Option A

Question 1

Neurons

Answer 1

• transmit electrical impulses

Question 2

Dendrites

Answer 2

• Short branched nerve fibres

- Ex) transmit impulses between neurons in one part of the brain or spinal cord

Question 3

Axons

Answer 3

• Elongated nerve fibres

- Ex) transmit impulses from the tips of the toes or the fingers to the spinal cord

Question 4

Myelintation

Answer 4

• the myelination of nerve fibres allow for saltatory conduction
• some nerve fibres are coated along most of theirlength by a material called myelin which consists of many layers of phospholipid bilayer
• special cells called Schwann cells deposit the myelin by growing round and round the nerve fibre; each time they grow around the nerve fibre, a double layer of phospholipid bilayer is deposited
• there many be 20 or more layers when the Schwann cell stops growing
• there is a gap between the myelin called a node of Ranvier

Question 5

Explain saltatory conduction

Answer 5

• in myelinated nerve fibres, the nerve impulse can jump from one node of Ranvier to the next
• it is much quicker than continuous transmission

Question 6

What is the resting potential of neurons and how is this resting potential acheived?

Answer 6

• resting potential is about -70mV
• neurons pump sodium and potassium ions across their membrane to generate a resting potential, creating an imbalance of positive and negative charges across the membrane:
  1. Sodium-potassium pumps transfer sodium and potassium ions across the membrane; 3 sodium ions are pumped out and 2 potassium ions are pumped in
  2. The membrane is about 50 times more permeable to potassium than sodium, so potassium ions leak back across the membrane faster than sodium ions
  3. There are proteins inside the nerve fibre that are negatively charged, which increases the charge imbalance

Question 7

What is meant by action potential?

Answer 7

• consists of depolarization and repolarization of the neuron
• depolarization is a change from negative to positive; due to the opening of sodium channels in the membrane, allowing sodium ions to diffuse into the neuron down the concentration gradient, raising the membrane potential to +30mV
• repolarization is a change back from positive to negative; occurs rapidly after depolarization and is due to the closing of the sodium channels and opening of potassium channels, allowing potassium to diffuse out of the neuron, down their concentration gradient; the potassium channels remain open until the membrane has fallen to a potential close to =70mV but the resting potential will not be fully restored because the cocnentration gradients of sodium and potassium have not yet been re-established

Question 8

How are action potentials propagated along the axons of neurons?

Answer 8

• a nerve impulse is an action potential that starts at one end of a neuron and is then propagated along the axon to the other end of the neuron
• the propagation of the action potential happens because the ion movements that depolarize one part of the neuron trigger depolarization in the neighbouring part of the neuron
• nerve impulses always move in one direction along neurons in humans
• impulses can be only be initiated at one terminal of a neuron and can only be passed on at the other terminal
• additionally. a refractive period after depolarization prevents propagation of an action potential backwards along an axon

Question 9

What are local currents?

Answer 9

• inside the axon, there is a higher sodium ion concentration in the depolarized part of the axon so sodium ions diffuse along inside the axon to the neighbouring part that is still polarized
• outside the axon, the concentration gradient is in the opposite direction, so sodium ions diffuse from the polarized part back to the part that has just depolarized
• these movements are referred to as local currents
• lcoal currents reduce the concentration gradient in the part of the neuron that has not yet depolarized from -70mV to -50mV (threshold potential)
• depolarization occurs when the threshold potential is reached; thus, local currents cause a wave of depolization and then repolarization to be propagated along the axon

Question 10

Synapse

Answer 10

• junctions between neurons and between neurons and receptor/effector cells
• chemicals called neurotransmitters are used to send signals across synapses

Question 11

Explain synaptic transmission

Answer 11

• When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels
• Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane
• The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft
• Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels
• The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal
• The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity)

Question 12

Acetylcholine

Answer 12

• used as a neurotransmitter in many synapses, including those between neurons and muscle fibres
• it produced in the pre-synaptic neuron by combining choline, abosrbed from the diet, with an acetyl group produced during aerobic respiration
• acetylcholine is loaded into vesicles and then released into the synaptic cleft durign synaptic transmission
• in the post-synaptic membrane, there are receptors with binding sites for acetylcholine; it will only remain bound for a short period of time before being broken down by the enzyme acetylcholinesterase into choline and acetate
• choline is reabsorbed into the pre-synaptic neuron

Question 13

How do neonicotinoid pesticides work?

Answer 13

• neonicotinoids are synthetic compounds similar to nicotine
• they bind to acetylcholine receptor in cholinergic synapses in the central nervous system of insects
• acetylcholinesterase does not break down neonicotinoids so the binding is irreversible
• now that the receptors are blocked, acetylcholine is unable to bind and synaptic transmission is prevented
• this results in the insect’s paralysis and death

Question 14

What are the advantages of neonicotinoids as pesticides?

Answer 14

They are not highly toxic to humans or other mammals because:

1. a much greater proportion of synapses in the central nervous system are chloinergic in instects than in mammals
2. neonicotinoids bind much less strongly to acetylcholine receptors in mammals than in insects

Question 15

What are the disadvantages of neonicotinoids as pesticides?

Answer 15

• concerns about the efects of these insecticides on honeybees and other beneficial insects

Question 16

Threshold potential

Answer 16

• approximately 50-55mV
• the threshold potential must be reached in order for a nerve impulse to be initated
• this is the potential at which voltage-gated sodium channels start to open, causing depolarization and local currents

Question 17

Embryogenesis

Answer 17

• The development of a fully-formed organism from a fertilised egg
• All tissues are derived from three initial germ layers (ectoderm, mesoderm, endoderm) formed via gastrulation
• In chordates, a flexible notochord will develop during gastrulation and lead to the subsequent formation of a neural tube

Question 18

Blastula

Answer 18

an animal embryo at the early stage of development when it is a hollow ball of cells.

