Page 28 - Biology_Form_3

Biology for Secondary Schools

called stimuli (singular: stimulus). Living nervous system. The central nervous system
organisms show response to stimuli such as (CNS) is made up of the brain and spinal
light, heat, cold, sound, smell, taste, touch, cord whereas peripheral nervous system
pressure, pain, water and force of gravity. (PNS) consists of nerve fibres. These nerve
The ability to sense, interpret and respond fibres branch from the central nervous
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to stimuli is called irritability or sensitivity. system to all parts of the body as seen in
Figure 2.1. Together CNS and PNS maintain
There are two types of stimuli which are homeostasis, enable movement, and process
external and internal. External stimuli sensory input efficiently. Homeostasis is a
are associated with the surrounding body’s ability to maintain stable internal
environment which include wind, cold, conditions, such as temperature, pH,
heat, light, odor, vibration, pressure, pain, hormones, metabolisms and nutrient levels,
water and gravity. Internal stimuli are those through different feedback mechanisms.
from within the organism; for example,
sense of body position, glucose level and Brain
blood pressure. Cranial nerves
Spinal cord

When an organism detects a stimulus
it initiates a response. A response is a
behaviuoral, physiological or muscular
activity initiated by a stimulus. For example, Spinal nerves
if you touch a very hot object accidentally,
you will quickly pull your hand away from
the hot object. In this example heat is the
stimulus and the reaction of moving away
the hand from the hot object is the response.

Nervous coordination in humans Peripheral nerves

Task 2.2
Search from the library and internet
sources for animations about the main
components of coordination in mammals.
Write short notes about the searched
information.
Figure 2.1: Human nervous system
In humans, nervous coordination is Components of nervous coordination
done through the nervous system. The Coordination is accomplished through a
mammalian nervous system is made up pathway of signals channeled into a series
of central nervous system and peripheral of nerve cells. Coordination in mammals

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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 21 KAMISHNA 23/10/2025 11:52:32 KAMISHNA