Final answer:
The patellar reflex is a stretch reflex elicited by tapping the patellar tendon, leading to quadriceps contraction via an excitatory synapse in the spinal cord while simultaneously inhibiting the antagonist muscles through reciprocal inhibition. This reflex tests spinal nerves at the L2-L4 level and ensures lower motor neuron function.
Step-by-step explanation:
The patellar reflex, commonly known as the knee reflex, is an example of a stretch reflex. When the tendon below the kneecap (patellar ligament) is struck with a reflex hammer, the quadriceps muscle in the thigh is quickly stretched. This stretch activates muscle spindle receptors in the muscle, which are sensitive to changes in muscle length.
A sensory neuron carries the signal from the muscle spindle to the spinal cord at the level of the lumbar spine. Inside the spinal cord, the sensory neuron forms a synapse with a motor neuron in the ventral horn, which is an excitatory synapse. This means that the motor neuron is stimulated to send an impulse to the quadriceps muscle, causing it to contract and produce the knee movement.
At the same time, a collateral fiber from the sensory neuron synapses with an inhibitory interneuron that in turn connects to the motor neuron controlling the hamstring muscles (the antagonists), causing them to relax, a process known as reciprocal inhibition.
This reflex helps to maintain posture and balance by compensating for changes in muscle length and is an indicator of proper lower motor neuron function. The patellar reflex tests specifically the L2–L4 level of the spinal cord and the corresponding spinal nerves. It is a simple reflex that serves as a vital part of a neurological examination.
As the given question is incomplete, the complete question is:
In your own words, explain what occurs during the patellar reflex (explain the diagram above). That is, explain the neural pathway. You must include the specific receptor, where the synapse points are, if the synapse is excitatory or inhibitory, if the neuron is stimulated or inhibited, if the effector is stimulated or inhibited and the effect that has on the response. You must reference the spinal nerve and the level of the spinal cord being tested. Be sure to include reciprocal inhibition in your explanation.