Question 19

Gastrula

Answer 19

an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells.

Question 20

Gastrulation

Answer 20

the process during embryonic development that changes the embryo from a blastula with a single layer of cells to a gastrula containing multiple layers of cells

Question 21

Explain neurulation

Answer 21

• The development of the neural tube
• Cells located in the outer germ layer (ectoderm) differentiate to form a neural plate
• The neural plate then bends dorsally, folding inwards to form a groove flanked by a neural crest
• The infolded groove closes off and separates from the neural crest to form the neural tube
• The neural tube will elongate as the embryo develops and form the central nervous system (brain and spinal cord)
• The cells of the neural crest will differentiate to form the components of the peripheral nervous system

Question 22

How are neurons initally produced?

Answer 22

• differentiation in the neural tube is the origin of neurons; this occurs during embryonic development
• in adulthood, new neurons are produced in several different areas of the brain

Question 23

What is spina bifida and what causes it?

Answer 23

• a condition where the two ends of the vertebral arch of the vertebra (part of the backbone) do not become properly fused together, leaving a gap
• is caused by the incomplete closure of the embryonic neural tube

Question 24

Neuronal migration

Answer 24

• the movement of neurons from one location to another
• immature neurons migrate to a final location
• the cytoplasm and organells in it are moved from the trailing end of the neuron to the leading edge by contratile actin filaments
• migation of neurons is important in brain development; some neurons are produced in one part of the developing brain for use in another part
• mature, functional neurons do not normally move, but their axons/dendrites can regrow if damaged

Question 25

Development and growth of axons

Answer 25

• an axon grows from each immature neuron in response to chemical stimuli
• chemical stimuli determine neuron differentiation when the axon grows out from the cell body and also the direction in which it grows in the developing embryo
• some axons extend beyond the neural tube to reach other parts of the body
• axons grow at their tips; they can be relatively short or very long
• axon is able to regrow if severed or damaged as long as the cell body of its neuron remains intact

Question 26

Development of synapses

Answer 26

• a developing neuron forms multiple synapses
• the growth of an axon/dendrite is directed so that it reaches a cell with which it interacts
• a synapse is then developed between the neuron and the other cell
• synapse development involves special structures being assembled in the membranes on either side of the synapse and in the synaptic cleft between them
• most neurons develop multiple synapses and some neurons in the brain develop hundreds, allowing complex patterns of communication

Question 27

Elimination of synapses

Answer 27

• synapses that are not used do not persist
• synapses often disappear if they are not used
• when transmission occurs at a synpase, chemical markers are left that cause the synapse to be strengthened
• synapses that are inactive do not have these markers and so become weaker until they are eventually eliminated

Question 28

Neural pruning

Answer 28

• invovles the loss of unused neurons

- the elimination of part of a neuron or the whole cell

Question 29

Apoptosis

Answer 29

• a process that unused neurons employ to destroy themselves

Question 30

Neural plasticity

Answer 30

• the ability of the nervous system to change and rewire itself with experience
• connections between neurons can be changed by growth of axons and dendrites, by the establishment of new synapses, the elimination of synapses and the pruning of dendirates/branches of axons/entire neurons
• there is a much higher degree of plasticiity up to the age of six than later
• the stimulus for a change in the connections between neurons comes from the experiences of a person and thus how their nervous system is used
• the basis for forming new memories and for certain forms of reasoning
• important in repairing damage to the brain and spinal cord

Question 31

What is a stroke, what causes it, and how does the body recover from it?

Answer 31

• an ischemic stroke is a disruption of the supply of blood to a part of the brain
• most strokes are caused by a blood clot blocking one of the small vessels in the brain
• another cause of strokes is bleeding from a blood vessel
• during a stroke, part of the brain is deprived of sufficient oxygen/glucose
• neurons that cannot perform cellular respiration will die
• strokes may promote reorganization of brain function; many cases of recovery involves part of the brain taking on new functions to supplement the damaged areas and requires the relearning of skills such as speech, writing, etc.

Question 32

Cephalization

Answer 32

• the development of a head
• includes the development of the brain, where the anterior part of the neural tube expands to form the brain (the rest and majority of the neural tube developes into the spinal cord)

Question 33

Medulla oblongata

Answer 33

Used in autonomic control of gut muscles, breathing, blood vessels and heart muscle

Question 34

Cerebellum

Answer 34

Coordinates unconcious functions such as posture, non-voluntary movement and balance

Question 35

Hypothalamus

Answer 35

The interface between the brain and the pituitary gland, synthesizing the hormones secreted by the posterior pituitary, and releasing factors that regulate the section of hormones by the anterior pituitary

Question 36

Pituitary gland

Answer 36

The posterior lobe stores and releases hormones produced by the hypothalamuc and the anterior lobe produces and secretes hormones that regulate many body functions

Question 37

Contralateral processing

Answer 37

when a stimulus is processed on the opposite side to where it was detected

Question 38

Cerebral hemispheres

Answer 38

• act as the intergrating centre for high complex functions such as learning, memory, emotions, decision-making, existential awareness
• carry out the most complex of the brain’s tasks known as higher order functions
• the left cerebral hemisphere receives sensory input from the sensory receptors in the right side of the body and vice-versa (contralateral processing)
• the left cerebral hemisphere controsl msucle activity in the right side of the body and vice-versa

