The case of a woman who seems unable to experience fear despite being able to express all the other array of emotions and performing well on mental tests puzzled scientists. They eventually knew a disease in childhood destroyed the amygdala on his brain, and could link this organ with the ability to experience fear

The case shows how the brain controls behavioural function, but the brain is a highly complex organ, so much we haven´t been able to simulate it by computer. It makes sense for psychologysts to focus on the biological aspect of behavior to try and achieve better understanding of what the brain does

=====================

Communication in the nervous system

- Behavior depends on rapid information processing

The nervous system is a complex communication network which constantly transmits, receives and integrates signals, handling information just as the circulatory system handles blood

Nervous system = tissue composed of cells

Cells = two categories, neurons and glia

Neurons = individual cells in the nervous system that receive, integrate and transmit information
	Basic links that permit communcation within the nervous system
	Most of them only communicate with other neurons

Parts of a neuron=
      Soma or body - Has the nucleus and the chemical machinery common to most cells
      Dendritic Trees = branch like structures that are specialized to receive information
      Axon = long thin fiber that transmits signals away from the soma to other neurons or to muscles or glands. Can be quite long and branch off to communcate with a number of other cells
      Myelin sheath = Insulating material encasing the axons and acting to speed up transmission of signals
      	     Multiple sclerosis disease is an example of myelin sheaths deteriorating
      Neurotransmitter, small knobs that secrete chemicals, located at the end of the axon. the chemicals serve as messengers to activate nearby neurons
      Synapses= Junctions where information travels  is transmitted from one neuron to another

Information Flow
	    Dendrites -> Soma -> Axon -> SYnapse -> Communication OK

Glia= cells that provide various types of support for neurons. Smaller but outnumber neurons 10 to 1
Glial cells account to the majority of brains volume

Functions = nourishment to neurons, help removing waste products and provide insulation around axons.
Myelin sheaths are derived from some special types of glial cells

Glia helps development of the nervous system in the human embryo

Recent research shows glial cells also play a part in information processing
       Memory formation (deterioration linked with Alzheimers), experience of chronic pain, impaired communcation between neurons and glials linked with psychological disorders

=======================================

The Neural Impulse, using energy to send information

Research by Alan Hodgkin and Andrew Huxley on 1952  showed what happens when the neuron is stimulated

A complex electrochemical reaction involving ions
  ions = electrically charged atoms and molecules

The neuron at rest behaves like a tiny battery with these charged particles, without stimulation it retains a negative charge due to flow rates of the particles

Resting potential = stable, negative charge when the cell is inactive

When the neuron is stimulated channels are opened in the cell membrane and positive ions can rush in, creating action potential

Action Potential = Very brief shift in a neurons electrical charge that travels along an axon

After the action potential, the cell membrane closes up again and requires a bit of time before being ready to repeat the process, this is called refractory period

Absolute Refractory period = minimum length of time after an action potential  during which another action potential can begin - 1 or 2 milliseconds

Relative refractory period = The neuron can fire, but requires more intense stimulation than usual

Neural impulse is an all of none proposition, either the neuron fires or it doesn't. Weaker stimuli doesn't produce smaller action potentials

To understand strength of stimulus, neurons vary the rate at which they fire action potentials

The stronger the stimulus, the faster the firing

Thicker axons transmit information faster

Neural impulses can travel up to 100 meters per second (+200 miles per hour)

==============================

The Synapse

The neurons don't touch each other to transmit information, they are separated by the synaptic cleft

    Synaptic cleft = Microscopic gap between the terminal button of one neuron and the cell membrane of another

Signals jump the gap to allow communication

Presynaptic neuron = neuron that sends the signal
Postsynaptic neuron = receives it

Arrival of action potential triggers the release of neurotransmitters

Neurotransmitter, chemical that transmits information from one neuron to another

SYnaptic vesicles = small sacks within the terminal buttons that store the neurotransmitters

Process flow

 Action Potential -> Vesicle fuses with membrane  of presynaptic cell -> Synaptic vesicles open -> Neurotransmitter released to the synaptic cleft -> Neurotransmitters jump the synapse and reach the membrane of the receiver

Receptor sites: Special molecules in the postsynaptic cell membrane  tuned to recognize specific kinds of neurotransmitters and respond to them


