Divisions of the nervous system
- Human nervous system is divided into two main sub-systems:
- Central Nervous System (CNS)- Brain and Spinal Cord
- Peripheral Nervous System (PNS)- neurons that carry messages to and from the CNS
- PNS is divided into:
- Autonomic Nervous System- Glands~ no control
- Somatic Nervous System- Muscles~ control
- AutonomicNervous System is broken down to:
- Sympathetic Nervous System- Quick reaction to threat (fight or flight response)
- Parasympatheic Nervous System - Returns body to normal levels of activity (homeostatis)
Neurons within the PNS
- Carries messages away from the CNS
- Short dendrites and long axons
- Neurons in spinal cord have bigger axons than the neurons in the brain
- Carries messages towards the CNS
- Long dendrites and short axons
Neurons within the PNS Continued...
Interconnecting Neurons/ Relay
- Found only in the visual system
- Transferes messages from sensory neurons to motor neurons
- Short dendrites and short or long axons
- Diagram (Table)
- Hammer Strikes knee --> Dectected by receptors --> sensory neurons --> CNS
- Interconnecting Neuron --> Motor Neuron ---> KNEE JERK
Structure and Function of Neurons
- Specialised gap (cleft) that allows messages to be conveyed between Neurons
- Impulse travels down a neuron. When it reaches the presynaptic terminal (end) it releases neurotransmitters
- Either diffuses across the gap and is taken up by receptors in the post synaptic neuron, or it is reabsorbed (destroyed).
- Too much Dopamine is linked to Schizophrenia
- Anti-psychotic medicine (chloromazine block receptor sites (dopamine levels decrease)
- Too little Serotonin is linked to depression. Anti-depressants block reabsorbtion (levels increase)
Localisation of Cortical Function
Specific areas of the brain (cerebral cortex) have specific behavioural functions
- Left and Right Hemispheres
- Left Hemisphere is responsible for the right side of the body (Vise versa)
Study; Broca~ Tan (left frontal lobe)
- Inability to clearly speak any words other than 'tan'.
- Lesion in the left cerebral hemisphere (specific area became known as Broca's area) cause by syphilis
- Damage to this area causes Broca's Aphasia~ slow speech
- left temporal lobe
- understanding speech
3 Layers of the Brain
1) Central Core (Brain Stem)
- Controls most primitive behaviours e.g. sleeping, breathing or sexual behaviour
- Controls involuntary behaviours e.g. sneezing
- Key Area= Hypothalamus
- Hypothalamus regulates primitive behaviours and the endocrine system~ Maintain homeostasis
2) Limbic System
- Key role in emotions and memory
- Contains Structures~ Hippocampus
- Patients had hippocampus removed to treate severe form of epilepsy- on recovery patient suffered from a severe form of anterograde amnesia
3 Layers of the Brain Continued...
3) Cerebrum (Grey Matter)
- Composed of right and left hemispheres connected by Corpus Callosum
- Enables messages that enter the right hemisphere to be conveyed to the left hemisphere and vise versa
- Higher intellectual functions (consciousness)
- Each hemisphere is divided into four lobes;
- Frontal- Awareness of activity within our environment (consciousness)
- Parietal- Sensory and motor movements
- Tempiral- Auditory (hearing) ability and memory acquisition (Wernicke's Area)
- Occipital- Vision
- Parietal lobe
- Controlling voluntary movements
- Damage to motor cortex~ impaired movements
Areas in the Cerebrum
- Pariental lobe
- Responds to temperature, touch, pain and sense of body movement
- The amount of Somatosensory Area in a particular area of the body is related to use and sensitivity
Split Brain Research
- Surgery performed in 1950s to treat severe epilepsy.
- Corpus Callosum is lesioned or cut.
- Provided evidence of independent function.
- Patient was asked what he would like to do for his career.
- One part of the brain was shut down individually, then the other.
- Left- Formula 1 Driver
- Right- Draftsman (Brain diagram)
Methods of Studying Cortical Specialisation
Relates to localisation/ lateralisation
- Earliest attempts= Phrenology (bumps on skull equate to behaviour)
- Two key types of methods~ Invasive and Non-invasive
- Invasive- Manipulation of structures within a brain (usually involves some form of surgery)
- Involves manipulation of structures of the brain by Ablations or lesions
- Ablation~ Areas removed/damaged
- Lesion~ Areas cut (usually neuron connections)
Case Study: Hubel & Wiesel~ Cat
- Inserted micro-electrode into the visual cortex (occipital lobe) of a cat. Images of light and dark was then projected infront of the cat
- Different neurons within the cat's brain fired quickly depending on the lines within the images.
