Motor Control of CNS : Spinal reflexes Flashcards
5 layers ( pathways ) of control for a muscle to move
1- muscle being controlled at neuromuscular junction
2- neuromuscular junction being fired by nerves part of spinal reflexes
3- control of reflexes by supra spinal input form medulla and pons
4- input controlled via cerebral cortex
5- cerebral cortex affected via basal ganglia and cerebellum
What are the levels of integration
1- Spinal cord level
2- Subcortical level
3- cortical level
Extrafusal vs Intrafusal fibers
Extrafusal : muscle fibres that develop force
Intrafusal fibers : lost most of their contractile proteins , wrapped in nerves and sense changes in length of muscle
What is the muscle spindle
A length transducer in ever muscle , in parallel with muscle
What are the 2 types of afferent fibres form spindle
Type 1a: large myelinated , fast conducting
Type 2: myelinated but slower conducting ( serve afferent arm of stretch reflex )
What are the efferents of the muscle spindle
Gama efferents that contract the muscle spindle
What are the types of fibres in the spindle , enervated by what and how do they work
1- fibres sensing velocity
- enervated by 1a afferents
- fast adapting when length changes
- phasic response ( senses muscle acceleration )
2- Fibres Sensing length
- enervated by Type 2 afferents
- slowly adapting
- when muscle changes in length output of nerve remains high
What does a phasic response of the fibres in muscle spindle mean
Means it senses muscle acceleration , changes in velocity of the muscle
What does a static response of the fibres in the muscle spindle mean
Means fibres that sense changes in length
What is the fusimotor system
The small motor system made of game efferents and alpha
As muscle contracts the spindle also contracts to maintain tightness of muscles . Alpha motor neurone shortens muscle as muscle contracts , gamma motor neurone shortens the spindle. Both activated together.
What is the purpose of the fusimotor system
Spindle will always be able to sense changes in length of the muscle. Prevents spindle unloading.
Sets baseline for alpha discharge and muscle tone
What is the stretch reflex ( explain in detail )
Monosynaptic reflex where the muscle contracts against the stretch. Smooths and dampens muscle movement so muscle can’t move in uncontrolled way. SO Spindle sends signals of length and velocity to brain via spinocerebellar and dorsal tracts .
What is the force transducer
The Golgi tendon organ
- embedded within the tendon ( in series with muscle )
- A lot of force is required for muscle to stretch
- Transducer fires in response to muscle contractile force
How does the force transducer synapse
Synapse via inhibitory neuron on alpha fibre
What is the inverse stretch reflex
GTO reflex, Turns off alpha output to muscle
- control system sending information about force in muscle centrally
- controls muscle force as well as length
Why do muscles vibrate when you’re doing difficult actions ( eg: lifting heavy weight , constipated )
Increased sensitivity of muscle spindles due to an action , sends signals centrally which results in a cycle of contraction and relaxation = tremor , Brian usually controls this
What is clonus
A rhythmic oscillating stretch reflex due to upper motor neuron lesion , where there is a lack of descending inhibitory input to gamma fibres from Brian , increasing spindle sensitivity and causing symptoms ( ex : tremors )
When can clonus be seen
Strokes , MS , cord lesions , hepatic encephalopathy, amyotrophic lateral sclerosis
What is Clasp-knife rigidity
Upper motor neuron lesion where there’s a great resistance in moving the arm as the amplified stretch reflex is preventing movement but all of a sudden the amplified inverse stretch reflex kicks in and arm gives away
What is tabs dorsals
imprecise walking gait. can move but movement was very obvious and exaggerated.
What is the cross extensor reflex
Ex: When you touch something hot as your hand to move away , rest of body stiffens in response to threat by contracting extensor muscles
One side flexes other side extensor muscles activated
What is the positive supporting reflex
ex: if you place finger on sole of baby foot and you move finger around then baby’s foot will be able to follow your finger
occurs in isolation of brain. Don’t see this in adults because they have developed more sophisticated reflexes
