Download The Nervous System - Marshall Middle

(Students: Bolded, italicized, and underlined sections will be on the exam)
The Nervous System:
I. Function of the System:
A. The nervous system controls and regulates the body’s activities. It is the
body's information gatherer, storage center and control system. It can
respond to stimuli, transmit nerve impulses, and activate muscles. It collects
information about the external conditions in relation to the body's external state,
analyzes this information, and initiates appropriate responses to satisfy certain
needs. The most powerful of these needs is survival.
B. Parts of the Nervous System: Nerves do not form one single system, but several
which are interrelated. The two main systems of the nervous system are:
1. The Central Nervous System: The brain and spinal cord make up the central
nervous system.
2. The Peripheral Nervous System: The peripheral nervous system is
responsible for the body functions which are not under conscious control like the heartbeat or the digestive system. The smooth operation of the
peripheral nervous system is achieved by dividing it into sympathetic and
parasympathetic systems. These are opposing actions and check on each
other to provide a balance.
C. How the System Works: The nervous system uses electro-chemical impulses
which travel along the length of the cells. The cell processes information from the
sensory nerves and initiates an action within milliseconds. These impulses travel at
up to 250 miles per hour, while other systems such as the endocrine may take
many hours to respond with hormones.
II. The Main Parts of the System: The Brain, Spinal Cord, and Nerves
The main organs in the nervous system are the brain, spinal cord and nerves. The
brain sends messages to the body, and the nerves make you feel things.
A. Brain: The brain (ganglion) controls movement and processes information
transmitted by the nerves. It controls some involuntary movement such as
breathing and the beating of the heart. Other involuntary movements are not
controlled by the brian, for example, the pulling your finger out of a fire. The
brain also sends messages to the nerves which in turn, allow you to feel. The
average adult brain is about three pounds, is pink-gray in color, and is divided
into three main regions:
1. The Cerebrum:
• is the largest part of the brain
• receives and interprets this information from the senses, and is the center
for rational thought and complex activities such as learning,
memorizing, and reasoning
• contains about 12 billion neurons
• is separated into two halves by a deep groove
• the right half of the cerebrum (right hemisphere) controls the left side of the
body, and visa versa
• the right side or hemisphere is responsible for creativity, emotions, art,
and music
• the left side (or hemisphere) is responsible for logical reasoning,
analytical, and math skills
2. The Cerebellum:
• lies below the cerebrum
• is the center for most of your motor skills and balance
• coordinates the voluntary muscles so that your actions are smooth and
efficient (such as swimming, threading a needle, and threading a needle)
3. The Medulla:
• is found at the base of the skull
• controls the vital involuntary actions of the body (such as heart rate,
breathing, muscular action of the digestive tract, swallowing, sneezing,
and coughing)
B. Spinal Cord: The spinal cord is a thick cord of neurons which allows all nerves to
connect to the brain. It runs the length of your spine, through a tube formed by
your vertebrae. Thirty-one pairs of nerves branch off the spinal cord. These
nerves:
1. Transmit feelings and messages to the spinal cord which sends messages to
the brain.
2. Controls actions that do not involve the brain (reflex actions)
C. Nerves (or Neurons): Nerves interpret feelings from the body. They can sense
movement sensations and give information to the spinal cord and brain. They
also receive information from the brain which allows you to move your body.
The main parts of a neuron are:
1. Soma (the main Cell Body): the main center, or core of the cell
2. Dendrite: a nerve fiber that carries messages toward the cell body. A
neuron usually has several dendrites.
3. Axon: a nerve fiber that carries messages away from the cell body. There
is only one axon for each neuron. Some axons are surrounded by a fatty
covering called a myelin sheath that protects the axon and allows
impulses to travel faster along the axon.
4. Synaptic Gap: Neurons do not touch each other, and between the axon of
one cell, and dendrite of another cell is a gap called a synapse or synaptic
gap. This gap is only about .005 millimeters wide.
5. Neurotransmitters: When an impulse reaches the end of an axon, the axon
releases a chemical neurotransmitter into the synapse, which then carries the
impulse to the dendrite of the next cell.
The three types of neurons are:
1. Sensory Neurons: pick up stimuli and send the impulses produced by stimuli
to the brain and spinal cord. Some of the stimuli picked up by sensory
neurons include color, heat, noise, touch, and hunger. They are found in the
skin, muscles, joints, internal organs, and sense organs.
2. Motor Neurons: transfer impulses from the spinal cord and brain to the
muscles and glands. Motor neurons control voluntary actions such as
walking, talking, or playing an instrument. They also control many
involuntary actions, such as heartbeat, enzymes, and the movement of food
through the digestive system.
3. Association Neurons: Association neurons relay impulses between sensory
and motor neurons. They also relay impulses from sensory and motor
neurons to the brain. They are found only inside the brain and spinal cord.
III. Interaction with Other Systems:
The nervous system interacts with every system, because it provides every system
with information that allows it to move and function. Some examples of systems
that directly interact with the system include:
• The Skeletal System: The skeletal system protects the major parts of the
nervous system (brain protected by the skull, and spinal cord surrounded
by vertebrae).
• The Integumentary System: Nerves use the skin to sense feelings. The skin is the
main body organ which allows nerves to receive information from an outside
environment.
• Muscular System: The muscular system needs information from the nervous
system to know what muscles to move. The nerves also tell the muscles to
move away from things that can harm the body.
IV. Some Diseases and Disorders:
• Paralysis: Occurs when motor neurons are not able to activate the mucles of the
body. Impulses from the brain to the muscles are cut off. Normally, paralysis
is a result of the vertebra in the backbone being pushed on top of another,
cutting or crusing the nerves in the nerve cord. As of now, no cure.
• Tourette Syndrome: A syndrome that begins in childhood and manifests itself
through tics. The tics include frequent, irregular movements of the head neck
and shoulders. As the syndrome progresses these tics may also include
snorting, sniffing, and involuntary vocalization. Meds may alleviate some of
the symptoms, but there is no cure.
• Parkinson’s Disease: Parkinson’s is diagnosed as slowing of the voluntary
movements, muscular rigidity, and tremor at rest. These symptoms result from a
reduction in neurons that make dopamine. Dopamine usually acts as an
inhibitory neurotransmitter, which allows for full muscle control, without this
it is impossible for patients to fully regain control.
• Huntington Disease: Patients usually exhibits symptoms in the third or fourth
decade of life. Those with huntington have a tendency to fidget which over
months or years develops into jerky, uncontrolled movements. As the disease
progresses it leads to dementia and usually death from infection.
• Alzheimer Disease: Alzheimer Disease is the most common cause of dementia
in western civilization. It affects more women than men, and lasts around
five years. The disease often causes memory loss and the inability to fully
function independently. There is no cure.
• Meningitis: Meningitis is a caused by a bacteria or virus in which the
protective membranes that surround the brain and spinal cord are
attacked. Death can occur.
Some of the major nerves in the body: