Reflex Arc
The Reflex Arc
 Includes
 Receptor
 Sensory Neuron
 Motor Neuron
 Effectors
Involved in a particular reflex
• interneurons may or may not be present
The arc makes a REFLEX possible- or
“rapid automatic responese to stimuli”
Reflexes make RAPID ADJUSTMENTS in the functions
of organs or organ systems
Kinds of Reflexes
Reflexes are categorized in several ways:
1) on the basis of DEVELOPMENT
a) INNATE REFLEXESresult from the connection of neurons that form
during normal development
Are genetically determined
Include: withdrawal from pain,
blinking and sucking
b) ACQUIRED REFLEXES
are still rapid, and automatic but are LEARNED
responses
2)
-by MOTOR RESPONSESa)
b)
SOMATIC REFLEXES
control activities of the muscular system
VISERAL REFLEXES
or autonomic involuntary reflexes- control the actions of
smooth and cardiac muscles and glands
3) - by PROCESSING SITEa) SPINAL REFLEXES
- control the activities of the muscular
system
b) CRANIAL REFLEXES
- are reflexes processed in the brain
4) – by the COMPLEXITY OF THE CIRCUITa) Monosynaptic Reflexes
- in which the sensory neuron synapses
DIRECTLY with the motor neuron
- there is little delay between sensory
input and motor output
- control the most RAPID reflexes
b)
Polysynaptic Reflexes
- involves a sensory neuron
an interneuron
and… a motor neuron
- the involvement of interneuron's allows for
the motor control of
several different muscle groups
- polysynaptic reflexes allow for more complicated
responses
Classification of Reflexes can be
Combined

A.
Examples:
Monosynaptic (complexity of circuit) spinal (processing site)
reflex
- The stretch reflex
-provides automatic regulation of
skeletal muscle length
- is responsible for muscle tone
-the STIMULUS is the stretching of the muscle
- the RECEPTORS are in the muscle cells
- the SENSORY NEURON synapses directly with
- the MOTOR NEURON which triggers and immediate
response in the
-EFFECTOR = the muscle
The Knee Jerk or PATELLAR REFLEX is an
example of a MONOSYNAPTIC REFLEX by
passive (relaxed) muscles
Postsynaptic Reflexes
- Can be one of two types:
IPSILATERAL- the sensory stimulus and motor
response are on the same side of the body
……or…..
CONTRALATERAL- the motor response is
required on the opposite side of the body
Five Basic Characteristics of
Postsynaptic Reflexes
They involve “pools” of neurons
They are “intersegmental” involve more than one pair of
spinal nerves
3. They involve reciprocal innervations
e.g. the contraction of one group of muscles is opposed by
the inhibition of another group of opposing muscles
The contraction of a flexing muscle may trigger the
STRETCH REFLEX of another muscle
4. They have reverberating circuits that PROLONG the reflex
motor response even after the initial stimulus has failed
5. Several reflexes may cooperate to produce a coordinated
controlled response
1.
2.
Example: Stepping on a Tack with your bare foot