Lecture 17 Brain and behaviour Flashcards
Nervous system in humans: basics
Central Nervous System (CNS)
-brain
-spinal cord
Peripheral Nervous System (PNS)
-Peripheral nerves: connect the CNS with the somatic(skin, muscles, skeleton) and autonomic(heart/blood vessels, internal organs, glands…) nervous system
neurons
Sensory neurons➢Detect external stimuli
Motor neurons➢Control muscle movements
“Connector” neurons➢Relay signal
Neuron/glia ratio ~1:1 ~170 million brain cells
The discovery of nerve cells
✓Discovered end of 19thcentury using Golgi staining that stains sparsely the whole cells
✓Golgi and Cajal shared the Nobel Prize for Physiology and Medicine in 1906 for their work on the structure of the nervous system
Nervous system across phylae
Bilaterian- Ceohalisation (head and tail)
coordinated behaviours
- hydra, jellyfish, sponges
Invertebrate
Invertebrate
-Nerve net, nerve ring(diffuse nerve cells)
-Cephalisation: CNS (ganglia, nerve chord, “proto-brain” [cerebral ganglia])
Vertebrate
✓Functional division (CNS/PNS)
✓Distinct brain structures
✓Use-dependent changes (e.g., size)
what does the nervous system allow for
Nervous system allows sensorimotor behaviour
Origin of the nervous system: earliest known CNS
was in the early Cambrian- 520 million years ago
earliest known CNS
✓Alalcomenaeusfossil dated 520-million-year-old with extremely well-preserved CNS
✓Belong to the megacheirans (“great appendage”), an extinct class of arthropods
✓Discovery helped clarify that the segment of proto-brain that innervates GA is the same as in the fangs of modern-days spiders and scorpions
Origin of the nervous system: how did it appear?
✓From jellyfishes to humans, neurons have the same fundamental morphology and function
✓The “raison d’être” of nerve cells is to transmit signals to other neurons = communicate. ➢Fundamental unit of the nervous system = synapses
In humans:~86 million neurons~1015million synapses
Synapses are small ‘computers’
Synapses host numerous (~2000) specialised proteins and protein complexes, which are essential for the release and interpretation of the neurotransmitter signals
Synaptic proteins precede synapses
Components of the synapses are present in single cells and do participate in cell-cell communication
Phylogenetic tree depicting taxonsof current relevance to synapse evolution
- Ursynapse is the key point in the phylogenetic tree
Vertebrate brain
Origin of the vertebrate brain
Haikouichthys(extinct): 530-million-year-old fossil (~3cm):
➢Protovertebrae
➢Mass of cartilage around primitive brain
✓Growth of body → evolution of myelinwhich allows more rapid transduction of nerve signals further away
➢Specialisation of glial cells = oligodendrocytes [CNS]/Schwann cells [PNS])
➢Specialisation of sensory and motor organs
-Complexification of behaviours
✓Evolution of homologous brain regions with specialised functions
➢E.g., cerebellum stabilises body in the water or on land
✓Different evolution for different lineages➢Land animals have developed cerebrum
-Development of cortex in mammal
development of cortex
✓Significant development of the cortex
oApparition of circumvolutions
o~90% of the human brain
✓Cortical functions evolved according to ecological niche
Sensory and motor homunculi
✓Representation of the entire body on the surface of the primary somatosensory and motor cortices
✓Cortical surface devoted to a specific organ depends on its usage
➢Homunculi: the body how the brain sees it
- in humans the sensory sees the whole body but especially the hands and mouth and ears
-the motor homonucli especially sees the hands and mouth and smell
What makes us human?
What is special about our brain that is not found in other mammals or even primates?
-humans have the highest brain to body/volume ratio
rapid evolution of brain size & frontal lob
Prefrontal cortex:
✓Executive function
✓Motivation
✓Speech & language
✓Working memory
✓Risk assessment
✓Decision making
✓Social behaviour
What event in human evolution seems to be at the origin of the rapid expansion of the brain of primates and why?
