There are about ten billion neurons in the human brain. Each of these has about ten thousand connections to other neurons. There are over two hundred known neurotransmitters interacting with the neurons. Axons are the single connection leading away from the neuron, sending out a frequency through 10,000 or so branches off to other neurons. Dendrites are the many connections leading in to the neuron. The incoming dendrite electric pulses are superimposed on each other. The intensity of the incoming wave is the important part. Even at rest a small pulse is maintained in the neuron. There is a set point, a preferred point that the population returns to between excitation states. As a person’s age increases the steady state amplitude increases, neurons acting as part of groups increases, so the amplitude increases, neurotransmitters can increase or decrease this amplitude.
Neurons are in the gray matter of the cortex. The ones you are born with are all you get. Neurons increase branching and size as you learn skills and knowledge, and die off if unused. If some do not die off mental illness results. They communicate using neurotransmitters. The shape varies by task. There are two main types of neurons in the brain, spiny and smooth. The spiny neurons make up about 80% of the neurons in the brain and are further broken into two groups, pyramidal and stellate. Neurons change their behavior with experience. Axons are in white matter of the cortex and form the long distance connections. They increase with age. The more white matter the faster communication occurs. Older people think faster. Neurons do not affect things individually. They each affect the conditions in the neighborhood. Each is connected to every other neuron in the brain with in a few connections. The neurons form populations that have many semi autonomous independent elements; each has many weak interactions with many others; the input-output relationships are nonlinear; and from the neuron’s point of view have endless energy coming in and leaving. The connections between neurons can be in series or in parallel, branch into many or reduce from many neurons to few or one. The feedback can be both cooperative, both inhibitory or one cooperative and the other inhibitory. Some neurons have only local connections and can be contributory or inhibitory. Some neurons are long distance, there are always excitatory.
When the density of connections is deep enough the neurons begin acting as part of the group rather than individuals. Chaotic attractors and point attractors form to stabilize the pattern. Once part of a group the neuron gives as many pulses as it receives. The 40hz background cycle keeps the steady state going instead of dying off. Positive and negative feed back loops are what allow for the intentional responses to stimuli.
A neuron takes the incoming pulses, converts them to waves, sums them, converts the integrated signal to a pulse train and sends it out on the axon if it is over a certain threshold. The charge travels down the dendrite toward the soma (main part of the cell ), jumping from one neuron to another which release neurotransmitters as the charge moves along. When the frequency of pulses increases each is diminished in the amount it adds to the wave amplitude so the amplitude can not increase above a certain amount. Incoming flows are excitatory, out going flows act as inhibitors. The neurotransmitters turn the flow off and on and then rapidly diminish. After firing neurons need time to recover before they can refire.
Neuromodulary neurons receive input from all over the brain, most importantly the limbic system during the formation of intentional action. They have widely branching axons, that do not form synapses but release the neuromodulators through out the brain forming a global influence, they move about in the neuropil. Neuromodulators (histamine, serotonin, dopamine, melatonin, CCK, endorphins, vasopressin, oxytocin, acetylcholine, noradrenaline and others) enhance or diminish effectiveness of synapses bringing lasting changes, cumulative changes.
Neurotransmitters act locally. One, oxytocin is a neurotransmitter that is released during orgasm, and childbirth, it erases memories and also is related to bonding between couples and parents and children. NMDA, mono modulation of glutamate may be related to intelligence.
The cerebral cortex is about 2.67 square feet when stretched out. It is about six cells deep. The major wrinkles are common to everyone, just as everyones basic face structure has two eyes, a nose and a mouth. The wrinkles are individual in the same way that peoples faces are individual despite the same basic features. The bottom two layers of the cortex send connections to other parts of the brain, the third layer from the bottom is incoming signals, the the top three layers receive input from the third from the bottom layer.
Large areas of the cortex are known to perform different tasks, such as language or math. Gifted people tend to have a more differentiated pre-frontal cortex, and brain organization is also different. There are also smaller areas about a half inch square areas known as ‘bumps’ or ‘patches’ each of these includes millions of neurons and flashes off and on at five to twenty times per second. Most perceptions, behaviors and experiences are somehow recorded in these patches.
The frontal lobes of the cortex contain the motor cortices,the connections to the muscles and nerves that control motion. This part of the brain also contains a map of the body. The frontal lobes are highly involved in forming intent, and length of attention spans. The rate of firing in pre-frontal cortex fires at different rates during delayed-choice tasks, depending on previous focus of attention, and is most active during IQ tests. Different small areas of the pre-frontal cortex are used for different types of tasks. The difference in the pre-frontal cortex is not in structure but in the places it connects to. The left pre-frontal cortex encodes memories and the right pre-frontal cortex retrieves memories. Working memory, also found in this area, is not just a blank scratch pad but performs other functions as well. Dorsal and lateral areas of the frontal lobe deal with cognitive functions. While the medial and ventral areas handle social skills and empathy.
The hippocampuses are two structures about the size and shape of your little finger deep inside your brain. They release ACh (acetylcholine) along one of the two cortex layers where dendrites are found when a new thing is to be learned. The hippocampuses are responsible for sending the signals to compress information into existing information; treat it as something new and separate; or recall existing information.
Human and animal learning is broken into three main groupings: instrumental conditioning; classical conditioning; and observational. In Instrumental Conditioning; specific behavior is rewarded or punished. In Classical Conditioning; two stimuli are presented together repeatedly, the animal or person learns to associate one stimuli with the other. This is the same as Pavlov’s conditioning of dogs with bells (to which the dog does not initially salivate) and food ( to which the dog does salivate from the beginning). In Observational; behavior is learned by watching others.
Memory in humans and animals has three main divisions: Sensory has after images persisting in the eye after focus is turned away; Short term working memory is where only a few things are kept, this is the working buffer or cache; Long term storage handles semi-permanent to permanent information storage.
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Neuropsycholoy, Brain and Brain Injury Resources
WJ Freeman Brain Dynamics
Society for Neuroscience Brain Briefings
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