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12b types of postural reflexes - Coggle Diagram
12b
types of postural reflexes
Broadly, postural reflexes
are of 2 types:
Static reflexes
are elicited by
gravitational pull
and involve
sustained contraction
of muscles.
are primarily involved in
adjustments to displacements produced by gravity.
These are of 3 types:
2.Segmental static reflexes and
are characterized by a bilateral reflex
response when stimulus is applied to one limb.
The best example of segmental static reflexes is crossed extensor reflex response component of withdrawal reflex.
In this reflex, a strong stimulus to one limb produces flexion in the ipsilateral limb and extension in the contralateral limb.
Role of Crossed Extensor Reflex
in Control of Posture
In the lower limb,
this reflex allows one limb to support the body while other is raised off the ground
.
eg when due to painful stimulus one limb is flexed reflexly, the extensor of the other limb compensates and sees to it that the body
is not thrown off balance.
The crossed extensor reflex also plays
an important role during walking.
During walking, on one side the flexors are active and the extensors are inhibited, while the reverse is seen on the other side.
3.General static reflexes.
are characterized by a generalized effect from
the many muscle groups in the body in response to a stimulus that arises at one side of the body.
eg- numerous postural adjustments occur in response to changes in the head position.
can be divided into 3 groups
1.Attitudinal or Statotonic Reflexes,
-are initiated when the attitude of the body is changed, i.e. while standing on an inclined plane.
are of 2 types:
Tonic labyrinthine reflexes
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Tonic neck reflexes.
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Combined response
of
tonic neck and labyrinthine reflexes
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2.Long-loop stretch reflexes and
3.Righting reflexes.
1.Local static reflexes,
As the name indicates,
the local static reflexes exert their effect on the
same limb from which the stimulus was initiated. Some of the important
local static reflexes include:
1.Reflex control of antigravity muscle tone,
The most important of the local static reflexes is basic stretch reflexes controlling tone in those extensor muscles which keep the body upright (antigravity muscles).
Muscle tone in antigravity muscles is best illustrated in decerebrate preparations, where it produces decerebrate rigidity.
The hypertonicity in decerebrate preparations has a characteristic extensor distribution, resulting in a caricature (i.e. exaggerated mimicry) of the normal posture.
2.Positive supporting reaction and
is characterized by simultaneous reflex contractions of both extensors and flexors of a limb (i.e. both the protagonists and antagonists) converting it into a solid rigid pillar.
plays an important role of steading the
ankle joint in standing position.
At the ankle joint, both dorsiflexion and plantar flexion are possible, but neither of them is desirable during standing position.
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3.Negative supporting reaction.
refers to disappearance of positive
supporting reaction.
It is also an active phenomenon initiated by stretch of the extensor muscles.
This helps the limbs to be used for activities other than supporting the body weight.
Statokinetic reflexes
also called phasic reflexes,
are elicited by
acceleratory displacement
of the body.
They maintain a stable postural background
for voluntary activity.
Both these types of postural reflexes
are integrated at various levels in the CNS
-from the spinal cord to
-cerebral cortex
and are affected largely by pyramidal pathways.