Page 42 - Biology_Form_3

Biology for Secondary Schools

Muscle contract Cell body of sensory White matter composed
and withdraw hand neurone in dorsal of myelinated neurones
Sensory receptors in skin from a hot plate root ganglion Dorsal root
of hand stimulated to Spinal nerve Ventral root
initiate response
Sensory neurone in
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spinal nerve of arm
Spinal nerve
Motor Grey matter
neurone composed of
cell bodies
Relay neurone
Motor nerve
ending

Stimulus (hot plate)

Figure 2.12: Example of reflex arc showing sequence of events when responding to a painful stimulus.
A conditioned reflex is a type of reflex action where the response is affected by past
experience. Conditioned reflexes are acquired through learning, but can subsequently
be performed without conscious thought. These reflexes are coordinated by the brain.
Examples of conditional reflex action is when a dog salivates when it sees food presented
to it. If a bell is rung just before food is presented to the dog routinely the dog will learn
to associate bell ringing with food.
In human beings, riding a bicycle, driving a car and typing documents on a computer or
typewriter are conditioned reflex actions. This is because these are learned behaviours
that become automatic with experience or repeated practices. Once learned, the actions
or behaviours can happen without much conscious efforts.

Table 2.1: The differences between simple reflex action and conditioned reflex action
S/N Simple reflex action Conditioned reflex action
1 Inborn response to external stimuli Learnt or modified patterns of behaviour
that is not learnt gained through experience

2 Are the same in all members of a Differ from one member to another of the
species same species
3 Initiated by a related stimulus Initiated by an unrelated stimulus
substituted by the one which normally
initiates the response

4 Single stimulus brings about response Combined stimuli when the pattern is
repeated brings about a response
5 Response coordinated by spinal cord Response coordinated by the brain

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