1b Neuromuscular Control Flashcards
(32 cards)
what are alpha motor neurones?
The lower motor neurones of the brainstem and the spinal cord that innervate the extrafusal muscle fibres of skeletal muscles
What does activation of the alpha motor neurones cause?
Muscle contraction
What is a motor neurone pool?
Pool which contains all the alpha motor neurones which innervate a single muscle
what is a motor unit?
a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force.
What does stimulation of a motor unit cause?
Contraction of all the muscle fibres in that unit
What are Type 1 muscle fibres?
Slow - smallest cell bodies and smalled dendritic trees, thinnest axons and slowest conduction velocity
What are Type 2A muscle fibres?
Fast, fatiguable - larger diameter cell bodies, larger dendritic trees, thicker axons and faster conductions
What are Type 2B muscle fibres?
Fast, fatigue resistant - larger diameter cell bodies, larger dendritic trees, thicker axons and faster conductions
What are Type 2B muscle fibres?
Fast, fatiguable - larger diameter cell bodies, larger dendritic trees, thicker axons and faster conductions
Which type of muscle fibre produces the largest amount of force?
Type 2B
How are the three motor unit types classified?
amount of tension generated, speed of contraction and fatiguability.
What are the two mechanisms by which the brain regulates the amount of force a single muscle produced?
rate coding and recruitment
What is recruitment?
When smaller units are recruited first, and as more force is required, larger units are then recruited - this allows for fine control when necessary
What is rate coding?
When different units can fire at different frequencies - higher firing rate is larger force
When does summation occur?
When the muscle units fire at a frequency which is too fast to allow the muscle to relax between AP’s
what are neurotrophic factors?
a type of growth factors which prevent neuronal death and promote the growth of the neurones after injury
What is the effect of neurotrophic factors?
If a fast twitch muscle and a slow muscle are cross innervated, the slow becomes fast and the fast becomes slow.
The motor neuron has some effect on the properties of the muscle fibres it innervates.
What causes a change from IIB to IIA fibres?
Training
What causes a change from Type I to Type II?
Severe deconditioning or spinal cord injury, or microgravity
What change is ageing associated with?
with loss of type I and II fibres but also preferential loss of type II fibres.
What is the evidence that ageing results in a loss of type 1 and 2 fibres, with a preferential loss of type 2?
Larger proportion of type 1 fibres = slower contraction times
What is a reflex?
An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness.
What is the Jendrassik Manoeuvre?
Try clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped. The reflex becomes larger
What type of control dominates in normal conditions?
Inhibitory control
