Overview of the Nervous System

Introduction: Welcome to Unit Three...we're almost done!!! The first major topic of unit three is the nervous system. In this section, we are going to take a look at the central nervous system, peripheral nervous system, tissues involved, the structure of a neuron as well as its parts, and the myelin sheath.

CNS & PNS
~Central Nervous System: Commonly seen abbreviated as CNS. It is composed of the brain and
spinal cord.

This picture depicts different sections of the CNS and was found at http://www.faqs.org.
~Peripheral Nervous System: Commonly seen abbreviated as PNS. It is composed of the nerves
that lie outside of the CNS.

Here is a picture of the PNS that breaks it even further into the parasympathetic and sympathetic that will be discussed later. This picture was found at http://users.rcn.com.



Functions

*Nervous System has 3 Functions

1. Receives Sensory Input:

*Sensory receptors respond to stimuli by generating nerve impulses

2. CNS Performs Integrations:

*Fancy way of saying it processes the information from sensory input, and then it decides what to do

3. CNS Generates Motor Output:

*Nerve impulses got to muscles and glands to stimulate movement (if at muscle) or secretion (if at glands)

Nervous TissuesThis is a picture of neuron tissue. It was found at http://washington.uwc.edu.

~Contains two types of cells

1. Neurons: Transmit nerve impulses

2. Neuroglia: Support and nourish neurons

Neuron Structure

Below is a picture of a Neuron Structure. Further in Major Topic One of Unit three, you can find a picture of my homemade neuron structure. The below picture was found at http://kvhs.nbed.nb.ca

~3 types of neurons

1. Sensory Neuron: takes messages (nerve impulses) from sensory

sensory receptor to CNS

2. Interneuron: take the messages and processes it

3. Motor Neuron: takes nerve impulses away from CNS to the effector,

Muscle or gland

~Other Definitions:

1. Sensory Receptor: detect changes in the environment (pain, heat, cold, etc.)

2. Effector: carries out responses to the changes, internal or external

~3 parts of a neuron

1. Cell Body: contains nucleus and other organelles

2. Dendrites: extensions that receive signals from sensory receptors or

other neurons

3. Axon: conducts nerve impulses, can be fairly long…sometimes

extending to the end of a limb (up to one meter long)

Above is a picture labeling the different parts of a neuron, which was found at http://training.seer.cancer.gov.

Myelin Sheath

~Protective covering over axons formed by a type of neuroglia called Schwann

Cells. (PNS)

~Oligodendrocytes do this in the CNS

~Gaps in between myelin sheath are called nodes of Ranvier

~Long axons tend to have it, but not shorter ones.

~Purposes:

1. Insulator

2. Nerve regeneration if an axon is severed, sheath remains and acts as a

Passageway for new fiber growth

3. Saltatory (“jumping”) propagation: makes action potential jump

To nodes which increases speed and conserves energy

The above picture from http://trc.ucdavis.edu, depicts the myelin sheath. It goes into further detail that will be addressed in the next section regarding the action and resting potential.


Conclusion: That was a brief overview of the nervous system of the human body. As you navigate your way through this section, you will go deeper into different aspects of the system. next up, let's take a look at nerve impulses, which include the resting and action potential.