Motor units Flashcards
What does the somatic motor system consist of?
the skeletal muscles and elements of the nervous system that control them
What is the function of UMNs?
supply input to LMNs to mosulate their activity
What is the function of alpha motor neurones?
innervate the bulk of fibres within a muscle that generate force
What is the function of gamma motor neuones?
innervate muscle spindles
What is the function of axial muscles?
control movements of the trunk- maintaining posture
What is a motor unit?
an alpha motor neurone and allof the SK muscle fibres it innervates
What is a motor neurone pool?
a collection of alpha motor neurones that innervate a single muscle
What are the factors that decide the force of muscle contraction?
frequency of AP discharge of the alpha-motor neurone and the recruitment of additional, synergisitc motor units
where are LMNs supplying axial muscles found in relation to distal muscles in the ventral horn?
foudn medial
Where are the LMNs innervating flexors compared to extensors found in the ventral horn?
dorsal
What are the 3 input sources that regulate alpha motor neurone activity?
dorsal root ganglion cells whose axons innervate the muscle spindles; UMNs in the motor cortex and brain stem; spinal interneurones
What are the features of type 1/slow-oxidative fibres?
ATP derived from oxidative phosphorylation- slow contraction and relaxation; fatigue resistant
What is the gross difference between type 2a and type 2b muscle fibres?
type 2a are red whereas type 2b are white
What is the difference between type 2a and type 2 b fibres?
2a- ATP derived from oxidative phosphorylation; fast contraction and relaxation; fatigue resistance; well vascularised; 2b- ATP dervied from glycolysis; fast contraction but not fatigue resistant; poorly vascularised
What is the difference in activation of slowm otor units vs fast motor units?
slow motor units (smaller a-MNs) are more easily activated
What is the myotatic reflex?
when an SK muscle is pulled, it pulls back
What are the parts of a muscle spindle?
fibrous capsule; intrafusal muscle fibres; sensory afferents; gamma motor neurone
What does stimulation of gamma MNs cause?
the spindle to contract so that intrafusal muscle fibres contract in parallel with extrafusal maintaining the sensitivity of the spindle
What are the 2 regions of an intrafusal muscle fibre?
non-contractile equatorial region innervated by 1a sensory neurones; contractile polar ends that are innervated by gamma MNs
What are the 2 main types of intrafusal fibres?
nuclear bag fibres; chain fibres
What is the difference between the 2 types of nuclear bag fibres?
bag 1- very sensitive to the rate of change of muscle length; bag 2- more senstiive to the absolute length of the muscle
What is the function of chain fibres?
snesitive to the absolute length of the muscle
What are the 2 types of afferent fibre that innervate intrafusal fibres?
1a afferents and 2 fibres
What is the appearane adn function of 1a afferents with intrafusal fibres?
form a primary annulospiral nerve ending winding around the centre of all intrafusal fibres
What is the funciton of 2 fibres with intrafusal fibres?
more slowly conudctin form flower spray endings on all intrafusal fibres except the bag 1 dynamic type
What is the difference etbween the sensitivity of 1a and 2 fibres?
1a are more sensitive to rate of change whereas 2 are more sensitive to the absolute length of the intrafusal fibres
When are dynamic gamma MNs active?
during behaviours in which muscle length changes rapidly and unpredicatbly
When are only static gamma MNs active?
in which muscle length changes slowly and predictably
Where a golgi tendon organs found?
at the junction of muscle and tendon
What is the difference between golgi tendon organs vs intrafusal fibres?
monitor changes in muscle tension in series with rather than parallel to extrafusal fibres
How are golgi tendon organs innervated?
group 1b sensory afferents
What is the function of golgi tendon organs?
to regulate muscle tendion to protect muscle rom overload and keep in optimal range
Where do group 1b afferents from the golgi tendon organs synpase?
upon inhibitory interneurones to form the reverse myotatic reflex
What type of fibres give proprioception from joints?
free nerve endings; golgi-type endings; paciniform endings; ruffini endings
What is the function of paciniform endings?
acceleration detectors
What is the function of ruffini endings?
static position and speed and movments
