Question

Describe in your own words the steps of the knee jerk reflex and how this is an example of a negative feedback mechanism.

Answer 1

STEPS OF THE KNEE JERK REFLEX.

1. A tap on the patellar tendon (tendon attached to the kneecap) is sensed by stretch receptors in the muscle (muscle spindles).

2. The muscle spindle produces a pattern of nerve impulses that are conveyed along a sensory (afferent) nerve fiber, past its cell body in the dorsal root ganglion, and to its termination on a motor neuron.

3. The nerve terminal releases neurotransmitters onto the motor neurons, which generate excitatory, postsynaptic potentials in the motor neurons’ dendrites and cell bodies.

4. The motor neuron generates action potentials, leading to the release of acetylcholine from its terminals on muscles.

5. The muscle responds to the acetylcholine by depolarizing and contracting.

How this is an example of negative feedback mechanism?

Tapping the patellar tendon stretches the quadriceps muscle. This causes the sensory receptor of the muscle, called a spindle fiber, to send a signal along the afferent neuron to the spinal cord. This causes the efferent neuron to return a signal to the quadriceps muscle to contract. The quadriceps is an extensor muscle so when it contracts it extends the angle of the knee joint by raising the lower leg. This action resists the initial stretch and therefore, is a classic example of negative feedback.