SS2 Third Term Biology Lesson Note – The Nervous System I

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WEEK 9

TOPIC: THE NERVOUS SYSTEM I

CONTENT:  

(1) Organization of the nervous system

(i) Central Nervous System (CNS)

(ii) Peripheral Nervous System (PNS)

(2) The Brain-position, structure and functions

(3) The Spinal Cord-position, structure and functions

SUB-TOPIC 1: ORGANIZATION OF THE NERVOUS SYSTEM

In a complex multicellular organism many activities go on almost simultaneously. These activities are coordinated by the endocrine and nervous system.  The two systems are linked by the hypothalamus.

The basic structural unit of the nervous system is the nerve cell (neurons). The nervous system is made up of millions of neurons.

The main parts of the nervous system are the central nervous system and the peripheral nervous system.

THE CENTRAL NERVOUS SYSTEM (CNS)

This consists of the brain and the spinal cord. The CNS coordinates the activities of the nervous system. It receives impulses from the organism’s internal and external environment, processes and integrates the information and sends out impulses to appropriate effector organs to take action.

The CNS has millions of interconnected nerves which are of two types;

1. the cranial nerves come out of the brain and enter mainly structures in the head (e.g. the eyes and ears).
2. The spinal nerves come out of the spinal cord and go into the arms, legs and various structures in the trunk.

EVALUATION

1. State two differences between the endocrine system and the nervous system.
2. Mention the major parts of the nervous system

SUB-TOPIC2: THE BRAIN.

The human brain is made up of billions of neurones which form the grey matter (nerve fibres). The grey matter occupies the peripheral region, while the white matter is situated in the central portion of the brain.

Within the white matter lie hollow chambers called ventricles. The ventricles contain cerebrospinal fluid and are continuous with the spinal cord.

The cerebrospinal fluid is formed from the blood and returns to the blood stream after bathing the neurons, supplying them with oxygen and nutrients as well as removing wastes. The fluid also acts as a shock absorber, so the brain is cushioned from damage when a person jumps around or bangs the head against an object.

The adult human brain weighs about 1.2 to 1.4 kilograms and forms about 2% of the body’s mass. The brain is protected by the cranium or brain case.

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