Runninig, biking, swimming, playing sports, dreaming, flying, jumping, singing, moving, surfing, jogging,
reading, eating, drinking, fighting, all these things wouldn't be possible with out yor nervous system. Your nervous system
is made up of the brain, spinal cord, nerves, and sense organs such as your eyes and ears. Your nervous system carries information
from your body to the brain and back.
Any thing that makes an organism react is called a stimulus. When an organism reacts to a stimulus it is called a response.
There are two kinds of responses; a voluntary response and an involuntary response. Voluntary responces are when you control
the response such as swatting a fly. Your heart beat however is involuntary.
In your nervous system there are many cells to help it do what it is designed to do. The cells that carry informtion through
your nervous system are nuerons. The messages that a neuron carries are called nerve impulses. Neurons are shaped so that
they can carry these nerve impulses. Nuerons have a large body containing the nucleus, thread-like extensions called dendrites,
and an axon.
The dendrites carry impulses towards the neuron's cell body while the axon carries impulses away. Nerve impulses begin in
the dendrite and go from there to the cell body, and on to the axon. A nueron has only one axon but can have many dendrites.
There can, however, be more than one tip on the axon. Another name for the axon and dendrites are nerve fibers. Nerve fibers
are aranged in parallel bundles and are covered with connective tissue. A bundle of nerve fibers is called a nerve.
There are three kinds of neurons in your body. these neurons are sensory neurons, interneurons, and motor neutrons. Sensory
neutrons pick up stimuli from the environment and converts it into a nerve impulse. The nerve impulse travels along the sensory
neuron until it reaches an interneuron. Interneurons carry nerve impulses from one neuron to another neutron. Sometimes interneutrons
pass impulses from sensory neurons to motor neutrons. A motor neutron sends an impulse to a muscle, and then the muscle reacts.
How a Nerve Impulse Travels
Each nerve impulse begins in the dendrites of a neuron. It moves toward the cell body, and on to the axon tip. the nerve impulse
travels along with the neuron in the form of electrical and chemical signals. When the impulse reaches the end of the neuron,
it can pass to another neuron or it can travel to a muscle or organ. This point is called a synapse. When a nerve impulse
passes at a synapse the dendrite and axon tip do not touch. The axon tips release chemicals that carry the impulse across.
Divisions of the Nervous System
Your nervous system is made up of two divisions, the central nervous system and the peripheral nervous system. the central
nervous system is made up of the brain and spinal cord, while the peripheral nervous system is made up of everything else.
The Central Nervous System
The main parts of the central nervous system is the brain and spinal cord. The brain, which is located in your head, controls
most of the functions of the body. The spinal cord is a very thick column of nervous tissue that links your brain to a lot
of the nerves in the peripheral nervous system.
Your brain contains about 100 billion interneurons. these neurons can recieve messages and give messages to about 1,000
more. There are three main regions in the brain that process information; the cerebrum, cerebellum, and the brain stem. the
cerebrum is the largest part of the brain. Different parts of the cerebrum control different movements and thoughts. The cerebrum
is divided into two halves. The right half is associated with creativity and artistic ability. the left half is associated
with logical thinking, such as mathematics. The cerebellum is responsible for for coordinating your muscles and helps keep
your body. The impulses that tell your feet to walk start in the cerebellum. The brain stem, which lies between the cerebellum
and the spinal column, controls your involuntary actions such as breathing and heart rate. The spinal cord is is merely the
link between your brain and peripheral nervous system.
The Peripheral Nervous System
The peripheral nervous system contains the network of nerves that branch out from the spinal cord, and connect it to the
rest of the body. There are 43 pairs of nerves in the peripheral nervous system. Twelve of the nerves pairs are in the brain
and the other 31 ore in the spinal column. The nerves in the spinal column are called spinal nerves. One nerve in each pair
goes to the right side, while the other nerve goes to the left side.
