Examples
A person standing upright begins to lean to one side. The postural muscles that are closely connected to the vertebral column on the side will stretch. Because of this, stretch receptors in those muscles contract to correct posture.
Other examples (followed by involved spinal nerves) are responses to stretch created by a blow upon a muscle tendon:
- Jaw jerk reflex (CN V)
- Biceps reflex C5/C6
- Brachioradialis reflex C6
- Extensor digitorum reflex C6/C7
- Triceps reflex C7/C8
- Patellar reflex L2-L4 (knee-jerk)
- Ankle jerk reflex S1/S2
Another example is the group of fibers in the calf muscle, which synapse with motor neurons supplying muscle fibers in the same muscle. A sudden stretch, such as tapping the Achilles' tendon, causes a reflex contraction in the muscle as the spindles sense the stretch and send an action potential to the motor neurons which then cause the muscle to contract; this particular reflex causes a contraction in the soleus-gastrocnemius group of muscles. Like the patellar reflex, this reflex can be enhanced by the Jendrassik maneuver.
There are basically four types of muscle fibers. This includes the slow twitch (ST) fibers, which are slow contracting and slow to fatigue. The fast twitch muscle fibers are sub-divided into several sub-classes and include fibers that are fast contracting and resistant to fatigue (FRF), fast contracting but more easily fatigued (FEF), and fast contracting fast fatiguing white fibers (FFF).
Read more about this topic: Stretch Reflex
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