Page 36 - Biology_Form_3

Biology for Secondary Schools

Forebrain the midbrain is to convey information
The forebrain is the anterior part of the brain. between the forebrain and hindbrain. It
It is composed of olfactory lobes, which are also controls the involuntary activities
concerned with smell. Also the roof of the and reflex movement of the head, neck
forebrain is enlarged and folded to form the and eyes.
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cerebrum. The cerebrum interlinks impulses
and coordinates responses. The folds makes Hindbrain
the brain more efficient because it increases The hindbrain is composed of the cerebellum
the surface area of the brain and the number and medulla oblongata. The cerebellum is
of neurones within it. The cerebrum is the concerned with body movements, balance
largest part of the brain. It is divided into and posture. It receives impulses from
two halves the right and left hemispheres skeletal muscles, tendons and the inner ear.
and these halves are collectively called These impulses are relayed to the forebrain
cerebral hemispheres. The two hemispheres where they are processed. The cerebellum
are connected by nerve fibres and are in also receives impulses from the organs in
constant communication with each other. the inner ear and from stretch receptors
The outer portion is grey in colour due in joints and muscles. Stretch receptors
to the concentration of cell bodies of the measure the degree of bending at a joint and
nerve cells and is called grey matter. The the degree of tension in muscle fibres. This
inner portion is white in colour due to high information is used to achieve balance and
concentration of axons and it is called white muscular coordination in activities such as
matter. The cerebrum controls all voluntary walking, running or riding a bicycle.
activities of the body. It is responsible
for speech, reasoning, memory, decision The medulla oblongata is the most posterior
making, behaviour, vision and imagination. part of the brain. It controls involuntary and
The cerebrum also controls activities such reflex activities such as breathing, heartbeat,
as running, walking, eating and playing. It digestion, dilation and constriction of blood
is also the centre of intelligence and will vessels, swallowing, sneezing, vomiting,
power. The cerebrum is extremely active in secretion of juices from glands and
humans compared to other animals. Thus, temperature regulation. Most of the time
humans are the most imaginative animals a person is not aware of these processes.
and the most intelligent organisms. However, excessive stimulation of the
medulla may result in impulses being sent
Midbrain to the cerebrum where conscious activities
The midbrain, also called mesencephalon are processed. In addition, during periods
of emotional stress impulses travel from
is the smallest part of the brain that the cerebrum to the medulla causing an
connects the hindbrain with the forebrain. increased rate of sweating, heartbeat and
The optic lobes are found between the breathing. Therefore, prolonged emotional
forebrain and hindbrain. The function of stress can result in high blood pressure.

29 Student’s Book - Form Three

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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 29