Motor Systems Flashcards
What is the most common innervator of skeletal muscle fibres?
Alpha motoneurones
What does a motor unit consist of?
A motoneurone and all of it’s associated muscle fibres
How is the contractile force of motor units evenly spread through the muscle?
One motoneurone synapses with many muscle fibres
What is the result of increases motor unit recruitment?
An increase in the strength of muscle contraction
What rule is followed in the recruitment if motor units?
Recruitment occurs from the smallest to the largest units
Muscle spindles signal information about what muscle features?
Length and velocity
What are the muscle fibres what are important in muscle spindle function?
Intrafusal muscle fibres keep the muscle spindles taut and sensitive to stretch
Intrafusal muscle fibres contribute to what input?
Proprioception - detection of position and movement in space
How are Intrafusal fibres innervated?
Gamma motoneurones
Main powerful muscle contractions are produces by which muscle fibres?
Extrafusal muscle fibres
What do alpha motoneurones innervate?
The extrafusal muscle fibres
When the CNS initiates muscle contraction, what coordination must take place?
Alpha-gamma coactivation
The Golgi tendon organ signals information about what muscle activities?
Load and force
What is the structure of GTO?
Capsules containing collagen fibres
How is the GTO innervated?
By primary afferents called group 1b fibres
What is a motoneurone pool?
Motoneurones clustered together all innervating the same muscle
What is a rate code used for?
To signal the amount if force to be exerted by a muscle
Describe a myotatic reflex.
Muscle stretch, activates 1a afferents, enter the dorsal root, synapse in the spinal cord directly on the alpha motoneurone, which innervates the initial muscle to contract
The myotatic reflex is an example of what type if pathway?
A mono synaptic pathway
What is the initiator of the myotatic reflex?
Muscle spindles (not GTO)
Muscles work in synchrony; how is this achieved?
Via the inhibition of stretch reflex
Why must an opposing muscle be inhibited?
To prevent the contraction of the opposing muscles at the same time, which would cause damage
How is stretch reflex inhibition achieved?
The 1a afferents bifurcates in the spinal cord, one branch innervates the 1a inhibitory interneurone
The GTO is involved in which inhibitory mechanism?
The autogenic inhibition reflex
Describe the autogenic inhibitory reflex.
Muscle tension, activates group 1b fibres, synapse on 1b inhibitory interneurone which synapse in an alpha motoneurone, reducing muscle contraction
Inhibitory mechanism are examples of what pathways?
Disynaptic reflex pathways
What are considered high level tasks in the motor system hierarchy?
The coordination of the activity at many limbs
What is considered to be low level tasks in the motor system hierarchy?
The programming of force and velocity required and maintenance of posture
What order does the motor system hierarchy follow?
Spinal cord, brain stem, motor cortex and association cortex
Which areas of the frontal lobe are involved in the motor cortex?
Primary motor cortex, pre-motor cortex, and supplementary motor cortex
Where is the primary motor cortex located?
In the precentral gyrus, and anterior paracentral lobule on the medial surface
What is required to elicit movements via the motor cortex?
Electrical stimulation
Which motor cortex area requires the least electrical stimulation to elicit a response?
Primary motor cortex
Which motor cortex areas require a higher electrical input for production of movements?
Premotor cortex and supplementary motor area
