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Coordination in animals

Reflex action from dendrites of another. The synapse is
A reflex action is a rapid, automatic response also known as neural junction. The sensory
to a stimulus. A reflex action is made possible neurones carrying the impulse enter the
by neural pathways called reflex arcs which dorsal root of the spinal cord from synapse
carry the impulses to and from the spinal with intermediate neurones in the grey
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cord. Thus, this pathway does not involve the matter. The intermediate neurones synapse
brain. Examples of reflex action includes; the with motor neurones. The motor neurones
changes in size of the pupil when subjected carrying the interpreted impulse leave the
to bright or dim light, sudden withdrawal of spinal cord by the ventral root and stimulate
hand or leg when pricked by a sharp or hot muscle cells to contract and eventually
object, coughing or sneezing, knees jerk in pull the hand from the hot plate. When a
response to a blow or someone stamping sufficient number of muscle fibres contract,
the leg, and salivation at the sight or smell the hand will automatically pull away from
of food. the hot plate.

Neural pathway of a reflex action Distinguishing simple from conditioned
reflex actions
Task 2.7
A simple reflex action is an automatic
Search from the library and internet response that is not learnt. Simple reflex
sources for the animations about the actions are always quick and automatic.
reflex arc. Watch the videos and write An example of reflex action is knee jerk.
short notes about them. The knee jerk reflex produces the same
response even if it is done many times.
A reflex arc is a neural pathway that links This is the characteristic of reflex action
sensory receptors and effectors, such as that is, the same stimulus will always result
muscles to make the response happen. into the same response. In reflex action
In its simplest form, three neurones response is coordinated by the spinal cord.
are involved in the reflex arc: sensory, In the simplest reflex action there is no
intermediate and motor neurones. Figure involvement of relay neurone. The stimulus
2.12 shows a reflex action involving the passes directly from the sensory to motor
quick removal of the hand from hot plate. neurone and only one synapse is involved.
Temperature and pain receptors in the skin
stimulate sensory neurones and impulses There are various reflex actions taking place
generated are conducted to the spinal cord in the body that we do not become aware of.
for interpretation. Impulse travels from These actions allow the body to maintain
one nerve cell to another via a gap called internal body environment. Examples of
synapse. It is also a transmission site such actions include breathing rate and
between a neurone and an effector cell or blood pressure.
organ. These are microscopic gaps that
separate terminal buttons of one neurone

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