1. Lecture - 2 Dr. Zahoor Ali Shaikh
SPINAL CORD REFLEXES
Lecture - 2
Dr. Zahoor Ali Shaikh

2. Spinal Reflex What is Reflex?
-- It is a response that occurs automatically without conscious effort.

3. Reflex
Components of reflex arc are Five: 1- Sensory Receptor 2- Afferent pathway 3- Center 4- Efferent pathway 5- Effector organ

4. Components of reflex arc

5. REFLEX
Receptor responds to the stimulus and produces action potential (AP)
AP is taken by afferent pathway to the integrating center (usually CNS)
Spinal cord and brain integrate basic (automatic) reflexes

6. REFLEX
Integrating center processes all the information and makes the decision about the response
Instruction from integrated center are sent via efferent pathway to the Effector organ (muscle or gland)

7. Classification of reflexes
Monosynaptic or stretch reflex or tendon jerk
eg. Bicep jerk ,tricep jerk, supinator jerk
knee jerk, ankle jerk
Polysynaptic reflex
eg. Withdrawal reflex
Abdominal reflex
Plantar reflex
Visceral reflex
eg. Micturation, defecation reflex
Jendressik Phenomenon

8. Stretch Reflex [monosynaptic]
Sudden stretch to a muscle leads to contraction of that muscle is known as stretch reflex.

9. Stretch Reflex [monosynaptic]
Stretch Reflex is basic (automatic) spinal reflex. We will take example Knee jerk
There are 5 components of Stretch Reflex
1- Sensory receptor – muscle spindle in skeletal muscle
2- Afferent pathway – 1a fibers
3- Center – spinal cord
4- Efferent fibers – α motor neuron
5- Effector organ – skeletal muscle contraction

10. Types of muscle fibers
Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron)
Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by
γ - motor neuron)

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

12. MUSCLE SPINDLE (INTRAFUSAL FIBERS)

13. MUSCLE EXTRAFUSAL FIBERS MUSCLE INTRAFUSAL FIBERS

14. Muscle spindle Nuclear bag fiber Nuclear chain fiber
Sensory innervations of muscle spindle
Ia – nuclear bag & nuclear chain fibers
II – nuclear chain fibers
Motor supply – γ motor neuron
Dynamic & Static

15. Types of motor neuron α – motor neuron (supply Extrafusal fibers )
γ - motor neuron (supply Intrafusal fibers)

16. Patellar Tendon Reflex
KNEE JERK – MONOSYNAPTIC REFLEX

18. Polysynaptic Reflex
In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway
We will study withdrawal reflex

19. POLYSYNAPTIC REFLEXES
Withdrawal Reflex
When a person touches a hot stove or pin prick, a withdrawal reflex occurs from the painful stimulus
1. Receptor- pain and Temperature Receptors stimulated
2. Afferent impulse travels via Action potential
3. Center– Spinal cord.( Excitatory interneuron stimulated that stimulate efferent fibers).

20. POLY SYNAPTIC REFLEX
4 .Efferent fibers to Biceps to cotract ( flextion of arm ) and inhibitory neuron stimulated to inhibit contraction of Triceps.
This type of connection causing stimulation of nerve supply to one muscle and simultaneous inhibition of the nerve to its Antagonistic muscle is known as RECIPROCAL INNERVATION.

21. Withdrawal reflex – Polysynaptic reflex

22. Poly synaptic reflex Important
Afferent neuron stimulate also interneuron that carry signals to the Brain ( Ascending tracts in the spinal cord )
Therefore Brain can modify the with drawl reflex. How?
By sending impulses via descending pathways to the efferent motor neuron supplying the involved muscles and prevent contracting of biceps inspite of painful stimulus e.g. pin prick

23. DIFFERENT REFLEXES SHOWN
Jendressik Phenomenon
(Reinforcement)

25. Jendressik Phenomenon
(Reinforcement)
Superficial
Reflexes

27. Summary

28. TRANSVERS SECTION OF SPINAL CORD

29. Dermatomes of Spinal roots and divisions of trigeminal nerve (V1 ,V2, V3)

30. Cranial Nerve
Spinal
Cord Reflexes

31. Other Reflexes 1- Golgi tendon Reflex 2- Crossed Extensor Reflex
We will discuss first Golgi endon Reflex

32. 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

33. The Golgi tendon reflex (inverse stretch reflex)

34. Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed

35. Crossed Extensor Reflex
Painful Stimuli
Flexion & withdrawal of stimulated limb
Extension of opposite limb

37. POLYSYNAPTIC REFLEX

38. 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.

39. 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.

40. Thank you