Reactions in the cell cause a postsynaptic potential when the neurotransmitter combines with the receiver
	  Postsynaptic potential = Voltage change at a receptor site on a postsynoptic cell membrane. This potential doesn't follow the all of none approach, the voltage change dependes on the strength of the signal and carries with him an increase or decrease on the capacity of that neuron to perform neural impulses, also linked to the voltage change

Types of Message = Excitatory and  Inhibitory
      Excitatory = positive voltage shift that increases the likelihood of the neuron firing action potentials
      Inhibitory: Negative, decreases the likelihood

Direction of the voltage shift depends on which receptor sites are activated in the neuron

The effects of the synapse only last a fraction of a second, after this, neurotransmitters drift away or are inactivated by enzymes to metabolize them into an inactive form

Reuptake - A process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane (enables recycling of materials)

A neuron receives thousands of signals, and it must integrate the signals arriving at a synapse before deciding if firing a neural impulse is the best case

The decision works adding up the excitation  or inhibition that arrives from other neurons and comparing the resulting voltage against the threshold. If it surpasses the threshold an action potential will fire

"Millions of neurons must fire in unison to produce the most trifling thought"

Firing a single neuron won't do anything, most neurons are heavily interlinked in complex ways.

Our perceptions, thoughts and actions depend on patterns of neural activity found in these complex neural networks, which involve firing together or sequentially interconnected neurons

As we use neurons, some new synaptic connections are made and some wither away, it seems to be more important the elimination of old synapse than the creation of the new to create neural networks. The nervous system normally forms more synapses than needed and then gradually eliminates the inactive

SYnaptic pruning, process of  removing the old synapses

=====================================================

Neurotransmitters and behavior

Neurotransmitters are fundamental on behavior, palying a key role in everything from muscle movements to moods and mental health

9 classic transmitters, 40 chemicals that can function as neurotransmitters, and a variety of recently recognized novel ones.

Specific neurotransmitters work with specific kinds of synapses, the binding process of a neurotransmitter to a membrane works like a lock and a key. This specialization helps making the nervous system more precise by reducing cross talk

Acetylcholine Ach =
	      Transmitter between motor neurons and voluntary muscles, all our voluntary movement relies on Ach
	      Contributes to attention, arousal and memory
	      Lack of supply associated with memory losses like Alzheimers

Activity of neurotransmitters can be influenced by other chemicals in the brain, an example is tobacco which fools the system into thinking is Ach and activating neurons.

Agonist = chemical that mimics the action of a neurotransmitter

Some chemicals block the pathway needed for neurotransmitters to bind to the mcell membrane

Antagonist = Chemical that opposes the action of a neurotransmitter

Monoamines
	Dopamine
	Norepinephrine
	Serotonin

Regulate many aspects of daily behaviour

Dopamine - Controls voluntary movements, degeneration causes Parkinsonism
Serotonin - Sleep and Wakefulness, eating behavior, aggresive behavior

Abnormal levels of monoamine in the brain have been linked with psychological disorders

Depressive disorders= low activation norepinephrine and serotonin
Eating Disorders = abnormal activation levels of Serotonin
OCD = abnormal activation levels of Serotonin
Schizophrenia = abnormally high  activation levels Dopamine

Drugs like amphetamines and cocaine seem to work by highly stimulating dopamine and norepinephrine synapses. Dopamine pathways are believed to be what leads to the craving and addiction of drugs


Gaba and Glutamante

Gaba = gamma-aminobutyric acid
- produces only inhibitory post synaptic potentials
- present in 40% of all synapses
- regulation of anxiety, abnormal levels linked to anxiety disorders

Glutamate
- only excitatory effects
- Linked with learning and memory
- Abnormal levels linked to schizophrenic disorders

Endorphins
- Resemble opiates in structure and effects
-Contribute to modulation of pain
- Contribute to eating behavior and body response to stress

Discovery of endorphine ha led to new theoriesand findings on the neurochemical bases of pain and pleasure

Researchers believe endorphins are capable of producing pleasure

Much still remains to be discovered regarding the nervous system, even if discovery of neurotransmitters helped to gain a lot new insights into it.