Notes

• Nervous system


  Made up of the brain and the spinal cord
• Peripheral nervous system (PNS)

  Relays messages from the environment to the CNS, via sensory neurones, and from the CNS to effectors, via motor neurones
• Subdivisions of the PNS

  • Autonomic nervous system
  • Somatic nervous system
• Autonomic nervous system


  Controls involuntary, vital functions of the body, such as maintaining heart rates and breathing rates
• Somatic nervous system


  Receives information from sensory receptors belonging to each of the 5 senses, and results in effectors being stimulated by the CNS, via motor neurones
• Branches of the autonomic nervous system


  • Sympathetic
  • Parasympathetic
• Sympathetic nervous system


  Increases heart rates, breathing rate, causes vasoconstriction and pupil dilation
• Parasympathetic nervous system


  Decreases heart rate, breathing rates, causes vasodilation and pupil constriction
• Endocrine system


  The main chemical messenger system of the body, where hormones are secreted into the bloodstream from glands, and then are transported towards target cells in the blood, with complementary receptors
• Pituitary gland


  Considered to be the 'master' gland because it controls the release of hormones from all other glands in the body
• Thyroid


  Releases the hormone thyroxine, which increases heart rate and therefore increases the rate of growth
• Adrenal gland


  Releases adrenaline which creates the physiological arousal preceding the fight or flight response, through increasing the activity within the sympathetic branch of the nervous system
• Fight or flight response

  1. The body senses and becomes aware of a stressor in the environment

  2. Through sensory receptors and sensory neurones in the PNS, this information is sent to the hypothalamus in the brain which coordinates a response and triggers increased levels of activity in the sympathetic branch of the ANS

  3. Adrenaline is released from the adrenal medulla in the adrenal glands, and is transported to target effectors, via the blood and through the action of the endocrine system

  4. This results in the rectum contracting, saliva production being inhibited and a greater breathing rate

  5. Once the stressor is no longer a threat, the hypothalamus triggers less activity in the sympathetic branch and more activity in the parasympathetic branch of the ANS
• Synaptic transmission


  A method of neurons communicating with each other, relaying information to the CNS across sensory neurons and carrying out responses dictated by the brain through sending information to effectors via motor neurons
• Synaptic transmission


  1. An action potential arrives at the presynaptic membrane, causing depolarisation through the opening of voltage-dependent calcium ion channels, and the consequent influx of calcium ions

  2. The increased concentration of calcium ions within the membrane causes the vesicles, containing neurotransmitter, to fuse with the presynaptic membrane and release their contents into the synaptic cleft through exocytosis

  3. The neurotransmitter diffuses across the synaptic cleft, down a concentration gradient, and binds to complementary receptors on the post-synaptic membrane. This can result in an inhibitory or excitatory effect in the postsynaptic membrane

  4. The resultant action potential will then be transmitted along the axon of the following neuron, resulting in a 'cascade' of neurotransmission
• Inhibitory neurotransmitters


  Reduce the potential difference across the postsynaptic membrane through the closure of the voltage-dependent sodium ion channels, reducing the likelihood that an action potential will be generated
• Excitatory neurotransmitters


  Increase the potential difference across the postsynaptic membrane through triggering the opening of more voltage-dependent sodium ion channels, increasing the likelihood that an action potential will be generated
• Localisation theory


  Certain areas of the brain are responsible for certain processes, behaviours and activities
• Motor area


  Separated from the auditory area by the central suclus and found in the frontal lobe, this area is involved in regulating and coordinating movements. Lesions or damage in the motor area result in an inability to control voluntary fine motor movements
• Auditory area


  An area of the temporal lobe, located on the superior temporal gyrus, which is responsible for processing auditory information and speech. Lesions or damage in the auditory area causes hearing loss, whereas damage to specific parts of the auditory area (Wernicke's area) results in Wernicke's aphasia
• Visual area


  An area in the occipital lobe which is responsible for processing visual information
• Somatosensory area


  An area of the parietal lobe which processes information associated with the senses e.g. touch, heat, pressure etc. Lesions in this area result in a loss of ability to denote sensitivity to particular bodily areas
• Wernicke's Area


