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NERVOUS SYSTEM
What is it and how does it work???
NERVOUS SYSTEM BASICS
The nervous system consists of the brain, spinal
cord, sensory organs, and all of the nerves that
connect these organs with the rest of the body.
Together, these organs are responsible for the
control of the body and communication among its
parts.
The nervous system is divided into the CNS and
the PNS.
1. CNS (Central Nervous System) which is the brain and spinal cord
2. PNS (Peripheral Nervous System) which consists of all of the nerves that
lie outside of the CNS
Central Nervous System
 The brain and spinal cord form the control
center known as the central nervous system
(CNS), where information is evaluated and
decisions made.
Peripheral Nervous System (PNS)
 The sensory nerves (neurons) and sense organs of the
peripheral nervous system (PNS) monitor conditions inside
and outside of the body and send this information to the
CNS.
 Motor neurons in the PNS carry signals from the control
center to the muscles, glands, and organs to regulate their
functions.
BRAIN
Center of the nervous system
Coordinates all of the body’s activities
Most complex organ in the human body
Made of approximately 100 billion nerve cells (neurons)
Three major parts are the cerebrum, cerebellum, and brain stem
 Cerebrum: higher brain functions, interpreting sensory
impulses, and initiating muscle movements; stores information
 Cerebellum: helps to control motor functions such as balance,
posture, and coordination of complex muscle activities
 Medulla: processes involuntary body functions related to
homeostasis; monitors blood pressure and oxygen levels and
regulates heart rate, controls the rate of breathing, vomiting,
sneezing, coughing, and swallowing reflexes
*How do messages from the brain reach all parts of
the body?
*How do messages from all parts of the body reach
the brain?
NERVE CELLS ARE CALLED NEURONS!!!
The messages are carried through electrical and chemical
signals.
The messages can travel at slightly different rates but some
have been recorded to travel up to 250 mph (366.7 feet per
second)!!!
(Messages to muscles for coordination are some of the fastest while those for pain are some
of the slowest)
How a Neuron Fires (video)
http://www.youtube.com/watch?v=C4Gt322-XxI
How does your body/brain know what to react to in
order to maintain homeostasis?
 The nervous system maintains homeostasis by controlling and
regulating the other parts of the body.
 A deviation from a normal set point acts as a stimulus to a receptor,
which sends nerve impulses to a regulating center in the brain.
 The brain sends information to act in such a way that a response to the
stimulus occurs. (Hmmm…respond to stimuli, adapt to changes, we
have heard this before…think, characteristics of living things)
Example: receptors throughout the body are constantly sensing
temperature, if the temperature deviates away from the average 98.6º F,
neurons take the information to the hypothalamus in the brain and the
information is interpreted, then a response in sent to parts of the body to
react in a specific way was a lowering of body temperature, the effector
acts to increase body temperature.
What helps the brain receive information from outside
the body?
The sensory organs (the five senses).
Sight
Hearing
Taste
Touch
Smell
Reflex vs. Reaction
 Reaction is voluntary while reflex is involuntary
 Reaction takes place through sensory nerves that bring back
messages from the brain to the motor nerve.
 In a reflex reaction, sensory nerves bypass the brain and go up to
the spinal cord.
 This is why a reflex is faster than a reaction.
Reflex Examples
NERVOUS SYSTEM
FUN FACTS
- There are more nerve cells in the human brain than there are
stars in the Milky Way.
- If we lined up all the neurons in our body it would be around
600 miles long.
- A newborn baby's brain grows almost 3 times during the course
of its first year.
- The left side of human brain controls the right side of the body
and the right side of the brain controls the left side of the body.
- A new born baby loses about half of their nerve cells before they
are born.
- As we get older, the brain loses almost one gram per year.
- There are about 13, 500,00 neurons in the human spinal cord.