Human organ systems: Human organ systems: The Nervous SystemThe Nervous System

What is the purpose of the What is the purpose of the nervous system?nervous system?

The chief responsibility of the The chief responsibility of the nervous system is to help the body nervous system is to help the body maintain homeostasis.maintain homeostasis.

The nervous system acts quickly and The nervous system acts quickly and its effects are generally short its effects are generally short lasting.lasting.

Along with the endocrine system, Along with the endocrine system, the nervous system works to the nervous system works to regulate your metabolic activities.regulate your metabolic activities.

Divisions of the Nervous Divisions of the Nervous SystemSystem

There are two main divisions of the There are two main divisions of the nervous system.nervous system. 1. The central nervous system (CNS): 1. The central nervous system (CNS):

Consists of your brain and spinal column. Consists of your brain and spinal column. 2. The peripheral nervous system (PNS): 2. The peripheral nervous system (PNS):

Consists of all the nerves that branch Consists of all the nerves that branch away from the central nervous system. away from the central nervous system. (This is further divided into the somatic (This is further divided into the somatic and autonomous nervous systems).and autonomous nervous systems).

Let’s draw part ILet’s draw part I

In the space provided on the note In the space provided on the note packet, copy and label the diagram packet, copy and label the diagram of the nervous system from the of the nervous system from the blackboard.blackboard.

Stimulus and response.Stimulus and response.

Your nervous system works through a Your nervous system works through a series of actions and reactions, often series of actions and reactions, often referred to as stimulus and response.referred to as stimulus and response.

A stimulus is any agent or substance A stimulus is any agent or substance that provokes a change in an that provokes a change in an organism by producing an impression organism by producing an impression on a sensory nerve or organ.on a sensory nerve or organ.

A response is a coordinated action to A response is a coordinated action to a stimulus.a stimulus.

Examples of stimulus and Examples of stimulus and response.response.

The stimulus can arise from both the interior The stimulus can arise from both the interior or exterior environment.or exterior environment.

Examples from interior environment:Examples from interior environment:

Stimulus: Pressure on the urinary bladder Stimulus: Pressure on the urinary bladder

Response: Brain signals need to use the bathroom.Response: Brain signals need to use the bathroom.

Stimulus: Lack of food in stomach.Stimulus: Lack of food in stomach.

Response: Brain signals that body needs to eat.Response: Brain signals that body needs to eat.

External StimuliExternal Stimuli

Some examples of external stimuliSome examples of external stimuli

Stimulus: Walking out of a dark Stimulus: Walking out of a dark room into sunshine.room into sunshine.

Response: Squinting or covering of Response: Squinting or covering of eyes.eyes.

Stimulus: Room is too warm.Stimulus: Room is too warm.

Response: Body begins to sweatResponse: Body begins to sweat

RelfexesRelfexes

A reflex is an unconscious response to a A reflex is an unconscious response to a stimulus.stimulus.

An example of a reflex action is when An example of a reflex action is when you accidentally put your hand on a hot you accidentally put your hand on a hot stove.stove.

You will draw your hand away without You will draw your hand away without ever thinking about what you are doing.ever thinking about what you are doing.

Reflexes are a survival mechanism.Reflexes are a survival mechanism. The reflex arc

Basic unit of the nervous Basic unit of the nervous system.system.

The basic unit of the nervous system is the nerve cell, or The basic unit of the nervous system is the nerve cell, or neuron.neuron.

Nerve cells are used to transmit information from sensory Nerve cells are used to transmit information from sensory organs, to the central nervous system and to the appropriate organs, to the central nervous system and to the appropriate muscles or organs.muscles or organs.

Neurons are generally bundled together with other neurons to Neurons are generally bundled together with other neurons to form nerves. Nerves can consist of only a dozen strands of form nerves. Nerves can consist of only a dozen strands of neurons or thousands.neurons or thousands.

Let’s Draw IILet’s Draw II

Copy and label the diagram of the Copy and label the diagram of the neuron from the blackboard.neuron from the blackboard.

Types of neuronsTypes of neurons There are three types of neurons.There are three types of neurons.

1. Afferent (Sensory) neurons. These 1. Afferent (Sensory) neurons. These neurons carry information from the sense neurons carry information from the sense organs to the central nervous system.organs to the central nervous system.

2. Interneurons. These neurons comprise 2. Interneurons. These neurons comprise the spinal column and brain. They function the spinal column and brain. They function to interpret the information received.to interpret the information received.

3. Efferent (motor) neurons. These 3. Efferent (motor) neurons. These neurons carry information from the central neurons carry information from the central nervous system to the muscles/organs.nervous system to the muscles/organs.

How does the message How does the message travel along neurons?travel along neurons?

You can think of your nervous system as a You can think of your nervous system as a series of one-way streets in your body. series of one-way streets in your body.

The information is sent as an alternating The information is sent as an alternating chemical/electrical message.chemical/electrical message.

The message travels as an electrical signal, The message travels as an electrical signal, originating in the cell body and sent along the originating in the cell body and sent along the axon. axon. The myelin sheath helps increase the speed the impulse travels.

The message reaches the axon terminals which The message reaches the axon terminals which causes a release of chemical neurotransmitters. causes a release of chemical neurotransmitters. chemicals are received by the dendrites of the chemicals are received by the dendrites of the adjacent neuron and converted back into an adjacent neuron and converted back into an electrical impulse.electrical impulse.

The space between neurons is called the The space between neurons is called the synapse.synapse.

animation of neurotrasmitters at work

Action potential and Action potential and thresholdthreshold

Nervous impulses are said to be all or nothing.Nervous impulses are said to be all or nothing. Either the sensory imput reaches the necessary Either the sensory imput reaches the necessary

threshold and begins to send an impulse or it threshold and begins to send an impulse or it does not.does not.

Once the threshold is reached, the neuron will Once the threshold is reached, the neuron will stimulate the next neuron in the chain, and so on stimulate the next neuron in the chain, and so on and so on until the message reaches the CNS.and so on until the message reaches the CNS.

The intensity of the message is controlled by two The intensity of the message is controlled by two factors, the number of neurons activated and the factors, the number of neurons activated and the frequency of the sensation.frequency of the sensation.

4 main tasks4 main tasks

The nervous system works with The nervous system works with information, information from both information, information from both your internal and external your internal and external environments. There are 4 things environments. There are 4 things the nervous system must do.the nervous system must do. 1. Receive information1. Receive information 2. Transmit information2. Transmit information 3. Interpret information3. Interpret information 4. Send information4. Send information

How it works.How it works. You place your hand on a hot iron.You place your hand on a hot iron.

Step 1. Your body Step 1. Your body receivesreceives information by information by the sensory neurons in your hand.the sensory neurons in your hand.

Step 2. Your afferent (sensory) neurons Step 2. Your afferent (sensory) neurons transmittransmit the information about the hot the information about the hot stove to your central nervous system.stove to your central nervous system.

Step 3. The interneurons in your brain and Step 3. The interneurons in your brain and spinal cord spinal cord interpretinterpret this information. this information.

Step 4. Efferent (motor) neurons Step 4. Efferent (motor) neurons sendsend the the command to move your hand to the command to move your hand to the appropriate muscles.appropriate muscles.