Reflexes are apart of your life. With out reflexes you wouldn’t be alive. Everything from an amoeba to a human rely on reflexes to survive.
Reflexes
A reflex is unconscious automatic response.
If we look at simple organisms like worms, lice, squids and amoebas we see simple reflexes.
Simple reflexes assist the animal to hunt, find shelter, mate, escape and avoid harmful environmental factors.
An Amoeba will move away from hostile environments (High concentrations of salts, Acids and Alkalis).
When tapped on the head worms will rapidly contract their muscles to pull it back into its burrow.
If you drop a cat upside down, it will almost always land on its feet. This is known as the Cat righting reflex.
Squids have a large neuron extending from their brain to their mantle. Once stimulated it sends signals to the muscles in the mantle, causing them to contract and shoot away.
This reflex is controlled by fear. Without this reflex in built, the squids they would most certainly die as infants.
This is an example of a simple reflex.
Simple animals use reflexes for the majority of their behaviour. The problem with this is that they find it difficult when an unfamiliar situation arises.
More complex animals use reflexes for some of their behaviour. We can decide how and when to react in new situations.
So, how do reflexes work?
In humans, reflexes are controlled by the reflex arc.
A signal will pass from a sensory neuron, via a relay neuron, to a motor neuron for an instant, unconscious action.
A reflex arc is a fast and automatic response. Watch the animation to the left, notice how the signal is split at the relay neuron.
This means your hand moves even before your brain knows. It is an innate behaviour.
If you’ve ever seen someone’s eyes, you’ll notice the pupil (black dot) changes size depending on the light in an environment.
This is called the pupil reflex.
The pupil shrinks in bright light, meaning less light enters the eye and does not damage the retina.
If we look at a baby, you’ll notice a lot of their movements are controlled by reflexes. Unconscious actions which help us survive.
Grasping reflex - Stroke your baby’s palm with your finger. She’ll immediately grab your finger and hold on so tight you might have to pry her little fingers off.
Tonic neck reflex - The head of a child who is relaxed and lying face up is moved to the side. The arm on the side where the head is facing reaches away from the body with the hand partly open. This happens when something or someone heads his way quickly.
Stepping reflex - If you hold the baby under his armpits and let his legs dangle, and slowly lower him so his toes touch the floor, he will start to make a walking motion.
Rooting reflex - Stroke one side of a baby’s check and it will turn his head towards you and begin to make a sucking movement with his mouth.
Questions
1. What is a reflex?
2. State the order of neurons involved in a reflex response
3. Why do we have reflexes?
4. Explain how the rooting reflex and tonic neck reflex assist in the survival of infants
