Question

Monosynaptic reflex is a
a) Complex reflex arc consisting of two sensory neurons and one motor neuron.
b) Simplex reflex arc consisting of two sensory and one motor neurons
c) Simple reflex arc consisting of one sensory and one motor neuron
d) Simple reflex arc consisting of one sensory and two motor neurons

Answer 1

Hint:The Reflex arc is the pathway of the nerve involved in a reflex action. This consists of the Receptor organ, Afferent nerve fibres, Interneurons, Efferent nerve fibres and Effector organs. Based on the number of synapses, the reflex is termed as Monosynaptic or Polysynaptic.

Complete answer:Reflex action is sudden and involuntary movement in response to a stimulus. It is a protective mechanism of the body. The reflex actions include withdrawal of hand on touching a hot object, sudden blinking of the eye if any object approaches it, sneezing due to dust, etc.

The pathway through which reflex action is carried out is the Reflex arc. The components of the reflex arc are
a) Receptor organs: These are skin, tendons, and muscles. These receive the stimulus.
b) Afferent nerve fibres: Nerve fibres arise from Sensory organs and these are also known as Afferent nerve fibres.
c) Integration centre: The afferent nerve fibres carry the stimulus to the spinal cord or brain stem and it synapses to form the motor fibres. Interneurons may or may be present.
d) Efferent fibres: Nerve fibres that arise from the brainstem or spinal cord are Motor neurons or Efferent neurons.
e) Effector organs: The efferent fibres innervates the effector organs like muscles that respond to the stimulus.

Based on the number of synapses, there are two types of reflexes. Monosynaptic and Polysynaptic. The Monosynaptic reflex consists of only one synapse while Polysynaptic consists of more than one synapse. Thus in Monosynaptic, the motor and sensory neurons are directly connected and thus interneurons are absent. This is a simple reflex.

Hence option ‘c’ is the correct answer.

Note:The Knee-jerk reflex or Patellar reflex is an example of a Monosynaptic reflex. It is faster than the Polysynaptic reflex. This reflex helps in proper posture and balance of the body.