Physiology of CNS Somatic Motor System: Inverse Stretch Reflex

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Physiology of CNS Somatic Motor System By Dr. Abdel Aziz M. Hussein Assist Prof of Medical Physiology

3. Inverse Stretch Reflex

4. Inverse Stretch Reflex • It is a reflex relaxation (or lengthening) of a ms in response to excessive stretch or contraction of that ms.

5. Inverse Stretch Reflex

6. Inverse Stretch Reflex

7. Inverse Stretch Reflex

8. Inverse Stretch Reflex Neural pathway: • Stimulus:↑ed ms tension by; • Overstretch or • Severe contraction • Receptors:Golgi tendon organs 1) Site: • tendons of skeletal ms in series with ms fibers 2) Structure: • Are encapsulated sensory receptor • 6-20 elastic fibers 3) Innervations: • Type Ib or A alpha afferent fibres

9. Golgi Tendon Organs (GTOs) Receptors: GTOs • Stimulated by ↑ed ms tension caused by passive overstretch or active contraction of the ms Afferents: • A alpha or Ib Center : a)inhibitory interneurons→ inhibit the α-MNs supplying the same ms b)excitatory interneurons→ excite the α-MNs supplying the antagonistic ms Response: • Relaxation of the same ms • Contraction of antagonistic group of ms.

11. Inverse Stretch Reflex Significance GTR: a)Physiological significance: • Protective reaction which prevent tearing of the ms or avulsion of its tendon from its bony attachment when the ms is overstretched.

12. Inverse Stretch Reflex Significance GTR: b)Clinical significance: (clasp knife effect) • Demonstrated clinically by passive flexion of a spastic limb (e.g. in upper motor neuron lesions) at its main joint. • As the limb is flexed, an initial resistance occurs due to contraction of this ms a result of the stretch reflex. • With persistent flexion, at a certain point, GTR is excited→ sudden disappearance of the initial resistance → the limb flexes easily, as occurs during closing-of a pocket knife→ clasp knife effect. • E.g. Flexion of knee and ankle

13. Tendon Jerk

14. Tendon Jerks Def., • Rapid contraction followed by relaxation of a ms due to sudden stretching of that ms by tapping on its tendon using a medical hammer Mechanism: • It is a dynamic type of the stretch reflex

15. The Tendon Reflex Primary afferent neuron stimulates inhibitory interneuron 6 To brain Primary afferent neuron stimulates alpha motor neuron to extensor muscle 4 Interneuron inhibits alpha motor neuron to flexor muscle 7 Alpha MNs 1ry endings Alpha motor neuron stimulates extensor muscle to contract 5 Primary afferent neuron excited 3 Ms contraction Sudden stretch Nuclear bag Muscle spindle stimulated 2 Flexor muscle (antagonist) relaxes Extensor muscle stretched 8 1

16. Tendon Jerks

17. Tendon Jerks • Cause of relaxation after contraction in the tendon jerk: • Stoppage of discharge from the ms spindles. • Stimulation of the Golgi tendon organs. • Stimulation of the Renshaw’s Cells.

18. Examples of Tendon Jerks

20. Biceps Jerk

21. Triceps Jerk

22. Knee Jerk

23. Ankle Jerk

24. Tendon Jerk Reinforcement of the tendon jerks • Response of the tendon jerks can be reinforced by facilitating the spinal centers. • Can be done by either; a) Jendrassik's maneuver→ ask the patient to hook his fingers or to clench his teeth→ send signals from the contracted ms which stimulating γ-MNs. b) Distracting patient’s attention→ prevents any voluntary inhibition of the reflex.

26. Clinical Significance of TJ 1. Localization of spinal cord lesions: • Loss of TJ means the lesion in its center e.g. ankle jerk is lost in sacral region lesion. 2. Assessment of the ms tone : • Inhyperreflexia (exaggerated tendon jerks) → hypertonia (↑ms tone). • In hyporeflexia (↓ed tendon jerks) → hypotonia (↓ms tone). • In areflexia (lost tendon jerks) → atonia (lost ms tone).

