MUSCLE SPINDLE & REFLEX ACTIVITY

1. DR NILESH KATE
MBBS,MD
PROFESSOR
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
REFLEX
ACTIVITY.

2. OBJECTIVES.
 Skeletal muscle :- the effector organ
 Motor unit
 Muscle sensors
 Muscle tone
 Reflex activity
 General considerations
 Spinal cord reflexes
 Clinical reflexes

3. Skeletal muscle :- The Effector organ
 Motor unit
 Muscle sensors
 Muscle spindle
 Golgi tendon organ
 Pacinian corpuscle
 Free nerve endings
 Muscle tone

4. Motor unit
 Single motor neuron &
the muscle fibre that it
innervates.
Tuesday, February 4, 2020

5. Muscle sensors
 Proprioceptors
present in muscles,
tendons, joints,
ligaments, fasciae.
 Gives information
about change in
position of different
parts of body in space.
Tuesday, February 4, 2020

6. Muscle Spindle
 Stretch receptors in
skeletal muscles
 Resposnsible for
proprioceptive
mechanism.
 Muscles for precision
movements contains
more muscle spindles
than postural muscles.
Tuesday, February 4, 2020

7. Structure
 Contains 3-10 small
intra-fusal fibres
 Encapsulated in a capsule
containing fluid.
 Present in between &
parallel to extra-fusal
fibers & their ends
attached to endomysium
of extra-fusal fibres.
Tuesday, February 4, 2020

8. Intra-fusal muscle fibre
 Contains central non-
contractile portion
without actin, myosin.
 2 ends called striated
poles which are
contractile.
 Central part is sensory
portion.
Tuesday, February 4, 2020

9. Types.
 Nuclear bag fibres
 2-5
 30 µm in diameter
 Length – 7 mm
 Nuclei present in central
bag like portion
 Nuclear chain fibres
 6-10
 15 µm in diameter
 Length – 4 mm
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10. Nerve supply of muscle
spindle
Only receptor in body which has
got motor nerve supply.
Tuesday, February 4, 2020

11. Nerve supply of muscle
spindle
 Sensory nerve supply
 Receptor – central
non-contractile
protion
 Sensory fibres -2 types
 Grp Ia
 Type II
Tuesday, February 4, 2020

12. Group Ia
 Primary sensory endings.
 Fibres spirally wind round
the intrafusal fibres, these
are also called
Annulospiral endings.
 Diameter of about 17μm
and carry impulses at the
rate of 70–120 m/s.
Tuesday, February 4, 2020

13. Group Ia
 Stimulated when the
muscle spindle is stretched.
 Dynamic response is
shown by nerve endings
supplying the nuclear bag
fibres
 Static response is shown
by the nerve endings
supplying the nuclear chain
fibres
Tuesday, February 4, 2020

14. Type II
Flower spray endings.
 Secondary sensory
endings
 Innervate the receptor
portion of mainly
nuclear chain fibres
on one side.
 Respond mainly to
sustained stretch, so
measure the muscle
length
Tuesday, February 4, 2020

15. Motor supply γ-fibres
two types
 Dynamic γ-fibres primarily innervate the
striated poles of nuclear bag fibres, where
they end as motor end plate, hence also
called plate endings.
 These fibres increase the sensitivity of the Ia
afferent fibres to stretch.
Tuesday, February 4, 2020

16. Static γ-fibres
 Primarily innervate the striated poles
of Nuclear chain fibres where they end as a
network of branches called trail endings.
 They increase the tonic activity in the Ia
afferent fibres at any given muscle
length
Tuesday, February 4, 2020

17. Functions of muscle spindle
 Role in stretch reflex
 Role in maintaining
muscle tone
 Role in maintaining
skeletal muscle at a
certain physiological
length.
 Role as a
proprioceptor
 Unconscious
proprioceptive
sensations and
 Conscious kinaesthetic
sensations
Tuesday, February 4, 2020

18. Golgi tendon organ
 High threshold stretch
receptors present in
the tendons.
 supplied by Group Ib
afferent fibres and
detect muscle tension
Tuesday, February 4, 2020