Question 39

List 4 ways that one could study the role of different brain parts

Answer 39

1. Animal experiments
2. Autopsy
3. Lesions
4. fMRI

Question 40

Explain how animal experiments can be used to study the role of different brain parts

Answer 40

• Animal experimentation can be used to identify function by stimulating regions with electrodes or removing via lobotomy
• Because such methods are highly invasive and potentially damaging, animal models are frequently used
• Experimentation on animals involves less ethical restrictions than human studies (although ethical standards do exist)
• Animal studies are limited by the differences between animal and human brains, making valid comparisons difficult
• Example: Animal studies using mice and rats have been used to develop drug treatments for diseases such as MS

Question 41

Explain how autopsy can be used to study the role of different brain parts

Answer 41

• Lesions are abnormal areas of brain tissue which can indicate the effect of the loss of a brain area
• Lesions can be identified via post-mortem analysis (autopsy) or via scans of the brain (CT scans or MRI)
• The effects of lesions can be difficult to identify, as many functions may involve multiple brain areas
• Additionally, the brain has the capacity to re-learn certain skills by re-routing instructions to other areas (plasticity)
• Example: Split brain patients have been used to identify specific roles of the left and right cerebral hemisphere

Question 42

Explain how lesions can be used to study the role of different brain parts

Answer 42

• An autopsy is a post-mortem examination of a corpse via dissection in order to evaluate causes of death
• Comparisons can be made between the brains of healthy and diseased corpses to identify affected brain areas
• Example: Cadavers who suffered from aphasia (language impairment) in life demonstrate damage to specific areas

Question 43

Explain how fMRI can be used to study the role of different brain parts

Answer 43

• Functional magnetic resonance imaging (fMRI) records changes in blood flow within the brain to identify activated areas
• Oxygenated haemoglobin responds differently to a magnetic field than deoxygenated haemoglobin
• These differences in oxygenation can be represented visually and reflect differences in the level of brain activity
• fMRI is non-invasive and can be used to identify multiple brain regions involved in complex, integrated brain activities
• Example: fMRI studies have been used to diagnose ADHD and dyslexia, as well as monitor recovery from strokes

Question 44

Visual cortex

Answer 44

• each of the two cerebral hemispheres has a visual cortex in which neural signals originating from light sensitive rod and cone cells in the retina of the eye are processed

Question 45

Broca’s area

Answer 45

• a part of the left cerebral hemisphere that controls the production of speech
• if there is damage to this area, the indiivudal knows what they want to say and can produce sounds, but they cannot articulate meaningful words and sentences

Question 46

Nucleus accumbens

Answer 46

• each of the cerebral hemispheres has a nucleus accumbens
• it is the pleasure or reward centre of the brain
• a variety of stimuli (ie. food) cause the release of the neurotransmitter dopamine in the nucleus accumbens which causes feelings of well-being, pleasure and satisfaction
• cocaine, heroin and nicotine are addictive because they artificially cause the release of dopamine in the nucleus accumbens

Question 47

Autonomic nervous system

Answer 47

• controls involuntary processes in the body using centres located in the medulla oblongata
• has two parts (sympathetic and parasympathetic) which often have cotnrary effects on an involuntary process

Question 48

Sympathetic nervous system

Answer 48

Sympathetic nerves release noradrenaline (adrenergic) to mobilise body systems (‘fight or flight’ responses)

Question 49

Parasympathetic nervous system

Answer 49

Parasympathetic nerves release acetylcholine (cholinergic) to relax body systems and conserve energy (‘rest and digest’)

Question 50

Somatic nervous system

Answer 50

Controls voluntary movement

Question 51

Outline three activities that are coordinated by the medulla

Answer 51

1. Swallowing
   - the first phase of swallowing (ie. moving food from the mouth cavity to the pharynx) is voluntary and is controlled by the cerebral cortex
   - the remaining phases, in which the food passes from the pharynx to the stomach via the esophagus, are involuntary and are coordinated by the swallowing centre of the medulla oblongata
2. Breathing
   - two centres in the medulla control breating; one controls the timing and the other controls the force
   - there are chemoreceptors in the medulla that monitor blood pH; a lower pH indicates a higher carbon dioside concentration, which results in deeper/more frequent breathing
3. Heart rate
   - the cardiovascular centre of the medulla regulates the rate at which the heart beats
   - blood pH and pressure are monitored by receptor cells in blood vessels and in the medulla
   - the cardiovascular centre can adjust the heart rate in response to blood pH/pressure by sending signals to the heart’s pacemaker
   - signals carried from the sympathetic system speed up the heart rate while signals from the paraympathetic system slow down the heart rate

Question 52

Explain how the pupil reflex can be used to evaluate brain damage

Answer 52

• the pupil reflex occurs when bright light suddenly shines into the eye
• photoreceptive ganglion cells inthe retina perceieve the bright light, sending signals through the optic nerve to the mid-brain
• this activates the parasympathetic system and causes the pupil to constrict in order to reduce the amount of light entering the eye to protect the retina from damage
• doctors can use this to test a patient’s brain function; if the pupils do not constrict when a light is shone into their eyes, then the medulla oblongata is likely damaged
• this is used in conjunction with other tests; if these tests consistently fail, then the patient has suffered brain death

Question 53

Cerebral cortex

Answer 53

• the outer layer of the cerebral hemispheres
• it is only 2-4mm thick, but up to 6 distinctively different layers of neurons can be identified ini sections studied under a microscope
• it has a highly complex architecture of neurons and processes the most complex tasks in the brain
• only mammals have a cerebral cortex; birds/repetiles have regions of the brain that perform a similar range of functions but they are structurally different, with cells arranged in clusters rather than layers
• forms a larger proportion of the brain and is more highly developed in humans than other animals

Question 54

Analyze the correlation between body size and brain size in different animals

Answer 54

• scattergraphs show a positive correlation between body size and brain size in animals
• the relationship is not directly porportional

Question 55

How much energy does brain metabolism require?

