UNIT 1. INTERACTION (NATURAL SCIENCE)

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.