in this segment we're going to discuss reflexes reflexes are an example of local processing that
occurs in the spinal cord itself they're influenced by the brain but it doesn't need your brain's
permission okay so when you have a reflex um definitely influencing from higher influences
of the brain and higher centers are going to have an impact on how brisk or dull that reflex is but
it doesn't need your brain's permission to go and as the sensory information that you
have participated in a reflex will be related to your brain but it's just a wee bit delayed
so that your brain gets the information but again it doesn't need your permission to have you don't
need your brains permission to undergo a reflex so what do you need to have a reflex well first
you need a receptor something in your skin your muscle a joint or even the viscera and
we'll talk more about those visceral reflexes in the autonomic section but you need some sort of
a receptor then you need that neuron that dorsal root ganglia neuron that is the sensory that that
receptor is attached to sometimes you'll use an inner neuron in the spinal cord and sometimes you
won't so inner neurons are usually there this is what distinguishes a poly synaptic ie more than
one synapse from a mono ie one synapse reflex and we'll talk about the difference between the
two you need an efferent motor fiber so that's the axon of the motor neuron that's going to cause the
movement part of the reflex and then you need some kind of an effector and that is going to
be the muscle and that can be striated or smooth depending on whether this is somatic or visceral
or even it could be a gland and so here's how it the basic workings of a reflex so out here in the
periphery there will be some sort of noxious stimulus and this could be stimulus and
this could be anything from you know stepping on a sharp stone or picking up something that's too
hot and the receptors for that are going to be in this skin so these are the peripheral processes of
these dorsal root ganglion neurons that live here in the dorsal root so the dorsal root
ganglion neuron then relays this information into the dorsal Horn and then it's going to synapse on
an inter neuron the inter neuron and is going to synapse on a great big motor neuron here and the
motor neuron then exits through the ventral root and then synapses on the muscle and causes it to
contract so this is the basic setup of your polysynaptic reflexes it's also called the
pain reflex or the flexor reflex because mostly it's going to be pulling your body pulling your
limbs or extremities and towards your body away from the noxious stimulus so noxious stimulus
nerve endings in the skin that are picking up that stimulus going through this the process of
the drg neuron which lives here the drg neuron then carries that information into the spinal
cord gray in the dorsal Horn synapse is on an inter neuron here the inter neuron synapses on a
motor neuron in the ventral horn which then sends its axon out through the ventral roots into the
spinal nerve which then it's a muscle that then moves this piece of skin away from that noxious
stimulus but be it like a sharp stone or or fire or something equally damaging in the next slide
we're going to talk about monosynaptic reflexes monosynaptic reflexes are special and these guys
are usually monosynaptic reflexes usually refer to the tendon reflex so the tendon reflex you've
probably had this happen whenever you go to the doctor and they come at you with that rubber
hammer okay and they're hitting you on your a tendon which is in your knee sometimes they'll
they can test tendons of other muscle groups if you look at the demo that Nico and Cristina did
heal Nico has described some of the ways that they test for reflexes tendon reflexes this is
a monosynaptic reflex there's a special receptor called a muscle spindle that lines up with your
with the rest of your skeletal muscle when this is stimulated the nerve endings of course have their
cell body in the dorsal root ganglion they come into the dorsal horn and they directly synapse
on a motor neuron the motor neuron then sends its axon out the ventral route to the muscle
this is why its monosynaptic there's no inter neuron here the way that this works I drew this
coil so this represents the the muscle spindle the distance between these coils so if it's very
tightly coiled like this it's sending one kind of a signal if it's loosely coiled like this it sends
another type of the signal and the difference between the space within the loops of the coil
are what activate this sensory neuron when it's activated then it directly synapses on a motor
neuron which directly synapses on the muscle to cause the reflex so you have two types of reflexes
pain or flexor reflexes which is a polysynaptic and it uses an interneuron and then we have the
monosynaptic reflex which is the tendon reflex which doesn't use an inter neuron and just has
the two neurons in the chain so to summarize what I want you to know is I need you to be able
to define a reflex and what are the components what all are all the different cellular neuronal
components that you need to have a reflex what's the difference between a mono and a polysynaptic
reflex and then how is your brain involved in reflexes or how is your brain not involved in
reset flexes if you're know all of these kinds of things then you're ready for the assessment