UNIT 1. INTERACTION
THE NERVOUS SYSTEM
Living organisms are made up of cells. A group of cells form
a tissue. A group of tissues form an organ. A group of organs form a system. We
have different systems, for example, the nervous system. It sends messages from
the brain to the different parts of our body, such as the locomotor system
which responds to the stimuli of our senses.
·
The central nervous system
The central nervous system has got two
parts: the brain and the spinal cord.
-
The brain controls our nervous system. It is
protected by the skull (or cranium) and it has three parts:
o
The cerebrum is the biggest part of our brain.
We process information from our senses and we do cognitive thinking (take
decisions, study, play…)
o
The crebellum controls our movements,
coordination and balance.
o
The brain stem is the continuation of the spinal
cord and it controls involuntary actions (brething, heartbeat…)
-
Th espinal cord is made up of nerve tissue . It
is protected by the vertebrae. It controls our réflex actions.
·
The peripheral nervous system
It is made up of nerves and nerves are made
up of neurons (tiny cells) that transform information using chemical and
electrical signals. Nneurons have different tasks:
1.
Sensory neurons collect information from our
sense organs.
2.
The brain interprets information and sends
signals to the rest of the body.
3.
Motor neurons send messages from the brain to
our locomotor system.
THE SENSES
·
Sight
1.
Light enters through the pupil and the cornea.
2.
The amount of light that enters is controlled by
the iris (it also gives the eye the colour).
3.
The lens focuses the light on the retina at the
back of the eye.
4.
Nerve receptors in the retina transmit the
information to the optic nerve which sends the information to the brain. The
place where the optic nerve leaves the eye is called a blind spot and it does
not respond to light.
·
Hearing
1.
Sound waves enter through the auditory canal in
the outer ear and the eardrum vibrates.
2.
These vibrations make the three small bones in
the middle ear víbrate too.
3.
The vibrations finally reach the cochlea in the
inner ear, where they become electrical signals.
4.
The auditory nerve sends the signals to the
brain.
·
Smell
Chemicals in the air enter our nose through
our nostrils. The chemicals come into contact with the nerve receptors which
send the information to the brain through the olfactory nerve.
·
Taste
Substances enter our mouth and come into
contact with our tongue, which is covered in taste buds that have receptor
cellls. The receptor cells detect the different tastes and send the information
to the brain.
·
Touch
The middle layer of our skin, the dermis,
contain nerves and blood vessels. These detect sensation. Th enerves send the
information to the brain through the periphral nervous system and the spinal
cord.
HOW ME VOVE
Our body moves in response to signals from the brain. These
signals travel from the nervous system to our muscles. They contract or relax
to allow us to move. The locomotor system is made up of: the skeleton, joints
and muscles.
·
The skeleton: is made up of bones. There are
three types of bones:
-
Short bones which provide support and stability
(vertebrae, for example).
-
Flat bones which protect the nternal organs
(ribs, pelvis)
-
Long bones form the limbs and are used for
movement.
·
Joints
Bones are connected at the joints by
ligaments. The ends of bones at the joint are covered in tissue called
cartilage. There are three types of joints:
-
Fixed: do not move like the skull.
-
Semi-flexible: that allow Little movement
(vertebrae in the spine)
-
Flexible: most of them are flexible and make
movements.
·
Muscles
Muscles are controlled by the nervous
system which makes them contract and relax. There are three types:
-
Skeletal muscles: are joined to the bones by the
tendons. They work in pairs. They are voluntary muscles.
-
Smooth muscles: are found in organs like the
intestines and the stomach. They are involuntary muscles.
-
The cardiac muscle: makes up our heart. It is an
involuntary muscle.
