Trauma and the Brain - Intro to the Nervous System

Here are the building blocks for our journey into trauma and the brain.

An Introduction to the Nervous System

A Fun Intro to the Nervous System

Neurons - The Functional Unit of the Nervous System

The Skinny on Neurons 

Nerves are comprised of neurons. A neuron is an electrically excitable cell that processes and transmits information through electrical (movement of ions like sodium and potassium) and chemical (neurotransmitters like epinephrine) signals. The transmitted information is exchanged at a junction called a synapse. Dendrites (like tiny branches of a tree) receive signals and axons deliver signals. An action potential (electrical impulse) begins at the axon hillock, travels down the axon (like the trunk of a tree), and triggers a response at the synapse. 

Neurons & Their Axons

White matter is made up of signal transmitting axons, many of which are covered in myelin. Parts of a neuron are analogous to an electric cord; the outlet is where the signal begins (axon hillock) and the axon is the wiring that transmits the signal. Think of myelin (fatty structures) as the plastic coating covering an electric cord in your house. What happens when that coating wears away and you grab the cord? You get shocked if it is plugged in to a working outlet. 

Neuron-Neuron Junction

Neurons can elicit a response from another neuron. When this happens, it is called a neuron-neuron synapse. The axon of one neuron will synapse (release a neurotransmitter) with a dendrite of a target neuron. Once this happens, the target neuron will respond accordingly. 

Neuromuscular Junction

Neurons can also elicit responses in muscles in much the same way. A signal, in the form of a neurotransmitter, triggers a cascade of events to occur in the muscle cell leading to a contraction.

The Brain

The Brain

The Nervous System is Complex

So let us begin by discussing the divisions of the nervous system. The Central Nervous System (CNS) includes the brain and the spinal cord and is insulated from the rest of the body. Neurons in the CNS do not regenerate (actually, the research is indicating that some parts of the CNS can be repaired) – this is important to understand when dealing with injury and/or pain. 

The Brain - Part of the Central Nervous System

The human brain – it can do magic. The brain is the control center of the nervous system - accepting and transmitting chemical and electrical signals. These signals allow us to see, hear, speak, move, love, understand, and ultimately – live. The brain’s complexity is utterly astounding. I read somewhere that the human brain has more molecular switches than all of the computers, routers, and Internet connections on the planet. Wow, right? 

White Matter Versus Gray Matter

There are two types of tissue (matter) found in the CNS – white matter and gray matter. White matter is made up of signal transmitting axons, many of which are covered in myelin. The myelin is a conductor and speeds up the transmission of an electrical impulse. Gray matter contains cell bodies, dendrites, and axon terminals – this is where synapses occur. In the brain white matter is found deep to gray matter.  In the spinal cord, the opposite is true. The spinal cord is a conduit for sensory and motor signals; sensory to the brain and motor away from the brain. In addition to transmitted information to and from the brain, the spinal cord also coordinates some reflex actions.

So what does the brain do, exactly? 

That is a loaded question, do a little research on the Internet and it will seem like we know TONS. In reality, we don’t know what we don’t know. I will tell you that the “10% brain use” myth is precisely that: a myth. So back to the question “…what does the brain do, exactly?” Well, the answer depends upon the area of the brain being discussed. The thing that makes us different from other animals is our cerebrum – where higher thinking happens. The brain (part of the CNS) is the control center of the nervous system accepting and transmitting chemical and electrical signals. These signals allow us to see, hear, create language, move, love, understand, and ultimately – live. The brain is an incredibly complex organ that scientists are still working to decipher.

What’s lobe got to do with it?

The frontal lobes of the cerebrum are responsible for our ability to think critically, solve problems, and feel emotion – the frontal lobes are the origin of personality. Have you heard the story of Phineas Gage, a train foreman from the mid-1800s? One day at work, Gage was struck through his left eye and into the frontal lobe of his brain with a tamping iron. By all reported evidence, Gage had been a personable guy prior to the accident…after the accident was a different story. Gage’s personality had changed drastically; he became a crude and difficult man. Historically, this was an important medical case because it was the first time brain trauma had been linked to a change in personality. 

Another great example often used to illustrate the power of the frontal lobe of the brain is contained in One Flew Over the Cuckoo’s Nest – a novel written in the 1960’s by a man who had worked as an orderly in a psychiatric hospital. In the novel “Ruckley”, a once hell-raising patient, was lobotomized in an effort to control his behavior. The lobotomy rendered Ruckley to a vegetative state in which he stared at a picture and occasionally screamed obscenities.

