Motor Control of CNS : Spinal reflexes

Question 1

5 layers ( pathways ) of control for a muscle to move

Answer 1

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

Question 2

What are the levels of integration

Answer 2

1- Spinal cord level
2- Subcortical level
3- cortical level

Question 3

Extrafusal vs Intrafusal fibers

Answer 3

Extrafusal : muscle fibres that develop force

Intrafusal fibers : lost most of their contractile proteins , wrapped in nerves and sense changes in length of muscle

Question 4

What is the muscle spindle

Answer 4

A length transducer in ever muscle , in parallel with muscle

Question 5

What are the 2 types of afferent fibres form spindle

Answer 5

Type 1a: large myelinated , fast conducting

Type 2: myelinated but slower conducting ( serve afferent arm of stretch reflex )

Question 6

What are the efferents of the muscle spindle

Answer 6

Gama efferents that contract the muscle spindle

Question 7

What are the types of fibres in the spindle , enervated by what and how do they work

Answer 7

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

Question 8

What does a phasic response of the fibres in muscle spindle mean

Answer 8

Means it senses muscle acceleration , changes in velocity of the muscle

Question 9

What does a static response of the fibres in the muscle spindle mean

Answer 9

Means fibres that sense changes in length

Question 10

What is the fusimotor system

Answer 10

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.

Question 11

What is the purpose of the fusimotor system

Answer 11

Spindle will always be able to sense changes in length of the muscle. Prevents spindle unloading.
Sets baseline for alpha discharge and muscle tone

Question 12

What is the stretch reflex ( explain in detail )

Answer 12

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 .

Question 13

What is the force transducer

Answer 13

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

Question 14

How does the force transducer synapse

Answer 14

Synapse via inhibitory neuron on alpha fibre

Question 15

What is the inverse stretch reflex

Answer 15

GTO reflex, Turns off alpha output to muscle

• control system sending information about force in muscle centrally
• controls muscle force as well as length

Question 16

Why do muscles vibrate when you’re doing difficult actions ( eg: lifting heavy weight , constipated )

Answer 16

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

Question 17

What is clonus

Answer 17

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 )

Question 18

When can clonus be seen

Answer 18

Strokes , MS , cord lesions , hepatic encephalopathy, amyotrophic lateral sclerosis

Question 19

What is Clasp-knife rigidity

Answer 19

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

Question 20

What is tabs dorsals

Answer 20

imprecise walking gait. can move but movement was very obvious and exaggerated.

Question 21

What is the cross extensor reflex

Answer 21

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

Question 22

What is the positive supporting reflex

Answer 22

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