1. Spinal Cord Reflexes CNS BLOCK 424 Dr. ShaikhMujeeb Ahmed Assistant Professor AlMaarefa College

2. Objectives • Describe the components of spinal reflexes. • Enumerate different types of spinal cord reflexes. • Explain the mechanism of spinal cord reflex occurs and their control. • Explain the clinical conditions which can affect the spinal cord reflex.

3. What is a reflex. • Any response that occurs automatically without conscious effort.

4. What are the types of reflexes.

5. Reflex Arc

6. Fig 13.1 – Monosynaptic and polysynaptic reflexes Silverthorn 2nd Ed

7. Stretch Reflex • Sudden stretch to a muscle leads to contraction of that muscle is known as stretch reflex. • The basic unit of this activity is a reflex arc comprises of; • Sense organ. • Afferent neuron. • Center • Efferent neuron • Effector organ.

9. Reflex Arc • Receptor • Muscle spindle • Afferent neuron • Sensory Nerve • Center • Spinal Segment • Efferent neuron • Motor Nerve • Effector Organ • Skeletal Muscle

10. Reflex arc

11. Skeletal Muscle Reflexes • How do they work? • Receptors in muscle send info to CNS • CNS decides should muscle contract (or relax) in response • CNS sends appropriate signal via somatic motor neurons • Somatic motor neurons are always excitatory: • CNS activates if contraction is right response • CNS inhibits if relaxation is right response

12. Receptors • Muscle receptors: • Sense muscle length and/or tension • Two types of stretch receptors: • Muscle spindles • Golgi tendon organs

13. Muscle Spindle Structure • Consist of collections of specialized muscle fibers known as intrafusal fibers • Lie within spindle-shaped connective tissue capsules parallel to extrafusal fibers • Each spindle has its own private efferent and afferent nerve supply • Play key role in stretch reflex

14. Fig 13.3 – Sensory receptors in muscle Silverthorn 2nd Ed

15. Receptor for the stretch reflex: Muscle Spindle Two types of intrafusal fibres: • Nuclear bag fibres: central area is dilated filled with group of nuclei (2 / spindle) • Nuclear chain fibres: smaller than nuclear bag fibres and have one line of nuclei spread in a chain along the receptor area (3-9 /spindle)

16. Muscle spindle

17. Golgi Tendon Organs • Composed of: • Nerve fiber endings that wind between collagen fibers inside connective tissue capsule • If muscle is stretched: • Free nerve endings are pinched and they fire • Activation of Golgi tendon organs: • Inhibits alpha motor neurons and decreases muscle contraction

18. Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed

19. Muscle Spindle Function

20. Stretch Reflex • Primary purpose is to resist tendency for passive stretch of extensor muscles by gravitational forces when person is standing upright • Classic example is patellar tendon, or knee-jerk reflex

21. Patellar Tendon Reflex

22. The Golgi tendon reflex(inverse stretch reflex) • excessive tension on the muscle (passive stretch of tendon or active muscle contraction) >> muscle relaxes opposite response to stretch reflex. • The receptors are Golgi tendon organs in muscle tendons stimulated >> muscle contract and pulled on the tendon (tension) • stimulate golgi organ>> A fibers > spinal cord > excitation of inhibitory interneuron>> inhibit alpha motor neuron > muscle relaxation • Protect muscle from rupture

23. The Golgi tendon reflex (inverse stretch reflex)

24. Withdrawal reflex(flexor reflex) • Stimulation of pain receptors in hand → impulses to spinal cord via A or C fibres → interneurons →anterior horn cells →stimulate hand flexor muscles → move the hand away from the injurious stimulus. • Its a polysynaptic reflex. • Stimulation of flexors muscle accompanied by inhibition of extensors. • Inhibitory inter neurons synapse with extensor motor neurons known as reciprocal innervations (reciprocal inhibition).

25. Reciprocal inhibition

26. Crossed Extensor Reflex

27. Fig 13.8 – Flexion reflex and the crossed extensor reflex Silverthorn 2nd Ed

28. Crossed extensor reflex

29. Clinical Importance of reflexes • To test the integrity of reflex arc. • Localization of neurological lesion. • Identifying the type of lesion. • Monitoring the progress of neurological deficit.

30. Clinical Importance of reflexes • Deep tendon reflexes are absent in lower motor neuron lesion. • The become exaggerated in upper motor neuron lesions. • Pendular jerks are observed in cerebellar lesions.

31. Centers for reflexes