Biopsychology A01

Lateralisation and Split brain research
1. Hemispheric Lateralisation
  1. Each hemisphere of the brain has specific functions
    1. Left hemisphere
      1. dominant for language and speech
    2. Right hemisphere
      1. Specialises in visuo-motor tasks
  2. The two hemispheres are connected by a bundle of nerve fibres, the corpus callosum, through which they exchange information.
    1. The connection via the corpus callosum means that we are still able to talk about things perceived by the right hemisphere.
  3. Broca reported that damage in a particular area of the left hemisphere led to language deficits, yet damage to the equivalent are of the right hemisphere did not.
2. Split brain research
  1. To treat severe epilepsy, surgeons would sometimes cut the nerve fibres of the corpus callosum. This would prevent seizures from affecting both halves of the brain.
    1. These “split-brain patients” were researched to explore how each half of the brain would respond to visual inputs when unable to communicate with the other hemisphere.
  2. Key Study - Sperry and Gazzaniga
    1. Procedures Studied split-brain patients. Presented visual information to either the left or right visual field. Asked patients to respond verbally or using their hands.
    2. Findings If a picture is shown to the left visual field, this information is processed by the right hemisphere, but it cannot respond verbally as there is no language centre. The left hemisphere does not receive information and therefore cannot talk about it, despite having a language centre.
Plasticity and Functional Recovery
1. Plasticity
  1. The brain continues to create new neural pathways and alter existing ones as a result of experience. The brain can develop new connections and prune away weak ones.
  2. For example, playing video games results in new synaptic transmission in brain areas involved in spatial recognition, working memory and motor performance.
  3. Davidson et al, found that experience mediators produced more gamma brainwaves than student volunteers, indicating meditation causes permanent changes.
2. Functional Recovery
  1. When brain cells are damaged, as they are during a stroke, other parts sometimes take over their functions. This can happen by neural unmasking in which dormant synapses can be reactivated when they receive more neural input than previously.
    1. Stem cells implanted into the brain may help to treat brain damage by:
      1. Forming a neural network linking uninjured areas with the damaged brain regions.
      2. Secreting growth factors that rescue injured cells
      3. Directly replacing damaged cells
Ways of studying the brain
1. Post Mortem
  1. If a researcher suspects a patient’s behavioural changes were caused by brain damage, they may look for abnormalities after the person dies. For example, Broca observed patient’s speech difficulties and found lesions in the brain.
    1. HM’s brain has been extensively investigated post-mortem, confirming damage to his hippocampus related to his inability to store new memories. Post – mortem studies have also identified brain abnormalities in schizophrenia and depression.
2. Functional Magnetic Resonance Imaging (fMRI)
  1. Measures change in blood flow, indicating increased neural activity, in particular brain areas. These are useful for identifying which areas of the brain are involved in particular mental activities
3. Electroencephalogram (EEG)
  1. Measures electrical activity in the brain via electrodes placed on the scalp. Patterns in patients with epilepsy show spikes of electrical activity. Alzheimer's patients often show overall slowing of electrical activity.
4. Event Related Potentials (ERPs)
  1. Very small voltage charges triggered by specific stimuli. Sensory ERPs occur in the first 100 meters after the stimulus, cognitive ERPs are generated later.
Nervous System
1. The nervous system is a specialised network of cells and our primary communication system. It has two main functions:
  1. To collect, process and respond to information in the environment
  2. To co-ordinate the working of different organs and cells in the body
2. It is divided into the central nervous system and the peripheral nervous system.
  1. The Central nervous system is made up of the brain and spinal cord
    1. The brain is centre of all awareness
    2. The outer layer of the brain, the cerebral cortex, is highly developed in humans and is what distinguishes our higher mental function from those of animals.
    3. The spinal cord is an extension of the brain and is responsible for reflex actions.
      1. It passes messages to and from the brain and connects nerves to the Peripheral Nervous System.
  2. The Peripheral nervous system transmits messages, via millions of neurons, to and from the nervous system.
    1. The Peripheral nervous system is further sub-divided into the autonomic nervous system and the somatic nervous system.
      1. The autonomic nervous system governs vital functions in the body such as breathing, heart rate, and digestion.
      2. The somatic nervous system controls muscle movement and receives information from sensory receptors.
Biological Rhythms
1. Ultradian Rhythms
  1. Cycles lasting less than 24 hours such as the sleep stages. Sleep involves a repeating cycle of 90 – 100 minutes, with five stages including REM sleep.
    1. The 90 minute rhythm continues during the day as the basic rest activity cycle (BRAC).
      1. Each of the five sleep stages shows a characteristic EEG pattern.
        During deep sleep, brainwaves slow and breathing and heart rate decrease.
        During REM sleep, the EEG pattern resembles waking brainwaves and dreams occur.
        The BRAC involves periods of alertness alternating with periods of physiological fatigue and low concentration.
