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DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
REGULATION
OF
POSTURE.
POSTURE
 Postural reflexes help to
maintain the body in
upright and balanced
position
 They also provide
adjustments necessary to
maintain a stable posture
during voluntary activity
Reflex Arc Of Postural Reflex
 Afferent Pathway- comes from the eyes, the
vestibular apparatus and the proprioceptors
 Integrating Centres- are formed by neuronal
network in the brain stem and spinal cord
 Efferent Pathway- α-motor neurons
supplying the various skeletal muscles i.e. the
effector organ
TYPES OF POSTURAL REFLEXES
 Postural reflexes are of two types-
(A) Static Reflexes
(B) Statokinetic Reflexes
(A) Static Reflexes
 Static reflexes are involved in adjustments to
displacements produced by gravity
 It is of three types-
(1) Local static reflexes
(2) Segmental static reflexes
(3) General static reflexes
(1) Local static reflexes
 They exert their effect on the same limb from
which the stimulus was initiated
 The centre -- Located in Spinal Cord
 Some important local static reflexes include:
i) Stretch reflex
ii) Positive supporting reaction
iii) Negative supporting reaction
I) STRETCH REFLEX
 This is the most
important local static
reflex which controls
the tone in those
extensor muscles
which keep the body
upright (antigravity
muscles)
II) POSITIVE SUPPORTING
REACTION
 It is characterized by
simultaneous reflex
contraction of both
extensors and flexors of a
limb
 It plays an important role
of steadying the ankle
joint in standing position
Sunday, May 22, 2016
III) NEGATIVE SUPPORTING
REACTION
 It refers to
disappearance of
positive supporting
reaction
 It is initiated by
stretch of the extensor
muscles
(2) SEGMENTAL STATIC
REFLEXES
 It is characterized by a bilateral
reflex response when stimulus
is applied to one limb
 The best example of segmental
static reflex is crossed extensor
reflex response component of
withdrawal reflex
 The centre of this reflex is in
spinal cord
(3) GENERAL STATIC REFLEXES
 It is characterized by a generalized effect from
many muscle groups in the body in response to
a stimulus that arises at one side of the body
 General static reflexes can be divided into three
groups:
a) Attitudinal reflexes
b) Long loop stretch reflexes
c) Righting reflexes
A) ATTITUDINAL REFLEXES
 These reflexes are initiated when the
attitude of the body is changed i.e. while
standing on an inclined plane
 These reflexes are of two types
1) Tonic Labyrinthine Reflex
2) Tonic Neck Reflex
1) TONIC LABYRINTHINE
REFLEX
 These reflexes are produced in response to
alternation in POSITION OF HEAD relative to
horizontal plane e.g. while standing on an
inclined plane
 Pathway of reflex arc-
 Stimulus- is gravity
 Receptors- Otolith organ (Utricle and Saccule
of labyrinth)
1) TONIC LABYRINTHINE
REFLEX
 Afferents- From receptors travel along the vestibular
nerve
 Centre- vestibular and reticular nuclei present in
spinal cord
 Efferents- vestibulospinal and reticulospinal tracts
which end on α-motor neurons of spinal cord
 Reflex reponse- contraction of extensor muscles of
limb
1) TONIC LABYRINTHINE
REFLEX
Sunday, May 22, 2016
2) TONIC NECK REFLEX
 These reflexes are produced in response to alternation
in the position of head relative to the body
 Pathway of reflex arc-
 Stimulus- stretch of neck muscles
 Receptors- pacinian corpuscles in the ligaments of
the cervical joint and muscle spindle of neck muscles
 Centre- in the Medulla oblongata
 Efferent- corticospinal tracts
2) TONIC NECK REFLEX
 Reflex response- depends on the position of the
head in relation to the body:
 Turning down of head causes flexion of the
forelimb and extension of the hind limb
 Turning up of head causes reverse of the above
 Turning the head sideways produces flexion of
the ipsilateral limbs and extension of
contralateral limbs
2) TONIC NECK REFLEX
B) LONG LOOP STRETCH
REFLEXES
 They are also called Functional stretch reflex
 These are polysynaptic reflexes with the centre
of reflex arc in cerebral cortex
 These reflexes are continuously active in erect
posture
 They bring about continuous correction of the
sways that occur from moment to moment
during standing
C) RIGHTING REFLEXES
 Righting reflexes help to correct the position
of the body when it goes off balance and falls
down
 These reflexes consists of a chain of reactions
following one another in an orderly sequence
C) RIGHTING REFLEXES
 For example, if an
animal is laid on it’s side
or back,
 head rights itself
 followed by body and
animal finally resumes
upright posture.
