Download The Nervous System - Valhalla High School

Human organ systems: The
Nervous System
What is the purpose of the nervous
system?
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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.
Divisions of the Nervous System
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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).
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Let’s draw part I
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In the space provided on the note packet, copy
and label the diagram of the nervous system
from the blackboard.
Stimulus and response.
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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.
Examples of stimulus and response.
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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.
External Stimuli
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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
Relfexes
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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
Basic unit of the nervous system.
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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.
Let’s Draw II
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Copy and label the diagram of the neuron from
the blackboard.
Types of neurons
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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.
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How does the message travel along
neurons?
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You can think of your nervous system as a series of oneway 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
Action potential and threshold
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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.
4 main tasks
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The nervous system works with information,
information from both your internal and
external environments. There are 4 things the
nervous system must do.
1.
 2.
 3.
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Receive information
Transmit information
Interpret information
Send information
How it works.
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You place your hand on a hot iron.
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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.
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