Answer 55

• brain metabolism requires large energy inputs
• energy releaesd by cellular respiration is needed to maintain the resting potential in neurons and to re-establish it after an action potential
• energy is also needed for the synthesis of neurotransmitters and other signal molecules
• the brain contains a huge number of neurons, so it needs much more oxygen and glucose to generate this energy by aerobic cellular respiration
• an adult human brain uses over 20% of the energy consumed by metabolism; it is even more in infants/small children

Question 56

Outline 4 sensory receptors

Answer 56

1. Mechaoreceptors: respond to mechanical forces and movements
2. Chemoreceptors: respond to chemical substances
3. Thermoreceptors: respond to heat
4. Photoreceptors: respond to light

Question 57

Explain how olfactory receptors work

Answer 57

• Olfaction is the ability to detect airborne chemicals (odorants) as scents or smells
• At the back of the nasal cavity is a patch of tissue called the olfactory epithelium, which is embedded with chemoreceptors
• The olfactory epithelium is lined with mucus, in which odorant molecules will dissolve before binding to the chemoreceptors
• Binding of an odorant molecule will trigger a nerve impulse, which is transferred via the olfactory bulb to the brain
• The combination of olfactory receptors activated determines the specific scent perceived by the brain

Question 58

List the two photoreceptors

Answer 58

1. Rods

2. Cones

Question 59

Rod cell

Answer 59

• Rod cells function better in low light conditions (twilight vision) – they become quickly bleached in bright light
• Rod cells all contain the same pigment (rhodopsin) which absorbs a wide range of wavelengths
• Rod cells cannot differentiate between different colours (monochromatic)
• Rod cells are abundant at the periphery of the retina and hence are responsible for peripheral vision
• Rod cells produce poorly resolved images as many rod cells synapse with a single bipolar neuron

Question 60

Cone cell

Answer 60

• Cone cells function better in bright light conditions (daylight vision) – they require more photons of light to become activated
• There are three different types of cone cells, each with a different pigment that absorbs a narrow range of wavelengths
• Cone cells can therefore differentiate between different colours (red, blue and green)
• Cone cells are abundant at the centre of the retina (within the fovea) and hence are involved in visual focusing
• Cone cells produce well defined images as each cone cell synapses with a single bipolar neuron

Question 61

Red-green colour-blindness

Answer 61

• Red-green colour blindness is a genetic disorder whereby an individual fails to discriminate between red and green hues
• There are three different types of cone cells, each of which absorbs different wavelengths (trichromatic: red, green, blue)
• The genes responsible for producing red or green photoreceptors are located on the X chromosome (sex-linked)
• If either of these genes are mutated, red and green wavelengths cannot be distinguished
• As these genes are recessive and located on the X chromosome, red-green colour-blindness is more common in males
• Red-green colour-blindness can be diagnosed using the Ishihara colour test

Question 62

Bipolar cell

Answer 62

• Bipolar cells transmit the nerve impulses produced by the photoreceptors to ganglion cells
• If rod/cone cells are not stimulated by light, then they depolarize and release an inhibitory neurotransmitter onto a bipolar cell, causing it to become hyperpolarized and not transmit impulses to the ganglion cell
• When rod/cone cells absorb light, they become hyperpolarized and stop sending inhibitory neurotransitter to the bipolar cell, allowing it to depolarize and activate the ganglion cell
• Many rod cells may synapse with a single bipolar cell, resulting in low resolution of sensory information (poor acuity)
• Most cone cells only synapse with a single bipolar cell, resulting in high resolution of sensory information (high acuity)

Question 63

Ganglion cell

Answer 63

• Ganglion cells transmit nerve impulses to the brain via long axonal fibres that compose the optic nerve
• Signals from ganglion cells may be sent to the visual cortex to form a composite representation of surroundings (i.e. sight)
• Alternatively, signals may be sent to other brain regions to coordinate eye movements or maintain circadian rhythm

Question 64

List the three middle ear bones (ossicles)

Answer 64

1. malleus (hammer)
2. incus (anvil)
3. stapes (stirrup)

Question 65

What is the purpose of the middle ear bones (ossicles)?

