Brain
The human nervous system consists of two large divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord. The PNS includes the nerves outside the CNS; they are in the rest (the periphery) of the body. The basic building blocks of the nervous system are nerves, neurons, and neurotransmitters and glial cells.
Neurochemical electrical changes throughout the nervous system serve as a basic mechanism for psychological functions.Because these electrical changes involve the movement of chemical ions, the transmission system is called an electrochemical system.
Neurotransmitters are chemicals that play a critical role in transmitting signals between neurons. The glial cells are cells within the nervous system that plays a variety of support roles for the neurons; they protect neurons from damage, repair them when they are damaged, and remove damaged or dead tissue when it can’t be repaired
Some scientists propose that the biological study of the brain is really the study of neurons in networks. This approach is known as the neurocomputational approach to brain functioning. It’s “computational” because these researchers base their models of brain functioning on the calculation processes of neurons in networks as they interact with each other by turning each other on and off with electrochemical signaling.
Scientists look at the nervous system in two basic ways: anatomical organization and functional organization. Looking at the nervous system from an anatomical (or anatomy) viewpoint essentially focuses on the parts, and the functional organization view is concerned with what those parts do with respect to mental processes and behavior.
A neuron is considered the information cell; it’s involved in the processing and storage of information. Neurons contain the following parts:
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Soma: The cell body of the neuron containing the nucleus and supportive structures of the cell, including the mitochondria
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Dendrite: Projections from the cell body that receive information from other neurons
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Axon: The nerve fiber that conducts the electrical impulse
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Terminal button: The end of the axon involved in neurotransmitter release and signaling to other neurons
when information from the environment (or inside the brain itself from other neurons) comes into the brain through the sensory organs and activates a particular neuron (or, more often, a set of neurons), an action potential is created.
Action potentials are the movement of electrochemical energy through a neuron toward its terminal button, toward other neurons. Something called the all-or-none law states that neurons are either “on” or “off”; they are either firing an action potential or not. After a neuron is activated, it fires. If it’s not activated: no action, no fire! It’s electrochemical.
When a neuron is not firing, it is considered to be in the state of a resting potential and its electrical charge is more negative on the inside relative to the outside.
When a neuron receives a signal from another neuron, gates in the cell membrane (its covering) open and positive ions rush into the negatively charged inside of the cell. When the action potential occurs, the cell cannot fire again for a short period of time. During this refractory period, small pumps in the cell membrane work to reset the neuron by moving positive ions back out of the cell, returning the chemical balance of the neuron to its original state to prepare for another round of action.
Neurons don’t actually connect to each other in a physical sense. There are gaps between them known as synapse, spaces between axon terminals of one neuron (the neuron sending the signal) and the dendrites of the next neuron (the neuron receiving the signal); this is where inter-neuronal communication happens through chemical messengers called neurotransmitters. Although they are only millionths of an inch apart, the sending neuron throws its “message in a bottle” into the synapse, where it drifts to the other shore (the receiving dendrite).
Neurotransmitters are stored in the axon of the sending cell. An action potential stimulates their release into the synapse. They travel (actually drift) to a receiving neuron in which specialized docks known as receptor sites are present. Different shaped neurotransmitters have different docks.
Basically, neurotransmitters have one of two effects; they either excite the receiving neuron (make it more likely to fire) or inhibit the receiving neuron (make it less likely to fire). Some neurotransmitters are excitatory and some are inhibitory. Whether a particular neuron fires (transmits a signal) depends on the balance between excitatory and inhibitory neurotransmitters.
Scientists have discovered more than 100 neurotransmitters in the human brain.
Many, including the following, play a major role: -
glutamate: The most common excitatory neurotransmitter
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GABA: The most common inhibitory transmitter; involved in eating, aggression, and sleep
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Acetylcholine: A common neurotransmitter with multiple excitatory and inhibitory functions; involved in movement and memory
Another group of four chemically similar neurotransmitters modify behavior in many ways. These neurotransmitters are particularly important regarding psychological disorders:
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Serotonin: An inhibitory transmitter that is involved in balancing excitatory transmitters as well as mood, sleep, eating, and pain
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Dopamine: Can be either inhibitory or excitatory and is implicated in attention, pleasure and reward, and movement
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Epinephrine: An excitatory transmitter related to stress responses, heart rate,
and blood pressure -
Norepinephrine: An excitatory transmitter involved in energy regulation, anxiety, and fear
Following the docking process, neurotransmitters are either broken down by enzymes or reabsorbed by the sending neurons in a process called reuptake. These two processes clear neurotransmitters from the synapse after they have done their job
Neurotransmitter manipulation is a primary mechanism of action for most psychiatric medications.