 The sequence of
righting reflexes will be
as follows :
Head righting reflex or
Labyrinthine righting reflex
 It is initiated when
animal’s head is in lateral
position
 Impulses arising from the
saccules reflexly
stimulate the appropriate
muscles to bring head
back to upright position
Sunday, May 22, 2016
2. BODY RIGHTING REFLEX
 When the 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
3. NECK RIGHTING REFLEX
 The head is righted by above two reflexes
but the body still remains in lateral
position
 This leads to twisting of neck and this
brings thorax and lumbar region
successively into upright posture
 If the righting of head is prevented ,
impulses from the body surface may
cause righting of the body directly (Body
on body righting reflex)
Sunday, May 22, 2016
4. LIMBS RIGHTING REFLEX
 Impulses arising from the limb muscles leads
to attainment of appropriate posture of limbs
5. OPTICAL RIGHTING
REFLEXES
 Optical impulses also cause righting of the
head in animals with intact visual cortex
CENTERS OF RIGHTING
REFLEXES
 Chief center for all righting reflexes, except
the optical righting reflex is Red Nucleus
lying in the mid brain
 The center for optical righting reflex is in
the Visual Cortex
Sunday, May 22, 2016
(B) Statokinetic Reflexes
1. Vestibular placing reaction
 Stimulus- linear acceleration
 Receptors- in utricle and saccule
 Center- cerebral cortex
 Response- as soon as foot comes in contact of
any firm surface, it is reflexly placed on
surface in position to support the body
(B) STATOKINETIC REFLEXES
2. Visual placing reaction
 Stimulus- visual cues
 Receptors- eyes
 Center- cerebral cortex
 Response – as in above
(B) STATOKINETIC REFLEXES
3. Hopping reaction
 Stimulus- lateral displacement while
standing
 Receptors- muscle spindle
 Center- cerebral cortex
 Response- hopping movement that keeps the
limb in position to support the body when
standing animal is pushed laterally
DECEREBRATE ANIMAL
 Decerebrate animal is one in whom the brain
stem is transected at intercollicular level i.e.
between superior and inferior colliculi
 Characteristic features-
(i) Decerebrate rigidity
 It refers to marked increase in tone of extensors
i.e. antigravity muscles
 Occurs immediately after decerebration
DECEREBRATE ANIMAL
 Features of decerebrate rigidity
- hyperextension of all four limbs
- dorsiflexion (hyperextension) of
tail and head
- extreme hyperextension of the
spine(opisthotonus) produces
concave configuration of the back
- the animal can be made to stand on
four limbs but is easily toppled by
slight push
MECHANISM OF DECEREBRATE
RIGIDITY
 Rigidity occurs due to increased activity of
motor neurons that facilitate stretch reflex
 Facilitation of stretch reflexes occur due to
increased rate of γ motor neuron discharge
MECHANISM OF
DECEREBRATE RIGIDITY
(ii) No spinal shock
(iii) Postural reflexes are those which have their
centre in spinal cord, medulla or pons. These
include-
- stretch reflexes, positive and negative
supporting reaction, crossed extensor reflex,
tonic neck and tonic labyrinthine reflex
(iv) Righting reflexes are absent
DECORTICATE ANIMAL
 Decorticate animal is one in whom the whole cerebral
cortex is removed but the basal ganglia and brain
stem are left intact
 Characteristic features:
(i) Moderate rigidity is present
 Cortex inhibit medullary reticulospinal tract
 Therefore, removal of cortex results in facilitation of γ
motor neuron discharge
 Seen only when the animal is at rest
CHARACTERISTIC FEATURES:
(ii) Typical posture in
decorticate man consists
of
- full extension of legs
- arms lying across the chest
- semiflexion at elbow
- slight pronation of forearm
- flexion of wrist and fingers
(iii) Righting reflexes are
present
Spinal animal
Preparation:
 Prepared by sectioning the cord at the cervical level.
