The nervous system
The Nervous System
Walking down a sidewalk, you quickly leap over a puddle of water to avoid getting wet. You continue on your walk, pretty pleased with your leaping skills.
"I could have jumped a puddle twice the length," you assert.
You are probably right, but you could not have done so without the help of your nervous system.
The main components of the nervous system work together to take in input and turn it into action in the body. Explore the main components and their functions below.
Component | Function |
Brain | Processes sensory information |
Spinal cord | Allows signals to be transmitted between sensory organs, neurons, and the brain |
Nerves | Send and receive signals for the body |
Neurons | Nerve cells that make up the nervous system |
Interneurons | Nerve cells found only in the brain and spinal cord that move nerve signals in both directions |
Motor neurons | Cells of the brain and spinal cord that send commands from the brain to muscles and organs to carry out functions |
Sensory neurons | Neurons that send signals to and from the body to the brain and spinal cord |
Glial cells | Cells that provide physical and chemical support to neurons |
The spinal cord within the vertebral column is made up of different matter that helps to pass signals throughout the body.
The outer layers of tissue that surround the spinal cord and the brain are called the meninges. These meninges layers produce cerebrospinal fluid that protects and cushions the spinal cord and brain.
White matter is the next layer and is found in the spinal cord and parts of the brain. White matter communicates between the gray matter and the body.
The inner material of the spinal cord and brain is called gray matter. Gray matter processes information and releases new information to the white matter to communicate that information to the body.
Parts of a Neuron
Focus Question
What are the parts of a neuron?
The nervous tissue is composed of cells called neurons. The structure of the neuron helps with its function in the nervous system. Explore the parts of the neuron below.
Parts of a Neuron
Background Image: Crossection of a neuron with Cell Body, Dendrites, Nucleus, Myelin Sheath, Axon, Axon Terminals, and Synapse
Dendrites
Fibrous roots that branch from the cell body. They receive and process signals from other neurons. The number and size vary based on function of particular nervous tissue.
Cell Body
This is also called the soma. The cell body contains all of the cell's organelles.
Nucleus
House the genetic material of the cell.
Myelin Sheath
Fatty substance that coats the axon to speed up signals.
Axon Terminals
Smaller fibrous roots branch from the axon's end. They send signals to other cells of the body.
Axon
Long structure that transmits signals through the nerve cell to and from other cells or tissues.
Synapse
The space between one neuron to another neuron or cell body. The nerve impulse travels through the synapse in the form of neurotransmitters.
Central and Peripheral
Focus Question
How is the nervous system divided?
The different components of the nervous system are combined into two main systems, the central nervous system and the peripheral nervous system. Then these systems are subdivided into additional systems based on what they accomplish for the body.
Central Nervous System (CNS)
If you place a finger on your nose, it will be roughly in the center of your body. That line would cut through the brain and spinal cord. It's an easy way to remember that the brain and spinal cord make up the central nervous system.
Peripheral Nervous System (PNS)
The nerves that extend out from the spinal cord make up the peripheral nervous system, or the periphery.
The peripheral nervous system is divided into different systems based on what they control for the body. Explore the systems below to see how they are organized.
Central Nervous System
Focus Question
What tissues makes up the central nervous system?
The main parts of the central nervous system are the brain and spinal cord. They are protected by the cranium (skull) and by the 24 vertebrae, sacrum, and coccyx of the spine.
The brain and the soft tissues of the spinal cord are also protected by the meninges [mi-nin-jeez], a three-layered section of connective tissues, blood vessels, and spinal fluid.
Dura Mater—This layer of the meninges is closest to the bone. It is composed of tough connective tissues.
Arachnoid Mater—This is the middle layer of the meninges. This netlike membrane includes a subarachnoid space that contains the cerebrospinal fluid.
Pia Mater—This layer is attached to the surfaces of the CNS. It supports and nourishes the underlying layers of brain and spinal cord.
Spinal fluid is more formally known as cerebrospinal fluid (CSF). It circulates through the spaces between the meninges. Cerebrospinal fluid protects the CNS from injury by spreading the force of an impact, like a blow to the head, over a larger area. Cerebrospinal fluid also removes metabolic wastes from the CNS.
Peripheral Nervous System
Focus Question
What nerves make up the peripheral nervous system (PNS)?
The cranial and spinal nerves of the peripheral nervous system lead in and out of the brain and spinal cord. Peripheral nerves also extend into the extremities of the body. As they connect to different tissues, they help manage various functions of the body. These peripheral nerves manage the task of interpreting and relaying information from all senses of the body, both voluntary and involuntary.
Learn how the nerves work together to support the roles of this extensive network. Be sure to record the general organization and function of each part of the nervous system in your guided notes.
Text Version
[Nervous system, central nervous system, peripheral nervous system]
Your nervous system, made up of the central nervous system and the peripheral nervous system, is kind of a big deal. It controls everything you do, including breathing, walking, thinking, and feeling.
But in this video, we’ll focus specifically on the system that connects the central nervous system to the limbs and organs—the peripheral nervous system.
The peripheral nervous system is responsible for sending information to and from the brain and spinal cord.
So if you grab onto a pot handle that’s super hot, your peripheral nervous system tells your brain that it hurts, and your brain tells your hand to move.
The peripheral nervous system is further divided into two divisions: the sensory somatic nervous system and the autonomic nervous system.
The sensory somatic nervous system—or SNS—is a voluntary system that interprets signals received from all your senses and responds to them.
Sensory equals senses.
