The nervous system

The nervous system is split into 2 parts:

1. The central nervous system (CNS) - comprises the brain and spinal cord. It receives information from the senses and controls the body's responses.

2. The autonomous nervous system (ANS) - governs the brain's involuntary activities and is self-regulating. It is divided into the sympathetic branch (fight-or-flight) and the parasympathetic branch (rest and digest).

The peripheral nervous system is the part of the nervous system that is outside the brain and spinal cord.

The somatic nervous system is the part of the peripheral nervous system responsible for carrying sensory and motor information to and from the central nervous system.

Brain - responsibe for coordinating sensation, intellectual and nervous activity.

Spinal cord - a bundle of nerve fibres enclosed within the spinal column and connects nearly all parts of the body with the brain.

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Function of the nervous system

The brain is involved in mental processng and it is in overall 'control' of body functions.

The spinal cord is responsible for passing messages from the brain to the rest of the body, and then transmitting messages back to the brain.

The somatic nervous system is responsible for passing messages to the brain from sensory organs, and from the brain to the muscles. It controls voluntary or conscious actions.

The autonomous nervous system controls the body's 'automatic' or involuntary actions such as breathing and heart rate. The autonomus functions of the body need to happen quickly rather than waiting for us to think about when to breathe or when our heart should beat.

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The sympathetic nervous systems

The sympathetic nervous system (SNS) is the body's alert system. It is involved in preparing the body to respond to threats.

  • Increased heart rate
  • Reduced activity within the stomach
  • Saliva production is inhibited
  • Pupil dilation
  • Relaxation of the bronchi of the lungs
  • Glucose is released
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The parasympathetic nervous system

The parasympathetic nervous system (PSNS) has the role of relaxing the body by counteracting the effects of SNS activation.

  • Decreased heart rate
  • Increased activity within the stomach
  • Saliva producton increased to aid digestion
  • Pupil contraction
  • Constriction of the bronchi of the lungs
  • Glucose is stored
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Sensory neurons carry nerve impulses from sensory receptors to the spinal cord and the brain.

Relay neurons allow sensory and motor neurons to communicate with each other.

Motor neurons form synapses with muscles and control their contractions.

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Synaptic transmission

Synaptic transmission - refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron to another.

Neurons communicate with each other by passing chemical messages across a synapse; the gap between two neurons. An electrical impulse is triggered in a neuron. This causes small vesicles containing neurotransmitters to travel down the neuron to the terminal button. The vesicles fuse with the other membrane of the terminal button and release neurotransmitters into the synaptic fluid of the synapse. These neurotransmitters are then absorbed by receptors on the adjacent neuron and converted into an electrical impulse, or they are reabsorbed by the releasing neuron in a process called reuptake.

Neurotransmitters - chemical substances that play an important part in the workings of the nervous system by transmitting nerve impulses across a synapse.

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Inhibitory and excitatory messages

When neurotransmitter messages have been passed across a synapse, they will be either inhibitory or excitatory.

Inhibitory neurotransmitters calm down the brain and nervous system.

Excitatory neurotransmitters stimulate activity in areas of the brain.

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The endocrine system

Endocrine system - a network of glands throughout the body that manufacture and secrete chemical messengers known as hormones.

Endocrine glands - special groups of cells within the endocrine system, whose function is to produce and secrete hormones.

Hormones - the body's chemical messengers. They travel through the bloodstream, influencing many different processes including mood, the stress response and bonding between mother and newborn baby.

Pituitary glands - the 'master gland', whose primary function is to influence the release of hormones from other glands.

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The function of the endocrine system

The nervous system and endocrine system are linked by the hypothamalus; a small structure in the brain that regulates a lot of body drives, such as hunger, thirst and sex.

The hypothalamus controls the pituitary gland by communicating to what hormones need to be released from which glands, and when. The pituitary gland is often referred to as the 'master gland' due to its role in stimulating other glands, such as the adrenal glands and testes/ovaries to produce their own hormones.

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Steps of the fight-or-flight response

Step 1: the amygdala identifies a threat. The hypothalamus communicates the threat to the sympathetic nervous system to trigger a fast response.

Step 2: the message travels down the sympathetic nervous system to the adrenal medulla. The adrenal medulla releases the hormone adrenaline into the bloodstream.

Step 3: adrenaline in the bloodstream will trigger the fight-or-flight response, preparing the body to stand and fight or to run away from the threat. The fight-or-flight response involves various physical changes, such as increased heart rate, increased blood pressure, pupil dilation and increased muscle tension.

Step 4: once the adrenaline has started to wear off, the parasympathetic nervous system acts to bring the body back to its normal state.

