Synapses & Reflexes - Reflexes and the Reflex Arc (GCSE Biology)
Reflexes and the Reflex Arc
Reflex Arc
Reflexes
- The reflex arc controls reflexes. The reflex arc is one of the most important neural circuits in the body. Reflexes are quick responses by the body, which are very important in avoiding damage. For example, if you touch a hot pan, your reflex is to immediately move away.
- The reflex arc doesn’t involve the brain. Reflexes do not involve the conscious part of the brain, and the reflex arc therefore just runs through the spinal cord, not the brain. Reflexes are therefore rapid and automatic. As they are fast, they can help prevent injuries.
- Reflexes are the same in everyone. Reflex actions are innate – i.e. they are built into us. We can’t control them too much and they don’t tend to vary much between people.
- Synapses in a reflex arc ensure that impulses only travel in one direction.
Reflex Arc Pathway
The reflex arc involves the pathway we learnt earlier:
- Receptor – the stimulus is picked up by the receptor.
- Sensory neurone – an impulse is then transmitted down the sensory neurone to the CNS.
- Relay neurone – in the CNS, there is a synapse and a relay neurone takes it through the CNS.
- Motor neurone – The impulse then moves from the CNS to the effector through the motor neurone.
- Effector – the effector then causes a protective response against the stimulus. The effector can be a muscle or a gland.
Examples of Reflex Arcs
Examples of reflexes include:
- Knee-jerk reflex – if you tap the patellar tendon in the knee (just under the knee-cap), the knee will jerk.
- Hot object – if you touch a hot object your hand will quickly move away to protect you from a burn.
Investigating Reaction Time
Reaction time is the time it takes for you to respond to a stimulus and different factors can affect this. For example, you can investigate the effect of caffeine on reaction time by doing a ruler test and you can see that caffeine can speed up reaction time:
- Get a person to rest their arm at the edge of a table with their hand off the table. Make sure they don’t move their arm up or down during the test.
- Place a ruler between their thumb and index finger with the zero mark level with their thumb and finger.
- Let go of the ruler without saying you are going to do so.
- The person should try to catch the ruler between their thumb and index finger as fast as they can.
- Observe your results. From the ruler, read off the number at the top of their thumb – this represents their reaction time. The bigger the number, the slower the reaction time.
- Repeat a few times and calculate a mean reaction time.
- The person should then take some caffeine. For example, having some coffee or a cola drink.
- Wait 15 minutes then repeat steps 1-6 and notice the difference in the mean reaction times.
FAQs
A reflex is an automatic, rapid response to a stimulus that occurs without conscious thought.
A reflex works by using a specific pathway, called the reflex arc, to quickly transmit information from the stimulus to the effector, such as a muscle, to produce a rapid response.
The reflex arc is the pathway that information follows in a reflex, including the sensory neurons that detect the stimulus, the interneurons that process the information, and the motor neurons that transmit the information to the effector to produce a response.
The components of a reflex arc include the receptor, sensory neuron, interneuron, motor neuron, and effector.
The sensory neuron plays the role of detecting the stimulus and transmitting the information to the interneuron.
The interneuron plays the role of processing the information from the sensory neuron and transmitting it to the motor neuron.
The motor neuron plays the role of transmitting the information from the interneuron to the effector, such as a muscle, to produce a rapid response.
Some examples of reflexes in biology include the knee-jerk reflex, the withdrawal reflex, and the pupillary reflex.
The purpose of reflexes in biology is to provide a rapid and automatic response to a stimulus, allowing the body to respond quickly to potential threats or changes in the environment without the need for conscious thought.
Still got a question? Leave a comment
Leave a comment