The musculoskeletal system
The musculoskeletal system consists of the skeleton and the muscular system. Both systems work
together to make the body move.

The skeleton
The skeleton consists of all the bones in the body. It supports the body, and enables us to move.
It protects delicate organs, such as the heart, lungs and brain.

 Joints
Joints are the places where two bones meet.
There are:
• Fixed joints, such as the skull
• Movable joints, such as the knee or elbow
• Gliding joints, such as between vertebrae. The ends of the bones are covered with flexible
tissue called cartilage. The bones of a joint are connected by strong elastic tissues called ligaments.

 The muscular system
The muscular system consists of all the muscles in the body.
The muscular system:
• Enables the body to move
• Gives the body its shape
• Protects organs, such as the liver Muscles can change in length:
• When they contract, they become shorter  and thicker.
• When they relax, they return to their original  length and thickness. Tissues called tendons connect muscles to bones

 Movement
Body movement occurs at movable joints. Two muscles are used in each movement. These muscles are called antagonistic because they perform opposite actions. When one muscle contracts, the other relaxes. For example, arms bend at the elbow  with a flexing movement. They straighten  with an extending movement.  The diagrams show how the arm muscles contract and relax.



 The nervous system
Functions
The nervous system sends and receives information. It coordinates the functions of internal organs.
It also coordinates systems like the digestive system.

 Parts of the nervous system
The central nervous system consists of the brain and the spinal cord. This system receives information, interprets it, and decides on a response.The brain has three parts:
• The cerebrum controls voluntary movements.
• The cerebellum coordinates movements and maintains balance.
• The brain stem regulates internal organs.
The spinal cord controls reflex movements. The peripheral nervous system consists of nerves.
It transmits information from the sense organs to the central nervous system and from the central nervous system to other organs.

 Neurons
Neurons are the principal cells of the nervous system. They receive and transmit information.
They are grouped together to form nerves. Reflex and voluntary movements.
There are two types of movements:
• Reflex movements: these are involuntary
movements in response to external stimuli.
• Voluntary movements: these movements are the result of decisions.

 Internal processes
The nervous system controls and coordinates all the body’s internal processes, such as  the beating of the heart and the digestion of food. To do this, it controls involuntary muscles and  the endocrine system.

 Involuntary muscles
Involuntary muscles work automatically. We cannot control them with our decisions.The body needs involuntary muscles in order to function correctly.

The endocrine system
The endocrine system is responsible for functions such as growth and reproduction.It consists of endocrine glands, which secretesubstances called hormones into the bloodstream.

Endocrine glands
The principal glands in the endocrine system are:
• Thyroid gland: it produces the hormone thyroxin, which enables the body to absorb nutrients.
• Pancreas: it produces insulin, which controls the amount of sugar in the bloodstream.
• Ovaries (female) and testes (male): they produce sex hormones, which are responsible for reproduction.
• Pituitary gland: it coordinates other endocrineglands and also produces growth hormone.

 Exercises
 . Match the two halves of each sentence.
1. The endocrine system                                              a. produces insulin.
2. The thyroid gland                                                     b. produces the growth hormone.
3. Thyroxin enables the body                                       c. is responsible for growth and reproduction.
4. The pancreas                                                            d. to absorb nutrients.
5. Insulin controls                                                        e. produces thyroxin.
6. The pituitary gland                                                  f. the amount of sugar in the bloodstream.