Application of Muscle spindle & GTO neurophysiology Flashcards
Neurophysiology underlying manual skills
*Muscle spindle psl: Quick muscle stretch & muscle tapping
*Muscle spindle psl: Vibration
GTO psl: Cross-fiber massage
Prolonged muscle stretch
1a phasic
1st into spinal cord and synapse directly to AMN to the mm with the msp. It ALSO branches to an interneuron (inhibitory neuron) which goes to antagonist mm (another muscle)
1a tonics
afferent sensory info- follows same path as phasic but also synapses with the ascending tract to the brain that brings proprioception to the brain-post central gyrus of the brain (area 312)
Ia phasics afferents
- primary annulospiral receptors
- arise from the dynamic nuclear bag central area
- sense both the rate of muscle lengthening (velocity) and muscle length changes
- facilitory [+] to the agonist through the alpha MN
- inhibitory [-] to the antagonist
Ia tonics afferents
- primary annulospiral receptors
- arise from the nuclear chain area
- sense muscle length changes
- facilitory [+] to the agonist through the alpha MN
- inhibitory [-] to the antagonist
Monosynaptic Reflex Arc
Receptor (muscle spindle) -> Ia afferents -> [+] alpha MN and contraction of extrafusal muscle fibers in the agonist/synergists muscles
Ia fiber branches -> inhibitory interneuron -> [-] antagonist muscles (reciprocal inhibition)
Muscle Spindles
Function: muscle spindle is to sense stretch (increase in muscle length) and elicit a reflex.
Deep tendon reflex (DTR)
especially activates Ia phasics (due to quick on/off of tendon tap)
Hypertonic
– uncontrolled or uninhibited reflex arc activity– overactive
- Hypersensitive to quick stretch
- CNS or UMN lesion
- Likely damaged INHIBITORY descending motor tracts
Hypotonic
– under facilitated reflex arc activity
- No response or very little response
- LMN lesion
- Likely damaged facilitatory descending motor tracts
Responsible for clonus
sustained monosynaptic reflex arc
***fast and effective reflex but not very flexible (“hard-wired)- monosynaptic reflex
Modified Ashworth Scale
numbers to scale someone’s hypertonicity in PROM–
normal= 0
Deep Tendon Reflex (test)
normal is 2
hypertonicity= 3-4
hypotonicity= 1-0
Hypotonicity
can be a result of a LMN or UMN injury
LMN = peripheral nerve (example: median nerve – carpal tunnel syndrome) LMN = nerve root at the spinal cord(in the intervertebral foramen) (example: L4 nerve root compression) UMN = damage to the spinal cord or cortex
Hypertonicity
always indicative of an UMN lesion
Uncontrolled reflex arc
TVR - tonic vibratory reflex
Vibrate skeletal muscle at a high frequency –> tonic contraction induced in muscle being vibrated
60 Hz effective on kids
100-120 Hz needed for adults
Selectively stimulates muscle spindle (Ia phasics).
Ia phasics fire at same frequency as the vibrator.
[+] agonist (facilitation) and [-] antagonist (reciprocal inhibition)
TVR
- progressively builds in strength and is maintained while vibration on muscle; gradually fades out (effects can last as much as 3 minutes) after vibrator is removed
- response is best on muscle belly or tendon? (Still unclear)
- Follow with resistance or active contraction to enhance muscle response and increase motor control/learning
If the biceps is hypertonic due to flexion synergy post stroke, what muscle would you vibrate?
Triceps
TVR Precautions
- Frequency over 200 Hz can damage skin or holding vibrator in one place too long can blister or bruise skin
- Be careful around head with a client with hydrocephalus (area of shunt)
- Be careful around carotid baroreceptors or major blood vessels around neck
GTO Physiology
- Cross fiber massage directly over the musculotendinous junction would cause firing of the GTO > Ib sensory nerve fiber firing
- Inhibition of the agonist
- Facilitation of the antagonist
If the biceps is hypertonic due to flexion synergy post stroke, what musculotendinous junction would you perform cross fiber massage on?
Biceps Tendon
Golgi tendon organ (GTO) Psl
Stretching of muscle pulls on the GTO and excites Ib afferents that synapses onto Ib inhibitory interneurons
Prolonged Stretch of a Muscle (GTO)
- may cause inhibition of the agonist being stretched if GTO input to agonist “wins out” over muscle spindle input to the agonist. [Ib is long-term so it “wins out” over Ia]
- GTO is connected to 15 to 20 muscle fibers.
- GTO responds to as little as 2 to 25 g of force (newer info)
Sensory Receptors’ Job
- primary function of sensory receptors is to monitor the internal & external environment
- Detect force
- Know where the body is in space and how the body is positioned
- Explore and manipulate the environment
- Detect potentially harmful environments or objects
Define Sensation
receptors receive and route information to the spinal cord and to higher centers (for processing).
“See” the information
Define Perception
- integration of sensory information from many sensory sources
- beginning to “make sense” of sensory information
Muscle Spindle Function
- Primary function of the muscle spindles and GTOs are PROPRIOCEPTION
- Primary input from the Ia phasics, Ia tonics, Ibs (afferent sensory information)
- Body in space and how it moves in space
III and IV afferents
- Cutaneous (baroreceptors) and joint receptors
- III and IV afferents bring proprioceptive information to the spinal cord, cerebellum and cortex
Joint Receptors
- appear to sense joint position more at the ends of range (short or long)
- Muscle spindles and GTOs appear to give us the “best” information about joint position
What contributes to the sense of proprioception?
