4.18. Segmental motor control Flashcards
what is innervation ratio? (has to do with fibers and one motor neuron)
why’s that important? (i.e. fine motor vs gross motor type muscles have which ratio?)
Why do we care: the things that do fine motor functions, like the eyes and the hands will have an alpha motor neuron innervating fewer muscle fibers, whereas that won’t be the case for postural muscles like the gastroc
muscle fiber types
S type: slow twitch; produce least amount of force; the most fatigue resistant
FF type: fast fatigable; produce the greatest amount of force; fatigue the quickest
FR type: fast, fatigue resistant
how is muscle force increased (what 2 things need to happen)?
Rate modulation >> increasing firing frequency of already-active motor units
Recruitment of more motor units
difference in mtoc amounts before and after heavy exercise
T/F: muscle fiber grouping during reinnervation is better compared to normal muscle fiber grouping
Increased mitochondria (thus increased ox phos) with increased physical activity (no muscle hypertrophy though)
Following reinnervation, there’s increased grouping of muscle fibers (pathological condition, i.e. not normal, no good)
sensory receptors involved in segmental motor control (3 groups; hint: smoking a joint, big gains, and thin skin)
Joint receptors
Muscle spindle and tendon organ receptors
Cutaneous receptors
functions of sensory muscle fibers
Proprioception: your internal sense of your body’s position in space
Kinesthesia: basically proprioception but it also allows feedback from the external environment
Motor learning: learning a motor skill
Compensation for unexpected movement: literally just that. For e.g. if you trip while you’re walking, your body can adjust for that
Calibration of movements: adapting to some change in the body’s environment
Postural control: just that also
what is the function of Type Ia and Type 1b receptor types?
Type 2’s are either spindle nerve endings and non-spindle nerve endings. What is the function of each?
Type 3’s are free nerve endings involved in what kind of pain?
Type 4’s are free nerve endings involved in which functions?
Type Ia (primary spindle ending): muscle velocity and acceleration
Type Ib (Golgi Tendon Organ): muscle force
**type Is are the largest diameter axons and they’re heavily myelinated**
Type 2 (secondary spindle ending): muscle length
Type 2 – non spindle ending: deep pressure
**type 2’s are small diameter axons; also myelinated
Type 3 – free nerve endings: pain; thinly myelinated
Type 4 – free nerve endings: pain, chemical stimuli and temperature
difference between intrafusal and extrafusal fibers (i.e. who has special sensory abilities and can regulate rate of change in ms length, and who’s a standard ms fiber?)
Intrafusal fibers - skeletal muscle fibers that serve as specialized sensory organs (proprioceptors) that detect the amount and rate of change in length of a muscle. They constitute the muscle spindle and are innervated by two axons, one sensory and one motor; they’re embedded between the extrafusal guys, and they’re innervated by gamma motor neuron axons; they have primary and secondary afferents, and they’re own motor innervation
Extrafusal fibers – standard muscle fibers (don’t have specialized sensory receptors and what not)
intrafusal fiber types (bags of chains)
3 motor neuron types and which fibers they innervate (a-g-b)
Types of intrafusal fibers:
Bag fibers – bigger fibers; tonic contraction
Chain fibers – smaller fibers; twitch contraction
Alpha motor neurons innervate only the extrafusal muscle fibers
Gamma motor neurons innervate only the intrafusal muscle fibers
Beta motor neurons innervate both muscle fiber types
spindle afferent activity when muscle is passively vs actively stretched
Afferent activity of the spindle is turned on when the muscle is passively stretched
Basically the spindle afferent is silenced when you actively contract the muscle
With increased spindle activity = ___ (increased/secondary) muscle velocity, which is mediated by ___ afferents (primary/secondary)
There’s also increased muscle length with increased muscle spindle activity, which is mediated by ___ (primary/secondary) afferents
With increased spindle activity = increased muscle velocity (mediated by primary afferents)
Basically length also increases with increased spindle activity (mediated by secondary afferents; they send that signal to the CNS)
role of dynamic gamma motor neurons during muscle contraction
Gamma motor neurons (the dynamic ones) provide continuous sensory feedback while muscle is actively shortening (i.e. that filling in response) if they’re activated along with the alpha motor neurons
what are the 2 types of gamma motor neurons?
Gamma static - basically silence the activity of the spindle/counteract whatever the dynamic ones do
Gamma dynamic - enhance the output of the primary afferent ending and thus make the spindle more sensitive to changes in muscle length (i.e. velocity and acceleration)
define fusimotor set
relationship between gamma motor neuron activation and behavior
Gamma motor neurons activated during more rigorous type of activity (like chasing after a toy mouse);
Fusimotor set: the gamma motor neurons are activated depending on the animal’s behavior (or their level of activity varies depending on the behavior)
tendon organ definition
function of tendon organs
relationship between tendon stretch and tendon organ firing
relationship between tendon organ firing and force generation
Tendon organ definition: receptors found in muscle tendons; most activated by muscle contraction;
very sensitive to muscle contraction; provide sensory feedback related to muscle force
Increased stretch of the tendon = increased afferent firing
Linear relationship between tendon organ firing and force generation
describe a typical reflex arc (plus the 5 things involved in it)
Reflex – a rapid response to a stimulus without conscious involvement
Receptor (1) – the receptor activates a nerve impulse in a sensory neuron in response to a stimulus
Sensory neuron (2) – neuron which conducts the nerve action potential from the receptor to its synaptic terminal in the CNS Interneurons (3) – area of integration
Motoneuron (4) – integrates and transmits action potential to organ
Effector (5) – the organ of the body which responds to the impulse from the motoneuron
stretch reflex:
which neurons are stimulated and which ones are inhibited? (and how?)
The Ia afferent motor neuron synapses with the homonymous motor neuron (excitatory synapse)
Stretch reflex: stimulation of synergistic motor neurons, and inhibition of antagonist motor neurons (via Ia inhibitory interneurons, which are disynaptic)
difference between tendon organ and muscle spindle in relation to extrafusal fibers (i.e. are they arranged in parallel or in series?)
tendon organ: arranged in series; muscle spindle: arranged in parallel
follow up servo pathway (which neurons are activated and when? what’s the final effect?)
Follow-up servo: motor command activates gamma motor neuron >> activates 1a afferents >> activated alpha motor neuron >> muscle contraction
alpha gamma coactivation servo assist pathway (which neurons are activated? how? what’s the final effect?)
Alpha-gamma co-activation servo-assist: alpha and gamma motor neurons co-activated >> spindle keeps its activity while muscle is actively contracting
rhenshaw inhibition (describe it)
where does it take place?
functions of this kind of inhibition (shape up tremor and contract together)
Recurrent collateral neurons excite the inhibitory interneurons, which then feedback to the same motor neuron (inhibit the alpha motor neurons)
This kind of inhibition is only present in the spinal cord
‘shaping’ motor output (limits output, contrast enhancement)
tremor reduction
co-contraction – via Ia inhibitory interneuron
