Option E - Neurobiology & behaviour

the standard level topics of this chapter (E1-E4)

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Define the terms stimulus, response and reflex

stimulus: a change in either the internal or external environment that is detected by a receptor and elicits a response

response: a change in an organism, produced by a stimulus

reflex: a rapid, unconscious response to a stimulus

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Explain the role of receptors, sensory & motor neu

receptors : to detect a stimulus; sensory cells, or nerve endings of sensory neurons

sensory neurons: receive messages from receptors across synapses from sensory cells or from nerve endings of sensory neurons. Transmit message to CNS

relay neurons: receive messages from sensory neurons across synapses. Transmit messages to motor neurons that cause an appropriate response

motor neurons: receive messages from relay neurons across synapses. Transmit messages to effector organs

effectors: receive messages from motor neurons. Produce a response such as muscles contract (or relax) ,glands secrete

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Draw and label a diagram of a reflex arc

reflex e.1.3 (http://click4biology.info/c4b/E/images/E1/e1.3.jpg)

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Explain how animal responses can be affected

Migration in Sylvia atricapilla, or blackcaps

  • this bird breeds in early summer across much of central and northern Europe, and then migrates in the fall. Until recently, populations in Germany migrated to Spain. Recently, 10% of blackcaps migrate to the UK. Experiments with eggs have shown that the direction of migration is genetically programmed and inherited. Blackcaps that migrate from Germany to the UK instinctively fly west. Blackcaps that migrate from Germany to Spain instinctively fly southwest

Timing of breeding in Parus major, or great ****

  • Parus major breeds in spring or early summer throughout much of Europe. Timing of egg laying is genetically influenced; day length is used to determine the time of year. Recent studies of birds in the Netherlands have shown:
  • date of egg laying is becoming earlier
  • adults that breed earlier have greater reproductive success
    • due to earlier opening of leaves on deciduous trees
    • earlier peak in biomass of invertebrates feeding on tree leaves
    • invertebrates = main food adults collect and feed to offspring
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Outline the diversity of stimuli

Mechanoreceptors: Mechanical energy in the form of sound waves. Movements due to pressure or gravity. --> Hair cells in the cochlea of the ear. Pressure receptor cells in the skin.

Chemoreceptor: Chemical substances dissolved in water (tongue). Chemical substances as vapours in the air (nose) --> receptor cells in the tongue. Nerve endings in the nose. (Hypothalamus in brain)

Thermoreceptors: Temperature --> Nerve endings in the skin detect warm or cold.

Photoreceptors: Electromagnetic radiation, usually in the form of light. --> Rod and cone cells in the eye.

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Label a diagram of the structure of the human eye


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Structures of the eye and their function


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Compare rod and cone cells.


  • Sensitive to light, better in dim.
  • absorb all wavelengths of visible light --> monochrome vision
  • Up to 200 rods pass impulses to SAME sensory neuron
  • More widely dispersed through the retina --> wider field of vision


  • Cones function well in bright light
  • three types of cone cell, sensitive to red, green and blue --> colour vision
  • many cone cells have their OWN individual neuron through which messages can be sent to the brain.
  • Concentrated near the fovea, giving one acute area of the field of vision  
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Explain the processing of visual stimuli

1. Convergence: Bipolar cells in retina combine impulses from rods and cones and pass them to ganglion cells (sensory neuron of optic nerve)

2. Edge enhancement: When light falls on the receptive field in the retina ganglion cells are stimulated. Two types of ganglion cells. One is stimulated if light falls on the centre of receptive field, the other if light falls on the periphery. Hence both types are more stimulated if the edge of light/dark areas is within the receptive field.

3. Contralateral processing: left and right optic nerve meet at optic chiasma. Here, neurons carrying impulses cross over to the opposite optic nerve. --> left optic nerve carries information from the right half and vice versa = allows brain to deduce distances and sizes.

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Label a diagram of the ear.


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Explain how sound is perceived by the ear

1. Eardrum: Soundwaves reach eardrum and makes it vibrate. vibration consists of rapid movements towards and away from the middle ear. The eardrum picks up "sound" and sends it to the middle ear.

2. Bones of middle ear: The ossicles are connected to each other and the first to the ear drum, the third to the oval window. Transmits sound waves to the oval window. Reducing the amplitude of the waves but increases the amplitude 20 times. The oval window helps in amplifying. Muscles atteched to the ossicles help protecting the ear from loud sounds.

3. The oval window: Transmits sound waves to the fluid filling the cochlea. The fluid is incompressible so second membranous window is needed: round window.