Significance:
 Segmental and intersegmental reflexes can be
studied.
Eg:Stretch reflex, Positive and negative supporting
reaction, Crossed extensor reflex.
Characteristics:
 Absence of reflexes for a period of days or weeks.
 Spinal man cannot stand unsupported.
Thalamic animal
Preparation:
 Thalamus intact in this animal.
 The rest of the cerebral hemispheres are removed.
 This preparation can be with the cerebellum or without
the cerebellum.
Significance:
 Used for studying righting reflexes.
Characteristics:
 Optical and limb righting reflexes are lost.
Vestibular apparatus &
equlibrium
Influence on
labyrinthine reflexes
-senses gravity and
rotational
movement
- Consist of
i)SCC
ii)Otolith organs
SEMICIRCULAR CANALS THE
AMPULLA
HAIR
CELLSNERVE
CELLS
kinocilium
sterocilia
cupula
THE AMPULLA
MECHANISM OF ACTIVATION AND
TRANSDUCTION
HAIR
CELLS
BENT
NERVE
CELLS
FIRE
INERTIAL FLUID
MOVEMENT
MOVEMENT OF HEAD
THE UTRICLE & SACCULUS
otolith organ
HAIR
CELLSNERVE
CELLS
OTOLITHIC
MEMBRANE-
GELATINOUS
LAYER
OTOCONIA
(CALCIUM
CARBONATE
CRYSTALS)
THE UTRICLE & SACCULUS MECHANISM
OF ACTIVATION AND TRANSDUCTION
HAIR
CELLSNERVE
CELLS
OTOLITHIC
MEMBRANE-
GELATINOUS
LAYER
OTOCONIA
(CALCIUM
CARBONATE
CRYSTALS)
HEAD MOVEMENT
Otolithic
membane
Hair cell
Anatomy: Maculae of Utricle or Saccule
Physiology: Linear acceleration of head
Effect of Gravity on Utricular
Receptor Cells
Figure 15.36
Vestibular reflexes
Vestibulo-Ocular reflex (VOR)
Vestibulo-Spinal reflex (VSR)
Function of vestibular
reflexes
 The VOR stabilizes gaze during fast head
movement
 The VSR sends information regarding
gravity and linear acceleration to body
muscles
Vestibulo-Spinal Reflex (VSR) –
maintaining posture
STIMULUS =
Gravity linear acceleration
Efferent = Spinal nerves
Effector = proximal limb Neck and
body musclesSensory=
Vestibular HC
Afferent = vestibular nerve
Center
increases extensor(antigravity)
tone to maintainposture
Vestibulo-Ocular Reflex (VOR)
STIMULUS =
Head movement
Efferent = oculomotor nerves
Effector = Extra-ocular muscles
Sensory=
Vestibular HC
Afferent = vestibular nerve
Center
Objectives
 Posture.
 Muscle tone & reflex arc.
 Gamma motor neuron.
 Decerebrate rigidity.
 Spinal animal.
 Thalamic animal.
 Postural reflexes.
 equlibrium & vestibular apparatus.
 Vestibular reflexes.
Sunday, May 22, 2016
Thank
You

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MOTOR SYSTEM IV REGULATION OF POSTURE

  • 1. DR NILESH KATE MBBS,MD ASSOCIATE PROF DEPT. OF PHYSIOLOGY REGULATION OF POSTURE.