Imagine a wide receiver, dashing down the field toward the end zone. He turns his head and sees the quarterback throwing a bomb his way. The receiver’s mind concentrates on the flight path of the ball, integrating information from his eyes and ears and communicating actions to his muscles, like “Run faster,” “Cut right,” “Reach,” “Catch.”
Conversely, the autonomic nervous system—or ANS—is an involuntary system that acts without our conscious control. It’s responsible for making sure that all the things your body needs to do to keep you going, like breathing and digestion, continue to work without your having to think about them.
Autonomic equals automatic.
So our wide receiver is voluntarily running and making moves to position himself to catch the ball, but without direct mental input, his heart automatically beats faster and adrenaline hormones are being pumped through his blood stream.
[Increases: energy use, heartbeat, blood pressure]
The autonomic nervous system is also divided into two divisions: the sympathetic, “fight or flight,” and the parasympathetic, “rest and digest,” nervous systems.
Say you’re hiking along a wooded path when, suddenly, an angry bear pops out of the brush. Do you stay and fight or do you turn and run away?
These are “fight or flight” responses.
[Increases: energy use, heartbeat, blood pressure]
In these types of situations, your sympathetic nervous system is called into action. It uses energy and increases your blood pressure and heartbeat to prepare your body for emergencies or crises. It has “sympathy” concerning the situation at hand, and signals for events such as dilating your pupils for better eyesight or increasing your adrenaline to prepare for a strenuous act.
FYI: In this situation, the “fight” response is not recommended.
The parasympathetic nervous system, on the other hand, returns the body back to normal.
So now you’re walking down a different path with no angry animals in sight. You decide to relax in the hammock you just happen to have in your backpack because that bear encounter took a lot out of you.
This calls for “rest and digest” responses.
Now is the time for the parasympathetic nervous system to work to save energy. This is when your blood pressure can decrease, your pulse rate can slow, and digestion can start on that Power Bar you ate before deciding to string up the ol’ hammock.
[Decreases: energy used, heartbeat; Increases: digestion]
Put simply, without a nervous system to organize things like movement, body temperature, blood flow, learning, and memory, the body would be in chaos, with each organ system acting independently of the other.
And that wouldn’t be pretty at all.
[No nervous system equals no order equals no way!]
There are three types of nerves: sensory nerves, motor nerves, and mixed nerves.
eripheral Nervous System
Text Version
The front of the card:
Sensory (afferent) nerves
Image of the human body highlighting some of the nerves in the peripheral nervous system with arrows moving toward the spine.
Show the back of the card:
The front of the card:
Motor (efferent) nerves
Image of the human body highlighting some of the nerves in the peripheral nervous system with arrows moving away from the spine.
Show the back of the card:
The front of the card:
Mixed nerves
Image of a human form, with only the nerves and brain displayed. Red arrows appear to be sending signals from the nerves up to the brain, and blue arrows appear to be sending signals from the brain through the nerves.
Show the back of the card:
Nervous System
The nervous system requires new vocabulary terms to identify the various parts. Check your current understanding of the key terms you have learned.
Nervous System
Text Version
Use one correct word from the list in each of the blanks:
The central nervous system includes the brain and .
Signals from senses and the body's are received by the brain and the spinal cord.
The peripheral nervous system is divided into two divisions, the nervous system and the sensory somatic nervous system.
The sensory somatic nervous system (or SNS) is a system. It interprets signals received from the senses and responds to them.
The autonomic nervous system (ANS) is further divided into the and the parasympathetic nervous systems.
The system returns the body to normal after an emergency.
autonomic
parasympathetic
spinal cord
voluntary
organs
sympathetic
Disorders and DiseaseFocus Question
What are some disorders that affect the nervous system?
Nervous system disorders are often referred to as neurological disorders. They can affect the brain, the spine, or any nerves connecting the two.
Neurological damage can occur through an external injury, like a car accident or an illness. Some can happen due to genetic factors or exposure to different environmental factors or chemicals. An example is radiation, which can damage tissue and cause a breakdown or disruption in the pathway. In some cases, the body creates these disorders with inflammation. Strokes and migraines are a couple of disorders that can happen due to a disruption in the pathways.
Explore other neurological disorders below.
Bell's Palsy
Bell's Palsy is a broadly named condition where swelling occurs around a facial nerve on one side. This leaves a distinct dropping and weakness in the muscles as the impulse from the nerve is unable to travel to the muscles. The disorder often resolves after the inflammation is addressed.
Parkinson's Disease
Parkinson's disease begins with the death of cells in the part of the brain that directs motor functions. There is still no known direct cause for the disorder, but symptoms are characterized as uncontrolled movements. With the brain being affected, the signals seem to change throughout the nervous system's pathway. Almost all patients with Parkinson's will develop dementia as the brain degrades further.
Start Animation
Multiple Sclerosis
Multiple sclerosis is another disorder that can cause uncontrolled body movements. However, the disorder is a breakdown of myelin sheath that covers the axon of nerve cells. The immune system, for some reason, attacks these cells. MS is a disorder that can happen at any age and does not lead to dementia since it has little to do with the brain. Generally, patients have a reduced ability to control specific movements of the body, like lifting their arms or legs properly.
Career Connection
Neurology
Neurologists specialize in many disorders. Their first goal is to determine what is causing symptoms. This can be done with a variety of imaging techniques. Body function tests can also give clues as to which part of the nervous system is affected. Next, a treatment plan is made to help reduce progression and hopefully lead to recovery. Unfortunately, there are several disorders with no real cure and minimal treatment options. However, it is a promising field with more being learned daily.