The parietal lobes of the brain are responsible for sensation and perception, and for the integration of sensory input (mainly with the visual system). If the right parietal lobe is damaged it causes the injured person to neglect part of their body or neglect space  on the left side– contralateral neglect. Seems ridiculous but it is true.

The temporal lobes of the brain are the primary organization of sensory information – auditory input and perception (hearing), visual perception, memory, and emotion. Damage to the temporal lobes can result in memory problems, disturbances in auditory and/or visual perception, and language comprehension. Injury in this area can also cause alterations in personality, affective behaviors, and sexual behavior.

The occipital lobes – located at the very back of the brain – are the home of the primary visual cortex and the visual association area. Damage to the posterior aspect of the brain will often lead to visual impairments.



The cerebellum is the most primitive areas of the human brain. It is responsible for movement, posture, and balance; things that we do not need to think about constantly.

Which lobe of the brain is responsible for speech and hearing?

  • Occipital
  • Temporal
  • Frontal
  • Cerebellum

The frontal lobe of the brain is responsible for (select all that apply):

  • Personality
  • Regulation of emotion
  • Problem solving
  • Visual association

The Spinal Cord

The Spinal Cord

The Spinal Cord

The spinal cord extends from the brainstem to T12/L1 (thoracic vertebra 12 & lumbar vertebra 1) where (at the Conus Medullaris) the spinal cord becomes a bundle of spinal nerves referred to as the Cauda Equina (because it looks like a horse's tail). The spinal cord is protected by the vertebrae that surround it.

This image (from Bandha Yoga) shows a transverse/cross section of the spinal cord. The gray, butterfly-shaped center is gray matter containing synapses where sensory and motor nerves communicate. The surrounding areas contain myelinated (white matter) nerve tracts that carry information to and from the brain. Keep this picture in your brain because we will return spinal cord functions again later.

Sensory information arrives through the dorsal ramus where it is interpreted in the gray matter of the spinal cord and a response then exits through the ventral ramus. 

The spinal cord is made of

  and .

The Peripheral Nervous System

The Peripheral Nervous System

The Nervous System is Complex

The Peripheral Nervous System (PNS) includes all somatic nerves and autonomic nerves. The Somatic (body) Nerves control voluntary movements through control of the skeletal muscles (muscles attached to bones). The Autonomic Nerves control our automated responses to stimuli through two divisions – sympathetic (fight or flight) and parasympathetic (rest and digest). 

Somatic Division

Some examples of somatic nerves include the Median Nerve in the arm and the Sciatic Nerve in the leg and foot. These nerves are derived from nerve cells and nerve plexi. A plexus is a network of nerves emerging from between the vertebrae.  These converge upon one another, regroup and intertwine forming nerves that travel on to innervate a section of the body.  The main plexi are the cervical plexus, brachial plexus (above), lumbar plexus, and sacral plexus. 


Autonomic Division

The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing. This system works automatically (autonomously), without conscious effort – it is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.

Sympathetic Division

The Sympathetic Division of the ANS is derived from the spinal cord and runs along either side of the vertebral column.  It is the sympathetic nervous system in control during a fight or flight response. What is the fight or flight response? Often described as hyper-arousal, the fight or flight response prepares your body by giving you the power to escape danger. The fight or flight response is a necessary protective function. In a sympathetic response the body prepares itself to stay and fight or to run away from the threat – both “choices” requiring a huge amount of energy. This begins to explain the stories you hear stories of women who have literally been able to lift a car off their trapped child or maybe of a woman who had been beaten and left for dead but managed to pull together enough energy to find help.

Parasympathetic Division

The parasympathetic division controls all of those functions that you would associate with resting and digesting. The parasympathetic nervous system restores homeostasis – balance – following a sympathetic response and maintains normal functional control of the body. The parasympathetic division is derived from two main sources, although there are a few “lesser” players, the Vagus Nerves (vagus = wanderer) and the Pelvic Splanchnic Nerves. The Vagus Nerves arise from the brain stem and then travel all over the body – cardiac organs, respiratory organs, and digestive organs. The Pelvic Splanchnic Nerves provide control for the lower digestive system, urinary system, and reproductive systems (sexual arousal is parasympathetic mediated).

The peripheral nervous system includes which of the following? Select as many answers as are correct.

  • brain
  • spinal cord
  • autonomic
  • somatic

Describe, in your own words, a sympathetic nervous system response.