Question

reflex arc and reflexes assessment b. holes human

Answer 1

Reflex action is the spontaneous reactivity (independent of will) of a person towards a sensory stimulus like knee-jerking, putting a finger on the flame, etc. the apparatus involved in this activity is called, reflex arc.

A reflex arc consists of the following parts.

• A sensory (receptor) organ (Eg: skin that contains thermoreceptors, nociceptors, pressure receptors etc.)
• A sensory nerve: (Afferent neuron) which terminates at the posterior nerve root of the spinal cord. This neuron carries impulses from the effector organ towards the CNS.
• Spinal cord: In the gray matter, the sensory stimulus is converted into a motor impulse.
• Interneuron: Neurons present in the spinal cord, which connect the afferent and efferent neurons.
• A motor nerve: (Efferent nerve) it arises from the anterior horn cells of the spinal cord, which transmits the impulses to the effector organ, in this case, the finger.

A simple reflex involves only two neurons, i.e. the afferent (sensory) neuron, and the efferent (motor) neuron. For example, patellar reflex or knee-jerk reflex is a simple stretch reflex (somatic reflex). Patellar reflex can be tested by knee-jerk. A person should be asked to sit on a bench with hanging legs freely, and tap the patellar ligament just below the knee with the reflex hammer. This excites the muscle spindle of quadriceps that is innervated by femoral nerve.