REFLEXES AND THEIR REASONS

  Scientific reasons behind various reflexes, including spasticity, rigidity, brisk reflexes, and tendon reflexes, in the context of Upper Motor Neuron Lesion (UMNL) and Lower Motor Neuron Lesion (LMNL) lesions:

Spasticity:

- Spasticity results from damage to upper motor neurons, as seen in conditions like stroke or cerebral palsy. With UMNL, the loss of inhibitory control from upper motor neurons leads to hyperexcitability of spinal reflexes. This causes exaggerated stretch reflexes, resulting in increased muscle tone and stiffness characteristic of spasticity.

Rigidity:

- Rigidity is common in conditions like Parkinson's disease, where there's dysfunction in the basal ganglia. In UMNL, rigidity can also occur due to disrupted inhibitory pathways from upper motor neurons. The imbalance in neurotransmitter activity, particularly reduced dopamine, leads to sustained muscle contractions and stiffness, resulting in rigidity.

Brisk Reflexes (Hyperreflexia):

- Brisk reflexes occur due to increased excitability of the stretch reflex arc, often seen in UMNL lesions such as stroke or spinal cord injury. Without normal inhibitory input from upper motor neurons, the stretch reflex becomes exaggerated. As a result, even slight stimuli can elicit brisk or exaggerated reflex responses.

Tendon Reflexes:

1. Biceps Reflex:

   - In UMNL, such as stroke, the biceps reflex may be brisk due to increased excitability of the stretch reflex arc caused by disrupted inhibitory pathways from upper motor neurons.

   - In LMNL, such as peripheral nerve damage, the biceps reflex may be diminished or absent due to interruption of the reflex arc at the level of the lower motor neuron.

2. Triceps Reflex:

   - In UMNL, the triceps reflex may be brisk due to disrupted inhibitory pathways from upper motor neurons.

  - In LMNL, such as cervical spinal cord injury, the triceps reflex may be diminished or absent due to disruption of lower motor neuron pathways.

3. Brachioradialis Reflex:

   -  In UMNL, the brachioradialis reflex may be brisk due to increased excitability of the stretch reflex arc.

   -In LMNL, such as radial nerve injury, the brachioradialis reflex may be diminished or absent due to interruption of lower motor neuron pathways.

4. Patellar Reflex:

   - In UMNL, such as stroke or cerebral palsy, the patellar reflex may be brisk due to increased muscle tone and hyperexcitability of the stretch reflex arc.

   - In LMNL, such as femoral nerve injury, the patellar reflex may be diminished or absent due to disruption of lower motor neuron pathways.

5. Achilles Reflex:

   -  In UMNL, such as stroke or spinal cord injury, the Achilles reflex may be brisk due to increased excitability of the stretch reflex arc.

   -  In LMNL, such as tibial nerve injury, the Achilles reflex may be diminished or absent due to disruption of lower motor neuron pathways.