12b - types of postural reflexes - Coggle Diagram
12b - types of postural reflexes
3.General static reflexes
long-loop stretch reflex
also called functional stretch reflexes,
are polysynaptic reflexes with their reflex arc centred in the cerebral cortex.
These reflexes are continuously active in the erect posture and bring about a continuous correction of the sways that occur from moment to moment during standing.
The human body behaves like an inverted pendulum hinged at the ankle joint.
eg, when the body sways forwards, there occurs stretching of the gastrocnemius muscle.
This initiates monosynaptic stretch reflex as well as long-loop polysynaptic reflex
which bring about reflex contraction in the
resulting in correction of forward sway.
In addition, the visual inputs which suggest that the body is swaying also initiate long-loop postural reflexes.
The two long-loop reflexes
(one proprioceptive, and the other, visual)
ensure that the body is not thrown off balance when tipped over its centre of gravity.
The importance of these two reflexes can be realized in patients with
lesions of dorsal column such as tabes dorsalis.
Sensory ataxia seen in such patients is accentuated on closing of the eyes
The Romberg’s sign is pathognomonic of sensory ataxia and helps to
differentiate it from cerebellar ataxia, in which this sign is absent.
help to correct the position of the body when it goes
off balance and falls down.
In other words, righting reflexes help to maintain head and body into an
erect position under all circumstances.
eg, if an animal is laid on its side or back, the head at once rights itself, body follows and the animal finally resumes the upright posture.
Decerebrate animal, though remains in the upright position, it can never actively resume the upright posture as it has no righting reflexes.
The righting reflexes consist of a chain of reactions following one another in an orderly sequence.
Each reflex causes the development of the succeeding one as follows:
1. Head righting reflex
also called labyrinthine righting reflex, is
initiated when the animal’s head is in lateral position.
The impulses arising from the saccules reflexly stimulate the appropriate muscles to
bring the head back to the upright position.
2. Body righting reflexes
or body-on-head righting reflex.
When an animal lies on the ground, the side in contact with the ground is constantly stimulated while the other side is not.
This differential stimulation of the deep structures in the body wall reflexly rights the head.
The head can thus be righted even after bilateral
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Centres of Righting Reflexes
for all the righting reflexes,
except the optical righting reflexes,
red nucleus lying in the midbrain.
Red nucleus controls these
reflexes through following tracts:
It arises from the small number of large nerve cells which form the nucleus magnocellularis part of the red nucleus.
It arises from the large number of small nerve
cells forming the nucleus parvocellularis part of the red nucleus.
Centre for optical righting reflex lies in the visual cortex, from where impulses ultimately pass to neck muscles to right the head.