The document discusses physiological mechanisms and behavior from the perspective of the nervous system and hormones. It provides details on the evolution of the nervous system across organisms from unicellular to multicellular to vertebrates. Key points made include the increasing differentiation and centralization of the nervous system correlating with increased behavioral complexity. Examples are given comparing nervous system anatomy and organization between invertebrate and vertebrate species in relation to different lifestyles and behaviors.

1. Physiological Mechanisms
and Behavior
•Nervous System
•Hormones

2. • Organised behaviour is a result of sensory
and motor integration in an organism –
nervous system (NS)
– How has behavioural needs shaped the
anatomy and organiszation of NS?
– Are there specific centres and pathways for
the control of particular behaviours?
– Are adaptive behaviours “hard-wired”?
– How is important information sifted from
“noise”?
– How do hormones affect behaviour and how
do they work alongside the NS?

3. • Behaviour is the tool with which an animal
manuvres itself in an organised and
directed way, and manipulates objects in
its environment to suit itself.
• This chapter deals with accounts of
behaviour in terms of physiological
mechanisms (“nuts and bolts” explanation)
(see Fig 3.1)

5. • Multicellular animals have developed a complex systems
of cells
• Detect, transmit, integrate, store information supplied by an
animals internal and external environment for decision
making processes
– sensory cells – detects changes in environment
– Nerve cells – transmits and integrates information
– Chemical messengers – transmits information around the body
(slower than NS)
– Muscle cells – translate information into action
• The scope and sophistication of behaviour in the animal
kingdom is linked with the evolution of neural complexity
• Vertebrate nervous systems are not always more
complex than those of invertebrates
• What then are the properties of NS that makes complex
behaviour possible?

6. • We will not discuss the neural anatomy
and physiology
• Read up on:
– Nerve cell structure (Fig 3.2)
– Nerve cell function
– Communication between neurones

8. Evolutionary trends in nervous systems and
behaviour
As we move from unicellular organisms to vertebrates
the NS changes in 2 ways:
•Greater differentiation
•Greater centralization

9. • In unicellular organisms (NO ns) there is spatial
differentiation between sensory and motor function
– Paramecium is covered in motile cilia – for helical
propulsion in water
– When it collides with obstacle, mechanoreceptors at
anterior end are stimulated and cilia beat in reverse and
organism move off in different direction (Fig 3.3a)
– If hit from rear posterior mechanoreceptors triggers
forward thrust
– How do the mechanoreceptors communicate in
absence of nerve fibre?
• Caused by changes in electrical potential of the cell
membrane and picked up by each cilia – entire
organism acts like a nerve cell!
(See Fig 3.3b)
– The control linking the receptor to effector is
unrefined

11. NS and behaviour in Invertebrates
• In multicellular animals the linking is taken over by axons
having dendrites and synapses
• In an advanced NS:
• Sensory receptor – cell or group of cells
• Afferent or sensory neuron – carrying impulse from sensor
• Efferent or motor neuron – carry impulse to effector
• Internuncial neuron or interneuron linking sensory and motor neuron
• Effector organ (performs the motor task)
• Nerve Nets
• Cnidarians (sea anemone, jelly fish, etc) and echinoderms (starfish,
urchin, etc) (See Fig. 3.4a & b) – diffused nets
• Lengthening and thickening of axons – fast action – withdrawal
action of sea anemone (Actinaria and Metridium)
• Behavior is stereotyped – exhibit reflex

13. • Nerve tracts and Centralization
– In platyhelminthes the tracts are more pronounced and ns shows trend
towards centralization (Fig 3.4c) – recognisable CNS and cephalisation
(concentration of nerve tissue in the head region into an anterior
ganglion or simple brain)
– Nerve cord extends down the body (Fig 3.4c) from anterior ganglion
– Nerve fibres extend from the cord to all regions of the body in a network
arrangement – peripheral ns ( in most vertebrates and all vertebrates) –
simplest in flatworms
– Peripeheral contain the sensory cells and the CNS has the motor nerve
cells
– Sensory cells in Planaria respond to touch, temp, chemicals, light
– Nerve cord allows for much rapid transmission – increase in speed and
variety of behavioral responses to different environmental stimuli
– The differentiation and centralisation of NS in flatworms allows for a
degree in learning ability – which way to turn in a T-maze and to avoid
noxious mechanical stimulus, assessment during mate choice

14. Nerve cords and Ganglia
• In higher invertebrates (metamerically segmented) –
annelids and arthropods and molluscs (non segmented)
the ns is differentiated into ganglia linked by nerve cords
(see Fig 3.3 c-e)
• Increasing centralisation – neural switchboard:
– Afferent fibres (sensory receptors) connect to interneurons and to
motor neurons
– Depending on input different motor neurons are brought into play
– In leeches ganglia has 400 cells; in Aplysia a mollusc has 1500
cells
• Function of ganglia
– regulation of local reflex arc – local control
– Long range coordinated control via long interneurons along nerve
cords facilitating coordinated operation of different body parts