Answer 65

• transmit and amplify the sound vibrations by acting like levers to reduce the force distribution
• sound travelling through air is mostly reflected when contacted by a liquid medium (due to the incompressibility of fluids)
• the amplification of sound by the middle ear bones allow the vibrational pressure to pass to the cochlear fluid with very little loss
• the oval window is smaller than the ear drum, which also assists in amplifying the sound energy
• during very loud sounds, the delicate sound-reception components of the ear are protected by contraction of the muscles attached to the bones in the middle ear which weakens the connections between the ossicles and so dampens the vibrations

Question 66

Cochlea

Answer 66

• part of the inner ear where vibrations are transducted into neural signals
• it is a tubular, coiled, fluid-filled structure
• layers of tissue (membranes) to which sensory cells are attached; each of these cells has a bundle of hairs
• when vibrations are transmitted from the oval window into the cochlea, they resonate with the hair bundles of particular hair cells, stimultaing these cells
• selective activation of different hair cells enables us to distinguish between sounds of different pitch

Question 67

Round window

Answer 67

• a thin sheet of flexible tissue, located between the middleand inner eat
• the flexibiltiy of the round window allows the fluid in the cochlea to move and thus allow the oval window to vibrate (otherwise, the fluid would be incompressible and the oval window would not be able to vibrate)
• when virbrations of hte oval window push the lfuid in the cochlea inwards, the round window moves outwards, and when the oval window moves outwards, the round window moves inwards, enabling the oval window to transmit vibrations through the fluid in the cochlea

Question 68

Auditory nerve

Answer 68

• impulses caused by sound perception are transmitted to the brain via the auditory nerve
• the auditory nerve is one of the branial nerves that serve the brain
• when a hair cell in the cochlea is depolarized by the vibrations that constitute sound, it releases neurotransmitters that trigger an action potential which is propagated along the auditory nerve

Question 69

Explain how cochlear implants work

Answer 69

• Cochlear implants may be used to stimulate the auditory centres of the brain in patients with non-functioning hair cells
• Standard hearing aids are ineffective in deaf patients as they amplify sounds but do not bypass defective hearing structures
• Cochlear implants consist of two parts – an external part (microphone / transmitter) and an internal part (receiver / stimulator)
• The external components detect sounds, filter out extraneous frequencies and then transmit the signals to the internal parts
• The internal components receive the transmissions and produce electrical signals via electrodes embedded in the cochlea
• The electrical signals are then transferred via the auditory nerve to be processed by the brain

Question 70

Explain how the ears can detect movement of the head

Answer 70

• hair cells in the semicircular canals detect movement of the head
• there are three fluid-filled semicircular canals in the inner ear that are at right angles to each other, so each is in a different plane
• when the head moves in the plane of one of the semicircular canals, the fluid inside of the canal flows past the cupula (a structure containing sensory hair cells embedded in gel)
• the hair cells detects this movement of fluid and sends impulses to the brain

Question 71

Innate behaviour

Answer 71

• behaviour that is genetically programmed, thus inherited from parents, and develops independently of the environment
• ie. palmar grasp reflex in babies

Question 72

Outline the two types of behaviour involving movement that can be investigated in an experiment

Answer 72

1. Taxis
   - movemnet towards or away from a directional stimulus
2. Kinesis
   - movement as a response but the direction of movement is not influenced by the stimulus
   - instead of direction, the speed or number of times an animal turns is changed as a result of the stimulus

Question 73

Reflexes

Answer 73

• autonomic and involunary responses to stimuli

Question 74

Reflex arc

Answer 74

• comprise the neurons that meditae reflexes

- the sequence of neruons that links the receptor to the effector

Question 75

Withdrawal reflex

Answer 75

• an innate response to a pain stimulus
• reflex to remove oneself/one’s body part (ie. hand) from a painful stimulus
• pain receptors activate sensory neurons which carry impulses to the spinal cord via the dorsal root of a sinal nerve; the impulses travel to the ends of the sensory neurons in the grey matter of the spinal cord where there are synapses with relay neurons
• the relay neurons have synapses with motor neurons, which carry impulses out of the spinal cord via the ventral root and to muscles
• messages are passed across synapses from motor neurons to muscle fibres, which contract and pull the body part away from the painful stimulus

Question 76

Learned behaviour

Answer 76

• develops as a result of experience
• offspring can learn behaviour patterns from their parents, from other individuals and from their own experience of the environment

Question 77

Explain the role of inheritance of learning in the development of birdsong

Answer 77

• all members of a bird species share innate aspects of song, allowing each individual to recognize other members of the species
• in many species, males learn mating calls from their father
• the learned aspects introduce differences, allowing males to be recognized by thir song, and in some species, mates are chosen by the quality of their singing
• innate and learned behaviour are both dependent on genes, but the development of learned behaviour is a result of experience while innate behaviour is independent of it; birds rely on both innate behaviours and learned behaviours to sing the birdsong

Question 78

Reflex conditioning

Answer 78

• involves forming new associations by establishing new neural pathways in the brain
• used extensively in animal behaviour and can greatly increase survival chances
• involves associating an involuntary behaviour with a stimulus (ie. Pavlov’s dogs acquiring the involuntary behavior of salivating in response to the stimulus of the bell if an example of reflex conditioning)

Question 79

Pavlov’s experiment

Answer 79

• Dogs normally salivate (unconditioned response) in anticipation of being fed (unconditioned stimulus)
• Pavlov sounded a bell (neutral stimulus) prior to feeding a dog
• After many repetitions, the dog came to associate the bell with food and began to salivate to the bell (conditioned response)
• Pavlov described this as a conditioned reflex – the stimulus that prompted the response had been changed

Question 80

Imprinting

Answer 80

• Imprinting is any kind of phase-sensitive learning that is rapid and independent of behavioural consequences
• Imprinting occurs during a short critical period in which the organism adopts behavioural characteristics from a stimulus
• Imprinted behaviour is not influenced by consequences – it does not require reinforcement to develop
• Examples of imprinting include filial imprinting (bonding to a parent) and sexual imprinting (developing sexual preferences)
• Filial imprinting was demonstrated by Konrad Lorenz, who imprinted baby geese to recognise him as a parental figure

Question 81

Operant conditioning

Answer 81

• a form of learning that consists of trial and error experiences
• initiated by an animal spontaneously testing out a behaviour pattern and finding out what its consequences are
• involves associating a voluntary behavior with a stimulus (ie. praising a child (positive stimulus/reward) for studying (voluntary behaviour) will encourage them to repeat the behaviour in the future

Question 82

Differentiate between relfex conditioning and operant conditioning

Answer 82

• reflex conditioning involves the association of involuntary behaviour with stimulus; usually caused by the environment imposing a stimulus onto the animal/person
• operant conditioning involves the association of voluntary behaviour with stimulus; usually caused by the animal/person trying something out and realizing the consequences of their actions

Question 83

Learning

Answer 83

• the acquisition of skill or knowledge
• a higher order function
• involve changes in neurons caused by slow-acting neurotransmitters, which cause the release of secondary messengers inside post-synaptic neurons to promote synaptic transmission by mechanisms such as an increase in the number of receptors in the post-synaptic membrane or chemical modication of these receptors to increase the rate of ion movement when a neurotransitter binds
• the secondary messengers can persist for days and may be central to the synaptic plasticity that is necessary for learning

Question 84

Memory

Answer 84

• the process of encoding, storing and accessing information
• a higher order function
• short term memory lasts up to about a minute and may or may not lead to long-term memory which can be retained for indefinite periods of time
• different parts of the brain have a role in the encoding, storage and accessing memory
• involve changes in neurons caused by slow-acting neurotransmitters, which cause the release of secondary messengers inside post-synaptic neurons to promote synaptic transmission by mechanisms such as an increase in the number of receptors in the post-synaptic membrane or chemical modication of these receptors to increase the rate of ion movement when a neurotransitter binds
• the secondary messengers can persist for days and may be central to the synaptic plasticity that is necessary for memory
• even longer term memories may be due to a remodelling of the synaptic conections between neurons

Question 85

Excitatory neurotransmitter

Answer 85

• neurotransmitters that generate excitatory post-synaptic potentials (EPSPs) by causing depolarisation (e.g. glutamate)

Question 86

Inhibitory neurotrasmitter

Answer 86

• neurotransmitters that generate inhibitory post-synaptic potentials (IPSPs) by causing hyperpolarisation (e.g. GABA)

Question 87

Sumation of neurotransmitters

Answer 87

• Nerve impulses are initiated or inhibited in postsynaptic neurons as a result of summation of all excitatory and inhibitory neurotransmitters received from presynaptic neurons
• The combination of graded potentials (EPSPs and IPSPs) in the post-synaptic neuron is known as summation
• Cancellation occurs when excitatory and inhibitory graded potentials cancel each other out (no threshold potential reached)
• Spatial summation occurs when EPSPs are generated from multiple presynaptic neurons simultaneously to reach threshold
• Temporal summation occurs when multiple EPSPs are generated from a single presynaptic neuron in quick succession
• These summative effects determine which nerve pathways are activated and hence lead to alternate decision-making processes

Question 88

Slow-acting neurotransmitters

Answer 88

• Slow-acting neurotransmitters bind to G-protein coupled receptors to initiate a slower response (milliseconds – minute)
• Slow-acting neurotransmitters trigger second messenger pathways within the post-synaptic cell, which allows for:
  1. A longer, more sustained duration of action (i.e. ion channels remain open for longer to mediate greater depolarisation)
  2. Long term alterations to cellular activity to improve synaptic transfer (i.e. increased expression of ion channels)
• Slow-acting neurotransmitters are called neuromodulators because they can modulate the efficiency of synaptic transfer
• By modulating the efficiency of synaptic transfer, slow-acting neurotransmitters can regulate fast synaptic transmission
• Slow-acting neurotransmitters can strengthen the neural pathways involved in learning and memory
• Examples of slow-acting neurotransmitters include dopamine, serotonin, acetylcholine and noradrenaline

Question 89

Explain how slow-acting neurotransmitters contribute to learning/memory

Answer 89

• Slow-acting neurotransmitters can strengthen the neural pathways involved in learning and memory
• By activating second messenger systems, they can trigger long-lasting changes to synaptic activity (long-term potentiation)
• When a neuron is repetitively stimulated by slow-acting neurotransmitters, second messengers promote cellular changes:
  1. There is an increase in dendritic receptors in the post-synaptic neutron (improving post-synaptic stimulation)
  2. There is an increase in the production of neurotransmitters in the pre-synaptic cell
  3. Neurons may undergo morphological changes to enlarge existing synaptic connections or form new synapses
• The net effect of this long-term potentiation is that certain neural pathways become easier to stimulate
• This makes certain memories easier to recall (i.e. forming long-term memories)
• This makes certain actions easier to repeat (i.e. learning of a new skill or aptitude)

Question 90

Fast-acting neurotransmitters

Answer 90

• Fast-acting neurotransmitters bind directly to ligand-gated ion channels to initiate a rapid response (<1 millisecond)
• Regulated by slow-acting neurotransmitters
• Examples of fast-acting neurotransmitters include glutamate (excitatory) and GABA (inhibitory)

Question 91

Psychoactive drugs

Answer 91

• Psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmissions
• Drugs that increase neurotransmission levels are called stimulants and increase psychomotor arousal and alertness; mimic the stimulation provided by the sympathetic nervous system
• Drugs that decrease neurotransmission levels are called depressants and slow down brain activities and relax muscles; reduce stimulation of the central nervous system and may induce sleep