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Localisation of function in the brain

Localisation of function - refers to the belief that specific areas of the brain are associated with specific cognitive processes.

Broca's area - an area in the frontal lobe of the brain, usually in the left hemisphere, related to speech production.

Motor cortex - a region of the brain responsible for the generation of voluntary motor movements.

Somatosensory cortex - a region of the brain that processes input from sensory receptors in the body that are sensitive to touch.

Wernicke's area - an area in the temporal lobe of the brain important in the comprehension of language.

Visual centres - many areas of the brain are involved in processing visual information. The visual cortex in the occipital lobe detects patterns and processes information.

Auditory centres - located in the temporal lobes. It is recognised and responded to in the auditory cortex.

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Evaluation of localisation of function

+ Case studies - case studies on brain damage support the idea of some localisation of function. For example, cases of aphasia (loss of language) are associated with damage to Broca's area.

- Other cognitive functions - the equipotentiality theory suggested that, apart from motor and sensory functions, other cognitive functions are spread across brain areas rather than localise in one site.

- Brain damage - Lashley experimented on rats during the 1930s and 1940s, systematically removing different brain areas to locate the area responsible for memory. He found that it was the total amount of brain damage rather than the destruction of any one site that affected memory.

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Hemispheric lateralisation

Hemispheric lateralisation - refers to the fact that some mental processes in the brain are mainly specialised to either the left or right hemisphere.

The brain consists of two hemispheres, which roughly mirror each other in terms of structure. Research shows that although they appear similar there are differences in terms of function in each hemisphere. This is called lateralisation.

The left hemisphere is responsible for processing language.

The right hemisphere processes intuitive and spatial information.

The hemispheres are connected by the corpus callosum; a bundle of fibres that act as a pathway for inter-hemispheric communication.

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Split-brain research

Split-brain research - research that studies individuals who have been subjected to the surgical separation of the two hemispheres of the brain as a result of severing the corpus callosum.

In order to treat people with severe epilepsy that spreads from one hemisphere to the other, the corpus callosum is occasionally surgically severed so that the hemispheres are no longer connected, thus controlling the seizures. These cases are known as 'split-brain' patients.

This offers psychologists an ideal chance to study hemisperic lateralisation because of the way vision is organised.

Images that are presented to the left visual field are processed in the right hemisphere, whereas images presented to the right visual field are processed in the left hemisphere.

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Supporting evidence: Sperry (1968)

Aim: to investigate the function of the left and right hemispheres of the brain in split-brain patients.

Procedure: a specially designed apparatus was used to control the visual input to split-brain patients so that objects presented to them were only available to one hemisphere.

Results: objects presented to the right visual field could be described using language. Object presented to the left could not because the right hemisphere has no language centres. However, if asked to point out which object was seen from an array, the patient could point it out with their left hand. An object projected to the left visual field is only recognised again when presented to that same field; it was not recognised if presented to the other field.

Conclusions: research shows that the two hemispheres have different specialisations, confirming that language is a left hemisphere function.

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Evaluation of lateralisation and S-B

+ Natural experiment - this is a natural experiment and it is the only ethical way to investigate the isolation of the hemispehres.

+ Useful - the research is very useful as it shows lateralisation of function exists.

- Generalisable - Sperry's work was based on only a few patients who had experienced long-term problems with epilepsy. These factors might limit generalisability from this sample to the population.

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Brain plasticity

Brain plasticity - refers to the brain's ability to modify its own structure and function as a result of experience.

Plasticity occurs at different levels within the brain. At one extreme, it could involve the wholescale re-mapping of the cortical structures in the brain in response to major brain trauma. At the other extreme, it happens at the level of individual neurons and synapses.

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Demonstrating plasticity

Synaptic pruning: as we age, neurons that do not transmit or receive information die in a process called apoptosis.This is a key feature of brain development in early childhood. As the brain adapts to its environment, it strengthens connective pathways that are being used and the weaker ones die through lack of use.

In response to damage: when an area of the brain is damaged, neighbouring neurons have reduced input. This actively stimulates other undamaged areas of the brain to compensate for the loss of function by creating new synapses to reroute the signals previously handled by the damaged areas.

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Evaluation of claims for plasticity

+ Research support Rosenzweig (1962) - demonstrated that rats raised in an enriched, stimulating environment had increased cortical volume showing evidence of a greater number of synapses compared to rats raised in a wire cage without enrichment.

+ Research support from Maguire (2000) - found that the hippocampal areas of the brains of London taxi drivers were larger than those of a control group. This was thought to be due to extensive learning of the routes around London affecting the brain.

