L5 Locomotion Flashcards
What are the three types of motor units?
small
intermediate
large
What is a motor unit?
one motor neuron and the muscle fibers it innervates
What is the motor neuron pool?
all motor neurons innervating a given muscle
Which motor units have high myoglobin content?
small and intermediate
Which motor units are recruited first?
small
Which motor units are recruited last?
large
What is a muscle spindle?
CT sheath that contains muscle fibers
How are muscle spindles arranged?
In parallel
What innervates intrafusal muscle fibers?
sensory nerve endings
How do sensory nerves enter the spinal cord?
Via dorsal roots
What do Ia fibers measure?
muscle length and rate of length change
What do group II fibers measure?
length
Which fiber group has a faster conduction speed?
Ia
What is reciprocal inhibition?
an inhibitory interneuron between Ia afferent and motor neurons
What do interneurons innervate?
Unstretched muscle
What is a stretch reflex?
a muscle is stretched, spindle afferents excite alpha motor neurons
What does the stretch reflex regulate?
muscle length via negative feedback
What is proprioception?
sense of relative position
What type of afferents provide proprioceptive information?
Ia afferents
What causes contraction of the two end of muscle fibers?
gamma motor neurons
What is the effect of gamma motoneuron activation?
contraction at the end of the muscle
stretches the middle
promotes Ia activity
What are the two classes of descending alpha motoneuron activation?
direct activation
indirect activation
What facilitates indirect activation of alpha motoneurons?
gamma loop
Describe the gamma loop?
gamma excited –> intrafusal fiber contract –> Ia stretches –> activates alpha motoneuron
what does alpha-gamma co-activation produce?
movement
What is the effect of alpha-gamma co-activation?
Ia spindles afferents remain active for load increase
Where are Ib nerve ending found?
small tendon fascicles
How are Ib fibers activated?
by tension produced by muscle contraction
What is the inverse myotatic reflex (tendon organ reflex)?
di-synaptic reflex arc
- synergistic muscles are inhibited
- antagonistic muscles are excited
What does the tendon organ reflex regulate?
muscle force via negative feedback
Why do we have the tendon organ reflex?
to reduce muscle force
T/F the stretch rflx and tendon organ rflx can work together
TRUE
What is muscle stiffness?
change in force / change in length
What the relationship b/n stretch rflx and muscle stiffness?
it increases muscle stiffness
What the relationship b/n tendon organ rflx and muscle stiffness?
it decrease muscle stiffness
What is the main effect of reflexes?
balancing support and shock absorption in anti gravity muscles
What the the flexor rflx a response to?
noxious stimulation of muscle or skin
What influence spinal cord motor units?
descending ptwys from the brain
What are upper motor neurons?
neurons in the brain
What changes occur in motor tone when upper motor neurons are damaged?
spinal shock (hypotonia)
spasticity (hypertonia)
What contributes to spasticity after spinal cord injury?
down-regulation of K-NA cotransporter KCC2
T/F BDNF can up regulate the transporter after spinal cord injury
True
What are the phases of step cycling?
extensor phase
flexor phase
What does reflex feedback influence?
phase duration and pattern
but is not necessary for rhythm generation
What can Dysfunctions in brainstem circuits cause?
REM sleep disorder (sleep walking)
What are the two classes of mechanism for Central pattern generator?
- cell have intrinsic burts of APs
- Emergent network property
What is the emergent network property?
reciprocal inhibition and adaption account for alternating activity in flexors and extensors
