hello anatomy colleagues and this is dr aclsup and in this video we
will be discussing some of the basic terminology of innervation
as this will be a consistent topic of discussion in anatomy throughout the year and you'll see it
come up in many of your clinical lectures as well so let's start building that foundation
and and we can go from there so first and foremost we need to focus on just the terms
afferent and efferent and getting those down and then we'll move more into distinguishing
between the different types of afferent and efferent fibers and what their functions are
so afferent and efferent two words that sound pretty darn similar but are have some fairly
significant differences so we'll start with afferent afferent neurons so we have the a here
afferent neurons will carry sensory information into the brain or spinal cord so aka the central
nervous system and it they're gonna it's gonna carry this information through cranial and spinal
nerves from either a sense organ like the eyes or the nasal mucosa or sensory receptors from
various parts of the skin or parts of the body particularly we talk about the skin you can kind
of see you know you have information from the skin being sent along say a spinal nerve and
making its way to the central nervous system so for our purposes when speaking of innervation
afferent will be synonymous with sensory innervation and so it will take information like
we have here say from the skin as you can see in this lovely cartoonish image or it could be from a
muscle or another organ and bring it back to the central nervous system for integration to occur
efferent neurons here with the e will carry information from the central nervous system
as you can kind of see here it was integrated here now it's going to carry that information from the
central nervous system to an effector such as a muscle or a gland and something will happen
like a muscle contraction or a glandular secretion again for our purposes efferent will be synonymous
when we're talking about innervation will be synonymous with motor and you will definitely
hear them used interchangeably so you may hear me say efferent you may hear me say motor so be aware
that those two terms are going to be synonymous when we're talking in innervation two other terms
i want to cover before we start breaking down nerve fiber types are somatic and visceral and
you can have somatic afferent and efferent fibers as well as visceral afferent and efferent fibers
so for somatic this means of the body which i must admit is a bit vague isn't everything kind
of of the body but what we're really meaning here is uh something that's more conscious
particularly with these structures than say what is going on with some of your deeper
organs or viscera but it's not always conscious this will involve skeletal muscle as well as
sensory receptors of the skin or sensory receptors within skeletal muscles and joints
and oftentimes times the special sensory receptors are lumped into this category
but we will discuss them separately because as their name suggests they are special then
we also have visceral visceral is associated with viscera that kind of goes together right
viscera means organs particularly when we're talking about the hollow organs
you have those i kind of think of those associated with gi the gastrointestinal tract it can have
be part of some of the reproduct reproductive organs but smooth muscle is also going to be
considered when we're talking visceral and glands are going to be considered visceral
so let's combine these terms that we just learned to get the four to five main categories of nerve
fibers starting with a very clinically important category that doesn't get as much air time
typically because it is afferent and not directly creating an effect and these will be the somatic
afferent fibers and you may hear these fibers referred to as general somatic efferent or gsa
i put these in italics and you'll see italics and a few other areas throughout this video
i put these here just to expose you to these terms but we won't use these here at u of m but be aware
that if you're looking at a textbook you may you may see this terminology it's very dependent on
what type of discipline you're talking about as to what we we use here but we're going with somatic
afferent fibers and what these fibers will do we'll send information regarding sensation from
the skin back to the central nervous system for certain ones of these fibers this information
can include signals indicating pain associated with the skin touch pressure temperature and
there are these awesomely amazing maps called dermatome maps that depict the areas of the skin
that are afferently innervated by a single cranial nerve or a single spinal nerve
right here this side i'm going to kind of draw this this side over here
is going to be the dermatome map this over here is a peripheral nerve map so let's focus on this area
for a second these maps are created based on clinical studies of lesions of specific nerves and
what happened when those areas were or those nerves were directly affected so what area
lost sensation if there was a lesion to a specific spinal nerve or a specific cranial
nerve so if you have lack of sensory innervation say to kind of this general area right here
you would this would be a possible indication that the spinal nerves l2 or l3 are damaged
so do not by any means try to memorize these maps right now this is solely here for illustration of
a concept we will touch on a few of these areas throughout the year and really focus more uh
when we get to neurology and the musculoskeletal content later on in this year but this is um this
this is a clinically important kind of map that could give you some indication of specific
nerve damage somatic afferent fibers don't just innervate the skin but also skeletal muscle and
their tendons and how they are affecting joints so if you've ever heard the term proprioception
this is talked quite a bit less in regards to sensory innervation but is very important in
terms of providing sensory information regarding the positioning of a joint or say stretch or
over stretch of a skeletal muscle without visual input so this will give you an idea
i always say kind of put your hand behind your back and start kind of
moving your fingers kind of back and forth you know that's happening right without
actually seeing it you're going to feeling it that's going to be more that proprioception
so when we talk about muscles we usually think efferent or what is causing a contraction but
there will also be afferent fibers associated for this proprioception proprioceptive function
visceral afferent fibers will convey information from hollow organs and blood vessels back to the
central nervous system or the cns so the type of information we are talking about include
pain or say subconscious visceral reflex information like blood pressure levels
or the over distension or over extension of an organ and we're typically not as conscious of
these but we certainly can be and they are much more vaguely localized so not what we
had say with that pretty set dermatomal map that we saw for the the somatic afferents
so um just because we're not as conscious even though we can be some uh you certainly
do still have sensation associated with these structures lastly in regards to afferents
there will be special afferent or you are more likely actually and i don't have this in italics
because you will hear this very often by us as well you will hear special sensory fibers
and these will be associated with certain cranial nerves you're seeing some of the
cranial nerves here we'll spend some time learning these a little bit later on but
certain cranial nerves will have special sensory fibers and these are associated with what we think
of as our special senses so things such as smell sight hearing balance or equilibrium and taste now
on to the efferent fibers so we've back to the e here and we'll start with somatic efferent fibers
these are going to transmit impulses to skeletal muscle and some form of contraction or relaxation
of the muscle will occur due to that and so you're having from a component of the central
nervous system and it sorry it's going to be more over here this would be the um the somatic over on
this side so you'll have from the central nervous system you'll have an axon it will head it will
be associated directly with that muscle and some type of effect will occur these are the muscles
that we are typically consciously aware of that will move the musculoskeletal system
so again kind of really focus on the fact that we're talking skeletal muscle here
and when we're discussing muscles throughout the year we will often talk about what innervates
that muscle and asks you to memorize that and ask you to know what innervates that muscle
and usually what we're getting at is either that cranial nerve or the spinal nerve
that will be sending the efferent fibers to that muscle allowing it to contract or relax
but keep in mind most name nerves will have both afferent and efferent fibers wrapped up
in this connective tissue so it will have efferent fibers they'll play a role in terms of contraction
and it will have those afferent fibers associated with the proprioception of that muscle
visceral efferent fibers are fun too and are associated generally with the autonomic nervous
system these fibers will transmit impulses from the central nervous system it will have a kind of
a neuron intermediate neuron associated with it where you'll have some synapse occurring before
it gets to its target effector and we'll talk a little bit more about this in the the next session
but this will transmit impulses from the central nervous system and eventually
will make its way to the target effectors which when we're talking about the visceral efferents
this will either be smooth muscle which are typically unconsciously controlled or
glands and so for a gland the effect will either be increasing or decreasing secretion
and smooth muscle will either be contraction or relaxation of that smooth muscle all right we
have made it to our trusty review slide which as always we recommend you use for your studying you
know i would kind of save these and refer to them throughout the year they can be helpful in that
way and it's really getting down to some of our bigger biggest picture concepts from this learning
objective please always feel free to reach out to myself or any of my anatomy colleagues with any
questions you may have thank you for your time and attention and have a great rest of your day