Nervous System and the Brain

Here is a brief tour of the Nervous System, which is composed of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS is composed of the brain and spinal cord. The PNS is made up of the nerves that run to and from the body and organs (sensory and motor fibers) to the CNS.

The sensory nerve fibers of the PNS carry nerve impulses (information) from the various senses, including pain, touch, temperature, etc. from throughout the body to the CNS.

Sensory information from the five senses are carried by special, heavy duty, cranial nerves and are also part of the PNS. The eyes are extensions of the brain. They are part of the brain and are budded off during the early stages of embryonic development.

Motor fibers of the PNS innervate the organs, muscles, endocrine glands, etc., of the body and cause them to respond to the CNS. There are two types. The somatic nervous system's nerves innervate skeletal muscles. Nerves of the Autonomic Nervous System innervate organs, the cardiovascular system, viscera, glands, and muscles.

Neurons

Neurons, or nerve cells, are the basic building blocks of the nervous system. Let us first talk a little about the basic structure of a neuron:

Basic structure of the neuron

Neurons are composed of a cell body, which contains the nucleus and other cell organelles (not shown). Coming off the  cell body are the axon and dendrites. These transmit the nerve impulses in the direction shown. Nerve impulses come in through the dendrites and travel down the axon.

Axons can be very long as in extending from our brains and down the spinal cord and down to our little toes. Dendrites are usually much shorter as indicated. Myelin covers many axons, providing insulation much as the rubberized (or plastic) insulation covering electrical wires. The myelin improves the nerve impulse transmission efficiency and speed.

Here is a photomicrograph of actual neurons: Photomicrograph of actual neurons

A very important part of how nerves work are at the synapses (singular, synapsis). At the synapsis there is a gap between the neurons that must be transversed. Neurotransmitters are biological molecules that ferry the nerve impulse across the gaps at the synapses.

There are all kinds of neurotransmitters. Two primary ones are acetylcholine and adrenalin (mentioned below). Another important one in terms of mood (as in depression) and anxiety is serotonin.

There are two basic types of neurons we want to mention at this point, motor neurons and sensory neurons. Motor neurons carry impulses from the brain to muscles and organs. Sensory neurons carry impulses from sensory receptors to the brain. Sensory receptors include the five senses (taste, smell, auditory, touch, sight) and many others.

Autonomic Nervous System (ANS)

As part of the PNS, the ANS is composed of two parts, the Sympathetic and Parasympathetic Divisions.

Sympathetic Division

The Sympathetic Division mobilizes body systems during emergencies. It activates the Flight-or Fight response system and secretes adrenalin. Its activation response is  augmented by the release of adrenalin and nor-adrenalin from the adrenal glands that sit atop the kidneys.

Parasympathetic Division

The Parasympathetic Division deactivates or counters the effects of the Sympathetic Division and results in relaxation and recuperation (and healing). It releases acetylcholine.

Central Nervous System (CNS)

The CNS can be divided into the “Higher”  and "Lower" Brain. Figure 1 shows a side view of the outside or higher brain, the cerebral cortex.

Side view of cerebral cortex and other parts of the CNS

The higher brain centers consists of the Cerebral Cortex. These make up the right and left cerebral hemispheres. The cerebral cortex is the “executive suite” of the nervous system, allowing consciousness and conscious behavior and makes up 40% of brain’s mass.

The frontal lobe is very important for analytic and voluntary motor activity, logic, personality, and perception. It also houses the emotion-cognition link with the limbic system (discussed below).

The pre-frontal lobe, a subdivision of the frontal lobe, is important for executive functions, which includes organizing complex tasks, decision making, personality, and social behaviors. This is often the trouble spot in our troubled teens because of its late development.

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“Lower” brain centers

The "lower" brain centers include everything “underneath” the cerebral hemispheres.  While the anatomy of the internal structure of the brain is very complex, for our purposes we can limit discussion to a few components shown in Figure 2:

Cross section of the brain cut longitudinally (mid-sagital).

The thalamus is the major relay station of the brain. It relays nerve impulses from lower brain centers and body to the cortex. Among its many functions, the thalamus is involved in memory processing.

The hypothalamus is the main visceral (= internal organs) control center for the body. It is an autonomic control center it functions “automatically”, that is, without conscious control. The hypothalamus controls body temperature, food intake, water balance, circadian (sleep-wake) cycles, and control of endocrine system (via pituitary gland). Its components also play a major role in emotional responses and behaviors. It is the heart of Limbic System (below).

Functional Brain Systems

Two functional brain systems are defined as anatomically diverse systems with specific functions. This means they are made up of several different anatomical parts that all work together for a specific function. They are networks of neurons (nerve fibers) that work together and span relatively large distances within the brain. They include the Reticular Activating System and the Limbic System.