16. • A number of behavioral advances are associated with
these developments
– Elaboration of appendages and musculature
– Emergence of fluid filled body (coelom)
• allows for subtle movements and complex manipulative tasks eg. In
the web building
• Elaborate courtship songs and ornamented nest construction of
some insect species
• Stimulus discrimination and learning but learning is short lived
(small capacity of the ganglia) just like the shortlive span of species
• Among invertebrates there is trend towards enlargement
of brain – amalgamation of somatic ganglia
• Somatic ganglia still retain considerable independence of control
• If cerebral ganglia is removed earthworms still can crawl, feed,
copulate but are hyperactive
• Nereids are able to learn certain tasks even after removal of
cerebral ganglia from CNS

17. Evolutionary trends in invertebrate brains
• Vary considerably is structure. At lower end, flatworms
brains have 2000 cells, insects with 34,000 cells while
cephalopods have 170 mil cells (a tenth of humans)
• The slow moving molluscs (gastropods - snails, slugs;
and lamellibranch -bivalve) have losse string of ganglia
(50,000 cells) as compared to the cephalopods
• The tendency towards fusion of ganglia in ns with
evolution of more sophisticated sensory system and
behaviour
(See Fig 3.5)

19. NS and Behaviour in Vertebrates
• Ns develops from dorsal tissues and as a tube rather than
as a solid structure
• Traces of ancestral segmented patterns are also present –
distribution of sensory and motor neurons
• Centralisation, cephalisation and functional differentiation
reaches its peak in vertebrates
• Structure and function of CNS (See Fig 3.6):
– Brain and spinal cord
– Brain has 3 regions and they can be further sub-divided: forebrain
prosencephalon), midbrain (mesencephalon), hindbrain
(rhombecephalon)

21. Evolutionary trends in vertebrate brains
• 2 main evolutionary trends:
– First, elaboration of the midbrain (shown in fish) – optic tectum
thickens and stratified – a integration center for information from
other parts of brain
– Second, elaboration of the cerebral hemisphere (shown in
mammals) shown in the forebrain – major association centres
(See Fig 3.7a & b)
• Forebrain of lower invertebrates remain in the form of
hippocampus but the neocortex in humans extends to the
whole of the brain
• Plot of brain and body size (See Fig 3.7c). The
discontinuity is a result of the elaboration of the forebrain
cortex (neocortex) in higher vertebrates
• In lower vertebrates brain is <0.1% of body mass, in birds
and mammals > 0.5%, in humans it is 2.1% (See Fig. 3.8)

22. • Neocortex has many visible divisions which reflect different
functional areas (See Fig. 3.8a)
• In advanced mammals voluntary motor control are in front of
somatic sensory functions and separated by deep fissures
• Part of the motor cortex communicates with the spinal cord via the
pyrimidal tract (see Fig. 3.7b)
• The 2 halves of the cortex are connected by the corpus collosum
– Severence of corpus collosum results in loss of speech control and
verbal comprehension
• Further motor control is at the corpus striatum (subcortical); in birds
it is important for sterotype bahaviour
• The limbic system (subcortical) – hippocampus, cingulate gyrus,
septum and amygdala – control arousal, learning, agnostic
behaviour and decision making (See Fig. 3.8b)
• The thalamus – relay information from retina, ear, cerebellum, and
tectum and function in appreciation of temp, pain and pleasure;
production of hormones in hypothalamus – emotional arousal,
sleep, feeding, aggression, osmoreceptors (drinking orintation
behaviour)

26. NS and the Adaptive Organisation of Behaviour
• There is association between organisation of ns and the
range and complexity of behaviour of different
taxonomic groups
• Behaviour results from coordinated neural control of the
effector system
• Variation in organisation reflects adaptive specialisation
between and within species
– Does gross anatomy of CNS reflect different adaptive behaviour
patterns?
– Are adaptive behaviours “hard wired” into nervous systems – do
they have neural circuits dedicated to their control?
• Can we infer about behaviour specialisations from
anatomy of nervous system from evolutionary trends
towards centralisation and cephalisation?

