Neurobiology and behaviour: cram notes

1. The cerebrum is the large folded upper part; its surface is the cerebral cortex, and the corpus callosum joins its two hemispheres.
2. The thalamus is in the centre; the hypothalamus is below it, with the pituitary gland hanging from it.
3. The cerebellum is at the back, below the cerebrum; the medulla oblongata joins the spinal cord.
4. The hippocampus lies deeper, on the inner side of each temporal lobe, so it is not in this section.

• Cerebrum: conscious thought, voluntary actions, learning, memory, reasoning, language and personality.
• Hypothalamus: temperature, water balance, hunger, thirst and sleep; controls the autonomic nervous system and the pituitary gland.
• Cerebellum: coordinates voluntary movement, balance, posture and learned motor skills.
• Medulla oblongata: ventilation centre and cardiovascular centre (breathing, heart rate, blood pressure); reflexes such as swallowing and coughing.
• Hippocampus: consolidates short-term memories into long-term memory; spatial memory; helps control cortisol.

1. The cardiovascular centre in the medulla oblongata controls the sinoatrial node (SAN).
2. Sympathetic neurones release noradrenaline, so the SAN fires faster and heart rate rises.
3. Parasympathetic (vagus) neurones release acetylcholine, so the SAN fires more slowly and heart rate falls.

• The hypothalamus receives nerve impulses and responds by releasing hormones.
• Posterior pituitary: hormones such as ADH are made in hypothalamus neurones, travel down their axons and are released into the blood.
• Anterior pituitary: releasing hormones from the hypothalamus reach it in a portal blood vessel and trigger release of its hormones.

The HPA axis

1. 1) Stress
2. 2) Hippocampus
3. 3) Hypothalamus releases CRH and vasopressin
4. 4) Anterior pituitary releases ACTH
5. 5) Adrenal glands release cortisol
6. 6) Cortisol binds receptors in the hippocampus, which inhibits the hypothalamus (negative feedback)

• The cortex is grey matter (cell bodies), 2 to 4 mm thick; folding increases the surface area, so there are more neurones and connections.
• Each hemisphere controls the opposite side of the body because nerve fibres cross over.
• Frontal lobe: reasoning, planning, personality; motor cortex; Broca's area.
• Parietal lobe: sensory cortex (touch, temperature, pain); spatial awareness.
• Temporal lobe: hearing (auditory cortex), Wernicke's area, memory.
• Occipital lobe: vision (visual cortex).

1. Motor cortex (in front of the central sulcus) sends impulses to skeletal muscles.
2. Sensory cortex (behind the central sulcus) receives impulses from receptors in the skin.
3. Visual cortex at the back; auditory cortex on the upper temporal lobe.
4. Association areas interpret information, link it with memories and plan responses.

• A homunculus shows each body part in proportion to the area of cortex devoted to it.
• Sensory homunculus: area is proportional to the density of sensory receptors (large fingertips, lips, tongue).
• Motor homunculus: area is proportional to the complexity and precision of movement (large hands and face).

• Language is usually controlled by the left hemisphere (lateralisation).
• Broca's area (frontal lobe) is a motor area that plans speech; damage gives slow, effortful speech with good understanding.
• Wernicke's area (temporal lobe) understands language; damage gives fluent but meaningless speech and poor understanding.
• The arcuate fasciculus links them; damage stops a person repeating words.
• Signing uses Broca's area, more motor cortex and the visual cortex.

• EEG: scalp electrodes record voltage changes (electrical activity) over milliseconds; used for epilepsy and sleep disorders; no structure shown.
• CT: many X-ray images combined into slices; shows structure such as tumours and bleeds; fast, but uses ionising radiation.
• MRI: strong magnetic field and radio waves; detailed soft tissue structure; no ionising radiation, but noisy, enclosed and not for people with metal implants.

• fMRI detects changes in blood oxygen: active areas receive more oxygenated blood.
• PET detects gamma rays from a radioactive glucose tracer (FDG): active cells take up more glucose.
• Both show activity during a task, so they suit studies of language; CT and MRI show only structure.
• PET shows reduced glucose use in Alzheimer's disease.

1. Synapses rise from about 2500 per neurone at birth to about 15 000 at 2 to 3 years.
2. Unused synapses are then pruned; used pathways are strengthened and become hard wired.

• A critical period is a window when the brain needs a particular stimulus to develop a skill normally.
• Language, especially grammar, has a critical period of about 0 to 5 years.
• Without stimulation, synapses for the skill are pruned, and it is very hard to learn later (feral and neglected children).

• Neuroplasticity: changes in neural pathways that let the brain respond to the environment and compensate for injury or disease.
• After a stroke, undamaged axons grow new branches and form new synapses and pathways; repetition strengthens them.
• Young brains are more plastic; adults have fewer synapses after pruning, so recovery is slower.
• Examples: deaf people's auditory cortex processes signing; taxi drivers have a larger posterior hippocampus.

