The Nervous System

It is a specialised network of cells in the human body and is our primary internal communcation system.

It has 2 main functions;

1) To collect, provess and respond to information in the environment

2) To co-ordinate the working of different ogans and cells in the body.

It is then divided into 2 sub-systems;

1) Central Nervous System

2) Peripheral Nervous System

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The Central Nervous System

The Central Nervous System is made up of the brain and the spinal cord.

  • The brain is the centre of all conscious awareness. The brains outer layer, the cerbal cortex is highly developed in humans.
  • The Spinal Cord is an extenstion of the brain - it is responsible for reflex actions. It passes messages to and from the brain and connects nerves to The Peripheral Nervous System.

The Peripheral Nervous System trasmits messages, via millions of neurons to and from The Central Nervous System. This system is then sub-divided into;

  • Autonomic Nervous System: Governs vital functions in the body such as breath, heart rate, digestion.
  • Somatic Nervous System: Controls muscle movement and receives information from sensory receports.
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The Endocrine System

Glands and Hormones:

  • The Endocrine System works along the Nervous Sytem to control vital functions.
  • The Endocrine System acts slower than the Nervous System but has powerful effects.
  • Various glands in the body produce hormones.
  • Hormones are secreated into the bloodstrean and affect any cell in the body that has a receptor for the particular hormone.
  • The major Endocrine Gland is the Pituitary Gland, located in the brain.
  • Often called the 'master gland' as it controls the release or hormones from all the other endocrine glands in the body,
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The Endocrine System

Endocrine and Autonomic Nervous System together:

  • When a stressor is preceived the first thing that happens is a part of the brain called the hypathalamus triggers activity in the sympathetic branch of the Autonomic Nervous System.
  • The Autonomic Nervous System changes from its resting state (parasympathetic state) to the physiologically aroused state (sympathetic state).
  • The stress hormone adreanline is released into the blood stream. This adrenaline triggers physiological changes in the body which creates the physiological changes in the body which creates the physiological arousal necessary for the flight or fight response.
  • All of this happens within an instance as soon as a threat is detected.
  • Once the threat has passes, the parasympathetic nervous system returns the body to its resting state.
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Localisation of Function in the Brain

Localisation versus holistic theory:

Broca & Wernicke -

  • Discovered specific areas of the brain are associated with specific functions. Before this investigation, scientists supported the holistic theory of the brain (all parts of the brain were involved in the processing of thought and action)
  • They argued for localisation of function. This is the idea that different parts of the brain perform different tasks and are involved with different parts of the body.
  • It follows then, that if a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected.
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Localisation of Function in the Brain

Hemishperes of the brain and the cerbal cortex

The brain is divided into 2 symmetrical halves; left and right hemispheres.

  • Some our our physical and psychological functions are controlled or dominated by a particular hemisphere (lateralisation)
  • Activity on the right side of your body is controlled by the left hemisphere while activity on the left side of the body is controlled by the right hemisphere.
  • The outer layer of both hemispheres is the cerbral cortex.
  • It is about 3mm thick and is what seperates us from other animals because the human cortex is much more developed. It is also a greyish colour due to the location of cell bodies.
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Localisation of Function in the Brain

The Motor, Somatosensory, Visual and Auditory Centres

The cortex of both hemispheres is sub-divided into 4 lobes.

1)Frontal Lobe   2)Parietal Lobe   3)Occipital Lobe   4)Temporal Lobe - each lobe is associated with different functions.

  • At the back of the frontal lobe, is the motor area which controls voluntary movement. Damage to this area of the brain may result in a loss of control over movements.
  • At the fron of both parietal lobes is the somatosensory area which is seperated from the motor areaby a valley called 'Central Sulcus'. The somatosensory area is where sensory information from the skin is represented.
  • The occipital lobe at the back of the brain is the visual area. Each eye send's information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex. This means damage to the left hemisphere can produce blindness.
  • The temporal lobes house the auditory area, which analyses speech-based information. Damage may produce partial hearing loss. In addition, damage to a specific area of the temporal lobe - Wernicke's area may affect ability to comprehend language.
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Localisation of Function in the Brain

The Language Area of the Brain

Language is restricted to the left side of the brain in most people.

1880s, Paul Broca - a surgeon, identified a small area in the left frontal lobe responsible for speech production.

  • Damage to Broca's area causes Broca's aphasia which is characterised by speech that is slow, laborious and lacking influency.
  • At the same time, Karl Wernicke was describing patients who had no problem producing language but severe difficulties understanding it, such that the speech they produced was fluent but meaningless. Wenicke identified a region (Wernicke's area) in the left temporal lobe as being responsible for language comprehension which would result in Wenicke's aphasia when damaged.
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Localisation of Function in the Brain


Brain scan evidence of localisation - Provides support for the idea that many neurological functions are localised, particularly in relation to language and memory. Peterson et al. used brain scans to demonstrate how Wernicke's areawas active during a listening taks and Broc'as area was active during a reading task, suggesting that these areas of the brain have different functions. 

