Reflexes Flashcards
what 3 sources provides us with sensory information about our movement?
proprioception
visual information
vestibular information
what is interdependent?
sensory input and movement
where are the cell bodies of our sensory neurons located?
in the dorsal root ganglia
how do sensory neurons send their messages to the spinal cord?
via the posterior roots
are peripheral nerves typically sensory or motor?
both, they are mixed
what information does the somatosensory system provide?
touch
proprioception
pain
temp
what are intrafusal muscle fibres encapsulated in?
connective tissue
what do intramural muscle fibres detect?
muscle length and velocity
what are the 2 types of sensory axons?
Type 1a
Type 2
what are type 1 axons wrapped around?
nuclear bag fibres
what are type 1a axons sensitive to?
changes in muscle length and velocity
what are type 2 axons wrapped around?
nuclear chain fibres
what do type 2 axons measure?
muscle length
what do alpha motor neurons innervate?
extrafusal muscle fibers
what are gamma motor neurons responsible for?
innervating the intramural muscle fibres
do alpha or gamma motor neurons have a lower threshold for activation?
gamma
what can gamma motor neurons be modulated by?
descending pathways
during active muscle contraction, which muscle fibres contract first?
gamma motor neurons cause the intramural fibres to contract at the same time as the extrafusal fibres
when does alpha-gamma co-activation only occur?
in movements initiated by the CNS (so it doesn’t happen during a reflex)
where are Golgi tendon organs found?
near the musculotendinous junction
what are Golgi tendon organs designed to measure?
muscle tension/force
what are the simplest form of movement?
reflexes
what does it mean that reflexes are stereotype?
evrytim you do an action you should see the sam response (tapping patellar tendon with reflex hammer)
what are reflexes largely controlled by?
local circuitry in the spinal cord
what happens if the input of the stimulus is increased?
larger amplitude
how do our descending pathways influence our reflexes?
reflexes can be excited or inhibited via descending control
why is the stretch reflex homonymous?
because the same muscle that stretched, is excited and contracts
what can both our reflexes and spindle sensitivity be modulated by?
UMNs
what is the purpose of the stretch reflex?
to maintain our muscle length or return the muscle to the desired position
what happens at the same time as the stretch reflex?
reciprocal inhibition
what is reciprocal inhibition?
the antagonist alpha motor neuron is inhibited while we get contraction of our agonist muscle
what type of sensory neurons go from he GTO tot her spinal cord in the GTO reflex?
sensory afferent 1B
what is the function of the GTO reflex?
release load to prevent muscle tearing and maintains muscle tone during muscle fatigue (ex: dropping a heavy weight so you do not tear muscle)
what are examples of the flexor withdrawal reflex?
stepping on a tack
grabbing a hot pan
what is the sensory input of the flexor withdrawal reflex?
noxious stimulus detected
what is activated by a noxious stimulus in the flexor withdrawal reflex?
Group 3 afferent neurons
what occurs with the flexor withdrawal reflex?
crossed extensor reflex
what is the function of the crossed extensor reflex?
ground stance limb to allow ipsilateral limb to withdraw
what reflex crossed the spinal cord?
crossed extensor reflex
how many spinal cord levels does the crossed extensor reflex span?
multiple spinal cord levels to activate many muscles (example activating ankle, knee, hip)
what is an UMN lesion?
damage to the descending tract before the anterior horn of the spinal cord
what is a typical response to an UMN injury/damage?
hyperreflexia
increased muscle tone (increased resistance to passive movement)
+Babinski/Hoffman
what is a 3+ stretch reflex?
brisk (increased; possibly abnormal)
what is a 4+ stretch reflex?
very brisk, hyperactive, with clonus
what is a 5+ stretch reflex?
sustained clonus
are we more likely to see hyperreflexia with UMN or LMN condition?
UMN
where does the reticulospinal tract originate?
reticular formation
where does the reticulospinal tract terminate?
bilaterally in the spinal cord
where does the reticulospinal tract recive input from?
both sides (ipsilateral and contralateral) of cortex
what is the dorsal/lateral reticulospinal tract responsible for?
descending inhibition (like the brakes of a car)
what is the medial reticulospinal tract responsible for?
descending excitation (like the gas in a car)
what is damaged in a SCI?
the lateralcorticospinal tract and reticulospinal tracts
what is an analogy for a SCI and the stretch reflex?
you are on cruise control, going down a hill, all gas no brakes
what causes hypertonia in a SCI and the stretch reflex?
hypertonia is due to a loss of descending control?
what tracts are damaged with stroke and the stretch reflex?
right lateral corticospinal and corticoreticular tracts
what is the analogy for stroke and the stretch reflex?
all gas no brake
what does loss of descending control and excessive neural firing contribute to?
hypersensitivity of the muscle spindle
excitable alpha motor neurons
where would damage to a LMN be located?
at or distal to the anterior horn
what are the hallmarks of a LMN injury?
hypotonia
hyporeflexia
what is a 1+ stretch reflex?
present but depressed
what is a 0 stretch reflex?
no response (areflexia)
