Segmental Motor Center Flashcards
Motor unit
motor neuron, axon & muscle fibers
‘Muscle unit’ = axon terminal & all the muscle fibers served
Contractile elements work best at what legnth
resting length
have the greatest number cross bridges
Contractile elements at lengthened and shortened legnths
they do not work as well b/c less to grab onto
Connective tissue and tension
Connective tissue that is surrounding the muscles can add some passive tension
when you pull on the connective tissue there is some force on the as well
Eccentric contraction vs. concentric in about of force producced
when you take the muscle beyond resting length there is passive tension that is added to the active tension
Slow,S (slow oxidative, SO
Small motor neuron
Small amount of muscle fibers
Innervates slow twitch muscle fibers for slow contraction and relaxation time; relatively small forces, resistant to fatigue
Activities with sustained muscular contraction
Fast, fatigue-resistant,FR
Largemotor neuron
mediumamount of muscle fibers/unit,
Innervates fast twitch muscle fibers (fast oxidative glycolytic, FOG) for fast contraction & relaxation; generate ~ 2x force as (S)
Fast, fast-fatigue, FF
Largemotor neuron,
Large amount of muscle fibers/unit,
Innervates very fast twitch muscle fibers (fast glycolytic, FG) for very fast contraction & relaxation time
Generate large, rapid force;particularly important for brief exertions that require large force,running, jumping.
size largest to smallest of FF SO and FG
FF FG S
the larger the axon what happens to the speed of transmission
gets faster
FF FG and S - which creates the greatest force
FF
has the most fibers per motor neuron
1A afferent primarily targets what type of motor unit
slow oxidative
Twitch tension time - slow
Slow rise of tension over a greater period of time (gradual force production)
Twitch tension time - fast
fast twitch therefore fast force production
Fatigue index Fast
rapid changes in high force production by not to be used for long periods
FR energy use
Not many capillaries, anerobic metabolism or aerobic (phosphocreatine and glycolysis for their energy production)
Have both enzymes so can do both – so when we are training these are normally what we are training
Not to be used continually
Slow: endurance
Endurance, use aerobic metabolism (have more capillary)
Highly vascularized
en recruit fibers what order do we go in
S > FR > FF
this is an example of pre writing
Sag
if you stimulate a certain rate that allows a relax in-between we will see a sag
rapidly formed cross bridges are less resistance to relaxtion
FF and FR
Potentiation
slow
the cross bridges form slowly so they are resistant to relax (strong covalent bonds)
fatigue time - FF
- FF are gone in less then a minute
- Loss of force
- FF are fatigable
fatique time - slow
- Slow can produce force for a long time
Three features of motor unit recruitment protect against fatigue:
Henneman’s size principle
SMC ‘half centers’
Asynchronous activation
Henneman’s size principle
principle gradual ramping of force;
S to FR and FF; ‘small to large’
Only get to the fast ones when we need them for force
SMC ‘half centers
extensor and flexor; alternating activation
Alternative activates between agonist and antagonist
Asynchronous activation
motor units activated intermittently during the voluntary contraction time
We do not used the same motor unit when we are doing a contraction, there are different motor neuron within the pool
Monosynaptic reflex
Ia afferent input from the muscle spindle to motor neuron activation back to the same (homonymous) muscle and its
Modified by descending and peripheral inputs
H-reflex, e.g. during locomotion
Electrical equivalent to the monosynaptic reflex
Consider why? Consequences if not reduced?
Bounding when running – descending paths influence stuff
Alpha is what
motor neuron
Gamma
MN to the muscle spindle to keep it sensitive
Alpha-gamma co-activation is activated for what kind of contractions
all contractions
Reciprocal inhibition
Ia Inhibitory Interneuron (IaIN) turns off (reciprocally inhibits) the antagonist SMC during activation of the agonist SMC
IB afferent from where
GTO sensory neuron
Autogenic inhibition point
Trying to turn off some motor neurons so that others must take over the load
IB inhibitory internuron does what
regulates recruitment of agonist AMNs in the MN pool at any one time; turns off some active MUs, others take over for force production (a non-reciprocal inhibition).
Recurrent inhibition
Renshaw (R) cells limit the rate and #of motor units active in the MN pool at any one time. (a non-reciprocal inhibition)
non-reciprocal inhibition example
Recurrent inhibition and Autogenic inhibition
reciprocal inhibition example
Reciprocal inhibition
The ventral horn is organized into two parts
Medial and lateral motor nuclei
Propriospinalinterneurons(INs) communicate infromation where
information over short and long distances within the spinal cord.
Only travel between segment of the spinal cord (communication within the spinal cord)
Medial motor nuclei go to what kind of muscles
axial and proximal limb girdle muscles
Medial motor nuclei connection
Have an interneuron that connects both sides – this allows us to activate things together
If there in an input on the medial side, there will be activation on both sides
Lateral motor nuclei to what kind of muscles
limb muscle - for limb movement
Lateral motor nuclei connection
Do not have a connection between the two sides – we normally move one limb at at a time
Descending connections medial MN
Ventromedial pathways impact medial MNs
Bilateral effects
Descending connections lateral MN
Dorsolateral pathways impact lateral MNs
Ascending connections for both medial and laterl MN
Ventrospinocerebellar tract
Spinoreticular/spinothalamic
Ventrospinocerebellar tract
To cerebellum – this compare what is happening the ventral horn to the cortex plans, and can make correction
Info: motor copy – telling about the state of the of a segmental motor neuron
Spinoreticular/spinothalamic
To brainstem centers
segmental motor center is made up of
medial and lateral MN
