1. Dr. Shaikh Mujeeb Ahmed Assistant Professor AlMaarefa College
Spinal Cord Reflexes
CNS BLOCK 424
Dr. Shaikh Mujeeb 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.
Development
Simple/Basic
Acquired
Location of receptor
Superficial
Deep
Visceral
Number of synapse
Monosynaptic
Polysynaptic

5. Reflex Arc
Receptor
Affrent Nerve
Center
Efferent Nerve
Effector organ

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 Muscle spindle Sensory Nerve Spinal Segment Motor Nerve
Receptor
Muscle spindle
Afferent neuron
Sensory Nerve
Center
Spinal Segment
Efferent neuron
Motor Nerve
Effector Organ
Skeletal Muscle
Receptor
Muscle spindle
Afferent neuron
Ia fiber (primary)
II fiber (secondary)
Center
Spinal Segment
Efferent neuron
Gamma motor neuron
Effector Organ
Intrafusal muscle fibers

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: Two types of stretch 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: If muscle is stretched:
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
Extension of opposite limb
Flexion & withdrawal of stimulated limb
Painful Stimuli

27. Fig 13. 8 – Flexion reflex and the crossed extensor reflex
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 Reflex Center (root value) Deep tendon reflex
Biceps Jerk and Brachioradialis
C5/C6
Triceps Jerk
C6/C7
Knee Jerk / Patellar reflex
L2-L4
Ankle S1
Superficial reflex
Corneal reflex (blink reflex)
5th and 7th cranial nerve
Abdominal reflex
T7 – T-12
Plantar reflex
L5-S1