DR. JITENDRA PATEL (MBBS, MD) Medical Educator & Researcher

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2 DR. JITENDRA PATEL (MBBS, MD) Medical Educator & Researcher Associate Professor in Physiology Web: 2

3 OUTLINE Stretch reflex overview Muscle spindle Mechanism Response Functions Inverse stretch reflex Withdrawal reflex Applied/clinical aspect 3

4 4 STRETCH REFLEX OVERVIEW

5 INTRODUCTION 5 It is the reflex contraction of skeletal muscles in response to passive stretch. It is also called myotatic or muscle spindle reflex Ex. knee jerk

6 INTRODUCTION.cont 6 It is the fundamental reflex which helps in maintenance of body posture. It is highly developed in antigravity group of muscles (extensors of lower limbs and flexors of upper limbs)

7 COMPONENTS 7 Stimulus: Receptors: Afferents: Centre: Efferent: Response: Passive stretch Muscle spindle Sensory neurons type Ia & II Spinal cord Alpha motor neurons Muscle contraction

8 8 Neuronal circuit of the stretch reflex

9 PROPERTIES 9 Spinal deep reflex. Monosynaptic. Central delay ( msec). Short reaction time (19-24 msec). Highly localised.

10 PROPERTIES 10 It shows reciprocal innervations. It is under higher centres control. Low oxygen consumption and fatigue is not rapid. It does not show after discharge. NT at central synapse is glutamic acid.

11 11 MUSCLE SPINDLE

12 INTRODUCTION 12 Muscle spindle is macroscopic encapsulated spindleshaped stretch receptors in belly of skeletal muscles. It is intrafusal muscle fibres. Number of muscle spindles in a muscle is variable (150/gm to 5/gm) Each Muscle spindle contain 2-12 muscle fibres

13 PECULIARITIES 13 Central non contractile receptor part Peripheral contractile part, its contraction stretches and stimulates the central receptor part. Macroscopic receptor Both afferent and efferent

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16 TYPES 16 Nuclear bag fibers: They have a dilated central area filled with nuclei They are about 2 in number Nuclear chain fibers: Their nuclei are arranged as a chain in the receptor area They are about 4-8 in number.

17 Sensory; Type Ia nerve fibres (Primary) 17 They are thick Ia (Aα) fibers of average diameter 17 microns They form annulo spiral endings Respond to both changes in length of the muscle and velocity at which being stretch

18 Sensory; Type II nerve fibres (Secondary) 18 They are II (Aβ) fibres, thinner and slower in conduction. 8 microns in diameter. Form flower spray endings. Mainly respond to sustain stretch, therefore measure the muscle length.

19 19 Motor; γ efferent fiber Aγ efferent fiber, diameter 3-6 μm High threshold of excitation Plate endings (dynamic/phasic): supply the nuclear bag fibers Trail endings (static/tonic): supply the nuclear chain fibers

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21 EXTRAFUSAL FIBERS INNERVATED BY 21 Extrafusal fibers are input by alpha motor neurons These neurons are large and fast.

22 MECHANISM OF STIMULATION 22 Stretch of the central receptor part of muscle spindle can be achieved by: Passive stretch of the whole muscle (Direct). Activation of gamma efferent fibers (Indirect).

23 23 RESPONSE

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27 α - γ Co-activation 27 It means simultaneous activation of both alpha motor neurons to the skeletal muscle and γ motor neurons to the intrafusal fibres. The role of this co-activation is to prevent shortening of intrafusal muscle fibres during contraction with subsequent reflex relaxation of the extrafusal muscle fibres.

28 28 PHYSIOLOGICAL SIGNIFICANCE/FUNCTION

29 FUNCTIONS 29 Maintenance of posture. Play an imp role in voluntary activity. Helps in regulation of muscle tone.

30 Dynamic stretch reflex (Knee-jerk) (Deep tendon reflex) 30

31 Dynamic stretch reflex (Knee-jerk) (Deep tendon reflex) 31 Deep tendon reflex (DTC) or muscle jerk are example of stretch reflex. DTR exaggerated in UMN lesion while sluggish in LMN lesion.

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33 Jendrassik s maneuver 33 If deep tendon reflexes cannot be elicited normally, the patient is asked to do reinforcement This is called Jendrassik s maneuver. It acts by increasing the excitability of the alpha motor neurons and by increasing the sensitivity of the muscle spindle primary sensory endings to stretch (by increased gamma efferent drive).

