Motor Units, Muscle Spindles, Golgi Tendon Organs and Joint Receptors Flashcards
From which 3 places can lower motor neurones (LMN) receive input?
1) Upper motor neurones 2) Proprioreceptors 3) interneurones
Which kind of neurones innervate that muscle fibres?
α-motor neurones (α-MNs)
Which kind of neurones innervate the muscle spindle (sensory)?
γ-motor neurones (γ-MNs)
How do LMNs exit the spinal cord?
Ventral routes (or cranial nerves)
What is the name of the nerve formed by the Ventral (anterior) and dorsal (posterior) roots?
Mixed spinal nerve
Where is the greatest number of motor neurones in the spinal cord?
Cervical Enlargement (C3-T1) and Lumbar Enlargement (L1-S3)
What is a motor unit?
An α-MN and all the muscle fibres it innervates.
What is a motor neurone pool?
The collection of α-MNs that innervate a single muscle.
What two mechanisms serve to increase force of muscle contraction?
1) Increased frequency of AP through α-MN
2) Recruitment of additional, synergistic motor units
What 3 factors dictate the degree of neuromuscular activation?
1) Firing rate of LMNs
2) Number of LMNs that innervate a muscle (motor units)
3) Co-ordination of movement (integration)
What 2 factors dictate the degree of force production?
1) Fibre size (hypertrophy)
2) Fibre phenotype (fast or slow contracting)
What is the basis for the categorisation of muscle types?
The speed at which myosin ATPase splits ATP to provide energy for cross bridge cycling
What is motor neurone recruitment?
the activation of additional motor units to accomplish an increase in contractile strength in a muscle. Slow motor units are recruited first, then faster, allowing graded development of muscle force.
What is the myotatic reflex?
If the muscle is stretched this is detected but the muscle spindle which triggers contraction.
What are the stages in the myotatic reflex?
1) Stretch of muscle spindle
2) Activation of Ia afferent
3) Excitatory synaptic transmission in spinal cord (glutamate)
4) activation of α-MN
5) Contraction of homonymous (stretched) muscle
Why does the body ensure that extrafusal (muscle) fibres and intrafusal (spindle) fibres contract in parallel?
α- and γ-MNs are normally co-activated during voluntary movement to prevent the spindle from going slack while the muscle contracts.
What are Golgi Tendon Organs?
Structures found in the junction between muscle and tendon which monitor changes in muscle tension.
What is the purpose of Ia sensory fibres?
They carry information from the muscle spindle.
What is the purpose of the Ib sensory fibres?
They carry information from the Golgi tendon organs.
What is the purpose of a Golgi Tendon Organ?
These prevent the muscle from overload (e.g. in weight-lifting). Ib afferents enter the spinal cord and synapse on the α-MN of the muscle being stretched. It is the opposite of the myotatic reflex.
