Reflexes

Reflexes are automatic reactions our body makes when something triggers them. They happen without us even thinking about it. There are many types of reflexes, but one we use often is the protective reflex. This reflex kicks in when we touch something too hot, like a hot plate. Our hand moves away from the plate to avoid getting burned. In this article, we'll explore different types of reflexes.

The nervous system and reflexes

The nervous system is divided two main parts, each with its own systems. The central nervous system (CNS) includes the brain and spinal cord, while the peripheral nervous system (PNS) is made up of nerve pairs that come from the brain or spinal cord.

The peripheral nervous system further divides into sensory and motor neurons. Sensory neurons carry nerve impulses from receptors to the central nervous system. Motor neurons carry nerve impulses away from the central nervous system to effectors.

A receptor is an organ or cell that detects a stimulus, like a change in temperature, and sends that information somewhere else in the body. An effector is a body part or cell that responds to the information conveyed by the receptor. For example, a muscle contracts to move a hand away from a hot plate.

The motor nervous system

The motor nervous system, which regulates muscle movement, is made up of two categories: the voluntary nervous system and the autonomic nervous system.

The voluntary nervous system carries nerve impulses from the CNS to muscle effectors, and is under conscious control. It is also called the somatic nervous system, and the reflexes it controls are called somatic reflexes. These reflexes affect muscles, like moving your leg when you step on something sharp.

The autonomic nervous system carries nerve impulses to glands, smooth muscle, and cardiac muscle. It is not under voluntary control and controls subconscious actions. Reflexes controlled by this system are called autonomic reflexes, which affect inner organs. Examples include breathing and heart rate control.

The two main types of reflexes are somatic reflexes and autonomic reflexes. Smooth muscle is a type of muscle that contracts automatically and slowly. It makes up the internal musculature of organs like the uterus and digestive system.

The spinal cord

The spinal cord is a long, thin, tubular structure of nervous tissue that is part of the central nervous system (CNS). It is located inside the vertebral column, a bone structure along the back. Pairs of nerves emerge at intervals along the spinal cord, and these nerves are responsible for carrying sensory information from the body to the CNS, and motor information from the CNS to the body. The spinal cord is also responsible for the processing of reflexes, which are automatic responses to certain stimuli. For example, if you accidentally touch a hot stove, the reflex arc of the spinal cord will automatically cause you to pull your hand away before the brain even registers the pain. Overall, the spinal cord is an essential part of the nervous system, responsible for relaying information between the brain and the rest of the body, as well as for the processing of reflexes.

Reflex arcs

Reflexes are involuntary

That reflexes being involuntary means that the decision-making part of our brain doesn't need to be involved in acting, allowing the brain to focus on more complex processes in the body. It's also true that the brain has the power to override reflexes if needed. For example, if there is food on a hot plate, the brain may override the reflex to move your hand away to prevent dropping the food. Regarding the words "unconscious" and "involuntary," you are correct that they have similar meanings in terms of actions that are not under conscious control. However, "unconscious" can also refer to a state of being where one is not aware of their surroundings, such as when sleeping or in a coma. "Involuntary" does not have this additional meaning and only refers to actions that are not under conscious control.

Reflexes are protective

Reflexes are not a learnt behaviour. We are simply born with them, so the same reflexes are present in all healthy humans. Some reflexes allow us to move away from danger, protecting ourselves and ensuring our survival. A protective reflex is blinking when something such as a ball comes flying towards your eyes. This reflex protects your eyes from being damaged by the object, keeping your vision safe.

Reflexes are rapid

Reflexes cause action to happen very quickly. This is because of the very short reflex arc pathway. This means that nervous impulses can travel from the receptor to the effector almost instantly. Furthermore, the fact that we do not have to make a decision about whether to act saves time too. This is beneficial as it helps us respond to danger as quickly as possible to keep ourselves safe.

Reflexes are short-lived and localised

‘Localised’ means that the response only affects the parts of the body involved, and ‘short-lived’ means that the response does not last for a long time. This is beneficial for the situations where reflexes are used as it allows us to resume normal behaviour as soon as the danger has passed. In the example above, the blinking response only affects your eyes and is over once the object has stopped coming towards you.

