Reflex arcs

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Reflexes are quick, automatic responses that occur without conscious control in response to particular sensory stimuli. Many reflexes act as protective mechanisms to help prevent injury, while others function to maintain homeostasis, such as regulating respiration and heart rate.

The basic components that make up every reflex are the same and collectively form a reflex arc. There are five major components to a reflex arc: sensory receptor, sensory neuron, integration center, motor neuron and effector organ. Reflexes can be broadly categorised into two-types: somatic and visceral reflexes. Somatic reflexes include all reflexes that involve skeletal muscles, whilst visceral reflexes regulate internal organs and are related to smooth and cardiac muscle or glands. Reflexes can also be categorised as either monosynaptic or polysynaptic, depending on the number of synapses involved in their reflex arcs. Monosynaptic reflexes involve a single synapse between the sensory and motor neurons within the integration centre, whilst polysynaptic reflexes involve at least two synapses.

Some of the most common somatic reflexes in the body include the stretch reflex, Golgi tendon reflex, flexion (withdrawal) reflex and crossed-extension reflex. The stretch reflex is an example of a monosynaptic reflex which is activated when a muscle is stretched beyond its optimal length. This reflex causes the stretched muscle to contract in order to restore it to its ideal length, maintaining muscle tone and protecting against overstretching injuries. The Golgi tendon reflex is an example of a polysynaptic reflex, which functions to prevent muscle damage from excessive tension. The flexion and crossed-extension reflexes, both examples of polysynaptic reflexes, work together to protect the body from painful stimuli by coordinating a rapid withdrawal of the affected limb and simultaneous stabilization of the opposite limb.

Watch the following video to learn more about reflex arcs and see these different types of reflexes in action.

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Reflex arcs

All reflexes in the body are composed of five basic components, which combine to form a reflex arc. Learn more about how these components come together and function below.

Muscle sensory receptors

Muscle spindles and tendon organs are specialized sensory receptors involved in the stretch and Golgi tendon reflexes, respectively. Learn more about their structure and function below.

Reflexes

The stretch, Golgi tendon, flexion and crossed-extension reflexes are all examples of somatic reflexes that function to protect the body from harm. Learn more about each of their reflex arcs below.

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