The document discusses the stretch reflex and muscle tone. It defines the stretch reflex as a monosynaptic reflex where stimulation of muscle spindles by stretching a muscle leads to contraction of the same muscle via alpha motor neurons. It describes the roles of gamma motor neurons in maintaining sensitivity of muscle spindles. Disorders of muscle tone like spasticity, rigidity, and hypotonia are explained in relation to lesions in the pyramidal and extrapyramidal systems. Clinical examination techniques for assessing muscle tone are also outlined.

1. Dr: Dina Merzeban
Dept ofPhysiology
Motor nervous system
Stretch reflex

2. What is a reflex?
• Response to a stimulus
• Stimulus Response
Task:
Write down 3 reflexes .

3. What is a reflex?
Afferent nerve
Central
connections
Efferent nerve
Receptor
Stimulus
Response
Effector organ

4. Stretch reflex
• This is a basic reflex present in the
spinal cord
• Stimulus: muscle stretch
• Response: contraction of the muscle
• Receptors: stretch receptors located
in the muscle spindle .

6. skeletal muscle
• two types of muscle fibres
– extrafusal
• normally contracting fibres
– intrafusal
• non contractile fibres present inside the
muscle spindle
• lie parallel to extrafusal fibres
• contains stretch receptors .

7. Extrafusal
fibre
Intrafusal
fibre

8. Contractile
areas Stretch
receptor

9. Nerve supply
Sensory to intrafusal fibre:
Ia afferent
II afferent
Motor:
to extrafusal fibre
 motor neuron
to intrafusal fibre
 motor neuron .

10. Ia afferent nerve
 motorneuron
one
synapse
muscle
stretchmuscle
contraction
Stretch reflex

11. • When a muscle is stretched
• stretch receptors in the intrafusal fibres
are stimulated
• via type Ia afferent impulse is transmitted
to the spinal cord
•  motor neuron isstimulated
• muscle is contracted
• Monosynaptic
• Neurotransmitter is glutamate

12. Stretch
Reflex

13. Stretch Reflex - Knee Jerk

14. – nuclear bag fibre
• primary (Ia) afferent
– supplies annulospiral ending in the centre
– nuclear chain fibre
• primary (Ia) and secondary (II) afferent
– supplies flower spray ending .
two types of intrafusal fibres

15. Ia afferent fibre
II afferent fibre
nuclear bag fibre
 motor
neuron
nuclear chain fibre
 motor
neuron

16. Plate ending
Trail ending
Annulospiral
ending
Flowerspray
ending

17. Importance of stretch reflex
• detects muscle length and changes
in muscle length .

18.  motorneuron
• cell body is located in the anterior
horn
• motor neuron travels through the
motor nerve
• supplies the intrafusal fibres
(contractile elements at either end) .

19.  motor
neuron
 motorneuron
 motor neuron

20. • When  motor neuron isactive
– extrafusal fibres are contracted
– muscle contracts
• when  motor neuron is active
– intrafusal fibres are contracted
– stretch receptors are stimulated
– stretch reflex is activated
– impulses will travel through Ia afferents
– alpha motor neuron is activated
– muscle contracts .

21. at rest
muscle
stretched
active  motor
neuron
Ia
Ia

Ia afferents are stimulated
stretch reflex is initiated .

22.  motor neuronactivity
• active all the time - mild contraction
• Maintain the sensitivity of the muscle
spindle to stretch
• modified by the descending pathways
• descending excitatory and inhibitory
influences
• sum effect is generally inhibitory in nature
.

24. Alpha gamma co-activation
• gamma motoneurons are activated in
parallel with alpha motoneurons to
maintain the firing of spindle afferents
when the extrafusal muscles shorten
• Prevent unloading

29. Stretch reflex 2 types
-Response that is transmitted:
Dynemic:
-when there is change in the length of the spindle receptor
(stretching of the sensory receptor area of the muscle spindle
by stretching of the muscle spindle or the whole muscle).
Detect Change in length.
-transmitted by the primary fiber Aα type
Static
continuous information about the length of the muscle
(not the change in length).
transmitted by both the primary Aα and secondary (Aβ
and Aγ)

30. STATIC AND DYNAMIC RESPONSE
OF MUSCLE
 SPINDLE AFFRENTS
 Static response is the discharge at any constant length of the
muscle. The greater the muscle length greater is the stretch in the
spindle and the higher is the static response of the spindle
affrents. Both the primary (Iα) and secondary II spindle affrents
gives static or length sensitive responses.
 The dynamic response of a spindle affrents refer to the discharge
during stretch of the muscle. If the spindle affrents gives greater
response during a fast stretch than it dose during a slow stretch
(velocity different but distance of stretch same) it is said to poses
a dynamic response component. Only the primary spindle affrents
gives a dynamic or velocity sensitive response.

31. STATIC AND DYNAMIC FUSIMOTOR
NEURONS
 Dynamic fusimotor fiber increase the dynamic response
of the primary spindle affrents (Iα) and have little or no
effect on secondary.
 Static fusimotor fibers increases the static response of
both the primary and secondary spindle affrents.
However the effect of static fusimotor fiber on primary
spindle affrents is less marked than their effect on the
secondary.
 Static fusimotor fiber terminate as trail endings (mostly
present in nuclear chain fibers).
 Experiment using depletion of muscle glycogen as an
index of muscle fiber activity have shown that repetitive
stimulation of the static fusimotor fiber result primarily in
chain fiber glycogen depletion.
 Dynamic fusimotor stimulation produces mostly bag
fiber glycogen depletion.