34 Dynamic stretch reflex Static stretch reflex 34

35 Stimulus Dynamic stretch reflex Sudden stretch (tapping on tendons) Static stretch reflex Maintained stretch (gravity) 35

36 Stimulus Receptor Dynamic stretch reflex Sudden stretch (tapping on tendons) Nuclear Bag Static stretch reflex Maintained stretch (gravity) Nuclear Chain 36

37 Stimulus Receptor Afferent Dynamic stretch reflex Sudden stretch (tapping on tendons) Nuclear Bag Type Ia Static stretch reflex Maintained stretch (gravity) Nuclear Chain Type II fibers. 37

38 Stimulus Receptor Afferent Response Dynamic stretch reflex Sudden stretch (tapping on tendons) Nuclear Bag Type Ia Brisk contraction and sudden relaxation Static stretch reflex Maintained stretch (gravity) Nuclear Chain Type II fibers. Maintained smooth contraction 38

39 Stimulus Receptor Afferent Response Function Dynamic stretch reflex Sudden stretch (tapping on tendons) Nuclear Bag Type Ia Brisk contraction and sudden relaxation Has clinical significance (tendon-jerk) Static stretch reflex Maintained stretch (gravity) Nuclear Chain Type II fibers. Maintained smooth contraction Production of muscle tone 39

40 Dynamic stretch reflex Static stretch reflex Stimulus Sudden stretch (tapping on tendons) Maintained stretch (gravity) Receptor Nuclear Bag Nuclear Chain Afferent Type Ia Type II fibers. Response Brisk contraction and sudden relaxation Maintained smooth contraction Function Has clinical significance (tendon-jerk) Production of muscle tone 40 Adaptation Rapidly adapting Slowly adapting

41 41 INVERSE STRETCH REFLEX

42 GOLGI TENDON SENSE ORGAN 42 Consists of a netlike collection of knobby Nerve endings among the fascicles of a tendon

43 INVERSE STRETCH REFLEX 43 Stimulus : Increased tension due to over stretch Receptor : Golgi tendon organ Afferents : type Ib nerve fibres Centre : Spinal cord Efferent : α motor neuron Response: Relaxation of same muscle

44 FUNCTIONS 44 It is a protective mechanism... to prevent tearing of the muscle or avulsion of the tendon.

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47 47 SUMMARY Muscle spindle denotes the muscle length Golgi tendon denotes the muscle tension Golgi tendon receive no efferent supply Neurotransmitter: Stretch reflex- glutamic acid Inverse Stretch reflex- glycine Stretch reflex highly developed in antigravity group of muscle Stretch reflex under higher centres control muscle tone maintained by the static response of the stretch reflex

48 48 WITHDRAWAL REFLEX

49 Flexor reflex

50 Polysynaptic Reflex: reverberating circuits After discharge

51 51 APPLIED ASPECT

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54 CLINICAL CLASSIFICATION Superficial 2. Deep 3. Visceral 4. Pathological

55 1. SUPERFICIAL REFLEXES 55 Corneal Reflex Conjunctival Reflex Cilio spianal Reflex Plantar Reflex Abdominal Reflex Cremasteric Reflex

56 Plantar Reflex (L5S1) 56 Superficial Most imp reflex Normal response Flexor Abnormal response Extensor

57 2. DEEP REFLEXES 57 Grading of Tendon Reflexes Grade 0: Absent Grade 1: Present (as a normal ankle jerk) (+) Grade 2: Brisk (as a normal knee jerk) (++) Grade 3: Very brisk (+++) Grade 4: Clonus (++++)

58 2. DEEP REFLEXES 58 Jaw Jerk Biceps Triceps Supinator Knee Ankle

59 3. VISCERAL / AUTONOMIC REFLEXES 59 These are the reflexes where at least one part of the reflex arc is formed by autonomic nerve. Light reflex, Accommodation reflex, Oculocardiac reflex, Carotid sinus reflex.

60 4. PATHOLOGICAL REFLEXES 60 A. Plantar extensor response(babinski sign +ve) B. Clonus C. Pendular movement D. Mass reflex

61 A. Babinski sign: A neurological eponym 61 Adult-pathological Joseph Babinski healthy newborn-physiological

62 B. Clonus 62 Patellar Ankle UMN Hypertonic

63 C. Pendular movement 63 Cerebellar lesion Hypotonia

64 D. Mass reflex 64 Central excitatory states After transaction of spinal cord Mild noxious stimulus withdrawal response and autonomic changes (urination, defecation, sweating and fluctuation in BP)

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68 REGULATION 68

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70 Control of γ efferent system Cerebral cortex Stimulatory signals The primary motor area (area 4) Inhibitory signals The premotor area (area 6) The basal ganglia The cerebellum The reticular formation The caudate nucleus ONLY The neocerebellum The facilitatory reticular formation The red nucleus and the lentiform nucleus The paleocerebellum The inhibitory reticular formation

71 Cont 71 Other factors which increase the γ efferent discharge Anxiety Stimulation of skin specially by noxious agents Unexpected movements

72 Control of α motor neuron 72 Vestibular nucleus: By direct action Proof: deafferentation

73 BIBLIOGRAPHY 73 Text book of medical physiology - Guyton & Hall - 11 th ed. Review of medical physiology Ganong 23 rd ed. Text book of physiology Prof. A.k jain 4 th ed. Web services

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75 Regarding Golgi tendon organ true is: A. Senses dynamic length of muscle B. Involved in reciprocal innervations C. Alpha-motor neuron stimulation D. Senses muscle tension 75 ANS = D