Option E: Neurobiology and Behavior

Stimulus: a change in the environment, either internal or external, 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.

Reflex arc Example - pain withdrawal reflex Receptors detect a stimulus; receptors can be sensory cells or nerve endings of sensory neurons (i.e. pain receptors are nerve endings of sensory neurons) Sensory neurons carry impulses from receptors to the central nervous system (spinal cord or brain); the impulse travel to ends of sensory neurons where there are synapses with relay neurons. Messages are passed by synaptic transmission. Relay neurons receive messages across synapses from sensory neurons, and pass them to the motor neurons that can cause the appropriate response Motor neurons receive messages across synapses from relay neurons and carry them to an effector Effector (e.g. muscle fibers) to carry out a response after receiving a message from a motor neuron; effectors can be muscles which respond by contracting, or glands, which respond by secreting

Natural Selection and responses Survival chances of animals are affected by behavioral responses Individuals with best-adapted responses are most likely to survive and produce offspring Offspring inherit successful types of response from parents Environment of an animal species changes – natural selection may then favor a different type of response

Example 1: Migration in Sylvia atricapilla (blackcap) This bird breeds during summer in Germany and, until recently, migrated to Spain for winter 10% of blackcaps now migrate to UK instead Eggs collected from parents which had migrated to UK in the previous winter and from parents who had migrated to Spain; the young were reared and the direction in which they migrated was recorded Birds whose parents had migrated to UK tended to fly west, wherever they were reared, and birds whose parents had migrated to Spain tended to fly southwest They responded to environmental stimuli at the time of migration in the same way as their parents In the 10% of birds migrating to the UK, the response had changed Warmer winters in UK were probably the agent of natural selection that caused this

Example 2: Timing of breeding in Parus major (great tit) Parus major breeds in spring or early summer throughout much of Europe Timing of egg laying is genetically determined. Day length is used to determine the time of year Studies in Netherlands show that mean date of egg laying is becoming earlier and adults breeding earlier are enjoying greater reproductive success Earlier opening of leaves on deciduous trees and an earlier peak in the biomass of invertebrates feeding on tree leaves These invertebrates are the main food that adults collect and feed to offspring

Diversity of Sensory Receptors Mechanoreceptors perceive movements (e.g. hair cells in the cochlea of ear, pressure receptor cells in the skin) Chemoreceptors perceive chemical substances (e.g. receptor cells in the tongue, nerve endings in the nose) Thermoreceptors perceive heat and temperature (e.g. nerve endings in skin detect warm or cold)  Photoreceptors perceive electromagnetic radiation, usually light (e.g. rod and cone cells in the eyes) 

Photoreceptors (rod & cone cells) in the retina convert light into nerve impulses. Nerve impulses are passed to bipolar cells, which relay the signal to the optic nerve via ganglion cells.Processing of Visual StimuliPerception of photons -> processing of visual stimuli -> impulses reaching brainConvergence - bipolar cells in retina combine impulses from groups of ROD or CONE cells and pass them on to GANGLION CELLS (sensory neurons of the optic nerve)Edge Enhancement - each ganglion cell is stimulated when light falls on a small circular area of retina called the RECEPTIVE FIELD. There are two types of ganglion cells. Light falling on the centre of receptive field stimulates the ganglion cell but this stimulation is reduced if light also falls on the periphery. Light falling on the periphery of receptive field stimulates the ganglion cell, but this stimulation is reduced if light also falls on the centre.  Both types of ganglion cells are more stimulated if the edge of light/dark areas is within the receptive field.Contralateral processing - left and right optic nerves meet at optic chiasma; some impulse from left eye pass to right side of the brain, and vice versa. The right side of the brain processes visual stimuli from the left, and vice versa. This allows the brain to deduce distances and sizes.

Perception of SoundEardrumSound waves that reach the eardrum at the end of the outer ear make it vibrateVibrations = rapid movements of the eardrum, towards and away from middle earRole of eardrum: pick up sound vibrations from air and transmit them to the middle earBones of middle earOssicles: series of very small bones in the middle ear; each ossicle touches the next oneFirst ossicle is attached to the eardrumThird ossicle is attached to the oval windowRole of ossicles: transmit sound waves from the eardrum to the oval window and act as levers (reduce amplitude of the waves but increasing their force, thus amplifying sounds by 20x; oval window's small size compared with the eardrum helps with amplification)(If sounds are too loud) muscles attached to ossicles protect ear from too-loud sounds by contracting (dampening vibrations in ossicles)Oval windowMembraneous structure, like the eardrumTransmits sound waves to the fluid filling the cochleaFluid is incompressible, so a second membranous window is needed called the round windowWhen oval window moves towards cochlea, round window moves away from it = fluid in cochlea can vibrate freely, with its volume remaining constantHair cells in the cochleaCochlea consists of a tube, wound to form a spiral shapeWithin the tube are membranes with receptors (sensory cells) called hair cells attachedThese hair cells have hair bundles, stretching from one of the membranes to anotherWhen sound waves pass through the fluid in the cochlea, the hair bundles vibrateGradual variations in width and thickness of the membranes allow us to distinguish different frequencies of sound (each hair bundle only resonates with particular frequencies)Hair bundles vibrate -> hair cells send messages across synapse and on to the brain via the auditory nerve