32. Significance of stretch
reflex
 Maintain muscle length
 Control of voluntary movement
 Muscle tone

33.  Servoassistant function:
alpha and gamma motor neurons
are coactivated during voluntary
movements
Damping function
Role of stretch reflex in the control of
voluntary movement

34. Muscle tone
Def.:continuous alternating reflex subtetanic
contraction of muscle fibers
Cause :continuous stretch of muscle spindle
(rest)
 Short dist. Between origin and insertion
 Gravity
 Gamma efferent discharge
No fatigue!

35. Function:
 Posture against gravity
 Background for voluntary movement
 Regulation of body temp.
 Venous and lymph return

36. Inverse stretch reflex
• When the muscle is strongly
stretched
• Golgi tendon organs are stimulated
• Via type Ib afferents impulse is
transmitted to the spinal cord
• inhibitory interneuron is stimulated
•  motor neuron is inhibited
• muscle is relaxed .

37. GOLGI TENDON ORGAN

38. Inverse Stretch Reflex

39.  motorneuron
Undue stretch
Golgi tendon organ
muscle
relaxation
Ib afferent nerve
inhibitory
interneuron
Inverse stretch reflex

40. Importance of inverse
stretch reflex
• detects muscle tension .

41. Supraspinal regulation
Facilitatory areas
 Facilitatory reticular
formation(pons)
 Area 4
 Neocerebellum
 Vestibular nuclei
Inhibitory areas
 Inhibitory reticular
formation (medulla)
 Area4s
 Paleocerebellum
 Basal ganglia
 Red nucleus

43. Disorders of muscle
tone
• Abnormalities of the tone :
Hypertonia –
Pyramidal hypertonia (Spasticity)
Extrapyramidal hypertonia (Rigidity)
Hypotonia

44. Pyramidal hypertonia (Spasticity)
• Spasticity – a motor disorder characterized by
velocity- dependent increase in muscle tone with
exaggerated tendon jerks, resulting from
hyperexcitability of the stretch reflex.
• Pyramidal hypertonia is most pronounced in the
muscle groups most used in voluntary
movements.

45. CLASP KNIFE REFLEX
 Seen in decerebrate rigidity
 On stretching the muscle beyond a point causes Ib
affrent inhibitory discharge from GTO which reflexly
inhibits homonymous stretched muscle

46. Spasticity
• Physiologic evidence suggests that interruption of
reticulospinal projections is important in the genesis of
spasticity.
• In spinal cord lesions, bilateral damage to the
pyramidal and reticulospinal pathways can produce
severe spasticity and flexor spasms, reflecting increased
tone in flexor muscle groups and weakness of extensor
muscles.

47. Clonus
• Clonus is the phenomenon of involuntary rhythmic contractions
in response to sudden sustained stretch.
• A sudden stretch activates muscle spindles, resulting inthe
stretch reflex.
• Tension produced by the muscle contraction activates the Golgi
tendon organs, which in turn activate an „inverse stretch reflex‟,
relaxing the muscle.
• If the stretch is sustained, the muscle spindles are again activated,
causing a cycle of alternating contractions and relaxations.

48. Cerebellum and muscle
tone
• The cerebellum does not seem to have a direct effect on
muscle tone determining spinal reflex pathways as
there is no direct descending cerebellospinal tract.
• The cerebellum mainly influences muscle tone through
its connections with the vestibular and brain stem
reticular nuclei.
• Pure cerebellar lesions classically produce hypotonia.

49. Extrapyramidal hypertonia
(Rigidity)
• Rigidity is characterized by an increase in muscle tone causing
resistance to externally imposed joint movements.
• It does not depend on imposed speed and can be elicited at
very low speeds of passive movement.
• It is felt in both agonist and antagonist muscles and in
movements in both directions.

50. Extrapyramidal hypertonia
(Rigidity)
• 'Cogwheel' rigidity and 'leadpipe' rigidity are two types.
• 'Leadpipe' rigidity results when an increase in muscle tone causes
a sustained resistance to passive movement throughout the
whole range of motion, with no fluctuations.
• 'Cogwheel' rigidity occus in association with tremor which
presents as a jerky resistance to passive movement as muscles
tense and relax.
• Basal ganglia structures are clearly implicated in pathophysiology
of rigidity.

51. Hypotonia
• Hypotonia may affect muscleresistance to passive
movement and/or its extensibility.
• Aetiological types of hypotonia :
1. Nerve trunk and root lesion
2. A lesion of anterior horn
3. Cerebellar lesions
4. Cerebral lesions

52. Hypotonia -
causes
Congenital
Genetic
Developmental
Acquired
Genetic
Infectious
Neuromuscular Jn

53. Clinical
Examination
 Tone is difficult to assess.
 The determination of tone is subjective and prone to interexaminer
variability.
 The most important part of the examination of tone is determination
of the resistance of relaxed muscles to passive manipulation as well
as the extensibility, flexibility, and range of motion.
 The examination of tone needs a relaxed & cooperative patient

54. Methods
• Inspection : Attitude of the limb atrest.
• Palpation : Feel of the muscle – normal, firm orflabby.
• Range of movement at the joints.
• Passive movement - first slowly and through complete range ofmotion
and then at varying speeds.
• Shake the distal part of the limb.
• Brace a limb and suddenly remove support.
• Bilateral examination of homologous parts helps comparefor
differences in tone on the two sides of the body.