Postural reflexes

Dr. KJG

Professor of Physiology

MGMCRI

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.

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

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

1. Stretch Reflex

Stretch Reflex

Spinalcord

Dorsal rootganglion

INVERSE SRTETCH REFLEX

Muscle

spindle

Sensory nerve

Motor nerve

α Motor neuron

Golgi tendon

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

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.

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.)

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

Tonic neck reflex

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

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

RIGHTING REFLEXES

(Reactions) – Reflexes that restore

posture, when such a posture is disturbed

Experimental Animal preparations to

study the Postural reflexes

1. Spinal animal

2. Decerebrate animal

3. Mid brain animal

4. Thalamic animal

5. Decorticate animal

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

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

Decerebrate rigidity

Facilitaory

areaInhibitory area

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

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

Thank You