HES 202- Week 2 Force Modulation and Muscle Spindles Flashcards
Week 2- Force Modulation and Muscle Spindles
Describe Input resistance
Small MN’s (Type 1) have high input resistance (leads to greater response and easier to excite)
What is Rheobase? What type of MN’s is the rheobase low?
Direct measure of the current that has to be put into a neuron to get it to fire- rheobase is low in small MN’s
Is the conduction velocity in small MN’s slow or fast?
Slow
Is the after-hyperpolarization (AHP) shorter or longer in large MN’s
Shorter
Describe the size principle?
MU’s recruited from smallest to largest.
What is a pro to the size principle and what is a con to the size principle?
Pro: Minimizes fatigue as slow twitch, fatigue resistant muscle fibres are activated first.
Con: Cannot selectively choose with MU’s to recruit
What is recruitment threshold?
amount of force needed to ‘turn on’ motor unit
Why does each MU produce partially fused tetanus?
Because units fire asynchronously with each other, the net force is smooth.
What is electromyography? (EMG)
Recording of the electrical activity from the muscle
What does an Indwelling EMG observe?
Somewhat invasive, but can observe a single motor unit.
What is a surface EMG
A global view
What is force modulation?
maximal voluntary contraction (MVC)
Describe divergence? What happens?
A single neuron synapases on multiple nuerons
Describe convergence? What happens?
Multiple neurons “converge” on fewer neurons
What is intrafusal?
skeletal muscle
What is extrafusal?
muscle spindles
Where do afferent signals go?
signals go away from the brain
Where do efferent signals go?
signals go towards the brain
What is the role of afferent/sensory input?
Each afferent projects centrally to the spinal cord (reflexes) and to more superior structures
Where is the cell body located in the afferent/sensory inputs
Cell body in the dorsal route ganglion
How are afferents labeled?
Based on cross sectional diameter. 1 is the largest, 2, 3, and 4 being the smallest.
What does conduction velocity depend on?
Depends on diameter. The larger the diameter, the faster the conduction
What are found in most skeletal muscle?
Spindle/fusiform shaped receptors
What types of muscles would have a higher density of spindles?
Hand muscles have a higher density of spindles, and more proximal muscles have fewer muscle spindles.
What are the two types of receptors?
Bag which can be further described as Bag 1 (Dynamic) and Bag 2 (Static) and Chain static
What are the two types of afferent and what do each of them innervate
Type 1a (primary)- length and velocity. Innervate bag 1, bag 2, and chain
Type 2 (secondary)- length. Innervate bag 2 and chain
What does a microneurography record
single unit action potentials
When you get a tendon tap, what does it stretch
stretches the intrafusal muscle fibers
Which afferent is sensitive to tap and vibration
Primaries (1a) are very sensitive to taps and vibration and can stop firing on release
What is the name of the only receptor that has its own efferent (motor) system
fusimotor or gamma system
What types of Gamma MN’s does it consist of?
dynamic and static gamma MN’s
Where doe alpha motor neurons send info to?
skeletal muscle
where do gamma motor neurons send info to
muscle spindles
Dynamic gamma sends info to…
Bag 1 (dynamic receptors)
Static gamma sends info to…
Bag 1, Bag 2, and static
Turning on the gamma system prevents what?
Prevents the spindle from becoming unloaded during shortening contractions and keeps it sensitive to stretch
Gamma dynamic makes the spindle more…
velocity sensitive
Gamma static makes the spindle more…
sensitive