27. Comparative studies of Invertebrates
• Lifestyle
– Early development are nerve nets – cnidarians – rapid through
conduction – quick response to noxious stimuli. This fast through
conduction is also in annelids and arthropods in the form of large
axons – giant fibres. The annelids and arthropods have wide
range of adaptive behavioural specialisations. Are these reflected
in the anaotomical arrangement of the fibres?
– There is difference in the oligochaetes (earthworms) and
polychaetes (ragworms) – anatomy and conduction of giant fibres
in terms of lifestyle
• In Lumbricus (burrowing oligochaete) (See Fig 3.9a) the primary
function of giant fibres is for fast contraction of longitudinal muscles
and forward and reversal withdrawal in response to mechanical
stimuli – emergency responses in burrowing organism
• The giant fibres makes up 10% of cross section area of the nerve
cord

29. • Among polychaetes the giant fibres make up 25-70% of
the cross section of nerve cord (Fig. 3.9b)
– In sedentary fan worms (Myxicola, Sabella, Branchiomma) the
function is for withdrawing the feeding mechanisms into burrow
– Errant polychaete (Neries) – are active surface predators – have
complex eyes and sensaory tentacles and have a large and well
differentiated brain, greater locomotory actions (withdrawal and
creeping), side-side swimming and rotary motion of the
parapodia
• The giant fibres in Nereis are same as in Lumbricus but there is
thickening of the lateral fibres (Fig 3.9c) – have extensive
connections and closer associatin with motor axons
• The 3 central fibres (median and paramedian) have control over
parapodia while control of longitudinal muscles Is by lateral fibres
• The division of labour has allowed for rapid but diverse locomotory
control – important to a mobile predator
• The brains of annelids and arthropods share broadly
similar glomeruli
– The relative sizes of glomeruli is related to differences in
behavior

30. • Hanstrom (1928) compared glomeruli between actively
hunting lycosids (wolf spiders) and web spinning
agelenids (Fig. 3.10)
– Lycosids – more extensive developed optic centres and corpora
pedunculata – glomeruli for sensory association and visual
memory
– Agelenids – larger central body – associated with integration of
preprogrammed behaviour
• The anatomy thus reflects the diferent lifestyles of the two
groups and their different demands on sensory integration
and motor skill
• A comparison across the insects shows a general
assocaition between the size and structure of the corpora
pedunculata and behaviour particularly to
– Social organisation
– Spatial complexity of foraging behaviour

32. Comparative Studies in Vertebrates
• Lifestyles
– Broad behavioural characteristics is correlated with brain – the
relative sizes of the different parts of the brain (see Fig 3.8)
• Otter example (See Fig 3.11) – as a group, otters have a
range of foraging skills and manipulating food with fore paw –
these skills vary with species
– Sea otter (Enhydra lutris) – clawless – breaks shellfish
against stone placed on its chest
– Clawed relatives (Lutra canadensis – river otter;
Pteroneura braziliensis – South American giant otter)
use their fore paws in a much less specialised way –
more emphasis on sensory information face and
vibrissae
• Radinsky (1968) showed differences in the cortex of the two
groups (See Fig 3.11) – forelimb projection in cortex for
handlers larger while sensory projections in cortex larger for
face and vibrissae information

34. • Songs in birds range from simple notes to complexity and
melody – song control system is due to discrete nuclei in
the forebrain that is projected to the syrinx (vocal organ)
• The nuclei are of 2 groups (See Fig 3.12a):
– Higher vocal centre (HVC) and robustus archistrialis (RA) – role in
song production
– Area X and lateral magnocellular nucleus (l-MAN) – song
acquisition
• DeVoogd et al. (1993) – compared HVC and Area X in 45
songbird that differed in song complexity – repertoire size
and number of syllable per song – using DNA phylogeny
– Positive correlation between size of song repertoire and volume of
HVC (Fig. 3.12b)
– Species with larger repertoires had larger nuclei associated with
control of song production

36. • Sex Differences in Brain Structure
– Ns differs between males and females in relation to reproductive
roles, ecology – many differences are also driven by hormones –
mediated by sex differences of hormone receptors in the brain
– In human there are 3 differences in structural architecture of the
brains of males and females resulting in different sexual
behaviour
• First, Dimorphism in size of nucleus INAH-3 – 2 to 3X larger
in males – packed with androgen sensitive cells – male typical
sexual behaviour
– High levels of androgens in women – male like assertive
sexual behaviour, small breasts, low vocal pitch,
hirsuteness
– Controversially INAH-3 has been linked to male
homosexuality (Levay, 1991 – studied males who died of
AIDS and men who did not die of AIDS)
» INAH-3 nucleus in homosexuals smaller than in
heterosexual males and roughly the same size as that
of women – this study is not conclusive 36

37. • Second, connection between the cerebral hemispheres
– the corpus collosum, anterior commisure, and nerve
fibre bundles are larger in women – greater empathy
and emotional sensitivity. Women have greater
connection between the 2 halves of the thalamus –
important relay for sensory information to cortex
• Third, ageing – men lose more brain tissue as they age
and earlier in life
– Tissue loss is in frontal and tempral lobe in men;
hippocampus and parietal area for women
– Accounts for personality and behaviour changes
with age
– Increased irritability for men and reduced memory
and visual skills for women

