1. Nervous System PhysiologyBy
Dr. SHAHAB SHAIKH
PhD MD MBBS
Lecture – 2: Spinal Cord Reflexes
••••••••••••••••••••••••••••••••••
Faculty of Medicine
Al Maarefa Colleges of Science & Technology

2. SPINAL CORD It is the elongated part of the Central nervous system
Begins as Continuation of Medulla Oblongata at Foramen Magnum and extends up to upper border of L2 vertebra
It contains white matter on the outside mainly and grey matter in the central region
Many Interneurons in the grey matter of spinal cord are Centers for spinal reflexes
Function:
Conduit for Information passage To & fro Brain
Center for some reflexes

3. TRANSVERS SECTION OF SPINAL CORD

4. Reflexes in the body may be …
Reflex : It is an automatic response to a stimuli that occurs without conscious effort
Reflexes in the body may be …
Simple or Basic
Conditioned or Acquired
Reflexes Important in maintaining homeotsasis
Examples
Reflexes carry out the automatic actions of swallowing, sneezing, coughing, vomiting.
Reflexes maintain balance and posture; e.g., spinal reflexes control trunk and limb muscles.
Brain reflexes involve reflex center in brainstem; e.g., reflexes for eye movement.

5. Components of reflex arc are:
SPINAL REFLEX
Reflex : It is an automatic response to a stimuli that occurs without conscious effort
Components of reflex arc are:
Sensory Receptor
Afferent pathway
Center
Efferent pathway
Effector organ

6. Receptor responds to the stimulus and produces action potential (AP)
REFLEX
Receptor responds to the stimulus and produces action potential (AP) ↓
AP is taken by afferent pathway to the integrating center (usually CNS)
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 reflex
Also called as stretch reflex or tendon jerk
e.g. Bicep jerk ,triceps jerk, knee jerk, ankle jerk
Polysynaptic reflex
e.g. Withdrawal reflex, Abdominal reflex, Plantar reflex
Visceral reflex
e.g. 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.
Stretch Reflex is a basic spinal reflex. Example Knee jerk
The 5 components of Stretch Reflex
Sensory receptor – Muscle Spindle in skeletal muscle
Afferent pathway – 1a fibers
Center – spinal cord
Efferent fibers – α-motor neuron
Effector organ – skeletal muscle contraction

9. Types of muscle fibers Extrafusal muscle fibers
Takes part in muscle contraction
Supplied by α - motor neuron
Intrafusal muscle fibers
Also called as Muscle Spindle
Receptors for stretch reflex
supplied by γ - motor neuron

10. Muscle spindle These are the receptors of the muscles
Consist of two types of fibers
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
Detect both dynamic and static changes in muscles

11. Muscle spindle

12. Types of Nerve Fibers

13. α - motor neuron γ - motor neuron Supply Extrafusal fibers
Types of motor neuron
α - motor neuron
Supply Extrafusal fibers
γ - motor neuron
Supply Intrafusal fibers

14. Stretch Reflex (Knee Jerk)
KNEE JERK – MONOSYNAPTIC REFLEX

15. Stretch Reflex (Knee Jerk)

16. Polysynaptic Reflex
In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway
Eg. Withdrawal reflex:
When a person touches a hot stove or pin prick, a withdrawal reflex occurs from the painful stimulus
Receptor- pain and Temperature Receptors stimulated
Afferent impulse travels via Sensory nerves
Efferent fibers to Biceps to contract ( flexion 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.

17. Withdrawal reflex – Polysynaptic reflex

18. 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

19. REFLEXES
Jendressik
Phenomenon
(Reinforcement)

21. Jendressik Phenomenon
(Reinforcement)
Superficial
Reflexes

22. Plantar Reflex

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

24. Cranial Nerve
Spinal
Cord Reflexes

25. Polysynaptic Reflexes
Golgi tendon Reflex
Crossed Extensor Reflex

26. Golgi Tendon Organs
Golgi tendon organ is present in the tendon and is Composed of Nerve fiber endings that wind between collagen fibers inside connective tissue capsule that make up the tendon.

27. Golgi Tendon Reflex
If muscle is stretched by striking the tendon Free nerve endings are pinched in the tendon and they fire
Activation of Golgi tendon organs Inhibits alpha motor neurons and decreases muscle contraction

28. Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed

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

30. Crossed Extensor Reflex

31. Crossed Extensor Reflex

32. Clinical Importance of reflexes
To test the integrity of reflex arc.
Localization of neurological lesion.
Deep tendon reflexes are absent in lower motor neuron lesion.
They become exaggerated in upper motor neuron lesions.
Pendular jerks are observed in cerebellar lesions.
Identifying the type of lesion.
Monitoring the progress of neurological deficit.

33. References
Human physiology by Lauralee Sherwood, 8th edition
Text Book Of Physiology by Guyton & Hall, 11th edition

34. THANK YOU