Question 92

Excitatory drugs

Answer 92

increase post-synaptic transmission

Question 93

Inhibitory drugs

Answer 93

decrease post-synaptic transmission

Question 94

Anaesthetics

Answer 94

• Anesthetics act on ion channels to block the conduction of sensory nerve signals to the central nervous system
• This results in the loss of sensation (numbness) in the affected region, allowing for surgical interventions to occur
• Anesthetics can be grouped into two classes – local anesthetics and general anesthetics
• Local anesthetics only affect a localised region – usually by blocking axonal sodium influx (conduction block)
• General anesthetics affect the whole body – this may involve blocking calcium influx to prevent neurotransmitter exocytosis
• Different types of anesthetics will affect consciousness in different ways:
• General anesthetics will induce a temporary loss of consciousness as they interfere with neural transmissions in the brain
• Local anesthesia will not result in a loss of consciousness and only cause a reversible loss of sensation to the affected area
• General anesthetics are typically inhaled (to affect the whole body), while local anaesthetics are injected into specific regions
• General anesthetics are administered by trained specialists who monitor patient vitals for the duration of the procedure

Question 95

Stimulant drugs

Answer 95

• drugs that increase neurotransmission levels
• increase psychomotor arousal and alertness
• mimic the stimulation provided by the sympathetic nervous system

Question 96

Depressant drugs

Answer 96

• drugs that decrease neurotransmission levels
• slow down brain activities and relax muscles
• reduce stimulation of the central nervous system and may induce sleep

Question 97

Explain the effect of cocaine on the nervous system

Answer 97

• Excitatory drug
• Dopamine initiates depolarization of post-synaptic membrane
• Cocaine binds to the proteins in the pre-synaptic membranes that are responsible for reabsorbing dopamine after synaptic transmission
• Since cocaine blocks the reabsorption of dopamine, it causes dopamine to build up in the synaptic cleft so that dopamine continues to stimulate the person (which leads to feelings of wellbeing, etc. and thus can become addictive)

Question 98

Explain the effect of amphetamine on the nervous system

Answer 98

• excitatory drug
• stimulates adrenergic synapses (sympathetic) and thus causes increased energy and alertness
• moves into nerve cells carrying dopamine and noradrenaline
• moves into presynaptic vesicles and causes release of neurotransmitters into the synaptic cleft
• interferes with neurotransmitter breakdown
• therefore, there is a build up of dopamine and noradrenaline which causes euphoria, alertness and energy

Question 99

Explain the effect of THC

Answer 99

• Sedative drug
• THC mimics the neurotransmitter anandamide by binding to cannabinoid receptors on presynaptic neurons
• Anandamide (and THC) blocks the release of inhibitory neurotransmitters that prevent dopamine secretion
• By preventing the inhibition of dopamine secretion, THC causes a sense of euphoria and emotional well-being

Question 100

Explain the effect of benzodiazepine

Answer 100

• Sedative drug
• Benzodiazepines bind to GABA receptors on the post-synaptic neuron and increase the efficiency of GABA action
• GABA triggers the opening of chloride channels to cause hyperpolarisation – benzodiazepines enhance this effect
• Benzodiazepines promote sleep-inducing and muscle relaxing responses by the body

Question 101

List 3 causes of drug addiction

Answer 101

Drug addiction can be affected by:

1. Genetic Predisposition
2. Social Environment
3. Dopamine Secretion

Question 102

Explain how genetic predispotition can lead to drug addition

Answer 102

• Particular addictions can run in families, suggesting a genetic predisposition (although social factors may contribute)
• Specific genes might influence the rate of drug metabolism or intensity of drug effect (i.e. dopamine secretion)
• Genetic factors may also contribute to personality types that are more inclined towards addictive behaviours
• The genetic predisposition for a particular addiction may be determined by polygenic inheritance

Question 103

Explain how social environment can lead to drug addition

Answer 103

• Individuals raised in environments with prevalent substance abuse are at higher risk of addiction (peer pressure risks)
• Individuals treated with neglect (child abuse) or suffering significant personal trauma are at a higher risk of addiction
• Certain cultures have a higher incidence of addictions (may reflect demographic influences or marketing forces)
• Low socioeconomic status (i.e. poverty) may increase the likelihood of addiction (poor education / lack of support networks)

Question 104

Explain how dopamine secretion can lead to drug addition

Answer 104

• Dopamine is a neurotransmitter released within the limbic system in response to reward (activates pleasure pathways)
• Certain drugs (e.g. cocaine, heroin) and particular activities (e.g. sex, gambling) enhance dopamine activity
• Long-term substance abuse will lead to the down-regulation of dopamine receptors, requiring higher doses to achieve effect
• Consequently, addicts must continue to repeat the addictive activity in order to achieve a diminishing level of reward

Question 105

Ethology

Answer 105

• the study of animal behaviour in natural conditions
• the modern field of ethology includes a number of well-known investigations into animal behaviour:
• migratory patterns in birds (such as blackcaps)
• reciprical altruism in animal species (such as vampire bats)
• breeding and courtship strategies in a number of different animals

Question 106

How is natural selection related to ethology?