• About a third of genes are expressed mainly in the brain, switched on and off at particular times and places.
• Mutations can change behaviour, for example FOXP2 and speech.
• Epigenetic changes (DNA methylation, histone acetylation) alter expression without changing the base sequence; the environment can cause them.
• Rat pups licked and groomed often have more glucocorticoid receptors in the hippocampus and grow into calm adults.

• Mental illnesses are polygenic; genes give susceptibility, and the environment decides whether illness develops.
• Childhood trauma can cause epigenetic changes, such as fewer glucocorticoid receptors in the hippocampus.
• Negative feedback on cortisol then fails, so cortisol stays high and the risk of depression and anxiety increases.
• Cushing's disease (too much ACTH, so high cortisol) is linked with mental illness.

1. Kinesis: speed or turning rate changes with the intensity of a stimulus, not its direction; woodlice slow down in humid air and gather there.
2. Taxis: movement towards or away from the direction of a stimulus; woodlice move away from light.
3. Both keep woodlice in damp, dark places, reducing water loss and predation.

1. Water on one side gives humid air; a drying agent on the other gives dry air; a gauze keeps the woodlice off the chemicals.
2. Count woodlice in each side at fixed times; repeat with the sides swapped; control light, temperature and number of woodlice.
3. Handle woodlice gently and return them to their habitat.
4. Test with chi-squared: null hypothesis of no difference; 1 degree of freedom; critical value 3.84 at p = 0.05.

• Learned behaviour: a relatively permanent change in behaviour due to past experience.
• Habituation: learning to ignore a repeated stimulus that brings no reward or punishment; saves energy and time.
• Imprinting: rapid learning in a critical period after hatching; young birds follow the first large moving object; later helps choose a mate of the right species.

1. Food (unconditioned stimulus) causes salivation (unconditioned response).
2. A bell rung repeatedly just before food becomes a conditioned stimulus, causing salivation alone (conditioned response).

• Operant conditioning: trial and error links a behaviour with a reward or punishment (Skinner's rats pressing a lever for food).
• Latent learning: exploring without reward, used later (Tolman's rats in a maze).
• Percentage change = (new − original) ÷ original × 100.

• Primates live in complex societies and learn socially.
• Imitation: copying another individual, so behaviour spreads quickly without genetic change (macaques washing sweet potatoes).
• Insight: solving a new problem suddenly using past experience, without trial and error (chimpanzees stacking boxes to reach bananas).

• Social behaviour: interactions between individuals of the same species forming structured groups.
• Advantages: defence, cooperative hunting and care of young, division of labour, learning from others.
• Disadvantages: competition, spread of disease, more visible to predators, low-ranking animals may not breed.
• A sign stimulus triggers a fixed action pattern: an innate, stereotyped sequence of movements (a red belly triggers attack in sticklebacks).
• Unlike a reflex, a fixed action pattern is more complex, can be modified by learning and depends on motivation.

• Eusocial colonies: care of others' young, overlapping generations, division of labour into castes.
• Honeybees: one fertile queen, male drones, and sterile female workers that build, clean, feed larvae, guard and forage.
• Sister workers share 75% of their genes because drones are haploid.
• Communication is innate: pheromones, touch and dances.

1. The angle of the waggle run from vertical on the comb equals the angle of the food from the sun.
2. The longer the waggle run, the further away the food; a round dance means the food is close.

• Dominance hierarchy: higher-ranking individuals are dominant over lower-ranking ones; needs individual recognition and learning.
• Kinds of group: egalitarian, despotic and linear (pecking order).
• Advantages: less aggression over food and mates; displays instead of fights reduce injury; the fittest pass on alleles.
• Costs: low-ranking animals get less food and may not breed.

• A territory is an area defended against members of the same species; it provides food, nest sites and mates.
• It is marked by scent, sound (robins singing) and sight, and defended by ritualised aggression.
• Courtship lets animals recognise the same species, the opposite sex and a receptive partner, and synchronises mating, so offspring are fertile.
• Courtship is often a chain of fixed action patterns, as in the stickleback zigzag dance.

• Sexual selection favours features that increase mating success; natural selection may oppose it because such features attract predators.
• Intra-sexual: males compete, so they become larger and more aggressive (elephant seals, red deer): sexual dimorphism.
• Inter-sexual: females choose; physical attractiveness model (bright stickleback throats) and male handicap model (peacock tails as an honest signal of quality).

• Noradrenaline for sympathetic, acetylcholine for parasympathetic.
• PET and fMRI show activity; CT and MRI show structure.
• Kineses are non-directional; taxes are directional.
• Divide by the original value in a percentage change.