53 terms

Muscle Spindle

What is the function and purpose of the muscle spindle?
it is the sensory unit of the skeletal muscle
What does the muscle spindle sense?
Change in muscle length and the velocity of that change
What are the two parts of the intrafusal fibers?
receptor area and contractile portion
What part of the intrafusal fibers are connected to the extrafusal fibers?
contractile portion
What happens when the contractile portion contracts?
The receptor area stretches
Does a muscle spindle have more Nuclear bag fibers or Nuclear chain fibers?
Nuclear chain fibers
What are the 2 types of Nuclear bag fibers?
dynamic (phasic)
static (tonic)
Where does the information from the muscle spindle go to?
ventral horn
dorsal horn
cortex (last to hear)
Where are the Type 1a dynamic (phasic) fibers in the muscle spindle?
wrapped around the bag fibers (mostly)
What do Type 1a dynamic (phasic) fibers sense?
speed of change
Where are the Type 1a static (tonic) fibers in the muscle spindle?
wrapped around the chain fibers
Where are the Type 2 fibers in the muscle spindle?
"flowersprays" on the chain fibers further out
Which type of fiber is fired with a quick stretch?
Type 1a dynamic (phasic)
Which type of fiber fades quickly after being fired?
Type 1a dynamic (phasic)
Which fiber travels the fastest?
Type 1a dynamic (phasic)
Which fibers conveys a maintained stretch like for postural changes?
Type 1a static (tonic)
Which fiber conveys tonic information at the end ranges?
Type 2 fibers
Where are alpha motor neurons located?
dorsal horn
When is the only time the alpha motor neuron is isolated?
when you are testing for stretch reflex
What does the Type 2 fiber use to communicate with alpha motor neurons?
What is a motor unit?
An alpha motor neuron and the muscle fibers that it innervates
What does the gamma motor neuron do?
maintains sensitivity of the muscle spindle throughout normal range of muscle length
Where does the gamma motor neuron go to?
if its static, it goes to the contractile portion of the chain fiber
if its dynamic, it goes to the contractile portion of the bag fiber
In alpha-gamma coactivation, what happens when the alpha motor neuron fires?
The gamma motor neuron fires as well
What do beta motor neurons do?
Same thing as alpha-gamma coactivation but with only one neuron
Where do beta motor neurons go?
skeletal muscle and intrafusal fibers
What is autogenic facilitation?
The signal comes from the agonist and goes back to monosynapse with the agonist, polysynapse with the synergist, and disynapse with the antagonist
What does it mean to disynapse with the antagonist (reciprocal inhibition)?
An inhibitory interneuron is used between the type 1a or 2 affernet and the alpha motor neuron
What is spindle afferent feedback to the CNS used for?
resistance training
What is the importance of muscle spindle bias (alpha-gamma coactivation)?
If the spindle was on slack, it would take longer for it to fire
What can be done to help activate the muscle spindle?
when gravity is acting on resistance lift
tapping the muscle
vibration works on type 1a fibers
What is the tonic vibration reflex?
high frequency vibration of a muscle or tendon evokes a reflexly mediated contraction
Where do you apply the vibration to cause a tonic vibration reflex?
Muscle belly or tendon (best)
What are the 3 motor effects of the tonic vibration reflex?
It inhibits the antagonist
causes reflex muscle contraction
DTR won't be as strong b/c you are tying up the connection line
What is the Jendrassik maneuver?
Tie up the cortex with isometric hand pull or complex focusing (you can suppress reflexes if you think about it)
What is the strength of the TVR influenced by?
initial length of the muscle
the use of at least 100Hz (or else you'll get inhibitory response)
won't get response if deinnervated or deafferent
if both agonist and antagonist are vibrated, you won't get resonse
What can you do to help a hyperactive muscle?
vibrate its antagonist
What does the supine position favor?
What does the prone position favor?
What type of synapse is the TVR?
polysynaptic (barbituates, which work on interneurons, suppress GTR)
Does the cerebellum need to be intact for muscle contraction from TVR to work?
Who is the WBV good for?
older individuals that have room to improve
individuals that wanted to increase bone density
WBV worked for patients with what conditions?
CP, PD, stroke, SCI
(mixed results for MS)
What is the purpose of the golgi tendon organ?
tension feedback system
What does the golgi tendon organ prevent?
over contraction or stretching
it works at the end range
What does the GTO sense?
force production
Give an situation that requires the GTO to be used?
holding a egg vs a heavy weight
holding a cup of coffee in a Styrofoam cup vs a mug
How does the GTO function?
Autogenic inhibition (stimulates the antagonist and may inhibit the agonist and synergist a little)
Does the GTO work on active or passive motion?
How is the GTO arranged?
series with muscle fiber
Where is the GTO located?
at the junction of the muscle and tendon
What afferent fiber does the GTO use to carry its information?
Type 1b (different pathway than 1a and slightly slower)
Why does contract-relax work?
visco-elastic properties of the muscle
stress relaxes the muscle
have an increase tolerance to stretch