Answer 106

• natural selection can change the frequency of observed behaviour; behaviours that increase the chances of survival and reproduction will become more prevalent in a population
• natural selection is the theme that runs through the whole of modern biology, including ethology

Question 107

Explain the breeding strategies of coho salmon populations

Answer 107

• Male coho salmon form two different breeding populations according to the strategy used for passing on genes:
• All males initially undergo a development phase as juveniles in which they grow within freshwater rivers (~12 months)
• Following that, the males migrate out to the ocean for a period of maturation, whereby they differentiate into two populations
• Some of the male salmon develop into ‘jacks’, while other male salmon will develop into ‘hooknoses’
• Jacks are smaller and well camouflaged – they only require ~ 6 months in the seawater to reach maturity
• Hooknoses are larger and brightly coloured – they require ~ 18 months in the seawater to reach maturity
• Jacks and hooknoses employ different breeding strategies in order to successfully reproduce with female coho salmon:
• Jacks sneak out from behind rocks or recesses in the riverbed and attempt to stealthily mate with a female
• Hooknoses swim within the open water and fight aggressively amongst one another for the opportunity to mate
• Having two breeding pathways improves the rates of successful reproduction and also increases levels of genetic variation
• Jacks have higher rates of survival (as they spend less time in seawater), but have more competition for reproduction
• Hooknoses have lower rates of survival but consequently experience less direct competition for successful mating

Question 108

Explain the synchronized oestrus in female lions

Answer 108

• Female lions synchronise their sexual receptiveness (oestrus) to increase chances of survival and reproduction of offspring
• Lionesses remain in the same pride their entire lives, living with genetic relatives (sisters, aunts, nieces)
• Male lions leave their birth group at a young age and in order to reproduce must replace males in existing prides
• Upon establishing dominance within a pride, a male lion will kill all cubs already present
• The loss of cubs triggers an innate, synchronised response whereby all lionesses enter a period of oestrus
• This synchronised oestrus is mediated by pheromone signals
• There are many advantages to synchronising oestrus:
• It increases the number of offspring the male lion can produce (risks of displacement are always present)
• It allows for shared lactation and nursing of cubs within the pride (all female lions nurse indiscriminately)
• It is easier for the lionesses to hunt and defend the pride if all cubs are of a comparable age

Question 109

Explain the migratory behaviour of blackcaps

Answer 109

• Migratory patterns in backcaps has been demonstrated to be genetic
• Blackcaps occupy summer breeding grounds in Germany, but migrate to different locations during the winter months
• Historically, most birds migrated south to Spain in the winter, with a minority migrating west to the UK
• Spain is further away but has generally had a more temperate winter climate than the UK, improving reproductive success
• With an increase in global temperatures, the migratory patterns of blackcaps are changing due to natural selection
• Blackcap populations in the UK are rising, as warmer temperatures are improving survival rates during the winter months
• UK blackcaps are reproducing more, as the shorter migration allows them to select the best breeding territories in Germany

Question 110

Explain bloodsharing in vampire bats

Answer 110

• Vampire bats commonly regurgitate blood to share with unlucky roost mates who were unable to gain independent sustenance
• Vampire bats cannot survive multiple successive days without food, however food can often be difficult to find
• The small cost of sharing blood (lost time until starvation) is less than the benefit received (time gained)
• Hence sharing blood improves the fitness of the entire brood (via reciprocal altruism), increasing the occurrence of altruism
• Vampire bats have been observed to not share blood with those who do not share with others; thus, the gene for altruism is selected for

Question 111

Explain the foraging behaviour in shore crabs

Answer 111

• Foraging is the act of searching for (and potentially finding) food resources in nature
• According to the optimal foraging theory, animals will adopt strategies that:
  1. Minimise the cost of foraging (i.e. the amount of energy used to capture and consume prey)
  2. Maximise the benefits to the consumer (i.e. the amount of energy yielded by a particular food source)
• Shore crabs demonstrate selectivity in the type of mussel foraged when the mussel population is abundant:
  1. Crabs will ignore smaller mussels (as the energy yield is less than that obtained from larger mussels)
  2. Crabs will also ignore larger mussels (difficult to crush, also risks potential damage to the crab’s claws)
  3. Crabs will selectively identify and feed on mid-sized mussels (provided the mussel supply is in abundance)

Question 112

Explain the courtship in birds of paradise

Answer 112

• Courtship describes a set of behavioural patterns whereby potential mates inform each other of a readiness to reproduce
• Courtship stimuli may be species-specific and will be performed differently by different individuals
• Courtship stimuli are often competitive among males and form the basis of assessment by females
• Courtship behaviour is especially pronounced in the different species of birds of paradise
• Whereas females appear drab, males will have bright plumage and display fancy behaviours to demonstrate their virility
• While these features make them a target for predators, they improve chances of attracting female attention (mate selection)
• Any exaggerated trait that improves reproductive fitness will become more prominent in future generations (sexual selection)

Question 113

Explain why learned behaviour can be spread through a population and be lost from it more rapidly than innate behaviour

Answer 113

• innate behaviours can only be modified slowly through natural selection because there must be variation in the alleles that affect behaviour and a chance in the allele frequencies of a population
• unlike innate behaviour, learned behaviour does not require several generations in order to be modified; new traits can be learned or forgotten and is independent of inheritance

Question 114

Explain the feeding on cream from milk bottles in blue tits

Answer 114

• Blue tits were first obseved pecking through the aluminium foil caps of milk bottles left outside houses, to drink the cream, in the 1920s
• Soon, this behaviour was observed 150 kilometres away- far further than blue tits normally fly
• German occupation of the Netherlands during WWII stopped deliveries of milk for eight years
• A few months after the milk deliveries resumed, the blue tits began to peck through the bottle tops again indicating that they learned the behaviour– they could not acquire an innate behaviour within a few months
• Recently, now that less milk is being delivered to houses and more people are consuming skim milk (without cream on top), the behaviour of pecking through bottle tops in blue tits is no longer observed