Muscle Spindle & GTO Neurophysiology & Application - E1 Flashcards
Learn the basics of mm spindle and GTO fibers and neurons and apply it to reflex Arcs, DTR, Clonus, Tonic Reflexes
What do muscle spindles sense?
Change in muscle length
What do GTOs sense?
Change in muscle tension/force
MM spindles run __ to true mm fibers (extrafusile)
Parallel
GTO run ___ to true mm fibers (extrafusile)
In series
What are mm spindles and GTOs primary function?
Proprioception
Where is the GTO?
At the musculotendinous junction b/t the tendon and muscle
List the two types of mm spindle fibers
Nuclear bag
Nuclear chain
What is a nuclear bag?
Either static or dynamic, a type of mm spindle fiber with a large diameter, with clustered, central nuclei
What is a nuclear chain?
A type of mm spindle fiber with a small diameter and nuclei spread out
T or F : mm spindles can contract
True - note striations at the end of mm spindle fibers
What is the primary receptor type of …
Ia phasics
Ia tonics
a&b) annulospiral receptors
What do a/b/c arise from?
a) Ia phasics
b) Ia tonics
c) Ib afferents
a) Dynamic nuclear bag cnetral area
b) Nuclear chain area
c) In GTO
What does (a/b/c) sense?
a) Ia phasics
b) Ia tonics
c) Ib afferents
a) Rate of mm lengthening (velocity) and mm length changes
b) Just mm length changes
c) Tension/force changes (passive/active elongation)
Ia phasics [facilitate/inhibit] the agonist via ___
Ia phasics FACILITATE the agonist via the alpha motor neuron (monosynaptic reflex arc)
Ia tonics [facilitate/inhibit] the agonist via ___
Ia tonics Facilitate the agonist via the alpha motor neuron (monosynaptic reflex arc)
Ia phasics [facilitate/inhibit] the antagonist via ___
Ia phasics INHIBIT the antagonist through the interneuron (diasynaptic reflex arc)
Ia tonics [facilitate/inhibit] the antagonist via ___
Ia tonics INHIBIT the antagonist through the interneuron (diasynaptic reflex arc)
What do the ascending fibers of Ia tonics, Ia phasics, and II afferents form?
The P/DCML
What does the quick stretch reflex stimulate?
The Ia tonic and Ia phasics
Give an example of reciprocal inhibition in an individual with a C7 SCI
Elicit contraction of triceps to facilitate (+) the triceps and inhibit the antagonist - biceps
Ib afferents [facilitate/inhibit] the agonist via ___
Ib afferent inhibit the agonist via an IN to alpha motor neuron (diasynaptic)
Ib afferents [facilitate/inhibit] the antagonist via ___
Ib afferent facilitate the antagonist via the alpha motor neuron (monosynaptic)
What is the basic mechanism to stimulate the GTO
cross fiber massage
How many mm fibers is a GTO connected to?
15-20 mm fibers
T or F: GTOs only respond to concentric changes
FALSE - respond to isometric, concentric, or eccentric w/as little as 2-25 g of force
Which fibers are responsible for crude gait?
II afferents with the crossed flexion-extension reflex (flexion ipsilateral, extension CL)
What neuron types are best at sensing quick stretch?
Ia phasics
What is clonus
Repeated, sustained contractions due to a quick stretch reflex
II afferents arise from ….
Flower spray receptors on the polar ends of the nuclear chain fibers and the static nuclear bag fibers
Stretch of mm spindle causes II afferents to ….
Send sensory information to the spinal cord
What neuron fibers contribute to crossed extension reflex?
II afferents
II afferents [facilitate/inhibit] the …. via _____
a) IPSI flexor
b) IPSI extensor
c) CL flexor
d) CL extensor
a) Facilitate the ipsilateral flexors via the alpha motor neuron (monosynaptic)
b) Inhibit the ipsilateral extensors via an IN to the alpha motor neuron (diasynaptic)
c) Inhibit the contralateral flexors via an interneuron to the alpha motor neuron (diasynaptic)
d) Facilitate the contralateral extensors via the alpha motor neuron (monosynaptic)
What are the key mm still function for an individual with a C4 SCI
Upper Traps, Accessory neck mm, deep neck mm, diaphragm
What are the key mm still function for an individual with a C5 SCI
Biceps, wrist extensors (ASIA - elbow flexors)
What are the key mm still function for an individual with a C6 SCI
Wrist extensors, SA, Lats (ASIA - wrist extensors)
What are the key mm still function for an individual with a C7 SCI
Triceps, Intercostals mm of first seven ribs, back extensors C1-C7 (ASIA - elbow extensors)
What is the scoring system for DTR?
