Muscle spindles Flashcards
What are Muscle Spindles?
Specialized muscle fibers containing contractile elements
Muscle spindles are encased in what?
Connective tissue sheath
Where are muscle spindles anchored to?
The endomysium and perimysium that surrounds the fascicles of the muscle
Contractile fibers within the muscle spindle are referred to as…
Intrafusal Muscle Fibers
Fibers that make up the bulk of a muscle are referred to as…
Extrafusal Muscle Fibers
True or False:
Both intrafusal and extrafusal muscle fibers have a typical sarcomere arrangement
True
True or False:
A muscle spindle contains several intrafusal muscle fibers within it.
True
Where are the Contractile Elements of the intrafusal fibers located at?
At the poles or ends of each fiber
Intrafusal fibers are multinucleated with all of the nuclei being located where?
Centrally (equatorially)
Muscle spindles have how many types of nuclear arragnements?
Two
- ) Nuclear bag
- ) Nuclear Chain
Nuclear Bag filaments are characterized by the nuclei looking like what?
“Clumped” in th emiddle forming a “bag-like” enlargement of the sarcolemma
Nuclear Chain filaments are characterized by the nuclei looking like what?
Arranged linearly in a “Chain-like” arrangement
Each filament has at least two sensory receptors. Explain the location of each
Located either:
- ) Centrally around the nuclear groups (primary)
- ) Peripherally near the contractile elements (secondary)
Primary receptors in the muscle spindle are located where?
Centrally
—around the nuclear groups
Secondary receptors in the muscle spindle are located where?
Peripherally
—near the contractile elements
The stimulus during a stretch is actually what?
Mechanical deformation of the afferent ending
Some of the primary endings are highly responsive to _____________ in muscle length, and in turn encode ____________.
—Rate of change
—Velocity of the muscle stretch
Primary endings that are responsive to the rate of change are also referred to as what?
Dynamic or phasic endings
The histological name for dynamic or phasic endings is what?
Annulospiral rings
Secondary endings (and some primary) are responsive to what?
The static muscle length
Secondary endings that are responsive to static muscle length are also refered to as what?
Static or Tonic endings
Static or Tonic endings have what histological name?
Flower Spray endings
Information from primary endings are carried into the CNS by what fiber type?
Type Ia
Information from secondary endings are carried by what fiber type?
Type II
Each fiber in the muscle spindle recieves an ending from what type of motor neuron?
γ motor neuron
Where does the muscle spindle recieve the ending of the γ motor neuron?
On each contractile component of each fiber
What do the γ motor neurons act to control?
The contraction of each spindle
Activiation of the γ motor neuron results in what?
Contraction of the intrafusal fibers
γ motor neurons can be used to adjust what within the muscle spindle?
The sensitivity of each receptor with the muscle spindle
True or False:
The adjustment of sensitivity by the γ motor neurons are specific and seperate to the dynamic and static receptors
True
What is the purpose of the motor activation within muscle spindles?
To prevent unloading of the receptor during extrafusal muscle contraction
The process of preventing “unloading” of the receptor during extrafusal muscle contraction is refered to as what?
Alpha-gamma coactivation
Explain alpha gamma co-activation
At the time of alpha motor neuron firing, the appropriate γ motor neuron are also activated.
—Resulting in muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber
Muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber occurs because of what?
Alpha gamma co-activation
If stimulation of the γ motor neuron takes place in a situation other than alpha-gamma coactivation what is the result?
An increase in the sensitivity of both the primary and secondary endings
What can influence an increase in the sensitivity of both the primary and secondary endings?
CNS pathways or cutaneous stimulation
—this allows for fine tuning of the spindle as the difficulty of the motor task increases
