Term
|
Definition
| Number of fibers in a motor unit. Smaller = finer control. |
|
|
Term
|
Definition
Slow twitch - Type I
Fast Fatigable Type IIB
Fatigue Resistant Type IIA |
|
|
Term
| Gradation of force is accomplished by: |
|
Definition
Recruit an increasing number of motor units (weakest recruited first)
Increase the firing rate of each motor unit |
|
|
Term
|
Definition
| Motor units with the smallest axons and cells bodies are activated first. |
|
|
Term
| Which motor units fire at higher frequency, fast or slow motor neurons? |
|
Definition
|
|
Term
| Recruitment of Fibers (order) |
|
Definition
| Smallest (highest membrane resistance), then the slow twitch, then fast. Fast fatigable are the last recruited. |
|
|
Term
| Describe Cocontraction and reciprical innervation |
|
Definition
Cocontraction - Both agonist and antagonist muscles contract. Increases stiffness.
Reciprical Innervation - Agonist contracts and antagonist relaxes. May decrease stiffness. Learned tasks become more recipricol. |
|
|
Term
| Muscle spindles vs golgi tendon organs |
|
Definition
| Muscle spindles - (and extrafusal muscle fibers) signal changes in length
Tendon organs - signal changes in tension. Both play major roles in the stretch reflex. |
|
|
Term
| Muscle Spindles (innervation, etc) |
|
Definition
| ~7 muscle fibers - intrafusal fibers - innervated by gamma motor axons (and type ia and group ii afferents).
Primary sensory ending - group ia. Secondary enging - group II
Primary more sensitive to rate of change of length. Sensitivity of muscle spindles in regulated by activity of gamma motor neurons.
Static length and dynamic length sensitivity are regulated by different gamma motor neurons. |
|
|
Term
| Golgi Tendon Organs (location, innervation) |
|
Definition
| Each tendon organ is innervated by a single Ib axon (increased tension = increased firing frequency). No motor component so sensitivity is not regulated. |
|
|
Term
| Muscle spindle/ GTO interaction |
|
Definition
| A muscle spindle will not fire when a muscle is contracted (slack-muscle shortened). A muscle spindle fire faster when there is stretch. In contrast, a GTO fires more when the spindle is contracted. Increases firing a little when a muscle is stretched. |
|
|
Term
| Differences between muscle spindles and PTOs (series vs parallel, sensitivity?, Innervation, stretch vs tension, Contraction activity? |
|
Definition
Muscle spindles are in parallel while GTOs are in series. Sensitivity of muscle spindles is regulated by the spinal cord (GTOs are not).
Muscle spindles are innervated by TypeIa and Type II afferents. GTOs by Ib afferents.
Muscle spindles signal stretch; GTOs signal tension.
Muscle spindle receptors fire less during contraction; GTOs fire more. GTOs fire more when stretched OR contracted. |
|
|
Term
|
Definition
| Essentially alpha motor neurons which innervate (extrafusal fibers) are activated when a muscle is contracted to compensate for the lack of sensation from the intrafusal fibers (gamma motor neurons). Alternatively the gamma motor neurons can act on their own (dynamic gamma neurons) to sense changes in length. |
|
|
Term
| The stretch reflex (tendon jerk reflex) |
|
Definition
Negative feedback (happens as muscle lengthens)
Ia afferents make monosynaptic excitatory synapses directly onto alpha motor neurons of the same muscle. Also make excitatory monosynaptic inputs onto other synergist muscles and excitatory inputs to inhibitory interneurons that make IPSPs on alpha motor neurons innervating antagonist muscles (slower than the excitatory). |
|
|
Term
| Is the stretch reflex phasic or tonic? |
|
Definition
| Could be either. Tonic usually only seen in decerebrate animals. Main neurons for polysynaptic groups are group II and Ib. Group II - tonic stretch. Ib - inhibit homonymous motor neurons (autogenic inhibition) and excite antagonistic-negative feedback. |
|
|
Term
|
Definition
| Force with which a muscle resists being lengthened (stiffness). Myotonia - excess stiffness. clonus - unsteady tone with repetitive involuntary contractions. |
|
|