19. Pacinian corpuscle
 Pressure receptors
situated in fasciae
throughout the
muscles, tendons,
joints and Periosteum.
 They are supplied by
group II afferent fibres
and detect vibration.
Tuesday, February 4, 2020

20. Free nerve endings
 Pain receptors situated
in the muscles, tendons,
fasciae and joints.
 They are supplied by
group III and IV
afferent fibres and
detect noxious stimuli.
Tuesday, February 4, 2020

21. Muscle tone
 Definition
 Basis of muscle tone
 Anomalies of muscle
tone
 Hypotonia
 hypertonia
Tuesday, February 4, 2020

22. Definition
 Muscle tone is defined
as a resistance offered
to active or passive
stretch.
OR
 sustained partial state
of contraction of the
muscle under resting
condition,
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23. Basis of muscle tone
 Purely a function of myotactic (stretch reflex),
occurring due to low frequency and
asynchronous discharge of γ motor neurons.
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24. Anomalies of muscle tone
 Hypotonia
 Hypertonia.
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25. Hypotonia
 muscle tone
 The hypotonic, flaccid
muscle.
 when the rate of γ
efferent discharge is
low, i.e. when
stretch reflex becomes
hypoactive.
Tuesday, February 4, 2020

26. Hypertonia
 muscle tone
 The hypertonic,
spastic muscle.
 when the rate of γ
efferent discharge is
high, i.e. when
stretch reflex becomes
hyperactive.
Tuesday, February 4, 2020

27. Types of hypertonia:
 Spasticity - confined to
only one group of
muscles.
 Example - lesions of
internal capsule and
upper motor neuron
lesions produce
spasticity.
Tuesday, February 4, 2020

28. Types of hypertonia:
 Rigidity - involves
both groups of
muscles, i.e. extensor
as well as flexors
equally.
 Example- lesions of
basal ganglia produce
rigidity
Tuesday, February 4, 2020

29. Reflex activity
 General
considerations
 Involuntary response
 Protective mechanism.
 Through involvement
of CNS.
Tuesday, February 4, 2020

30. ANATOMICAL ASPECTS
 Reflex arc – Pathway for
reflex activity.
 Components are
 Afferent limb – Receptor
& Sensory nerve
 Center – synapse directly
or by Interneurons.
 Efferent limb – Motor
nerve & Effector organ
Tuesday, February 4, 2020

31. Classification of reflexes
 Depending on number of synapse
 Anatomical classification
 Physiolgical classification
 Inborn vs acquired
 Clinical classification
Tuesday, February 4, 2020

32.  Monosynaptic -e.g.
stretch reflexes (biceps,
triceps or knee jerk).
 Disynaptic - e.g. inverse
stretch reflex.
 Polysynaptic - e.g.
withdrawal reflex, cross
flexor reflex and cross
extensor reflex
Tuesday, February 4, 2020
Depending on number of
synapse

33. Anatomical classification
 Depending upon the location of reflex arc
centre
 Cortical reflexes
 Cerebellar reflexes have the centre of reflex arc in
cerebellum
 Mid brain reflexes
 Bulbar or medullary reflexes and
 Spinal reflexes
Tuesday, February 4, 2020

34. Physiolgical classification
 Flexor reflexes -
characterized by
flexion
 Also called withdrawl
reflexes.
 Extensor reflexes
 antigravity reflexes.
Tuesday, February 4, 2020

35. Inborn vs acquired
 Inborn or unconditional reflexes –
 Reflex salivation when any object is kept in mouth.
 Acquired or conditional reflexes
 Reflex salivation by the sight,
smell, thought or hearing of a known edible
substance.
Tuesday, February 4, 2020

36. Clinical classification
 Superficial
 Deep,
 Visceral and
 Pathological reflexes
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37. Animal preparation for study
of reflexes
 Spinal preparation – reflexes are studies by
transecting spinal cord at different levels
 Decerebrate preparation - transection is
taken in the brain stem between superior
and inferior colliculi
Tuesday, February 4, 2020

38. Tuesday, February 4, 2020