18 reflexes Flashcards
name 3 types of movements
involuntary
voluntary
rhytmic
What 2 rough mechanisms maintain posture?
feedback
feedforward (anticipation)
Where must the centre of mass be to maintain balance?
within our foot area
What do postural muscles need?
maintain tone to maintain a constant state of partial
contraction
corrective reflexes
What do proprioceptors sense?
muscle length and tension
Which other organ helps with stability?
What reflexes does this involve?
the eyes and their saccades
vestibulo-ocular reflex
optokinetic reflex
What 4 origins may sensory feeback arise from?
(vestibulo-ocular reflex and optiokinetic reflex)
visual system
vestibular system
(somesthesia)
skin receptors
prorioreceptors
Name 2 proprioception organs
Muscle spindle fibres
Golgi tendon organs
What do muscle spindles measure, and what is their structure?
measure length (dynamic and static changes, for rate of change too) in parallel to muscle fibres
What do golgi tendon organs measure and how are they arranged?
measure tension
in series with muscle fibres
what are the 2 main regions of the muscle spindle fibre?
central region
polar regions
What comprises the central region of muscle spindles?
non-contractile fibres
primary and secondary sensory afferent endings
What innervates the polar regions of muscle spindles and what is their function?
Gamm motor neurones
doesn’t contribute to overall force, but adjusts the sensitivity of the spindle
In muscle spindles, what is the function of secondary afferents?
innervate the eds of the central region and respond to static length
In muscle spindles, what is the function of primary afferents?
innervate central region and respond to velocity of lengthening
What elements do secondary afferents of muscle spindles have?
anulospiral elements
What elements to primary afferents of muscle spindles have?
splay endings
What is tonic signalling?
1 - extrafusal muscle fibres at resting length
2 - sensory neuron is tonically active
3 - spine integrates function
4 - alpha motor neurons to extrafusal fibres receive tonic input
5 - extrafusal fibres maintain a certain level of tension even at rest
What is the problm with stretching a muscle accidentally?
it will contract
This might be a muscle next to the spindle, pushing on the spindle fibres
What maintains spindle function when muscles contract?
alpha-gamma co-activation
How does alpha-gamma co-activation work?
alpha and gamma motor neurones fire
muscle contracts
stretch on centres of intrafusal fibres unchanged, firing rate of afferent neuron remains constant
What is the Servo-loop hypothesis?
when the muscle i s stretched, the gamma mn enable the contracted muscle to stay at the desired length
there was a theory that gamma neurones were controlling muscle length, by controlling alpha neurones, but this doesn’t really hold up anymore
What is the practical implication of the servo-loop hypothesis?
we can maintain muscle stiffness when piling on loads
Are reflexes context dependent?
yes
How can feeedofrward mechanisms work?
gamma mn control feedback gain of spinal loops via feedforward mechanisms from higher motor centres
Where to reflexes go through?
ventral horns for the motor bit, the ascending tract pat won’t bother with this as its’ job is to stimulate somatic sensation
What effect do golgi tendon organs have on alpha motor neurones?
inhibit them (glycinergic)
What will the golgi tendon organ do in an overload situation?
the tension will increase massively, and the golgi tendon will inhibit contraction to save the muscle
