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Lecture 4:
Reflexes and Spinal Circuits
Afferent pathway
Sensory
systems
CNS
Efferent pathway
Movement
Reflex...
 A simple
neural circuit example of
sensory and motor systems.
 Involuntary action or movement
that occurs in response to a
stimulus.
For example: sneeze, cough, yawn,
blink.
Examples...
 Cough,
irritant enters the windpipe
and we need to expel it through our
mouth.
 Sneeze,
clear out nasal air
passages of irritants and allergens.
Sensory neurons:
Also named afferent neurons:
Carry messages to the CNS
(brain and/or spinal cord).
Motor neurons :
Also named efferent neurons:
Carry messages away from the
CNS (brain and/or spinal cord).
Each reflexive action usually
involves more than two neurons
between nerve cells (neurons).
Interneurons
 A nerve
cell that forms
synapses with sensory and
motor neurons to integrate
sensory input and motor output.
Motor example:
Knee Jerk Reflex (Patellar reflex)
Knee Jerk reflex ...
 Also
named a monosynaptic reflex.
(one connection, therefore two neurons)
Monosynaptic reflex
Only one synapse in the neural circuit is
needed to complete the reflex.
 The tap below the knee causes the
thigh muscle to stretch.
 Information is sent to the spinal cord,
where it’s sent back to the muscle and
we get a reflex.

Reflexes:
 Serve
as primitive responses to
protect our bodies from danger.
 Help us to adjust to our
surroundings.
Are all movements reflexive
monosynaptic??