biopsychology

what is the nervous system?

• specialised network of cells, neutrons, makes use of electrical and chemical signals to relay information from one place to another in the body

• consists of the PNS and CNS

structure and functions of the nervous system

the 2 main functions are:

• collect, process and respond to environmental stimuli

• coordinate the working of different organs and cells in the body

central nervous system (CNS)

• consists of the brain and spinal chord

• origin of complex commands and decisions

peripheral nervous system (PNS)

• relays information to CNS via neurones from outside world and back to muscles and glands

• divided into somatic and autonomic systems

• somatic: controls vital functions eg breathing, heart rate, stress and sexual arousal, controls voluntary muscles and transmits sensory information to CNS

• autonomic: controls involuntary body functions, muscle movement and receives information from sensory receptors

somatic nervous system (SNS)

transmits information from receptor cells in sense organs to CNS, and from CNS to muscles

autonomic nervous system (ANS)

transmits information to and from internal bodily organs, with 2 divisions, sympathetic and parasympathetic

structure of the brain

• divided into left and right hemisphere

• outer layer, cerebral cortex, only 3mm thick, covers mammals brains

• the ridges and valleys of the cerebral cortex increase the brains SA

• the human brain is very developed, distinguishing us from animals as we have superior mental functions

• the brain developed in 3 stages: reptilian brain is least developed (insinct, survival), then the limbic system (emotions) followed by the neocortex (speech, logic, higher thinking skills)

structure of the spinal chord

• extension of the brain, passes messages to and from the brain

• connects nerves to the peripheral nervous system and responsible for reflex actions

• protected by the spine (vertebrae)

endocrine system

• major information system instructing gland to release hormone into the bloodstream to carry to target organs, communicates via chemicals

• works alongside the nervous system to control vital functions

• acts more slowly than the nervous system but has more widespread effects

glands

• an organ that synthesises substances eg hormones, glands in the body produce hormones

• thyroid gland: produces thyroxine

• pituitary gland: 'master gland' located in the brain, controls release of hormones from all other endocrine glands

hormones

a biochemical substance that circulates in the blood affecting target organs, produced in large quantities but disappear quickly

function of thyroxine (hormone)

• affects cells in the heart, increasing heart rate

• increases: metabolic rates and affects growth rate, protein synthesis, glucose metabolism, oxygen consumption

• regulates: digestion, reproduction, bone growth, muscle tone, development of nerve cells

fight or flight response

• how animals respond when stressed, the endocrine system and autonomic nervous system work together during a stressful event

• a stressor is perceived eg an approaching car

• a part of the brain called the hypothalamus activates the pituitary gland

• triggers activity in the sympathetic branch of the ANS

• ANS switches from parasympathetic state (resting) to sympathetic (aroused) state eg dilated pupils, rapid heart rate and breathing, trembling etc

arenaline

• hormone produced by the adrenal glands, affecting the cardiovascular system

• released from the adrenal medulla, part of the adrenal gland near the kidneys, and released into the bloodstream

• triggers physiological changes in the body, increases heart rate and deeper breathing

• creates the physiological arousal necessary for fight or flight responses

immediate sympathetic responses

• as soon as a threat is detected, there is an acute and automatic sympathetic response

• this includes: increased breathing and heart rate, constriction of blood vessel, high blood sugar, inhibition of stomach acid/ digestion/ saliva production, converts glycogen to glucose, contracts rectum

parasympathetic action

• once the threat is gone, the parasympathetic nervous system kicks back in, returning the body to its resting state

• the PNS works in opposition to the ANS (antagonistic) acting like a break to reduce the activities, the reset and digest phase

• includes: decreasing heart and breathing rates, constricts pupils, lungs reduce oxygen intake, stomach contracts, stimulates digestion and saliva production, relaxes rectum

structure of a neuron

• the basic building blocks of the nervous system, nerve cells that process and transmit messages through electrical and chemical systems, provide the nervous system with its primary means of communication

• can be less than 1mm, shortest is trochlear nerve (moves eyes towards nose), longest is sciatic nerve (from lower back down each leg)

• there are 100bn nerve cells in the human nervous system, 80% in brain

roles of neuron structures

• cell body (soma): includes a nucleus, contains genetic material

• dendrites: branch like structures off cell body, carry impulses from nearby neurons to cell body