Innate behaviour: animal behaviour that develop independently of the environmental context Genetically determined/inherited from parents No environmental input, learning, or modification of behaviour Evolved through natural selection Present in all members of the population E.g. Blackcap southern/western migration Learned behaviour: behaviour that develop as a result of the animal's experiences Learned/developed/changed through experiences and trial/error New behaviour developed, old behaviour modified Individuals of a population may show variation in the behaviour E.g. Chimpanzees use narrow twigs to extract termites from termite mounds, Hedgehogs in Britain learn to run across busy roads instead of rolling up into a ball, Foxes learn to avoid touching electric fencces after receiving shocks

Innate behaviour in invertebratesQuantitative investigation of kinesis in slaters (woodlice)Kinesis - a change in activity rate in response to a stimulus Involves movement as a response, but the direction of movement isn't influenced by stimulus Speed of movement/number of times the animal turns is varied E.g. slower movement, with more frequent turning when woodlice are transferred from drier to more damp conditions Stages in designing an investigation: Place the animals in conditions that are similar to the natural habitat Observe the behaviour and see what stimuli affect movement Choose one stimulus that appears to cause a taxis or kinesis Devise an experiment to test responses to the stimulus Ensure that other factors do not have an effect on the movement Decide how you will measure the movement of the invertebrates

ExperimentWoodlice have gills for respiration that will tend to dry out in dry conditions Step 1:  Place a woodlouse in a dry petri dish and mark its movements every 30 seconds Step 2:  Repeat for a second woodlouse placed in moist conditions Step 3:  Compare the rate of movement for the two woodlice (should be more in dry dish) Results:The woodlice should display more random movement in a dry environmentWoodlice are prone to dehydration (of gills) and will move faster and turn more to improve chances of leaving dry areasIn both cases, the invertebrate behaviour should improve its conditions, resulting in a better chance of survival and reproduction

Learning can improve the chances of survivalLearned behaviour develops as a result of experienceAlthough offspring inherit the capacity to learn, they do not inherit specific patterns of behaviour (behaviour of offspring is similar to parents because they learn, not because of genes they've inherited)Learned behaviour has some advantages over innate behaviour- Allows responsiveness to change/variation in environment- New behaviour patterns spread quickly, improving chances of survival E.g. Bees learning new locations and types of flowers with most nectar, animals learning to avoid eating poisonous plants or animals, animals learning to avoid stinging plants or animals, animals learning to avoid predator attacks and other dangers E.g. Chimpanzees use narrow twigs to extract termites from termite mounds, Hedgehogs in Britain learn to run across busy roads instead of rolling up into a ball, Foxes learn to avoid touching electric fencces after receiving shocks

Development of birdsongBirdsong has been shown in some species to be partly innate and partly learned: The male chaffinch uses their song to keep other males out of their territory and to attract females Song varies slightly between individuals - allows identification of individuals Song of the bird reared in isolation had some features of the normal song (correct length and number of notes, meaning it is innate) but there is a narrower range of frequencies and fewer distinctive phases (learned from other chaffinches)

Pavlov and conditioning in dogsIvan Pavlov investigated salivation reflex in dogsHe found that dogs secreted saliva when they saw or tasted food Unconditioned stimulus: sight or taste of smell Unconditioned response: secretion of saliva Pavlov gave dogs a neutral stimulus (ringing of bell/ticking metronome/flashing light/musical box playing) before giving dogs the unconditioned stimulus (sight/taste of food) Conditioned stimulus: bell/metronome/light/music Conditioned response: secretion of saliva before the unconditioned stimulus Dogs learned to associate two external stimuli (bell and food) - this is called conditioning - an alteration in the behavior of an animal as a result of the association of external stimuli

Stimuli and response

Perception of stimuli

Innate and learned behavior