Somatosensory 1 Flashcards
What do muscle spindles do
and what are they
how do they run and whats another name
run parallel to skeletal muscle,
specialized sensory receptors that provide feedback on muscle stretching and send the info to the CNS
Intrafusal muscle fibres run in parallel with skeletal (extrafusal) muscle fibres
Muscle spindle anatomy PARTS
muscle spindle anatomy NEURONS
Intrafusal fibers: non- force producing muscle fibers that lengthen and stretch with changes in muscle length.
Afferent axons: Innervate sensory endings of muscle spindle and send feedback to the spinal cord.
Efferent axons: MNs innervate polar ends (contractile) of intrafusal fibers and send excitatory inputs from the spinal cord. efferent axons end up in Gamma
Gamma motor neuron endings: stimulate intrafusal muscle fibers.
Sensory endings: sense length of intrafusal muscle fibres
Central/Non-contractile Region: of muscle spindle
Capsule: connective tissue surrounding intrafusal fibers and sensory receptors that compose the spindle
Extrafusal fibers: Fibers that cause muscle contraction. They are in parallel with intrafusal fibres
Primary afferents (Group Ia) wrap around all types of
intrafusal fibres (“annulospiral endings”), but most commonly the nuclear bag type. A primary afferent and the intrafusal fibres it wraps around is called a MUSCLE SPINDLE PRIMARY ENDING.
primarys are more about measuring velocity
▪ Secondary afferents (Group II) make ‘flower spray endings’ onto ONLY nuclear chain type intrafusal fibres. A secondary afferent and the intrafusal fibres it contacts is called a MUSCLE SPINDLE SECONDARY ENDING.
secondaru are about measuring length
Sensory coding of muscle stretch
what endings are involved in each
the firing rate of aciton potentials of muscle spindles corresponds to changes in length of muscle.
differences in the initial and the final length of the muscle and dynamic phase of muscle stretch
both supply the CNS with sensory input proportional to how fast or how long the muscle is stretched
Stretch responses of primary and secondary endings have different qualities.
Primary endings are more sensitive to the dynamic phase of movement – their firing rates during this dynamic phase closely correspond to the velocity of muscle stretching
Stretch responses of primary and secondary endings have different qualities. Secondary endings are more sensitive to muscle length – they are not sensitive to muscle stretch velocity, however, their firing rates more closely correspond to muscle length than primary endings.
Mechanically gated ion channels
sensory endings are wrapped around the muscle spindles, there are ion channels in the endings,
more Na+ enters the cell the faster or longer the stretch is
Coding of muscle length and velocity
Comparing the responses of primary (Ia) and secondary (II) muscle spindles to a series of
muscle stretches, we can see primary muscle spindle firing rate is more related to the velocity of
stretch (BLUE is where velocity is HIGH), whereas secondary muscle spindle firing is related to
length of the muscle (RED is where the offset from initial muscle length – “static offset” – is HIGH
Fusimotor system and yMNs
whats the roles of yMNs
WITHOUT MNs: if the muscle were to contract to a
shorter length, the intrafusal fibres would become slack
(floppy) and the spindle would stop providing feedback about where your limbs are!
gamma motor neurons make sure the spindles are at the same length as the skeletal muscle fibres and make sure the action potentials fire. PULL ON THE NON FORCE PRODUCING INTRAFUSAL FIBRES
▪ WITH MNs: when MNs are stimulated at the same time as the αMNs, the intrafusal fibres contract along with the extrafusal (skeletal) muscle fibres, which allows the muscle spindle to keep responding during contractions
what is co activation
why do they happen
when the same motor commands come the cerebral cortex and connect to gamma and alpha motor neurons and make them contract together
human microneurography
whats the response
inserting an electrode into a peripheral nerve to record action potentials from sensory and motor neurons
higher velocity flexions resulted in larger dynamic responses
Proprioception and Kinesthesia
vibration envoked illusion
why are muscle spindles important in this
what types are more prevelant in which
proprioception: our bodies understanding of where we are in space
Kinesthesia: Brain’s understanding of movement and how are limbs and moving
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a vibrator pushing on the tendon pulls muscle which activates muscle spindles making it think that it is being stretched but it isn’t. showing that muscle spindles are important in maintaining direction
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Secondary afferents are used more in proprioception, and tell us WHERE we are in the world
primary afferent endings tell us about our MOVEMENT and what we are currently doing
