Reflexes 2 Flashcards
what are 3 main features of muscle reflexes?
- they are automatic and fast
- they do not require conscious intervention for movement control
- they produce stereotyped response to a given stimulus (which means they can be used for diagnosis)
what are features of a monosynaptic reflex arc?
+ sensory receptor
+ afferent component (sensory input)
+ central component (spinal processing)
+ efferent component (motor output)
what are features of polysynaptic reflex arc?
one or more interneurons connect afferent (sensory) and efferent (motor) signals
+ sensory receptor
+ afferent component (sensory input)
+ central component (spinal processing)
+ efferent component (motor output)
what are the two classes of reflexes?
- intrasegmental
2. intersegmental
what does it mean if a reflex is classified as intrasegmental?
the reflex arc is restricted to one or two spinal cord segments
what does it mean if a reflex is classified as intersegmental?
the reflex arc involves a number of spinal cord segments
what does the central portion of the spindle provide?
provides the sensory output for muscle length, however it is sensitive only over a relatively small change in length
when is the spindle less sensitive?
when the muscle is completely contracted
what are the steps of the muscle reflex mechanism?
- activation of sensory receptors
- conduction to CNS along nerve fibres from receptors
- transmission across neuron/neuron synapses in CNS
- conduction from CNS along nerve fibres to muscle
- activation of muscle contractile machinery
what is the structure of muscle spindles?
- extrafusal fibres
- intrafusal fibres (2 types, bag and chain, depending on nuclei location)
- nucleated portion of intrafusal fibres
- spindle capsule
- gamma motor neuron (efferent)
- Grp II sensory fibre (afferent)
- Grp 1A sensory fibre (afferent)
what are the 3 portions of the spindle fibre?
1x less elastic/contractile sensory portion (central)
2x contractile (gamma MNs) and elastic portion (ends)
what are features of the central portion of the spindle?
- provides sensory output for muscle length
- sensitive only over a relatively small change in length
describe spindle sensitivity when almost completely contracted:
- spindle sensitivity is at the most compressed part of its range and is LESS SENSITIVE
to prevent this:
- length of spindle adjusted to keep it within its most sensitive range by extending or shortening contractile spindle ends
how is the CNS involved in adjusting the length of the spindle?
CNS activates the gamma motor efferents to the spindle in concert with the alpha motor neuron activation of the extrafusal muscle fibres
what are the 2 types of spindle fibres?
- chain fibres
2. bag fibres
what are features of chain fibres?
- innervated by both 1 A and II sensory nerve fibres
- most common fibre type in spindle
- so called because fibres’ nuclei are arranged in central portion
what are features of bag fibres?
- only innervated by type 1A fibres
- only 1 or 2 per spindle
- so called because of swelling in the equatorial region which houses the nuclei
what info do 1A fibres provide?
info about rate of change in length
what info do type II fibres provide?
info about total length
what are features of mechanism of reciprocal innervation?
- influence of spindle sensory nerve fibres from one (homonymous) muscle on motor neurones projecting to antagonist muscles
- the effect is opposite to that on their own muscle
- relaxes antagonist muscles and facilitates shortening oh homonymous muscle
- requires involvement of a local inhibitory neuron in the reflex onto the antagonist muscles
what is the definition of reciprocal innervation?
innervation so that the contraction of a muscle or set of muscles (as of a joint) is accompanied by the simultaneous inhibition of an antagonistic muscle or set of muscles
what happens when a voluntary signal for muscular contraction leaves the spinal cord?
- it travels to both intrafusal (via gamma MNs) and extrafusal (via alpha MNs) causing both sets of fibres to contract
- spindle fibre ends shorten in concert with extrafusal fibres, which keeps central position constant in length, so anulospiral sensory endings do not detect a change in muscle length
what happens in voluntary muscle lengthening?
- actually passive but involves inhibition
- intrafusal ends inhibited (excited less)
- can stretch but no change in centre so no change in signal
what are functional features of anulospiral endings?
- if anulospiral endings do not change their length, there is no change in sensory nerve activity
- only unpredicted changes in muscle length alter extension of anulospiral endings
- therefore unpredicted changes in muscle length cause a change in sensory nerve activity
