Patellar reflex

Patellar reflex

The reflex triggered by the stretching of the thigh extensor muscle is the patellar reflex.

Biology

Keywords

patellar reflex, unconditioned reflex, spinal cord reflex, plexor, reflex arc, muscle spindle, extensor muscle, sensory nerve fibers, motor fibers, spinal cord, motor end plate, postural reflex, human, biology

Related items

Scenes

  • sensory nerve fibers - The impulse triggered by the stimulus is transmitted to the spinal cord by these fibers, which are the axons of sensory neurons, wrapped in myelin sheath.
  • motor nerve fibers
  • - It is the center of the patellar reflex, where the signal is processed and the response is planned. Impulses spreading towards the spinal cord (afferent impulses) are transmitted by sensory nerve fibers while impulses carried away from the spinal cord (efferent impulses) are transmitted by motor nerve fibers.

  • - It is the center of the patellar reflex, where the signal is processed and the response is planned. Impulses spreading towards the spinal cord (afferent impulses) are transmitted by sensory nerve fibers while impulses carried away from the spinal cord (efferent impulses) are transmitted by motor nerve fibers.
  • sensory nerve fibers - The impulse caused by the stimulus is transmitted to the spinal cord by these fibers, which are the projections of sensory neurons, wrapped in myelin sheath.
  • motor nerve fibers
  • - When the patellar ligament is lightly tapped with a hammer, the extensor muscle is slightly stretched. This produces a stimulus for the receptors, the muscle spindles. The impulse is transmitted to the spinal cord by the sensory nerve fibers.

  • - This matter of the spinal cord (and the brain) is composed mainly of myelinated axons, nerve fibers.
  • anterior horn of gray matter - This is where the cell bodies of α motoneurons are located. Motor nerve fibers exit the spinal cord here.
  • posterior horn of gray matter - This is where sensory nerve fibers enter the spinal cord.
  • - Their cell bodies are located outside the spinal cord. These cells have two long projections that transmit impulses in the posterior horn of the gray matter of the spinal cord. Sensory nerve fibers are the myelinated projections of sensory neurons.
  • - Their cell bodies are located in the anterior horn of the gray matter of the spinal cord. They have one long axon wrapped in a myelin sheath. Motor nerve fibers are the myelinated axons of motor neurons.

  • muscle fiber - Skeletal muscles are composed of these fibers that contract when stimuli arrive through the motor nerve fibers.
  • sensory nerve fibers - The impulse caused by the stimulus is transmitted to the spinal cord by these fibers, which are the projections of sensory neurons, wrapped in myelin sheath.
  • motor nerve fibers
  • - It is composed of the branched endings of motor nerve fibers and the membrane of muscle fibers. The nerve ending releases neurotransmitters, acetylcholine, which causes the muscle to contract.
  • - When the patellar ligament is lightly tapped with a hammer, the extensor muscle stretches slightly. This produces a stimulus for the receptors, the muscle spindles. The impulse is transmitted to the spinal cord by sensory nerve fibers.

Narration

The patellar reflex serves to prevent the excessive stretching of the thigh extensor muscles.

The reflex is tested in sitting position, with legs freely hanging. When the patellar ligament is lightly tapped with a hammer, the extensor muscle is slightly stretched. This produces a stimulus for the muscle spindles, which is transmitted to the spinal cord by the sensory nerve fibers. The impulse is then transferred directly onto the motor neurons and conducted back into the extensor muscle, where it triggers contraction, which causes the leg to kick.

The patellar reflex is a monosynaptic stretch reflex of muscular origin, this is because the receptors are located inside the muscle, the reflex center is located in the spinal cord and it involves a single synapse.

Related items

The withdrawal reflex

The withdrawal reflex is a spinal reflex that ensures moving away from potentially damaging stimuli.

Anatomy of the spinal cord

The spinal cord is the part of the central nervous system running inside the spinal column from which spinal nerves branch out.

Knee joint

The knee joint is made up by the femur, the tibia and the kneecap.

Nervous system

The central nervous system consists of the brain and the spinal cord, the peripheral nervous system consists of nerves and ganglia.

Neurons, nervous tissue

Neurons are cells specialized for transmitting electric signals.

Bones of the upper limbs

Bones of the upper limbs form the pectoral girdle and the arms.

Human muscles

Skeletal muscles form the active part of the locomotor system: they move the bones they are attached to.

Layers of the skin; cutaneous senses

The skin is the soft outer covering of our body, its three layers are the epidermis, the dermis and the hypodermis.

Medical conditions of the spine

Scoliosis is a medical condition in which a person's spine has a lateral deviation.

Muscles of the upper arm

The arms are moved by flexor and extensor muscles.

Parts of the human brain

The main parts of the human brain are the brain stem, the cerebellum, the diencephalon, and the cerebrum, which is divided into lobes.

Synaptic transmission

Neurons transmit electrical signals via chemical and electrical synapses.

The ear and the mechanism of hearing

The ear converts the vibrations of air into electric signals which are then processed by the brain.

The human brain

The main parts of the human brain are the brain stem, the cerebellum, the diencephalon, and the cerebrum.

The skull and the spine

The two main parts of the central nervous system, the brain and the spinal cord are protected by the skull and the spinal column.

Types of bone articulations

Human bones are joined together by cartilaginous or synovial joints, sutures or they can fuse together.

Types of synovial joints

Synovial joints can be categorised by the direction of movement they allow.

Bones of the lower limbs

Bones of the lower limbs are connected to the trunk by the pelvis.

Muscle tissues

The three types of muscle found in the human body are the smooth, the striated and the cardiac muscle.

Structure of skeletal muscles

This animation demonstrates the fine molecular structure and mechanism of muscles.

Added to your cart.