Muscle Spindle Fun Facts Flashcards
Muscles involved in fine movement (hand) have more or less spindles than coarse moving muscles (back)?
Have MORE
Stretch Reflex–> if the muscle is stretched then what happens??
1-a axon is stimulated and this sends impulses to the ventral horn
What does the 1-a axon stimulate in the ventral horn?
alpha motor neuron (Again remember this is on the EXTRAFUSAL fiber) and this will tell the stretched muscle it needs to contract
In addition to the 1-a neuron stimulating alpha motor neurons of the muscle, what does the 1-a neuron send inhibitory interneurons to?
Inhibit the alpha motor neuron of the antagonist muscle (this is known as reciprocal innervation)
Again when the alpha motor is stimulated, the muscles does what??
shortens or contracts
When the alpha and gamma motor are both stimulated, what does the muscle do?
the intrafusal (gamma) and the extrafusal fibers (alpha) will contract together
Now for 1-b fibers in the golgi tendon organ, if the muscle is contracted or shortened then what happens with 1-b axons??
this increases the firing rate of the 1-b axon
An increase 1b axon firing rate will cause what???
Increase inhibition on the alpha motor neuron
What effect does 1-b firing having on patients?
ensures even distribution of tension and contraction as well as avoiding excessive contract to the point of damage (known as reverse myotactic reflex)
The number of muscle fibers in a motor unit increases or decreases with increasing fine motor control???
DECREASES (muscles of hand are about 10 fibers) (So remember more spindles but less fibers)
Type 1 muscle??
Slow twitch muscle fibers, low tension; fatigue resistance; aerobic; innervated by large motor neurons and axons
Type IIA muscle??
Fast fatigue-resistant; large tension
Type IIB muscle??
Fast Fatigable; large tension (running from a bear situation)
Hypotonia is due to damage to what?
1a afferent or alpha motor efferent
The cell bodies of all muscle afferent are where?
DRG
What are the two major sensory organs?
Muscle Spindle –> measures length 1a fiber
Golgi tendon –> measures tension: 1-b fiber
where are muscle spindles located?
Encapsulated structures found in most skeletal muscles used to monitor its length
what are the components of the spindle?
Small group of 2-12 intrafusal fiber
large diameter myelinated sensory axon (1a-axon) with sensory ending in the intrafusal belly
small diameter myelinated motor axon that innervate the distal contractile regions
What are Renshaw cells?
are inhibitory interneurons of the anterior horn that receive collaterals form the alpha motor neuron and work to avoid damage in the event of excessive contraction (golgi)
A motor axon branches at its muscles and what happens to the fibers that these branches connect with?
each fiber receives only one ending of the branching
Where is the NMJ located?
in the center of the muscle fiber and is where AP are generated
The force developed by the muscle fiber increases with?
increasing firing rate of the motor neuron
The force will also increase as more what are recruited
more motor units are recruited to the excited state