Muscle spindles, golgi tendon organs, joint receptors and cutaneous receptors all contribute to the sense of proprioception
Dorsal Column Medial Lemniscus
- Proprioception
- Ascending sensory information
DCML: 1st order neurons
The first-order neurons (Ia phasic & tonics, Ibs) terminate at the nuclei (fasciculus gracilis (LE) and fasciculus cuneatus (UE)) in the lower medulla.
ascend ipsilaterally to the medulla
DCML: 2nd order neurons
located in the caudal medulla, the gracile and cuneate nuclei.
Their axons, referred to as internal arcuate fibers, decussate to form the medial lemniscus, which ascends the contralateral brainstem to project to the ventral posterolateral (VPL) nucleus of the thalamus.
DCML: 3rd Order Neuron
third order VPL neurons
send axons through the posterior limb of the internal capsule to the somatosensory cortex (areas 3, 1, 2)
Gamma MNs
- Contract msp so it won’t go slack during muscle contraction
- Helps with proprioception of muscle going from long to short (only fire the gamma from long to short)
- They can passive elongate the msp when you’re elongating a muscle (eccentric)
- Static and Dynamic
Static Gamma MN
innervate the contractile ends of the static nuclear bag and nuclear chain fibers (intrafusal)
Dynamic Gamma MN
innervate the contractile ends of the dynamic nuclear bag fibers (intrafusal)
Alpha MN
innervate the extrafusal muscle fibers
Intrafusal Fibers and Extrafusal Fibers: Eccentric Contraction
only need to activate the AMN because when the extrafusal fibers are lengthening the intrafusal fibers are already passively lengthening an staying sensitive so there is no need to fire the GMN
Intrafusal Fibers and Extrafusal Fibers: Concentric Contraction
the GMN and AMN need to be fired because if the extrafusal muscle fibers contract the intrafusal fibers lengthen and get sloppy, so they will not get good info.
So whether it’s passive or actively shortening the extrafusal fibers the GMN will fire because the intrafusal muscle fibers need to be shortened along with the extrafusal in order to keep accurate and good proprioceptive info.
Intrafusal Fibers and Extrafusal Fibers and contraction
Intrafusal fibers have to be contractile tissue so the fibers do not stay slacken when the extrafusal fibers contract. If the intrafusal fibers do not contract they slacken and then cannot take in proprioceptive information (if the muscle/extrafusal fibers are lengthening or shortening).
Enhanced Proprioception
- When dynamic and static gamma MNs are firing, this creates enhanced sensitivity of the msp
- Descending tract can fire faster if the body needs the enhanced proprioception
- example: gamma MNs are firing at night when you are trying to walk in the dark. Enhanced proprioception to sense objects on the floor
Sensory Unit
Sensory receptors, one sensory neuron and its many branches
Sensory Receptors
- All sensory receptors are transducers: they convert one type of energy to another & usually the end result is electro-chemical
- Some receptors tend to be modality specific
- -Ex: Meissner’s corpuscle- only a mechno-receptor (pressure)
- -Ex: Corpuscle of Ruffini- only sense warmth AND Kruase only senses cold
- Other receptors are polymodal – respond to multiple stimuli (good example: free nerve endings (hot pain and hot warmth, cannot sense pressure to a point)
Free nerve endings
- Unmyelinated receptors/terminals of myelinated and unmyelinated neurons
- Found especially in the skin, cornea, mucous membranes, intermuscular connective tissue, pulp of teeth
- Example modalities: COLD, WARMTH, TOUCH, AND PAIN
- –Polymodal
- Free nerve endings that terminate in the wall of the stomach give rise to discomfort and the pains of distention, hunger, cramps
Free nerve endings and hair follicles
that wrap around hair follicles act as sensitive tactile receptors when the hair is moved (sense direction of light moving touch)
Mechanoreceptors
- Respond to physical stimulation that causes mechanical displacement of one or more tissues
- Touch and pressure
- -Ex: Meissner’s corpuscles
- –Encapsulated ovoid bodies just beneath the epidermis of the skin
- –Usually in the hairless portions of the skin (palms, soles, toes, fingers)
Mechanoreceptors: Pacinian corpuscles (PC)
- Central unmyelinated tip surrounded by concentric lamellae (“onion”)
- -“gel” like fluid in the middle
- Deep tactile and vibration in joints, tendon sheaths & skin
- Mechanical deformation causes sudden opening of ion channels (Na+ influx, K+ efflux) -> depolarization
Pacinian Corpuscles Example
- a phasic receptor – fast adapting
- Pressure/touch deforms Pacinian corpuscle (depolarization) “on”
- “Balloon-like” = fluid redistributes quickly in the corpuscle following deformation “off”
- When the mechanical stimulus is removed, PC changes shape again (depolarization) “on”
Phasic receptor
fast adapting
Milliseconds
gives us info quickly then stops giving us info
Example:
Pacinian corpuscle [quick info then stops]
Meissner’s corpuscle
Tonic receptor
slow adapting minutes, hours, days gives you info for a long period of time Examples: muscle spindle GTOs pain receptors carotid baroreceptor [takes 2 days to adapt]
Thermoreceptors
- Changes in temperature alter the permeability of Na+ in the neuron membrane
- Cold - Krause receptors
- Warm - Ruffini corpuscle
- Pain receptors
- Temperature ranges stimulate the three thermal receptors
Nociceptors
pain - detect actual or potentially destructive mechanical, chemical, or thermal changes in the immediate tissue
