1. Ginus Partadiredja Department of Physiology
REFLEX
Ginus Partadiredja
Department of Physiology

2. REFLEX: A Fast, automatic, predictable involuntary response
to a particular stimulus
REFLEX: - Inborn (pulling hand away from a hot surface)
- Acquired (Driving expertise)
REFLEX: 1. Somatic (skeletal muscle)
2. Autonomic (glands, cardiac & smooth muscle)
REFLEX: 1. Spinal reflex
2. Cranial reflex

3. REFLEX ARC COMPONENTS:
Sensory receptor  Sensory/ afferent neuron  Integrating center  Motor/ Efferent neuron  Effector
REFLEX: 1. Monosynaptic reflex (e.g. stretch reflex)
2. Polysynaptic reflex (e.g. withdrawal reflex)

4. SOMATIC SPINAL REFLEXES
Stretch reflex
Tendon reflex
Flexor (withdrawal reflex)
Crossed extensor reflex
STRETCH (MYOTATIC) REFLEX
Control muscle length  muscle contraction response
Monosynaptic reflex
Tapping tendons at the elbow (biceps & triceps reflexes),
wrist, knee (knee jerk/ patellar reflex), ankle (Achilles
reflex)

5. Biceps reflex
Triceps reflex 
Achilles reflex
Patellar
reflex 

6. PATELLAR REFLEX: Tendon  Muscle spindle  Ia afferent
neuron  Spinal cord   motor neuron excited
Monosynaptic, ipsilateral reflex
Reciprocal innervation  polysynaptic  antagonistic muscle
inhibited

9. MUSCLES:
Extrafusal
Intrafusal (muscle spindle) fibres
MUSCLE SPINDLE:
Nuclear bag fibre
Nuclear chain fibre
SENSORY NEURONS:
Nuclear bag fibre  Ia afferent fibres
Nuclear chain fibre  Ia and II afferent fibres
MOTOR NEURONS:
Extrafusal fibres  Alpha motor neuron
Intrafusal fibres  Gamma motor neuron

10. Nuclear bag fibres  dynamic stretch reflex stretch
Nuclear chain fibres  static stretch reflex reflex
GAMMA MOTOR NEURON:
Regulated by the brain, voluntary
Smooth out the movement during muscle contractions
Preventing jerky movements
Alpha & gamma motor neurons are stimulated
simultaneously

11. 2. TENDON REFLEX
Control muscle tension  muscle relaxation response
Polysynaptic, ipsilateral
Golgi tendon organs  Ib afferent neuron  Spinal cord 
a.Inhibitory interneuron  Motor neuron inhibited/ muscle relaxes
b.Excitatory interneuron Motor neuron excited/ antagonistic muscle contracts

13. 3. FLEXOR REFLEX
Withdrawal reflex
Polysynaptic, ipsilateral, intersegmental
Pain receptor  Sensory neuron  Integrating center 
Interneuron  Motor neuron  Ipsilateral flexor muscles
- Reciprocal innervation  extensor muscles

14. WITHDRAWAL
REFLEX:
Polysynaptic
Ipsilateral
Intersegmental

15. 4. CROSSED EXTENSOR REFLEX
Polysynaptic, contralateral,
intersegmental
Contralateral reflex arc
Pain receptor  Sensory neuron
 Integrating center 
Interneuron  Motor neuron 
Contralateral extensor muscles
Reciprocal innervation  Flexor
muscles

16. DIAGNOSTICS
Muscle tone
- Poliomyelitis  hypotonia/ atonia
- Stroke  hypertonia
- Muscle spasm (broken bone, peritonitis), cramps
Reflex
- Afferent fibers/ lower motor neuron lesions (e.g. poliomyelitis,
diabetes, syphilis)  hyporeflexia
- Descending motor pathways from the brain (e.g. stroke)
 hyperreflexia
- Mass reflex

17. 3. Patellar reflex
Diabetes mellitus, neurosyphilis  decrease/ absent
Motor tracts descending from the brain disorders 
increase/ hyperreflexia
4. Achilles reflex
Diabetes mellitus, neurosyphilis, alcoholism,
subarachnoid hemorrhages  decrease/ absent
Cervical cord compression, motor tracts lesion 
increase
5. Abdominal reflex
6. Pupillary light reflex (autonomic reflex)  brain injury indicator
7. Babinski sign

18. References
Carola R, Harley JP, Noback, CR (1990). Human Anatomy and Physiology, Chapter 12, Pages:
Ganong WF (2005). Review of Medical Physiology, 22nd ed. Chapter 6, Pages:
Guyton AC & Hall JE (2006). Textbook of Medical Physiology, 11th ed. Chapter 54, Pages:
Tortora GJ & Derrickson B (2006). Principles of Anatomy and Physiology, 11th ed. Chapter 13, Pages: