Deep Reflexse

Question 1

What is the basis of deep reflexes?

Answer 1

Dynamic stretch reflex, which is triggered by sudden and quick muscle stretch, involving nuclear bag fibers, primary (Ia) afferents, α-motor neurons, and producing a sudden, strong muscle contraction followed by relaxation.

Question 2

How are tendon jerks tested?

Answer 2

• The muscle must be slightly stretched.
• Use a reflex hammer to strike the tendon suddenly and strongly.
• Compare responses on both sides.
• Reinforce weak reflexes using techniques like clenching teeth (UL) or Jendrassik’s maneuver (LL).

Question 3

What are the mechanisms behind reinforcement techniques for weak reflexes?

Answer 3

• Increase discharge of γ-efferent neurons.
• Distract the patient to prevent voluntary inhibition of the reflex.

Question 4

What is the center and response of the biceps reflex?

Answer 4

• Center: C5, C6.
• Response: Contraction of the biceps and flexion of the elbow.

Question 5

What is the center and response of the triceps reflex?

Answer 5

• Center: C6, C7, C8.
• Response: Contraction of the triceps and extension of the elbow.

Question 6

What is the center and response of the knee jerk reflex?

Answer 6

• Center: L2, L3, L4.
• Response: Contraction of the quadriceps and extension of the knee.

Question 7

What is the center and response of the ankle jerk reflex?

Answer 7

• Center: L5, S1, S2.
• Response: Contraction of the calf muscles (gastrocnemius and soleus) and plantar flexion of the ankle.

Question 8

What is the center and response of the jaw jerk reflex?

Answer 8

• Center: Trigeminal nerve nuclei.
• Response: Flexion of the mandible.

Question 9

What is the significance of tendon jerks in clinical assessment?

Answer 9

• Localization of spinal cord lesions.
• Assessment of muscle tone and stretch reflex:
  (a) Areflexia and atonia: Due to interruption of the reflex arc (e.g., peripheral neuritis, poliomyelitis, tabes dorsalis, spinal shock).
  (b) Hyperreflexia and hypertonia: Due to interruption of supraspinal inhibitory impulses (e.g., anxiety, hyperthyroidism, UMNL, tetany).
  (c) Hyporeflexia and hypotonia: Due to interruption of supraspinal facilitatory impulses (e.g., sleep, hypothyroidism, LMNL, neocerebellar syndrome).

Question 10

What is the Golgi tendon reflex?

Answer 10

• A reflex initiated by marked muscle stretch.
• Receptors: Golgi tendon organs.
• Afferents: Myelinated Ib fibers.
• Response: Relaxation of the same muscle to prevent tearing by reducing tension (negative feedback).

Question 11

What is clasp knife rigidity, and what causes it?

Answer 11

• It is a lengthening reaction where resistance during passive stretch of hypertonic muscles disappears suddenly (resembling a pocketknife closure).
• Mechanism: Moderate stretch triggers the stretch reflex (increased resistance), while marked stretch triggers the inverse stretch reflex (sudden relaxation).

Question 12

What is clonus, and how is it initiated?

Answer 12

• Regular rhythmic contractions and relaxations of a muscle when subjected to sudden maintained stretch.
• Example: Ankle clonus (initiated by maintained dorsiflexion of the foot, causing rhythmic plantar flexion).
• Mechanism: Alternating activation of the stretch reflex and inverse stretch reflex.