Muscle tone and stretch reflex and grading.ppt

TONE
Eva Snehlata KujurLecturer (O.T)
NILD
Kolkata

TONE
 DEFINITION:
Tone of the skeletal muscles is the sustained
partially contracted state, which is found in
the living muscle.
Hyotonia-
Hypertonia-

TONE
 Tone of skeletal muscles is altered in many
diseases of the nervous system, like
a)Pyramidal tract
b)lower motor neuron lesion
c)damage of the extra pyramidal system
e)damage of the dorsal root of the spinal
cord and so on.

TONE
 Tone of the skeletal muscle is maintained by
two fundamental mechanisms
 i)the spinal mechanisms(stretch reflex)
 ii)the supraspinal mechanism, that is control
by the brain via descending tracts(both
pyramidal and extra pyramidal ,but the extra
pyramidal is more important which influence
the stretch reflex.

STRETCH REFLEX
 The stretch reflex (myostatic reflex) is a
muscle contraction in response to stretching
within the muscle. It is a monosynaptic reflex
which provides automatic regulation of
skeletal muscle length.
 When a muscle lengthens, the muscle spindle is
stretched and its nerve activity increases. This
increases alpha motor neuron activity, causing the
muscle fibers to contract and thus resist the
stretching. A secondary set of neurons also causes
the opposing muscle to relax. The reflex functions
to maintain the muscle at a constant length.

STRETCH REFLEX
 Gamma motorneurons regulate how sensitive
the stretch reflex is by tightening or relaxing
the fibers within the spindle. There are
several theories as to what may trigger
gamma motor neurons to increase the reflex's
sensitivity. For example, alpha-gamma co-
activation might keep the spindles taut when
a muscle is contracted, preserving stretch
reflex sensitivity even as the muscle fibers
become shorter. Otherwise the spindles
would become slack and the reflex would
cease to function.

STRETCH REFLEX(GRADING)
 Grading of stretch reflexes upon tapping
muscle tendon Grade Response Significance
 0-no response always abnormal
 1+ -slight but definitely present response
may or may not be normal
 2+-brisk response normal
 3+-very brisk response may or may not be
normal
 4+-clonus always abnormal.

SPINAL MECHANISM:REFLEX ARC
 The Arc:
 The afferent limb of
the stretch reflex
consists of:
 i)the receptor called
the muscle spindle.
 ii)afferent nerve
belonging to Ia
category of fibers
 The center of reflex
the spinal cord
segment.

SPINAL MECHANISM:REFLEX ARC
 Efferent limb :
 i)Lower motor
neuron (A alpha
nerve fiber )
 ii)Muscle within
the spindle within
which it is
situated.

MODE OF ACTION OF STRETCH
REFLEX.
-When the afferent
nerve is stimulated, the
A alpha fibers are
reflexly stimulated and
as a result the muscle
contracts. The Ia
afferents and as a result
the muscle contracts.
-The Ia afferents are
stimulated when the
central region of the
spindle, called ‘nuclear
bag region’ is stretched.

MODE OF ACTION OF STRETCH
REFLEX.
 The stretching of the
central region(more
popularly known as
the equatorial zone)
is caused by either
 i)Stretching of the
extrafusal fibers ,that
is when the muscle is
stretched.
 ii)When the intrafusal
fibers contract.

THE MUSCLE SPINDLE
 Skeletal muscle-
Muscle spindle.
 Muscle spindles
within muscle belly.
 Fibers of belly
called extrafusal
fibers.
 Many spindles in a
single muscle belly.

FUNCTIONAL ANATOMY OF THE
SPINDLE
 Each spindle contains a
few delicate striated
muscle fibers called
intrafusal fibers within
the fibrous capsule of the
spindle.
 The intrafusal fibers are
attached to the fibrous
capsule of the
spindle ,the capsule of
the spindle in turn is
attached with the
extrafusal fibers or
tendon of the muscle.

FUNCTIONAL ANATOMY OF THE
SPINDLE
 Spindle
 Tapering ends –polar
regions
 Broad central
region-Equatorial
zone
 Intrafusal fibers are
of two types
 i)nuclear bag
 ii)nuclear chain

STRETCH REFLEX
 The whole arrangement
ensures:
a)When the intrafusal
muscle fibers contract –
stretching of zone of
nuclear bag occurs –
stimulation of sensory
fiber-stimulation of A
alfha motor neurons-
contraction of
extrafusal fibers(stretch
reflex)-shortening of
main muscle belly.

b)The intrafusal fibers are
parallel to the extrafusal
fibers. further ,the
capsule of the spindle
is ,as stated earlier,
attached with extrafusal
fibers. Therefore when
the extrafusal fibers
are ,stretched the
stretch is transmitted to
the intrafusal fibers-
stimulation of Ia fibers-
shortening of the main
muscle belly.