+ Case studies - evidence from case studies of functional recovery after trauma also adds validity to the claims for brain plasticity.

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Functional recovery

Functional recovery - refers to the recovery of abilities and mental processes that have been compromised as a result of brain injury or disease.

It is affected by various factors:

  • Age - the younger the person is when the damage occurs, the more likely it is that functional recovery will happen.
  • Years spent in education - people who have spent longer in education, recover better than those who did not go to college.
  • Perseverance - recovery from brain injury takes a lot of time and effort.
  • Gender - some evidence suggests that women recover better from brain injuries than men because their brain functions are not as lateralised in the first place.
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Evaluation of functional recovery

+ Research support from Marquez (2008) - found that patients older than 40 years regained less function after treatment than younger patients. This is probably due to younger brains being more plastic than older brains.

- Research support from Tajiri (2013) - under controlled conditions, Tajiri showed that rats injected with stem cells near the site of the injury displayed evidence of neural recovery, whereas those given a control solution did not.

- Case studies - case studies frequently show functional recovery, but have limited generalisability and, although high in mundane realism, lack the necessary control to scientifically validate the process.

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Ways of studying the brain

Electroencephalogram (EEG) - a method of recording changes in the electrical activity of the brain using electrodes attached to the scalp. It is used to detect anomalies or identify big changes in brainwave activity.

Event-related potential (ERP) - a technique that takes raw EEG data and uses it to investigate cognitive processing of a specific event. It achieves this by taking multiple readings and averaging them in order to filter out all brain activity that is not related to the appearance of the stimulus. 

Functional magnetic resonance imaging (fMRI) - a technique for measuring brain activity. It works by detecting changes in blood oxygenation and flow that indicate increased neural activity.

Post-mortem examinations - a way of examining the brains of people who have shown particular psychological abnormalities prior to their death in an attempt to establish the possible neurobiological cause for this behaviour.

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Evaluation of ways of studying the brain


+ No radiation - doesn't expose the brain to potentially harmful radiation.

- Not valid - it may only be measuring communication between parts of the brain, so it may not be a valid measure of function.


Records in real time - it provides a recording of the brain's activity in real time rather than a still image of the passive brain. This means that the researcher can accurately measure a particular task or activity with the brain activity associated with it.

- Not useful - electrical activity can be picked up by several neighbouring electrodes, therefore the EEG signal is not useful for pinpointing the exact source of an activity. As a result, it does not allow researchers to distinguish between activities originating in different, but closely adjacent locations in the brain.

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Evaluation of ways of studying the brain


+ Continuous measure -  in response to a particular stimulus, it makes it possible to determine how processing is affected by a specific experimental manipulation.

- Requires a large number of trials - because ERP's are so small and difficult to pick out from other electrical activity in the brain to gain meaningful data. This places limitations on the types of question that ERP readings can realistically answer.

Post-mortem examinations:

+ Anatomical analysis - allows for a more detailed examination of anatomical and neurochemical aspects of the brain than would be possible with the sole use of non-invasive scanning techniques.

- Retrospective - the person is already dead. As a result, the researcher is unable to follow up on anything that arises from the post-mortem concerning a possible relationship between brain abnormalities and cognitive functioning.

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Circadian rhythms

Circadian rhythms - a pattern of behaviour that occurs or recurs approximately every 24 hours, and which is set and reset by environmental light levels.

Circadian rhythms:

Sleep-wake cycle - refers to alternating states of sleep and waking that are dependent on the 24-hour circadian cycle.

  • Light and darkness are external signals.
  • Dips and rises at different times of the day. The sleep drive occurs in two dips; between 2-4 am and between 1-3 pm.

Core body temperature:

  • At it's lowest (36 degrees C) at about 4.30 am and at its highest (38 degrees C) at about 6 pm.
  • Sleep when it drops and awake when it rises.
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Circadian rhythms

Hormone production:

  • The production and release of melatonin from the pineal gland in the brain follows a circadian rhythm, with peak levels occurring during the hours of darkness. When it is dark, more melatonin is produced, and when it is light again, the production of melatonin drops and the person awakes.
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Evaluation of circadian rhythms

+ Research support from Siffre (1975) - spent time in a deep cave and his bodily rhythms, including his sleep-wake cycle, were monitored. His natural circadian rhythm extended to around 25 hours, but was still regular despite a lack of cues, showing the regulating action of the SCN.

- Individual differences - in the onset and duration of rhythms, suggesting that a purely biological explanation of the rhythm is too reductionist, as other factors play a part.

