1. Human organ systems: The Nervous System

2. What is the purpose of the nervous system?
The chief responsibility of the nervous system is to help the body maintain homeostasis.
The nervous system acts quickly and its effects are generally short lasting.
Along with the endocrine system, the nervous system works to regulate your metabolic activities.

3. Divisions of the Nervous System
There are two main divisions of the nervous system.
1. The central nervous system (CNS): Consists of your brain and spinal column.
2. The peripheral nervous system (PNS): Consists of all the nerves that branch away from the central nervous system. (This is further divided into the somatic and autonomous nervous systems).

4. Let’s draw part I
In the space provided on the note packet, copy and label the diagram of the nervous system from the blackboard.

5. Stimulus and response.
Your nervous system works through a series of actions and reactions, often referred to as stimulus and response.
A stimulus is any agent or substance that provokes a change in an organism by producing an impression on a sensory nerve or organ.
A response is a coordinated action to a stimulus.

6. Examples of stimulus and response.
The stimulus can arise from both the interior or exterior environment.
Examples from interior environment:
Stimulus: Pressure on the urinary bladder
Response: Brain signals need to use the bathroom.
Stimulus: Lack of food in stomach.
Response: Brain signals that body needs to eat.

7. External Stimuli Some examples of external stimuli
Stimulus: Walking out of a dark room into sunshine.
Response: Squinting or covering of eyes.
Stimulus: Room is too warm.
Response: Body begins to sweat

8. Reflexes A reflex is an unconscious response to a stimulus.
An example of a reflex action is when you accidentally put your hand on a hot stove.
You will draw your hand away without ever thinking about what you are doing.
Reflexes are a survival mechanism.
The reflex arc

9. Basic unit of the nervous system.
The basic unit of the nervous system is the nerve cell, or neuron.
Nerve cells are used to transmit information from sensory organs, to the central nervous system and to the appropriate muscles or organs.
Neurons are generally bundled together with other neurons to form nerves. Nerves can consist of only a dozen strands of neurons or thousands.

10. Let’s Draw II
Copy and label the diagram of the neuron from the blackboard.

11. Types of neurons There are three types of neurons.
1. Afferent (Sensory) neurons. These neurons carry information from the sense organs to the central nervous system.
2. Interneurons. These neurons comprise the spinal column and brain. They function to interpret the information received.
3. Efferent (motor) neurons. These neurons carry information from the central nervous system to the muscles/organs.

12. How does the message travel along neurons?
You can think of your nervous system as a series of one-way streets in your body.
The information is sent as an alternating chemical/electrical message.
The message travels as an electrical signal, originating in the cell body and sent along the axon. The myelin sheath helps increase the speed the impulse travels.
The message reaches the axon terminals which causes a release of chemical neurotransmitters. chemicals are received by the dendrites of the adjacent neuron and converted back into an electrical impulse.
The space between neurons is called the synapse.
animation of neurotrasmitters at work

13. Action potential and threshold
Nervous impulses are said to be all or nothing.
Either the sensory imput reaches the necessary threshold and begins to send an impulse or it does not.
Once the threshold is reached, the neuron will stimulate the next neuron in the chain, and so on and so on until the message reaches the CNS.
The intensity of the message is controlled by two factors, the number of neurons activated and the frequency of the sensation.

14. 4 main tasks
The nervous system works with information, information from both your internal and external environments. There are 4 things the nervous system must do.
1. Receive information
2. Transmit information
3. Interpret information
4. Send information

15. How it works. You place your hand on a hot iron.
Step 1. Your body receives information by the sensory neurons in your hand.
Step 2. Your afferent (sensory) neurons transmit the information about the hot stove to your central nervous system.
Step 3. The interneurons in your brain and spinal cord interpret this information.
Step 4. Efferent (motor) neurons send the command to move your hand to the appropriate muscles.