KIN421 - Muscle Spindle Physiology
steps in the stimulation of muscle spindles
(1) Impulses are conveyed by primary afferents (2) To the spinal cord (3) Connection are made with alpha motorneurons (4) Causes extrafusal fibers (muscle fibers) to contract (5) Relieves the spindle of the stretch (6) Connections are made to interneurons (7) Connections excite synergistic muscles and inhibit antagonistic muscles
how do spindles work during stretching?
- Stimulation of the spindles may occur from an external force or a weight that stretches extrafusal fibers (muscle fibers) - This is called an external stretch. - When the ends of the spindles are stimulated by the gamma afferents, the stretch is called an internal stretch - Either way, impulses are conveyed by primary afferents to the spinal cord where connections are made with alpha motoneurons to cause extrafusal fibers (muscle) to contract, to relieve the spindle of the stretch - Connections are made to interneurons which excite synergistic muscles and with connections that inhibit antagonistic muscles
Hold-Relax w/ Agonist Contraction
- if you add a concentric contraction of the agonist muscle to the passive stretch, you would also get reciprocal inhibition and increased ROM - repetition of these contractions are called successive induction
sensory mechanisms of PNF
- muscle spindle = inhibition → less resistant to muscle tissue elongation - GTO = stimulation → causes relaxation
What 4 things increase bag fiber stimulation resulting in contraction of antagonists?
- repeated stretching beyond comfortable ROM - painful stretching position - ballistic or quick stretch maneuvers - repetitive bouncing to achieve a stretch
steps of GTO stimulation
1) GTO detect tension applied to a tendon 2) sensory neurons send AP to spinal cord 3) sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons 4) inhibition of the alpha motor neurons causes muscle to relax, reliving the tension applied to the tendon
what are the 3 PNF maneuvers?
1) Hold-Relax 2) Hold-Relax w/ Agonist Contraction 3) Contract-Relax
what are the two systems of the autonomic nervous system?
1) SNS (sympathetic NS) 2) PNS (parasympathetic NS)
what are the two divisions of the PNS?
1) efferent division 2) afferent division
what are the 2 functions of secondary afferents ?
1) inhibits contraction of extrafusal fibers in muscle being stretched 2) facilitates contraction in opposite muscle
steps in muscle spindle stimulation
1) muscle spindles detect stretch of the muscle 2) sensory neurons conduct APs to the spinal cord 3) sensory neurons synapse with alpha motor neurons 4) stimulation of the alpha motor neurons causes the muscle to contract and resist being stretch
what two things do sensory receptors include?
1) nerve endings 2) cells at the end of nerve endings
Contract-Relax
1) passive prestretch = 10 secs till point of tight sensation 2) concentric contractions of antagonistic muscle then relax (shoulder extension contraction to 90degrees) 3) after relaxation → further passive stretch → uses principle of autogenic inhibition (passive shoulder flexion)
what are the two systems of efferent division?
1) somatice nervous system 2) autonomic nervous system
steps of myotatic (stretch) reflex
1) stimulus is transmitted to the CNS via the afferent neuron 2) in the CNS, association neurons activate efferent neurons that result in contraction of the agonist and relaxation of antagonist 3) gamma efferent neurons innervate the muscle spindles and help provide smooth, coordinated movements
what is the diameter of a muscle spindle?
10-24% of an extrafusal fiber
gamma motor neurons comprise _______% of all motor neurons to muscle
30%
how many gamma motor neurons activate each muscle spindle?
7-15 gamma motor neurons
sensory receptors provide info to the __________
CNS - knowledge of the world around us is gained through those sensory receptors
efferent division signals from the ________ to effect ____________
CNS organs
chemoreceptors sense ___________________________
Co2 concentration
PNF stretching stimulates ________
GTO
what are Type 1b nerve endings?
GTO
PNF is more effective than passive stretches due to its effect on ___________ located near the _______________________________ (sensitive to increasing tension within a muscle)
GTO musculotendinoous junction
what are GTOs?
