Proprioceptors Flashcards
what motor neurone cause contractility of skeletal muscle?
alpha - motor neurons
lower motor neurone
where do a motor neurone have their cell bodies
in the anterior horn of the spinal cord
where do a motor neurone axons project out to (2)
muscle fibres with a single synapse
can a single fibre have many nerves innervating it?
nope it can only have one
whats a motor unit
an a MN innervating a muscle fibre
what are the 3 ways of modifying force of contraction
- frequency of action potential firing
- number of active motor units
- change type of active motor units
whats the general rule in terms of size of motor neurones cell body
the bigger the neurone cell body, the bigger the stimulation you have to give it to get it up fire an action potential. (smallest and weakest will always be active)
what is the balance of whether a cell produces an AP based on?
balance of excitatory and inhibitory inputs - allows very fine control of movement
what does the arm sagging down to the effect of gravity cause? (muscle spindle fibres)
unintended stretch of a muscle due to the muscle contracting too little
spindle gets stretched and this will cause the sensory afferents to send signals to the spinal cord and will increase excitation of the MN pool innervating the same muscle.
so increased AP firing and contraction of more and bigger myofibrils and so muscle will contract with more force allowing to maintain position.
what are the two nerves of the muscle spindle fibre
gamma motor neurone axons
stretch sensitive afferents
what are intrafusal fibres
modified muscle fibres
where do intrafusal fibres have their contractile machinery
at the poles (ends)
so poles are contractile and change length at same time as main muscle
what are the sensory stretch afferents associated with
the elastic inner bit - so if that stretches, spindles will be activated to try and stop it
what are the poles of the intrafusal fibres innervated by
gamma motor neurones
how are alpha and gamma MNs activated and deactivated so that the central portion of the intrafusal fibres are unaffected by movement
they are activated and deactivated simulataneously
what do muscle spindles also ensure
accuracy of movements
what will inhibition of the MN pool causes
decrease contraction of the muscle as a whole
whats involved when the muscle stretches as part of a voluntary movement
the descending control systems activate inhibitory interneurons that dampen down activity - so muscle doesn’t resist stretching
what do muscle spindle fibres do in unintentional movement
if you have unintended stretch of the muscle it will reflexly contract
what is reciprocal inhibition
e.g. contraction of biceps and so you get inhibition of stretch from gamma neurones for triceps so they relax
properties of interneurons
glycinergic
inotropic receptors (LGICR)
allow cl- in for example - hyper polarising it
what are GABAb receptors
metabatropic
what does flaccid paralysis cause
weakness
wasting
loss of reflexes
fasciculation’s
where do upper motor neurone have their cell bodies?
in the brain