Reticular Activating Systems (RAS)

The RAS controls arousal of the brain as a whole and determines to what we pay attention. It acts as a filter, determining to which incoming information we will pay attention. Here is a primary area that affects ADHD. The difficulties ADHD individuals have in focusing their attention or keeping it focused may be due to a suboptimally functioning RAS. The RAS also in involved in controlling the wake-sleep (circadian) cycles along with hypothalamus. The RAS is housed in the brain stem--the upper part of the spinal cord just before it goes into the brain.

Limbic System

The Limbic System is Our Emotional Brain. It is closely connected to the smell part of our brain. Hence, the strong association between odors and emotions. It structures lie in the midbrain. The hypothalamus, again, lies at the heart of this system. The amygdala (not shown), for example, plays a critical role in fear, anger, and the flight-or-fight response.

The Limbic System plays a major role in psychosomatic illnesses. It mediates the intimate relationship between our thoughts and our feelings. Communication between the cerebral hemispheres and Limbic System explains anatomically why emotions can override logic and, conversely, why reason can affect emotions.

This system is a key structure in the evolutionary development from reptiles to mammals. Reptiles have a greatly reduced limbic system, if you can speak of it at all as a "system". About all a poor lizard has in way of emotions is your basic flight-or-fight emotions, fear and anger.

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Cerebral Cortex Lateralization (a.k.a. left brain and right brain)

In our business (mental health) and many of areas of specialization you will often here people talk about being left brain or right brain. They are actually referring to the two sides (hemispheres) of the cerebral cortex.

The two hemispheres of the cerebral cortex are specialized. More recent studies with functional MRI's has shown the picture is more complicated than described below. However, the general description below will do for our purposes. The situation is given for right handed individuals. Technically, it is not actually "reversed" for left handed individuals (about 15% of the population).

Left Hemisphere

The left hemisphere is specialized for speech and linear, logical, rational thought. It is the dominant hemisphere in language. Restated, it is our language or verbal hemisphere. It "thinks" in a detail, sequential, linear manner (sort of 1+1+1=3).

This is the side that most talk therapy engages. Unfortunately, a lot of the mental health issues are in the subconscious (or unconscious, I use these interchangeably). this is the right hemisphere's domain.

Right Hemisphere

The right hemisphere is the non-verbal, intuitive, non-linear part of the brain. It is better able to deal with the big picture and make intuitive jumps to solutions or relationships. For it, 1+1 ≠ 2.

Experiential therapy , focus on right hemispheric processes which are then moved over to the left hemisphere where we can talk about them. These include, hypnotherapy and equine-assisted psychotherapy, art therapy, music therapy, non-traditional or complimentary therapies, touch therapy, spiritual healing, and shamanism. Ancient healing methods focused on right brain functions.

Comment: Our Left-Brain Society

Western society and education systems are nearly entirely left-brain directed. They “educate” the left brain. Only in the arts and humanities is more of our education directed toward the right brain side of things. What's wrong with this picture?

Brain Wave EEG Patterns

The brain has four basic types of brain waves, alpha, beta, theta, and delta.

Alpha waves

These are low amplitude, slow synchronous waves of 8-13 cycles per second (cps). They indicate a calm, relaxed state of wakefulness. These type of waves are seen during meditation with experienced meditators. They also play an important role in the healing process in mental health. We talk about their role in healing in our "Neruobiology of Healing" section. They are involved in what is called the Integrative Mode of Consciousness, a special healing mode.

There is also some evidence indicating that when two people are placed in a room together and one is in a relaxed, alpha wave state, it will entrain the other persons brain to move into the alpha wave mode too. Cool, no? Dr. Y uses this approach a lot with his teens.

Beta waves

These waves are also rhythmic but more irregular than alpha and of higher frequency—(14-25 cps). They predominate when we are awake and mentally alert, as in trying to solve a problem, carry on a conversation, reading, and many of our activities during our awake hours. These are the waves of talk therapy.

Theta waves

Theta waves are more irregular than either alpha or beta waves. They have a frequency of 4-7cps. These are slow waves. They occur in children and adults in early and REM (Rapid Eye Movement=dream) sleep. Also occur during Integrative Mode of Consciousness.

Delta waves

These are high amplitude, low frequency (≤ 4 cps) waves that are seen during deep sleep and when the Reticular Activating System is damped as in a coma or anesthesia.

Psychobiology-Index

Neurogenesis and Healing

Addiction and the Teen Brain

The Triune Brain
Stress

State-Dependent Memory, Learning, and Behaviors and Trauma

Basic Genetics Series

Nature and Mind

  • Clinical Psychobiology