Spinal Reflexes Flashcards
while spinal reflexes can be modulated by supraspinal control, they largely function as reliable input-output functions that do not require ( )
volition
reflexes happen where?
at spinal level
3 different “I need a drink” pathways
1) conscious desire to move
2) unconscious control of movement
3) reflexes
what participate in reflex function?
1) sensory afferents
2) spinal interneurons
3) motoneurons
muscles have what types of sensors?
both length and force sensors (muscle spindles and Golgi tendon organ and associated fibers)
the sensitivity of muscle spindles can be maintained over a range of muscle lengths by activation of the spindle’s ( ) fibers via ( )
- intrafusal
- gamma motoneurons
monosynaptic and disynaptic spinal reflexes are mediated through ( )
muscle afferents
simplest of muscle afferent spinal reflexes
stretch/myotactic reflex
stretch/myotactic reflex: a short stretch of the muscle’s spindles results in a synchronous volley of activity in ( ) and ( ) afferents that in turn causes that muscle’s motoneurons to be activated in a ( ) reflex arc
- group Ia and group II
- two neuron, monosynaptic reflex arc
the activation of a muscle’s stretch receptors also usually leads to activation of ( ) innervating synergist muscles
motoneurons
muscle spindle afferent fibers
group Ia and II
golgi tendon afferent fibers
group Ib
muscle spindle activation on motoneurons of anatagonist muscle reflex: the same muscle afferents synapse on a population of interneurons called ( ) that then synapse on ( ) to prevent them from being activated
- Ia inhibitory interneurons
- antagonist motoneurons
the stretch reflex can be mimicked using
electrical stimulation (the Hoffman reflex)
golgi tendon: when too much force happens, motoneurons of the activated muscle are ( ) and motoneurons of antagonist muscles are ( )
- inhibitied
- activated
Ib inhibitory interneurons recieve not only afferent input but also ( )
supraspinal input
motoneurons have ( ) in addition to their main axon that reaches the muscle and thes activate inhibitory Renshaw cells that then synapse back on the activated motoneurons to limit their activity
collateral branches
Renshaw cells are also conntect to ( ) through other interneurons so that the activity in one group of motoneurons eventually leads to their own inactivation and the easier activation of their antagonists
antagonist muscle motoneuron pools
interneurons of spinal cord also receive non-muscle afferent input that participates in reflexes that, in the case of the flexor reflex/crossed extensor reflex, coordinates activity within motoneurons located where?
on both sides of the spinal cord
the stepping on nail reflex is mediated through multiple levels of interneurons and is therefore ( )
polysynaptic
there are also ( ) connections to coordinate activity between different levels of the spinal cord
intra-spinal
intra-spinal connections allow for ( ) across motoneuron pools of the entire arm or leg but also of arms with legs or limbs with trunk muscles for certain motor tasks
coordination
there is circuitry for locomotion located in the ( ) of the spinal cord and this is connected to similar circuitry in the cervical enlargement so that arm swing and stepping may be coordinated
lumbar enlargement
intra-spinal connections make up the ( )
fasciculus proprius
neural circuits within the spinal cord that permit the coordination bw flexors and extensors
stretch reflex and reciprical inhibition
movements across multiple joints and between right and left limbs
crossed extensor reflex
if you lose medial frontal lobe, where would be the deficit?
?
can a single neuron control only one motor unit?
no, it can control multiple
what are made up of neural circuits that can carry out rhythmic locomotion?
central pattern generators (CPGs)
how are the functions of interneurons for CPGs different than the functions for Ia interneurons or Renshaw cells?
CPG interneurons are not as well identified as the others
stepping can be initiated in rhythm generaor interneurons in the isolated spinal cord using ( ) but it can also be initiated from a collection of supraspinal sites as well
afferent input or drugs
afferent input, descending signals from supraspinal centers and drugs can also change the ( ) of stepping through these rhythm generator interneurons
speed and pattern