• axon: carry impulses away from cell body

• myelin sheath: fatty layer covering axon, protects it and speeds up electrical transmission

• nodes of ranvier: gaps in myelin sheath that speeds up transmission, impulses can jump

• terminal buttons: communicate with next neuron across synapse

sensory neuron

• takes information from the environment (senses) towards the CNS, carry messages from PNS to CNS

• when you touch something hot, this neuron will be activated

• long dendrites and short axons, in PNS in clusters called ganglias

relay neuron

• found in the CNS between sensory and motor neurons

• the electrical impulse from the sensory neuron detailing the hot surface is passed to a relay neuron which passes it to a motor neuron

• found in CNS, short dendrites and axons, 97% of all neurons, mostly found in the brain and visual system

motor neuron

• start in CNS, receive electrical impulse from relay neurons and take it to effectors eg muscles and glands

• short dendrites and long axons (long axons from part of PNS)

synaptic transmission

the process by which neighbouring neurons communicate with each other by sending chemical messages across the gap that separates them

neurotransmitters

• brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another, can be excitatory or inhibitory, diffuse across the synapse to the next neuron

• can only travel in one direction as receptors are only on the postsynaptic neuron, each neurotransmitter has a unique molecular structure and fits perfectly into the receptor site (induced fit model)

• each neurotransmitter has a specialist function eg Acetylcholine (Act) found where motor neuron meets a muscle, causes muscle to contract

excitation

• excitatory neurotransmitters eg glutamate, noradrenaline adrenaline (both a hormone and a neurotransmitter)

• increases the positive charge of the postsynaptic neuron, increases the likelihood that the postsynaptic neuron will pass on the electrical impulse

inhibition

• inhibitory neurotransmitters eg GABA, Glycine, serotonin (affects mood and social behaviour, cause of depression)

• increases the negative charge of the postsynaptic neuron, decreases the likelihood that the postsynaptic neuron will pass on the electrical impulse

chemical transmission

• neurons talk to other neurons in groups called neural networks

• neurons are separated by a small gap called the synapse

• inside the neuron, signals are transmitted electrically, between neurons, signals are transmitted chemically

stages of synaptic transmission

1. action potential (electrical impulse) travels down the axon

2. action potential reaches the presynaptic terminal

3. triggers neurotransmitters to be released from synaptic vesicles into synaptic cleft

4. neurotransmitter diffuses across the synaptic cleft

5. neurotransmitters are taken up by the postsynaptic receptors

6. neurotransmitter is converted back to an action potential

electrical transmission

• resting potential: the inside of a neuron is negatively charged compared to the outside of it

• when activated by a stimulus, the inside becomes positively charged for a short period, triggers an action potential which travels down the axon towards the neuron

why is dopamine an unusual neurotransmitter?

it is equally likely to have excitatory or inhibitory effects on the postsynaptic neuron

summation

• excitatory and inhibitory influences are added up (summed)

• if the overall effect on the postsynaptic neuron is inhibitory, its less likely to fire, if its excitatory, its more likely to fire

• an action potential in the postsynaptic neuron will only be triggered if the sum of signals reaches the threshold

localisation of function

the theory that different areas of the brain are responsible for specific behaviours, processes or activities

localisation vs holistic theory

• scientists historically supported the holistic theory of the brain, all parts of the brain involved in the processing of thought and action

• when Broca and Wernicke discovered specific areas of the brain are associated with particular functions, it supported localisation of function, different parts of the brain perform different tasks and control different body parts

• if a certain area of the brain gets damaged, the theory suggests the specific function is also affected

hemispheres of the brain

• cerebrum is divided into 2 symmetrical halves, left and right

• some functions are controlled by a particular hemisphere (lateralisation), activity on the left side of the body is controlled by the right of the body and vice versa

functions of the left hemisphere

• sensory stimulus from right side

• motor control of right side

• speech, language, comprehension

• analysis and calculations

• time and sequencing

• recognition of words, letters, numbers

functions of the right hemisphere

• sensory stimulus from left side

• motor control of left side

• creativity

• spatial ability, context, perception

• recognition of faces, places, objects

centres of the cortex

• cerebral cortex: outer layer of both hemispheres-cerebral cortex: outer layer of both hemispheres

• divided into 4 centres, the lobes of the brain: frontal, parietal, occipital, temporal

