Reflexes

Introduction Being a human is a risky endeavor There are more than a few different ways that a person can hurt themselves In these scenarios the body has to help the human get out of danger… in spite of itself Let me give you an example

Introduction As you can see from the previous video, there are situations where a person has to respond to a stimulus in a very quick fashion If there is a non response to a stimulus there could be a situation where there is injury or death

Introduction The body needs a system that helps it protect you from the environment A reflex is an involuntary response to a stimulus A reflex is involuntary because it is designed to happen faster than the body can respond This gets the person out of harms way in the quickest way possible

Demonstration Sometimes reflexes are easy to see There are certain body parts that we can stimulate to create reflexes Today we are going to try to stimulate the patellar reflex

Reflex Arc The entire wiring of a single reflex is called a reflex arc To understand how a reflex works, lets look at the wiring of a single reflex The reflex we are going to look at right now is the withdrawal reflex This happens when the body is trying to escape a stimulus

Reflex Arc 1) A stimulus arrives and activates a receptor During the first stage of a reflex arc, receptor neuron(s) pick up a change in the environment In our example you can think about a nail on the floor as an example

Reflex Arc 2) Activation of a sensory neuron The physical or chemical receptor neurons will cause an action potential to propagate down a series of neurons In our example the receptor neurons would cause an action potential to propagate to the spine via the dorsal root from the foot Note – They can also trigger different types of neurons. An example would be a loud noise and head motion

Reflex Arc 3) Information Processing The information that is being held in the action potential is brought to the spine The sensory neuron transfers information to an interneuron An interneuron can communicate between sensory and motor neurons The interneuron passes information to a motor neuron

Reflex Arc 4) Activation of a Motor Neuron The axons of the motor neurons carry information towards an effector The information carried tells the effector what to do In our example the message might be to contract the muscles that control the foot

Reflex Arc 5) The response of an effector The release of neurotransmitters at the effector organ synaptic terminals causes a change in the effector organ In our example it would cause a change in the tibialis anterior to raise the toes and change the stimuli

Types of Reflexes There are many different categories of reflexes This is because there are such a large number of reflexes, that we have to categorize them differently to understand them There are four different ways that reflexes can be categorized

Types of Reflexes Reflexes can be categorized based on… Their progress in your development The resulting of the major motor response The complexity of the neural circuit involved The site of information processing

Developmental Reflexes There are many different reflexes that you are born with Babies are well known for their instincts and reflexes An example would be the suckling reflex If anything of a certain size is put in a babies mouth, they suckle on it This type of reflex is called a Innate reflex

Developmental Reflexes More complex reflex patterns that are learned are called acquired reflexes A great example of this is when my mother slams on the breaks She always extends her right arm to stop me from going forward, even though it probably will not do much anymore…

Developmental Reflexes Innate and acquired reflexes can be reprogramed through training and time This happens all the time in athletic training Gladiators used to train themselves not to blink when faced with loud noises and impacts UFC fighters are taught to step into certain punches and kicks to close the distance between themselves and the opponent

Response Reflexes Reflexes can also be categorized by the type of response that is seen from the stimulus The patellar reflex moves muscles in your body However when you see an ex that you recently broke up with, you might feel your face flush

Response Reflexes Reflexes that respond to a stimulus with the muscular system are called somatic reflexes There are several types but all involve the movement of the muscular system as a response Imagine having the simple game “crack an egg” played on your head

Response Reflexes Visceral reflexes control the activities of all of the other systems If you have ever gone into a haunted house before you might have shared this reflex You probably had a nervous feeling, started to sweat or felt like there was a knot in your stomach

Complexity of the Circuit Some of the reflexes that are seen are not easy to quantify Sometimes the inner workings of the circuit define the type of reflex that is being used These reflexes are defined by the complexity of the pathway that they follow through the nervous system

Complexity of the Circuit Some reflex arcs are very simple In these types of reflexes a sensory neuron connects directly to a motor neuron to reduce the time of the reflex These reflexes are called monosynaptic reflexes The patellar reflex that we tested earlier in class is an example of this reflex

Complexity of the Circuit When the spinal chord is involved with processing and interneurons are used the reflex is called a polysynaptic reflex With more synapses that are involved with the reflex, speed of the reflex slows The withdrawal reflex (from pain) is an example of a polysynaptic reflex

Processing Sites Not every reflex is a simple movement Some reflexes are actually a complex series of movements or actions Depending on the complexity that is needed within the reflex itself, it might need to be handled within different parts of the nervous system

Processing Sites In a spinal reflex, the important interconnections and processing events happen within the spinal cord Generally these are not complex reactions to stimuli A waiter adjusting to the weight of an unexpected plate on his tray would be an example of this reflex

Processing Sites A reflex that is processed by the brain is called a cranial reflex Generally these types of reflexes are more complex and will involve multiple actions or movements The complex eye movements that are required to read this sentence are cranial reflexes

Brain Control Over Reflex Have you ever noticed that you can fight a reflex if you have brain control over the pain Maybe you know something painful is coming, however it might be good for you Something like a vaccination at the doctors office might be and example Or sometimes you know something that is painful is coming that is not good for you… v=7AXB8nGq5jc v=7AXB8nGq5jc

Brain Control Over Reflex The motor control that is exhibited by reflexes can also be shown by the brain Remember it is not only your spine that can make your leg move So the brain can control the same aspects of the body that the reflexes do

Brain Control Over Reflex So with conscious brain control, there are many examples where people can diminish or cancel out the action of a reflex However, this is not always the case The brain at times cannot control the outcome if a reflex happens before the brain has a chance to intercede