2. Circadian Rhythms
  1. Sleep/wake cycle
    1. The sleep/wake cycle is an example of a circadian rhythm. These are rhythms which are subject to a 24 hour cycle.
  2. Siffre’s cave study
    1. Siffre is a self styled caveman who spent several extended periods underground to study the effects on his own biological rhythm. Deprived of exposure to natural light and sound, but with access to adequate food and drink, Siffre re-surfaced in mid September 1962 after spending 2 months in the caves. In each case, his free running biological clock settled down to one that was just beyond the usual 24 hours though he did continue to fall asleep and wake up on a regular schedule.
  3. Cycles lasting 24 hours
3. Endogenous Pacemakers and Exogenous Zeitgebers
  1. Endogenous Pacemakers
    1. There are internal body clocks in the brain. The SCN in the hypothalamus acts as the master clock controlling other pacemakers in the body. It receives information about the light levels via the optic nerve which keeps the SCN’s circadian rhythm synchronised with daylight. The SCN sends a signal to the pineal gland which produces the hormone melatonin at night.
      1. Neurons in the SCN spontaneously synchronise with each other. They have links with other brain regions controlling sleep and arousal, with peripheral pacemakers. There is also a neural pathway connecting the SCN and the pineal gland. Melatonin from the pineal gland inhibits brain mechanisms that promote wakefulness and so induces sleep.
  2. Exogeneous Zeitgebers
    1. These are environmental events which affect the biological clock. Light resets the biological clock each day, keeping it on a 24 hour cycle. We are also influenced by social cues from the activity of people around us.
      1. Specialised lighting cells in the retina contain melanopsin. They gauge brightness and sends signals to the SCN to set the the daily clock. This system works in most blind people too, even in the absence of rods and cones or visual perception.
4. Infradian Rhythms
  1. Cycles with a duration longer than 24 hours, for example the female menstrual cycle. This can vary between 23 days and 36 days, but averages 28 days. It is regulated by hormones and ovulation takes place roughly half way through the cycle.
    1. There may also be weekly Infradian rhythms, with changes in hormone levels and blood pressure at weekends.
      1. Annual rhythms can be seen in seasonal variations of mood, increased rates of heart attacks in winter, and a peak of deaths in January.
5. All living organisms – plants, animals and people – are subject to biological rhythms and these exert an important influence on the way in which body systems behave. All biological rhythms are governed by two things – the body’s internal biological clock which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers.
Endocrine System
1. The endocrine system works alongside the nervous system to control vital functions in the body through the action of hormones. It works slower than the nervous system but has widespread and powerful effects.
2. Glands are organs in the body that produce hormones.
  1. The major endocrine gland is the pituitary gland located in the brain. It is called the master gland because it controls the release of hormones form all the other endocrine glands in the body.
3. Hormones are secreted in the bloodstream and affect any cell in the body that has a receptor for that particular hormone.
4. Often the endocrine system and the ANS work in parallel for instance during a stressful event.
  1. When a stressor is perceived, the hypothalamus triggers activity in the sympathetic branch of the ANS. The ANS changes from its normal resting state to the physiologically aroused sympathetic state.
    1. The stress hormone adrenaline is released from the adrenal medulla into the bloodstream.
      1. Adrenaline triggers physiological changes in target organs in the body and causes , e.g. increased heart rate and dilation of the pupils. This is called the fight or flight response.
        Once the threat has passed, the parasympathetic nervous system returns the body to its resting state. This acts as a brake and reduces the activity of the body that were increased by the actions of the sympathetic branch.
Neurons and Synapses
1. Motor Neurones
  1. Carry signals from the CNS to effectors
  2. Short dendrites and long axons
2. Sensory Neurons
  1. Carry signals from receptors to the spinal cord and brain
  2. Long dendrites and short axons
3. Relay Neurons
  1. Carry messages from one part of the CNS to another
    1. Short dendrites and short or long axons
4. Synaptic Transmission
  1. An electrical impulse travels along the axon of the transmitting neuron
    1. This triggers the nerve-ending of the pre-synaptic neuron to release chemical messengers called neurotransmitters
      1. These chemicals diffuse across the synaptic cleft and bind with the receptor molecules on the membrane of the next neuron.
        The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. this stimulates the second neuron to transmit the electrical impulse
        Reuptake: The neurotransmitter is reabsorbed in the vesicles of the pre-synaptic neuron after it has performed its function of transmitting a neural impulse.
5. Action potential
  1. When a neuron is not sending a signal, it is at rest.
    1. When a neuron is at rest, the inside of the neuron is negative relative to the outside
  2. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a short time
    1. This creates the electrical impulse that travels through the axon to the end of the neuron
6. Excitatory and Inhibitory effects
  1. Some neurotransmitters act by making the neuron more negatively charged so the post synaptic neuron is less likely to fire.
    1. This is an inhibitory effect.
  2. Some neurotransmitters increase the positive charge so make the post synaptic neuron more likely to fire.
    1. This is excitatory effect
7. Synapse
  1. Neurons do not make contact. There are gaps between each one called a synapse

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	Criado por Jaskarran Lally quase 8 anos atrás