Golgi tendon organs - located at the insertion of muscle fibers into the tendon - primary purpose is to protect the muscle from overexertion - Type 1b afferents
Nerves whose cell bodies arise inside the CNS and travel outside the CNS compromise the ____________________________
Peripheral Nervous System
what is PNF?
Proprioceptive Neuromuscular Facilitation (Passive Stretching)
other names for primary afferents
Type 1a annulospiral
Other researchers suggest depression of H-reflexes after contraction which are related to muscle excitability thereby enhancing stretch. Muscle relaxes due to reduced ___________________________ activity and reduced ___________________________ activity and greater relaxation.
Type IA afferent gamma motorneuron activity However, EMG activity remains the same or increases after a contraction. Thus the concept of neural inhibition with respect to reduced alpha motorneuron excitability is questionable. The possibility of reduced gamma motorneuron excitability remains.
other names for secondary afferents
Type II flower sprayed
A concentric muscle action in the agonist pattern is used during a passive stretch of the antagonist muscle to achieve reciprocal inhibition. This is called ______________________________
agonist contraction
what does bag fiber stimulation allow?
allows muscle to adjust to a variety of loads with right amount of force necessary to accomplish a task and to protect tissue around the joints - if muscle force indicated by EMG didn't increase rapidly, the stress on the skeletal joints could be excessive and lead to injury
the somatic nervous system has what kind of neurons?
alpha motoneurons
other names for Type 1a afferent
annulospiral nerve endings primary nerve endings
PNF allows contraction of the ____________________ muscle of the muscle being stretched
antagonist (Allows contraction of the muscle being stretched in the opposite muscle before stretching)
the muscle that is being stretched is called the ____________________ and the opposite muscle is called the ___________________
antagonist agonist
autogenic inhibition increases GTO activation of _______________________ muscle during _________________ contraction
antagonist isometric
Contract-Relax uses principles of _________________ inhibition
autogenic
Hold-Relax uses _______________________ inhibition
autogenic
Muscle experiences a refractory period after contraction known as _____________________________
autogenic inhibition (refractory period = a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation)
impulses generated by stimulation of proprioceptors are conveyed by __________ to the _________________
axons spinal cord
Ballistic Stretches activate the _________ fibers causing contractions of these fibers
bag
the spindle is composed of the __________ fiber and the ____________ fiber
bag chain
Type 1a nerve ending (annulospiral) wraps around both a ________ and a _______ fiber and goes into the cord and synapses with the alpha motor neuron and goes out into the muscle where the spindle lies ________________ to the muscle.
bag chain parallel
why are progressive increases in contractions very important?
because maximal muscle contraction is followed by maximal relaxation If the muscle to be stretched contracts maximally, then it will relax maximally
what are gamma motor neurons?
cell bodies in the brain which cause contraction of the spindles (internal stretch) muscle spindles are stimulated by gamma motor neurons
the gamma efferent system is excited by regions of the brain stem which receive input from the _____________________ and the ____________________________
cerebellum cerebral cortex
Static Stretches activate ______________ fibers
chain
Type II nerve ending (flower sprayed) connects to the ____________ fiber
chain
the concentric muscle action is called the _______________
contract
how do you produce autogenic inhibition?
contract a muscle immediately before a passive stretch of the same muscle
what is successive induction?
contraction against a maximal resistance increases subsequent demand for maximal contraction of the opposite muscle
secondary afferents are stimulated by ___________ of stretch, not by velocity of stretch
degree
when the preferred length is reached, the spindles fire minimally, thus the muscle seeks out the contraction that will reduce ________________________ to a minimum
firing frequency
other names for Type II afferent
flower sprayed nerve endings
what are muscle spindles?
