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Properties of reflexes
1. PROPERTIES OF
REFLEXES
DR NILESH N KATE
PROFESSOR
DEPARTMENT OF PHYSIOLOGY
ESIC MEDICAL COLLEGE AND HOSPITAL,
SEDAM ROAD, GULBARGA.
Tuesday, February 4, 2020
2. Properties of reflexes
Final common
pathway
Recruitment
Irradiation
Summation
Inhibition
Rebound phenomenon
Subliminal fringe
Occlusion
Facilitation
Adequate stimulus
Fractionation
Fatigue
Delay
One way conduction
Sensitization
After discharge.
Tuesday, February 4, 2020
3. Final common pathway
α-motor neurons that
supply the extrafusal
muscle fibres.
If an α-motor neuron
Stimulated, skeletal
muscle fibres contract
If is not stimulated, the
skeletal muscle fibres
relax
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4. Recruitment
As excitatory nerve stimulated for long time
Progressive motor neurons gets activated
progressive increase in response of reflex
activity occurs.
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5. Irradiation
When sensory stimulus too strong – it spread
to neighbouring neurons
Produce wide response.
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6. Summation
Both temporal and
spatial – Facilitate the
responses during the
reflex activity
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8. Rebound phenomenon
When reflex activity inhibited & the
inhibition is over reflex activity reappears &
becomes more powerful.
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10. Occlusion
Simultaneous
stimulation of 2 nerves
with weak shock
evolkes lesser response
than sum total of
response of individual .
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11. Facilitation
When reflex elicited repeatedly –
Response becomes progressively higher
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12. Adequate stimulus
Reflex response is obtained only
when a precise stimulus for a given reflex
activity is applied.
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13. Fractionation
The force of a muscle contraction is much
higher when it is stimulated directly through
motor nerves than sensory
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14. Fatigue
When a particular reflex is elicited
repeatedly at frequent intervals
the response is reduced
progressively and
then disappears all together
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15. Delay
Time interval between the application of
stimulus and starting of the response.
Delay is minimum in a monosynaptic reflex.
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16. One way conduction
Impulses are
transmitted in only one
direction through the
reflex arc as per the
Bell–Magendie law.
The impulses pass
from the receptors to
the centre and then
from the centre to
the effector organ.
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17. Sensitization
When an injurious stimulus is repeatedly
applied
Intensification of response.
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18. After discharge.
When a reflex action is elicited continuously
for some time, and then the stimulation is
stopped
the reflex response (contraction) may
continue for some time even after cessation
of the stimulus.
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19. Spinal cord reflexes
Depending upon origin, reflexes are 2 types
Muscle reflex
Stretch reflex
Lengthening reaction or golgi tendon reflex.
Cutaneous reflex
Withdrawl reflex.
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20. Stretch reflex.
Myotactic
The reflex contraction
of a muscle that is
stretched.
Type – Monosynaptic
Stimulus – Stretch
Reaction time -19–24
ms.
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21. Stretch reflex.
Central delay - 0.6–0.9 ms.
Well developed in
antigravity muscles, such as
extensor group of muscles
of legs and flexor groups of
muscles of arm
Examples -- knee jerk,
ankle jerk, biceps jerk and
triceps jerk
Tuesday, February 4, 2020
22. Reflex arc of stretch reflex
Afferent limb
Receptor – Muscle spindle
Afferent nerve – Ia & II
Center – Ventral gery
horn, act on α Motor
neuron
Efferent limb
Efferent nerve – from αMN
Effector organ - Muscles
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23. Reciprocal innervation of
stretch reflex
Excitation of one
group of muscles is
associated
with inhibition of the
antagonistic group of
muscles on the
same side.
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24. Reciprocal innervation of
stretch reflex –Pathway.
biphasic.
A collateral from each Ia fibre passes in the
spinal cord to an inhibitory interneuron
(Golgi bottle neuron) that synapses directly
on one of the motor neurons supplying the
antagonist muscles.
This is an example of Post-synaptic
inhibition
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26. Significance of reciprocal
innervation
In locomotion.
It helps in the forward
movement of one limb
while causing the
Backward movement
of other limb
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27. Dynamic vs static stretch
reflex
Dynamic stretch
reflex
Static stretch reflex
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28. Tuesday, February 4, 2020
Dynamic stretch reflex
Muscle
stretched
suddenly
Muscle
spindle
length
increas
es
Stimulate
primary
nerve
endings
Shows
dynamic
response.
Discharg
e rapidly
Send strong
signals to
spinal cord
Causes
very
strong
reflex
contract
ion of
same
muscle.
Thus
oppose
sudden
change
29. Static stretch reflex
muscle is stretched slowly
and kept stretched
primary and secondary nerve endings from
nuclear chain fibres send signals continuously
and cause reflex contraction of the muscle
Causes muscle contraction as long as
the muscle is stretched.