Examples of reflexes

There are many different types of reflexes in our body. Four key examples of reflexes include:

The stretch reflex. The flexor (withdrawal) reflex. The crossed-extensor reflex. The Golgi tendon reflex.

The stretch reflex

When a muscle is stretched, muscle spindle receptors will send nervous impulses to the spinal cord, causing the same muscle to contract. At the same time, the antagonistic muscle is relaxed. Some muscles work in ‘antagonistic pairs.’ As one muscle contracts, the other muscle relaxes or lengthens. An example of an antagonistic pair is the biceps and triceps. When our biceps contract, our triceps relax and vice versa. Another common example of this reflex is the knee jerk reflex. Doctors do this test on patients to test that specific spinal cord segments are working. It involves striking a tendon near the knee (called the patellar tendon) with a rubber hammer. This will cause the patellar tendon to pull on the leg’s quadriceps muscle (the effector). The stretch reflex will then counteract this stretch as the muscle ‘thinks’ it is stretching very rapidly. The response to this will be that the knee will jerk, which is why the reflex is called the ‘knee jerk reflex’!

Flexor (withdrawal) reflex

When a body part comes into something dangerous, such as touching a hot plate as mentioned above, the body part will reflexively pull away. This occurs because sensory receptors in the skin send nervous impulses to the spinal cord, which will cause the body part to contract and move away. The sensory information for this type of reflex will also travel to the brain so conscious decision-making can occur and override the reflex from happening. If you were having a vaccine injected into your arm you might reflexively move it away due to the pain. However, you can override this reflex by keeping your arm still.

Crossed-extensor reflex

As we saw above, stepping on a sharp object causes a withdrawal reflex of the leg. You might wonder why this doesn’t cause us to topple over, and the answer to this is the crossed-extensor reflex. When the withdrawal reflex of the injured leg happens, the opposite leg extends at the same time, so that the person can appropriately shift their balance to the opposite foot during the reflex.

Golgi tendon reflex

This is a reflex that happens due to the Golgi tendon organs. Golgi tendon organs are types of sensory receptors that sense changes in muscle tension. They lie in between a muscle and its tendon. When a muscle is stimulated by a stretch that is too much or too long, the Golgi tendon organs will detect this and send nervous impulses to the spinal cord that cause the stretched muscle to relax. Due to this, the Golgi tendon reflex is also referred to as the ‘inverse stretch reflex’ as it has the opposite effect to the stretch reflex. In the stretch reflex, the antagonistic (opposite) muscle is relaxed, whereas in the inverse stretch reflex, it is the muscle that is stretching that is relaxed.

Reflexes - Key takeaways A reflex is an involuntary, automatic action that the body makes in response to a stimulus. Our nervous system has different divisions. The two major ones are the central nervous system and peripheral nervous system. A reflex arc is the pathway of neurones that are involved in a reflex. The three major neurones involved in reflex arcs are sensory neurones, relay neurones, and motor neurones. Reflexes are rapid, protective, involuntary, short-lived, and localised. We have different types of reflexes in the body. Four key examples are the stretch reflex, the flexor reflex, the crossed-extensor reflex, and the Golgi tendon reflex.

Reflexes

What are the two main types of reflexes?

The two main types of reflexes are somatic reflexes, which are performed consciously, and autonomic reflexes, which are performed subconsciously. The effectors for somatic reflexes are muscles, whilst the effectors for autonomic reflexes are inner organs.

What are the four types of reflexes?

The four types of reflex are the stretch reflex, the flexor (withdrawal) reflex, the crossed-extensor reflex, and the Golgi Tendon reflex

What are examples of reflexes?

Common somatic reflexes include moving your hand away when you touch a hot object or moving your leg away when you step on a sharp object. Common autonomic reflexes include breathing and swallowing.

What is reflex action?

A reflex, or reflex action, is an involuntary, automatic action that the body makes in response to a stimulus.

Why are reflexes important?

Reflexes are important for our protection from danger and survival. This is firstly because they are involuntary, so the decision-making part of our brain doesn’t need to be involved in carrying out the action. Secondly, they are rapid, meaning that we can respond to danger quickly. Thirdly, they are short-lived and localised meaning that they only affect the body part susceptible to danger and allow us to resume normal behaviour once the danger has passed.

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