Question

"Describe the steps involved in the monosynaptic stretch reflex and the reciprocal inhibition" and adds. "You are welcome to use this patellar reflex to illustrate your point"

Answer 1

Reflex:The nervous system controls the reflex reaction in human body. Reflex action is a sudden spontaneous response to a stimulus without consciousness.
There mainly two parts for a reflex process:

• 1. Afferent path: afferent path brings the information of the stimulus from the receptors to the central nervous system.
• 2. Efferent path: efferent path carries information away from the central nervous system to respond to the stimuli.

One of the most common reflex is the muscle stretch reflex. In muscles stretch reflex once a muscle is stretched, reflex tries to contract the muscle to get rid of the the injury. For example, knee jerk reflex./Patellar reflex. The patellar reflex is an easy example for monosynaptic reflex.This can be illustrated by a physician by tapping just below the patella using a rubber hammer, by the time our leg will kick out spontaneously. This is an involuntary response of leg to the stimulus of hitting the patella with rubber hammer. The mechanism behind this reflex is stretching of the tendon associated with the patella followed by the rapid stretching of of the large femoris muscle of thigh. The receptors present on the thigh skeletal muscle (called muscle spindles) receives this stimulus. These muscle spindles fibres are stretches when the associated muscle stretches. The neurone axons wrapping around this muscle spindles detects the stretch and carries information to central nervous system. These axons travel through the peripheral nervous system and enters to the spinal cord or brain stem. These somatosensory neurones have ganglions situated very close to the spinal cord or brainstem. This is the afferent part or somatosensory neurones. This somatosensory neurone forms an excitatory synapse with another neurone inside the central nervous system. This neurone send its axon out of CNS through the nerves of the peripheral nervous system back to the stretched muscle to excite that muscle to contract. This is the response to the stimuli. The efferent pathway constitutes the lower motor neurones that causes the response of contraction in the muscle that is stretched.
Any damage to the afferent or efferent pathway in this stretch reflex can cause delayed or impaired reflex. Higher parts of the the central nervous system like cerebrum don't take part in this process. Only lower segments of the central nervous system along with peripheral nervous system take part in the reflex action. That is why it occurs unconsciously.

Reciprocal inhibition

Simultaneously there will be relaxation of the muscle on the back of the thigh, while the front muscle contracts. This occurs by the somatic sensory neurones that carry the sensory information to the central nervous system, sends axon terminals to another neuron with an inhibitory synapse to the muscles of the opposite side. This neurone which is normally excitatory in action on the back muscle to bend the knee; causes relaxation of this muscle due to the inhibitory synapse resulting in kicking of the leg.

Simultaneous contraction of the anterior muscle(Extensors) and relaxation of the posterior muscle(Flexors) causes an exaggerated action of leg to straighten the knee.