1. The document discusses various postural reflexes that help maintain upright posture and balance. It describes segmental, tonic, and righting reflexes in detail. 2. Segmental reflexes like the stretch reflex and crossed extensor reflex act at the spinal cord level. Tonic reflexes like the tonic neck reflex integrate signals at the medulla. Righting reflexes like the labyrinthine righting reflex restore posture at the midbrain level. 3. Experimental preparations are used to study the postural reflexes at different levels, including spinal, decerebrate, midbrain, thalamic, and decorticate preparations. Decerebrate animals exhibit decerebrate

1. Postural reflexes
Dr. KJG
Professor of Physiology
MGMCRI

2. Objectives
1 Reflexes to maintain the posture.
2.Types of reflexes
3. Experimental evidences to prove the
mechanisms integrated at different levels
in regulation of posture.

3. Types of postural reflexes
S.No Types Center
1 Segmental 1. Stretch reflex
2. Crossed extensor
3. Positive support reaction
4. Negative support reaction
Spinal cord
2 Tonic 1. Tonic neck
2. Tonic labyrinthine
Medulla
3 Righting 1. Neck righting
2. Labyrinthine righting
3. Body righting
4. Limb righting
5. Optical righting
Mid brain
Cerebral cortex

4. S.No Reflex Stimuli Response Receptor Center
1 Stretch
Reflex
Stretch Muscle
Contraction
Muscle
Spindle
Spinal
Cord
2 Crossed
extensor
reflex
Stretch Flexion of limb
with extension
of opposite limb
Proprioceptor
3 Positive
supporting
Reaction
Contact
with sole
Foot extended
to support body
Proprioceptor
In distal flexor
4 Negative
supporting
reaction
Stretch Release of
positive
supporting
reaction
Proprioceptor
of extensors
1. Segmental reflexes

5. 1. Stretch Reflex

6. Stretch Reflex

7. Spinal
cord
Dorsal root
ganglion
INVERSE SRTETCH REFLEX
Muscle
spindle
Sensory nerve
Motor nerve
α Motor neuron
Golgi tendon

8. 2.Crossed extensor reflex
Flexion of a limb  Extension of the opposite limb
( 0.2-0.5 seconds later)  entire body pushed away
from the stimuli causing pain.
Stimuli – noxious stimuli
CIRCUITRY
Sensory fibers cross to the opposite side of the cord
to activate the reverberatory circuits among the
internuncuial cells  extensor muscles stimulated
Used in walking.
Center - spinal cord

10. 3.Positive supporting reaction
Used to support the body.
Magnet reaction ( locus of pressure determines
the direction of extension)
• Stimuli = Press the pads of (fingers, toes) and
dorsiflex the (hand, foot)
• Afferent = from the skin & muscle.
• Effect = Hand, foot extended to support the
body.
• Limbs become as solid rigid pillars.
• CAT & DOG can stand up to 3 minutes.

11. 4.Negative supporting reaction
Opposite to the positive supporting reaction.
• Stimulus - stretch
• Receptor - Proprioceptor in extensors
• Center - spinal cord
• Response - Release of positive supporting
reaction.(the limb no longer supports the body
weight.)

12. Reflex Stimulus Response Receptor Center
Tonic neck
reflexes
Head
turned
to side
Change in pattern of
extensor contraction
Neck
Proprio
ceptor
Medulla
Up Forelegs extend
Hind legs flex
Down Forelegs flex
Hind legs extend
Tonic
labyrinthine
Reflexes
Gravity Change in pattern of
rigidity of limbs
according to posture
Otolith
organs
2. Tonic reflexes

13. Tonic neck reflex

14. Reflex Stimuli Response Receptor Center
Labyrinthine
Righting
reflexes
Gravity Righting of
head
Otolith
organs
Midbrain
Neck righting
reflexes
Stretch of
neck
muscles
Righting of
thorax,
shoulders &
pelvis
Muscle
spindle
Body righting
reflexes
a. Body on
head
Pressure
on side of
body
Righting of
head
Exteroceptors
Body righting
reflexes
b. Body on
body
Pressure
on side of
body
Righting of
body even
when head
held sideways
Exteroceptors
3. Righting reflexes

15. Reaction Stimuli Response Receptor Center
Limb
Righting
a. Placing
reactions
b. Hopping
reactions
Lateral
displaceme
nt while
standing
Hops or
places limbs
to support
body
Muscle
spindles
Cerebral
cortex
Optical
righting
reflex
Visual cues Righting of
head
Retina

16. RIGHTING REFLEXES
(Reactions) – Reflexes that restore
posture, when such a posture is disturbed

18. Experimental Animal preparations to
study the Postural reflexes
1. Spinal animal
2. Decerebrate animal
3. Mid brain animal
4. Thalamic animal
5. Decorticate animal

19. Experimental animals
Animal Level of
section
1.Segmental
reflex
2.Tonic
Neck &
Labyrinthine
3.Righting
Labyrinthine,
Neck, Body
Limb &
optical
Spinal Below
medulla
++ -- -- --
--
1000
De
cerebrate
Mid
collicular
++ ++ -- --
--
(Severe
Rigidity)
1100
Mid brain Above
Mid brain
++ ++ ++ --
--
1110
De
corticate
Removal
of cortex
++ ++ ++ --
--
(CR lost)
1110
Thalamic Thalamus
intact
++ ++ ++ Limb ++
Optical --
1111

20. Decerebrate animal
•Decerebrate rigidity
•Limbs hyperextended
•Tail and head dorsiflexed
•Back concave – extreme hyperextension of
spine (OPISTHOTONOS)
•Carricature of standing
•Can be made to stand on four legs

21. Decerebrate rigidity

22. Facilitaory
area
Inhibitory area

23. Release phenomenon
• Inhibitory influence on γ – motor neuron activity
from the cerebra cortex and basal ganglia is lost.
• Unopposed facilitatory effect of brain stem areas
& vestibular nucleus on γ and ά motor neuron
activity ↑ muscle tone
• Section of the posterior nerve roots abolishes
rigidity in those muscles.
• Decerebellation ↑ muscle tone in cat.
• Decerebellation ↓ muscle tone in human beings

24. S.No Sherrington’s Classical
Decerebration
Pollack & Davis Ischaemic
Decerebration
1 Section at mid collicular level Ligation of carotids
2 Fatal procedure Safe procedure
3 Cerebellum intact Damaged
4 De cerebrate rigidity Same features
5 γ-rigidity. ά- rigidity
6 Rigidity increased by removal of
cerebellum
No such effect
7 Rigidity abolished by
deafferentation
No such effect
8 Rigidity abolished by drugs
Like phenothiazine.
No such effect

25. Thank You