Motor system reflexes for students

1. Motor system Reflexes Prof. Vajira Weerasinghe Professor of Physiology Faculty of Medicine

2. Motor Functions 1. Voluntary Functions Voluntary movement 2. Involuntary Functions Reflexes

3. What is a reflex? Response to a stimulus Involuntary, without significant involvement of the brain Stimulus Response Task: Write down 3 reflexes

4. What is a reflex? Stimulus Effector organ Response Central connections Efferent nerve Afferent nerve Receptor Higher centre control

5. 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 fibres present inside the muscle spindle lie parallel to extrafusal fibres either end of the fibre contractile central part 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 A  motor neuron to intrafusal fibre A  motor neuron

10. Ia afferent nerve  motor neuron one synapse muscle stretch muscle 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 is stimulated 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 provide information on muscle length and velocity (phasic response) fast stretch reflex nuclear chain fibre primary ( Ia ) and secondary (II) afferent supplies flower spray ending monitor the length of the muscle (tonic response ) – slow stretch reflex Two types of intrafusal fibres

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

16. Importance of stretch reflex detects muscle length and changes in muscle length

17. Phasic stretch reflex Stretching the quadriceps muscle quickly (e.g. by tapping the patellar tendon) evokes a discharge in the primary afferent ( Ia ) fibres These form monosynaptic excitatory connections with  motor neurons supplying physiological extensors of the knee, which contract briefly Tonic stretch reflex Passive bending of the joint elicits a discharge from the group II afferents that increases the tone of physiological extensor (antigravity) muscles Tonic stretch reflex is important for maintaining erect body posture

18.  motor neuron 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  motor neuron  motor neuron

20. When  motor neuron is active 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 neuron activity 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

23. 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 Activity from brain centres often causes simultaneous contraction of both extra- and intrafusal fibres, thereby ensuring that the spindle is sensitive to stretch at all muscle lengths

24. Inverse stretch reflex When the muscle is strongly stretched -> muscle is relaxed 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

25.  motor neuron Undue stretch Golgi tendon organ muscle relaxation Inverse stretch reflex Ib afferent nerve inhibitory interneuron

26.  motor neuron Undue stretch Golgi tendon organ muscle relaxation Inverse stretch reflex Ib afferent nerve inhibitory interneuron

27. Inverse Stretch Reflex

28. Importance of inverse stretch reflex detects muscle tension

29. Deep tendon reflexes (DTR) Biceps jerk Triceps jerk Supinator jerk Knee jerk Ankle jerk Jaw jerk

30. reflex level biceps jerk C56 supinator jerk C56 triceps jerk C78 knee jerk L34 ankle jerk S12 Spinal cord level of stretch reflexes (tendon jerks)

31. Superficial reflexes Withdrawal reflex Superficial abdominal reflex Flexor plantar reflex

32. Withdrawal Reflex Stimulus: cutaneous stimulation (usually noxious) Response: withdrawal of the hand Polysynaptic reflex

33. Withdrawal Reflex

34. muscle contraction Withdrawal reflex cutaneous receptors polysynaptic

35. muscle contraction Withdrawal reflex cutaneous receptors

36. Withdrawal Reflex

37. Elbow flexion, extension Wrist flexion, extension Forearm supination, pronation Shoulder adduction, abduction Hip flexion, extension Thigh adduction, abduction Knee flexion, extension Ankle dorsiflexion, plantar flexion

38. Reciprocal innervation inside the spinal cord Agonist and antagonistic muscles are reciprocally innervated stimulation of flexor muscles inhibition of extensor muscles excitatory neurotransmitter is glutamate inhibitory neurotransmitter is glycine flexor extensor +++ ----

39. Reciprocal Innervation

40. Withdrawal Reflex Flexor & Crossed extensor reflex

41. Withdrawal Reflex

42. Superficial abdominal reflexes light scratch of the abdominal skin brisk unilateral contraction of the abdominal wall

43. Flexor plantar reflex Scratching the sole of foot Plantar flexion Normal response

44. Primitive reflexes

45. Primitive reflexes These are reflexes present in newborn babies but disappear as the child develops They were evolutionarily primitive in origin In adults these reflexes are inhibited by the higher centres

46. Other primitive reflexes Moro reflex: startle reaction Walking/stepping reflex Sucking reflex Tonic neck reflex Palmar grasp reflex

47. Babinski sign when outer border of the sole of the foot is scratched upward movement of big toe (dorsiflexion) fanning out of other toes also called extensor plantar reflex feature of upper motor neuron lesion seen in infants during 1st year of life (because of immature corticospinal tract)

48. positive Babinski sign

49. Clinical Importance of reflexes (tendon jerks) Locate a lesion in the motor system To differentiate upper motor neuron lesion from a lower motor neuron lesion