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Ultradian rhythms

Ultradian rhythms - cycles that last less than 24 hours, such as the cycle of sleep stages that occur throughout the night.

Stages of sleep:

1. 4-5%; light sleep; muscle activity slows down; occasional muscle twitching.

2. 45-55%; breathing pattern and heart rate slows; slight decrease in body temperature.

3. 4-6%; deep sleep begins; brain begins to generate slow delta waves.

4. 12-15%; very deep sleep; rhythmic breathing; limited muscle activity; brain produces delta waves.

5. 20-25%; rapid eye movement; brainwaves speed up and dreaming occurs; muscles relax and heart rate increases; breathing is rapid and shallow.

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Ultradian rhythms

The Basic Rest Activity Cycle (BRAC):

  • 90 minute cycle.
  • During the day, rather than moving through sleep stages, we move progressively from a state of alertness into a state of physiological fatigue approximately every 90 minutes.
  • Research suggests that the human mind can focus for a period of about 90 minutes, and towards the end of this period, the body begins to run out of resources.
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Evaluation of ultradian rhythms

+ EEGs - strong evidence for the sleep cycle. EEGs monitor brainwaves as people sleep and show distinct stages in the sleep cycle that repeats several times a night.

- Research from Tucker (2007) - showed large individual differences in the duration of stages.

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Infradian rhythms

Infradian rhythms - rhythms that have a duration of over 24 hours, and may be weekly, monthly or even annually.

Weekly rhythm example:

Although male testosterone levels are elevated at weekends and young couples report more sexual activity at weekends than on weekdays, the frequency of births at weekends is lower than on weekdays.

Monthly rhythm example:

The human menstrual cycle lasts about a month. There are variations in the length of this cycle, with some women experiencing a relatively short 23-day cycle wheres others have a cycle as long as 36 days. The average is 28 days. The cycle is regulated by hormones, which either promote ovulation or stimulate the uterus for fertilisation. After the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an embryo.

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Infradian rhythms

Annual rhythm example:

Research suggests that a seasonal variation in mood in humans, especially in women, with some people becoming severely depressed during the winter months. The winter is also associated with an increase in heart attacks, which varies seasonally and peaks in winter.

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Evaluation of infradian rhythms

- Individual differences - in the duration of rhythms, which may be due to biological causes or to external or exogenous factors that affect the onset of rhythms.

- Influences mate choice (Penton-Voak, 1999) - suggests that human mate choice varies across the menstrual cycle; different stages of the cycle. It found that women generally expressed a preference for 'slightly feminised' male faces when choosing for a long-term relationship. When in the ovulatory phase, women showed preference for more masculinised faces.

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Endogenous pacemakers & exogenous zeitgebers

Endogenous pacemakers - mechanisms within the body that govern the internal, biological bodily rhythms.

The suprachistmatic nucleus (SCN) - a small group of brain cells - is also known as the body clock. It is the main endogenous pacemaker.

  • The SCN causes the pineal gland to release a hormone called melatonin. This happens when the optic nerve reduces its activity as night falls. Melatonin reduces brain activity and makes us sleepy.
  • Melatonin production stops when activity on the optic nerve increases as daylight levels increase.

In the absence of exogenous cues, the SCN operates independently on a 25-hour or longer cycle. Our sleep-wake cycle is therefore longer than 24 hours when we are isolated from external time cues (zeitgebers).

The SCN is entrained by exogenous factors so that our sleep pattern follows a circadian or 24-hour rhythm.

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Endogenous pacemakers & exogenous zeitgebers

Our internal body clock is entrained by exogenous factors which synchronise our internal timekeeper with the external world.

The key exogenous factor that affects the sleep-wake cycle is light levels.

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Endogenous pacemakers & exogenous zeitgebers

Exogenous zeitgebers - an environmental cue, such as light, that helps us to regulate the biological clock in an organism.

Social cues, such as bedtime routines or mealtimes, are known to affect the cycle. The sleep-wake cycle of travellers synchronise more quickly if they engage in the activities of the new time zone, suggesting that these quicken entrainment and reset the body clock.

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Evaluation of pacemakers and zeitgebers

+ Research support from Morgan (1995) - removed the SCN from hamsters, obliterating the sleep-wake cycle. When SCN transplantation was done, they resumed a normal pattern, providing strong evidence that the SCN is the body clock.

+ Development for strategies for shift work and jet lag - research has led to the development of strategies to reduce the impact of shift work and jet lag. The manipulation of light levels, for example, allows shift workers to sleep when they would normally be awake.

- Lack ecological validity - the studies used artificial light, which could affect the way the body clock works.

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