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.
- Effector(muscle) is stimulated.