Imp in posture, gravity causes continuous stretch
& causes antigravity muscles always contracted.
Tuesday, February 4, 2020
30. Role of gamma motor neurons.
Role of γ efferent
discharge in
adjusting the spindle
sensitivity by
preventing
unloading.
Role of co-activation
of α & γ motor
neurons.
Role of gamma loop
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31. Role of γ efferent discharge in adjusting
the spindle sensitivity by preventing
unloading.
Muscle fibre stretched
Ia fibre firing increases
Α motor neuron activity
Causes reflex contraction of muscle
Makes the muscle slack
firing rate of Ia fibre
Decreased rate of firing of Ia afferent is called Unloading
of muscle spindle.
Disadv- CNS stops receiving information about
the rate and extent of muscle shortening
Tuesday, February 4, 2020
32. γ-motor neurons- prevents
this unloading.
The striated poles of intrafusal fibres
contracts along with shortening of
extrafusal fibres during muscle contraction.
The central receptor region of the intrafusal
fibres remains stretched
Unloading does not occur
Tuesday, February 4, 2020
33. Controls dynamic & static
response
Dynamic γ-motor neurons primarily innervate the
striated poles of nuclear bag fibres
When they are fired, only nuclear bag fibres
shorten.
Since they are responsible for the phasic (i.e.
velocity sensitive) portion of Ia afferent response to
stretch, stimulation of the dynamic γ-fibres
increases phasic activity without affecting static
activity & same for static response.
Tuesday, February 4, 2020
34. Length Servomechanism
This γ-motor neuron-mediated change in
length of intrafusal fibres.
System of negative feedback that operates to
maintain muscle length during body
movements and thus helps in regulation of
posture
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35. Role of co-activation of α- and
γ-motor neurons
During lifting weights -- active shortening
of the extrafusal fibres – slacking of the
muscle spindles (i.e. unload the spindle)--
tend to decrease Ia discharge.
Tuesday, February 4, 2020
36. During voluntary contraction -
α–γ co-activation -- increased
γ-discharge along with the increased α-
discharge-- maintains constant Ia discharge -
- constant level of Ia input to the CNS during
a voluntary movement indicates that motor
command is being carried out.
This is called Followup servomechanism
Tuesday, February 4, 2020
37. Role of γ-loop.
CNS can initiate movements directly by stimulating
only γ-motor neurons, using a pathway called the γ-loop
The loop begins with γ-motor neuron -- which
discharges to cause intrafusal muscle fibre contraction --
increase in Ia afferent fibre activity -- causes increased γ-
motor neuron discharge via a monosynaptic reflex causing
muscle contraction.
But normally it does not happen.
Tuesday, February 4, 2020
38. Higher control of stretch
reflex.
Brain areas that facilitate or inhibit the stretch reflex are
Facilitatory reticular formation
Inhibitory reticular formation
Cerebral motor cortex and cerebellum stimulating the
inhibitory reticular formation
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39. Other factors which influence γ-
efferent discharge:
Anxiety causes an increased discharge- explains the hyperactive
tendon reflexes sometimes seen in the anxious patients.
Stimulation of skin, by noxious agents, increases
γ-efferent discharge to ipsilateral flexor muscle spindles
and decreases that to extensors and produces the opposite
pattern in opposite limb.
This fact is sometimes used as a reinforcement to elicit deep tendon
reflexes (such as knee jerk), which are not being elicited otherwise.
Jendrassik’s manoeuvre.
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40. Functions of stretch reflex
Role in maintaining muscle tone
Role in maintaining posture
Role in controlling voluntary movements
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41. Role in maintaining muscle
tone
BRAIN – has 2 areas
Fascilitatory – Pons
Inhibitory – Lower medulla.
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42. Role in maintaining muscle
tone
Facilitatory area is intrinsically
active - continues to discharge
facilitatory impulses
causing constant activation of γ-
motor neurons --This causes
stretching of the muscle spindle
fibres resulting into reflex
slight contraction of the extrafusal
fibres of muscle under resting state
(producing muscle tone).
Inhibitory area -- becomes active
only if it receives impulses from
the cerebellum or cerebral cortex.
Tuesday, February 4, 2020
43. Role in maintaining posture
Static component of stretch reflex, the
fundamental posture control mechanism, is
especially prominent in the medial extensor
muscles and antigravity muscles
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44. Role in controlling voluntary
movements
During motor activity the group Ia fibres from the muscle
spindle inform the motor control system about the
changes in muscle length.
The constant level of Ia input to the CNS during a
movement indicates that the motor command is being
carried out.
An increase in activity of Ia indicates that motor
command is not being carried out.
CNS uses this information to readjust its command to the
spinal cord.
Tuesday, February 4, 2020