4. Hair cells in the cochlea: When the sound waves pass through the fluid in cochlea, the hair bundles vibrate. Each hair cell resonates in response to specific wavelengths of sound due to gradual gradations in width and thickness of cochlear membrane when hair bundles vibrate. Hair cells transmit action potentials across synapse with auditory nerve  -->travel to auditory cortex in brain

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Distinguish between innate and learned behaviour

innate behavior

  • behaviour shown in all normal members of a species
  • despite any variation in environmental influences

learned behavior

  • modification of behavior as a result of experience
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Design experiments to investigate innate behaviour


  • locomotion of an organism
  • in a particular direction
  • in response to an external stimulus
  • examples:
    • Planaria moves towards food = positive chemotaxis
    • Euglena moves towards light = positive phototaxis


  • the movement (as opposed to growth) of an organism or a cell
  • in response to a stimulus
  • such that rate depends on intensity, but not direction, of the stimulus
  • example:
    • woodlice move about less in optimum, humid, conditions, and more in unfavorable, dry conditions
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Discuss the process of learning

Some chimpanzees learn to catch termites by poking sticks into termite mounds.

Many bird species learn to take avoiding actions when they hear alarm calls warning for predators.

Foxes learn to avoid touching electric fences after recieving an electric shock

Hedgehogs in UK have learned to run across busy raods, instead of rolling up into a ball.

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E.3.5 Outline Pavlov's experiments into conditioni

Uploaded Image (http://intranet.canacad.ac.jp:3445/BiologyIBHL2/admin/image.html?imageid=1029891)

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E.3.6 Outline the role of inheritance and learning

  • chaffinches, or Fringilla coelebs, birdsong: partly innante/partly learned
  • male chaffinches use song to deter males from entering their territory and to attract mates
  • song varies somewhat between males which allows identification of male. Also differs from other related species
    • rear some chaffinches in boxes where they can hear other adult male chaffinches singing
    • rear other chaffinches in isolated, sound-proof box
      • chaffinch song shows some relationship to normal song
        • correct length
        • correct number of notes
      • chaffinch song shows some features that differ from normal song
        • narrower range of frequencies
        • fewer distinctive phrase 
  • length and number of notes of song are innate
  • frequencies and distinctive phrases are learned from other chaffinches
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E.4.1 State that some pre-synaptic neurons excite

well read the title...

(p.136 revisionguide)

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E.4.2 Explain how decision-making in the CNS can r

decision-making in the CNS

  • synapses are the sites of decision-making
  • a post-synaptic neuron's membrane potential is the summation of input from pre-synaptic neurons
    • EPSPs depolarize post-synaptic neurons
    • IPSPs hyper-polarize post-synaptic neurons
  • if the post-synaptic neuron reaches threshold potential at its axon hillock, it will produce an action potential
  • pre-synaptic neurons can vary in the frequency, but not intensity of their input, since action potentials are "all-or-none"
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E.4.3 Explain how psychoactive drugs affect the br

By disrupting synaptic transmission.

  • Some have a chemical structure similar to a neurotransmitter and so binds to receptors for that neurotransmitter. --> block the receptors, preventing the neurotransmitter from having its usual effect.
  • Others with the same chemical structure have the same effect as a neurotransmitter. However, they are not broken down so when they bind to the receptor --> the effect lasts longer.
  • Some interfere with the breakdown of neurotransmitters or the reabsorption into the presynaptic neuron --> prolong the effect of neurotransmitters.
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E.4.4 List three examples of excitatory and three


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E.4.5 Explain the effects of THC and cocaine in te


THC is an inhibitory psychoactive drug that decreases synaptic transmission. THC affects synapses where the post-synaptic neuron releases a signal chemical that binds to cannabinoid receptors on pre-synaptic neurons. THC also binds to cannabinoid receptors inhibiting the release of excitatory neurotransmitters from the pre-synaptic neurons. Cannabinoid receptors are found in various brain locations. Cerebellum: THC thus impairs motor functions. Hippocapus: THC thus impairs short-term memory functions. Cerebral cortex: THC thus affects higher order thinking.


Cocaine is an excitatory psychoactive drugs that increases synaptic transmission. Cocaine stimulates transmission at synapses in the brain that use dopamine as a NT. cocaine binds to membrane proteins that pump dopamine back into the pre-synaptic neurons thus causing a build-up of dopamine in the synapse. Cocaine excites dopaminergic synapses, normally associated with pleasure, thus producing feelings we get when eg,. eating or sex. Cocaine is addictive. Brain adapts to regular cocaine use by reducing dopamine receptors therefore, cocaine withdrawal often causes depression. Crack is a form of cocaine that is heated and inhaled as a vapor rapidly absorbed producing greater intensity of effects greater addictive potential.

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E.4.6 Discuss the causes of addiction, including g


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