An estimated 86 billion neurons live in the human brain and form trillions of connections among themselves.
The brain is a “massively parallel” information-processing system. If each neuron was connected to only one other neuron, the neuron system would be considered “massively serial.” Compared to electronic signals, neural signals travel very slowly (like 5–100 mph), so it is efficient to do many things at once ― called parallel processing.
Not every neuron is connected to every other neuron, but neurons are connected to multiple others that form clusters or networks involved in particular psychological processes and behaviors.
Brain develops from bottom to top and from back to front. This order reflects the evolutionary age of the areas of the brain. The oldest parts of the brain—the ones also present in our ancient ancestors and animal cousins—develop first, at the base of the brain near the spine. They control breathing, senses, emotions, sex, pleasure, sleep, hunger and thirst, or the “animal propensities”. Roughly speaking, these areas are what we consider to be the emotional brain.
The most forward part of the brain—literally and figuratively—is the frontal lobe, located just behind the forehead. The most recent part of the brain to have evolved in humans, it is also the final area of the brain to mature in each individual. Nicknamed the “executive functioning center” and the “seat of civilization,” the frontal lobe is where reason and judgment reside. It is where rational thoughts balance, and regulate, the feelings and impulses of the emotional brain.
The area of the brain that processes probability and time, the frontal lobe is also where we tackle uncertainty. This allows us to think not only about the present but also about the future. It is where we quiet our emotions long enough to anticipate the likely consequences of our behavior and plan accordingly for tomorrow, even though no outcome is certain and the future is unknown. This front part of the brain is where we do our Forward Thinking.
Consider twentiethand twenty-first-century patients with frontal lobe damage, several of whom have been written about extensively. What stands out about these patients is that, although their intellect is unchanged and their ability to solve concrete problems remains intact, they show significant deficits in personal and social decision-making. They make choices in friends, partners, and activities that go against their own best interests. They find it difficult to see an abstract goal in terms of the concrete steps needed to reach it. They have trouble planning their days and their years.
Historian Malcolm Macmillan suggests that Phineas Gage benefited from a sort of “social recovery.” The regular routines of stagecoach driving allowed Gage’s frontal lobe to relearn many of the skills compromised in the accident. The experiences he had, day in and day out, allowed Gage to again be personally and socially deliberate, to again be forward-thinking.
Thus, Phineas Gage provided doctors not only with some of the earliest information about the functional areas of the brain but also with some of the earliest evidence of the brain’s plasticity. Gage’s social recovery, and countless subsequent studies of the brain, tell us that the brain changes in response to the environment. This is especially true in the twentysomething years as the brain caps off its second—and final—growth spurt.
In the first eighteen months of life, the brain experiences its first growth spurt, producing far more neurons than it can use. The infant brain overprepares, readying itself for whatever life brings, such as to speak any language within earshot. This is how we go from being one-year-olds who understand fewer than one hundred words to being six-year-olds who know more than ten thousand.
But this same rapid overproduction of neurons creates an overly crowded network, and this leads to cognitive inefficiency, which is not adaptive. That’s why these same spongelike toddlers struggle to string together a few words in a sentence, and they forget to put on their socks before their shoes. Potential and confusion rule the day. To make neural networks more efficient, this first growth spurt is followed by pruning. Across years, the brain keeps the neurons and connections that are used while those that are neglected are pruned, or allowed to die off.
The connectome is the complete description of the structural connectivity (the physical wiring) of an organism’s nervous system. The field of science dealing with the assembly, mapping and analysis of data on neural connections is called connectomics.
The thalamus is a mostly gray matter structure of the diencephalon that has many essential roles in human physiology. The thalamus is composed of different nuclei that each serve a unique role, ranging from relaying sensory and motor signals, as well as regulation of consciousness and alertness.
Look into
- Phineas Gage’s injury