ib biology sl option e

Neurobiology and Behaviour (Option E)

E.1) Stimulus and ResponseE.1.1) Define the following terms:

Stimulus: A change in the environment (internal or external) that is detected by a receptor and elicits a response

Response: A change in an organism due to a stimulus Reflex: A rapid unconscious response to a stimulus

E.1.2) Explain the role of the following in response to stimuli

Receptors: detect a stimulus; can be sensory cells or nerve endings of sensory neurons Sensory neurons: receive messages across synapse from receptors and carry them to CNS Relay neurons: receive messages across synapse from sensory neurons and carry them to the

motor neurons Motor neurons: receive messages across synapse from relay neurons and carry them to an

effector Effector: receive messages across synapse from motor neurons and carries out a response;

these can be muscles (contract) or glands (secrete).

E.1.3) Draw and label a reflex arc for a pain withdrawal reflex.

*Red boxes: parts that must be labelled


E.1.4) Explain how animal responses can be affected by natural selection, using two examples

Example 1: Migration of European blackcaps o These bird usually migrate between Spain and Germanyo Spain – winter and GE – spring&summero Lately, some of these birds go to UK instead of Spain for wintero Scientists realise that the ones in UK go to Germany 10 days earlier than the Spanish

ones This gives them more choice of territory and they laid more eggs This is an advantage to the UK ones

o Thus, eggs were collected from both the UK and Spanish birdso No parents were around to teach the young which direction to flyo All of the birds tended to migrate in the same direction that their parents had gone

Thus, this shows how blackcaps are genetically programmed to fly in a certain direction

Example 2: Timing of breeding of the Great Tit o Usually breeds in spring/early summero Timing of egg laying is genetically determinedo Until recently, the date of egg laying is becoming earlier

This is because adults that breed earlier enjoy greater reproductive success Earlier opening of leaves on deciduous trees Earlier peak of insects(food) feeding on the leaves of these trees

o Thus, more food for offspring and better chances of survival


E.2) Perception of StimuliE.2.1) Outline the diversity of stimuli that can be detected by human sensory receptors

Type Stimulus ExampleMechanoreceptors Generate nerve impulses when stimulated –

may indicate touch, pressure, gravityLungs, tips of fingers, skin

Chemoreceptor Responds to chemicals in solution Nose, tongueThermoreceptors Detect temperature SkinPhotoreceptors Respond to light Rod and cone cells in eye

E.2.2) Label a diagram of the structure of the human eye


E.2.3) Annotate a diagram of the retina to show the cell types and the direction in which the light moves

*Note: notice the direction of the light

E.2.4) Compare rod and cone cells

Rod cells Cone cellsMore sensitive to light and functions well in dim light

Less sensitive to light and functions well in bright light

One type of rod cell - absorbs all wavelengths of visible light

Three types of cone cells – sensitive to red, blue and green light, giving colour vision

More widely dispersed, giving wider field of vision

More concentrated, giving one acute area of field of vision

A group of rod cells pass impulses to a sensory neuron of the optic nerve

A single cone cell passes impulses to a sensory neuron of the optic nerve

Cone cells

Rod cells

Layer of pigmented cellsNerve fibres of

ganglion cells


E.2.5) Explain the processing of visual stimuli, including edge enhancement and contralateral processing

Edge enhancement o Each ganglion cell is stimulated when light falls on receptive fieldo Two types of ganglion cells:

Ganglion stimulated if light falls on the centre of receptive field BUT reduced if light falls on the periphery

Ganglion stimulated if light falls on periphery of receptive field BUT reduced if light falls on the centre

o This can be proved with Herman grid – illusion of grey areas

Contralateral processing o Left and right optic nerves meet at OPTIC CHIASMAo Here, the neurons carrying the impulses from the half of the retina closest to the nose,

crosses over to the opposite optic nerve Thus left optic nerve carries information from right half of field of vision And vice versa

o This allows the brain to deduce distances and sizes

E.2.6) Label a diagram of a ear.

E.2.7) Explain how sound is perceived by the ear.

*note the notes under the underlined words in the diagram above. Know those!!!!!