27. Clinical Significance of TJ 3. Assessment of the integrity of pathway of stretch reflex: so areflexia or absent tendon jerk may be due to; 4. Assessment of the state of Supraspinal centers:

28. Pendular Knee Jerk • Occurs in the neocerebellar syndrome and chorea. • Characterized by hyporeflexia & hypotonia • Knee jerk is weak than normal and during relaxation of the quadriceps ms, the leg falls like a dead weight(due to hypotonia) & swings for sometime like a pendulum before resting.

29. Clonus Def. • Alternating regular rhythmic contractions with incomplete relaxations of a ms (its MNs is in a state of facilitation) in response to sudden maintained stretch. Cause: • UMNL

30. Clonus Types 1) Ankle Clonus: • Produced by sudden maintained dorsiflexion of the foot  leads to regular rhythmic planter flexions due to rhythmic contractions of soleus and gastrocnemius muscles. 2) Knee Clonus: • Produced by the sudden downward displacement of the patella  rhythmic oscillations of the patella.

32. Clonus Mechanism of clonus: • Clonus is the result of a stretch reflex - inverse stretch reflex sequence, which occurs as follows : • Sudden stretch of the ms results in its contraction through the stretch reflex. • This is followed by relaxation due to; a) Stoppage of impulse discharge from the ms spindles. b) Initiation of an inverse stretch reflex due to stimulation of the GTOs. • As stretch is maintained, a new stretch reflex occurs (helped by the state of excessive spinal facilitation), and the cycle is repeated.

33. Somatic Motor System

34. Somatic Motor System Higher Motor Centers in CC Midbrain Descending Motor Tracts L Pons A Lower MNs In Brain Stem Medulla Motor centers in brain stem e.g. RF Lower MNs in AHCS Spinal Cord

35. Somatic Motor System • Consists of 2 sets of motor neurons; 1. Upper Motor neurons: • Cell bodies are present in motor areas of cerebral cortex and other motor centers in brain stem • Axons form descending motor tracts 2. Lower motor neurons: • Cell bodies are present in AHCs of spinal cord or motor nuclei of cranial nerves • Axons form peripheral nerves that supply skeletal ms

36. Upper Motor Neuron Higher Motor Centers in CC Midbrain Upper Motor Neuron L Pons A Brain Stem Nuclei Medulla Motor centers in brain stem e.g. RF AHCS Spinal Cord

37. Lower Motor neurons Somatic Motor nuclei of cranial nerves Midbrain Left Internal Capsule L Pons A Medulla AHCs Spinal Cord

38. Cortical Motor Areas (Motor Cortex)

39. Motor Cortex • Initiation and performance of voluntary movements are the result of motor commands signals from the motor cortex to the lower motor centers via the descending motor tracts • Motor cortex is located in the frontal lobe, and comprises;

40. Supplemental area Area 4 Premotor area 4 6

41. Primary Motor Area Area (4)

42. Primary Motor Area (MI) • Site: • Precentral gyrus in frontal lobe Central sulcus Precentral gyrus

43. Primary Motor Area (MI) Body representation: 1. Contralateral: i.e. Body ms from the Rt side of the body is represented in the left hemisphere and Lt half of body is represented in Rt hemisphere N.B. some facial muscles are represented bilaterally

44. Primary Motor Area Body representation: 2. Inverted: i.e. the ms of the face are controlled by the lowermost part of area 4 & muscles of the lower limbs controlled by the upper most part of area 4

45. Primary Motor Area Homunculus Body representation: 3. Ms involved in fine voluntary movements are represented by relatively large areas than those involved in gross movements

46. Primary Motor Area (MI) Premotor and supplemental motor areas. Connections: Area 4 a) Afferents: Visual and auditory areas Basal ganglia and cerebellum. Prefrontal area Proprioceptors (Sensory Feedback)

47. Primary Motor Area Connections: Area 4 b) Efferents: Area 4 on opposite side Basal ganglia and cerebellum (Large No. of fibers. Red nucleus and RF (moderate No. of fibers) Corticobulbospinal tract (30%)

48. Primary Motor Area Functions:

49. Primary Motor Area Lesion:

50. Premotor Area Area (6)