  Responsible for speech comprehension and located in the temporal lobe (the left temporal lobe for most people). Lesions or damage results in Wernicke's aphasia, which is characterised by the use of nonsensical words (called syllogisms), no awareness of using incorrect words, but no issues with pronunciation and intonation
• Broca's Area


  Responsible for speech production and located in the frontal lobe, usually in the left hemisphere. Lesions or damage results in Broca's aphasia, characterised by difficulty forming complete sentences and understanding sentences, as well as failing to understand the order of words in a sentence and who they are directed towards i.e. I, you, we, him, me etc.
• The left hemisphere of the brain is associated with language production and comprehension. Therefore, language is an example of a cognitive ability which is both localised and lateralised (to the left hemisphere)
• Supporting evidence for localisation of brain function

  • Tulving et al demonstrated, using PET scans, that semantic memories were recalled from the left prefrontal cortex, whilst episodic memories were recalled from the right prefrontal cortex
  • Petersen et al (1988) found that Wernicke's area activation is required for listening tasks, whereas Broca's area is required for reading tasks
• Supporting Case Studies


  • Phineas Gage was injured by a blasting rod which intersected the left side of his face, tearing through his prefrontal cortex. The damage involved both left and right prefrontal cortices in a pattern that, as confirmed by Gage's modern counterparts, causes a defect in rational decision making and the processing of emotion
• The opposite to localisation theory would be a holistic view of brain function, suggesting that each function requires several brain areas to be activated and that these functions are not restricted to these areas
• Evidence supporting the link between certain brain areas and symptoms of OCD

  • Dougherty et al (2002) studied 44 OCD sufferers who'd undergone lesioning of the cingulate gyrus (cingulotomy) in order to control their symptoms. After being assessed using the Structured Clinical Interview for DSM-III-R, the researchers found that "At mean follow-up of 32 months after one or more cingulotomies, 32% met criteria for treatment response, and 14% were partial responders. 32-45% of patients previously unresponsive to medication and behavioural treatments for OCD were at least partly improved after cingulotomy"
• Plasticity


  Refers to the brain's ability to physically and functionally adapt and change in response trauma, new experiences and learning
• The idea of plasticity opposes the previous theory that there is a 'critical window' for synaptic and neuronal connection formation, which occurred during the first 3 years of life, after which no new neuronal connections would be formed
• Synaptic pruning


  The process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions
• Evidence supporting plasticity


  • Maguire et al. found a larger grey matter volume in the mid-posterior hippocampi (and a lower volume in the anterior hippocampi) of the brains of London taxi drivers, alongside a positive correlation between an increasing grey matter volume and the longer the individuals had been taxi drivers
• Functional recovery


  The ability of the brain to transfer the functions of areas damaged through trauma, to other healthy parts of the brain, thus allowing for normal functioning to carry on
• Examples of functional recovery

  • Ramachandran's research into phantom limb syndrome, which he explained as being "caused by the sensory input from the face skin 'invading' and activating deafferented hand zones in the cortex and thalamus"
  • The case of Jodi Miller, whose entire left hemisphere was removed in an attempt to control her epileptic seizures, but through the mechanisms of neuroplasticity, she was still able to control the right side of her body through the use of cerebral spinal fluid
• Neuroplasticity occurs in animals too
• Evidence of neuroplasticity in animals


  • Hubel and Weisel (1970) sutured the right eye of kittens, who are blind from birth, for a period of 6 months, opening the eyes and several points and monitoring brain activity in the visual cortex. The researchers found that, although the right eye was closed, there was still activity in the left visual cortex, corresponding to the development of occular dominance columns
• Hubel and Weisel (1970) experiment on kittens

  1. Sutured the right eye of kittens who are blind from birth for 6 months

  2. Opened the eyes at several points

  3. Monitored brain activity in the visual cortex
• Although the right eye was closed, there was still activity in the left visual cortex, corresponding to the development of occular dominance columns
• During the period of high susceptibility in the fourth and fifth weeks, eye closure for as little as 3-4 days leads to a sharp decline in the number of cells that can be driven from both eyes