What is the purpose of the patellar reflex?

The primary purpose of the patellar reflex, which is the stretch reflex of the quadriceps femoris muscle in your anterior thigh, is to prevent the stretching of the quadriceps. The patellar reflex is illustrated in Figure 2. The patellar tendon attaches the quadriceps muscle to the tibia bone of the lower leg.

Which nerve is responsible for patellar reflex?

Although the knee jerk reflex is mediated by the L3 and L4 nerve roots, evidence exists that altered knee jerk expression may occur with exclusively L5 radiculopathy.

What happens in the patellar reflex?

Knee-jerk reflex, also called patellar reflex, sudden kicking movement of the lower leg in response to a sharp tap on the patellar tendon, which lies just below the kneecap. In reaction these muscles contract, and the contraction tends to straighten the leg in a kicking motion.

What role does a neuron play in a knee jerk?

In the knee-jerk reflex, the sensory neurons from a particular muscle connect directly to the motor neurons that innervate that same muscle, causing it to contract after it has been stretched. The sensory neuron activates the motor neuron, causing the quadriceps muscle to contract.

Does the patellar reflex involve the brain?

The normal knee-jerk or, “patellar jerk,” reflex is elicited when the knee is tapped below the knee cap (patella). Sensors that detect stretching of the tendon of this area send electrical impulses back to the spinal cord. The brain is never involved in the reflex.

What does an abnormal patellar reflex indicate?

Abnormal patellar tendon reflexes can indicate neurological disease. [4][5][6][7] In particular, diminished reflex responses are associated with the peripheral nervous system (PNS) disorders, while hyper reflexive responses are related to the central nervous system (CNS) disorders.

Does the knee jerk reflex involve the brain?

Doctors will test reflexes by tapping the tendon just below the knee, and this causes the leg to kick out. This knee-jerk reflex is an example of a simple monosynaptic reflex. This quick response is called a reflex, and reflexes occur without conscious thinking or planning, meaning the brain is not involved in them.

How does the patellar reflex protect us?

Striking of the patellar tendon with a reflex hammer just below the patella stretches the muscle spindle in the quadriceps muscle. This is a reflex of proprioception which helps maintain posture and balance, allowing to keep one’s balance with little effort or conscious thought.

What is the main function of the motor neuron?

Motor neurons of the spinal cord are part of the central nervous system (CNS) and connect to muscles, glands and organs throughout the body. These neurons transmit impulses from the spinal cord to skeletal and smooth muscles (such as those in your stomach), and so directly control all of our muscle movements.

Why does hitting the knee make you kick?

The most familiar reflex is the knee jerk, when a healthcare provider taps on the tendon below your knee with a reflex hammer and that leg kicks out. This communication, from a sensory nerve to the spinal cord and on to a motor (movement) nerve (without going to the brain), is known as a reflex arc.

Which reflex is most difficult to test?

Ankle jerks (S1/S2 myotome)—The ankle jerk is the most difficult reflex to elicit, and palpation of the Achilles tendon before striking to ensure the hammer is striking the correct location can be helpful when difficulties in interpretation are encountered (fig 3).

How is the patellar tendon a monosynaptic reflex?

The monosynaptic patellar reflex. A tap to the patellar tendon stretches the quadriceps muscle (1) resulting in activation of the muscle spindle (2). The afferent neuron of the muscle spindle, detecting stretch, sends a signal to the spinal cord (3) and synapses directly with a motor neuron (4) that causes the quadriceps muscle to contract (5).

Why is it important to test patellar reflexes?

Reflex testing is of clinical value. Testing of the patellar response indicates: The relative health of the muscle spindle, afferent (sensory) and efferent (motor) neurons, neuromuscular junctions, and the extrafusal (contractile) muscle fibers. An appropriate balance of excitatory and inhibitory regulation from the central nervous system.

Where does the reflex hammer synapse in the spinal cord?

Striking the patellar tendon with a reflex hammer stretches the muscle spindle in the quadriceps femoris muscle; this produces a signal that synapses directly onto an alpha-motor neuron at the level of L3 or L4 in the spinal cord.

What are the reflexes of the peripheral nervous system?

1 Stretch Reflex. The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. 2 Golgi Tendon Reflex. The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. 3 Crossed Extensor Reflex. 4 Withdrawal Reflex.