Reflexes .pptx

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1. Reflexes

2. SCHEME Definition Reflex Arc Classification of Reflexes Structure of the Muscle spindle Muscle Stretch Reflex Inverse Stretch Reflex Withdrawal and Crossed Extensor Reflex Properties of Reflexes

3. Reflex (Definition) It is defined as an involuntary & reproducible effector response to a sensory stimulus (with the involvement of the brain or spinal cord ).

4. Reflex Arc or Pathway of The Reflex Stimulus Sensory receptor Sensory (afferent) neuron CNS integration (Center) Efferent (motor) neuron Effector (target tissue) Response (movement) Feedback to CNS

5. Reflex Arc

6. Reflex (Classification) A) Developmental classification: Inborn or Unconditioned reflexes Acquired or Conditioned reflexes

7. B) According to no. of synapses: Monosynaptic reflexes Polysynaptic reflexes

8. C) Clinical classification: Superficial reflexes: plantar, etc Deep reflexes: Knee jerk, etc Visceral reflexes Pathological reflexes: Babinski sign, Mass reflex, Clonus and Pendular movements .

9. D) Functional classification: Somatic reflex: Knee jerk Autonomic reflex: Sino-aortic reflex

10. Autonomic Reflexes: “Visceral Reflexes” Regulate internal organs Integrate in spinal cord or lower brain Coordinate with hormones & pacemakers

11. E) Anatomical classification Segmental reflexes Intersegmental reflexes Suprasegmental reflexes

12. Organization of the Spinal Cord for Motor Functions

13. Animal Preparations For Study Of Reflexes Spinal Animal , the spinal cord is transected, frequently in the neck. Immediately after preparation most spinal cord function below the level of transection is severely depressed. After a few hours in rats and cats or a few days to weeks in monkeys, most of the intrinsic spinal cord functions return to nearly normal.

14. Decerebrate Animal , in which the brain stem is transected in the middle to lower part of the mesencephalon which blocks normal inhibitory signals from the higher control centers of the brain to the pontile and vestibular muscle control nuclei. This allows these nuclei to become tonically active. Used to study the intrinsic excitatory motor functions of the cord.

15. Structure of Muscle Spindle

16. Sensory Innervation of the Muscle Spindle Sensory endings found in central receptor area Primary or Annulospiral Endings Secondary or Flower-spray Endings

17. Motor Innervation of the Muscle Spindle Small gamma motor nerve fibers (gamma efferent fibers of Leksell ) : Originate from type A gamma motor neurons in the anterior horns of the spinal cord. They form plate endings on nuclear bag fibers and trail endings primarily on nuclear chain fibers .

18. Two types of gamma motor axons produce two functional types of responses. Stimulation of one type increases dynamic response (dynamic fusimotor axons), and stimulation of the other increases static discharge at constant length (static fusimotor axons).

19. Muscle Spindle receptor can be excited by Lengthening the whole muscle stretches the midportion of the spindle. Contraction of the end portions of the spindle’s intrafusal fibers. Receptor Function Of The Muscle Spindle

20. Stretch Reflex ( Myotatic Reflex or Deep Tendon Reflex)

21. Neuronal Circuitry of

22. Components of Stretch Reflex Static Stretch Reflexes : Elicited by the continuous static receptor signals transmitted by both primary and secondary endings. The importance of the static stretch reflex is that it causes the degree of muscle contraction to remain reasonably constant.

23. Dynamic Stretch Reflex : Elicited by the potent dynamic signal transmitted from the primary sensory endings of the muscle spindles, caused by rapid stretch or unstretches . This causes an instantaneous strong reflex contraction (or decrease in contraction) of the same muscle. Thus, the reflex functions to oppose sudden changes in muscle length .

24. "Damping" Function of the Dynamic and Static Stretch Reflexes Damping Mechanism in Smoothing Muscle Contraction: Signals from the spinal cord are often transmitted to a muscle in an unsmooth form, When the muscle spindle apparatus is not functioning satisfactorily, the muscle contraction is jerky during the course of such a signal. This is also called as signal averaging function of the muscle spindle reflex.

25. Role of the Muscle Spindle in Voluntary Motor Activity Coactivation of the alpha and gamma motor neurons . Purpose: It keeps the length of the receptor portion of the muscle spindle from changing during the course of the whole muscle contraction. It maintains the proper damping function of the muscle spindle, regardless of any change in muscle length.

26. Brain Areas for Control of the Gamma Motor System Excited specifically by signals from the bulboreticular facilitatory region of the brain stem and, secondarily, by impulses transmitted into the bulboreticular area from cerebellum, basal ganglia, cerebral cortex . Bulboreticular facilitatory area is particularly concerned with antigravity contractions.

27. Muscle Spindle System Stabilizes Body Position During Tense Action If the spindles on both sides of each joint are activated at the same time by the excitatory signals through the gamma nerve fibers, reflex excitation of the skeletal muscles on both sides of the joint also increases, producing tight, tense muscles opposing each other at the joint.

28. Reciprocal Inhibition Reflexes Impulses in the Ia fibers from the muscle spindles of the protagonist muscle cause postsynaptic inhibition of the motor neurons to the antagonists through an inhibitory interneuron (Golgi bottle neuron).