➢Fire→ cooked food = more calories in minimum time
➢Allows to increase number of neurons (high energy cost) without spending more time searching for food
➢More time to develop new abilities
What makes us human: size matters but…
the density of neurons per brain size in humans is 7x higher than that of African bush elephants and is generally more dense than that of non-primates
Example of corvids (crows) and parrots
✓Use tool
✓Plan action
✓Resolve complex (and new) problem = transfer of knowledge
✓Recognize themselves in mirror (self-conscious?)
What makes Brain size and brain cell density intelligent
Evolved brains help to make predictions and plans and develop behaviours to fulfil long-term goals
✓Language
✓Use of tools
Interim summary
❖Nervous system evolved during the Cambrian period and exist in 3 main forms
✓Primitive nerve net and nerve ring (Cnidarian –e.g., Hydraand jellyfish)
✓CNS/ganglia with cephalisation (bilaterian clade)
✓CNS/brain + PNS (vertebrates subphylum)
❖Evolution of the nervous system allowed diversification and complexification of behaviours
❖Vertebrates have developed a brain which functions evolved according to ecological niche (e.g., sensorimotor cortical specialisation, prefrontal cortex in humans)
❖The brain of ‘intelligent’ species have an increased brain/body size and brain cell density
Evolution of behaviour: basics
✓A behaviour is an internally generated response to an external or internal stimulus
✓It is (in most cases) produced by the nervous system
✓As other phenotypic traits, behaviour can evolve through natural selection because:
➢It can be inherited as (partially) determined by genes
➢It varies across individuals
➢It serves the fitness of individual
How to study evolution of behaviour?
Behavioural ecology explores the evolutionary significance of behaviour
1.How does it work?
2.How does it develop?
3.How/why did it evolve?
4.What is its adaptive value
The case of bird song(≠ calls)
1.How does it work? Mechanisms?
2.How does it develop? Ontogeny?
- How did it evolve? Phylogeny?
- what is its adaptive value? fitness?
Neurons/circuits/genes involved
Early exposure to an adult “tutor” is needed to learn
Advertise their quality to mates & competitors and mark territory(increase fitness)
Song structure changes during evolution
Does sleep have an evolutionary significance? How does it work?
✓Produced by the brain
✓Coordinate the response of the organism to a combination of internal and external stimuli:
➢‘Fatigue’ (sleep pressure)
➢Circadian rhythms
➢Light
➢Genetics
do all animals sleep?How do we define sleep (behaviour)?
Behavioural description of sleep
1.Sleep is a quiescent behavioural state associated with:
✓reduced sensory responsiveness to weak stimuli (≠ immobility during wake)
✓rapid reversibility in response to strong stimuli (≠ physiological and pathophysiologic quiescent states such as torpor, hibernation, and coma)
- Preventing sleep leads to more or ‘deeper’ sleep (= sleep homeostasis)
Sleep phylogeny
✓Some form a sleep-like state has been described in all animals studied so far (in 6 out of 36 known phyla…)
✓Likely to have appeared early in animal evolution
✓Nerve cells, but not a brain nor CNS, are required for sleep behaviour
Adaption of sleep behaviour
Sleep behaviour and duration can vary significantly across species due to factors such as:
➢Environmental factor (e.g.temperature)
➢Dietary requirements
➢Migration periods
➢Mating behaviour
Sleep adapts and will happen no matter what
What is sleep’s adaptive value?
“The evolutionary persistence of sleep, in the face of apparent costs of vulnerability to predation and absence of foraging or reproduction, suggests that it has an essential function.”
“If sleep doesn’t serve an absolutely vital function, it is the biggest mistake evolution ever made.”
Sleep serves a fundamental role for metabolic coordination/allocation
Sleep allows “a temporal structure and organizational principle for coping with the energetic and chemical demands of life, given the constraints of time and space.”
Given the prevalence of sleep across animals and the diversity of the animal kingdom and their respective physiological demands, there is a considerable chance that sleep evolved to accumulate several different adaptive functions, which occurrence during sleep is advantageous and provides benefits in an organism-specific manner.
- evolution is the addition of new functions to a core function- resulting in adaptive functions
Current views on sleep function(s)
-Restorative function (immune/growth/waste clearance)
-Energy conservation/allocation (metabolic)
-Neuroplasticity (development/memory
