Neurons (or nerve cells) carry and process electrical signals which are the basis of cognition and the peak of cognition—rational thought. Neurons are the basic cell of the nervous system of all vertebrates as well as all invertebrates from the jellyfish up. Later the discussion will take up the increase in brain complexity as found in nature which leads to the human brain. Notice in the tree of life, the vertebrates in the lower left splitting off before fish and all the creatures great and small that have found their niche often confirmed by their different brain powers.
Caveat and Simplification
The human body, the nervous system, and the brain are immensely complex systems. In Mental Construction, the discussion is restricted to support its theme, the role of neurons in affecting how we think. Many important and interesting facts and discoveries will not covered to retain the clarity of the argument. With that understanding of the simplifications in explanations, I will continue.
Human Nervous System
Although all the operative elements are neurons, the interconnections between the neurons is not the same throughout the system. It is lowest in the periphery and highest in the cortex, which corresponds well to the difference between passing sensory signals and processing information.
The peripheral nervous system addresses three functional tasks.
- External senses to brain. I find it useful to consider the senses as two types—direct experience and remote sensing. Direct experience senses are touch, taste, and proprioceptor (body orientation). The remote senses are sight, hearing, and smell.
- Brain to external action. The actions are of two distinct classes—muscle movement and speech.
- Homeostasis. The third branch monitors internal organs and maintains decent levels so that our bodies carry on. Sensory information is delivered from our internal organs to the brain. The brain adjusts physiological the levels with action instructions that controls heart rate, breathing, digestion, and the like. This cycling of information and action is also entirely without conscious control as is captured in its name the autonomic nervous system.
The brain is composed of 100 billion neurons, accumulated into significant structures which bear directly on cognition.
Homeostatis is mainly accomplished in the medulla and the pons – the brainstem. Although they are small portion of the brain, they handle 90+% of incoming sensory information, without it traveling any higher in the brain. Only 30 to 100 nerve impulses out of 100 million per second need to be passed from the brainstem into the midbrain and then to the cerebrum (the cortex).
This huge collection of particularly wired neurons (in a fashion unlike that of the cortex) is known to provide balance and the smooth operation of our body. That is, once the higher cognitive centers in the prefrontal cortex had decided on an physical action.
In the structural image of the brain above, the midbrain represents the limbic system, although there are important features not shown here.
The limbic system is incredibly important to human thinking and behavior. Among other places, the role of the limbic system will be highlighted in the discussion of concept elevation, the manner in which current experience gets blended with past experience to create one’s inner view of the world.
The amygdala has been identified as the repository of flight-or-fight feelings—the development and identification of emotional states supports our thinking. The hypothalamus is crucial to memory and memory is essential to relating current situations to past situations so that the results back then can guide our reactions now.
The latest evolved layer, the cortex, holds immense power in our cognition. This bundle of 12 billion neurons are very uniformly and densely interconnected. Manfred Spitzer (p 138) highlights a major feature in his statement, “the cortex works as a rule-extraction machine.” We come into this life with a very few bits of a priori operations, for example ability to discern edges and direction of motion. From those humble beginnings, we learn to distinguish objects, smells, and sounds. The biological imperatives which shape learning stages forms the conversation in Sensory and Semantic Maps among other sections.
Although uniform, all parts of the cortex do not compete to handle incoming sensory information. Clinical observation and laboratory experiments have demonstrated each lobe handles distinct senses. Visual data is directed to the rear of the brain, the occipital lobe. Auditory data comes from the ears into the adjacent temporal lobe. Touch, feel, and bodily pain come up the spinal
It was debated whether the nervous system was continuous or composed of many active neurons. That question has been settled and the fruits from the neural theory are many and reveal the pattern-matching and similarity aspects of our cognition and thinking.
Neurons dendrites and axons
Neural Threshold & Almost Gate