E.3) Innate and Learned BehaviourE.3.1) Distinguish between innate and learned behaviour

Innate Learned Instinctive – genetically based Unaffected by environment Controlled by genes Inherited from parents

Based on experience Affected by environment Not controlled by genes Not inheritable

E.3.2) Design experiment to investigate innate behaviour in invertebrates, including either a taxis or a kinesis

Taxis – movement towards or away from a directional stimulus o Experiments with flatworms

Flatworms placed in a shallow dish with small pieces of food in a part of dish The flatworms would move towards it Other variables should be kept constant – i.e. amount of light A line is drawn across the middle of the dish – with or without food Number of flatworms are recorded each minute during exp

Kinesis – response to non-directional stimulus; rate of movement/turning depends on stimuli o Experiment with woodlice

Humidity rises, movement of woodlice is less Number of turns less, distance covered is more Woodlice – like small, humid spaces = increases their chance of survival

E.3.4) Discuss how the process of learning can improve the change of survival.

Some examples are:o Chimpanzees learn to stick a branch into a termite nest, pull it out and eat the termiteso Many bird species learn to take avoiding action when they hear alarm calls warning

them of a predatoro Foxes learn to avoid touching electric fences after receiving electric shockso Hedgehogs learn to run across busy roads, instead of rolling up into a ball


E.3.5) Outline Pavlov’s experiments into conditioning of dogs

Pavlov observed that his dogs secreted saliva when they saw/tasted foodo Sight/taste of meat = unconditioned stimuluso Secretion of saliva = unconditioned response

He then gave them a neutral stimulus – sound of bell/metronome Before giving the meat, he would ring the bell He repeated this for a few days After awhile, they would secrete saliva when they heard the bell

o Sound of bell = conditioned stimuluso Secretion of saliva before meat = conditioned response

This is called conditioning

E.3.6) Outline the role of inheritance and learning in the development of birdsong in young birds.

Male chaffinches use their song to keep other males out of their territory and to attract females Song varies a little between males, allowing identification of individuals

o Scientists took two different songs: A normal chaffinch song A song from a bird reared in isolation

Innate – length and number of notes Learned – narrow range of frequencies


E.4) Neurotransmitters and SynapsesE.4.1) State that

some presynaptic neurones excite postsynaptic neurones = excitatory synapseso causes +vely charged ions to enter, allowing it to depolarize and cause action potential

others inhibit postsynaptic transmission = inhibitory synapseso causes –vely charged ions to enter, increasing polarization (hyperpolarization)

E.4.2) Explain how decision making in CNS can result from interaction between the activities of excitatory and inhibitory presynaptic neurones at synapses

Synapses are the sites at which decisions are made A rapid sequence of pulses of neurotransmitter is needed to cause postsynaptic transmission

o This could come from the same presynaptic neuron or different ones Where many presynaptic neurons form synapses with a postsynaptic neuron, some of these

synapses will be excitatory and others will be inhibitoryo Effect of excitatory neurotransmitters may be cancelled out if inhibitory

neurotransmitter is also being released Whether an action potential in initiated in the postsynaptic neuron is therefore decided by the

summation of messages from all synapses In this way, decision can be made by CNS

E.4.3) Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission

Some psychoactive drugs have a chemical structure similar to a neurotransmittero Binds to receptors for that neurotransmitter in postsynaptic membraneso Block the receptors, preventing neurotransmitter from having its usual effect

Some have similar chemical structure and have same effect to a neurotransmittero But they are not broken downo So when they bind, it has a longer lasting effect

Some interfere with the breakdown of neurotransmitterso Prolong effect of neurotransmitters


E.4.4) List three examples of excitatory and inhibitory psychoactive drugs each

Excitatory Inhibitory Nicotine Amphetamines Cocaine

Benzodiazepines Alcohol THC

E.4.5) Explain the effects of THC and cocaine in terms of their action at the synapses in the brain.

Cocaine THC Excitatory psychoactive drug

Stimulates transmission of synapses in the brain that uses dopamine.

Causes the release of dopamine into the synapses of the brain

Stimulates ‘reward pathway’ Blocks transporters, causing a

build-up of dopamine in the synapse

Thus, this gives the user feelings of euphoria, increased energy, alertness & talkativeness

Inhibitory psychoactive drug

Affects transmission at synapse, where postsynaptic neuron can release a signalling chemical that binds to receptors in the membrane of the presynaptic neuron

Also binds to cannabinoid receptors, blocking the release of excitatory neurotransmitters

Thus, short-term effects are memory impairment, intoxication and stimulation of appetite

E.4.6) Discuss the causes of addiction.

Dopamine secretion o The number of dopamine receptors is decreased due to overuse, causing receptors to

be less sensitive. Thus, more of the drug is needed to achieve feelings.o Dependent on the feelings that dopamine promotes

Genetic predisposition o Addictions are more common in some families than otherso Genes can make some people predisposed

Social factors o Can either prevent or encourage ito Culture, peer pressure, family, poverty and mental health = factors influencing addiction