- Simple Cells- Respnds to lines at certain angles
- Complex Cells- Responds to lines of certain angles traveling in specific directions
- Shows how the Visual Cortex builds up imaged from simple to complex representations
- Investigation (Hubel & Weisel) was incredibly expensive (equipment)
- Invasive, so tends t be used on animals (problems of generalisation and ethics)
- Great deal of control. Can target specific areas (single neurons, etc)
- Damaging a single area may have an unseen affect on other areas of the brain
Invasive Methods Continued...
Electrical and Chemical Stimulation
Case Study- Olds & Milner~ Rats
- Electrodes were placed in the septal area of the Limbic System. Light electric currents produced pleasure and rats would repeatedly press a lever that delivered the current to them.
- Chemical test to establish which hemisphere (lateralisation) is responsible for which function (mainly memory and speech) used before surgery
- Each hemisphere is anasthetised in turn to establish lateralisation of these functions
- Tends to be less invasive so fewer ethical implications
- However, nature of the investigation tends to mean emphasis on animal experimentation
Invasive Methods furthered...
- Draw of a patient involved in a longitudinal study because of some behavioural deficit/ disorder
- Brain is examined after death
- Broca's and Wernicke's Area were found through this method
- Study~ Tan (see earlier study)
- Difficulty in obtaining brains- many patients object before death etc.
- Other techniques are now more sophisticated and brains can be scanned.
- No need for Post Mortems
- Electrodes are placed onto the scalp (usually arranged in a cap)
- Voltage differences in the brain are measured
- Filtered signal is then displayed as an image on the screen
- Contributed to understanding sleed disorders and epilepsy
- Non-invasive~ less ethical issues, natural brain activity
- Less accurate than other technigues (only looks at general areas of activity
1) Cat Scans/ CT Scans (computerised axial tomography)
- Narrow x-ray beam is passed through the patients head
- Beam can be passed through multiple axes
- The amount of radiation absorbed is measured
- Useful to detect swelling due to trauma (head injury) and also assessing the size of ventricles (fluid filled spaces)
- Detailed knowledge of active areas (whilst behaving)
- Non-invasive so fewer ethical problems
Scanning Technigues Continued...
2) PET Scans (Positron Emission Tomography)
- Radioactive glucose injected into the bloodstream
- Brain activity requires glucose
- Active areas have highest radioactivity
- Injection involved- invasive? Ethics~ fear of needles
- Can be very time consuming process.
Scanning Technigues Furthered...
3) MRI Scans (Magnetic Resonance Imaging)
- Strong magnetic fiels generate detailed (three dimensional) images of the body
- Patient is placed in a tunnel surrounded by a large magnet
- Causes tissues to resonate (give out a signal)
- Produces a three dimensional image of the brain
- Very useful in diagnosing diseases of the brain and spinal cord e.g. multiple sclerosis (not able to be detected by CAT Scan
Autonomic Nervous System
Two key divisions:
- Quick reaction to threat (fight or flight response)
- Speeds up heart papitations
- Dilates bronchi
- Returns body to normal levels of activity (homeostatis)
- Rest or digest
- Slows heart rate
- Constricts bronchi
Autonomic Nervous System Continued...
- Composed of a number of glands that release hormones directly into the bloodstream
- Acts more slowly than fast-acting nervous system
- Most major endocrine gland is the Pituitary Gland (brain) which is also known as the 'Master Gland' and controls the release of hormones from all other endocrine glands
Fight or Flight- Endocrine Response
- Pituitary gland releases ACTH hormone (major stress hormone)
- ACTH stimulates adrenal glands (particularly adrenal medulla) which releases adrenalin directly to the bloodstream
- Adrenaline ids the fight or flight response by constricting blood vessels in the stomach inhibiting digestion and by increasing the heart rate
- Diagram of the location of the glands
Autonomic Nervous System Furthered...
Effects of the Stress Response
- Prolonged exposure to the fight or flight stress hormones can be particularly damaging physically and psychologically
- Common side-effects are disruption to sex life, digestion problems and in sever cases heart disease
- Autonomic nervous system being involuntary not always the case e.g. practices of Zen Buddhists
- Able to control several autonomic functions including heart rate and oxygen consumption
- Not due to the decrease of physical activity of meditation because physical changes exceed what occurs during sleep or hypnosis
- Able to control any potential negative effects of stress
Genotype and Phenotype
- Geneotype: Individual's genetic make-up (particular set of genes the individual possesses.
- Pheotype: Observable characteristics (traits) shown e.g. height, weight or eye colour
- Geneotype is the major influencing factor in the development of the phenotype along with the environment
Genotype + Environment = Phenotype
- PKU: Genetic disorder, when treated with a specific diet, the individual can develop normally
- Haemophilia: The individual does not always develop the disease, and can be a carrier instead.