A continuum:
0 & 1: hypoactive
2: normal
3 & 4: hyperactive
0 = absent \+ = hypoactive \++ = normal \+++ = brisk \++++ = hyperactive
What is a hypertonic reflex indicative of?
An UMN lesion -
An uncontrolled or uninhibited reflex arc activity
What is a hypotonic reflex indicative of?
A LMN or UMN lesion -
An underfacilitated relfex arc activity
What do you measure with a modified ashworth scale (MAS)?
Hypertonicity only
What do you measure with DTRs?
Hypertonicity or hypotonicity
What is the scoring system of the modified ashworth scale (MAS)?
A continuum:
0 = normal
1, 1+, 2, 3, 4 = increasing levels of hypertonicity
When is passive stretching the MOST appropriate?
When there are NO FUNCTIONING mm around the joint - neither agonist, synergist, or antagonist
What is the most appropriate stretching mechanism with a mm contraction end-feel?
Active stretching technique to stretch mm better
What is the most appropriate stretching mechanism with a myofascial restriction end-feel?
Myofascial release techniques
What is the most appropriate stretching mechanism with a soft end-feel?
Soft tissue mobilization (superficial to deep), scar mobilization, or functional massage
What is the most appropriate stretching mechanism with a joint/capsular end-feel?
Joint mobilization - not quite a “stretch”
Contract - Relax steps
1) go to point of restriction
2) pull against resistance (allow Pt to move a little)
3) As Pt relaxes, take the Pt out as far as they can –> new point of resistance
What is the neurophysiology behind contract - relax
Active concentric contraction of the agnoist may induce relaxation of the agonist (mm spindle neurophys)
Hold - Relax steps
1) Go to the point of restriction
2) Have Pt hooooooooold against resistance (NO MVMT)
3) As Pt relaxes, bring them into a new range
What is the neurophysiology behind hold- relax
Strong contraction of the agonist may trigger the GTO to inhibit the agonist (GTO neurophys) OR may cause immediate relax of the agonist after the strong contraction (mm spindle neurophys)
What are the steps of reciprocal inhibition
1) Go to the point of restriction
2) Have Pt hold against antagonist
3) Bring Pt into new range
What is the neurophysiology behind reciprocal inhibition
Facilitate the agnoist and Inhibit the antagonist via the mm spindle neurophys (Ia phasics come in and go to IN to inhibit the antagonist )
Cross fiber massage steps
1) Find mm tendon @ musculotendinous junction
2) Start at end of range
3) do cross fiber massage to stimulate GTO to get inhibition and more range
4) Move Pt into the new range
What is mm spindle bias?
The tendency for the mm to resume its original length since the mm spindle wants to assume its original, pre-stretch length
What is TVR?
Tonic vibratory reflex: vibrating the skeletal mm at a high frequency to induce a tonic contraction of the mm being vibrated
How does TVR work?
It selectively stimulates the mm spindle (Ia phasics) causing them to fire at the same frequency of the vibrator to facilitate the agonist and inhibit the antagonist
What Hz do you want to do TVR at?
60 Hz kids
100-120 for adults
over 200 can cause damage
Where should you be cautions with TVR?
Around the carotid arteries or other major blood vessels
- do not want to dislodge a clot and cause a stroke
What is the neurophys behind cross fiber massage
Cause firing of the GTO to be >
Ib sensory nerve firing to inhibit agonist and facilitate the antagonist
What is the primary function of sensory receptors
To monitor the internal and external environment (detect force, proprioception, explore/manipulate the environment, detect harm)
Define sensation
Receptors receive and route info to SC to higher centers (for processing)
Define perception
The integration of sensory info from many sensory sources
What are III and IV afferents?
Cutaneous and joint receptors that bring proprioceptive info to the SC, cerebellum, and cortex BUT mostly just at extremes of range
What gives us the best information about joint position?
MM spindles and GTOs
How does the CNS regulate the sensitivity of our proprioceptive system?
Efferent motor neurons -
when they are firing, they create enhanced sensitivity of the mm spindle
List some efferent neurons
Gamma motor neurons - static and dynamic
Alpha motor neurons
What do … innervate?
a) static gamma mn
b) dynamic gamma mn
c) alpha mn
a) static gamma mn innervate the contractile ends of the static nuclear bag and nuclear chain fibers (intrafusal)
b) dynamic gamma mn innervate the contractile ends of the dynamic nuclear bag fibers (intrafusal)
c) alpha mn innervate the extrafusal mm fibers
What regulates the efferent mn pathways?
Descending motor tracts
eg: CST, VST, RST, etc
Give an example of enhanced proprioception
The firing of dynamic and static gamma mn at night to help increase proprioception to sense objects while walking at night
What composes a sensory unit?
