What is the basis of deep reflexes?
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.
How are tendon jerks tested?
- 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).
What are the mechanisms behind reinforcement techniques for weak reflexes?
- Increase discharge of γ-efferent neurons.
- Distract the patient to prevent voluntary inhibition of the reflex.
What is the center and response of the biceps reflex?
- Center: C5, C6.
- Response: Contraction of the biceps and flexion of the elbow.
What is the center and response of the triceps reflex?
- Center: C6, C7, C8.
- Response: Contraction of the triceps and extension of the elbow.
What is the center and response of the knee jerk reflex?
- Center: L2, L3, L4.
- Response: Contraction of the quadriceps and extension of the knee.
What is the center and response of the ankle jerk reflex?
- Center: L5, S1, S2.
- Response: Contraction of the calf muscles (gastrocnemius and soleus) and plantar flexion of the ankle.
What is the center and response of the jaw jerk reflex?
- Center: Trigeminal nerve nuclei.
- Response: Flexion of the mandible.
What is the significance of tendon jerks in clinical assessment?
- 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).
What is the Golgi tendon reflex?
- 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).
What is clasp knife rigidity, and what causes it?
- 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).
What is clonus, and how is it initiated?
- 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.