 Conversly, when extrafusal
fibers shorten(due to
contraction),the nuclear bag
relaxes and the Ia ceases
to fire----relaxation of
extrafusal fiber occurs.
Muscle spindle, thus is
length detecting device.
 Further the stretch reflex
ensures constancy of the
length of the extrafusal fibers,
ie-of the muscle belly itself .In
short the muscle spindle is a
homeostatic organ.

 In the anterior horn
cells of the spinal cord
there exists two types
of nerve cell soma,
viz,
 (i) A alpha
 (ii)A gamma
 From the A alpha broad
diametered fast
conducting nerve
fibers terminate on the
extrafusal fibers.

 The A gamma motor
neurons terminate on
the intrafusal
fibers .Stimulation of
the alpha and gamma
motor neurons
cause ,therefore
contraction of
extrafusal and
intrafusal fibers
respectively.

THE IA AFFERENT SYNAPSES WITH
THE ALPHA MOTOR NEURON
 When the gamma
motor neuron is
stimulated there is
stretching of the
nuclear bag
zone--- stretch
reflex (shortening
of the main muscle
belly)

THE IA AFFERENT SYNAPSES WITH
THE ALPHA MOTOR NEURON
 Nuclear chain fibers,
secondary endings
gamma 1and gamma
2 neuron.
 The intrafusal fibers
of the spindle are of
two classes, viz,(i)
nuclear bag fibers
and the (ii) nuclear
chain fibers,

THE GAMMA AFFERENT
 Gamma motor
neuron(small motor
neuron)
 Two types-Gamma
1(dynamic)
 Gamma 2(static)

FUNCTIONS OF GAMMA MOTOR
NEURON
 1.Gamma motor fibers
are stimulated tone
increases , the stretch
reflex is initiated and
the tone increases.
 Maintenance of
posture(eg-standing) or
changing the posture
are affected by
appropriate adjustment
of gamma motor
activities of different
group of muscles.

NEURON
2. Initiation of skeletal muscular
contraction,stimulation of alpha motor
neurons are necessary. Evidence indicates
that along with alpha motor neuron
firing ,the gamma motor neurons also fire
concomitantly.so that a skeletal muscle
contraction can be made effective.


FUNCTIONS OF GAMMA MOTOR NEURON
 Stimulation of the alpha motor
neuron----initiation of
contraction of extrafusal fibers,
but this contraction will also
cause,(as there is shortening of
the extrafusal fibers),relieving
of the stretch of the nuclear
bag region, causing Ia afferents
to stop its discharge, which in
turn will lead to lengthening of
the extrafusal fibers, ie,
cancellation of the alpha motor
stimulation effect. The
concomitant firing of gamma
efferent prevent this.

NEURON
3.Stimulation of gamma
efferent ,by causing the
stretch of the nuclear
bag region, keeps the
muscle fiber sensitive
for the stretch reflex.
In some
diseases(pyramidal
tract lesion)this
sensitivity increases and
produce exaggerated
tendon jerks.

NEURON
 The gamma motor fibers receive impulses
from the descending fibers from the brain
which exert control over the stretch reflex.
Damage to the descending fibers or their
nuclei of origin, therefore leads to alteration
of gamma motor activity and the tone (e.g
development of spasticity, lead pipe rigidity
etc)

ALTERATION IN TONE
 Neural factor: Changes in tone due to
changes in CNS
Hypertonia(Spasticity)
 Non Neural Changes:Changes in tone due to
changes in the muscle,(secondaryfactor).

GUIDELINES FOR EVALUATION
OF TONE
 Record the test position of the patient because
body and head position influence muscle
tone.Patients upper extremity muscle tone is
evaluated in sitting position when possible.
 Grasp the patients limb proximal and distal to the
joint to be tested to its range to determine the
free and early ROM available.
 The therapists hand hold the limb on the lateral
aspects ,avoid giving tactile stimulation to the
muscle belly of the muscle being tested ,Note also
if the limbs feel light or heavy indicating the ability
of the limb adapt automatically to changes in
position against gravity .

GUIDELINES FOR EVALUATION
OF TONE
 Clinical examination of abnormal muscle
tone involves holding the patients limbs as
just described or moving it rapidly through
its full range while the patient is relaxed.
 Remember that the patients posture ie-
(patient sitting symmetrically, weight
bearing versus slumpe or leaning on one side
will affect the results of the tone evaluation
facilitate the maintenance of symmetrical
sitting position for testing as feasible.

GRADING OF TONE
 Bohanan and Smith 1987 modified the
Asworths’ scale by adding one more level(+1)
 Incorporating the angle at which the
resistance appeared.
 Controlling the speed of passive movement
with 1 second count.

MODIFIED ASWORTHS’ SCALE
 Grade 0-No increase in muscle tone.
 Grade 1-Slight increase in tone, manifested by a
catch and release or by minimal resistance at the
end range of motion when the affected part is
moved in flexion and extension
 Grade 2-Slight increase in tone ,manifested by a
catch, followed by minimal resistance throughout
the remainder (less than half) of the ROM.
 Grade 3-Considerable increase in muscle tone,
passive movement difficult.
 Grade 4-Affected part rigid in flexion and
extension.

MODIFIED ASWORTHS’ SCALE
 It is used for assessing the degree of
spasticity
 The resistance encountered to passive
movement rated on this 5 point scale.

ABNORMAL MUSCLE TONE
 Abnormal muscle tone is described by the
following terms :
 Flaccidity
 Hypotonus
 Hypertonia
 Spasticity
 Rigidity

SPASTICITY
 Spasticity-
 It is characterised by hypertonic stretch
reflex, clasp knife phenomenon, clonus in
spastic muscle there is range of free
movement, then strong contraction of
muscle in response to stretch and free
movements again when the muscle relaxes
suddenly.
 Spasticity is velocity dependent ,it is due to
upper motor neuron lesion.

SCALE OF SEVERITY OF
SPASTICITY
 Mild spasticity
 Moderate spasticity
 Severe spasticity

MILD SPASTICITY
 Mild or weak stretch reflexes evoke during passive
movement and often not until late in the ROM.
 a slight decrease in balance of tone between
agonist and antagonist.
 A mild increase of resistance to passive stretch ,but
it is possible for the therapist to move the part
through the complete ROM with relative ease.
 A slight decrease in mobility ,gross movements are
performed with fairly normal co-ordination.
 A decreased ability to perform selective motion,
fine movement is impossible or performed clumsily.

MODERATE SPASTICITY
 Moderate spasticity is characterised by strong
stretch reflexes evoke during passive motion and
often earlier in the ROM than seen in slight
spasticity.
 A marked imbalanced of tone between agonist
antagonist muscle.
 Considerable resistance to passive stretch reflex
that is felt through the ROM,but it is possible for
the therapist to move the part to complete ROM
with same effort.
 Some gross movements can be performed slowly
with much effort but with abnormal co-ordination.

SEVERE SPASTICITY
 Strong stretch reflexes evoke during passive
motion are often in the initial segment of the
ROM.
 Marked resistance to passive movements.
 Inability to complete the Rom passively because
of the strength or severity of spasticity.
 Presence of joint contracture because severe
spasticity makes affective ROM, nearly
impossible and the spasticity may not respond,
well to techniques for relaxation.
 Severely decreased mobility and lack of any
active movement.

FLACIDITY
 It refers to the absence of tone .The patient
will have the absence of deep tendon reflex.
Active movement is absent. Flaccidity can
result from spinal or cerebral shock
immediately after a spinal or cerebral insult.
In traumatic upper motor neuron lesions of
cerebral or spinal origin. Flaccidity is usually
present initially and then changes to
hypertonocity within a few weeks

FLACIDITY
 It can also result from lower motor neuron
dysfunction ,such as peripheral nerve injury
or a disruption of the reflex arc at the Alpha
motor neuron level. The muscles feel soft
and offer no resistance to passive
movement ,if flaccid and offer no resistance
to passive movement.If flaccid limb is moved
passively ,it will feel hwavy if moved to a
given position and released,the limb will
drop because the muscles are unable to
resist gravity.

RIGIDITY
 It is an increase in muscle tone of agonist and
antagonist muscles simultaneously. Both groups
of muscles contract steadily ,leading to
increased resistance to passive movement in any
direction and throughout the ROM. Rigidity
signals involvement of the extrapyramidal
pathways in the circuitry of the basal
ganglia ,diencephalon and brain stem.It occurs in
isolated form in disorders such as parkinsons
disease,traumatic brain injury,some
degennerative diseases,encephalitis, tumors and
certain toxins and after co poisoning.and it is not
velocity dependent.

TYPES OF RIGIDITY
 Lead pipe Rigidity :
 Constant resistance is felt throughout the ROM
when psrt is moved slowly and passively in any
direction,The rigidity feels similar to the
feeling of bending a lead pipe thus its name.
 Cogwheel Rigidity:
 A ryhtmic give occurs in resistance throughout
the ROM,much like the feeling of turning a
cogwheel.It is thought that cogwheel rigidity
may be a rigidity superimposed on tremors .

TYPES OF RIGIDITY
 Decorticate Rigidity:
 Bilateral cortical lesions can result in
decorticate rigidity ,which appears as flexion
hypertonus in upper extremity and as
extension in lower extremity. Supine
positioning increase the abnormal tone.
 Decrebrate Rigidity:
 Results from lesions in the bilateral
hemisphere of the diencephalon and
midbrain. It appears as rigid extension.

Muscle tone and stretch reflex and grading.ppt

More Related Content

Similar to Muscle tone and stretch reflex and grading.ppt

Recently uploaded

Muscle tone and stretch reflex and grading.ppt