• each lobe has a different function

motor cortex

• at the back of the frontal lobe in both hemispheres

• controls voluntary movement on the opposite side of the body

• damage here could cause a loss of control over fine movements

somatosensory cortex

• at the front of both parietal lobes

• separated from the motor cortex by a valley, the central sulcus

• represents sensory information from the skin, the amount of area devoted to a specific body part denotes its sensitivity

• eg receptors for face and hands occupies over half the area

visual cortex

• in the occipital lobe

• each eye sends information from the RVF to the left visual cortex and from the LVF to the right visual cortex

• damage to the left hemisphere could cause blindness in the RVF of both eyes

auditory cortex

• in the temporal lobe

• analyses speech based information , damage could produce partial or more extensive hearing loss

• damage to Wernicke's area could affect language comprehension

language centres- Broca's area

• language is usually restricted to the left hemisphere

• 1880s Broca identified a small area in the left frontal lobe responsible for speech production

• damage here causes Broca's aphasia, slow speech, lacking in fluency, patient 'tan' could only say the word 'tan'

• struggle with prepositions and conjunctions (a, the, and)

language centres- Wernicke's area

• Wernicke's area in the left temporal lobe, results in Wernicke's aphasia when damaged, often produce nonsense words (neologisms)

• 1880s Wernicke discovered patients with no problem producing language but difficulties understanding it, speech produced is fluent but meaningless

case study evidence of localisation of function

• Phineas Gage had damage to his left frontal lobe, it changed him from a calm person to someone rude, supports localisation theory as personality is localised in the frontal lobe

• however, case studies are difficult to generalise and researcher may interpret them subjectively

strength of localisation of function- support from neurosurgery

• neurosurgery is used to treat mental disorders eg a cingulotomy involves isolating the cingulate gyrus, disfunction of this area may cause OCD

• Dougherty et al. (2002) studied 44 people with OCD who had a cingulotomy, at follow up, 30% met the criteria for successful response and 14% for partial

• the success of such procedures strongly suggests behaviours associated with serious mental disorders may be localised

strength of localisation of function- brain scan evidence to support

• Petersen et al. (1988) used brain scans to show activity in Wernicke's area during a listening task and in Broca's during a reading task

• also, a study of LTM by Tulving et al. (1994) revealed semantic and episodic memories are located in different parts of the prefrontal cortex

• theres now a number of sophisticated and objective methods for measuring activity in the brain, providing scientific evidence of localisation of function

counterpoint of brain scan evidence to support localisation of function

• Lashley removed areas of the cortex, up to 50%, in rats learning the route through a maze, learning required all the cortex rather than being confined to a specific area

• suggests higher cognitive processes eg learning aren’t localised but distributed in a more holistic way in the brain

limitation of localisation of function- the language localisation model has been questioned

• Dick + Tremblay (2016) found very few researchers still believe language is still only in Broca's and Wernicke's area

• advanced techniques eg fMRI have identified regions in the RH and the thalamus

• suggests rather than being confined to a few key areas, language may be organised more holistically in the brain, contradicts localisation theory

evaluation of localisation of function- case study evidence

• unique cases of neurological damage support localisation theory eg Phineas Gage

• however, its difficult to make meaningful generalisations from a single individual and conclusions may depends on the researchers subjective interpretation

• suggests some evidence supporting localisation may lack validity, oversimplifying brain processes and undermining the theory

hemispheric lateralisation

the idea that the 2 brain hemispheres are functionally different and certain mental processes and behaviours are mainly controlled by one hemisphere

what's the difference between localisation and lateralisation?

• localisation: some functions being controlled by different areas in the brain

• lateralisation: the 2 hemispheres are functionally different

• in some functions, the localised areas are in both hemispheres eg vision, visual cortex in both left and right occipital lobe

how is language lateralised?

• the 2 main language areas, Broca's and Wernicke's, are only in the left hemisphere, language is lateralised as its performed by only one hemisphere

• right hemisphere can only produce basic words and phrases but gives emotional context to what it said

• left hemisphere is the analyser, right hemisphere is the synthesiser

how are the cortex's lateralised?

• vision, motor and somatosensory areas are in both hemispheres

• motor cortex has contralateral wiring, the RH controls movement on the left side and vice versa

• vision is contralateral and ipsilateral, each eye gets light from the LVF and the RVF, LVF of each eye is connected to the RH, RVF of each eye is connected to the LH

• this aids depth perception and provides different perspectives

• auditory cortex has a similar cross over, allows us to locate sounds

what is split brain research?

