Muscle spindle and reflex activity

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

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

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

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

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

Muscle Spindle
 Stretch receptors in
skeletal muscles
 Resposnsible for
proprioceptive
mechanism.
 Muscles for precision
movements contains
more muscle spindles
than postural muscles.

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.

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.

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

Nerve supply of muscle
spindle
Only receptor in body which has
got motor nerve supply.

Nerve supply of muscle
spindle
 Sensory nerve supply
 Receptor – central
non-contractile
protion
 Sensory fibres -2 types
 Grp Ia
 Type II

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.

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

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

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.

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

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

Golgi tendon organ
 High threshold stretch
receptors present in
the tendons.
 supplied by Group Ib
afferent fibres and
detect muscle tension

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.

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.

Muscle tone
 Definition
 Basis of muscle tone
 Anomalies of muscle
tone
 Hypotonia
 hypertonia

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,

Basis of muscle tone
 Purely a function of myotactic (stretch reflex),
occurring due to low frequency and
asynchronous discharge of γ motor neurons.

Anomalies of muscle tone
 Hypotonia
 Hypertonia.

Hypotonia
 muscle tone
 The hypotonic, flaccid
muscle.
 when the rate of γ
efferent discharge is
low, i.e. when
stretch reflex becomes
hypoactive.

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

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

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

Reflex activity
 General
considerations
 Involuntary response
 Protective mechanism.
 Through involvement
of CNS.

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

Classification of reflexes
 Depending on number of synapse
 Anatomical classification
 Physiolgical classification
 Inborn vs acquired
 Clinical classification

 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
Depending on number of
synapse

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

Physiolgical classification
 Flexor reflexes -
characterized by
flexion
 Also called withdrawl
reflexes.
 Extensor reflexes
 antigravity reflexes.

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.

Clinical classification
 Superficial
 Deep,
 Visceral and
 Pathological reflexes

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

Muscle spindle and reflex activity

More Related Content

What's hot

Similar to Muscle spindle and reflex activity

More from Dr Nilesh Kate

Recently uploaded

Muscle spindle and reflex activity