. High levels
of cortisol are linked to depression. Corticosteroids suppress the immune
system in two ways: by direct action on helper T cells and second by inhibiting
the secretion of interleukin-l by macrophages.
4 marks Style
12 marks Content: SNS 8 marks; CRH etc. 8 marks
4 marks Understanding
| Back to Questions |
Back to Revision Notes |