An Introduction to the Brain and Nervous System
We all know that we have a brain and a nervous system but most of us as adults, do not remember much about our high school basic biology class to even have the most simplistic idea about it. Here is a an attempt to bring you up to speed on the basics!
The Brain and Nervous System make up the communication network of the body. It allows us to gather information, decipher it and then create a response. These roles of the nervous system are organized into three separate categories. They are the sensory, integrative and motor function categories.
1. Sensory Function: This allows us to gather information on changes in both our internal and external environment.
2. Integrative Function: The ability of the nervous system to assimilate and decipher information in order to generate an appropriate response.
3. Motor Function: The appropriate response based on our sensory information input.
This sounds great on paper but how does it really work in the reality of life. Here are a few examples of this process in action. Let's say you are driving in your car down the road on a hot summer day with the intention of getting from your home to the grocery store. Along the way you need to turn left onto another street to head in the correct direction of the grocery store. As you see a street up ahead (Sensory function), you recognize that it is the street that takes you to the store (Integrative function), and then you automatically trigger the left turn blinker (Motor function). You now proceed down the road into the parking lot. As you enter the parking lot to the store you see several parking spaces that you might park in (Sensory function). You notice that one parking space seems to be in the shade (Integrative function) and you turn the steering wheel and bring the car to a stop in the shady parking space (Motor function).
You proceed into the grocery store with your list of grocery items to purchase. You look at the first item on the list (Sensory function) and of course it is something yummy like ice cream!!!!! You recall that the freezer section in the store is in the back (Integrative function) and you head to the freezer section (Motor function)!! This process continues until you have finished shopping. It continues to as you pull out of your parking space and safely return home. Your brain is making thousands of choices per minute, without your conscious awareness. It is a never-ending process!!!
Nervous System Divisions – The Nervous System is divided into two interdependent aspects. These are the Central Nervous System and the Peripheral Nervous System. The Central Nervous System consists of the brain and spinal cord . The Peripheral Nervous System is responsible for both sensory/afferent and motor/efferent neural transmissions to the rest of the body.
Central Nervous System: Brain and Spinal Cord
The brain rests in and is protected by the skull and the spinal cord is runs through the vertebral bodies of the spine. The spinal cord extends to the second lumbar vertebra, generally the height of the navel, where the spinal cord breaks into several individual nerves that travel from the second lumbar vertebra to the fifth sacral vertebra. These individual nerves branch out and are known as the Cauda Equina or "the horse tail".
Cerebrospinal fluid is the lubricant, shock absorber and supplier of nutrients to the brain and spinal cord. It flows between the brain tissue and the bones of the skull and up and down the central canal of the vertebral bodies where the spinal cord is located.
Peripheral Nervous System
The Peripheral Nervous System consists of the twelve cranial nerves, thirty one pairs of spinal nerves and sensory receptors. These nerves serve two major functions. They provide the neural connection for the Central Nervous System to achieve two primary goals. Firstly they send out efferent information to activate the different systems of the body. Output from the brain is labeled as efferent information. Secondly, these nerves also constantly gather afferent information from sensory receptors in the various bodily organs, fascia, and joints about the dynamic and static nature of the body and its environment. The brain is constantly receiving a never-ending stream of information from these nerves. This input to the brain is labeled as afferent. These two functions create two separate divisions in the Peripheral Nervous System.
The Peripheral Nervous System is divided into an Efferent Division and Afferent Division based on the functionality of the nerves. The Afferent Division of the Peripheral Nervous System consists of sensory receptors that picks up information from sources both outside of us and inside of us from our 19 senses. (See Blog On Sensing) This is information that the brain and spinal cord can use to create an appropriate response to. The response that the brain sends out comes from the Efferent Division. The Efferent Division is further broken down into two separate sections. They are the Somatic Nervous System and The Autonomic Nervous System:
The Somatic Nervous System – These nerves are connected solely to the skeletal muscles of the body and they allow the nervous system to generate movement. Our motor nerves of the of the Somatic Nervous System are the first to go through the process of myelination when we are babies, indicating the importance of moving in order to have feedback about movement. In the Somatic Nervous System our brain makes a choice about movement (an intention map about where we want to move), thus triggering an actual movement action. The movement action occurs, creating new sensations which give us a new observation. This active observation allows our brain to make a different choice about how it will make the movement next time which leads to new motor responses or refinement of the old motor patterns. To actively observe indicates that we focus our attention towards a very specific stimuli. The stimuli we choose to record, consciously or unconsciously, are a part of the process of organizing the incoming sensory information into recognizable observations on which to base further motor responses. Choice → Action → Observation → Response.
The Autonomic Nervous System is one that most of us are familiar with in some regard. Most of us have heard the term "fight or flight" as associated with our response to stress. The Autonomic Nervous System is divided into the sympathetic and parasympathetic nervous system. The Sympathetic Nervous System is the nervous system state that the term "fight or flight" refers to. There is much more to it than just "fight or flight". The Parasympathetic Nervous System is often referred to as the "rest and digest" nervous system. There is also much more to it than this term implies. Both of these systems work in a coordinated effort to regulate the functioning of all of the other tissues (i.e. fascia, joints) and organs in the body that are not skeletal muscle. It is the coordination of these two systems that allow our body to maintain in a homeostatic state. Balance of cellular chemistry, blood, water, hormones, internal pressure, structural support and muscular excitability must be maintained. For our normal every day lives and activities typically the balance between the Parasympathetic and Sympathetic that maintains homeostasis is one that is more Parasympathetic dominant. If I were a soldier on active duty in Afghanistan, the balance between the Parasympathetic and Sympathetic that maintains homeostasis would be Sympathetic dominant. A very different state of arousal both chemically and muscularly is needed for an active duty soldier than for a desk jockey in Portland, Oregon.