fluid filled capsules which lie parallel to muscle fibers
even at rest, there is constant stimulation of intrafusal fibers known as ____________________
gamma bias - muscle contraction is maintained at various levels of force - there is always some activation at rest → increases muscle tone = inherent tightness
the spindle also has a motor efferent innervation carried by ____________________ neurons , which is used by the nervous system to modify the spindle's ______________________
gamma motor sensitivity
internal stretch of muscle spindles is activated by ________________________________
gamma motor neurons
thermoreceptors sense ___________ or ____________
heat cold
the sensitivity of spindle afferents to external stretch is increased when gamma bias is _________
high high gamma bias = high tautness = high sensitivity
the isometric portion is called the _______________
hold
if muscle force indicated by EMG didn't __________________________, the stress on the skeletal joints could be excessive and lead to injury
increase rapidly
when GTO are stimulated, they _________________ contraction in that muscle and stimulate ______________________ in opposite muscle
inhibit co-contraction
The breaking point in muscle contraction may be related to __________________ caused by activation of ____________
inhibition GTO GTO stimulation may overcome the voluntary effort to maintain contraction.
connections are then made to ______________________, which excite __________________ muscles, and with connections that inhibit ____________________ muscles
interneurons synergistic antagonistic
(proprioceptors) _____________________ in the spinal cord carry the impulses to a ______________________ which then help to elicit appropriate responses from the right muscles
interneurons motorneuron
muscle spindles are ___________________ fibers
intrafusal - intrafusal muscle fibers are skeletal muscle fibers that comprise the muscle spindle and are innervated by gamma motor neurons - these fibers are proprioceptors that detect the amount and rate of change in length of a muscle
Both ___________________ and ___________________ muscle actions in the antagonist pattern are used prior to a passive stretch of the antagonist to achieve autogenic inhibition
isometric concentric
this dynamic sense is termed _____________________ while _______________________ describes the general state of body awareness in the resting state
kinesthesis (Perception of body movements. It involves being able to detect changes in body position/movements without relying on info from the five senses) proprioception
muscle spindles are sensitive to _________________
length
GTO stimulation increases during a ____________________________ stretch of a muscle that lasts at least _____ secs
maximum isometric 6secs
What increases GTO stimulation?
maximum isometric stretch of a muscle at least 6 secs (preferably 10 secs) - positive influence to increase soft tissue length - inhibits the stretch reflex if held for more than 8 secs after a contraction - PNF can provide a muscle-specific stretch at the end of an activity - more research needs to be done using varying PNF techniques to see if it doesn't impair strength or power when performed prior to the event - research now suggests that it does impair the ability to perform repeated contractions at a submaximal level.
what are proprioceptors innervated by?
movements of skeletal joints and muscles
High gamma activation → gamma bias increases _________________________
muscle tone
nociceptors sense _________________________
pain or physical/chemical damage (Type 3 and 4 nociceptors)
muscle spindles are fluid filled capsules which lie _________________ to muscle fibers
parallel
Hold-Relax
passive pre-stretch - place a muscle in an elongated position for 10 sec to the point of tight sensation - hold - relax slowly - further passive stretch to new found ROM - can use agonist muscle - 30 secs - autogenic inhibition = increases GTO activation of antagonist muscle during isometric contraction
__________________ muscles have many secondary afferents (extensor muscles)
postural Postural muscles constantly bombarded by neural stimuli. They must maintain their readiness to respond to voluntary movements and maintain some degree of residual activity to counter the pull of gravity from the upright posture
PNF uses _________________ stretching to stretch a muscle
pre-contraction
baroreceptors sense ___________________
pressure
(a-y coactivation) when externally stretched, impulses are conveyed by ____________________________ and ____________________________ to the spinal cord where connections are made with____________________________ of _____________________ fibers so that muscles can contract to relieve the spindle of the stretch
primary afferent neurons secondary afferents alpha motorneurons extrafusal
in both external/internal stretch, impulses are conveyed by ____________________________ to the _________________ where connections are made with ____________________________ to cause extrafusal fibers to contract and to relieve the spindle of the stretch
primary afferents spinal cord alpha motoneurons
muscle spindles and golgi tendon organs are examples of ________________________
proprioceptors
external stretch of muscle spindles has what kind of velocity?
rate of change of length in muscle
how do sensory receptors receive information?
