reflexes Flashcards
what is a motor unit?
a single motor neurone and the muscle fibres it contacts
how does different level of input affect different motor units
low levels of input to a motorneurone pool stimulate small motor units which high levels of input also stimulate large ones
where does proprioceptive feedback come from
golgi tendon organs and muscle spindle
what is the muscle spindle
parallel to extrafusal fibres, contains intrafusal fibres, are stretch receptors
muscle spindle afferants are type Aalpha/ 1a (large diameter) and Abeta/ 2 (medium diameter)
muscle spindle sensitivity is controlled by gamma efferent system from gamma MNs
what are golgi tendon organs
in the musculo-tendinous junction, in series with muscles, is a tension receptor afferent types are 1b (slightly smaller than 1a)
how can reflexes be modulated
reflexes can be modulated by descending pathways from higher motor centres in brain
what type of reflex is the short latency response stretch reflex?
monosynaptic, 1a afferents directly input into motor neurones, can be elecited with tendon jerk
what type of reflex is long latency response stretch reflex?
activated during stretch during active contraction, it is polysynaptic and involves supraspinal structures
what is purpose of stretch reflex
to control intended muscle length during contraction against loads
why is alpha gamma motor neurone coactivation important
if only alpha motor neurones were activated the extrafusal muscle fibre contraction would unload the muscle spindle and silence its output. in most movements they are coactivated but they can be activated seperately so supraspinal systems can control spindle sensitivity
in antagonistic muscle what is the difference between muscles
muscle being contracted is involved in monosynaptic reflex, muscle being relaxed is disynatpic since an inhibitory interneurone must be connected, the 1a afferent connects to a 1a interneurone
what is the h reflex?
while recording a muscle EMG, electrical stimulation of motor nerve first activates largest diameter fibres (1a) which initiate a monosynaptic reflex, detected as the h wave. Increasing stimulus strength also causes a quicker reflex, the m wave. As stimulus size increases M wave predominates. This is because M wave travels orthodromically which cancels out H wave which travels in antidromic direction
what is the golgi tendon reflex?
also called inverse myotatic relfex, golgi tendon afferents (1b) synapse onto 1b interneurones which are inhibitory to agonist muscles and other excitatory interneurones that synapse onto antagonist muscles, acts as mediator to spindle stretch reflex for fine control of muscle tension
