Intro to the Nervous System

The Nervous System

The nervous system’s primary function is to control and communicate with other organs in the body. This includes organs such as muscles and bones. The nervous systemThe organ system that controls body functions using electrical and chemical signals. can be thought of as an anatomical system. We break it up into two parts. The central nervous systemComposed of the brain and spinal cord; integrates and processes information.  (CNS) consists only of the brain and spinal cordThe central nervous system structure that relays signals between the brain and body.. The peripheral nervous systemPNS All nervous tissue outside the CNS; includes nerves and ganglia. (PNS) includes everything else.  When I say everything else what I mean is all of the nerves that are in your somatic tissues. There are two kinds of nerves that arise from the central nervous system. These are cranial nervesNerves that arise from the brain and control head and neck functions. and spinal nerves.

Spinal and Cranial  Nerves

A nerve itself is a collection of neuronsThe functional cells of the nervous system that transmit signals.. A neuron is a nervous system cell. It exhibits the purpose of having an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission. to control other organs in the body. As pictured here this is the brachial which means upper arm and plexus which only means network. Your own or nerve, the nerve that you hit when you bump your funny bone, is a collection of neurons. It arises from this upper arm network of nerves. These nerves have left the spinal cord in the lower neckNarrow region just below the head; common fracture site. and upper back region.  In the image on the right, you can see an inferiorBelow or toward the lower part of the body. view of the brain. We are looking up from underneath the brain. This wrinkly part here is the cerebellumThe brain region responsible for balance, coordination, and fine motor control., or the little brain, which is posterior. All of these little yellowy things are the 12 pairs of cranial nerves. They arise from the brain stem and other inferior structures in the brain.

Nervous System Organization

To be perfectly honest, the nervous system has such varied functions. It really can’t be thought of as an anatomical system. No part works alone. There can be thousands of neurons just helping you scratch your headRounded proximal end that fits into the acetabulum of the hip bone. in amazement right now.  Do it. Scratch your head.  Therefore more often in this class we will think of the nervous system organized more into function. Let’s examine some of the terminology on this slide. We will use this terminology consistently throughout the next four chapters of the nervous system.

As you may have guessed sensory over here on the right is information that is incoming to the brain. A mosquito lands on your arm. You have a pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. sensor that senses its touch on your skinThe body’s largest organ, providing protection and regulation.. It sends an action potential or an electrical currentThe flow of electrical charge, as in ions moving across a neuron’s membrane. to your brain. This alerts it that a mosquito is about to suck your blood. Those sensory neuronsNeurons that carry information from sensory receptors to the CNS. and nerves would also be thought of as somatic because they are part of your skin bone and muscle and not part of your squishy organs.

Right now you have chemosensors in your stomach. They are sending signals to other parts of your digestive system. These signals coordinate its movements and digestive activity. Those sensors are sensory but they are visceral because they are in your guts. Over on the other side of this picture is a similar setup. You have motor output in neurons and nerves. There are motor output neurons that go to somatic tissues like bone and muscle. We’ve talked about something called the neuromuscular junctionThe connection between a motor neuron and a muscle fiber. which is motor somatic output of an action potential.  Right now there are regions in your brain stem. They influence your breathing rate. They also affect your heart rate. The neurons leaving those centers and innovating your heart and lungs would be visceral motor neuronsNeurons that carry outgoing information from the CNS to effector organs..