  • 2. POSTURE  Postural reflexes help to maintain the body in upright and balanced position  They also provide adjustments necessary to maintain a stable posture during voluntary activity
  • 3. Reflex Arc Of Postural Reflex  Afferent Pathway- comes from the eyes, the vestibular apparatus and the proprioceptors  Integrating Centres- are formed by neuronal network in the brain stem and spinal cord  Efferent Pathway- α-motor neurons supplying the various skeletal muscles i.e. the effector organ
  • 4. TYPES OF POSTURAL REFLEXES  Postural reflexes are of two types- (A) Static Reflexes (B) Statokinetic Reflexes
  • 5. (A) Static Reflexes  Static reflexes are involved in adjustments to displacements produced by gravity  It is of three types- (1) Local static reflexes (2) Segmental static reflexes (3) General static reflexes
  • 6. (1) Local static reflexes  They exert their effect on the same limb from which the stimulus was initiated  The centre -- Located in Spinal Cord  Some important local static reflexes include: i) Stretch reflex ii) Positive supporting reaction iii) Negative supporting reaction
  • 7. I) STRETCH REFLEX  This is the most important local static reflex which controls the tone in those extensor muscles which keep the body upright (antigravity muscles)
  • 8. II) POSITIVE SUPPORTING REACTION  It is characterized by simultaneous reflex contraction of both extensors and flexors of a limb  It plays an important role of steadying the ankle joint in standing position Sunday, May 22, 2016
  • 9. III) NEGATIVE SUPPORTING REACTION  It refers to disappearance of positive supporting reaction  It is initiated by stretch of the extensor muscles
  • 10. (2) SEGMENTAL STATIC REFLEXES  It is characterized by a bilateral reflex response when stimulus is applied to one limb  The best example of segmental static reflex is crossed extensor reflex response component of withdrawal reflex  The centre of this reflex is in spinal cord
  • 11. (3) GENERAL STATIC REFLEXES  It is characterized by a generalized effect from many muscle groups in the body in response to a stimulus that arises at one side of the body  General static reflexes can be divided into three groups: a) Attitudinal reflexes b) Long loop stretch reflexes c) Righting reflexes
  • 12. A) ATTITUDINAL REFLEXES  These reflexes are initiated when the attitude of the body is changed i.e. while standing on an inclined plane  These reflexes are of two types 1) Tonic Labyrinthine Reflex 2) Tonic Neck Reflex
  • 13. 1) TONIC LABYRINTHINE REFLEX  These reflexes are produced in response to alternation in POSITION OF HEAD relative to horizontal plane e.g. while standing on an inclined plane  Pathway of reflex arc-  Stimulus- is gravity  Receptors- Otolith organ (Utricle and Saccule of labyrinth)
  • 14. 1) TONIC LABYRINTHINE REFLEX  Afferents- From receptors travel along the vestibular nerve  Centre- vestibular and reticular nuclei present in spinal cord  Efferents- vestibulospinal and reticulospinal tracts which end on α-motor neurons of spinal cord  Reflex reponse- contraction of extensor muscles of limb
  • 16. 2) TONIC NECK REFLEX  These reflexes are produced in response to alternation in the position of head relative to the body  Pathway of reflex arc-  Stimulus- stretch of neck muscles  Receptors- pacinian corpuscles in the ligaments of the cervical joint and muscle spindle of neck muscles  Centre- in the Medulla oblongata  Efferent- corticospinal tracts
  • 17. 2) TONIC NECK REFLEX  Reflex response- depends on the position of the head in relation to the body:  Turning down of head causes flexion of the forelimb and extension of the hind limb  Turning up of head causes reverse of the above  Turning the head sideways produces flexion of the ipsilateral limbs and extension of contralateral limbs
  • 18. 2) TONIC NECK REFLEX
  • 19. B) LONG LOOP STRETCH REFLEXES  They are also called Functional stretch reflex  These are polysynaptic reflexes with the centre of reflex arc in cerebral cortex  These reflexes are continuously active in erect posture  They bring about continuous correction of the sways that occur from moment to moment during standing
  • 20. C) RIGHTING REFLEXES  Righting reflexes help to correct the position of the body when it goes off balance and falls down  These reflexes consists of a chain of reactions following one another in an orderly sequence
