2. Actions performed automatically in response to a stimulus
without conscious thought or decision are calledreflex
actionsorreflexes.
Simple reflex actions are handled by thespinal cordwithout
involvement of the brain.
Other reflexes are carried out in various relay centers in
thelower brain or brainstem , butno conscious thoughtis
involved.
Reflex actions carried out by the spinal cord occur
automatically, but at the same time as the reflex occurs, sometimes
a signal is sent to the brain by a connecting interneuron.When this
happens, a stimulus is processed by the spinal cord as an arc and a
response is sent back to the periphery, but a signal is also sent
to the brain for interpretation and additionalreaction .
3. Examples of each of these are: a. Knee jerk response
(simple/spinal cord only) 4. b. Sneezing one of the reflex centers
in the medulla (involvesbrainstem activity only) 5. c. Hand on a
hot stove a simple reflex pulls the hand away (spinal cord arc
only, no brain involvement) followed by a reaction due to an
interneuron connection to the brain from the spinal cord. 6.
**optional
The systems described above represent the simplest units of the
nervous system and are calledreflex arcs .There are 5 parts to
these:
1.Sensory receptor(s)is/are stimulated.
Sensory neuron(s)send(s) message to the spinal cord.
** Interneuron(s)in CNS transmit the message to one or more
motor neurons.
Motor neuronstransmit the message to the effector.