38. • Ecology and Sexual Dimorphism in Brain
Structure (long term selection pressure)
– Sexes differ in general features and brain
anatomy but specific differences can arise due
to ecological selection pressure – eg. spatial
memory and navigational skills (greater in
males)
– Males have larger home range or territories –
greater spatial learning tasks. Males would
have greater development of the brain related
to spatial memory – the hippocampus (spatial
awareness and navigation)
– Studies show that males do have larger
hippocampus (for birds and mammals) – there
are exceptions however!
38

39. – Studies by Sherry et al. (1993) on brown headed
cowbirds (Molothrus ater) – brood parasites
• The females search for host nests and lay single egg in each
nest – up to 40 eggs in each breeding season. Male cowbirds
play no part.
• On this basis Sherry et al. predicted that spatial abilities of
females (locate and return to host nest) would show larger
hippocampus than males – females have larger hippocampi
than males (Fig. 3.13)
• Sherry also compared with closely related non parasitic birds
(control species – Red winged blackbird and the Grackle)
• Sex differences in brain structures do not always reflect
differences in associated behaviour.

41. – Clayton et al. (1997) however showed that sex
difference in size of cowbirds hippocampus (female
and male) was related to breeding season when birds
are actively looking for host
– The size of forebrain nuclei (controlling song) in
canaries also show cyclical variation with season and
thus song production
– This suggest adaptive plasticity in brain development
– the cowbirds and canaries are not alone!

42. • Brain Development and Experience
– Some species of birds store food for later retreival – spatial
memory required to retrieve items
• Black capped chikadees (Parus atricapillus) scatter-hoard
seeds and insects in bark and moss clumps over a wide area
• Items are hidden individually and each location used only
once and can retrieve the food items even after a month!
(Hitchcock & Sherry, 1990)
• Birds remember specific sites – the Clarks’s nutcracker
(Nucifraga columbiana) can hide 9000 items and can find
them 9 months later – birds really do remember specific sites
- not using approximates of visual or odour cues to detect
food about the area to search for food
• Birds not only can remember what items they hide in different
places but also can time the recovery of the items according
to how fast they decay – episodic memory

43. – The region of the brain involved in the episodic
memory is the hippocampus – so food hoarding
species would have larger hippocampus than closely
related species that that do not – this is the case
• Size of hippocampus appears to be affected by the
hoarding experience of individual birds
• Clayton & Krebs (1994) experiment on marsh tits
(Parus palustris) – divided birds into 2 groups – first
group allowed to cache sunflower seeds and
second not able to
• They then examine brain of both groups – second
group had smaller hippocampi (Fig 3.14 b) –
experience of hoarding had profound effect on
hippocampus development

44. • Macguire et al. (2000) used MRI to study
the spatial learning in taxi drivers
– Taxi drivers who had completed training had
larger posterior hippocampus as compared to
controls and increased with the length of time
the drivers had been operating (Fig 3.14c)

46. Is Adaptive Behaviour “hard wired”?
• In previous section – adaptive behaviour patterns can be
linked to particular areas of the brain
• Size of these areas reflect the relative importance of the
behaviour in different species and individuals
• Is there a particular component of the ns as the
mechanism controlling a behaviour?
• Do adaptive behaviours have neural circuits?
• Answer is YES and it depends on the definition and
complexity and on the nature of information processing
within the ns

47. • Local versus distributed processing
– Before 1990 – behaviour was thought to be mapped
to simple neuronal circuits – local and self contained
– Now it is thought as neural networks (different ways
and different times) and distributed processing system
(at immediate site and away – Connectionist view –
even simple tasks may require 100 million cells or
more (John et al., 1986)

48. • Reflexes
– A simple form of behaviour – an automatic, quick,
stereotype unit of behaviour in response to a stimulus
(internal and external)
– Can examine the relationship between behaviour and the
functioning of specific neural circuits – eg., knee-jerk
response and limb withdrawal from a painful stimulus
(Reflex arc, Fig 3.15)
– Limb withdrawal reflex involves
• Simultaneously contract flexor muscles and relax the
antagonistic extensor muscles so that limb can be pulled
towards body
• 1st – flexion reflex – as affected limb is flexed, has to use
other muscles to steady itself (cross-extension reflexes)
– in combination the 2 allow for emergency actions and
locomotion
• Stretch reflexes – to grade flexion and extension in
antagonistic muscles so that limb is controlled in stages
and not in one violent action

50. • There is no elaborate CNS in invertebrates but sensory
and effector organs still communicate through the central
nerve cord and ganglia. Eg.in the gill withdrawal
response of sea hare Aplysia (a mollusc)
• The gills are retracted into the mantle cavity in response
to weak mechanical stimulation of the siphon
• The reflex arc involes – excitatory and inhibitory
interneurons relaying sensoty information from siphon to
motor neurons in the abdominal ganglia which causes
withdrawal of gill (Fig 3.16)