The =
Nervous
System
-
The nervous system is made up of the brain, the spinal cord, =
and
all the nerves in your body.
-
It detects and responds to changes inside and outside of your body. (Receiv=
es
information; interprets information; then responds to the information.)
- =
ex. Doorbell ring.
- = Nerves in ear receives information and sends it to brain<= o:p>
- =
Brain interprets information as sound of ring
- =
Brain responds by sending message to arms and legs muscle=
s,
to go to the door
Nerves Cells
-
The nervous system is made up of billions of nerve cells called neurons
-
which are the basic unit of structure and function in the nervous system
-
The job of neurons is to carry messages
The neuron is made up of three part=
s
1.
2.
3.
There
are three kinds of neurons
1.
2.
3.
The
messages neurons send are called impulses
The Brain
-
The brain is the control center of your body
-
It is made up of three main parts
1.
·
the large upper portion of brain
·
controls movement and speech
·
interprets information from sense organs
·
controls functions like thinking, reasoning, and remember=
ing
2.
·
Back of head; beneath cerebellum
·
Smaller than cerebrum
·
Impulses pass through this after it begins in cerebrum
·
Adjusts impulses so movements are smooth and graceful
·
Also maintains balance
3.
·
Nerves from cerebrum and cerebellum form a thick stalk ca=
lled
the brain stem
·
The medulla is the lower part of the brain stem
·
It connects the brain to the spinal cord
·
Controls many involuntary actions, such as, digestion,
breathing, blood pressure and heart rate
The Spinal Cord
-The
spinal cord is made up of many nerves that extend from the medulla all the =
way
down the back.
-All
sensory and motor nerves found below the neck pass through the spinal cord =
on
their way to the brain.
-Vertebrae
protect your spinal cord from injury.
-31
pairs of nerves extend from the spinal cord.
-These
nerves go to different parts of the body.
The Nerve Pathways
-The synapse are tiny gaps betwe=
en the
dendrites of one neuron and the axon of the other.
-This
is how impulses pass from one neuron to another.
-Chemicals
are the reason impulses can get across a synapse for example, a shiver
response.
-A
reflex is an automatic response controlled by the spinal cord and allow the body to react quickl=
y to
painful or dangerous situations.
-Unlike
most actions of the body your brain does not control reflexes. Your spinal =
cord
controls reflexes. for exampl=
e,
touching a hot stove.
-Receptors
in your skin transfer impulses to sensory neurons. Impulses are then sent to the spin=
al
cord.
-Impulses
pass through associative neurons to the motor neurons carrying impulses
to
the muscles in your hand.
-The
muscles contract and cause you to pull your hand away.
-The
spinal cord sends the messages to the brain. The brain receives and interpr=
ets
the message.
-Then
sends the message to pain receptors in your hand. “Ouch!”
The Five Senses
-Your
senses organs include your eyes, ears, skin, tongue, and nose.
-
Each sense organ has special cells that detect information.
-
These cells are called receptor cells.
-
The receptor cells send nerve impulses to sensory neurons, which carry the
impulses to the brain.
-
The brain interprets the impulses as a particular sensation, such as taste =
or
vision.
Vision
-
Eyes are very sensitive to light.
Can see a lit match 80 km away – i.e. if on mountain top
-
Light first enters the cornea =
(a
clear, curved layer of eye)
-
Behind the cornea is a smooth muscle called the iris. This is the
coloured part of the eye.
-
The iris controls the amount of light that enters the eye.
-
The opening in the middle of the iris is the pupil.
-
In dim light the iris widens to let more in (makes pupil larger).
-In
bright light the iris narrows to permit less light (makes pupil smaller).
-
Light the passes through the pupil enters the lens.
-
Light is then projected to the ret=
ina.
-
The retina has two types of receptor cells, which are Rods and Cones.
-
Rods can only detect black and white, and are sensitive to dim light
-
Cones detect all other colors, and are sensitive to bright light.
-When
light strikes the rods and cones, impulses are produced .
-The
impulses are carried by the optic nerve&nb=
sp;
to the brain.
Hearing
-Special
receptors in your ears respond to vibrations made by sound waves.
-The
ear is divided into 3 main parts: outer ear, middle ear and inner ear.
-The
outer consists of the ear flap and the ear canal.
-Sound
waves collected by the ear flap travel down the canal and strike the ear dr=
um.
-The ear drum is a thin membrane separating the ear canal from the middle ear. <= o:p>
-When
sound waves hit the ear drum it begins to vibrate. The vibrations then pass on to bon=
es in
the middle ear. These bones a=
re the
smallest bones in your body.
-Vibrations
leave the middle ear bones and are transferred to a coiled fluid filled
structure called the cochlea.
-Nerve
impulses are carried to the brain by the auditory nerve where they are
interpreted as sound.
-Your
ears also help maintain balance.
Touch
-Your
skin is the largest sense organ in your body.
-Your
skin can sense touch, pressure, pain, heat and cold.
-Touch
receptors are found at the surface of the skin or near the surface of the s=
kin.
-Pressure
and pain receptors are found deep in the skin.
-Skin
receptors are not evenly distributed on the body ie: finger tips have more =
than
your back.
Taste
-This organ is stimulated by
chemicals.
-Receptors
for taste are located on your taste buds (tongue).
-These
are activated when food mixes with saliva.
-Nerve
impulses are sent to the brain and interpreted as taste.
-Taste
buds can detect only four tastes: sweet, sour, salty and bitter.
-Different
food flavours are detected because of different combinations of these
receptors.
Smell
-Flavour of food is also detecte=
d by
the odour receptors in your nose.
-When
your nose is blocked your odour receptors do not function as well. This is why food often tastes blan=
d when
you have a cold.