  • 21. C) RIGHTING REFLEXES  For example, if an animal is laid on it’s side or back,  head rights itself  followed by body and animal finally resumes upright posture.  The sequence of righting reflexes will be as follows :
  • 22. Head righting reflex or Labyrinthine righting reflex  It is initiated when animal’s head is in lateral position  Impulses arising from the saccules reflexly stimulate the appropriate muscles to bring head back to upright position Sunday, May 22, 2016
  • 23. 2. BODY RIGHTING REFLEX  When the 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
  • 24. 3. NECK RIGHTING REFLEX  The head is righted by above two reflexes but the body still remains in lateral position  This leads to twisting of neck and this brings thorax and lumbar region successively into upright posture  If the righting of head is prevented , impulses from the body surface may cause righting of the body directly (Body on body righting reflex) Sunday, May 22, 2016
  • 25. 4. LIMBS RIGHTING REFLEX  Impulses arising from the limb muscles leads to attainment of appropriate posture of limbs
  • 26. 5. OPTICAL RIGHTING REFLEXES  Optical impulses also cause righting of the head in animals with intact visual cortex
  • 27. CENTERS OF RIGHTING REFLEXES  Chief center for all righting reflexes, except the optical righting reflex is Red Nucleus lying in the mid brain  The center for optical righting reflex is in the Visual Cortex Sunday, May 22, 2016
  • 28. (B) Statokinetic Reflexes 1. Vestibular placing reaction  Stimulus- linear acceleration  Receptors- in utricle and saccule  Center- cerebral cortex  Response- as soon as foot comes in contact of any firm surface, it is reflexly placed on surface in position to support the body
  • 29. (B) STATOKINETIC REFLEXES 2. Visual placing reaction  Stimulus- visual cues  Receptors- eyes  Center- cerebral cortex  Response – as in above
  • 30. (B) STATOKINETIC REFLEXES 3. Hopping reaction  Stimulus- lateral displacement while standing  Receptors- muscle spindle  Center- cerebral cortex  Response- hopping movement that keeps the limb in position to support the body when standing animal is pushed laterally
  • 31. DECEREBRATE ANIMAL  Decerebrate animal is one in whom the brain stem is transected at intercollicular level i.e. between superior and inferior colliculi  Characteristic features- (i) Decerebrate rigidity  It refers to marked increase in tone of extensors i.e. antigravity muscles  Occurs immediately after decerebration
  • 32. DECEREBRATE ANIMAL  Features of decerebrate rigidity - hyperextension of all four limbs - dorsiflexion (hyperextension) of tail and head - extreme hyperextension of the spine(opisthotonus) produces concave configuration of the back - the animal can be made to stand on four limbs but is easily toppled by slight push
  • 33. MECHANISM OF DECEREBRATE RIGIDITY  Rigidity occurs due to increased activity of motor neurons that facilitate stretch reflex  Facilitation of stretch reflexes occur due to increased rate of γ motor neuron discharge
  • 34. MECHANISM OF DECEREBRATE RIGIDITY (ii) No spinal shock (iii) Postural reflexes are those which have their centre in spinal cord, medulla or pons. These include- - stretch reflexes, positive and negative supporting reaction, crossed extensor reflex, tonic neck and tonic labyrinthine reflex (iv) Righting reflexes are absent
  • 35. DECORTICATE ANIMAL  Decorticate animal is one in whom the whole cerebral cortex is removed but the basal ganglia and brain stem are left intact  Characteristic features: (i) Moderate rigidity is present  Cortex inhibit medullary reticulospinal tract  Therefore, removal of cortex results in facilitation of γ motor neuron discharge  Seen only when the animal is at rest
  • 36. CHARACTERISTIC FEATURES: (ii) Typical posture in decorticate man consists of - full extension of legs - arms lying across the chest - semiflexion at elbow - slight pronation of forearm - flexion of wrist and fingers (iii) Righting reflexes are present
  • 37. Spinal animal Preparation:  Prepared by sectioning the cord at the cervical level. Significance:  Segmental and intersegmental reflexes can be studied. Eg:Stretch reflex, Positive and negative supporting reaction, Crossed extensor reflex. Characteristics:  Absence of reflexes for a period of days or weeks.  Spinal man cannot stand unsupported.