- Mononzygotic twins, with the same geneotype may have different phenotypes e.g. one twin was fed a more nutritious diet and so would be physically much taller and stronger
- Form when a zygote divides to form two embryos
- Genetically identical~ Same DNA
- Often look less alike as they grow older~ lifestyle choices etc.
Dizygotic~ Non-identical/ fraternal
- Form when two seperate eggs are fertilised
- No more genetically alike than normal siblings
- Twin Studies are used to investigate the genetic basis of behaviour
- E.g. Monozygotic twins seperated at birth, what is the likelihood of them both developing a mental disorder such as Schizophrenia
- If both twins have Schizophrenia it leads to the conclusion it is a genetic disorder
Investigating the Genetic Basis of Behaviour
- Comparison between twins or across the types of twins
- Attempts to separate genetics from the environment
- If characteristic is genetic there should be 100% concordance between Monozygotic Twins and low concordance between Dizygotic Twins
Study: Wilson~ Intelligence
- Longitudinal study and found that by the age of 18 moonths, monozygotic twins were more similar than Dizygotic twins on tests of infant intelligence
- Follow-up data over next 13 years showed monozygotic twins were more similar than dizygotic twins in intellectual performance.
Study: Bailey& Pillard~ Sexual Orientation
- Participating male twins where at least one of the pair was gay
- 52% of monzygotic brothers were concordant for homosexuality
- 22% of dizygotic brothers
Investigating the Genetic Basis of Behaviour Conti
- Criticisms of the way participants were recruited e.g. through homosexual media, whose target audience is clearly homosexual
- Monozygotic Twins are more likely to be treated the same (same clothes, toys etc)
- More likely to have the same genotype and phenotype
Study- Krishnan~ Addiction
- Sons of aloholics are more likely to be alcoholics themselves than those selected at random
- When the sons drank alcohol, they tended to release more neurotransmitter endorphin than other people
- Suggesting biological predisposition towards alcoholism
Investigating the Genetic Basis of Behaviour Furth
Study: Zajonic & Markus~ family size & birth order
- Researcged IQ of 40,000 Dutch males who were born in 1944
- IQ related to birth order and family size due to attention given by parents
- E.g. large family means each child has a smaller amount of perental attention and perhaps more physically deprived environment resulting in a lower IQ.
- Comparing traits/ characteristics between adopted children and their biological or adoptive parents
- Biological trait~ concordance between child and birth parents
- Environmental trait~ concordance between child and adoptive parents
- Adopted children in one family may be compared with biological children in another famiily or adopted children and biological children within the same family may be studied.
Investigating the Genetic Basis of Behaviour Exten
Study: Corley and DeFries~ Age
- As adopted children approached the age of 16, they became more similar to their biological parents in cognitive and verbal ability compared to their adoptive parents
- Suggests a genetic influence
Study: Scarr and Weinberg~ Intelligence
- Black children from low socio-economic backgrounds were adopted into white middle-class families with at least one biological child
- Initially found black children more intellectually similar to biological parents (0.43 concordance) than their adooptive parents (0.29 concordance)
- Supporting genetic basis for intelligence
- However, adopted siblings (white biological child and black adopted child) showed intellectual similarities
- Supporting environmental basis
Investigating the Genetic Basis of Behaviour addit
- Adoption studies must be viewed with caution
- Adoptive families usually smaller, financially richer and may provide a more stimulating environment than some biological parents therefore causing an increase in intelligence.
- Artificially selecting male and female animals for a particular trait, which are then bred to produce offspring
- Plomin: if selective breeding doesn't alter the trait/ characteristic, then must assume it is dependent on environmental factors.
Investigating the Genetic Basis of Behaviour Conti
Study: Tryon~ Learning
- Trained large number of rats to run a complex maze, the quickest through the maze were bred together (maze bright) and the slowest were bred together (maze dull).
- Breeding process continued for a number of generations.
- Dependent variables: number of errors and speed the rats learned the paths through the maze.
- Maze bright rats learned the path quicker and made fewer errors than the maze dull rats.
Study: Cooper and Zubeck
- Similar to Tryon but found very different results.
- Reared maze dull rats in one of two environments:
- Impoverished (boring) environment cosisting of a barren wire-meshed cage
- Stimulating envirnment containg tunnels, ramps etc.
- At maturity, maze dull rats in the stimulating environment made same number of learning errors as the maze bright rats in a stiulating environment.
- Shows environment is an important factor in determining behaviour.
Investigating the Genetic Basis of Behaviour Furth
- Quick way to select for paticular traits with effects of artificial selection being seen in just a few generations
- Generalisation and validity issues (animals--> Humans)