The nerves of the peripheral nervous system can be divided into two groups, the somatic and autonomatic. the somatic nerves
control voluntary actions, and the autonomatic nerves control involuntary actions.
Sometimes your body moves with out you thinking about it. When this happens it is called a reflex. A reflex is an automatic
response that occurs without conscious control. Usually your movements are are controlled by the brain. With reflexes your
body feels that you are in danger and acts with out your brain. Sensory neurons travel to your spinal cord, and transfer the
the impulse to interneurons. These interneurons take the impulse back to the point of origin and signal that body part to
move. Without reflexes we could get seriously hurt.
A concussion is when your brain gets knocked into your skull. This produces a bruislike injury to your brain. Spinal cord
injuries can occur when your spinal cord is cut or crushed. When this happens the axons are broken and impulses cannot pass
through them. This usually results in paralysis.
THe sense organs pick up information about the world around you, change the information into a nerve impulse, and send
the impulse to your brain.
Your eyes enable you to see what is around you. Your eyes respond to the stimulus of light. They then convert that light
into nerve impulses, which the brain can read in order for you to see. When light hits your eye it first strikes your cornea,
which is a light layer of tissue. It then passes to your pupil. The pupil is the opening where light enters your eye. The
iris is a circular structure that regulates how much light gets into your pupil. Light that passes through the pupil it hits
the lens. the lens focuses light. Once the light goes through the lens it strikes the retina. The retina is a layer of cells
that lines the back of the eye. It contains about 130 million receptor cells that respond to the light. These receptor cells
are separated into two types: rods and cones. Rods allow you to see black white and gray. Cones enable you to see colors.
When the light strikes the rods and cones nerve impulses travel to teh cerebrum.
Your ears are the sense organs that respond to sound. Sound is produced by vibrations. These vibrations can be produced
by anything. Your outer ear is designed to catch sound vibrations in the ear. The vibrations travel down a canal called the
ear canal. At the end of the ear canal is the eardrum. When sound vibrations hit the eardrum it begins to vibrate. These vibrations
pass to three small bones called the hammer, anvil, and stirrup. The hammer passes the vibrations to the anvil, and the anvil
to the stirrup. The stirrup vibrates against a membrane. The membranes channel the vibrations to the cochlea. The cochlea
is a snail-shaped tube that is lined with cells that respond to sound. Finally these cells are stimulated and send the impulses
to the cerebrum.
Smell and Taste
The sense of smell and taste aer closely related. Both depend on chemicals in food or in the air. The chemicals trigger
receptors in the mout and nose. Then nerve impulses travel to the brain. The human nose can distinguish about 50 different
smells, but can only taste five sensations. These are sweet, sour, salty, bitter, and a meatlike taste called umami. You experience
a very wide variety of tases when you eat because you are influenced by taste and smell.
Unlike your other senses the sense of touch is found all over your skin. Your skin has many different touch receptors,
some that respond to hard pressure and some to light. Others respond to temperature change and some to pain. The receptors
the respond to light touch are in the top part of your skin. Receptors deeper in the skin pick up the feeling of pressure.
A drug is any chemical taken into the body that causes changes in a persons body or behavior. Deliberately misusing drugs
is called drug abuse. Any drug can be misused. When drugs like alchohol, marijuana, or cocaine are misuused the effects can
be devastating. Drugs like these are dangerous because they have imediate effects on your brain and other parts of your nervous
systam. There are many diferent kinds of abused drugs. Depressants are drugs that slow down the activity of the centralnervous
system. Depressants may cause relaxed muscles and sleepyness. Stimulants are like the opposite of depressants. They make the
heart beat faster and the breathing rate increase. Inhalants produce mood altering effects. Some althletes take steroids to
improve their perfomance. Steroids are chemicals that are similar to hormones. Alchohol is a drug that is found in many drinks.
Alchohol is a very powerful depressant. The more alchohol you ingest the worse off you'll be. Alchohol absorbs into the organs
and can cause som very bad effects.