  • 38. Thalamic animal Preparation:  Thalamus intact in this animal.  The rest of the cerebral hemispheres are removed.  This preparation can be with the cerebellum or without the cerebellum. Significance:  Used for studying righting reflexes. Characteristics:  Optical and limb righting reflexes are lost.
  • 39. Vestibular apparatus & equlibrium Influence on labyrinthine reflexes -senses gravity and rotational movement - Consist of i)SCC ii)Otolith organs
  • 41. THE AMPULLA MECHANISM OF ACTIVATION AND TRANSDUCTION HAIR CELLS BENT NERVE CELLS FIRE INERTIAL FLUID MOVEMENT MOVEMENT OF HEAD
  • 42. THE UTRICLE & SACCULUS otolith organ HAIR CELLSNERVE CELLS OTOLITHIC MEMBRANE- GELATINOUS LAYER OTOCONIA (CALCIUM CARBONATE CRYSTALS)
  • 43. THE UTRICLE & SACCULUS MECHANISM OF ACTIVATION AND TRANSDUCTION HAIR CELLSNERVE CELLS OTOLITHIC MEMBRANE- GELATINOUS LAYER OTOCONIA (CALCIUM CARBONATE CRYSTALS) HEAD MOVEMENT
  • 44. Otolithic membane Hair cell Anatomy: Maculae of Utricle or Saccule Physiology: Linear acceleration of head
  • 45. Effect of Gravity on Utricular Receptor Cells Figure 15.36
  • 46. Vestibular reflexes Vestibulo-Ocular reflex (VOR) Vestibulo-Spinal reflex (VSR)
  • 47. Function of vestibular reflexes  The VOR stabilizes gaze during fast head movement  The VSR sends information regarding gravity and linear acceleration to body muscles
  • 48. Vestibulo-Spinal Reflex (VSR) – maintaining posture STIMULUS = Gravity linear acceleration Efferent = Spinal nerves Effector = proximal limb Neck and body musclesSensory= Vestibular HC Afferent = vestibular nerve Center increases extensor(antigravity) tone to maintainposture
  • 49. Vestibulo-Ocular Reflex (VOR) STIMULUS = Head movement Efferent = oculomotor nerves Effector = Extra-ocular muscles Sensory= Vestibular HC Afferent = vestibular nerve Center
  • 50. Objectives  Posture.  Muscle tone & reflex arc.  Gamma motor neuron.  Decerebrate rigidity.  Spinal animal.  Thalamic animal.  Postural reflexes.  equlibrium & vestibular apparatus.  Vestibular reflexes.

Hinweis der Redaktion

  1. Proprioceptors- gives information of change of position of the body in space eg-muscle spindle, joint receptor . Golgi tendon organ
  2. Antigravity muscles see pg 976 jain
  3. Muscle tone- certain amount of tension present in resting muscles due to discharge of gamma motor neuron which produces resistance of a muscle to stretch
  4. crossed extensor reflex – a strong stimulus to one limb produces flexion in ipsilateral limb and extension in the contralateral limb
  5. e.g. numerous postural adjustments occur in response to changes in the head position
  6. the cervical joint particularly alanto-occipital joint
  7. In man optical righting reflex is more important than Labyrinthine righting reflex
  8. Reticulospinal tract mainly influence gamma motor neuron and causes alternation in muscle tone