The document summarizes the key human body systems involved in interaction: the sense organs, nervous system, and locomotor system. It describes how the sense organs (sight, smell, taste, hearing, touch) detect stimuli and send this information to the brain via sensory neurons. The brain then interprets the information and sends orders to the muscles via the nervous system. Upon receiving signals, the muscles and skeleton (via joints) work together as the locomotor system to move the body and allow interaction with the environment.

1. Unit 2 INTERACTION SUMMARY
1
THE SENSE
ORGANS
HUMANS are LIVING THINGS who carry out
INTERACTION using…
PROCESS The sense organs detect
the change (something
different)
The sensory
neurons send
information to
the brain.
The brain interprets
the information and
decides what to do.
The brain sends an
order to the muscles.
The muscles move
the body.
Stimulous
Sense organs
Locomotor System
Nervous System
SIGHT
1. Light enters our eye through the
cornea and the pupil.
2. The iris is a muscle that makes the
pupil bigger or smaller.
3. The lens focuses the light which
allows images to be projected onto
the retina at the back of our eye.
4. Nerve receptors in the retina send
this information along the optic
nerve to our brain.
SMELL
Our sense of smell detects chemicals in
the air. When air enters our nose
through our nostrils, these chemicals
come into contact with the nerve
receptors. The nerve receptors send this
information along the olfactory nerve
to our brain.
TASTE
The receptor cells for taste
are on the tongue inside
each taste bud. They detect
different tastes (bitter,
sour, salty and sweet).
HEARING
1. Sound waves enter our ear through the auditory canal (outer ear) and make
the eardrum vibrate.
2. This vibration also causes the three small bones in our middle ear to vibrate.
3. When these vibrations reach the cochlea in our inner ear, they are
transformed into electrical signals.
4. The auditory nerve sends these signals to our brain.
The main function of the semicircular canals in our inner ear is to keep our
balance and equilibrium.
TOUCH
The middle layer of skin,
called the dermis,
contains nerves and tiny
blood vessels. These
nerves detect sensations,
such as temperature,
pain and texture and
send this information to
our brain.

2. Unit 2 INTERACTION SUMMARY
2
CONCEPT It is the system that we use to receive information from the
sense organs, and after analyzing and interpreting this
information, it responds sending messages which cause the body
to react. It is made up of neurons. It is divided into two parts: the
central nervous system and the peripheral nervous system.
PARTS
The
nervous
system is
made up
of...
THE NERVOUS
SYSTEM
Central
Nervous S.
Peripheral
Nervous S.
 The brain: protected by the cranium, it controls
the body and has three parts:
1.The cerebrum controls thoughts, emotions,
language and behavior. Also our voluntary
movements. It is divided into the left and right
hemispheres.
2.The cerebellum co-ordinates movements and
balance.
3.The brain-stem controls involuntary
movements.
 The Spinal Cord goes from the bottom of the
brain to the bottom of the spine and it is protected
by the spinal column.
It is formed by the nerves, which carry messages
to and from the central nervous system. Nerves can
be:
1. The sensory nerves carry information from the
sense organs to the Central Nervous System.
2. The motor nerves carry orders from the Central
Nervous System to the muscles and organs.

3. Unit 2 INTERACTION SUMMARY
3
THE
LOCOMOTOR
SYSTEM
Function
1. The muscle receives an order from the brain.
2. The muscle contracts (gets shorter) and pulls
from the bone connected to it.
3. The order stops and the muscle relaxes (it goes
back to normal), having the bone return to its
original position.
MUSCLES. They contract and relax and give
our body shape. Tissues called tendons
connect muscles to bones. We have voluntary
and involuntary muscles.
JOINTS. Our bones are connected to the joints
by ligaments. There are three types (fixed
joints, semi-flexible joints and flexible joints)
THE SKELETON. It supports, gives
shape and protects the internal
organs. It is made up of bones
(hard bone tissue) and cartilage
(flexible tissue). 3 types of bones
(short, flat, long)