Chapter 02 - Neuroscience, Genetics, and Behaviors

• Franz Gall developed the false theory called Phrenology – where bumps on the head dictate personality and intelligence. But the theory did direct our attention to brain region and function.
• Psychologists that study these connections between biology and behavior are called Biological Psychologists.

 
Neural Communication

• Our Neural System is basically made up of nerve cells or neurons. Each neuron is composed of Dendrites ~ message receiving fibers and Axons ~ message sending fibers which are insulated by the Myelin Sheath ~ fatty cells that help \speed up impulses.
• Impulses or Action Potential is a brief electrical charge that travels down the axon as it becomes Depolarized due to the movement of positively charged ions entering the axon. After the transmission, the axon becomes Polarized as positive ions are pumped out during the Refractory Period.
• The intensity of a stimulus is called the Threshold. A stimulus must exceed the threshold in order for a transmission to occur. The neuron will either fire or it won’t. Much like a gun, the neuron either fires or it doesn’t, there are no half-fires. This is called the all-or-none-response; if a stimulus is really strong, only the number of neurons firing will increase, not their speed.
• The axon terminal of the sending neuron is separated from the receiving neuron by a tiny gap called the Synapse (or Synaptic Cleft). Once the action potential reaches the synapse, neurotransmitters, or chemical messengers, are released into the gap where it will bind onto specific receptor sites on the receiving neuron.
• The most well know neurotransmitter is Acetylcholine (ACh), it causes muscles to contract in movement.
• Endorphins are natural opiates produced in the body to control pain and induce pleasure. ("Morphine within")
• Agonists are molecules which mimics the shape of natural neurotransmitters (Morphine)
• Antagonists are molecules which block neurotransmitters from binding on receptor sites
• The brain has a Blood-brain barrier which filters out unwanted chemicals in blood stream.

 
Neural and Hormonal Systems

•  The Nervous System is composed of the Central Nervous System (CNS) – brain and spinal cord, and Peripheral Nervous System (PNS) – links CNS to body’s muscles and glands by means of nerves which are bundles of sensory and Motor Neurons (they carry incoming and outgoing information respectively).
•  The Autonomic Nervous System (under PNS) has Sympathetic Nervous System – arouses the body for defense (increase heartbeat, dilating pupils, inhibit digestion etc.) and Parasympathetic Nervous System – calms the body after stress.
•  A simple Reflex is an automatic response to stimuli (like knee-jerk) involving messages from Sensory to  Interneuron (Spinal Cord) to Motor Neuron.
• The Endocrine System (slow hormone secreting system) communicates by releasing Hormones (chemical messengers) into the bloodstream.
• In times of stress the ANS will signal Adrenal Glands (above kidney) to release epinephrine and norepinephrine hormones (also called adrenaline and noradrenaline.)
•  Pituitary gland is the most powerful endocrine gland, and under the influence of hypothalamus in brain, pituitary releases hormones that regulate glands and growth.

 
The Brain

• Lesions – remove brain tissue
• Electroencephalogram (EEG) – measures brain electric activity
• Computed Tomograph (CT or CAT Scan) – taking x-ray photographs of brain
• Positron emission tomograph (PET Scan) – detects radioactive glucose consumption in brain
• Magnetic Resonance imaging (MRI) – generates brain images from magnetic activity
• The brainstem – oldest portion in brain forms into the Medulla Oblongata – regulates involuntary processes like heartbeat and breathing.
• Within the brainstem lies the reticular formation (looks like a finger-shaped net) which controls arousal, when you wake or sleep.
• The Thalamus lies above brainstem and is shaped like two eggs. Its function is to act as a sensory switchboard relaying incoming signals to appropriate brain regions. But does not relay sensory signals dealing with smell.
• The Cerebellum stores partial memory and learning capacities. But it mainly controls balance.
• Limbic System includes Amygdala – influence emotions (fear, anger), and the Hippocampus – process memory . Removal of amygdala results in emotionless organisms upon arousal.
• The Hypothalamus maintains body homeostasis (temperature, hunger, growth) and governs pituitary.
• Glial cells guide and support nerve cells in the brain.
• The brain is divided into 4 regions.
• Frontal Lobe – behind forehead – has Motor Cortex (located at the back of frontal lobe, the cortex controls voluntary movement)
• Parietal Lobe – top to back of head – has Sensory Cortex (located in the beginning of parietal lobe, the cortex processes \bodily senses)
• Occipital Lobe – back of head – regulates vision.
• Temporal Lobe – above ears – regulates hearing
• ¾ of the brain is uncommitted to motor or sensory functions. Theses brain regions are called Association Areas – areas involved in thinking, remembering, and speaking. The larger the association area, the more intelligent the species for they are able to anticipate future events.
• The case with Phineas Gage showed researchers that damages in the frontal lobe could result in personality alterations because their normal "restraints" or inhibitions are erased. This was due to a tamping rod that shot from his left cheek and out his head, separating his internal motives and external judgement.
• Stages of Language :

1. Visual Cortex – occipital lobe (back of head) – sees the visual stimulation (words)
2. Angular Gyrus – mid-side of parietal lobe – converts words into auditory code
3. Wernicke’s Area – between temporal and parietal lobe (side of head) - derives meaning from auditory code
4. Broca’s Area – mid-bottom of frontal lobe – controls motor cortex
5. Motor Cortex – back of frontal lobe – activates speech muscles to pronounce word

•  Damage to (1) cannot see, (2) cannot read, (3) cannot understand, (4) and (5) cannot speak.
• Corpus Callosum joins the two hemispheres and is separated to cure epileptic seizures.
• People with separated corpus callosums are referred to as Spilt-brain patients. They are unable to say what they see in their left visual field because speech is in left hemisphere and the hemispheres regulate opposite sides of body.
• When split-brainers are asked to say what they saw, the left hemisphere will say what is seen in right visual field; when asked to point, get, or write what they saw, the right hemisphere will dictate what is seen in the left visual field.
• Sign language is nevertheless language and is control by left hemisphere, if deaf people get a stroke in left hemisphere, signing will be disrupted.
• Left Hemisphere : Mathematics, language, logical, reasoning. meaning
• Right Hemisphere : Perceptual tasks, musical, artistic, emotion, face recognition, copying information.

 
Genetics and Behavior

• Chromosomes contain Genes which are made up of DNA. There are 23 chromosomes in human egg and sperm; they are combined (fertilized) to make a 46 chromosome cell.
• Evolutionary Psychologists study the effects of evolution of behavior of organisms.
• Behavior Geneticists study genetic and environmental effects on behavior. – using Linkage Analysis.
• Psychologists study Identical Twins (two babies within one egg) and Fraternal Twins (two babies in 2 separate eggs) to contrast adoption studies.
• Identical twins have more similarities than fraternal twins.
• Hertitability tell us what percentage of traits are because of genetic factors. Traits (height, intelligence, eye color etc.) are either due to genetic or environment there are no half-halves. If heritability of intelligence is 70%, that means 70% of the people will have inherited intelligence.  

Bibliography

Myers, David G., Psychology Fifth Edition. Worth Publishers, Inc. New York, NY ©1998