Neurosurgical Evidence - Removing or destroying areas of the brain to control aspects of behaviour developed in the 1950s.

Case Study Evidence - Unique cases of neurological damage support localisation theory such as the case of Gage.

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Plasticity and Functional Recovery of the Brain af

Brain Plasticity

  • During infancy, the brain experiences a rapid growth in the number of synaptic conncections it has, peaking at approximately 15,000 at ages 2-3. This is about twice as many as there are in the adult brain.
  • As we age, rarely used connections are deleted and frequently used conncections are strengthened (synaptic pruning).
  • Scientists thought such changes were restricted to childhood, and that the adult brain having moved beyond the critical period, would remain fixed in terms of its  function and structure. 
  • However, more recent research suggest that at any time in life existing neural connections can change, or new neural connections can be formed, as a result of learning and experience.
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Plasticity and Functional Recovery of the Brain af

Research into Plasticity

Eleanor Maguire et al. studied the brains of london taxi drivers and found significantly more volume of grey matter in the hippocampus than in a matched control group. 

  • This part of the brain is associated with the development of spatial and navigational skills in humans and other animals.
  • As part of their training, London cabbies must take a complex test in which assesses their recall of the city streets and possible routes. It appers that the result of this learning expereinces is to alter the structure of the 'taxi drivers' brains. 
  • The longer they had been in the job, the more pronounced was the structural difference. 

Draganski et al. imaged the brains of medical students three months before and after their exams. Learning-induced changes were seen to have occured in the posterior hippocampus and the parietal cortex presumably.

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Plasticity and Functional Recovery of the Brain af

Functional Recovery of the brain after trauma

  • Following physical injury, or other forms of trauma such as the experience of a stroke, unaffected areas of the brain are often able to adapt and compensate for those areas that are damaged.
  • The functional recovery that may occur in the brain after trauma is another example of neural plasticity. 
  • Healthy brain areas may take over the functions of those areas that are damaged, destroyed or even missing. 
  • Neuroscientists suggest that this process can occur quickly after trauma and then slow down after several weeks or months. 
  • At this point the individual may require rehabilitative therapy to further their recovery. 
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Plasticity and Functional Recovery of the Brain af

What Happens During Brain Recovery

  • The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage. Secondary neural pathways that would not typically be used to carry out certain functions are activated to enable functioning to continue, often in the same way as before. This process is supported by a number of structural changes in the brain inclduing:

1) Axonal Sprouting - The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways. 

2) Reformating of blood vessels 

3) Recruitment of homologous - areas on the opposite side of the brain to perform specific tasks. E.g. if Broca's area was damaged on the left side of the brain, the right-sided equivalent would carry out its functions.. After a period of time, functionality may then shift back to the left side. 

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Plasticity and Functional Recovery of the Brain af


Practical Evaluation:Following illness or injury to the brain, spontaneious recovery tends to slow down after a number of weeks so forms of physical therapy may be required to improve functioning. Shows brain has a capacity to fix itself to a point, this process requires further intervention if it is to be completely successful. 

Negative Plasticity: The brains ability to rewire itself can sometimes have maladaptive behavioural consequences. Prolonged drug use, has been shown to result in poorer cognitive functioning as well as an increased risk of dementia later in life. Also, 60-80% of amputees have been known to develop phantom limb syndrome - the continued experience of sensations in the missing limb as if it were still there. 

Age and Plasticity: Plasticity tends to reduce with age. The brain has a greater propensity for reorganisation in childhood as it is constantly adapting to new experiences and learning. 

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Split-Brain Research into Hemispheric Lateralisati

Split-Brain Research

Hemispheric Lateralisation: As we have already seen, the ability to produce and understand language for most people is controlled by the left hemisphere.

  • This suggests that for the majority of us, language is subject to hemispheric lateralisation.
  • In other words, the specialised areas associated with language are found in one of the brain's hemispheres rather than both. 
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Split-Brain Research into Hemispheric Lateralisati

Split-Brain Studies

Sperry's: Studies involved a unique group of individuals, all of whom had undergone the same surgical procedure (commissurotomy) - in which the corpus callosum and other tissues which connect the two hemispheres were cut down the middle in order to seperate the two hemispheres and control frequent and severe epileptic seizures.

  • This meant that for these split-brain patients the main communication line between the two hemispheres was removed.
  • This allowed Sperry and his colleagues to see the extent to which the two hemispheres were specialised for certain functions, and whether the hemispheres performed tasks independently of one another.
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Split-Brain Research into Hemispheric Lateralisati


  • Sperry devised a general procedure in which an image or word could be projected to a patients right visual field (processed by the left hemisphere) and the same, or different, image could be projected to the left visual field (processes by the right hemisphere).
  • In the 'normal' brain, the corpus callosum would immediately share the information between both hemispheres giving a complete picture of the visual world.
  • However, presenting the image to one hemisphere of a split-brain patient meants that the information could not be conveyed from the hemisphere to the other.
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