• a series of studies beginning in the 1960s (ongoing) involving people with epilepsy who had experienced surgical separation of the brain hemispheres by serving the corpus callosum to reduce the severity of their epilepsy as during a seizure excessive electrical activity travels from one hemisphere to another

• allows researchers to test lateral functions of the brain in isolation

Roger Sperry (1968) split brain research- procedure

• used 11 people who had a split brain operation, used the set up to project images to the LVF and RVF, either the same or different

• normal brain: corpus callosum would share the information between both hemispheres, provides a complete picture

• split brain: information can't be conveyed from one hemisphere to another

Roger Sperry (1968) split brain research- findings

• image shown to RVF, participant can describe what they see, image shown to LVF, can't describe it + say there's nothing there but could select a matching object with left hand/ most closely related

• in normal brain messages from RH would be relayed to language centres in LH, not possible in split brain patients, because the LH is dominant for verbal processing the patients answer matches the word, the RH can't share information with the left so can't say what he saw but can draw it

• emotional reaction to images presented to LVF but couldn't report what they'd seen

Roger Sperry (1968) split brain research- conclusions

• certain functions are lateralised in the brain

• LH is verbal, RH is silent but emotional

strength of hemispheric lateralisation- evidence of lateralised brain functions in 'normal' brains

• Fink et al. (1996) used PET scans to see which areas were active in a visual processing task

• show when 'normal' participants attend to global elements of an image, the RH is more active, when required to focus on more detail the specific areas of the LH tend to dominate

• suggests hemispheric lateralisation is a feature of connected brains and split brains as even in connected brains the 2 hemispheres process information differently

limitation of hemispheric lateralisation- idea of analyser vs synthesiser may be wrong

• may be different processes in the RH and LH but research suggests people don't have a dominant side, creating a different personality

• Neilson et al. (2013) analysed over 1000 brain scans, finding people did use certain hemispheres for certain tasks but no dominance

• suggests the notion of right or left brained people is wrong eg artist brain

limitation of hemispheric lateralisation- lateralisation vs plasticity

• lateralisation is adaptive, enabling 2 simultaneous tasks more efficiently eg only lateralised chickens better at finding food while watching for predators (Rogers et al. 2004)

• on the other hand, neural plasticity is also adaptive, after damage to brain, language function can 'switch sides' (Holland et al. 1996), functions are taken over by non specialised areas in the opposite hemisphere

• suggests lateralisation is first preference but ultimately plasticity is more important

strength of hemispheric lateralisation- support from more recent brain studies

• Luck et al. (1989) showed split brain participants are better than normal controls on certain tasks eg 2x as fast at identifying the odd one out in an array of similar objects

• in the normal brain, the LH's superior processing abilities are 'watered down' by the inferior RH (Kingstone et al. 1995)

• supports Sperry's findings that the left and right brains are distinct in functions and abilities

limitation of hemispheric lateralisation- causal relationships are hard to establish

• in Sperry's research, the behaviour of split brain participants was compared to a neurotypical control group

• however, none of the control group had epilepsy, any differences between the groups may be due to epilepsy not the split brain (confounding variable)

• means that some of the unique features of the split brain participants cognitive abilities may be due to their epilepsy

limitation of hemispheric lateralisation- ethics

• Sperry's participants weren't deliberately harmed and procedures were explained in advance to gain informed consent

• however, participants may not have understood they would be tested for many years and participation was stressful

• suggests there was no deliberate harm but the negative consequences make the study unethical

plasticity

the brains tendency to change and adapt as a result of experience and new learning, generally involves the growth of new connections

functional recovery

a form of plasticity, following damage through trauma, the brains ability to redistribute or transfer functions usually performed by a damaged area to other undamaged areas

how does brain plasticity change the brain?

the brain can change throughout your life

• infancy: rapid growth, increasing number of synaptic connections

• 2/3 years: peaks at 15000 synaptic connections per neurone, adult brain has about half this number

synaptic pruning

• as we age we lose synaptic connections, those that are rarely used are removed, those that are frequently used are strengthened

• allows lifelong plasticity, new neural connections are formed as demands on the brain change