Neuromuscular control Flashcards
What are the alpha neurones?
lower motor neurones of the brainstem and spinal cord
innervate extrafusal muscle fibres of the skeletal muscles
Activation causes contraction
What does the motor neurone pool contain?
All alpha motor neurones innervating 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.
How many muscle fibres does a motor neurone supply?
About 600 muscle fibres
Stimulation of one motor unit, contracts all the muscle fibres in that unit
What are the different types of motor unit fibres?
Slow, type I
Fast fatigue resistant FR, IIA
Fast fatigue able FF, IIB
describe slow motor unit fibres?
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
Describe FR fibres?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
Describe FF?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
What are the motor units classified by?
amount of tension generated
speed of contraction
fatiguability
LOOK AT GRAPHS
What is recruitment?
Not randomly recruited.
size principle -> smaller units are recruited first
as more force is required more units are recruited
this allows fine control
What is rate coding?
motor units can fire at a range of frequencies.
slow units will fire at lower frequencies
as firing rate increases, the force produced by the unit increases
summation occurs when the units fire at a frequency too fast to allow the muscle to relax between arriving action potentials.
What are neurotrophic factors?
are a type of growth factors, which prevent neuronal death -> promote growth of neurons after injury
Talk to me about cross innervation?
characterises of the muscle depend on the nerve which innervates them,
if fast twitch and slow twitch are cross innervated the muscles alternate
Do motor units have plasticity?
Fibre types can change properties under many conditions.
IIB -> IIA
I -> II in severe deconditioning or spinal injury and microgravity in a spaceflight can do the same
How does ageing affect fibres?
loss of type I + II but also loss of type II fibres
so you result into more type I fibres
What is a reflex?
automatic response to a stimulus which involves a nerve impulse from receptor to the nerve centre and then to the effector
no level of consciousness
What does magnitude and timing of reflex depend on?
Intensity and onset of stimulus
What is the Jendrassik manoeuvre
exaggerated reflex when doing another movement (eg clenching teeth)
How does the manoeuvre work?
CNS centres send inhibitory and excitatory regulation upon reflex reflex
inhibitory is key in normal conditions
decerebration reveals excitatory control from supraspinal areas
(rigidity and spasticity can result from brain damage giving over reactive or tonic stretch reflex)
LOOK AT SUPRASPINAL REFLEX CONTROL
What is hyperreflexia
overreactive reflexes
loss of descending inhibition
UM lesions
What is hyper reflexia/ clonus?
involuntary and rhythmic muscle contraction
loss of descending inhibition
associated with UMN lesion
What is the Babinski sign?
it is a sign of hyper reflexia
sole is stimulated with blunt instrument, big tow
curl downwards -> normal
curl upwards -> abnormal in adults, as it is Babinski
sign
UMN lesions
toe curls upwards in infants
What is hypo reflexia
below normal
associated with LMN disease