Sensory receptors, a sensory neuron, and its many branches
List the sensory receptors - superficial to deep
Meissner's corpuscle Merkle corpuscle Free nerve endings Krause Corpuscle of ruffini Pacinian corpuscle
T or F: Sensory receptors are transducers
True; they all convert one type of E to another (electro-chemical end result)
What is modality specific
when a receptor responds most efficiently to one type of sensory stimulus
What is a polymodal recptor?
responds to multiple stimuli - free nerve endings
What do meissner’s corpuscles sense?
Pressure and touch (they are mechanoreceptors)
What do Krause receptors sense?
Cold
What do ruffini corpuscles sense
Warm
What to pacinian corpuscles sense
Touch and vibration in joints, tendon sheaths, and skin (mechanoreceptors)
What is a free nerve ending?
An unmyelinated terminal of myelinated and unmyelinated neurons
How are we able to sense the direction our hair is moved?
Free nerve endings that wrap around a hair follicle tell us direction of light touch
What do free nerve endings sense?
Cold, warm, touch, and pain
Define mechanoreceptor
Respond to physical stimulation that causes mechanical displacement of one or more tissues
Where do you typically find meissner’s corpuscles
In the hairless portions of the skin (palms, soles, toes, fingers)
How does a pacinian corpuscle work?
It is a phasic receptor -
1) Pressure touch deforms it (depolorization) “on”
2) Fluid redistributes quickly in the corpuscle following deformation “off”
3) when stimulus is then removed, PC changes shape again (depolorazation) “on”
Phasic vs tonic receptor
Phasics are fast adapting (miliseconds) and tonic receptors are slow adapting (minutes, hours, days)
What are examples of phasic receptors?
Meissner's corpuscle (RA1) Pacinian corpuscle (RA 2)
What are examples of tonic receptors?
MM spindle GTO Merkel cell (SA 1) Ruffini ending (SA 2) Carotid baroreceptor
What is on the pain ends of temperature feeling? (cold-pain and hot-pain)
Free nerve endings
0-15 and >45-50
What is the approximate T range for Krause receptors to be active (Celcius)
10-45 C w/peak between 20 & 30
What is the approximate T range for Ruffini receptors to be active (Celcius)
30-45 w/peak 40-45 C
What factors contribute to our perceievd temperature?
Air T
Wind speed
Solar and thermal radiation
Humidity
What are nociceptors
Detect pain -
They detect actual or potentially destructive mechanical, chemical, or thermal changes in the immediate tissue
Hypertonicity is a result of a _MN lesion
UMN always
Hypotonicity is a result of a _MN lesion
UMN or LMN lesion
Two-point discrimination - from closest to farthest
a) forearm
b) back
c) Fingertip
Finger tip > forearm > back
What broadman areas is the pre-central gyrus
4
What broadman areas is the post-central gyrus
3, 1, 2
What is a receptive field
An area of the sense organ that when stimulated, will activate a single afferent neuron w/the center being the most sensitive to the stimulus
How does 2-pt discrimination work?
You will only perceive two different points if you overlap 2 different receptive fields. Receptive field size changes dependent upon where you are
Relationship b/t size of receptive field and sensory acuity
Inversely proportional - the smaller the receptive field the greater the sensory acuity
What is perception?
Give an example
The integration of sensory information from many sensory sources (Vision, hearing, smelling, and touching)
- Recognizing your dog or cat as your own
What is graphesthesia
The ability to identify characters that are written on the skin - tests cortical sensation/perception
What are some ways to test cortical sensation/perception
Graphesthesia and sterognosis
What is sterognosis
The ability to identify objects placed in the hand with eyes closed
Asterognosis
The inability to distinguish two objects placed in the hand (tactile agnosia) or by sight (visual agnosia)
What is body image
Awareness of body parts and their relationship to one another and the environment
What are body image disorders?
Perceptual disorders associated w/PARIETAL*** and temporal lobe lesions (most commonly w/Right brain lesions)
What is asomatognosia
Lack of awareness of the body structure and the rln of body parts to one another
What is hemi-asomatognosia
Decreased awareness of one side of the body (usually on the Left)
What is hemi-spatial neglect
Most common on the RIGHT (non-dominant) PARIETAL cortex, causing patients to neglect the left side of their environment
What is apraxia
inability to follow a motor command that is not due to a primary motor deficit or language impairment, but a deficit in higher-order planning PLUS inability to carry out the motor plan
What is ideomotor apraxia
Can plan/conceptualize, but not carry out the motor tasks
able to make gestures spontaneously, but cannot produce same movements if asked
What is ideational apraxia
Cannot come up with the plan or concept of the task & cannot carry out the action spontaneously or on command
