16 Innervation of muscle Flashcards
Which cortical layer are the upper motor neurones located in?
V.
Which Brodmann areas contain the cortex?
4 + 6.
How do axons from the corticospinal tract descend through the spinal cord?
95% are contralateral in posterior/lateral CST.
5% are ipsilateral in anterior/ventral CST.
What is the function of the minority of CST neurones that descend ipsilaterally?
Innervation of postural muscles.
Where do UMNs meet LMNs?
Ventral grey horn of the spinal cord.
Which lamina are LMNs localised to in the ventral grey horn?
IX.
Where is lamina IX largest and why?
At cervical and lumbar segments.
Control the muscles of the limbs.
What is the motor neurone pool?
The group of alpha neurones that innervates one muscle.
How are motor neurone pools distributed the spinal cord?
Rostro-caudally.
What is the segmental distribution of lower motor neurones in the spinal cord?
Dorsal: flexors.
Ventral: extensors.
Medial: axial muscles.
Lateral: distal muscles.
What is a motor unit?
Alpha motor neuron and all the fibres it innervates.
How many axons are received by a muscle fibre?
ONE.
Why do motor units vary in size?
Degree of force and level of control needed.
How are motor units recruited?
Small units (that control small number of fibres) are recruited first.
Describe slow motor units: (3).
Small motor units.
‘Red’ fibres that generate low force.
Resistant to fatigue.
Describe fast fatiguable motor units: (3).
Large motor units.
Pale muscle fibres that generate large force.
Fatiguable.
Describe fast, fatigue resistant motor units: (2).
Intermediate force produced.
Some fatigue.
What does an EMG measure?
Electromyograph.
Measures the electrical activity of one motor unit.
What are the three sources of input into alpha motor neurones?
Sensory from peripheral proprioceptors.
Local from spinal interneurons.
Descending from upper motor neurones.
Describe the location of muscle spindles:
Intrafusal and parallel to muscle fibres.
What is the function of muscle spindles?
Detect changes in muscle length and contribute to proprioception.
What are the two classes of muscle spindle fibres?
Bag and chain.
What are chain spindles innervated by?
What do they encode?
Ia and IIa fibres.
Static muscle response (stretch vs no stretch).
What are bag spindles innervated by?
What do they encode?
Ia fibres.
Dynamic muscle response (rate of stretch change).
