2.24 Motor SC 3 Flashcards
reflexes
involuntary, relatively short-latency, and stereotyped response set into motion by an environmental stimulus
components of a reflex arc
- receptor
- afferent fiber
- reflex center in CNS
- efferent fiber
- effector
polysynaptic reflex
if there’s an interneuron in the reflex arc (doesn’t have to be)
monosynaptic reflex
no interneuron
What are the 3 major reflexes?
- Stretch (myotatic) reflex
- Inverse myotatic reflex
- Flexion and Crossed Extension Reflex
simplest and best studied reflex
stretch (myotatic)
stretch reflex (overall)
- elicited by tapping tendon of the muscle with a reflex hammer
- brief and brisk contraction of the stretched muscle
stretch reflex mediated by
muscle spindle
stretch reflex is (mono/poly)synaptic
monosynaptic
reciprocal inhibition
- agonist contracts
- antagonist relaxes
What would happen without reciprocal inhibition?
the antagonist muscle would prevent the reflex from happening
process of reciprocal inhibition
- tapping tendon stretches muscle
- monosynaptic reflex sends out positive signal to quad to contract
- polysynaptic mechanism sends negative signal to hamstring muscle telling it to relax
At agonist, the reflex is (mono/poly)synaptic
monosynaptic
At antagonist, the reflex is (mono/poly)synaptic
polysynaptic
purpose of stretch reflex
controls muscle directly by causing agonist contraction
inverse myotatic reflex is mediated by
Golgi Tendon Organs (GTOs) located in tendons that respond to muscle tension
autogenic inhibition generally results in
relaxation of the agonist and contraction of the antagonist
inverse myotatic reflex: mechanism
- polysynaptic reflex (with interneuron) between afferent and efferent
- targeted muscle gets a negative (relaxation) signal
- antagonist gets a positive signal
function of GTO
- cause relaxation of the muscles
- GTO helps with proprioception during movement
- measures the amount of tension on the tendons
- helps create proprioceptive schema so we know where all body parts are at any point in time
Flexion and Crossed Extension Reflex is a response to
a suddenly applied noxious stimulus
In the flexion and crossed extension reflex, adaptive withdrawal of limb from offending stimulus causes an excitatory discharge that spreads through many segments via
spinospinal system
flexion and crossed extension reflex: ipsilateral limb
- reciprocal inhibition of the antagonists
- flexion
flexion and crossed extension reflex: contralateral limb
extends
flexion and crossed extension reflex mediated by
interneurons that decussate
flexion and crossed extension reflex: inteneuron activity
- crossing pathways
- inhibit extensors, activating flexors
Why do pathways cross for the flexion/crossed extension reflex?
- opposite thing happens on the other side
- need to stabilize and bear weight on the other leg
What are the other reflexes we talked about?
- somatomotor reflex
- viscerovisceral reflex
- somatovisceral reflex
- viscerosomatic reflex
somatomor reflex
works via long descending tracts (pyramidal tracts)
viscerovisceral reflex
- ANS only
- contribute to muscle tone of bladder, etc.
- monosynaptic
somatovisceral reflex
- skin cooling: reflex activates muscles that give you chill bumps
- monosynaptic
viscerosomatic reflex
- noxious stimulus activates muscle guarding
- primal reflex of movement
- works similarly to stretch reflex, except it’s polysynaptic
clinical connection: evaluation
- Is the reflex present?
- If present, is status altered (grading)?
- Are pathological reflexes present?
hyporeflexia indicates damage to:
What happens?
- LMN
- LMN isn’t adequately stimulating the muscle
hyporeflexia is a (PNS/CNS) problem
PNS
hyperreflexia is a (PNS/CNS) problem
CNS
hyperreflexia indicates
UMN is not properly modulating activity of LMN in long descending motor tracts
UMN is typically (excitatory/inhibitory) in reflexes
inhibitory
reflexes and knee stability if knee is moderately hyperextended
hamstring stretch reflexes will cause contraction of hamstrings and relieve strain on ACL
