Muscle spindle and reflex activity

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

12. Group Ia
Primary sensory endings.
Fibres spirally wind round
the intrafusalfibres, these
are also called
Annulospiralendings.
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 responseis
shown by nerve endings
supplying the nuclear bag
fibres
Static responseis 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-fibresprimarily 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 fibreswhere 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 IIafferent 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 fibresand
detect noxious stimuli.
Tuesday, February 4, 2020

21. Muscle tone
Definition
Basis of muscle tone
Anomalies of muscle
tone
Hypotonia
hypertonia
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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,
spasticmuscle.
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 & Effectororgan
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 locationof reflex arc
centre
Cortical reflexes
Cerebellar reflexes have the centre of reflex arc in
cerebellum
Mid brain reflexes
Bulbar or medullaryreflexes 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
Decerebratepreparation-transectionis
taken in the brain stem between superior
and inferior colliculi
Tuesday, February 4, 2020

38. Tuesday, February 4, 2020