receive info from the stimulation of the body's surface and deep lying tissue
Hold-Relax w/ Agonist Contraction uses _______________________ inhibition
reciprocal
If the relaxation occurs in the muscle opposing the muscle experiencing the increased tension, the result is called _____________________________
reciprocal inhibition
if you add a concentric contraction of the agonist muscle to the passive stretch, you would also get __________________________ and increased ________. Repetition of these contractions are called __________________________
reciprocal inhibition ROM successive induction
muscle spindles and golgi tendon organs both function by _____________ action
reflex
(autogenic inhibition) tension produced during the contraction stimulates the GTO causing a _______________________ of the _______________ muscle during the subsequent passive stretch
reflex relaxation same
(GTO stimulation) inhibition of the alpha motor neurons causes muscle to ___________, reliving the ___________ applied to the tendon
relax tension
Successive induction = contraction against a maximal _____________________ increases subsequent demand for maximal contraction of the _____________________ muscle.
resistance opposite This will result in stronger and stronger contractions of the opposite muscle
postural muscles have many _____________________ afferents
secondary afferents
the afferent division has what kind of receptors?
sensory receptors
during a passive stretch, reciprocal inhibition is accomplished by doing what?
simultaneously contracting the muscle opposing the muscle being stretched the tension in the contracting muscle stimulates the GTO and causes simultaneous reflex relaxation in the opposite muscle reciprocal inhibition describes the process of muscles on one side of a joint relaxing to accommodate contraction on the other side of that joint
(inr GTO stimulation) positive influence to increase ____________________________
soft tissue length
what happens during internal stretch?
stimulation by the gamma afferents
what is external stretch?
stimulation that occurs from an external force/weight that stretches the extrafusal fibers (muscle fibers)
external stretch of muscle spindles is stimulated by _____________
stretch (final length of muscle)
(inr GTO stimulation) inhibits the _____________________ if held for more than 8 secs after a contraction
stretch reflex
Some researchers report that increases in ROM after a contraction are due to increased _____________________________ rather than a neural effect. These researchers suggest that increased tension stimulates GTO activity which subsequently leading to greater _______________
stretch tolerance (feeling less pain for the same amount of force to a muscle → the ability of the muscle to stretch is enhanced) relaxation
Advantage in PNF lies in their effectiveness in creating an atmosphere that _______________ soft tissue and enhances the right ______________ mechanisms
stretches sensory
In successive induction, each successive contraction is _____________________ than the previous one
stronger
golgi tendon organs are sensitive to _________________
tension
when _____________ is too great, GTO is stimulated
tension
muscle contraction increases __________________ applied to tendons → in response, _______________________________ are conducted to the spinal cord
tension action potentials
In an isometric contraction → if the muscle tendon unit is already elongated, when the muscle contracts, what is the net effect?
the net effect is that the muscle pulls on/stretches the connective tissue framework further increasing the stretch
postural (antigravity) muscles inhibit contraction in ___________________ muscle but produce _______________________ in the _______________________ muscles
their own co-contraction opposite
what is the purpose of alpha-gamma coactivation?
to cause the right degree of muscle tension to effect a smooth movement → gives CNS info about how much a contraction is needed to provide continual afferent feedback from the contracting muscle that informs the CNS of muscle length continually during a contraction and to let the CNS know how many MU are required for a smooth contraction
what is the function of the gamma motoneuron?
to maintain a constant tension (taut) on the intrafusal muscle fibers by causing them to contract in response to alpha motoneuron-stimulated contraction of extrafusual muscle fibers - this allows the spindle to monitor muscle length.
T/F GTO lie in a series → 10-20 muscle fibers belong to different MU
true
T/F PNF also uses the principle of successive induction
true
T/F Important for the CNS to obtain instantaneous info in order to orchestrate a fluid movement. Each receptor is stimulated through a specific form of energy, i.e. light energy, which is translated to an AP before being transmitted along sensory fibers.
true
T/F the contraction of the spindle allows the spindle to be at near optimal sensitivity regardless of the changing length of the extrafusal fibers
true
what is alpha-gamma co-activation?
when externally stretched, impulses are conveyed by primary and secondary gamma afferent neurons to the spinal cord where connections are made with alpha motorneurons of extrafusal fibers so that muscles can contract to relieve the spindle of the stretch