29. Inverse Stretch Reflex or Autogenic Inhibition

30. Inverse Stretch Reflex or Autogenic Inhibition Relaxation in response to strong stretch. Receptor – Golgi tendon organ Stimulation of Ib fibers leads to production of IPSPs on the motor neurons that supply the muscle from which the fiber arise. The degree of stimulation by passive stretch is not great, the more elastic muscle fibers take up much of the stretch, and this is why it takes a strong stretch to produce relaxation.

31. The major difference in excitation of the Golgi tendon organ versus the muscle spindle is that the spindle detects muscle length and changes in muscle length, whereas the tendon organ detects muscle tension as reflected by the tension in itself.

32. Lengthening Reaction When tension on the muscle and, therefore, on the tendon becomes extreme, the inhibitory effect from the tendon organ can be so great that it leads to a sudden reaction in the spinal cord that causes instantaneous relaxation of the entire muscle. It occurs at the point where autogenic inhibition is great enough to overcome the stretch reflex excitation

33. Clinical Applications of the Stretch Reflex Knee Jerk and Other Muscle Jerks: To assess the degree of facilitation of spinal cord centers. Clonus – Oscillation of Muscle Jerks: When the stretch reflex is highly sensitized by facilitatory impulses from the brain. Clonus signifies hyperflexia and hypertonia associated with increased gamma efferent activity.

34. Withdrawal Reflex Also called as Flexion Reflex or Nociceptive Reflex or pain reflex. It is a typical polysynaptic reflex that occurs in response to a noxious and usually painful stimulation of the skin or subcutaneous tissue and muscle.

35. Crossed Extensor Reflex To Keep the Balance Opposite leg Extensors stimulated Flexors inhibited Body supported

36. Local Sign: The exact nature of the limb movement and the final position of the limb vary depending upon the site of stimulation. Because of local sign, the withdrawal of the limb from damaging stimuli is usually appropriate in both magnitude and direction.

37. Postural Reflexes of the Cord Positive Supportive Reaction : If an animal whose spinal cord has been transected for several months, i.e. after the reflexes have become exaggerated, is placed on its feet, the reflex often stiffens the limbs sufficiently to support the weight of the body. This helps keep an animal from falling.

38. Cord "Righting" Reflexes : When a spinal animal is laid on its side, it will make incoordinate movements trying to raise itself to the standing position. Such a reflex demonstrates that some relatively complex reflexes associated with posture are integrated in the spinal cord.

39. Scratch Reflex : Important cord reflex in some animals, which is initiated by itch or tickle sensation. It involves two functions: a position sense that allows the paw to find the exact point of irritation on the surface of the body a to-and-fro scratching movement .

40. Mass Reflex : In chronically paraplegic humans, a mild noxious stimulus may cause, in addition to prolonged withdrawal-extension, urination, defecation, sweating, and blood pressure fluctuations. This is because the excitatory impulses irradiate not only to many somatic areas of the spinal cord but also to autonomic areas.

41. Properties Of Reflexes Adequate stimulus : Reflex response is obtained only when a precise stimulus for a given reflex activity is applied. The precise stimulus which involves a reflex response is called adequate stimulus for that particular reflex.

42. Delay or Reaction Time : The time between the application of the stimulus and the response. For the knee jerk – 19-24 ms. Central delay: Time taken for the reflex activity to traverse the spinal cord. For the knee jerk – 0.6-0.9 ms.

43. One – way conduction : During any reflex activity, the impulses are transmitted in only one direction through the reflex arc as per Bell-Magendie law.

44. Summation : Play an important role in the facilitation of response during the reflex activity. Temporal Summation: When the nerve fiber is stimulated repeatedly with subthreshold stimuli in quick succession, due to summation of EPSPs response does occur. Spatial Summation: When two or more nerve fibers supplying the same muscle are stimulated simultaneously with subthreshold stimuli.

45. Occlusion : Stimulation of two neighbouring nerves simultaneously evokes lesser response than sum total of the responses obtained when each nerve is separately stimulated. This is due to sharing of neurons by both paths which fire only once when both paths stimulated simultaneously.

46. Subliminal fringe : When a reflex path is activated, other reflex associated paths are partially stimulated, & can easily fire. Paths are said to be in the subliminal fringe if they are not discharged by an afferent but do have their excitability increased.

47. Recruitment : When an excitatory nerve is stimulated with a stimulus of constant strength for a long time, there occurs progressive increase in the response of reflex activity. This is due to the progressive increase in the number of motor units activated.

48. Irradiation : When sensory stimulus is too strong, impulse spread to many neighbouring neurons through collaterals & a wider response is obtained.

49. Facilitation : If a reflex is repeatedly elicited at proper intervals, initially the response increases due to facilitation occurring at the synapse.

50. Final common pathway : α -motor neurons that supply the extrafusal muscle fibers are the final common pathway for reflexes because all neural influences affecting muscular contraction ultimately funnel through them to the muscle.

51. Fractionation : The force of muscle contraction is much higher when it is stimulated directly through motor nerve as compared to when it is stimulated reflexly through a sensory nerve. This is due to occlusion of the motor neurons when sensory nerve is stimulated.

52. After- discharge : After a reflex is elicited, response persists for sometime even after cessation of the stimulus. This occurs because the centre continues to discharge. This is mainly because of the interneurons which continues to transmit impulses to the centre even after the cessation of stimulus.

53. Habituation : If a reflex is repeatedly elicited at frequent intervals, without reward or punishment, response gradually decreases. Sensitization : Increased response due to application of a noxious stimulus. These properties are basis for learning and memory .

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