Brain Centre of Nervous System

We know that the nerves carry impulses to the brain. We know that the brain sends these impulses along so that they go to the right place. The brain is made up of three parts. The cerebrum sits like a cap on the cerebellum. And the medulla is that long portion connect­ing the brain with the spinal cord. The cerebrum has certain parts that do certain work. Scientists have found out about these areas from various experiments with animals, and from studying human being whose brains have been accidentally injured. For instance, they have discovered that the part for thought, memory, and feeling is found in the cerebrum, and the part for sight in the back of the cerebrum.

Many experiments have shown that the brain is the center of feel­ing and understanding. The nerve cells in the brain can be “put to sleep” with ether or other anesthetics. Then the brain does not feel any impulses from the part being operated on. Sometimes the nerve cells near the part of our body being treated may be deadened by no- vocaine, as when the dentist pulls a tooth. Novocaine prevents the impulses from getting to the brain from the nerve in the tooth.

The cerebellum is the centre for making your muscles work as a team. The medulla is the centre of certain of our most important acts: breathing and heartbeat, on which life itself depends. The medulla also helps to control acts such as swallowing and yawning.

[ 2_] Read the text and answer the questions.

1. What is respiration?

2. What does the lung consist of?

3. What is the capacity of the thorax?

4. Describe the respiratory movements.

Movements of Breathing. Mechanism of Inhalation and Exhalation

Respiration consists of rhythmically repeated inhalations and ex­halations. Inhalation takes place as follows: the muscles participating in inhalation contract under the influence of nerve impulses. While contracting the diaphragm descends (flattens) increasing the vertical size of the thoracic cavity. Contraction of the external intercostal

muscles elevates the ribs thereby increasing both the anteroposterior and transverse size of the thoracic cavity. Thus muscular contraction increases the capacity of the thorax. Since the thoracic cavity has no air and the pressure in it is negative the lungs extend simultaneously with the increase in capacity in the thorax. The lungs expanding, the air pressure in them drops (it falls below atmospheric pressure) and atmospheric air rushes into the lungs through the air passages. Hence an inhalation involves a contraction of muscles, an increase in the capacity of the thorax, an expansion of the lungs with the drop in the pressure in them, and entrance of the atmospheric air into the lungs (hrough the air passages.

Inhalation is followed by exhalation. The muscles participating in inhalation relax (the diaphragm rises). The ribs drop as a result of contracting of the external intercostal and other muscles and because of their own weight. The capacity of the thorax decreasing, the lungs become compressed, the pressure in them rises (becomes higher than atmospheric) and the air rushes out through the air passages.

The respiratory movements are rhythmic. An adult at rest makes 16—20 respiratory movements per minute, children make more move­ments (a newborn makes up to 60 movements a minute).

Unit 7 SKELETAL SYSTEM